Human perinatal immunity in physiological conditions and during infection
© The Author(s). 2017
Received: 29 November 2016
Accepted: 27 March 2017
Published: 21 April 2017
The intrauterine environment was long considered sterile. However, several infectious threats are already present during fetal life. This review focuses on the postnatal immunological consequences of prenatal exposure to microorganisms and related inflammatory stimuli. Both the innate and adaptive immune systems of the fetus and neonate are immature, which makes them highly susceptible to infections. There is good evidence that prenatal infections are a primary cause of preterm births. Additionally, the association between antenatal inflammation and adverse neonatal outcomes has been well established. The lung, gastrointestinal tract, and skin are exposed to amniotic fluid during pregnancy and are probable targets of infection and subsequent inflammation during pregnancy. We found a large number of studies focusing on prenatal infection and the host response. Intrauterine infection and fetal immune responses are well studied, and we describe clinical data on cellular, cytokine, and humoral responses to different microbial challenges. The link to postnatal immunological effects including immune paralysis and/or excessive immune activation, however, turned out to be much more complicated. We found studies relating prenatal infectious or inflammatory hits to well-known neonatal diseases such as respiratory distress syndrome, bronchopulmonary dysplasia, and necrotizing enterocolitis. Despite these data, a direct link between prenatal hits and postnatal immunological outcome could not be undisputedly established. We did however identify several unresolved topics and propose questions for further research.
Healthy living has its origin before birth. Although the intrauterine setting is considered to be a safe environment for the unborn, several threats are already present. One of them is exposure to microorganisms and subsequent inflammatory responses in both maternal (chorionic) and fetal (amniotic) tissues . Antenatal inflammatory responses to infectious stimuli may have positive or negative effects on the fetus and potentially influence its immune responses later in life. The immune system of both the fetus and the (preterm) neonate itself has limited capacity because of gestational immaturity and needs stimulation to develop . Fetuses and neonates therefore rely to a significant extent on their innate immune system [3, 4]. This might enhance neonatal vulnerability to infection but may also protect against collateral inflammatory damage. Although several infectious challenges are present, even prenatally, and immune responses are downregulated, not all fetuses and neonates will develop serious infections. Intrauterine infections may induce premature delivery; prematurity raises the risk for serious neonatal infections, but it is unknown whether this is independently correlated with immature immune responses.
What can we learn from the nature of immune responses in preterm and term neonates with and without infections? In other words, do prenatal microbial challenges affect postnatal immunity and if so, how?
This review focuses on postnatal immunological consequences of prenatal exposure to microorganisms and other inflammatory stimuli. We will also summarize what is known about the microbial triggers and inflammatory consequences of clinically well-known neonatal immune-mediated diseases, such as respiratory distress syndrome (RDS), bronchopulmonary dysplasia (BPD), and necrotizing enterocolitis (NEC).
The electronic databases MEDLINE (PubMed) and Google Scholar were searched. Articles related to fetal and neonatal immunity and infection, as well as articles related to postnatal immunological consequences of prenatal infection/inflammation, were acquired. We did not intend to perform a systematic review and focused on identification of unresolved topics and questions for further research.
The fetal immune response
The developing immune cells and tissues
The development of the human immune system starts with the production of hematopoietic stem cells (HSCs) during embryogenesis, which have the ability to differentiate into myeloid and lymphoid cells . At weeks 4–6 of gestation, HSCs migrate to the liver, which becomes the main site of hematopoiesis until week 22 of gestation. HSCs colonize the thymus at week 8 of gestation and bone marrow between 70 and 80 days of gestation [5, 7]. During the third trimester, hepatic hematopoiesis decreases and terminates shortly after birth . The development of secondary lymphoid tissues (e.g., spleen, lymph nodes, and Peyer’s patches) starts at week 8 of gestation .
Embryonic macrophages are the first immune cells found in the yolk sac at weeks 3–4 of gestation [9, 10]. The majority of macrophages are still negative for the important major histocompatibility complex (MHC)-II. MHC-II-positive macrophages start to appear in the liver around weeks 7–8 of gestation, in the lymph nodes between weeks 11 and 13 of gestation, and in the developing thymic medulla around week 16 of gestation .
Two months after conception, monocytes are present in high quantities in the circulation as a result of established hematopoiesis in the fetal liver. Their amount, phagocytic function, and antigen presenting capacity increase with gestational age (GA) [5, 10].
In contrast to the high levels of circulating monocytes, neutrophil levels are low before 31 weeks of GA. After 31 weeks, they increase substantially .
Fetal blood samples collected between 21 and 32 weeks of GA showed that the functionality of neutrophils is impaired during fetal life. Fetal neutrophils express lower amounts of adhesion molecules compared to neonatal and adult neutrophils, which reduces their ability to adhere and extravasate from the bloodstream. As a consequence, their chemotactic ability is limited [13, 14]. Their ability to migrate gradually increases after 32 weeks of GA, and in full-term neonates, migration ability reaches adult levels.
Dendritic cells (DCs) act as a link between innate and adaptive immunity and originate from both myeloid and lymphoid progenitor cells .
Also of significant importance in the early phases of life is the natural killer (NK) cell. Although derived from bone marrow lymphoid progenitor cells, NK cells are classified between innate and adaptive immunity. They are detectable from 6 weeks of GA onwards in the embryonic liver . The amount of NK cells correlates with GA. Levels reach a maximum at birth . The cytolytic function of fetal NK cells is considerably lower compared to that of adults. Even at term, the cytolytic capacity is only 50–80% of adult levels .
The thymus is the T cell-producing organ and starts to develop during week 6 of gestation. Progenitor T cells start to colonize the fetal thymus around week 8 of gestation . At week 15 of gestation, fetal thymocytes express a complete set of TCRs . The amount of T cells starts to increase from 19 weeks of gestation and peaks at about 6 to 7 months postnatally .
B cells are derived from HSCs in the bone marrow and fetal liver. Pre-B cells are detectable in the fetal liver from week 7 of gestation and in the bone marrow around week 12 [19–21]. At the time B cells express immunoglobulin M (IgM) on their surface, they start to migrate from the bone marrow to the peripheral circulation. IgM-positive B cells are present in the peripheral circulation by week 12 of gestation. Between weeks 10 and 12 of gestation, different immunoglobulin isotypes start to appear in the peripheral circulation: B cells with surface immunoglobulin D (IgD), surface immunoglobulin G (IgG), and surface immunoglobulin A (IgA). During fetal life, the number of B cells increases to adult levels by week 22 of gestation. The amount of plasma cells is low until weeks 18–20 of gestation . The fetus is already able to mount an antigen-specific antibody response; however, this response is at a lower intensity compared to that of adults. Neonatal antibody responses depend on the type of antigen, with better responses to proteins compared to polysaccharides. Antibody responses to polysaccharide antigens only reach mature levels after 2 years of age in childhood [22, 23].
