• Immunohistochemistry;
  • Leukocyte subsets;
  • Major histocompatibility complex class II;
  • Plasma cells;
  • T cells

The aim of this study was to characterize the phenotype of leukocytes infiltrating the duodenal mucosa of cats with inflammatory bowel disease (IBD) by using immunohistochemistry and computer-aided morphometry to assess whether immunologic markers would aid in characterization of IBD. Frozen and formalin-fixed duodenal biopsies were collected from cats referred for investigation of chronic vomiting, diarrhea, or both (n = 34). Reference ranges were previously established by using duodenal samples from healthy cats (n = 16). No significant difference was found in the number of immunoglobulin G+ (IgG+) or IgA+ in either the villous lamina propria or the crypt lamina propria between cats with IBD and control cats. T cells (CD3+) increased in number from crypt to the tip of the villi in biopsies from both diseased (mean ± SD for each group was 18.8±6.6 and 17.7±4.2 cells/10,000μm2 in cryptal areas to 25.2±9.5 and 29.1±13.3 cells/10,000μm2 in villous areas) and healthy animals (17.9±3.9 cells/10,000μm2 in cryptal areas to 24.1±9.3 cells/10,000μm2 in villous areas) and no significant difference was found between diseased and control cats. By contrast, major histocompatibility complex (MHC) class II expression by leukocytes with dendritic cell or macrophage morphology in the lamina propria was significantly greater in cats with IBD (13.3±4.2 cells/10,000μm2 in cryptal area; P= .016) than in healthy cats (11.9±3.0 cells/10,000μm2) and MHC class II expression by enterocytes also was more pronounced in these cats showing an overall intensity of expression of 7.1±4.0 cells/10,000μm2 in cats with IBD as opposed to 0.0±0.0 cells/10,000μm2 to 0.3±0.7 cells/10,000μm2 in healthy cats. These findings suggest that a subtle immunologic dysregulation occurs in spontaneously arising feline IBD.