Human peripheral blood lymphocytes (PBL) exhibited spontaneous cytotoxicity against OKT3 monoclonal antibody (mAb)-expressing murine hybridoma cells (OKT3 hybridomas). In contrast, other murine hybridomas expressing OKT4, OKT8, anti-HLA DR, and anti-HLA A, B, and C mAb were not lysed. PBL showed much lower levels of cytotoxicity (3 folds) against OKT3 hybridomas as compared with NK activity against the K562 targets. Lymph node (LN) cells exhibited the inverse relationship of cytotoxicity levels. The addition of OKT3 mAb to the effector cells totally blocked both the binding and the lysis of OKT3 hybridoma targets, indicating that the CD3 antigen on the effector cells may be involved in recognition of the targets. The addition of concanavalin (Con A) also inhibited the cytotoxicity of OKT3 hybridomas. OKT4 mAb-expressing hybridomas became susceptible to lysis after chemical attachment of OKT3 mAb with CrCl3. The kinetics of lysis of OKT3 hybridomas resembled that of NK activity. Both cytotoxicities were detectable after 1 to 2 hr and reached plateau levels by 4 to 6 hr. Effector cells responsible for lysis of OKT3 hybridomas expressed T3, T8, and Leu 7 antigens, but lacked T4 and Leu 11b antigens, and were sensitive to the treatment with L-leucine methyl ester. These results indicate that T3+, T8+, Leu 7+ and T4-, and Leu 11- granular lymphocytes have a spontaneous cytotoxic activity against OKT3 hybridomas which is different from classic NK activity. These findings may provide a method for the assessment of T-cell cytotoxicity mediated presumably by in vivo generated cytotoxic T lymphocytes in blood and the other immune organs.
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