Dendritic Cells Expressing MyD88 Molecule Are Necessary and Sufficient for CpG-Mediated Inhibition of IgE Production in Vivo

Elevated levels of immunoglobulin E (IgE) are associated with allergies and other immunological disorders. Experimentally, sensitization with alum adjuvant favors IgE production while CpG-ODN adjuvant, a synthetic toll-like receptor 9 (TLR9) agonist, inhibits it. The cellular mechanisms underlying TLR-regulation of immunoglobulin production are still controversial. Specifically, TLR-mediated IgE regulation in vivo is not yet known. We show that augmented levels of IgE induced by sensitizations to OVA with or without alum adjuvant or with OVA-pulsed dendritic cells (DCs) were inhibited when sensitization to OVA was performed in the presence of CpG. Notably, CpG-mediated suppression of IgE production required MyD88-expression on DCs but not on B-cells. This contrasts with previous reports of in vitro regulation IgE where CpG acted directly on B cells via MyD88 pathway. In addition, CpG also inhibited IgE production in a MyD88-dependent manner when sensitization was performed with OVA-pulsed DCs. Finally, CpG signaling through MyD88 pathway was also necessary and sufficient to prevent anaphylactic antibody production involved in active cutaneous anaphylaxis.