Further dissection of the functional heterogeneity within the OKT4+ and OKT8+ human T cell subsets.

Previous studies have suggested functional heterogeneity within the OKT4+ and the OKT8+ populations. For example, after activation the OKT4+ population contains not only helper cells but also cells capable of suppressing B cell differentiation. Previous studies also indicate that the reciprocal T cell population, OKT8+, does not provide helper activity but contains cytotoxic effector cells and radiosensitive cells important in the suppression of B cell differentiation. Using a new differentiation antigen, OKT17, which recognizes a surface antigen present on the majority of resting normal peripheral T lymphocytes but is present only on a subset of OKT4+ cells after activation, evidence was obtained that two functionally mature subsets can be distinguished within the OKT4+ population itself: OKT4+17+ radiosensitive suppressor cells and OKT4+17- radiosensitive helper cells. Recently, another monoclonal antibody, OKT20, has been described which is present on a small percentage of resting lymphocytes but is expressed in varying proportions on activated T cells. Functional analysis of normal resting human T lymphocytes demonstrated that the OKT20-depleted T cell subset was able to generate cytotoxic cells and to suppress antibody production to the same extent as did OKT8+ cells. On the other hand, when unselected T lymphocytes were cultured for six days in a mixed lymphocyte reaction and then depleted of OKT20 reactive cells, the cytotoxic effector T cells were eliminated. In contrast, OKT20-depleted T cells after identical activation were still able to suppress antibody production. These data provide evidence that following activation of OKT8+ cells, the OKT20 differentiation antigen becomes selectively expressed on cytotoxic effectors but not on suppressor cells.