Abstract
MHC-II antigen presentation by B cells is essential in order for B cells to receive optimal costimulation from helper CD4+ T cells. This process is facilitated and focused through the extremely efficient uptake, processing, and presentation of antigen recognized by an individual B cell's unique B-cell receptor (BCR). The investigation of human B-cell antigen presentation has been limited by the varied specificity of BCR found in the mixed populations of B cells in vivo. As a result, there is no readily available method to measure BCR-mediated antigen presentation in this heterogeneous population of B cells. We have overcome this limitation by developing HLA-DR-restricted T-cell lines capable of recognizing a specific antigen taken up via the BCR and presented by the mixed B-cell population through this physiologically relevant mechanism. BCR-mediated presentation was enhanced >4 logs compared to presentation by B cells taking up the antigen through nonspecific mechanisms. The studies presented here characterize T-cell hybridoma lines developed for HLA-DRB1*0101+ and HLA-DRB1*1501+ B cells, but clones could be generated for other HLA-DR types using the methods described. These hybridomas have potential applications including study of the mechanisms of BCR-mediated enhancement of presentation, determination of adjuvant effects on presentation, and optimization of vaccine antigen preparations. Therefore, these T-cell lines could significantly facilitate the study of BCR-mediated antigen presentation required by T helper cell-dependent vaccines in humans.