The studies performed on a mouse model of colitis (dextran sodium sulfate-induced colitis) showed that the introduction of anaerobic, noncultivatable segmented filamentous bacteria stimulates Th17 development, while commensals such as Bacteroides fragilis or Clostridium species, facilitate the differentiation of regulatory T-cell and IL-10 production in the gut. The gene discussed is IL10; the disease is colitis.