Extrafollicular B cell response regulation during influenza infection

PROJECT SUMMARY Infection-induced B cell activation occurs in the context of complex innate immune responses, including the elaboration of cytokines, and the remodeling of secondary lymph tissues draining sites of infection. Our long-term objective is to determine how optimal protective humoral immunity to infections is induced and maintained. Exploring infection-induced innate stimuli that modulate adaptive immunity, we showed that infection-induced and TLR-agonist adjuvanted s.c. immunization provide required B cell intrinsic TLR signaling via both adaptors (MyD88 and TRIF) for extrafollicular responses, as deletion of both adaptors abrogated EF responses. While B cell intrinsic MyD88 stimulation drives B cell proliferation, TRIF signaling does not, indicating distinct yet unknown mechanisms of TRIF-mediated support for EF formation. When and where, during B cell activation, these innate signals regulate B cell fate is unknown. Recently we identified an early induced, post proliferative, influenza specific B cell population with a unique phenotype and transcript profile that might represent an activation intermediate of EF. The objectives for this project are to test the hypothesis that early in influenza infection B cell intrinsic TRIF/TLR3 and MyD88-mediated signals support EF differentiation via two distinct differentiation paths, each differently affecting extrafollicular antibody quality, acting on antigen-stimulated, post-proliferative B cells. To achieve our objectives, we will test in Specific Aim 1 the hypothesis that B cell intrinsic TLR3-signals support effective plasmablast differentiation by enhancing B cell responsiveness to IL2, while MyD88 principally drives proliferation followed by terminal differentiation, differentially affecting antibody quality. In Specific Aim 2 we will determine the extent to which the population of transcriptionally distinct, antigen-experienced, mostly non-switched and post-proliferative B cells that appear in the draining LN at 5 dpi with influenza virus, represent an intermediary, quiescent stage in B cell activation to EF, extrafollicular memory B cells and/or GC development and determine the impact of TLR signaling on their development and fate. Successful completion of the work would provide significant conceptual advances to understanding early B cell activation and extrafollicular memory B and plasma cell response induction. It would also identify a novel role for TLR3 in support of EF development and clarify the function of TLRs on B cell responses. Collectively these advances would identify new, critical junctures in B cell activation, regulated by innate immune signals for potential exploitation in vaccine design.