Imbalanced shift of cytokine expression between T helper 1 and T helper 2 (Th1/Th2) in intestinal mucosa of patients with post-infectious irritable bowel syndrome

Background: Irritable bowel syndrome (IBS) is a common functional bowel disorder. The post-infectious IBS (PI-IBS) occurs in IBS patients with a history of intestinal infection preceding the onset of symptoms. However, the underlying cause of PI-IBS is not fully understood, and the purpose of this study was to investigate the immune regulatory mechanism of PI-IBS. Methods: Participants enrolled in this study were divided into three groups including PI-IBS patients (n = 20), IBS patients without a history of infection (non-PI-IBS, n = 18), and healthy controls (n = 20). The expression levels of the Th1-derived cytokines IFN-gamma and IL-12, and the Th2-derived cytokines IL-4 and IL-10 in the mucosal specimens, and in the ascending colon, the descending colon, and the rectal segments were measured by RT-PCR and western blot. Results: The IFN-gamma mRNA levels in the intestinal mucosa were significantly higher in the PI-IBS group than in the non-PI-IBS or control group (both P < 0.05), but there was no difference between the non-PI-IBS and control groups. A trend toward IFN-gamma protein upregulation was found in the PI-IBS group, while the IL-12 and IL-4 mRNA and protein levels were not different between any groups. The IL-10 mRNA and protein levels in the PI-IBS group were both significantly lower than in the non-PI-IBS or control groups (P< 0.05, respectively), but there was no difference between the non-PI-IBS and control groups. There were no differences in the cytokine mRNA and protein levels among the ascending colon, the descending colon, and the rectum of all groups. Conclusions: An increase in IFN-gamma levels and a decrease in IL-10 levels were found in the intestinal mucosa of PI-IBS patients, suggesting that the infection may affect the Th1/Th2 balance. Thus, the dysregulation of the immune response is likely an important cause of IBS.