Functional analysis of human T cell subsets defined by monoclonal antibodies. III. Regulation of helper factor production by T cell subsets

In the present report we extended our previous studies demonstrating that obligatory T-T interactions are important in regulating human immune responses in vitro. Functionally distinct human T cell subsets were isolated by complement-mediated lysis using the monoclonal antibodies OKT4 and OKT8. Evidence was obtained that during allogeneic interactions, OKT4 ⁺, but not OKT8 ⁺, responder T cells are required to generate helper factor(s) capable of polyclonally activating human B cells independent of additional T cell help. Importantly, the alloantigen-induced helper factor(s) production and/or release was found to be suppressed by addition of graded numbers of radiosensitive OKT8 ⁺ cells. On the other hand, no evidence was obtained that supernatant derived from alloactivated OKT8 ⁺ cells could counterbalance the helper activity generated in the presence of supernatant from alloactivated OKT4 ⁺ cells. Furthermore, OKT8 ⁺ cells, known to suppress PWM-driven B cell differentiation in the presence of OKT4 ⁺ cells, do not suppress B cell differentiation induced by preformed helper factor even in the presence of OKT4 ⁺ cells. These data further underscore the importance of functional T-T interactions in immunoregulation in vitro and support the idea that the target of suppression of B cell differentiation, induced either by alloantigen-triggered helper factor or PWM, are OKT4 ⁺ cells and not B cells themselves.