DISTRIBUTION, DENSITY AND HETEROGENEITY OF CANINE MAST-CELLS AND INFLUENCE OF FIXATION TECHNIQUES

The present study was carried out to determine the physiological distr ibution of mast cell numbers and types in the dog according to tissue location, staining and fixation methods. Tissue samples from stomach, duodenum, lung, lymph node, skin and uterus were evaluated. Samples we re fixed in formalin as well as in Carnoy's fluid. The average number of mast cells was determined using a metachromatic staining method. Pr otease content of mast cells was examined with a double enzyme-immunoh istochemical staining technique, using a histochemical reaction for ch loroacetate esterase to detect chymase activity and an immunohistochem ical staining method for the detection of tryptase. Canine mast cells can be subdivided into formalin-sensitive and -resistant mast cells. T hree subtypes were identified according to their content of the mast c ell-specific proteases tryptase (T) and chymase (C): T-, TC- and C-mas t cells. Significant differences regarding the distribution of mast ce ll subtypes as well as the influence of the fixation method can be obs erved. This underlines the fact that data regarding mast cell heteroge neity from other species, obtained by different fixation methods, are not comparable. This fact has to be taken into consideration when eval uating mast cell subtypes under pathological conditions.