Plasma IL-22 Levels, But Not IL-17, are Significantly Higher in Inflammatory Bowel Disease Patients Compared to the Healthy Adults

Abstract

Purpose: Inflammatory Bowel Disease (IBD) is characterized by abnormal and exacerbated immune response in gastrointestinal (GI) tract. The recent discovery of T helper 17 cells (Th17) and its signature cytokines, Interleukin-17 (IL-17) and Interleukin-22 (IL-22), represent an important mechanism in immune regulation. Our study objective is to compare plasma IL-17 and IL-22 levels in IBD patients and healthy controls. Methods: In our ongoing prospective cohort study, we have enrolled 17 patients with either Ulcerative Colitis (UC) (n=7) or Crohn's Disease (CD) (n=10) and 18 healthy controls. We measured the serum levels of IL-17 and IL-22 in all the IBD patients and healthy controls using ELISA assays according to the manufacturer's instructions. Results: Comparisons were made in the serum levels of IL-22 and IL-17 between healthy controls and IBD patients as well as between healthy controls and UC and CD separately. Wilcoxon 2 sample test was used to test the equality of medians between groups. Plasma IL-22 levels were significantly higher in IBD group when compared with controls (p-value of 0.004). Similarly, plasma IL-22 levels were significantly higher in both UC and CD when compared separately with healthy controls (p-value of 0.007 and 0.01, respectively). Plasma IL-17 did not show any significant difference between IBD and healthy controls as well as UC and CD with healthy controls (p-value of 0.76, 0.74 and 0.87, respectively). Conclusion: IL-22 is a strong activator of the pro-inflammatory gene expression in IBD. The exact function of IL-22 in human IBD still remains to be elucidated. The levels of plasma IL-22 were significantly higher in both UC and CD when compared to the healthy controls. Therefore, we believe that better understanding of the role of IL-22 might provide a valuable insight into the pathogenesis of IBD. This research was supported by an industry grant from Johnson and Johnson Pharmaceutical Research and Development, L.L.C.