Quantification of intraepithelial canine melanocytes in different somatic areas.

Background: In humans, the presence of an even distribution of melanocytes within the epidermal basal layer allows for uniform pigmentation in healthy and young individuals. Moreover, despite high variability in skin colours and tones, interindividual melanocyte density variability is low. However, dogs display a high intraindividual pigmentary variability in different anatomical areas.

Hypothesis/objective: Data on canine melanocytes, including their distribution and density, are limited. This study aimed to assess melanocyte density across different anatomical areas in dogs of various breeds.

Materials and methods: Samples were harvested postmortem from 22 dogs of different breeds and ages. Samples were collected from the following: haired skin (back, ventral abdomen, head and pinnae), oral and conjunctival mucocutaneous junctions, oral mucosa (buccal mucosa, gingiva, palate) and nose. Immunohistochemical investigation using a cocktail containing Melan-A and SOX-10 antibodies was performed to evaluate the melanocytes:keratinocytes ratio (M:K ratio).

Results: Variable melanocyte density was recorded in different anatomical areas, with a higher M:K ratio on the eyelid (median: 1:4; interquartile range [IQR]: 1:3.8-1:5.1) and on the nose (median: 1:6.5; IQR: 1:5.2-1:9.6). Lower ratios were observed on the haired skin, particularly on the head (median: 1:113.6; IQR: 1:37.8-1:255.1).

Conclusions and clinical relevance: Together with different melanocyte densities in different anatomical areas, dogs showed a high interindividual variability, particularly on haired skin. This finding could be associated with colour phenotype, sun exposure, and breed. Variable densities of melanocytes also might justify different incidence of melanocytic tumours in hyperpigmented breeds and in different somatic areas, as well as provide an increased protective effect in chronically sun-exposed areas.