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 rearranged 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 expressed surface and cytoplasmic IgM. Radioimmunoprecipitation analysis of surface IgM revealed that both cell lines used transfected mu-heavy chain and host-derived kappa-light chain. The T-cell line, MRT-2, specific 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-Ed,k,p,r but not by anti-I-Ad monoclonal antibody. Although the AME-transfectant lines secrete IgM into the culture medium, double chamber-type culture-experiments revealed that MRT-2 proliferation is not mediated by the uptake of secreted IgM. The results suggest that B cells process and present their own immunoglobulin heavy-chain V-region peptides to T cells in the context of MHC class-II molecules.