The immunohistochemical identification of human oral mucosal melanocytes

With the aim of identifying melanocytes, 60 samples of wax-embedded palatal and buccal mucosa from 30 autopsies were analysed for expression of S100, HMB-45 and NKI/C3 in combination with a Masson-Fontana stain. The counts of positive cells were compared with those derived from 3,4 dihydroxyphenylalanine (DOPA) staining in fresh samples of gingiva. Polyclonal antisera to S100 stained dendritic cells throughout the epithelium, but monoclonal antibodies to S100, HMB-45 and NKI/C3 labelled cells that were restricted to the basal layer, often in clusters with some sections negative. The mean counts of positive basal dendritic cells per millimetre basement-membrane length were 4.3 (polyclonal S100+, range 0–19), 0.8 (monoclonal S100+, range 0–7.3), 2.0 (HMB-45, range 0–17.8) and 0.9 (NKI/C3, range 0–14.9). Of the last three, HMB-45 produced the clearest and most specific staining. Counts of basal dendritic cells were significantly higher (p < 0.0005) with polyclonal antisera to S100 than with all other markers except DOPA, but HLA-DR staining showed that Langerhans cells may also be located in the basal layer. The highest values were always in buccal mucosa, but statistically significantly so (p < 0.0005) only with polyclonal anti-S100. Basally located DOPA+ cells had a mean density of 4.6 per millimetre basement-membrane length, but in five cases DOPA also labelled suprabasal dendritic cells, presumably Langerhans cells. The mean basal DOPA+ values were significantly higher than those with monoclonal antibodies to S100, HMB-45 and NKI/C3 (p < 0.001). The variable cell counts suggest that S100, HMB-45 and NKI/C3 are markers of melanocytes in normal oral mucosa, but are not constitutively expressed and may be induced during function.