β-Carotene–induced enhancement of natural killer cell activity in elderly men: an investigation of the role of cytokines

Abstract

We showed previously that natural killer (NK) cell activity is significantly greater in elderly men supplemented with β-carotene than in those taking placebo. In an attempt to determine the mechanism of β-carotene’s effect, we analyzed the production of NK cell–enhancing cytokines (interferon α, interferon γ, and interleukin 12). Boston-area participants in the Physicians’ Health Study (men aged 65–88 y; mean age, 73 y) who had been supplemented with β-carotene (50 mg on alternate days) for an average of 12 y were enrolled in a randomized, placebo-controlled, double-blind study. Elderly subjects taking β-carotene supplements had significantly greater plasma β-carotene concentrations than those taking placebo. β-carotene–supplemented elderly men had significantly greater NK cell activity than did elderly men receiving placebo. Percentages of NK cells (CD16+CD56+) were not significantly different between the β-carotene and placebo groups. Production of interleukin 12, interferon α, or concanavalin A–stimulated interferon γ by cultured peripheral blood mononuclear cells was not significantly different between β-carotene–supplemented elderly and those taking placebo. Our results indicate that β-carotene–induced enhancement of NK cell activity is not mediated by changes in percentages of CD16+CD56+ NK cells nor through up-regulation of interleukin 12 or interferon α. Am J Clin Nutr 1998;68:164–70.