The adaptive immune system and T cell immunity in particular is still immature in the fetus . Adaptive responses in general are downregulated in the fetal stage of development. The biological function of this phenomenon is related to the sophisticated immune balance between the mother and the fetus. Mechanisms that control downregulation of adaptive immunity in mother and fetus include local immunosuppression, lack of DC migration to local lymph nodes, and presence of intrauterine Tregs during pregnancy [24, 25]. The delicate process of fetal development should evidently not be disturbed by potentially harmful inflammatory responses. To avoid inflammation, fetal cells such as macrophages are hyporesponsive, and soluble inflammatory mediators are scarce. Additionally, the fetal adaptive immune response is characterized by suppressed Th1 responses and upregulated Th2 responses. This shift from Th1 to Th2 is caused by the production of mediators through the placenta, such as the anti-inflammatory cytokine interleukin (IL)-10, prostaglandin E2, and progesterone .
A typical cytokine profile characterizing fetal immune responses consists of low levels of type I IFNs, such as IFN-α and IFN-γ; IL-12 and higher levels of innate inflammatory cytokines IL-1β, IL-6, IL-23; and much higher anti-inflammatory IL-10 levels .
Prenatal infection and immunity
The intrauterine environment was long considered to be sterile. This classical dogma has been questioned over the past decade, and there is evidence that gut microbiota colonization already starts in utero [26, 27]. Microbes have been found in placental tissue, umbilical cord blood, fetal membranes, amniotic fluid, and meconium. It remains unclear how this colonization occurs. It is possible that microbes originate from the vagina or maternal digestive tract. A study by Aagaard et al.  showed that the placental microbiome is most akin to the human oral microbiome. This study makes it plausible that microbes may also originate from the oral cavity of the mother.
Stage 1 is defined by neutrophils in the chorionic vessels (chorionic vasculitis) and/or umbilical vein (umbilical phlebitis).
Stage 2 is reached when neutrophils enter the wall of the umbilical artery (umbilical arteritis), with or without minor degrees of extravasation into Wharton’s jelly.
Stage 3 is heralded by organization of neutrophils in Wharton’s jelly into arc-like bands surrounding one or more umbilical vessels (concentric umbilical perivasculitis or necrotizing funisitis).
Gomez et al.  showed that fetuses with severe neonatal morbidity had a lower mean GA and a higher proportion of CA. Furthermore, these fetuses had significantly higher levels of IL-6 in amniotic fluid and fetal plasma .
Preterm birth may result from either spontaneous developments or medically indicated interventions. Although a large proportion of preterm births are labeled idiopathic, i.e., without known cause, there is good evidence that infections are a primary cause of a substantial proportion of preterm births  since (a) the amniotic fluid of women with preterm labor has higher rates of microbial colonization and levels of inflammatory cytokines than that of women not in labor and women in labor; (b) extrauterine maternal infections such as pyelonephritis, pneumonia, and periodontal disease have been associated with premature parturition; (c) subclinical intrauterine infections are associated with preterm labor and delivery; and (d) patients with intra-amniotic infection or intrauterine inflammation are at risk for subsequent preterm delivery . Additionally, pro-inflammatory cytokine production (IL-1β, IL-6, tumor necrosis factor (TNF)-α) in response to intrauterine infection and inflammation is more likely to cause preterm labor than anti-inflammatory cytokine production (IL-10) . Romero et al.  showed evidence for the contribution of IL-1β to preterm birth: (1) IL-1β is produced by human decidua in response to bacterial products; (2) IL-1β can stimulate prostaglandin production of human amnion and decidua; (3) IL-1β concentration and bioactivity were increased in the amniotic fluid of women with preterm labor and infection; and (4) IL-1β could stimulate myometrial contractions . They also showed evidence for a supporting role of TNF-α in preterm birth . This was based on the following observations: (1) TNF-α stimulates prostaglandin production by amnion, decidua, and myometrium; (2) human decidua can produce TNF-α in response to bacterial products; (3) amniotic fluid TNF-α bioactivity and immunoreactive concentrations are elevated in women with preterm labor and intra-amniotic infection; (4) in women with preterm premature rupture of membranes (PPROM) and intra-amniotic infection, TNF-α concentrations are higher in the presence of labor; (5) TNF-α can stimulate the production of matrix metalloproteinases (MMPs), which may play a role in membrane rupture and cervical ripening; and (6) TNF-α application in the cervix induces changes that resemble cervical ripening .
There is growing evidence that normal spontaneous labor at term age is an inflammatory process on itself [37–40], but the extent to which the mechanisms of normal and preterm labor (abnormal) overlap remains largely unknown .
The neonatal immune response
Neonates are highly susceptible to infectious agents. Limited exposure to antigens in utero and the lack of preexisting immunological memory contribute to this sensitivity . Additionally, pro-inflammatory responses are suppressed in neonates [41, 42]. Therefore, neonates rely heavily on their innate immune system in fighting infections [3, 43]. Pre- and postnatally, there is an age-dependent maturation of the immune responses, both in cellular and humoral. Prenatal and postnatal exposure to environmental microorganisms activates the neonatal immune system and accelerates this maturation process .
Toll-like receptors (TLRs) are key elements in activation of the innate response. Several studies investigated the expression pattern of TLRs on neonatal immune cells. Levy et al.  and Dasari et al.  showed that the expression of TLRs on monocytes and granulocytes did not significantly differ between newborns and adult. In contrast, Quinello et al.  and Marchant et al.  described that the expression of TLR2 and TLR4 on monocytes and TLR4 on mature DCs was reduced among preterm and full-term newborns compared to adults. Additionally, the possibility of neonates to activate the TLR pathway seems to be reduced. Exposure to TLR ligands results in lower TNF-α, IL-6, and IL-12/23p40 production in neonates compared to adults [44, 47]. This impaired TLR activation at birth enhances neonatal vulnerability to infections. The neonatal TLR system undergoes rapid and differential development during the first month of life. Whereas the ability to produce Th1-type cytokines in response to agonists for TLR3, TLR7, and TLR9 rapidly increases to adult levels during the first month of life, TLR4-mediated responses remain impaired at least up to 1 month of age . Research by Marchant et al.  and Sharma et al.  investigated the effect of CA on the ontogeny of innate cytokines production via TLR activation. Cord blood and whole blood was collected to determine cytokine production in response to TLR activation. They showed that CA did not alter the innate cytokine production. This suggests a developmental maturation of the TLR response instead of an attenuated response due to infection.
In addition to TLRs, nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) and retinoic acid-inducing gene (RIG)-like helicases (RLHs) also play an important role in pathogen recognition. No data were found on the ontogeny and function of NLR and RLH in the fetus or neonate.
