Figure 4.

IgG in intestinal homeostasis. FcRn-mediated placental and epithelial transport contributes to the neonatal anti-microbial IgG repertoire in early life, mediating protection against opportunistic mucosal invasion. Maternally-derived IgG contributes to protection from allergic responses through FcRn-mediated antigen presentation by DCs to T cells for regulatory T cell induction. IgG-mediated transfer of microbial molecules, such as SCFAs, also supports appropriate immune cell development. In adult humans and mice, anti-microbial IgG is generated throughout life in GALT, contributing to systemic protection from infection through engagement of FcγRs on myeloid cells. In humans, FcRn is continuously expressed within the intestinal epithelium, allowing for bidirectional trafficking of IgG and immune complexes between the intestinal lumen and lamina propria for antigen delivery to local FcγR-expressing myeloid cells. SCFA, short-chain fatty acids; ILC3, group 3 innate lymphoid cell; FcRn, neonatal Fc receptor; AHR, aryl hydrocarbon receptor.