Effect of Welsh onion (Allium fistulosum L.) green leaf extract on immune response in healthy subjects: a randomized, double-blind, placebo-controlled study

Background: Welsh onion belongs to genus Allium. Although its medicinal benefit such as cold prevention is well known by tradition, the underlying mechanism and active components have never been elucidated. The recent study revealed that Welsh onion mucus enhances tumor necrosis factor-alpha and monocyte chemotactic protein-1 production from RAW 264 cells and natural killer (NK) cell activity in murine spleen cells. This mucilage was abundant in the leaf blade of Welsh onion. Thus, we investigated the effect of Welsh onion green leaf extract (GLE) on immune competence in human clinical trials. Methods: A randomized, double-blind, placebo-controlled trial was conducted. Fifty-five healthy subjects were enrolled after the screening based on NK cell activity, and each sample (placebo, low-dose GLE or high-dose GLE) was supplemented for four weeks. The immune competence activity was evaluated through the primary endpoints that were NK cell activity and the score of immunological vigor (SIV). The SIV was calculated from lymphocyte subset analysis by flow cytometry method. Results: NK cell activity was enhanced in all supplemented groups including placebo; especially, NK cell activity was significant in both GLE groups. The immune score result showed that the immunity of the high-dose GLE group did not change although it was significantly lowered in the placebo group (p<0.01), suggesting that GLE ameliorated the immunity suppression. In addition, when SIV was compared between pre- and post-intake, the ratios of the improved subjects in two GLE groups were higher than that of the placebo group while those of the aggravated subjects showed the opposite result. In particular, they were remarkable in high-dose GLE group. Conclusion: These results suggest that the intake of low- or high-dose GLE might positively regulate immune competence.