TLR and CD40 signalings synergize to induce negative regulators that inhibit B cell class-switching and plasma cell differentiation: relevance to antibody responses

Abstract

Abstract During host immune responses to microbial pathogens and allergens, a B cell is exposed to T-independent (e.g. TLR ligands) and T-dependent (e.g., CD40 ligand, CD154) stimuli and integrates different signals for effective antibody responses. We have previously shown that engagement of TLRs (e.g., TLR4 by LPS and TLR9 by CpG) or CD40 induces Ig class switch DNA recombination (CSR) and B cell differentiation into plasma cells, albeit to different degrees. Here, we showed that combined stimulation of B cells through TLR and CD40 (by LPS plus CD154 or CpG plus CD154) abrogated CSR to IgG1, IgG2b, IgG3, IgA and IgE as well as plasma cell differentiation. Combined TLR/CD40 stimulation, however, did not significantly affect IgH germline IH-CH transcription or AID expression, both of which are critical for CSR, or expression of Blimp-1, a master transcription factor in plasma cell differentiation. Rather, LPS and CD154 synergized to upregulate (up to 3000-fold) expression of genes encoding EBI3 and p28, the two subunits of the cytokine IL-27. An anti–p28 blocking antibody could partially restore CSR and plasma cell differentiation in TLR/CD40 co-stimulated B cells. This together with CSR rescue by transduction of replication-defective lentiviral particles, which could inhibit IL-27 functions, indicates a negatively regulating role of IL-27 in B cell differentiation. It also suggests that engagement of TLRs and CD40 by microbial components and T helper cells may shape the antibody response by modulating B cell-intrinsic functions. Supported by NIH grants AI 079705 and AI 105813 grants to P.C.