B-cell antigen receptor signaling requirements for targeting antigen to the MHC class II presentation pathway.

The ability of B lymphocytes to capture, process and present antigens to T cells is requisite for normal humoral immune responses and contributes to the pathogenesis of both B- and T-cell-mediated autoimmune diseases. B lymphocytes preferentially capture polyvalent antigens, which are capable of eliciting a coordinated series of cellular responses that ensure that even low-affinity antigens are productively captured. Polyvalency not only accelerates transit through the endocytic pathway but also induces a reorganization of the antigen-processing compartment, activates degradative pathways and determines how antigenic peptides are presented to T cells. Similar changes are observed in maturing dendritic cells, indicating that some cellular responses to foreign antigens are conserved.