Complement activity is low among newborns compared to that of adults . Antimicrobial peptides and proteins are present from early gestation, and levels increase with GA and interact with TLRs [51, 52]. Mannose-binding lectin (MBL) also interacts with TLRs by upregulation of TLR2 and TLR6 signaling. MBL levels are low among (preterm) infants, which significantly increase the risk of early- and late-onset neonatal sepses . These deficiencies in complement are probably one of the causes of the increased susceptibility of neonates and preterm infants to infectious agents . Additionally, neutrophil levels are low among preterm and growth-restricted infants; this further enhances their vulnerability to infections . Neutrophil function is also reduced: their chemotactic ability is reduced, as well as their ability to adhere to endothelial cells .
As in the fetus, NK cells and phagocytic cells such as monocytes, neutrophils, and DCs orchestrate neonatal innate immune responses. The phagocytic capacity of monocytes and macrophages of neonates and preterm infants are comparable to that of adults. However, their capacity to instruct the adaptive immune response is significantly reduced [56, 57]. NK cell levels of term neonates are comparable to adult levels. Their expression of inhibitory receptors is higher than among that of adults, whereas their expression of activating receptors is lower. An important function of NK cells is the production of cytokines, especially IFN-γ, which stimulates the activation of macrophages and Th1 cells. Their capacity of producing IFN-γ is significantly higher than in adults. NK cell degranulation capacity and lytic function are reduced compared to those of adult NK cells .
Although neonates have higher number of DCs compared with adults, their function is reduced. A study by Quinello et al.  showed that all newborns had lower levels of TLR4 on cDCs compared to adults. Additionally, neonatal DCs are less efficient inducers of T cell responses at birth compared to maturated DCs .
A Th2-driven response characterizes both fetal and neonatal adaptive immune responses. Th1-type immune responses are downregulated in several ways. Th1 cytokine IFN-γ production is reduced . Upon birth, Th2 polarization will be skewed towards a Th1 profile. Infants with delayed skewing have an increased frequency of bloodstream infections early in life .
Children under the age of 2 months express a combined Th2 and Th17 cell cytokine profile and display only weak Th1 polarization upon challenge with immune stimuli, which is a typical innate immune signature for newborns . Given the limited exposure to antigens in early life, both T and B cells show age-dependent maturation profiles, with low numbers of class-switched memory cells detectable after birth into early infancy.
Infants born at term benefit from supplemental protection afforded by maternal antibodies transferred through the placenta. Extreme preterm infants, however, benefit to a lesser extent from transfer of maternal antibodies, which largely occurs during the third trimester of gestation [60, 63].
Adaptive immunity does play a role in fetuses and neonates but is downregulated to decrease Th1-type pro-inflammatory cytokine responses. On the one hand, this distinct functional pattern of adaptive immunity, skewed by innate immune responses, is important because Th1 cytokines, and especially TNF-α, are directly related to preterm labor and birth. On the other hand, this defensive functional expression of immunity contributes to enhanced neonatal vulnerability to infection.
Postnatal effects of prenatal immune activation
Immunity is an interaction between all factors of defense, which are aimed to maintain host immune homeostasis. The human body is able to protect itself from infectious disease via three different strategies: avoidance, resistance, and tolerance. Avoidance reduces the risk of exposure to infectious agents. When an infectious agent invades the body, pathogen burden is reduced by resistance mechanisms, such as detection, neutralization, destruction, or expulsion of the pathogen. Tolerance strategies are aimed to reduce the negative impact of infection or inflammation on the host. The balance between the resistance and tolerance determines the degree of tissue damage in the host .
A substantial proportion of fetuses exposed to microorganisms in utero develop FIRS. This is associated with the production of pro-inflammatory cytokines IL-1β, IL-6, IL-8, and TNF-α, which predisposes for PPROM and premature labor. Fetuses with FIRS have a higher rate of severe neonatal morbidity. Funisitis and chorionic vasculitis, observed on pathological examination of the umbilical cord, are the histopathologic hallmarks of FIRS . Funisitis is associated with endothelial activation, a key mechanism in the development of organ damage [65, 66]. The lung, gastrointestinal tract, and skin are exposed to amniotic fluid during pregnancy and are notorious targets of infection and subsequent inflammation during pregnancy. Besides the fact that antenatal infection and inflammation can predispose to organ damage, such an infection may also have an effect on organ-specific immunity. In the next part, we will summarize what is known about the effects of prenatal inflammatory exposure on skin, lung, and gut-specific immunity.
The epidermis is the first line of defense against microbial pathogens. Epidermal keratinocytes express TLRs and antimicrobial peptides belonging to the cathelicidin gene family and β-defensin family . Normally, these peptides are present in low concentrations. At the time of infection, the epidermal keratinocytes start to synthesize these peptides, resulting in a rapid increase . Cathelicidins have the ability to inhibit growth or destroy bacteria . Cathelicidin expression is increased in the skin of both fetus and neonate, resulting in an enhanced innate immune barrier of the skin . This enhanced barrier may protect the newborn from infection. CA leads to the upregulation of TLR2 and TLR4 and concomitant upregulation of cytokines and chemokines as well as antimicrobial factors in epidermal keratinocytes . Neutrophils, lymphocytes, and histiocytes are the primary cells infiltrating the superficial dermis, causing dermatitis . It is unknown whether this prenatal immune response of the skin influences postnatal immunity of the skin.
Lung (RDS and BPD)
The sentinel immune cell of the lung is the alveolar macrophage . No data was found on the ontogeny of alveolar macrophages in humans. Animal studies revealed that a CA infection is able to induce maturation of lung monocytes into functionally mature alveolar macrophages . Human data on this topic are currently lacking.
Respiratory distress syndrome
RDS is a syndrome caused by lung immaturity and developmental insufficiency of surfactant production. Surfactant consists of phospholipids, neutral lipids, and proteins. There are four surfactant-associated proteins (SP), SP-A, SP-B, SP-C, and SP-D. The most important phospholipids are phosphatidylcholine (70–80%) and phosphatidylglycerol (5–10%). These phospholipids line the alveoli, in which surfactant proteins stabilize the phospholipid layer. This layer reduces the surface tension and, subsequently, neonatal work of breathing and prevents transudation of fluid. Infants with RDS have low levels of phosphatidylcholine and phosphatidylglycerol is absent, resulting in an unstable surfactant monolayer, which does not effectively reduce surface tension. Thus, infants with RDS have low lung volume, incompliant lungs, and increased work of breathing .
Preterm birth is associated with RDS, and it affects primarily children born before 32 weeks of gestation . CA is also strongly correlated with preterm birth, but conversely, CA and intrauterine inflammation are reported to decrease the risk of developing RDS [75–78]. Histologically, CA increases the fetal pulmonary surfactant concentration in the amniotic fluid [79, 80]. It is unknown whether this CA-driven effect is pathogen-specific. Additionally, CA stimulates IL-6 production by fetal immunocompetent cells, alveolar macrophages, type II alveolar cells, and placental cells . IL-6 promotes lung maturation by stimulating SP-A synthesis . In turn, SP-A is able to stimulate IL-6 and TNF-α production [81, 82]. Additionally, SP-A promotes phagocytosis of specific pulmonary pathogens by alveolar macrophages . An increase in SP-A might accelerate lung maturation, which decreases the incidence of RDS .
