In mice, Bacteroides fragilis secreted polysaccharide A binding to Toll-like receptor 2 (TLR2) on Treg cells, which can enhance the expansion of Tregs while suppressing the proinflammatory Th17 response (Figure 1), this indicated that polysaccharide A secreted by Bacteroides fragilis is able to prevent and cure experimental colitis in animals (36, 37). The gene discussed is TLR2; the disease is colitis.