Carlson College of Veterinary Medicine

Intestinal mononuclear phagocytes (MPs) are composed of heterogeneous dendritic cell (DC) and macrophage subsets necessary for the initiation of immune response and control of inflammation. Although MPs in the normal intestine have been extensively studied, the heterogeneity and function of inflammatory MPs remain poorly defined. We performed phenotypical, transcriptional, and functional analyses of inflammatory MPs in infectious colitis and identified CX3CR1 MPs as the most prevalent inflammatory cell type. CX3CR1 MPs were further divided into three distinct populations, namely, CX3CR1, CX3CR1 (lymph migratory), and CX3CR1 (mucosa resident), all of which were transcriptionally aligned with macrophages and derived from monocytes. In follow-up experiments in vivo, intestinal CX3CR1 macrophages were superior to conventional DC1 (cDC1) and cDC2 in inducing -specific mucosal IgA. We next examined spatial organization of the immune response induced by CX3CR1 macrophage subsets and identified mucosa-resident CX3CR1 macrophages as the antigen-presenting cells responsible for recruitment and activation of CD4 T and B cells to the sites of invasion, followed by tertiary lymphoid structure formation and the local pathogen-specific IgA response. Using mice we developed with a floxed allele, we showed that this local IgA response developed independently of migration of the CX3CR1 population to the mesenteric lymph nodes and contributed to the total mucosal IgA response to infection. The differential activity of intestinal macrophage subsets in promoting mucosal IgA responses should be considered in the development of vaccines to prevent infection and in the design of anti-inflammatory therapies aimed at modulating macrophage function in inflammatory bowel disease.