Antigens specific for human T-lymphocytes detected by xenoantisera to HD-MAR cells: their differential expression on various T-cell lines

Sera elicited in rabbits by immunization with a newly established T-cell line. HD-MAR, and absorbed with human B-cell lines, were found to posses distinct properties. Although they killed the majority of human thymus cells, they killed no more than 20% of peripheral blood lymphocytes (PBL). HD-MAR antisera failed to react with B lymphocytes and with the Molt-4 and Peer T-cell lines, but exerted a strong cytotoxic effect on the HD-MAR, Be-13, HPB-ALL, and Amsalem T-cell lines. Following absorption with Amsalem cells, HD-MAR antiserum failed to react with Amsalem cells, yet reacted strongly with thymus cells and HD-MAR cells. The sensitivity of the various cell lines to the cytotoxic activity of HD-MAR antiserum absorbed with Amsalem cells showed a striking correlation with their capacity to form E-rosettes. Trypsin treatment of Amsalem cells eliminated their sensitivity to the cytotoxic effect of HD-MAR antisera. In contrast, trypsin-treated thymus and HD-MAR cells maintained their sensitivity to HD-MAR antiserum. Absorption of HD-MAR antiserum with trypsinized thymus cells did not affect the activity of the antiserum on untreated thymus, HD-MAR, and Amsalem cells, but eliminated its activity on trypsinized cells. Thus, all T-cell types tested seem to share a trypsin sensitive antigen. Amsalem cells, however, lack a trypsin resistant antigen present in other T-cell lines. A third antigenic determinant detected by HD-MAR antiserum seemed to be associated with the E-receptor. Preliminary observations indicate that HD-MAR antiserum is strongly cytotoxic for activated T-lymphocytes. The relationship of the antigenic specificities detected by the antiserum and the antigenic changes occurring in the membrane of activated T cells is under investigation.