Intestinal Monocyte-Derived Macrophages Control Commensal-Specific Th17 Responses

• Intestinal CD103 DCs are dispensable for induction of Th17 cells by a gut commensal
• Intestinal CX3CR1 macrophages are required for Th17 cell induction by SFB
• Intestinal CX3CR1 macrophages are required for a commensal antigen-specific response

SummaryGeneration of different CD4 T cell responses to commensal and pathogenic bacteria is crucial for maintaining a healthy gut environment, but the associated cellular mechanisms are poorly understood. Dendritic cells (DCs) and macrophages (Mfs) integrate microbial signals and direct adaptive immunity. Although the role of DCs in initiating T cell responses is well appreciated, how Mfs contribute to the generation of CD4 T cell responses to intestinal microbes is unclear. Th17 cells are critical for mucosal immune protection and at steady state are induced by commensal bacteria, such as segmented filamentous bacteria (SFB). Here, we examined the roles of mucosal DCs and Mfs in Th17 induction by SFB in vivo. We show that Mfs, and not conventional CD103+ DCs, are essential for the generation of SFB-specific Th17 responses. Thus, Mfs drive mucosal T cell responses to certain commensal bacteria.

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