Induction of the rat in vitro plaque-forming response to sheep erythrocytes by a soluble factor(s) derived from concanavalin A-activated rat T lymphocytes.

Macrophages suppress the in vitro PFC response to sheep erythrocytes by rat spleen cells. We report the activity of a soluble factor released by rat splenic T-lymphocytes following a short incubation (60 min) with Con A (100 micrograms/ml). Culture supernatants added to rat spleen cells in the presence of SRBC significantly increased the PFC response at day 5. The effect was time and dose dependent. The Con A supernatant was effective in increasing PFC response if added to splenocytes during the first 16 h of the culture. The increased response if added to splenocytes during the first 16 h of the culture. The increased response was dose dependent giving maximum PFC at 1%. Depletion of macrophages from the spleen cell population produced a significant increase of the in vitro PFC response, but minimized the enhancing activity of the Con A supernatants. These studies suggest that an activated T-cell product can increase the antibody response to SRBC by completing the helper signal.