Modulation of human T-lymphocyte functions by the consumption of carotenoid-rich vegetables

A human intervention study was conducted to determine the effect of the con sumption of carotenoid-rich vegetables on the immune system. Subjects, (twe nty-three men), who were nonsmokers, were not restricted in their daily die t, except that they had to abstain from fruit and vegetables high in carote noids throughout the whole study period. The study was divided into four pe riods, each lasting 2 weeks: weeks 1-2. low-carotenoid period; throughout w eeks 3-8: daily consumption of 330 mi tomato juice (40 mg lycopene/d, 1.5 m g beta-carotene/d) (weeks 3-4), 330 mi carrot juice (21.6 mg beta-carotene/ d, 15.7 mg alpha-carotene/d, 0.5 mg lutein/d) (weeks 5-6), 10 g dried spina ch powder (11.3 mg lutein/d, 3.1 mg beta-carotene/d) (weeks 7-8). Blood was collected weekly from subjects after a 12 h fast. T-lymphocyte functions w ere assessed by measuring proliferation and secretion of immunoreactive cyt okines. The consumption of a low-carotenoid diet resulted in a significantl y reduced proliferation of peripheral blood mononuclear cells (PBMC) cultur ed with concanavalin A. After 2 weeks of tomato juice consumption and until the end of the intervention period lymphocyte proliferation was not signif icantly changed compared with proliferation at the end of the depletion per iod. Secretion of cytokines by T-helper-1-like lymphocytes (interleukin (IL )2 and by T- helper-2-like lymphocytes (IL-4) was influenced by the dietary intervention. IL-2 and IL-4 secretion values were significantly suppressed after the low-carotenoid diet (P < 0.001 and P<0.05 respectively compared with baseline). Tomato juice consumption significantly enhanced IL-2 (P<0.0 01) and IL-4 secretion (P<0.05) compared with the end of depletion period. After carrot juice and spinach powder consumption the cytokine secretion ca pacity of PBMC was not significantly different from that at the end of the depletion period. In conclusion, the results of the present study indicate that a low-carotenoid diet reduces T-lymphocyte functions and addition of t omato juice restores these functions. This modulation could not be explaine d by changes in the plasma carotenoid concentrations. The active constituen ts in tomato juice as well as the biological significance of this immunomod ulation remain to be determined.