Northway et al.  first described BPD in 1967 and defined it as a chronic lung disease affecting preterm infants with severe lung injury resulting from mechanical ventilation and oxygen toxicity. Due to the introduction of surfactant treatment for RDS, more protective ventilation strategies, and the use of antenatal glucocorticoids, BPD is now mostly seen among very immature infants, which are of a much younger GA then 30 years ago. In these infants, high concentrations of oxygen and high positive airway pressures are mostly avoided [85, 86]. In essence, these infants have a different disease compared to “old BPD.” This “new BPD” is more a clinical picture of immaturity . The common denominator, however, is still stress and inflammation as a cause of histological changes and developmental delay.
Very preterm delivery is associated with CA. Many studies have examined the relationship between CA and BPD. However, the results are contradictory. A systematic review and meta-analysis by Hartling et al.  assessed the current available literature on the association between CA and BPD in preterm infants and showed a significant association between CA and BPD. After controlling for publication bias, results were no longer significant. Additionally, the analyses showed that GA and birth weight were confounders in the association between CA and BPD. The problem is that studies differ in their definitions used for histological CA. A study by Kim et al.  aimed to investigate the relationship between histological CA and neonatal morbidity using a definition of histological CA that reflects the site and extent of inflammation. Histological CA encompasses amnionitis, choriodeciduitis, and funisitis and placental inflammation. This study showed that amnionitis, which is the final stage of CA, was associated with BPD. Again, pathogen specificity was not considered. Conversely, funisitis was not associated with the development of BPD. Pro-inflammatory cytokines produced in a response to CA can be aspired by the fetus and make direct contact with respiratory epithelium, which induces pulmonary inflammation. The induction of pulmonary inflammation via the aspiration of inflammatory cytokines makes it likely that direct contact of pro-inflammatory stimuli with airway epithelium contributes to the development of BPD. This is also a possible explanation for the fact that amnionitis is associated with BPD and funisitis is not .
This also leads to a relevant research question: does prenatal infection and subsequent inflammation influence the function of alveolar macrophages, the production of surfactant proteins, and local cytokine responses in the lung? Further studies are needed to address this important question.
The gastrointestinal (GI) tract is covered with epithelial cells, which are the first layer of defense. So-called M cells are specialized epithelium cells of the gut and are expressed in the follicle-associated epithelium of Peyer’s patches in the lower parts of the small intestine (ileum). These cells are involved in transport of antigens from the intestinal lumen to Peyer’s patches. Here, antigens are processed by antigen-presenting cells, which present the antigens to naïve T cells. Additionally, the lamina propria also contains immune cells, such as DCs and macrophages .
The development of the intestinal immune system starts during the fetal period. TLR2 and TLR4 are present on the fetal intestinal epithelial cell during weeks 18–21 of gestation . Exposure of fetal intestinal epithelial cells to LPS/endotoxin results in higher levels of nuclear factor-κB (NF-κB) activation and IL-8 secretion compared to that of control subjects [93, 94]. IL-8 is a chemokine that recruits neutrophils. Shortly after birth, this response to endotoxin is no longer observed, indicating perinatal induction of negative regulatory control mechanisms in epithelial TLR signaling. The underlying mechanism of this hyporesponsiveness is on the one hand downregulation of IL-1-receptor-associated kinase I (IRAK1), which is essential for epithelial TLR4 signaling . Downregulation of IRAK1 acts as a negative regulatory mechanism of TLR4 signaling. On the other hand, it has been long accepted that epidermal growth factor (EGF) has the potential to inhibit TLR4 signaling . EGF is present in amniotic fluid [95, 96] and breast milk . EGF is able to inhibit TLR4 signaling through EGF-mediated epidermal growth factor receptor (EGFR) activation . These mechanisms of tolerance induction may facilitate microbial colonization in the newborn, so establishing its own microbiome. Additionally, these are important mechanisms for the induction of oral tolerance in newborns, which explains why most infants show no adverse immune reaction when exposed to environmental and dietary proteins. In this context, it is interesting that failure to downregulate TLR4 signaling and therewith an excessive IL-8 response  in preterm infants has been associated with the development of necrotizing enterocolitis (NEC). Since research has shown that breast milk can prevent the development of NEC, it is of great importance to develop a clinical feeding formula in which breast milk components are incorporated. Research has not yet clearly proved if EGF is the sole component in breast milk that has a protective capacity in preventing NEC. It is necessary to investigate the most effective composition of nutrition for preterm infants in order to reduce the incidence of NEC.
It was long considered that the gut is sterile at birth and that microbial colonization starts during and after delivery. The infant becomes colonized with maternal vaginal and fecal bacteria during delivery or when delivery is accomplished; via cesarean section, the infant becomes colonized with bacteria from the skin and hospital environment . A review by Koleva et al. , however, reports preliminary evidence that microbial colonization of the gut starts in utero, which has been suggested in experimental setup by Jiménez . An important research topic is the relation between prenatal gut colonization, the neonatal microbiome, and the development of NEC.
NEC is one of the most common and devastating diseases among neonates with high mortality and morbidity [99, 100]. An imbalance in homeostasis leading to inflammation predisposes an infant to development of NEC. Initial bacterial colonization of the newborn gut also plays an important role in the development of NEC [93, 101]. Additionally, it seems that neonates with NEC have a different microbiome compared to neonates without NEC . During the last trimester of pregnancy, the fetus swallows amniotic fluid in large quantities. Microbial DNA found in meconium suggests that the fetal intestine is already exposed to the microbes in the amniotic fluid . NEC is characterized by excessive infiltration of neutrophils contributing to inflammatory necrosis . Exposure of the immature or fetal enterocyte to LPS leads to an excessive production of IL-8 [93, 103]. Nanthakumar et al.  demonstrated that this excessive inflammatory response is caused by a developmental immaturity of innate immune response genes. Next to the developmental immaturity of the innate immune response genes, Weitkamp et al.  investigated that the proportion of Treg cells in the lamina propria of the intestine of premature infants is significantly reduced. The reduced amount of Treg cells may contribute to the pathology of NEC.
It is likely that antenatal inflammation is associated with the development of NEC. A systematic review and meta-analysis by Been et al.  investigated the association between CA and NEC. This review demonstrated that histological CA with fetal involvement was associated with a threefold increased risk of NEC and clinical CA was associated with a modest increased risk of NEC.
