Recent studies have found that mucosal immune dysfunction plays an important role in the pathogenesis of IBS, colonic mucosa of patients with IBS has increased number of immune cells (CD3+, CD4+ and CD8+ T cells) and increased production of cytokines (such as IL-5, IL-13, IL-6, TNF-α, and IL-1β) (Feili-Hariri, Falkner & Morel, 2005; Ohman & Simren, 2010; Vickery et al., 2011). This evidence concerns the gene CD8A and immune system disorder.