CD4 and irritable bowel syndrome: There is increasing recognition that the mucosal immune response mediated by CD4+ and CD8+ T cells plays an important role in the bowel symptoms of IBS.6 The numbers of mucosal CD3+, CD4+, and CD8+ T cells and mast cells and mucosal infiltration by CD4+ T cells are increased in colonic biopsies from a large subset of IBS patients.