Inhibition of human antigen-induced lymphoblastoid B-cell function by an in vivo-induced suppressor T cell

Lymphoblastoid (LB) B cells which spontaneously produce antitetanus toxoid IgG antibodies (Tet-IgG) in short-term cultures (3 days) appear in the circulation 5-7 days after immunization with tetanus toxoid. Addition of pokeweed mitogen (PWM), normally a stimulator of antibody production, caused instead a reduction in the in vitro synthesis of Tet-IgG by the LB cells. In order for this inhibition of antibody production to occur, T cells had to be present, and the inhibition was proportional to the number of T cells added to the culture, demonstrating the existence of PWM-inducible suppressor cells. The cells mediating the suppression had the OKT8 phenotype and also exhibited the following characteristics: (1) a PWM pretreatment period as little as 14 hr was enough to complete activation; (2) conventional inhibitors of suppressor T cells as hydrocortisone and cyclosporin A only partially reversed its effect; and (3) DNA synthesis was not required. The T-suppressor activity was detectable in the circulation before immunization, increased two- to fourfold by 5-12 days after boosting, and waned after 3 weeks. The mechanism of action of this suppression does not appear to involve conventional cytotoxic T cells as (1) the suppression was mediated across allogeneic barriers and (2) the suppression could not be reversed by inclusion of anti-Leu-2a antibodies in the culture. These results suggest that this suppressor T-cell subset may be important in the normal regulation of activated stages of human B lymphocytes.