Beta-carotene stimulates human leukocytes to secrete a novel cytokine

The effect of beta-carotene on cytokine production by human peripheral blood leukocytes was tested. Beta-carotene stimulated the secretion of a novel cytotoxic cytokine when peripheral blood cells were exposed to carotenoid concentrations between 10^-6 and 10^-10M. Beta-carotene-treated supernatants caused the cytolysis of four out of the six human tumor cell lines tested. Low level toxicity was also observed when normal diploid fibroblast lines were exposed to beta-carotene-treated leukocyte supernatants. The cytotoxic activity elicited by beta-carotene was found to be distinct from characterized cytokines based on both antisera neutralization and target cell specificity studies. This study demonstrates that beta-carotene can induce human leukocytes to secrete one or more cytokines that can manifest cytotoxic activity against human tumor cells in vitro.