Interleukin-12-Producing CD103+CD11b-CD8+ Dendritic Cells Are Responsible for Eliciting Gut Intraepithelial Lymphocyte Response against Encephalitozoon cuniculi

Microsporidia, which belong to the kingdom Fungi, are important opportunistic pathogens in HIV-infected populations and organ transplant recipients that are often associated with a broad range of symptoms, such as diarrhea, nephritis, and encephalitis. Natural infection occurs via the oral route, and as a consequence, gut immunity plays an important role in restricting the dissemination of these pathogens. Studies from our laboratory have reported that the pathogens induce a rapid intraepithelial lymphocyte (IEL) response important for host protection. Although mucosal dendritic cells (DC) are likely involved in triggering an antigen-specific IEL response, the specific subset(s) responsible has yet to be identified. Toward this goal, we demonstrate a very important role for mucosal CD11b(-) CD8(+) DC in the initiation of an antigen-specific IEL in vivo. Effectively, after Encephalitozoon cuniculi infection, CD11b(-) CD8(+) DC were activated in the lamina propria (LP) and acquired the ability to process retinoic acid (RA). However, this subset did not produce interleukin 12 (IL-12) but upregulated CD103, which is essential for migration to the mesenteric lymph nodes (MLN). Interestingly, CD103(+) CD11b(-) CD8(+) DC in the MLN, in addition to processing RA, also secreted IL-12 and were responsible for gut imprinting specificity on mucosal CD8 T cells. To the best of our knowledge, this is the first report describing the importance of MLN CD103(+) CD11b(-) CD8(+) DC isolated from infected animals in the generation of an IEL response against a live pathogen.