B cell subsets have different capacities for phagocytosis and subsequent presentation of antigen to cognate T cells

Abstract

B cells have been shown to be phagocytic under some circumstances. However, the phagocytic capacity of different B cell subsets and how this is linked to Antigen (Ag) presentation or other functions has not been characterized. To address this, we developed 2 {micro}m phagocytic Ag conjugated bead targets that target phagocytic pathways including the BCR, scavenger, Fc, and complement receptors to study potential pathways by which B cells phagocytose both cognate and non-cognate Ags. We found that while follicular B2 (Fo B), marginal zone, and B1 B cells are highly phagocytic of BCR-engaging targets through their BCR, only peritoneal cavity B1 cells could uptake non-cognate Ag-coated beads or bacteria. Despite this, B1 cells were not effective at presenting Ag to activate cognate T cells or at killing phagocytosed bacteria. Finally, analysis of scRNA-seq data revealed that these differences in phagocytic capacity could not be explained by differential expression of relevant phagocytic receptors, implying that there is likely some form of regulation in place preventing non-cognate Ag uptake by Fo B cells. Our work will help contribute to a better understanding of non-classical Ag uptake mechanisms employed by B cells and their relevance to inflammation.