An inhibitor of lymphocyte proliferation produced by a human colonic adenocarcinoma cell line in culture.

The culture fluid taken from a human colonic adenocarcinoma cell line, SKCO-1, inhibited mitogenic stimulation of mouse lymphocytes measured by reductions in blast information or [3H]thymidine uptake. The inhibitor was not cytotoxic to lymphocytes nor did it alter the growth rates of 21 other cell lines examined. However, the in vitro growth rates of two murine lymphoid tumor lines were also markedly reduced by the SKCO-1 medium. The tumor cell culture media could be added up to 40 hr after concanavalin A stimulation and still effect complete inhibition of [3H]thymidine uptake. A similar inhibition was observed for phytohemagglutinin (from red kidney bean), lipopolysaccharide, and mixed lymphocyte response assays. The inhibitor has a molecular weight of greater than 100,000 and is stable to heat and ultraviolet radiation, but is destroyed by mild periodate oxidation. The inhibitor may play a role in immunosuppression.