Heavy-metal mitogenesis: thymocyte activation by Zn++ requires 2-mercaptoethanol and lipopolysaccharide as cofactors

Thymocytes from Balb/C mice were activated in vitro by Zn++ as noted by the several-fold increases in 3H-thymidine incorporation at 144 h of culture. Thymocyte activation by Zn++ required the presence of 2-mercaptoethanol (2-ME) and bacterial lipopolysaccharide (LPS) in concentrations as low as 1.0 ng/ml. Thymocytes were not stimulated by these agents in the absence of Zn++. Bovine serum products, thought to contain trace amounts of LPS, appeared to satisfy this LPS requirement. Interleukin 1 (IL 1) could not replace LPS as a cofactor. Thymocytes did not respond to Hg++ under the culture conditions used here. Thymocyte subpopulation studies showed that cell preparations enriched for peanut lectin receptor-negative, mature thymocytes were activated by Zn++ and required LPS for the response.