Figure 3.

Schematic of major leukocyte populations in the intestine during homeostasis and their expression of FcγRs. Migratory DCs promote B cell IgA class-switching and T cell polarization in GALT and MLNs, including regulatory T cells (Treg) and Th17 cells. The balance of Tregs and Th17 cells is critical for maintaining intestinal homeostasis and suppressing excessive responses to the microbiota. CD11b⁺ cDC2s have an A:I ratio skewed toward FcγRIIB expression, as observed in DCs in other organs. FcγR-expressing DCs and monocyte-derived macrophages within the lamina propria support T cell and ILC3 activation via commensal-dependent production of cytokines, including IL-1β and IL-23. Tissue-resident macrophages are dependent on IL-10 for their suppressive function. APRIL and BAFF production by DCs and macrophages supports local plasma cell survival. Macrophage A:I ratio is skewed toward activating FcγRs and tuneable to the local milieu. Plasma cells and B cells express FcγRIIB, regulating survival and BCR activation threshold in these cells, respectively. Blue receptor, activating FcγR; red receptor, inhibitory FcγRIIB; S-IgA, secretory IgA; MLN, mesenteric lymph node; GALT, gut-associated lymphoid tissue; DC, dendritic cell; APRIL, a proliferation-inducing ligand; BAFF, B cell activating factor; IESC, intestinal epithelial stem cell; ILC3, group 3 innate lymphoid cell.