Reactive oxygen species regulate early development of the intestinal macrophage-microbiome interface

• ROS produced by monocytes, and macrophages are essential to maintain intestinal homeostasis.

• The wildling model substantially improves preclinical modelling of the complex inflammatory bowel disease phenotype in CGD.

Controlled development of cellular intestinal immunity in the face of dynamic microbiota emergence constitutes a major challenge in very early life, and a bottleneck for sustained growth and well-being. Early-onset inflammatory bowel disease (IBD) represents an extreme disturbance of intestinal immunity. It is a hallmark, and often the first manifestation of chronic granulomatous disease (CGD), caused by inborn defects in the NADPH oxidase NOX2 and thus the failure to produce reactive oxygen species (ROS) in phagocytes. However, in contrast to the known role of ROS in antimicrobial defense, the mechanisms underlying intestinal immunopathology in CGD remain enigmatic. This is partly due to the incomplete recapitulation of the CGD-IBD phenotype in established mouse models. We found that mice deficient in the NOX2 subunits p47phox or gp91phox showed similar baseline disturbances in lamina-propria macrophage differentiation, but they responded differently to chemically-induced colitis. Although p47phox and gp91phox-deficient mice differed markedly in microbiota composition, cross-fostering failed to equalize discrepant IBD phenotypes and microbiota, pointing at extremely early and functionally important microbiota fixation under specific pathogen-free housing conditions. In contrast, neonatal acquisition of a complex wild-mouse-microbiota triggered spontaneous IBD, granuloma formation and secondary sepsis with intestinal pathogens in both NOX2-deficient mouse lines, which was in part dependent on NOX2 in intestinal macrophages. Thus, in experimental CGD, the aberrant development of tissue immunity and the microbiota are closely intertwined immediately after birth.