Uncontrolled activation of intestinal lymphocytes has been suggested as one of the underlying reasons for inflammatory bowel disease (IBD). However, little is known about the lymphocyte populations in the neonatal and adult canine gut.

The aim of this study is the characterization of intraepithelial lymphocytes (IEL) in the canine intestinal mucosa. Differences between IEL in neonatal versus adult beagle dogs from different sections of the intestine were analyzed. Tissue samples were obtained from 15 adult (mean age 8.2 ± 2.1 years) and 6 neonatal beagle dogs (mean age 1.1 ± 1 days) in order to reduce the heterogenicity due to differences in breeds. T cell populations and distributions were phenotypically characterized by immunohistochemistry and flow cytometry using T cell-specific markers, including CD45, CD3, CD4, CD8α, CD8β, TCRαb and TCRγδ.

Results indicate that there are significant differences between adult and neonatal dogs in the distribution of different lymphocyte subsets. In the IEL population of the small bowel (SB) of adult dogs CD3⁺TCRαβ⁺, CD8αβ⁺TCRαβ⁺, and CD4⁺TCRαβ⁺ T cells predominate, whereas CD8αβ⁺TCRγδ⁺ and double negative TCRγδ⁺ Tcells were found in increased numbers in the SB IEL population of newborn dogs. In the IEL compartment of the large bowel (LB) the same significant differences could be found.

These data obtained from healthy dogs give first insight into the developmental population of the intestinal mucosa by immune cells. They will not only allow future comparisons with intestinal lymphocyte populations in dogs suffering from IBD, but also help to develop a better understanding of the pathogenesis of IBD.