Comparison of effects of beta-carotene and lycopene supplementation on the expression of functionally associated molecules on human monocytes.

Abstract

Consumption of diets rich in fruits and vegetables, particularly those containing high amounts of carotenoids such as B-carotene and lycopene, is associated with a reduced incidence of cancer [ 11. It has been suggested that carotenoids might prevent carcinogenesis by enhancing immune cell activity [2]. Cell mediated immune responses are initiated by the stimulation of appropriate T lymphocytes by antigen-presenting cells. A pre-requisite for this function is the cell surface expression of MHC class I1 molecules (HLA-DR, -DP & -DQ), present on the majority of human blood monocytes, and adhesion molecules which provide co-stimulatory signals. Since it has been shown that the percentage of MHC class II-positive monocytes and the density of these molecules on the cell surface can alter the degree of immune responsiveness of an individual [3] it is possible that carotenoids might enhance cell mediated immune responses by enhancing the cell surface expression of these molecules. Therefore, we undertook two independent double-blind placebo-controlled cross-over studies to compare the effects of B-carotene and lycopene supplementation, given at dietary achievable levels, on blood monocyte surface expression of MHC class I1 molecules and of several adhesion molecules known to be required for antigen presentation. For each of the 2 studies, healthy non-smoking males (age range 18-60 y, who were not taking regular medication or vitamin supplements) were randomly allocated into two groups. Following baseline 12 h-fasting blood sampling, participants in Group 1 were provided with 27 placebo capsules (containing vegetable oil) and instructed to consume one capsule per day; participants in Group 2 were given 27 identical capsules supplemented with either Bcarotene (Study I ; 15 mg, equivalent to eating 150 g carrotdday) or lycopene (Study 2; 15 mg; equivalent to eating 250 g tomatoedday) and were similarly instructed After a further fastingblood sample was taken on Day 28 of each study, the participants were crossed over onto the other capsules (placebo or supplement) and a final blood sample was taken after a further 28 d. Blood monocytes were purified by density centrifugation (over NycoPrep 1.068) and were immunofluorescently stained with monoclonal antibodies raised against the MHC class I1 molecules, and the adhesion molecules ICAM-1, LFA -1 and LFA-3. Both the percentage of monocytes expressing each of these molecules and the intensity of expression of each molecule was quantified by flow cytometry [4]. Table 1 shows that in Study I there was a significant increase in plasma levels of B-carotene in both participant groups following dietary supplementation, and plasma levels remained elevated in Grp 2 following 28 d of placebo treatment. Plasma levels of several other dietary antioxidants studied did not change significantly.