FoxP3-positive T regulatory cells and its effector mechanisms in Crohn's disease: an immunohistochemical and image morphometric analysis on endoscopic mucosal biopsies.

Objective: Crohn's disease (CD) is an immune inflammatory disorder of the gastrointestinal tract arising from a complex interplay of genetic, environmental, microbiome, and immune factors. Regulatory T cells (Tregs), characterized by FoxP3 expression, are crucial for maintaining immune homeostasis through PD-1/PD-L1 interaction, interleukin (IL)-10 release, and granzyme (GrB) production. This study aimed to elucidate the role of FoxP3 positive (+) Tregs in CD.

Methods: Segmental colonoscopic biopsies from 46 treatment-naive CD cases (34 adults and 12 children) categorized into noninflamed [ n  = 32; Nancy histologic index (NHI) 0, 1] and inflamed ( n  = 100; NHI 2-4) mucosae using NHI. CD4, FoxP3, PD-1, IL-10, and GrB immunoexpression were analyzed by eyeballing and image morphometry. Findings were correlated with activity, granulomas, and skip lesions; and compared with site-matched non-inflammatory bowel disease (IBD) controls ( n  = 30).

Results: FoxP3+ Tregs, IL-10, PD-1, and GrB expressions were significantly higher in NHI 3-4 mucosae than in NHI 0-1 and controls ( P  < 0.05). No significant differences were observed between adults and children, whereas those with granulomas had increased expression ( P  = 0.045). The FoxP3 : CD4 ratio positively correlated with IL-10 (Spearman, r  = 0.307, P  = 0.002), GrB ( r  = 0.302, P  = 0.002), but not with PD-1 ( r  = 0.98, P  = 0.33).

Conclusions: Our findings point to the possibility of a qualitative defect in FoxP3+ Tregs in CD. The functional arms of Tregs in CD need to be elucidated further in larger prospective cohorts to validate our observations and pave the way for future immunotherapy.