Suppression of interleukin-2 production by human concanavalin A-induced suppressor cells.

When PHA-activated normal responder cells (R cells) were cocultured with mononuclear cells (MN cells) which had been preincubated for 48 hr in medium alone (C cells) an enhanced proliferative response was observed. This enhancement was only obtained when the R cells were cultured with allogeneic C cells or when PHA was in the cocultures for the entire culture period. This effect was due to greater production of interleukin 2 (IL-2) by irradiated C cells in the presence of allogeneic or mitogenic stimulation. Con A-treated mononuclear cells (S cells) cultured with PHA-activated allogeneic or autologous responder cells showed reduced [3H]thymidine incorporation and IL-2 production as compared to activated R cells alone. Glutaraldehyde-treated S cells (which retained the ability to absorb IL-2) did not affect the proliferative response or IL-2 production by the R cells, indicating that passive absorption of IL-2 was not entirely responsible for suppression induced by S cells. S cells, pretreated with IL-2, still inhibited R-cell activity. These results show that Con A-treated MN cells suppressed or prevented [3H]thymidine incorporation by actively inhibiting IL-2 production.