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.

S. boulardii improved IBS-QOL better than placebo but was not superior for individual symptoms in patients with diarrhea-predominant IBS or mixed-type IBS.

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