Characterization of the Mucosal Effector and Memory CD4 T Cell Response to Oral Bacterial Infection

Listeria monocytogenes (LM) is an enteroinvasive pathogen and the cause of listeriosis, a highly fatal food borne infection. Using an oral LM infection model, we show that a subset of blood-borne listeriolysin O (LLO)-specific CD4 T cells transiently express the α4β7 integrin early after infection. Subsequently, antigen-specific CD4 T cells rapidly accumulated and retained long-term in the gut mucosal tissues, and exhibited a robust recall response. These data suggested that priming in the mucosal lymphoid tissues generated a subset of mucosa-seeking CD4 T cells with high memory potential in an IL-15 independent manner. Phenotipically, naive CD4 T cells (CD44low, CD62Lhigh) contained two distinct subsets: Ly6Chigh/CD27high and Ly6Clow/CD27high. At day 9 post-infection, the majority of LLO-specific CD4 T cells in the mucosal tissues were Ly6Clow/CD27low and this population persisted throughout memory. In contrast, LLO-specific CD4 T cells isolated from the spleen and MLNs were comprised of four subsets based on CD27 and Ly6C expression. Mucosal CD27lowLy6Clow CD4 T cells produced IFN-γ and IL-2 while CD27low as well as both Ly6Clow and Ly6Chigh splenic and MLN CD4 T cells expressed the same cytokines as well. Interestingly, IL-17 production increased in mucosal memory CD4 T cells. In the absence of CD69 expression, IL-17 production is substantially increased in mucosal CD4 T cells. However, mixed bone marrow chimera studies indicate that this phenomenon is not a CD4 T cell intrinsic affect. Also, the absence of IL-15 leads to more IL-17 production of mucosal CD4 T cells. Depletion of CD4 T cells leads to a higher bacterial burden in the gut and spleen. These results indicate that antigen-specific intestinal mucosal effector and memory CD4 T cells are phenotypically and functionally distinct compared to their splenic counterparts. Thus, our findings demonstrate an important role for mucosal memory CD4 T cells in protection against oral infection and in maintaining barrier infection