B cell intrinsic Toll-like receptor 9 signaling regulates class switching to IgE

Abstract

Abstract Chronic allergic diseases such as allergic asthma are driven by excessive production of allergen specific IgE. B cells produce IgE by class switch recombination (CSR) in response to T cell help and Th2 cytokines. However, development of allergic diseases can also be influenced by factors such as early-life exposure to microbial products. In vivo, stimulation of Toll-like receptor 9 (TLR9) with microbial DNA reduces IgE levels, largely thought to be a response to Th1 cytokines. However, the directeffects of TLR9 signaling on B cell class switching to IgE remain unclear. To delineate the B cell intrinsic effects of TLR9 stimulation, we treated mouse splenic B cells in vitrowith IL-4 and anti-CD40 antibody with or without a synthetic TLR9 agonist, CpG oligodeoxynucleotides (CpG). Compared to stimulation with IL-4 and anti-CD40 alone, the addition of CpG decreased IgE production. Using B cells from reporter mice that track germline transcription, a prerequisite for CSR, we found that CpG inhibited Iɛ but increased Iγ1 germline transcription. By Western blot analyses, we probed the expression of transcription factors known to negatively regulate Iɛ and positively regulate Iγ1 transcription. These transcription factors were synergistically upregulated in the presence of CpG with IL-4 and anti-CD40. Together, these data illustrate a molecular mechanism by which microbial products directly perturb the production of IgE and influence the development of allergic disease. R01 HL165120