Generation of CFUc suppressor T cells in vitro. IV. Effect of time on the inhibitory activity of mitogen-primed normal T lymphocytes

Bone marrow and peripheral blood T cells were obtained from 15 normal individuals by E rosetting and cultured in round-bottomed microwells for 7 days in RPMI or in RPMI supplemented with mitogens (pokeweed mitogen, phytohemagglutinin or concanavalin A). Supernatants and cells were harvested on days 1,2,3,4 and 7 and co-cultured with normal marrow cells in semi-solid agar to test their CFU-c suppressor activity. The results of this study indicate that RPMI treated cells and their supernatants have no effect or an enhancing effect on CFU-c growth; all 3 mitogens generate CFU-c suppressor T cells on day 1 culture; the inhibitory activity is detectable until day 4 of culture, though overall reduced, and is completely lost on day 7; the trend for supernatants of mitogen-treated T cells is quite similar with a tendency to complete loss of the inhibitory effect on day 7. We interpret these data as indicating that T cells release a soluble inhibitor of CFU-c growth within a few hours from polyclonal activation, the production of which is either controlled or lost with time in culture.