In conclusion, we summarized the infectious and inflammatory threats for fetuses and (preterm) neonates, already present before birth. We highlighted the most prominent features of fetal and neonatal immunity and the cells and cytokines involved and also how they develop in time during gestation. We found a large number of studies focusing on prenatal infection and the host response. Maternal CA and subsequent fetal immune responses are well studied, and we found clinical data on cellular and cytokine responses to different microbial challenges. The link to postnatal immunological effects, however, turned out to be much more complicated. We found studies relating prenatal infectious and inflammatory hits to well-known neonatal diseases as well as analyses on cells and proteins involved in these processes. We also found studies with immunological-based pathogenic mechanisms for these diseases. A direct link with prenatal hits, however, could not undisputedly be established. We did however identify several unresolved topics such as neonatal consequences of labor as an inflammatory process on itself and the role of pattern recognition receptors in neonatal immunity. We also propose several questions for further research such as what is the influence of prenatal immune responses on postnatal immunity of the skin, does prenatal infection and subsequent inflammation influence the function of alveolar macrophages, the production of surfactant proteins and local cytokine responses in the lung, and what is the most appropriate nutrition for preterm infants in order to reduce the incidence of NEC? Multiple research questions on NEC remain: what is the effect of prematurity on the risk of developing NEC and how does this relate to antenatal inflammatory hits? What is the role of antenatal infection on the fetal microbiota and the host immune response and does this influence the risk of developing NEC? What cell types and cytokines are involved in NEC and what are the differences in babies with and without prenatal inflammatory hits? Further studies are needed to explore these topics.
No funding was received for this review.
GvW and BK conceived and designed this review. GvW and LD acquired the data from the literature and drafted the manuscript. BK and TW critically revised the manuscript. All authors approved the final version of the manuscript and are accountable for all aspects of the work.
The authors declare that they have no competing interests.
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- Goldenberg RL, Hauth JC, Andrews WW (2000) Intrauterine infection and preterm delivery. N Engl J Med 342(20):1500–1507PubMedView ArticleGoogle Scholar
- Holt P, Jones C (2000) The development of the immune system during pregnancy and early life. Allergy 55(8):688–697PubMedView ArticleGoogle Scholar
- Adkins B, Leclerc C, Marshall-Clarke S (2004) Neonatal adaptive immunity comes of age. Nat Rev Immunol 4(7):553–564PubMedView ArticleGoogle Scholar
- Marodi L (2006) Innate cellular immune responses in newborns. Clin Immunol (Orlando, Fla) 118(2-3):137–144View ArticleGoogle Scholar
- Ygberg S, Nilsson A (2012) The developing immune system—from foetus to toddler. Acta Paediatr (Oslo, Norway : 1992) 101(2):120–127View ArticleGoogle Scholar
- Tavian M, Biasch K, Sinka L, Vallet J, Peault B (2010) Embryonic origin of human hematopoiesis. Int J Dev Biol 54(6-7):1061–1065PubMedView ArticleGoogle Scholar
- Mikkola HK, Orkin SH (2006) The journey of developing hematopoietic stem cells. Development 133(19):3733–3744PubMedView ArticleGoogle Scholar
- Cupedo T (2011) Human lymph node development: an inflammatory interaction. Immunol Lett 138(1):4–6PubMedView ArticleGoogle Scholar
- Takashina T (1987) Haemopoiesis in the human yolk sac. J Anat 151:125PubMedPubMed CentralGoogle Scholar
- Ginhoux F, Jung S (2014) Monocytes and macrophages: developmental pathways and tissue homeostasis. Nat Rev Immunol 14(6):392–404PubMedView ArticleGoogle Scholar
- Janossy G, Bofill M, Poulter LW, Rawlings E, Burford GD, Navarrete C et al (1986) Separate ontogeny of two macrophage-like accessory cell populations in the human fetus. J Immunol 136(12):4354–4361PubMedGoogle Scholar
- Davies NP, Buggins AG, Snijders RJ, Jenkins E, Layton DM, Nicolaides KH (1992) Blood leucocyte count in the human fetus. Arch Dis Child 67(4 Spec No):399–403PubMedPubMed CentralView ArticleGoogle Scholar
- Carr R (2000) Neutrophil production and function in newborn infants. Br J Haematol 110(1):18–28PubMedView ArticleGoogle Scholar
- Strunk T, Temming P, Gembruch U, Reiss I, Bucsky P, Schultz C (2004) Differential maturation of the innate immune response in human fetuses. Pediatr Res 56(2):219–226PubMedView ArticleGoogle Scholar
- Liu K, Nussenzweig MC (2010) Origin and development of dendritic cells. Immunol Rev 234(1):45–54PubMedView ArticleGoogle Scholar
- Phillips JH, Hori T, Nagler A, Bhat N, Spits H, Lanier LL (1992) Ontogeny of human natural killer (NK) cells: fetal NK cells mediate cytolytic function and express cytoplasmic CD3 epsilon, delta proteins. J Exp Med 175(4):1055–1066PubMedView ArticleGoogle Scholar
- Sato T, Laver JH, Aiba Y, Ogawa M (1999) NK cell colony formation from human fetal thymocytes. Exp Hematol 27(4):726–733PubMedView ArticleGoogle Scholar
- Cantani A (2008) Pediatric allergy, asthma and immunology. Springer Science & Business Media, BerlinGoogle Scholar
- Bofill M, Janossy G, Janossa M, Burford GD, Seymour GJ, Wernet P et al (1985) Human B cell development. II. Subpopulations in the human fetus. J Immunol 134(3):1531–1538PubMedGoogle Scholar
- Allman D, Miller JP (2003) Common lymphoid progenitors, early B-lineage precursors, and IL-7: characterizing the trophic and instructive signals underlying early B cell development. Immunol Res 27(2-3):131–140PubMedView ArticleGoogle Scholar
- Nagasawa T (2006) Microenvironmental niches in the bone marrow required for B-cell development. Nat Rev Immunol 6(2):107–116PubMedView ArticleGoogle Scholar
