Differential Enteric Glial and Mast Cell Characteristics Distinguish Microscopic Colitis Subtypes Relative to Healthy and Disease Controls, with Treatment-Associated Reductions in Glial Reactivity and Mast Cell Degranulation in Collagenous Colitis

Microscopic colitis (MC) is an inflammatory bowel disease characterized by chronic watery diarrhea. Although barrier dysfunction and immune activation are implicated, underlying mechanisms remain unclear. The aim of this study was to characterize enteric glial cells (EGCs) and mast cell distribution across MC subtypes, assess treatment effects, and explore EGCs-related gene expression and barrier markers. Colonic biopsies from patients with active collagenous colitis (aCC), budesonide-refractory CC (rCC), and active lymphocytic colitis (LC) were compared to irritable bowel syndrome (IBS), ulcerative colitis (UC), and healthy controls (HC). A subset of CC patients was studied during active disease (aCC) and in clinical remission due to budesonide treatment (tCC). Immunofluorescence quantified EGCs positive for glial fibrillary acidic protein (EGCsGFAP+) and S100 calcium-binding protein B (EGCsS100β+), mast cell tryptase, and tight junction proteins. RNA-sequencing assessed EGCs-related gene expression. Results showed that EGCsGFAP+ cells were highest in rCC and decreased following budesonide treatment in aCC, whereas EGCsS100β+ cells were highest in aCC, remained unchanged following treatment, resembled IBS, and were reduced compared with UC. Mast cell numbers were higher in aCC than in HC and rCC but remained unchanged following treatment, while mast cell degranulation decreased after treatment. Tight junction proteins were unchanged. RNA-sequencing indicated differential regulation of EGCs-related genes. In conclusion, MC shows subtype-specific alterations involving EGCs and mast cells, suggesting distinct glial states and differential treatment responsiveness. Our findings support the presence of distinct neuroimmune alterations in CC and LC and highlight EGCs as potential contributors to MC pathophysiology.