<prompt> Common site of regional enteritis is -ColonRectumDistal ileum and colonCaecum  <response>: Crohn disease Terminal ileitis or regional enteritis Crohn disease CD is an inflammatory bowel disease, characterized by -Sharply delineated and typically transmural involvement of the bowel by an inflammatory process with mucosal damage.The presence of non-caseating granulomas.Fissuring with the formation of a fistula.Any portion of intention can be involved but most commonly small intestine is involved.Small intestine 40Small intestine colon 30Colon 30Terminal ileum involved most commonly and rectum is usually spared.CD is associated with HLA-DM1DQw5 and NOD 2 genes and an abnormal T-cell response, particularly CD4 T cells Th1 cells 