CLASS II-RESTRICTED PRESENTATION OF AN IMMUNOGLOBULIN HEAVY-CHAIN-GENE PRODUCT BY A GENE-TRANSFECTED B-CELL LINE

The presentation of an antigen endogenously processed by B lymphocytes was investigated. The expression plasmid vectors, harboring genomic r earranged V genes from two monoclonal B cells and genomic mu-constant region gene, were constructed. Two B-cell lines, the MOPC104E myeloma mu-heavy chain expressing AMB line and the control hybridoma mu-heavy chain expressing AHB line, were established by gene transfection into A20.2J B lymphoma cell line. The cloned transfectant cell lines expres sed surface and cytoplasmic IgM. Radioimmunoprecipitation analysis of surface IgM revealed that both cell lines used transfected mu-heavy ch ain and host-derived kappa-light chain. The T-cell line, MRT-2, specif ic for the MOPC104E protein, proliferated on AME B cell lines but not on control AHB-cell lines. MRT-2 proliferation was inhibited by anti-I -E(d,k,p,r) but not by anti-I-A(d) monoclonal antibody. Although the A ME-transfectant lines secrete IgM into the culture medium, double cham ber-type culture-experiments revealed that MRT-2 proliferation is not mediated by the uptake of secreted IgM. The results suggest that B cel ls process and present their own immunoglobulin heavy-chain V-region p eptides to T cells in the context of MHC class-II molecules.