Luminal Bacteria Recruit CD103⁺ Dendritic Cells into the Intestinal Epithelium to Sample Bacterial Antigens for Presentation

CD103⁺ dendritic cells (DCs) carry bacteria from the small intestine and can present antigens to T cells. Yet they have not been recorded sampling luminal bacteria or presenting bacterial antigens in mesentery lymph nodes. We used 2-photon microscopy in live Cx3cr1^+/gfp × Cd11c-YFP mice to study these processes. At steady state, sparse CD103⁺ DCs occupied the epithelium. They patrolled among enterocytes while extending dendrites toward the lumen, likely using tight-junction proteins to penetrate the epithelium. Challenge with Salmonella triggered chemokine- and toll-like receptor (TLR)-dependent recruitment of additional DCs from the lamina propria (LP). The DCs efficiently phagocytosed the bacteria using intraepithelial dendrites. Noninvasive bacteria were similarly sampled. In contrast, CD103⁺ DCs sampled soluble luminal antigen inefficiently. In mice harboring CD103⁺ DCs, antigen-specific CD8 T cells were subsequently activated in MLNs. Intestinal CD103⁺ DCs are therefore equipped with unique mechanisms to independently complete the processes of uptake, transportation, and presentation of bacterial antigens.