Antigen Processing and Presentation by B Cells

Abstract

Interest in the question of whether B cells can present antigen to T cells emanates from a consideration of two findings in relation to the immune response to T dependent antigens. The first observation showed that the antigenic determinants recognized by T cells and B cells must be present on the same macromolecule in order for effective antigen-specific T cell help to be delivered to B cells (1). The second important observation to be considered for T-dependent responses was that the accessory cells had to “process” the antigen and display it in the context of the MHC encoded la molecules for the recognition by and activation of helper T cells (2,3). Previous to these findings the phenomenon of hapten-carrier linked recognition of antigen by T and B cells had been interpreted as strong evidence in support of the concept that in order to obtain effective T-B cooperation, antigen had to serve as a bridging unit to allow the physical interaction between carrier specific T cells and hapten-specific B cells and that this interaction was required for an effective immune response (1). However, since in order for T cells to recognize and respond to antigen, the antigen must be processed and presented by an accessory cell in the context of MHC gene products, the postulate that antigen forms a simple bridge between a carrier-specific T cell receptor and a hapten-specific B cell receptor became untenable. This apparent discrepancy between the concept of antigen bridging for effective T-B interactions and the requirement of accessory cell processing and presentation of antigen for T cell recognition would be reconciled if B cells could serve as an antigen presenting accessory cell. The purpose of this paper is to review the evidence in favor of the concept that B cells can in fact serve as antigen presenting accessory cells to T cells of the helper/inducer subset.