The effects of dietary proteins containing different levels of sulfur amino acid on the responsiveness of splenocytes to concanavalin A (Con A) were examined. The Con A-induced DNA synthesis of splenocytes in mice fed a purified egg protein (PEP) diet was significantly higher than those in mice fed a soy protein isolate (SPI) or casein diet. Reduced glutathione (GSH) and 2-mercaptoethanol (2-ME) markedly stimulated Con A-induced DNA synthesis in vitro, and the stimulatory effects of 2-ME were more marked in SPI and casein diet groups compared to the PEP diet group. In contrast, L-buthionine- (S,R)-sulfoximine(BSO) markedly inhibited Con A-induced DNA synthesis in splernocytes. The degree of inhibition was greater in the order SPI, casein and PEP diet groups. These results suggest that the sulfur amino acids concentration in the dietary protein may play a key role in the regulation of lymphocyte responsiveness to Con A in growing mice.
