EGCG - a major polyphenol found in green tea - has been found to increase the number of regulatory T cells which play an important role in immune function and suppression of autoimmune disease. The research - conducted in vitro and in mice - found that the effects of EGCG were not as strong as pharmacologic agents, there were fewer concerns about long-term toxicity. (Induction of regulatory T cells by green tea polyphenol EGCG, Carmen P. Wonga, Linda P. Nguyena, Sang K. Nohb, Tammy M. Braya, Richard S. Brunob and Emily Ho. Immunology Letters. doi:10.1016/j.imlet.2011.04.009).