Modulatory effects of garlic extracts on proliferation of T-lymphocytes in vitro stimulated with concanavalin A.

Different active components from the garlic (Allium sativum) possess immunomodulatory activity both in vitro and in vivo. However, mechanisms of their actions are not sufficiently elucidated. In this study we examined the effects of garlic aqueous extract (GAE) and garlic ethanolic extract (GEE), prepared from two different garlic powder samples, on proliferation of rat thymocytes and splenocytes in culture, stimulated with concanavalin A (Con A). It has been shown that the extracts from both samples significantly modulate lymphocyte proliferation, triggered by this potent T-cell mitogen, depending on the type and dilutions of extracts and concentrations of Con A. The extracts, alone, were not mitogenic for lymphocytes. Generally, higher concentrations of the extracts showed inhibitory effects, whereas lower concentrations significantly augmented proliferation of lymphocytes. The stimulatory effect of GAE was stronger using splenocytes and suboptimal concentrations of Con A as a consequence of increased interleukin 2 (IL-2) production as well as the expression of IL-2 receptor alpha (IL-2Ralpha). The relationship between these two phenomena was demonstrated using neutralizing anti-IL-2Ralpha monoclonal antibody. The inhibitory effect of GAE correlated with a decrease in IL-2 production, but was not followed by down-regulation of IL-2Ralpha expression. The addition of IL-2 almost completely abolished inhibition of lymphocyte proliferation in the presence of higher concentrations of GAE.