IMMUNOMODULATORY EFFECT OF BETA-CAROTENE ON T-LYMPHOCYTE SUBSETS IN PATIENTS WITH RESECTED COLONIC POLYPS AND CANCER

Results from a number of studies suggest that beta-carotene-containing foods prevent the initiation or progression of various cancers. One p ossible mechanism for this effect could be enhancement of the immune r esponse. The aim of this study was to determine whether beta-carotene modulates T lymphocyte subsets in patients affected with colonic polyp s or cancerous lesions. Patients with previous adenomatous colonic pol yps (n = 18) or colon cancers (n = 19) were randomized to receive plac ebo or beta-carotene (30 mg/day) for three months. Percentages of T ly mphocyte subsets were determined using flow cytometry in blood samples collected before randomization and at three months. T lymphocyte subs ets of 14 normal control subjects were also determined for comparison. Initially, there was no difference in total leukocyte counts, percent age of lymphocytes, and various subsets of lymphocytes among the three groups, although in cancer patients there was a lower percentage of C D4 and interleukin-2 (IL-2) receptor-positive (IL-2R(+)) cells than in patients with polyps and in controls. After supplementation with beta -carotene, a significant increase in IL-2R(+) T lymphocytes (from 12.7 +/- 3.0% to 26.0 +/- 1.9%) and CD4(+) lymphocytes (from 40.9 +/- 3.1% to 45.6 +/- 3.2%) was seen only in the cancer patients. These percent ages remained unchanged in patients with adenomatous polyps receiving placebo or beta-carotene. We concluded that beta-carotene increased th e number of IL-2R(+) T lymphocytes and CD4(+) lymphocytes, which in tu rn may produce IL-2 only in patients with cancer who may already have some deficiency in their immune system. This increase in activated T l ymphocytes may mediate cytotoxic reactions to cancer cells via cytokin e production.