Histochemical comparison of mast cells obtained from the airways of mongrel dogs and Basenji-Greyhound dogs by bronchoalveolar lavage

An abnomally large number of mast cells in the airway lumen may be an important factor in the pathogenesis of bronchial hyperreactivity. However, it is unclear just how many mast cells are present in the lumen of normal or hyperreactive airways, in part because of differences in the histochemical techniques that have been used to identify mast cells and questions about the heterogeneity of mast cells. The present study was done (1) to compare the effectiveness of six techniques in the identification of mast cells obtained from dogs by bronchoalveolar lavage (BAL), (2) to compare the mast cells in the airways of normal mongrel dogs with those from a breed of dog (Basenji-Greyhound) known to have bronchial hyperreactivity, and (3) to determine whether the two-type histochemical classification used for rodent mast cells (formaldehyde-resistant or typical and formaldehyde-sensitive or atypical) applies meaningfully to the mast cells in BAL fluid from dogs. Cells obtained by BAL were fixed with Mota's basic lead acetate or formaldehyde. Mast cells were identified by metachromatic staining with toluidine blue or methylene blue, staining of highly sulfated proteoglycans with Alcian blue or berberine sulfate, and a histochemical reaction for chloroacetate esterase (mast cell chymase). After Mota's fixation, the methods were relatively similar in their effectiveness in determining the number of mast cells in lavage fluid from the mongrel dogs, in that all of the values fell within a narrow range: 0.53 to 0.96% of the total number of cells. Furthermore, the methods identified approximately the same number of mast cells in the Basenji-Greyhounds as in the mongrel dogs, with the exception of the chloroacetate esterase reaction, which was abnormally weak in the Basenji-Greyhounds. However, after formaldehyde fixation, the methods stained from as few as 0% to as many as 67% of the total complement of mast cells, and thus the proportion of atypical mast cells ranged from 100 to 33%, depending upon the stain. We conclude, on the one hand, that all the methods we used can detect approximately the same total number of mast cells, and that bronchial hyperreactivity can occur in Basenji-Greyhounds without an increase in the total number of mast cells in the airway lumen. On the other hand, differences in the proportion of atypical mast cells revealed by the different methods suggest that mast cells in the airways of dogs are too heterogeneous to fit meaningfully into the two-type classification (typical and atypical) used for rodent mast cells.