Mast cell density and subtypes in the skin of Shar Pei dogs with cutaneousmucinosis

Skin biopsies from 13 Shar Peis showing signs of cutaneous mucinosis and 13 control dogs of different breeds with no clinical or histological evidence of skin disease were examined. One section of each tissue sample was stain ed with haematoxylin and eosin, and another with toluidine blue to demonstr ate the sulphated acid glycosaminoglycans in mast cell (MC) granules. To in vestigate the MC subtypes involved, the tryptase and chymase content of mas t cells was evaluated by a double enzyme-immunohistochemical staining techn ique. Regardless of the staining technique, a significantly lower mast cell density in the skin of Shar Peis was demonstrated. In the dermis of contro l dogs, we detected a median mast cell density of 31.2 MC/mm(2) using the t oluidine blue staining method and 27.5 MC/mm2 using the double labelling te chnique. In Shar Peis only 9.1 MC/mm(2) were found by toluidine blue staini ng (P = 0.001) and 14.8 MC/mm2 by the double labelling method (P = 0.0387). The percentile distribution of mast cell subtypes was also significantly d ifferent in Shar Peis as compared to control dogs. Whereas in the dermis of control dogs the predominant mast cell subtype was the tryptase and chymas e containing MC (TC-MC) (60.4%), in Shar Pei skin the only chymase containi ng MC (C-MC) predominated (62.2%) and the percentage of TC-MC was significa ntly lower (32.9 %; P = 0.0016). The percentage of only tryptase containing MC (T-MC) (4.7 %) was higher in Shar Peis compared to control dogs (1.9 % P = 0.0178). The data obtained indicate a possible involvement of mast cell subtypes in the pathogenesis of cutaneous mucinosis. Further investigations on the pathophysiological role of mast cell subtypes may foster understanding of the pathogenesis of cutaneous mucinosis.