Comparison of target antigens of monoclonal reagents OKT5, OKT8, and Leu2A, which inhibit effector function of human cytotoxic T lymphocytes.

The OKT8 antigen, which is present on a subset of thymocytes and peripheral blood T lymphocytes, was examined utilizing a variety of biochemical techniques. It is shown to be a glycoprotein of 34 kD molecular weight which contains a hydrophobic region. Further, under nonreducing conditions, dimers of 76 kD and 67 kD are found. These species are most likely generated by differences in internal disulfide bonding. When two previously described antigens, OKT5 and Leu2A, were compared with OKT8, no structural differences could be found among the three antigens. Evidence is presented, however, which indicates that the three monoclonals recognize different epitopes on the molecule. Functional analysis on cytotoxic T lymphocyte (CTL) clones confirmed the biochemical findings concerning the identity of the three proteins.