Enteric Flora Expands Gut Lamina Propria CX3CR1+ Dendritic Cells Supporting Inflammatory Immune Responses Under Normal and Inflammatory Conditions

CD103 or CX(3)CR1 surface expression defines distinct dendritic cells (DCs) and macrophages in the murine lamina propria of the colon (cLP). We investigated the surface marker and functional phenotype of CD103(+) and CX(3)CR1(+) cLP DCs and their role in transfer colitis. cLP CD11c(+) cells were isolated from specific pathogen-free or germ-free mice to elucidate the role of the commensal flora in their development. The cLP CD11c(+) cells are a heterogeneous cell population that includes 16% CX(3)CR1(+), 34% CD103(+), 30% CD103(-)CX(3)CR1(-) DCs, and 17% CD68(+/)F4/80(+)CX(3)CR1(+)CD11c(+) macrophages. All DCs expressed high levels of MHC II but low levels of costimulatory (CD40, CD86, and CD80) and coinhibitory (programmed death ligand-1) molecules. Ex vivo confocal microscopy demonstrated that CX(3)CR1(+)CD11c(+) cells, but not CD103(+) DCs, were reduced in the cLP of germ-free (CX(3)CR1-GFP) mice. The absence of the enteric flora prevents the formation of transepithelial processes by the CX(3)CR1(+) DCs. CX(3)CR1(+) DCs preferentially supported Th1/Th17 CD4 T cell differentiation. CD103(+) DCs preferentially induced the differentiation of Foxp3-expressing regulatory T cells. The stimulation of cLP DCs with fractalkine/CX(3)CL1 increased the release of IL-6 and TNF-alpha. In the absence of CX(3)CR1, the CD45RB(high) CD4 transfer colitis was suppressed and associated with reduced numbers of DCs in the mesenteric lymph nodes and a reduction in serum IFN-gamma and IL-17. The local bacteria-driven accumulation of CX(3)CR1(+) DCs seems to support inflammatory immune responses.