Fig. 1.

Innate immune circuits control intestinal homeostasis. a During steady state conditions, a number of specialized myeloid cell populations act in concert with IEC and dietary metabolites such as RA to promote tolerance to luminal antigens. b In IBD, there is a dramatic alteration in the composition and functions of myeloid cells in the intestinal lamina propria. They produce elevated levels of inflammatory cytokines that drive the activation of additional populations of innate and adaptive leucocytes, resulting in chronic inflammatory pathology. TSLP = Thymic stromal lymphopoietin; sIgA = secretory IgA.