Colonic immune cells in irritable bowel syndrome: A systematic review and meta-analysis

Background & Aims: Increases in mucosal immune cells have frequently been observed in irritable bowel syndrome (IBS) patients. However, this finding is not completely consistent between studies, possibly due to a combination of methodological variability, population differences and small sample sizes. We performed a meta-analysis of case–control studies that compared immune cell counts in colonic biopsies of IBS patients and controls. Methods: PubMed and Embase were searched in February 2017. Results were pooled using standardized mean difference (SMD) and were considered significant when zero was not within the 95% confidence interval (CI). Heterogeneity was assessed based on I² statistics where I² ≤ 50% and I² > 50% indicated fixed and random effect models, respectively. Key Results: Twenty-two studies on 706 IBS patients and 401 controls were included. Mast cells were increased in the rectosigmoid (SMD: 0.38 [95% CI: 0.06-0.71]; P =.02) and descending colon (SMD: 1.69 [95% CI: 0.65-2.73]; P =.001) of IBS patients. Increased mast cells were observed in both constipation (IBS-C) and diarrhea predominant IBS (IBS-D). CD3⁺ T cells were increased in the rectosigmoid (SMD: 0.53 [95% CI: 0.21-0.85]; P =.001) and the descending colon of the IBS patients (SMD: 0.79, 95% CI [0.28-1.30]; P =.002). This was possibly in relation to higher CD4⁺ T cells in IBS (SMD: 0.33 [95% CI: 0.01-0.65]; P =.04) as there were no differences in CD8⁺ T cells. Conclusions & Inferences: Mast cells and CD3⁺ T cells are increased in colonic biopsies of patients with IBS vs non-inflamed controls. These changes are segmental and sometimes IBS-subtype dependent. The diagnostic value of the quantification of colonic mucosal cells in IBS requires further investigation.