Fig. 2

Intestinal tissue oxygen levels after infection or chronic inflammation. a One hour after infection, infiltration by neutrophils causes an increase in ROS production and subsequent decrease in oxygen levels, from 7 % to almost 5 %. Vasodilators are released to promote microvessel perfusion. Epithelial barrier is intact, and bacterial spread is contained. b As the infection progresses, pro-inflammatory cytokines are released and more PMNs are recruited to the tissue further decreasing local oxygen levels to less than 1 %. The epithelial layer is disrupted, and blood vessels become constricted because of clotting. Several hypoxia-dependent genes are upregulated. c In tissues with chronic inflammation, infiltrating neutrophils also lead to depletion of oxygen. Transcriptional changes in hypoxia-dependent genes along with aberrant vascularization create a severe hypoxic environment (2–4 %) [7, 8, 11]