Tu144 - Autophagy-related Lipid Kinase vps34 Is Required for B Cell Homeostasis and Humoral Immunity

Abstract Text: Autophagy is a highly conserved degradation process that delivers cytoplasmic products to lysosomes for recycling. The lipid kinase Vps34/PIK3C3 is vital for autophagosome formation, endosomal sorting, and phagocytosis. We studied mice with a Vps34 ablation either conditionally in pro-B cells with CD19-Cre (Vps34∆B mice) or inducibly in mature B cells by huCD20-CreERT2 (Vps34i∆B mice). Vps34∆B mice showed reduced numbers of follicular and marginal zone B2 cells and a major defect in peritoneal B1 cells. LPS-stimulated splenic B cells exhibited lower mitochondrial respiration, more ROS, and increased expression of IL-10. These mice developed varied responses to distinct T cell-dependent (TD) immunization, with either enhanced or modestly reduced total or antigen-specific germinal center (GC) B cells. However, tamoxifen-treated Vps34i∆B mice exhibited major defects to TD immunization, indicating that early Vps34 depletion endows the resulting B cells with advantages in primary responses. Lastly, B cells from Vps34∆B mice exhibited reduced expression of MHC II- bound CLIP and, surprisingly, elevated MHC II-restricted presentation of cytosolic but not membrane-bound self-antigens. Thus, we propose that Vps34-deficient B cells exhibit mitochondrial stress with accumulation of ROS, resulting in an anti-inflammatory cytokine profile, defective B cell homeostasis, and altered immune responsiveness. These studies will inform the development of B cell-based vaccines and immunotherapies.