CX3CR1+ cells facilitate the activation of CD4 T cells in the colonic lamina propria during antigen-driven colitis

Abstract

Dendritic cells (DCs) and macrophages populate the intestinal lamina propria to initiate immune responses required for the maintenance of intestinal homeostasis. To investigate whether CX3CR1(+) phagocytes communicate with CD4 T cells during the development of transfer colitis, we established an antigen-driven colitis model induced by the adoptive transfer of DsRed OT-II cells in CX3CR1(GFP/+) × RAG(-/-) recipients challenged with Escherichia coli expressing ovalbumin (OVA) fused to a cyan fluorescent protein (CFP). After colonization of CX3CR1(GFP/+) × RAG(-/-) animals with red fluorescent E. coli pCherry-OVA, colonic CX3CR1(+) cells but not CD103(+) DCs phagocytosed E. coli pCherry-OVA. Degraded bacterial-derived antigens are transported by CD103(+) DCs to mesenteric lymph nodes (MLNs), where CD103(+) DCs prime naive T cells. In RAG(-/-) recipients reconstituted with OT II cells and gavaged with OVA-expressing E. coli, colonic CX3CR1(+) phagocytes are in close contact with CD4 T cells and presented bacterial-derived antigens to CD4 T cells to activate and expand effector T cells.

Diversity and functions of intestinal mononuclear phagocytes

“…Indeed bacteria have been detected within lamina propria m from steady state intestine 99 and CX3CR1 + m account for most of the uptake of organisms when E coli are administered orally. 147 In this regard CX3CR1 + phagocytes have been observed to send processes from the LP across the epithelium to capture luminal bacteria in a CX3CL1-dependent manner and although originally thought to be cDC, 148 it now seems likely that these were m . 108 As noted above, intestinal m are actively bactericidal, possibly reflecting the constitutive expression of mediators such as TNF and metallothionein-dependent Zn 2+ cations.…”

“…147,164 In the case of protein antigen, this transfer process has been suggested to involve Connexin 43 (Cx43) mediated gap junctions formed between m and cDC and leads to the induction of oral tolerance. 164 Division of labour amongst intestinal m and CD103 + cDC of this kind has also been suggested to be involved in the induction of local Th17 responses to SFB.…”

The urokinase plasminogen activator receptor (uPAR) controls macrophage phagocytosis in intestinal inflammation

“…The fractalkaline receptor (CX 3 CR 1 ) has been recently related to regulatory macrophages 25. We therefore analysed its expression in uPAR + macrophages by confocal microscopy.…”

“…Recently, Ly6C hi monocytes have been recognised as precursors of either regulatory macrophages or pro-inflammatory DCs in the intestine, depending on the local environmental conditions 38. Moreover, a new organisational scheme of intestinal DCs and macrophages has been proposed, in relationship to the expression of the non-overlapping marker CD103 (α E integrin) and of CX 3 CR 1 (fractalkaline receptor) 24 25 38. Remarkably, we proved that even if uPAR is broadly expressed by different cell types, during intestinal inflammation it is specifically enhanced in CX 3 CR 1 + regulatory macrophages, crucially involved in sampling bacteria and with a distinct anti-inflammatory phenotype 23 25…”

Expression of Fluorescent Proteins in Bifidobacteria for Analysis of Host-Microbe Interactions

“…This demonstrates that detection of bifidobacteria inside relevant host cell populations is possible. Using similar systems, we and others have successfully visualized fluorescent strains of C. rodentium, Salmonella enterica serovar Typhimurium, E. coli, and L. monocytogenes within host tissues and identified specific host cell populations that are associated with or have phagocytosed these labeled strains (60)(61)(62)(63)(64).…”