Characterization of immune cell populations in oral mucosal tissue of healthy adult cats.

The aim of this study was to characterize the leucocyte subsets present in the oral mucosa of healthy cats. Immunohistochemical labelling and computer-assisted morphometric analysis was used to identify expression of MHC class II, CD3, CD79a, IgG, IgM, IgA, and leucocyte antigen L1 (L1) by cells in sections from 19 cats, and expression of CD4 and CD8 by cells in sections from 17 cats. Mast cells were detected by toluidine blue staining. In the epithelial compartment, CD3(+) intraepithelial lymphocytes were detected, and CD8(+) cells were more common than CD4(+) cells. MHC class II labelling revealed intraepithelial and subepithelial cells with a characteristic dendritic morphology. In some sections these dendritic cells were closely associated with subepithelial clusters of CD3(+) T cells containing both CD4(+) and CD8(+) cells. In the lamina propria and submucosal compartments, the cells most commonly identified were mast cells. CD3(+) T-lymphocytes were also observed, and CD4(+) and CD8(+) cells were detected in similar numbers. L1(+) and CD79(+) cells were detected least frequently. The few plasma cells present were generally found to be either IgG(+) or IgA(+). Within the stroma surrounding the salivary glands, CD79a(+) and IgA(+) cells predominated. Slight epithelial labelling for L1 was seen in some sections. The normal feline oral mucosa clearly contains a range of immune cell populations.