- Siegrist C-A (2007) The challenges of vaccine responses in early life: selected examples. J Comp Pathol 137:S4–S9PubMedView ArticleGoogle Scholar
- Weller S, Braun MC, Tan BK, Rosenwald A, Cordier C, Conley ME et al (2004) Human blood IgM “memory” B cells are circulating splenic marginal zone B cells harboring a prediversified immunoglobulin repertoire. Blood 104(12):3647–3654PubMedPubMed CentralView ArticleGoogle Scholar
- Wegmann T (1984) Foetal protection against abortion: is it immunosuppression or immunostimulation? Annales de l’Institut Pasteur. Immunologie. Centre national de la recherche scientifique, ParisGoogle Scholar
- Rugeles MT, Shearer GM (2004) Alloantigen recognition in utero: dual advantage for the fetus? Trends Immunol 25(7):348–352PubMedView ArticleGoogle Scholar
- Koleva PT, Kim JS, Scott JA, Kozyrskyj AL (2015) Microbial programming of health and disease starts during fetal life. Birth Defects Res C Embryo Today 105(4):265–277PubMedView ArticleGoogle Scholar
- Jiménez E, Marín ML, Martín R, Odriozola JM, Olivares M, Xaus J et al (2008) Is meconium from healthy newborns actually sterile? Res Microbiol 159(3):187–193PubMedView ArticleGoogle Scholar
- Aagaard K, Ma J, Antony KM, Ganu R, Petrosino J, Versalovic J (2014) The placenta harbors a unique microbiome. Sci Transl Med 6(237):237ra65-ra65View ArticleGoogle Scholar
- Kallapur SG, Presicce P, Rueda CM, Jobe AH, Chougnet CA (2014) Fetal immune response to chorioamnionitis. Semin Reprod Med 32(1):56–67PubMedPubMed CentralView ArticleGoogle Scholar
- Czikk MJ, McCarthy FP, Murphy KE (2011) Chorioamnionitis: from pathogenesis to treatment. Clin Microbiol Infect 17(9):1304–1311PubMedView ArticleGoogle Scholar
- Galinsky R, Polglase GR, Hooper SB, Black MJ, Moss TJ (2013) The consequences of chorioamnionitis: preterm birth and effects on development. J Pregnancy 2013:412831PubMedPubMed CentralView ArticleGoogle Scholar
- Redline RW (2012) Inflammatory response in acute chorioamnionitis. Semin Fetal Neonatal Med 17(1):20–25PubMedView ArticleGoogle Scholar
- Redline RW, Faye-Petersen O, Heller D, Qureshi F, Savell V, Vogler C (2003) Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns. Pediatr Dev Pathol 6(5):435–448PubMedView ArticleGoogle Scholar
- Gomez R, Romero R, Ghezzi F, Yoon BH, Mazor M, Berry SM (1998) The fetal inflammatory response syndrome. Am J Obstet Gynecol 179(1):194–202PubMedView ArticleGoogle Scholar
- Agrawal V, Hirsch E (2012) Intrauterine infection and preterm labor. Semin Fetal Neonatal Med 17(1):12–19PubMedView ArticleGoogle Scholar
- Romero R, Gotsch F, Pineles B, Kusanovic JP (2007) Inflammation in pregnancy: its roles in reproductive physiology, obstetrical complications, and fetal injury. Nutr Rev 65(12 Pt 2):S194–S202PubMedView ArticleGoogle Scholar
- Bokström H, Brännström M, Alexandersson M, Norström A (1997) Leukocyte subpopulations in the human uterine cervical stroma at early and term pregnancy. Hum Reprod 12(3):586–590PubMedView ArticleGoogle Scholar
- Osman I, Young A, Ledingham MA, Thomson AJ, Jordan F, Greer IA et al (2003) Leukocyte density and pro‐inflammatory cytokine expression in human fetal membranes, decidua, cervix and myometrium before and during labour at term. Mol Hum Reprod 9(1):41–45PubMedView ArticleGoogle Scholar
- Thomson AJ, Telfer JF, Young A, Campbell S, Stewart CJ, Cameron IT et al (1999) Leukocytes infiltrate the myometrium during human parturition: further evidence that labour is an inflammatory process. Hum Reprod 14(1):229–236PubMedView ArticleGoogle Scholar
- Winkler M, Kemp B, Fischer D, Ruck P, Rath W (2003) Expression of adhesion molecules in the lower uterine segment during term and preterm parturition. Microsc Res Tech 60(4):430–444PubMedView ArticleGoogle Scholar
- Adkins B (2007) Heterogeneity in the CD4 T cell compartment and the variability of neonatal immune responsiveness. Curr Immunol Rev 3(3):151PubMedPubMed CentralView ArticleGoogle Scholar
- Dowling DJ, Levy O (2014) Ontogeny of early life immunity. Trends Immunol 35(7):299–310PubMedPubMed CentralView ArticleGoogle Scholar
- Levy O (2007) Innate immunity of the newborn: basic mechanisms and clinical correlates. Nat Rev Immunol 7(5):379–390PubMedView ArticleGoogle Scholar
- Levy O, Zarember KA, Roy RM, Cywes C, Godowski PJ, Wessels MR (2004) Selective impairment of TLR-mediated innate immunity in human newborns: neonatal blood plasma reduces monocyte TNF-alpha induction by bacterial lipopeptides, lipopolysaccharide, and imiquimod, but preserves the response to R-848. J Immunol 173(7):4627–4634PubMedView ArticleGoogle Scholar
- Dasari P, Zola H, Nicholson IC (2011) Expression of Toll‐like receptors by neonatal leukocytes. Pediatr Allergy Immunol 22(2):221–228PubMedView ArticleGoogle Scholar
- Quinello C, Silveira‐Lessa A, Ceccon M, Cianciarullo M, Carneiro‐Sampaio M, Palmeira P (2014) Phenotypic differences in leucocyte populations among healthy preterm and full-term newborns. Scand J Immunol 80(1):57–70PubMedView ArticleGoogle Scholar
- Marchant EA, Kan B, Sharma AA, van Zanten A, Kollmann TR, Brant R, et al (2015) Attenuated innate immune defenses in very premature neonates during the neonatal period. Pediatr Res 78(5):492–7Google Scholar
- Belderbos ME, van Bleek GM, Levy O, Blanken MO, Houben ML, Schuijff L et al (2009) Skewed pattern of Toll-like receptor 4-mediated cytokine production in human neonatal blood: low LPS-induced IL-12p70 and high IL-10 persist throughout the first month of life. Clin Immunol (Orlando, Fla) 133(2):228–237View ArticleGoogle Scholar
- Sharma AA, Jen R, Brant R, Ladd M, Huang Q, Skoll A et al (2014) Hierarchical maturation of innate immune defences in very preterm neonates. Neonatology 106(1):1–9PubMedPubMed CentralView ArticleGoogle Scholar
- Firth MA, Shewen PE, Hodgins DC (2005) Passive and active components of neonatal innate immune defenses. Anim Health Res Rev 6(2):143–158PubMedView ArticleGoogle Scholar
- Levy O (2004) Antimicrobial proteins and peptides: anti-infective molecules of mammalian leukocytes. J Leukoc Biol 76(5):909–925PubMedView ArticleGoogle Scholar
