Suppressor cell function of human granular lymphocytes identified by the HNK-1 (Leu 7) monoclonal antibody

The HNK-1 (Leu 7) differentiation antigen defines a subpopulation of human granular lymphocytes with natural killer (NK) and K cell function. In this study, we investigated whether HNK-1⁺ cells, identified with the monoclonal antibody and purified with a fluorescence-activated cell sorter (FACS) could function as suppressor cells. The results demonstrated that purified HNK-1⁺ cells efficiently suppressed both PWM-induced IgG production by B cells and T cell proliferation in mixed lymphocyte reactions (MLR). Manifestation of this suppressor cell activity required immune complex activation and was partially sensitive to 2000 rad irradiation. This suppressor cell activity was predominantly mediated by a subset of HNK-1⁺ cells that have previously been shown to have maximum NK function and lack expression of the E rosette (ER) receptor and T cell antigens (e.g., T3 and T8). Thus, HNK-1⁺ER^- cells suppressed a MLR by an average 52%; HNK-1⁺ER⁺ were one-half as efficient, causing an average 23% suppression. For comparison, we also examined the characteristics of Leu 2a⁺ suppressor T lymphocytes. In contrast to HNK-1⁺ cells, unactivated Leu 2a⁺ cells suppressed both B and T cell responses. This suppressor activity was not augmented by immune complex activation and was absolutely radiosensitive in PWM assays. HNK-1⁺ cells, especially the HNK⁺ER^- subset, can therefore mediate suppressor cell function in addition to their spontaneous cytotoxic function. Furthermore, some of their suppressor cell properties are distinct from those attributed to other types of suppressor lymphocytes.