Early BCR Events and Antigen Capture, Processing, and Loading on MHC Class II on B Cells

B cells are efficient antigen-presenting cells (APCs), relying on antigen uptake through the B cell receptor (BCR). The mechanism of antigen recognition remains a topic of debate; while the prevalent view holds that antigens need to be multivalent for BCR activation, monovalent antigens can also initiate B cell responses. In this review, we describe the steps required for antigen uptake, processing, and loading of peptides onto MHC Class II compartments in B cells for efficient presentation to CD4 T cells, with a special focus in the initial steps of BCR recognition of antigen.