Mast cell density and subtypes in the skin of dogs with atopic dermatitis

Skin biopsies from seven dogs with atopic dermatitis and 13 dogs with no cl inical or histological evidence of skin diseases were examined. The study o f the atopic dogs included 11 biopsy samples of nonlesional skin and biopsy samples of lesional skin. One section of each tissue sample was stained wi th haematoxylin and eosin and another with toluidine blue to demonstrate th e sulphated acid glycosaminoglycans in mast cell (MC) granules. To investig ate MC subtypes, the MC-specific proteases tryptase and chymase were examin ed by a double enzyme-immunohistochemical staining technique. With the doub le labelling technique a significantly lower mast cell density was demonstr ated in lesional (P=0.0023) and nonlesional (P=0.0004) skin samples of the atopic dogs than in the skin of control dogs. In the dermis of control dogs , a median mast cell density of 31.2 MC/mm(2) was detected with the toluidi ne blue staining method and of 27.5 MC/mm(2) with the double labelling tech nique. In lesional dermis of atopic dogs 29.8 MC/mm(2) were seen with tolui dine blue while only 12.4 MC/mm(2) were stained with the double labelling m ethod (P=0.0027). A similar difference was observed in nonlesional dermis s amples, in which a mast cell density of 23.3 MC/mm(2) was detected with tol uidine blue but only 6.4 MC/mm(2) with the double labelling method (P=0.012 7). The data provide evidence that mast cell granule heterogeneity exists i n the dog and suggests that degranulation occurs selectively, depending on the pathological condition of the canine skin. Further investigations on th e pathophysiological role of mast cell subtypes may help to elucidate the p athogenesis of atopic dermatitis. (C) 1999 W.B. Saunders Company Limited.