Mast cell density and subtypes in the skin of Shar Pei dogs with cutaneous mucinosis.

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 stained with haematoxylin and eosin, and another with toluidine blue to demonstrate the sulphated acid glycosaminoglycans in mast cell (MC) granules. To investigate the MC subtypes involved, the tryptase and chymase content of mast cells was evaluated by a double enzyme-immunohistochemical staining technique. Regardless of the staining technique, a significantly lower mast cell density in the skin of Shar Peis was demonstrated. In the dermis of control dogs, we detected a median mast cell density of 31.2 MC/mm2 using the toluidine blue staining method and 27.5 MC/mm2 using the double labelling technique. In Shar Peis only 9.1 MC/mm2 were found by toluidine blue staining (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 different in Shar Peis as compared to control dogs. Whereas in the dermis of control dogs the predominant mast cell subtype was the tryptase and chymase containing MC (TC-MC) (60.4%), in Shar Pei skin the only chymase containing MC (C-MC) predominated (62.2%) and the percentage of TC-MC was significantly 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.