The distribution of leucocyte subsets in the small intestine of healthy cats

The aim of this study was to investigate the distribution of leucocyte subsets in the small intestine of healthy adult cats (n=16). Immunohistochemical methods were used to identify leucocyte subsets within the mucosa of the duodenum, jejunum and ileum. Computer-aided morphometry was used to enumerate cells within the epithelial compartment, villous lamina propria and lamina propria adjacent to upper and lower crypt. Throughout the small intestine, IgA+ and IgM+ plasma cells were more prominent in the lamina propria adjacent to the lower crypt than in the villus, whereas IgG+ plasma cells were present in equal numbers in the crypt and villous regions. Overall, IgA+ plasma cells predominated and IgM+ plasma cells were higher in number than IgG+ plasma cells at each of the three anatomical locations. By contrast, T cells (CD3+) and T-cell subsets (CD4+ and CD8+) were present in greater numbers in the villous lamina propria than in the lamina adjacent to the crypts. Intraepithelial lymphocytes (IELs) were also characterized phenotypically, the majority being CD8+ T lymphocytes. Lamina propria macrophages and dendritic cells were characterized by expression of L1 and major histocompatibility complex (MHC) class II, and MHC class II expression by enterocytes overlying Peyer's patches, although rare, was also shown. The qualitative and quantitative data from this study provide a basis for comparison with cats with inflammatory enteropathies.