Serum and colonic mucosal immune markers in irritable bowel syndrome

Abstract

Objectives: Low-grade colonic mucosal inflammation has been postulated to have an important role in the pathophysiology of irritable bowel syndrome (IBS). The objectives of this study were (i) to identify serum and tissue-based immunological and neuroendocrine markers associated with mucosal inflammation in male (M) and female (F) patients with non-post-infectious IBS (non-PI-IBS) compared with healthy controls and (ii) to assess possible correlations of such markers with IBS symptoms.

Methods: Sigmoid mucosal biopsies were obtained from 45 Rome II positive IBS patients without a history of PI-IBS (26 F, 35.5% IBS-C, 33.3% IBS-D, 31.1% IBS-A/M) and 41 healthy controls (22 F) in order to measure immunological markers (serum cytokine levels, colonic mucosal mRNA levels of cytokines, mucosal immune cell counts) and neuroendocrine markers associated with mucosal inflammation (corticotropin releasing factor- and neurokinin (NK)-related ligands and receptors, enterochromaffin cells). Symptoms were measured using validated questionnaires.

Results: Of all the serum and mucosal cytokines measured, only interleukin-10 (IL-10) mRNA expression showed a group difference, with female, but not male, patients showing lower levels compared with female controls (18.0±2.9 vs. 29.5±4.0, P=0.006). Mucosal mRNA expression of NK-1 receptor was significantly lower (1.15±0.19 vs. 2.66±0.56, P=0.008) in female, but not male, patients compared with healthy controls. No other significant differences were observed.

Conclusions: Immune cell counts and levels of cytokines and neuropeptides that are associated with inflammation were not significantly elevated in the colonic mucosa of non-PI-IBS patients, and did not correlate with symptoms. Thus, these findings do not support that colonic mucosal inflammation consistently has a primary role in these patients. However, the finding of decreased IL-10 mRNA expression may be a possible biomarker of IBS and warrants further investigation.

Figure 1

Serum cytokine levels in irritable bowel syndrome (IBS) and healthy controls are shown. Modified boxplots of serum cytokine levels (pg/ml) in male and female IBS patients and healthy controls within males (a) and females (b) are shown. The horizontal line indicates the median value and the lower and upper brackets indicate the 25th percentile—1.5 interquartile range (IQR) and 75th percentile + IQR, respectively. The open circles represent values outside of the bracket range and are potential outliers. There were no significant differences between IBS patients and controls. TNF, tumor necrosis factor.

Figure 2

Colonic mucosal cytokine levels in irritable bowel syndrome (IBS) and healthy controls are shown. Modified boxplots of colonic mucosal cytokine mRNA expression in IBS patients and healthy controls within males (a) and females (b) are shown. The horizontal line indicates the median value and the lower and upper brackets indicate the 25th percentile—1.5 inter-quartile range (IQR) and 75th percentile + IQR, respectively. The open circles represent values outside of the bracket range and are potential outliers. The only significant difference was lower levels of interleukin-10 (IL-10) mRNA in IBS females compared with healthy females (P = 0.006). For IL-12, 92% of samples were available. TNF, tumor necrosis factor.

Figure 3

Individual data for colonic mucosal interleukin-10 (IL-10) mRNA levels in both female controls and irritable bowel syndrome (IBS) patients are shown. IL-10 mRNA levels were significantly lower in IBS patients vs. controls (P = 0.006).

Figure 4

Representative immunohistochemistry images of 20× scanned slides. (Top row) (a–c) Colonic mucosa from a healthy control subject stained for serotonin (a), CD4 (b), and mast cell tryptase (c). (Bottom row) (d–f) Colonic mucosa from a patient with IBS-D stained for serotonin (d), CD4 (e), and mast cell tryptase (f). There are no qualitative differences based on immunohistochemically detected enterochromaffin, CD4T, or mast cells between healthy controls and IBS patients.

Figure 5

Individual data for colonic mucosal neurokinin (NK)-1R mRNA levels in both female controls and irritable bowel syndrome (IBS) patients are shown. NK-1R expression was significantly lower in IBS patients vs. controls (P = 0.008).