THE EFFECT OF BETA-CAROTENE SUPPLEMENTATION ON THE IMMUNE FUNCTION OFBLOOD MONOCYTES FROM HEALTHY MALE NONSMOKERS

Although there is strong epidemiologic evidence that diets rich in car otenoids such as beta-carotene are associated with a reduced incidence of cancer, the cellular mechanisms underlying this phenomenon remain unknown. This article describes the effect of dietary beta-carotene su pplementation on both the expression of functionally associated surfac e molecules on human monocytes and on the secretion of the cytokine tu mor necrosis factor-alpha (TNF-alpha) by monocytes, all of which are i nvolved in the initiation and regulation of immune responses involved in tumor surveillance. A double-blind, placebo-controlled, crossover s tudy was undertaken in which 25 healthy, adult male nonsmokers were ra ndomly assigned to receive beta-carotene (15 mg daily) or placebo for 26 days, followed by the alternative treatment for a further 26 days. The expression of functionally related monocyte surface molecules was quantified by flow cytometry, and ex vivo secretion of TNF-alpha was q uantified by an enzyme-linked immunosorbent assay, before and after ea ch treatment period. After dietary supplementation there were signific ant increases in plasma levels of beta-carotene and in the percentages of monocytes expressing the major histocompatibility complex class II molecule HLA-DR and the adhesion molecules intercellular adhesion mol ecule-1 and leukocyte function-associated antigen-3. In addition, the ex vivo TNF-alpha secretion by blood monocytes was significantly incre ased after supplementation. These findings suggest that moderate incre ases in the dietary intake of beta-carotene can enhance cell-mediated immune responses within a relatively short period of time, providing a potential mechanism for the anticarcinogenic properties attributed to beta-carotene.