QUANTITATIVE AND QUALITATIVE IMMUNOHISTOCHEMISTRY OF T-CELL SUBSETS AND MHC CLASS-II EXPRESSION IN THE CANINE SMALL-INTESTINE

In man and rodents, cells of the gastrointestinal immune system includ e B and T lymphocytes, granulocytes, macrophages and dendritic cells. Abnormalities in leucocyte numbers and function have been described in diseases of humans, such as coeliac disease and inflammatory bowel di sease. The purpose of this study is to describe the normal distributio n of T cells and MHC Class II expression in the small intestine of cli nically normal dogs, to allow subsequent comparison with disease state s. Full-thickness sections of duodenum, jejunum and ileum from seven y oung adult beagle dogs were immediately snap-frozen following euthanas ia. Avidin-biotin-enhanced immunocytochemistry was used to detect expr ession of canine CD3, CD4, CD8 and MHC Class II antigens. Positively s tained lamina propria cells were quantified using an eyepiece graticul e, and positively stained intraepithelial cells by counts per 100 epit helial cells. In the lamina propria, the density of all leucocyte subs ets was significantly increased towards the villus tip for all regions (p<0.05). There was no apparent difference in the distribution of CD3 (+), CD4(+) and CD8(+) leucocytes between the three portions of the sm all intestine. The ratios of CD4(+) cells to CD8(+) cells in the lamin a propria and epithelium were 59:41 and 15:85, respectively. Subtracti ve analysis suggested that 50-55% of CD3(+) intraepithelial cells were CD4(-)CD8(-), MHC Class II expression was apparent upon lamina propri a cells with a dendritic morphology, as well as round cells. Epithelia l MHC Class II expression was apparent in 7/7 ileal sections, compared with only 1/7 duodenal and 1/7 jejunal sections. This study shows tha t the small intestinal mucosa of the dog contains similar leucocyte po pulations to those found in other species, and suggests that these cel ls may play similar roles in gastrointestinal immunity. (C) 1997 Elsev ier Science B.V.