B cell intrinsic TLR3 and TLR7 signaling synergistically enhance B cell differentiation during influenza infection-induced extrafollicular responses 3781

Abstract Description The extrafollicular (EF) B cell response induces virus-neutralizing, class switched antibodies rapid enough to impact influenza virus clearance after acute infection. Previously we showed that MyD88 and TRIF are both required for robust EF responses, acting in a B cell intrinsic manner. While MyD88 was shown previously to affect B cell activation, how TRIF and its upstream receptor(s) support EF responses is unknown. To address this, MyD88-/- TLR3-/- double-deficient total and B cell-specific KO mice were infected with influenza A/PR/8 (IAV) alongside controls. Both, global and B cell-intrinsic MyD88-/-TLR3-/- double-deficient mice had significantly reduced EF-derived B cells, plasma cells (PCs), and hemagglutinin (HA)+ EF-derived PCs and reduced IAV-specific serum IgG post-infection days 7 and 9, respectively, indicating a critical role for TLR3 in early B cell stimulation. Consistent with these findings, stimulation of negatively enriched naïve splenic B cells with TLR3 ligand POLY(I:C) induced surface expression of CD25, CD69, and CD86 by 24 hours of culture but not proliferation, while the combined stimulation with POLY(I:C) and TLR7 agonist (CL097), significantly and synergistically increased proliferation and BLIMP+ CD138+ PC differentiation by 96 hours. Together this data shows a novel role for B cell intrinsic TRIF/TLR3, in B cell differentiation when combined with a second, MyD88-dependent agonist. Funding Sources This work was supported by NIH R01 AI117890, AI184867 (to NB) and NIH T32 HL007013-40 (to EJK and JHL). Topic Categories Immune Response Regulation: Cellular Mechanisms (IRC)