In vitro generation of splenic suppressor cells by trypsin

Rat spleen cells were mitogenically stimulated with concanavalin A (Con A) or sodium periodate and cultured for 14-20 hr with trypsin. When these trypsin-activated cells were co-cultured with fresh mitogenically stimulated cells, [3H]-thymidine incorporation into the fresh cells was suppressed. Artifactual and trivial effects of trypsin (e.g. increased release of cold thymidine, decreased cell viability, and a change in thymidine transport) could not account for the suppressor effect. Suppressor activity was not affected by removing B cells or macrophages before trypsin activation nor by treating the trypsinized cells with mitomycin C. Suppressor activity could only be generated when the spleen cells were stimulated with Con A or periodate during culture with trypsin, and supernates from the trypsin-activated cells did not have suppressor activity. The physiological significance of the results and possible mechanisms of action of the suppressor cells are discussed.