Peyer's patches contain abundant isotype-switched B cells with activated phenotypes and are inductive sites for T-independent anti-DNA IgA

Peyer's patches (PPs) are inductive sites for IgA production; however, the induction mechanism of IgA remains largely unknown. We found that the activated phenotypes of isotype-switched PP B cells were more abundant than those of splenic B cells. Immunoglobulins (Igs) from PP B cells reacted to several substances, including DNA and diet extract. Hybridomas established from PP B cells of untreated mice revealed that IgA mainly react with DNA. PP-deficient mice revealed that PPs were dispensable for a total intestinal IgA amount but were required for intestinal anti-diet extract and anti-DNA IgA. Antibiotic-treated mice and CD4(+) T cell-depleted mice demonstrated that the intestinal anti-DNA IgA was induced by microbiota in a T-independent manner. Interestingly, the oral administration of IgA led to the expansion of intestinal bacteria in a reactivity-independent manner. Our findings suggest that PPs are unique and efficient inductive sites for IgA, particularly against T independent antigens.