Regulation of pokeweed mitogen-induced human B-cell differentiation: effects of hydrocortisone

Hydrocortisone (HC), when added in pharmacologically attainable concentrations (10(-6)M) to pokeweed mitogen (PWM) cultures of unseparated human mononuclear cells (MNC) caused a marked enhancement of the in vitro secretion of all three major immunoglobulin (Ig) classes and of two out of three antibody specificities tested x (Ig) M anti-IgG antibodies and anti ss-DNA antibodies, but not anti-tetanus toxoid antibodies). Such an effect was not observed when HC was added to cocultures of isolated B cells with mitomycin C-treated autologous T cells. This result suggests, that HC effects on T-mediated suppressor mechanisms--rather than direct stimulatory effects--on B cells are involved in the observed enhancement of PWM induced in vitro B cell differentiation. One possible explanation for this phenomenon might be that HC, by inhibiting interleukin 2 release, inhibits also suppressor T-cell acitivation. This hypothesis would also fit the observation that HC significantly inhibits concanavalin A-mediated suppression of PWM-induced B cell differentiation, but that it has no effect on in vivo preactivated suppressor T cells from human cord blood.