Low Concentrations of Flavonoid - Rich Fraction of Shallot Extract Induce Delayed - Type Hypersensitivity and TH1 Cytokine IFN-gamma Expression in Balb/C Mice

Flavonoids are potentially immunomodulatory factors and it may be inferred that these phytochemicals contribute to immunomodulatory properties of the Allium family. In the present study, we investigated the potential mechanism underlying the immunomodulatory effect of shallot and its ethyl acetate (EA) fraction as flavonoid-rich sources. Ex vivo, effects of a hydroalcoholic extract of shallot, its fractions and quercetin on lymphocyte viability were evaluated. The proliferative effects of the fractions were examined using naive mouse lymphocytes to determine the fraction with highest impact/ activity. In addition, in a mouse model, both delayed- type hypersensitivity (DTH) responses and production of a key cytokine (interferon [IFN]-gamma) were evaluated. Both the shallot extract and its fractions inhibited lymphocytes cell growth and survival in a concentration- dependent manner. The findings also showed that the extract and especially the ethyl acetate (EA) fraction could induce lymphocyte proliferation. The evaluation of the extract and its EA fraction on DTH responses indicated that both caused a significant increase in DTH response. Furthermore, they triggered significant increases in IFNγ and decreases in interleukin (IL)-4 production by splenic mononuclear cells. Because of the significant immunomodulatory activity displayed in these studies, it is plausible that shallot could have a potential use as an immunomodulatory agent in clinical settings.