Abstract
The regulation of antibody production by B cells is governed in large part by the interactions between mutually exclusive T cell subsets with different functional properties, such as T4+ helper/inducer and T8+ suppressor/cytotoxic subsets. The mere expression of such antigenic markers on T cells, however, dose not necessarily imply the presence of proper functions usually attributed to these subsets. For example, T8+ cells lacking Ia-like antigen on their surface from healthy adults did not have any suppressor activity on B cell differentiation in Nocardia water-soluble mitogen (NWSM)-driven coculture system, whereas atypical lymphocytes expressing both T8+ and Ia-like antigens, as a probable sign of in vivo activation, in acute infectious mononucleosis exerted active suppression.
In vitro stimulation of T cells with mitogens indicated that Tac antigen appeared in the early stage of G1 phase of the cell cycle and then, Ia-like antigen in the S phase or later. The expression ability of Tac antigen on stimulation might be correlated well with T cell proliferation capability, while the expression of Ia-like antigen might imply some functional activation or differentiation of these T cells.
If the expression of Ia-like antigen on T4+ subset was inhibited by the addition of anti-Tac antibody, B cell differentiation in PWM-driven coculture system was markedly impaired. Analysis of functional property of PWM-prestimulated T4+ subset in NWSM-driven coculture system indicated that suppressor precursors in T8+ subset might be activated to become active suppressors only by their interaction with these PWM-prestimulated T4+ cells. The T4+, Ia+ cells as well as T4+, Ia- cells generated after 8 day-stimulation with PWM exerted a similar help on B cell differentiation in PWM-driven coculture system, while suppressor precursors in T8+ subset were activated only after the interaction with T4+, Ia+ cells, but not with T4+, Ia- cells, indicating these T4+, Ia+ cells having had a pivotal role for suppressor induction.
These results suggest that the T cell ability to express Ia-like antigen on stimulation might be important for the acquisition of their proper immunoregulatory functions. In this regard, the fact that poor expression of Ia-like antigen on stimulated cord blood T cells was markedly augmented in the presence of high concentrations of human γ-interferon is informative for the ontogenic maturation of T cell functional repertoires.
