Significance of serum Il-9 levels in inflammatory bowel disease

IL-9, which may be an inflammatory or regulatory cytokine, can be experimentally produced in a Th17 or modified Th2 context in the presence of T cell receptor (TCR) stimulation. The primary aim of this study was to measure serum IL-9 levels in patients with inflammatory bowel disease (IBD), and evaluate their relationships with the patients’ clinical characteristics. The secondary aim was to determine the levels of interferon-γ (IFN (interferon)-γ), Th2 cytokines (IL- 4, IL-5 and IL-13), and IL-6 in order to clarify the context of detectable peripheral cytokines in which IL-9 is produced. Venous blood samples of 43 IBD patients (20 with Crohn’s disease [CD] and 23 with ulcerative colitis [UC]) were analysed by means of quantitative enzyme-linked immunosorbent assays using purified anti-human IL-4, IL-5, IL-13, IFN-γ, IL-9 and IL-6 antibodies, and the laboratory findings were statistically correlated with their clinical expression. None of the patients showed the peripheral presence of IL-4, IL-5 and IL-13. Forty (93%) were positive for IFN-γ, thus confirming the presence of Th1 in both UC and CD, and IFN-γ levels correlated with disease activity (P = 0.045). Eighteen patients (41%) were positive for IL-9, which was associated with a severe prognosis (P <0.001), and 72.2% of the IL-9-positive patients were also IL-6 positive. There was a significant correlation between disease severity and IL-9 in the CD patients (P <0.001), but not in the UC patients (P = 0.1). Our findings confirm the presence of common Th1 cytokines in UC and CD. However the IL-9 positivity indicates the presence of an alternative population of T cells that respond to antigen stimulation and condition the prognosis of IBD. The fact that the same serum IL-9 levels were differentially associated with clinical measures of CD and UC activity suggest that the same cytokine can be produced in different contexts.