CD4 and inflammatory bowel disease: In addition to the conventional T helper (Th) 1/Th2 and Th17/T regulatory (Treg) lymphocytes, a latest described Th subset, IL-9-producing CD4(+) T helper cells (Th9), was reported to induce infection, tumor, asthma, inflammatory bowel disease, and other allergic or autoimmune diseases mainly through the interleukin-9 (IL-9) pathway [7–10].