TLR3 Signaling is Required for Robust Extrafollicular B Cell Response (EF) in Influenza A/PR/8 Infection

Abstract

Abstract Following influenza A virus (IAV) infection B cells rapidly proliferate and differentiate into plasma cells (PCs) in extrafollicular foci (EF) within mediastinal lymph nodes (medLN), resulting in protective antibody secretion. We had shown that co-expression of both TLR adaptor proteins, TRIF and MyD88, is required for robust EF responses. Only two TLRs, TLR3 and 4, signal using TRIF. As shown previously TLR3 and 7, but not TLR4, expression were upregulated by medLN B cells within 2 days post infection (dpi) in a Type-I IFN-dependent manner, suggesting that TLR3 might utilize TRIF in B cells during IAV infection. To test this we generated MyD88 × TLR3 double-deficient (DKO) mice. Flow cytometry on MedLN at 7 dpi showed significantly reduced EF B cells (CD19 loB220 loCD38 loCD24 hi) and CD138 +plasma cells (PCs), including IAV-specific PCs, as well as reduced serum IAV-specific IgG and IgG 2Cin DKO compared to C57BL/6 or single- MyD88 and TLR3 deficient mice. IAV infection of mixed bone marrow chimeras indicated that the TLR3-TRIF axis contributes to EF formation at least in part in a B cell-intrinsic manner. In vitro stimulation of B cells with the TLR3 agonist, Poly: IC, caused expression of several activation/costimulatory molecules but did not induce proliferation. Together, the data suggest that TLR3-mediated B cell is a non-redundant driver of rapid protective antibody responses. Supported by NIH/NIAID R01AI117890 (NB) and NIH T32 HL007013-40 (JHL and EJK).