Plaque-forming cells in man. III. Generation of plaque-forming cells in allogeneic in vitro cultures of HLA-D/DR-incompatible B and T lymphocytes

We have investigated the ability of allogeneic, irradiated T lymphocytes to induce proliferation and immunoglobulin (Ig) secretion in untreated peripheral blood B lymphocytes. Non-mitogen-activated co-cultures of isolated T and B lymphocytes from selected, full-house HLA-A,B and D/DR antigen-phenotyped donors were reconstituted in a ratio of 4:1. Proliferation was assessed on day 5-6 of culture by the 3H-thymidine incorporation technique, and the Ig secretion was monitored on day 6 with a protein A plaque-forming cell (PFC) assay. B lymphocytes were able to differentiate into PFC, and the number of plaques was significantly higher in cultures of cells with two HLA-D/DR antigen incompatibilities than in those sharing one antigen. In cultures of peripheral blood lymphocytes with no HLA-D/DR antigen difference, only a few PFC developed. HLA-A and B antigens had no influence on the response. Further, monocytes were not an absolute requirement for allogeneic activation of B cells. Sonicated T cells and culture supernatants from allogeneic T- and B-cells cultures were not able to induce PFC formation in B lymphocytes. Our results indicate that the PFC response obtained in non-mitogen-activated cultures of allogeneic T and B lymphocytes is dependent on HLA-D/DR disparity or on genes encoded in the HLA-D/DR region.