- Strunk T, Currie A, Richmond P, Simmer K, Burgner D (2011) Innate immunity in human newborn infants: prematurity means more than immaturity. J Matern Fetal Neonatal Med 24(1):25–31PubMedView ArticleGoogle Scholar
- Ip WK, Takahashi K, Moore KJ, Stuart LM, Ezekowitz RA (2008) Mannose-binding lectin enhances Toll-like receptors 2 and 6 signaling from the phagosome. J Exp Med 205(1):169–181PubMedPubMed CentralView ArticleGoogle Scholar
- Gessler P, Luders R, Konig S, Haas N, Lasch P, Kachel W (1995) Neonatal neutropenia in low birthweight premature infants. Am J Perinatol 12(1):34–38PubMedView ArticleGoogle Scholar
- Anderson DC, Abbassi O, Kishimoto TK, Koenig JM, McIntire LV, Smith CW (1991) Diminished lectin-, epidermal growth factor-, complement binding domain-cell adhesion molecule-1 on neonatal neutrophils underlies their impaired CD18-independent adhesion to endothelial cells in vitro. J Immunol 146(10):3372–3379PubMedGoogle Scholar
- Hallwirth U, Pomberger G, Pollak A, Roth E, Spittler A (2004) Monocyte switch in neonates: high phagocytic capacity and low HLA-DR expression in VLBWI are inverted during gestational aging. Pediatr Allergy Immunol 15(6):513–516PubMedView ArticleGoogle Scholar
- Gille C, Spring B, Tewes L, Poets CF, Orlikowsky T (2006) A new method to quantify phagocytosis and intracellular degradation using green fluorescent protein-labeled Escherichia coli: comparison of cord blood macrophages and peripheral blood macrophages of healthy adults. Cytometry A 69(3):152–154PubMedView ArticleGoogle Scholar
- Le Garff-Tavernier M, Beziat V, Decocq J, Siguret V, Gandjbakhch F, Pautas E et al (2010) Human NK cells display major phenotypic and functional changes over the life span. Aging Cell 9(4):527–535PubMedView ArticleGoogle Scholar
- Langrish CL, Buddle JC, Thrasher AJ, Goldblatt D (2002) Neonatal dendritic cells are intrinsically biased against Th-1 immune responses. Clin Exp Immunol 128(1):118–123PubMedPubMed CentralView ArticleGoogle Scholar
- Malek A, Sager R, Kuhn P, Nicolaides KH, Schneider H (1996) Evolution of maternofetal transport of immunoglobulins during human pregnancy. Am J Reprod Immunol (New York, NY : 1989) 36(5):248–255View ArticleGoogle Scholar
- Gasparoni A, Ciardelli L, Avanzini A, Castellazzi AM, Carini R, Rondini G et al (2003) Age-related changes in intracellular TH1/TH2 cytokine production, immunoproliferative T lymphocyte response and natural killer cell activity in newborns, children and adults. Neonatology 84(4):297–303View ArticleGoogle Scholar
- Schelonka RL, Maheshwari A, Carlo WA, Taylor S, Hansen NI, Schendel DE et al (2011) T cell cytokines and the risk of blood stream infection in extremely low birth weight infants. Cytokine 53(2):249–255PubMedView ArticleGoogle Scholar
- van den Berg JP, Westerbeek EA, Berbers GA, van Gageldonk PG, van der Klis FR, van Elburg RM (2010) Transplacental transport of IgG antibodies specific for pertussis, diphtheria, tetanus, haemophilus influenzae type b, and Neisseria meningitidis serogroup C is lower in preterm compared with term infants. Pediatr Infect Dis J 29(9):801–805PubMedView ArticleGoogle Scholar
- Medzhitov R, Schneider DS, Soares MP (2012) Disease tolerance as a defense strategy. Science (New York, NY) 335(6071):936–941View ArticleGoogle Scholar
- Pacora P, Chaiworapongsa T, Maymon E, Kim YM, Gomez R, Yoon BH et al (2002) Funisitis and chorionic vasculitis: the histological counterpart of the fetal inflammatory response syndrome. J Matern Fetal Neonatal Med 11(1):18–25PubMedView ArticleGoogle Scholar
- Romero R, Espinoza J, Goncalves LF, Kusanovic JP, Friel LA, Nien JK (2006) Inflammation in preterm and term labour and delivery. Semin Fetal Neonatal Med 11(5):317–326PubMedView ArticleGoogle Scholar
- Dorschner RA, Lin KH, Murakami M, Gallo RL (2003) Neonatal skin in mice and humans expresses increased levels of antimicrobial peptides: innate immunity during development of the adaptive response. Pediatr Res 53(4):566–572PubMedView ArticleGoogle Scholar
- Dorschner RA, Pestonjamasp VK, Tamakuwala S, Ohtake T, Rudisill J, Nizet V et al (2001) Cutaneous injury induces the release of cathelicidin anti-microbial peptides active against group A Streptococcus. J Invest Dermatol 117(1):91–97PubMedView ArticleGoogle Scholar
- Yang D, Chertov O, Oppenheim JJ (2001) The role of mammalian antimicrobial peptides and proteins in awakening of innate host defenses and adaptive immunity. Cell Mol Life Sci 58(7):978–989PubMedView ArticleGoogle Scholar
- Kim YM, Romero R, Chaiworapongsa T, Espinoza J, Mor G, Kim CJ (2006) Dermatitis as a component of the fetal inflammatory response syndrome is associated with activation of Toll-like receptors in epidermal keratinocytes. Histopathology 49(5):506–514PubMedPubMed CentralView ArticleGoogle Scholar
- Jobe A, Whitsett J, Abman S (2016) Fetal & neonatal lung development. Cambridge University Press, CambridgeGoogle Scholar
- Kramer BW, Joshi SN, Moss TJ, Newnham JP, Sindelar R, Jobe AH et al (2007) Endotoxin-induced maturation of monocytes in preterm fetal sheep lung. Am J Physiol Lung Cell Mol Physiol 293(2):L345–L353PubMedView ArticleGoogle Scholar
- Greenough A, Murthy V (2008) Respiratory distress syndrome. Fetal Matern Med Rev 19(03):203–225View ArticleGoogle Scholar
- Marttila R, Kaprio J, Hallman M (2004) Respiratory distress syndrome in twin infants compared with singletons. Am J Obstet Gynecol 191(1):271–276PubMedView ArticleGoogle Scholar
- Watterberg KL, Demers LM, Scott SM, Murphy S (1996) Chorioamnionitis and early lung inflammation in infants in whom bronchopulmonary dysplasia develops. Pediatrics 97(2):210–215PubMedGoogle Scholar
- Lahra MM, Beeby PJ, Jeffery HE (2009) Maternal versus fetal inflammation and respiratory distress syndrome: a 10-year hospital cohort study. Arch Dis Child Fetal Neonatal Ed 94(1):F13–F16PubMedView ArticleGoogle Scholar
- Dempsey E, Chen M-F, Kokottis T, Vallerand D, Usher R (2005) Outcome of neonates less than 30 weeks gestation with histologic chorioamnionitis. Obstet Gynecol Surv 60(10):639–640View ArticleGoogle Scholar
