Role of carotenoids in the immune response.

The well-established provitamin A activities of certain carotenoids have hampered past research into their possible specific functions. More recently, research interests on carotenoids have been revived, largely because of their anticancer activities. beta-Carotene and other carotenoids have been reported to possess immunomodulatory activities in humans and animals. These carotenoids enhance lymphocyte blastogenesis, increase the population of specific lymphocyte subsets, increase lymphocyte cytotoxic activity, and stimulate the production of various cytokines. In addition, carotenoids also stimulate the phagocytic and bacteria-killing ability of blood neutrophils and peritoneal macrophages. The action of these carotenoids is widely accepted to be independent of their provitamin A activity. The immunostimulatory action of carotenoids may be translated into improved health, including mammary and reproductive health in dairy cattle. More studies are needed to establish fully the beneficial effects of supplementation of different carotenoids on the health of dairy cattle. Furthermore, studies on carotenoids other than beta-carotene are needed.