Preliminary Characterisation of Immune Cell Populations in the Oral Mucosa of a Small Cohort of Healthy Dogs (<i>Canis lupus familiaris</i>)

Pre-determined anatomical locations in the oral cavity were biopsied, and their histomorphology was characterised using haematoxylin and eosin staining (H&E). The most abundant cell type was of dendritic morphology. Lymphocyte foci were not evident in the palatoglossal folds or the gingiva. Immunohistochemical staining (IHC) for validated leukocyte markers followed, including CD3, CD20, CD79α, CD204, and Iba1. Consistent with H&E findings, CD204 immunoreactivity predominated amongst all niches. With the exception of the alveolar mucosa and palatoglossal folds, we also demonstrate a significant difference in the population of macrophages by region for only the Iba1 antigen (p < 0.0001). B lymphocytes were found, and a significant difference was noted in the sub-epithelium where CD20-positive cells outnumbered those labelled as CD79a positive (p = 0.001), suggesting the possibility that these cells are in an active state in health. A similar significant difference was found in the subepithelial tissue for myeloid cells, as there were more cells labelled as CD204 positive over Iba1, which, along with their distribution pattern, indicates a possible functional and morphological overlap between these cells. No significant difference was found in epithelial tissues for cells of either myeloid or lymphoid origins. The results from this study suggest different regions of the oral cavity exhibit variations in the distribution of immune cells, particularly macrophages and B lymphocytes. Though more studies would be needed to confirm these findings, these differences may have implications for the immune response and overall health of the oral mucosa.