- Lee J, Seong HS, Kim BJ, Jun JK, Romero R, Yoon BH (2009) Evidence to support that spontaneous preterm labor is adaptive in nature: neonatal RDS is more common in “indicated” than in “spontaneous” preterm birth. J Perinat Med 37(1):53–58PubMedPubMed CentralView ArticleGoogle Scholar
- Kunzmann S, Collins JJ, Kuypers E, Kramer BW (2013) Thrown off balance: the effect of antenatal inflammation on the developing lung and immune system. Am J Obstet Gynecol 208(6):429–437PubMedView ArticleGoogle Scholar
- Shimoya K, Taniguchi T, Matsuzaki N, Moriyama A, Murata Y, Kitajima H et al (2000) Chorioamnionitis decreased incidence of respiratory distress syndrome by elevating fetal interleukin-6 serum concentration. Hum Reprod 15(10):2234–2240PubMedView ArticleGoogle Scholar
- McIntosh JC, Mervin-Blake S, Conner E, Wright J (1996) Surfactant protein A protects growing cells and reduces TNF-alpha activity from LPS-stimulated macrophages. Am J Physiol Lung Cell Mol Physiol 271(2):L310–L319Google Scholar
- Kremlev SG, Phelps DS (1994) Surfactant protein A stimulation of inflammatory cytokine and immunoglobulin production. Am J Physiol Lung Cell Mol Physiol 267(6):L712–L719Google Scholar
- Tino M, Wright J (1996) Surfactant protein A stimulates phagocytosis of specific pulmonary pathogens by alveolar macrophages. Am J Physiol Lung Cell Mol Physiol 270(4):L677–L688Google Scholar
- Northway WH Jr, Rosan RC, Porter DY (1967) Pulmonary disease following respirator therapy of hyaline-membrane disease: bronchopulmonary dysplasia. N Engl J Med 276(7):357–368PubMedView ArticleGoogle Scholar
- Rojas MA, Gonzalez A, Bancalari E, Claure N, Poole C, Silva-Neto G (1995) Changing trends in the epidemiology and pathogenesis of neonatal chronic lung disease. J Pediatr 126(4):605–610PubMedView ArticleGoogle Scholar
- Charafeddine L, D’Angio CT, Phelps DL (1999) Atypical chronic lung disease patterns in neonates. Pediatrics 103(4):759–765PubMedView ArticleGoogle Scholar
- Coalson JJ (2006) Pathology of bronchopulmonary dysplasia. Semin Perinatol 30(4):179–184PubMedView ArticleGoogle Scholar
- Hartling L, Liang Y, Lacaze-Masmonteil T (2012) Chorioamnionitis as a risk factor for bronchopulmonary dysplasia: a systematic review and meta-analysis. Arch Dis Child Fetal Neonatal Ed 97(1):F8–F17PubMedView ArticleGoogle Scholar
- Kim SY, Choi CW, Jung E, Lee J, Lee JA, Kim H et al (2015) Neonatal Morbidities Associated with Histologic Chorioamnionitis Defined Based on the Site and Extent of Inflammation in Very Low Birth Weight Infants. J Korean Med Sci 30(10):1476–1482PubMedPubMed CentralView ArticleGoogle Scholar
- Ambalavanan N, Carlo WA, D’Angio CT, McDonald SA, Das A, Schendel D et al (2009) Cytokines associated with bronchopulmonary dysplasia or death in extremely low birth weight infants. Pediatrics 123(4):1132–1141PubMedPubMed CentralView ArticleGoogle Scholar
- Abreu MT, Fukata M, Arditi M (2005) TLR signaling in the gut in health and disease. J Immunol 174(8):4453–4460PubMedView ArticleGoogle Scholar
- Fusunyan RD, Nanthakumar NN, Baldeon ME, Walker WA (2001) Evidence for an innate immune response in the immature human intestine: toll-like receptors on fetal enterocytes. Pediatr Res 49(4):589–593PubMedView ArticleGoogle Scholar
- Nanthakumar NN, Fusunyan RD, Sanderson I, Walker WA (2000) Inflammation in the developing human intestine: A possible pathophysiologic contribution to necrotizing enterocolitis. Proc Natl Acad Sci 97(11):6043–6048PubMedPubMed CentralView ArticleGoogle Scholar
- Lotz M, Gütle D, Walther S, Ménard S, Bogdan C, Hornef MW (2006) Postnatal acquisition of endotoxin tolerance in intestinal epithelial cells. J Exp Med 203(4):973–984PubMedPubMed CentralView ArticleGoogle Scholar
- Good M, Siggers RH, Sodhi CP, Afrazi A, Alkhudari F, Egan CE et al (2012) Amniotic fluid inhibits Toll-like receptor 4 signaling in the fetal and neonatal intestinal epithelium. Proc Natl Acad Sci 109(28):11330–11335PubMedPubMed CentralView ArticleGoogle Scholar
- Hofmann GE, Abramowicz JS (1990) Epidermal growth factor (EGF) concentrations in amniotic fluid and maternal urine during pregnancy. Acta Obstet Gynecol Scand 69(3):217–21Google Scholar
- Chatterton DE, Nguyen DN, Bering SB, Sangild PT (2013) Anti-inflammatory mechanisms of bioactive milk proteins in the intestine of newborns. Int J Biochem Cell Biol 45(8):1730–1747PubMedView ArticleGoogle Scholar
- Dominguez-Bello MG, Costello EK, Contreras M, Magris M, Hidalgo G, Fierer N et al (2010) Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. Proc Natl Acad Sci 107(26):11971–11975PubMedPubMed CentralView ArticleGoogle Scholar
- Lin PW, Stoll BJ (2006) Necrotising enterocolitis. Lancet 368(9543):1271–1283PubMedView ArticleGoogle Scholar
- Neu J, Walker WA (2011) Necrotizing enterocolitis. N Engl J Med 364(3):255–264PubMedPubMed CentralView ArticleGoogle Scholar
- de Meij TG, van der Schee MP, Berkhout DJ, van de Velde ME, Jansen AE, Kramer BW et al (2015) Early detection of necrotizing enterocolitis by fecal volatile organic compounds analysis. J Pediatr 167(3):562–7. e1PubMedGoogle Scholar
- Torrazza RM, Neu J (2013) The altered gut microbiome and necrotizing enterocolitis. Clin Perinatol 40(1):93–108PubMedPubMed CentralView ArticleGoogle Scholar
- Nanthakumar N, Meng D, Goldstein AM, Zhu W, Lu L, Uauy R et al (2011) The mechanism of excessive intestinal inflammation in necrotizing enterocolitis: an immature innate immune response. PLoS One 6(3):e17776PubMedPubMed CentralView ArticleGoogle Scholar
- Weitkamp J-H, Koyama T, Rock MT, Correa H, Goettel JA, Matta P et al (2013) Necrotising enterocolitis is characterised by disrupted immune regulation and diminished mucosal regulatory (FOXP3)/effector (CD4, CD8) T cell ratios. Gut 62(1):73–82PubMedView ArticleGoogle Scholar
- Been JV, Lievense S, Zimmermann LJ, Kramer BW, Wolfs TG (2013) Chorioamnionitis as a risk factor for necrotizing enterocolitis: a systematic review and meta-analysis. J Pediatr 162(2):236–42. e2PubMedView ArticleGoogle Scholar