Assessment of CD3+ T cell density in the intestinal mucosa of dogs with inflammatory bowel disease.

BACKGROUND: T lymphocytes play a central role in the intestinal immune response in dogs with immunomodulator-responsive enteropathy (IRE), but the clinical relevance of mucosal T-cell infiltration remains unclear. HYPOTHESIS/OBJECTIVES: Compare mucosal CD3+ T-cell density between dogs with IRE and healthy comparison dogs across intestinal segments, and assess associations with clinical, biochemical, and histologic severity markers. ANIMALS: Forty-two client-owned dogs with IRE and 12 healthy research dogs. METHODS: Retrospective multicenter study. Archived endoscopic biopsy samples from the duodenum, ileum, and colon were evaluated using the Simplified Histopathological Scoring System. Immunohistochemistry for CD3 was quantified by digital image analysis (QuPath) and expressed as relative CD3+ density (RCD3). Group comparisons, receiver operating characteristic curve analyses, mixed linear models, and correlation analyses were performed. RESULTS: Relative CD3+ density was significantly higher in dogs with IRE than in comparison dogs in the duodenum (median, 6.34% vs 1.42%; P = .03), ileum (9.79% vs 0.85%; P < .001), and colon (3.88% vs 1.32%; P = .002). The area under the curve values were 0.833, 0.896, and 0.811, respectively. The RCD3 was not correlated with clinical indices, serum albumin concentration, or histologic scores, but ileal histologic score was negatively correlated with RCD3 (ρ = -0.37; P = .04). CONCLUSIONS AND CLINICAL IMPORTANCE: Mucosal CD3+ T-cell density is increased in dogs with IRE but is not associated with clinical or overall histologic disease severity. Quantification of CD3+ should not be used as a solitary monitoring tool but may contribute to immunophenotyping.