Immunomodulatory effects of beta-sitosterol on human Jurkat

Plant sterols are specific phytochemicals that resemble cholesterol in structure but are found exclusively in plants [1]. The most common phytosterols in the human diet are β-sitosterol, campesterol and stigmasterol. Although plant sterols have been described as immunomodulatory compounds [2] there are a limited number of studies reporting the effects of these compounds on immune modulation. In the present study we investigated the effects of β-sitosterol on cytokine release in mitogen-treated Jurkat cells. Human Jurkat T cells (2×105/ml) were supplemented with increasing concentrations of β-sitosterol (10–100µM) in the presence or absence of the mitogen phorbol-12-myristate-13-acetate (10ng/ml) plus ionomycin (350ng/ml) (PMA/IoM) for 24h. Cell viability and growth were determined by the MTT assay. IL-2 release from the cells was measured by enzyme-linked immunosorbent assay (ELISA). Supplementation with the phytosterol alone did not induce IL-2 release from the cells. The presence of the mitogen PMA/IoM increased IL-2 release 100-fold (648.5 pg/ml) compared with untreated cells (6.9pg/ml). β-sitosterol significantly decreased IL-2 release from mitogen-stimulated Jurkat cells in a dose-dependent manner. In the presence of 10µM β-sitosterol IL-2 release was only slightly reduced whereas at a higher concentration (50µM) IL-2 release was reduced by 76% (P<0.01). At a concentration of 100µM, β-sitosterol significantly inhibited the release of IL-2 from PMA-IoM treated Jurkat cells by 50% (P<0.01). These findings suggest that β-sitosterol exhibits immunomodulatory effects in human Jurkat T cells and that further research is warranted on the role of phytosterols in modulation of the immune system.