The Clinical Significance of Eosinophils in Ulcerative Colitis: A Systematic Review

Background and Aims: Ulcerative colitis [UC] is characterised by an unpredictable disease course and variable response to therapy. Recent studies suggest a role for eosinophils in both pathogenesis and predicting treatment response. The goal of this study was to determine the association between eosinophils and clinical outcomes in UC. Methods: A systematic review of the literature from database inception to May 2021 was performed to identify all studies evaluating the relationship between eosinophils and/or eosinophil-derived proteins [EDPs] and clinical outcomes, such as disease activity, clinical relapse, severity of disease, and response to treatment. Results: A total of 55 studies were identified. Of these, 34 studies evaluated the relationship between eosinophils in colonic tissue and outcomes and 15 in blood. Eighteen studies assessed the relationship between EDPs and outcomes. In 25 of 34 studies, a positive correlation between eosinophils and/or EDPs and disease activity was reported, three studies found a negative correlation, and nine studies found no correlation. Positive correlations between eosinophils and clinical relapse were shown in four of nine studies, and with disease outcome severity in five of seven studies. Four of 15 studies showed that subjects with higher eosinophil levels had a poor response to treatment. Conclusions: These findings suggest that higher eosinophil levels may be associated with increased disease activity and poorer clinical outcomes and response to therapy. Future studies are needed to determine whether a distinct eosinophil-rich UC phenotype exists and whether eosinophil-targeted therapy can alter the disease course.