Stage-specific IgA/IgG plasma cell patterns in ulcerative colitis rectal mucosa: An exploratory pilot study

Plasma cell infiltration is characteristic of ulcerative colitis (UC), yet immunoglobulin subtype-specific alterations across disease stages remain poorly defined. This study aimed to characterize quantitative and distributional patterns of IgA- and IgG-positive plasma cells in UC rectal mucosa across disease stages. Rectal biopsies from healthy controls ( n = 6) and UC patients at different stages—active inflammation ( n = 6), chronic quiescent ( n = 6), and 5-aminosalicylic acid (5-ASA) -induced remission ( n = 6)—were retrospectively collected between June 2024 and June 2025. H&E staining and immunohistochemical (IHC) analysis for IgA- and IgG-positive cells were assessed. A dextran sulfate sodium (DSS)-induced murine colitis model with 5-ASA therapy was established for experimental validation. Active UC demonstrated fragmented, sparse superficial IgA distribution with reduced IHC scores compared to healthy controls (continuous banding pattern), while IgG showed diffuse transmural infiltration with elevated scores. Chronic quiescent UC exhibited patchy, discontinuous superficial IgA with partially recovered scores, alongside persistent transmural IgG with decreased scores. Post-treatment remission restored continuous IgA banding with further increased scores. In the murine model, IgA-positive cells decreased dose-dependently, while IgG-positive cells increased. 5-ASA treatment reversed these alterations. Stage-specific quantitative and distributional patterns of IgA- and IgG-positive cells constitute preliminary evidence of distinctive immunopathological patterns in UC. These preliminary findings suggest potential stage-specific immunophenotypic patterns that warrant validation in larger cohorts.