CD8a+and CD8a-DC subsets from BCG-infected mice inhibit allergic Th2-cell responses by enhancing Th1-cell and Treg-cell activity respectively

The hygiene hypothesis has suggested an inhibitory effect of infections on allergic diseases, but the related mechanism remains unclear. We recently reported that DCs played a critical role in Mycobacterium bovis Bacille CalmetteGuerin (BCG)-mediated inhibition of allergy, which depended on IL-12 and IL-10-related mechanisms. Here, we tested the hypothesis that BCG infection could modulate the function of DC subsets, which might in turn inhibit allergic responses through different mechanisms. We sorted CD8a+ and CD8a- DCs from BCG-infected mice and tested their ability to modulate Th2-cell responses to ovalbumin (OVA) using in vitro and in vivo approaches. We found that both DC subsets could inhibit the allergic Th2-cell response in both a DC:T-cell co-culture system and after adoptive transfer. These subsets exhibited different co-stimulatory marker expression and cytokine production patterns and were different in inducing Th1 and Treg cells. Specifically, we found that CD8a+ DCs produced higher IL-12, inducing higher Th1 cell response, while CD8a- DCs expressed higher ICOS-L and produced higher IL-10, inducing CD4+CD25+FoxP3+Treg cells with IL-10 production and membrane-bound TGF-beta expression. The finding suggests that one infection may inhibit allergy by both immune deviation and regulation mechanisms through modulation of DC subsets.