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

Mast cells can be distinguished according to various characteristics: rodent mast cells have been subtyped by histochemical criteria, wherea s canine and human mast cells have been classified according to their proteases. Comparisons of mast cells from different species have there fore resulted in contradictory and confusing opinions on mast cell het erogeneity. Thus, it is essential to obtain species-specific data on m ast cell density and heterogeneity. The present study was carried out to determine the physiological distribution of mast cell numbers and t ypes in bovines according to tissue location, staining, and fixation m ethods. Samples were fixed in formalin or Carnoy's fluid. The average number of mast cells was determined by using a metachromatic staining method. Protease content of mast cells was examined with a double-enzy me-immunohistochemical staining technique. Three mast cell subtypes we re distinguished: T-, TC-, and C-mast cells. The T-mast cell was the p redominant subtype in nearly all investigated organs and tissue locati ons. Only tryptase-positive mast cells could be demonstrated in bovine skin and uterus. No chymase activity was found in these organs, regar dless of the fixation type. A larger number of mast cells was observed after fixation in Carnoy's fluid. The three different mast cell subty pes were only demonstrated in formalin-fixed tissue; chymase-positive mast cells were not found after fixation in Carnoy's fluid. Increasing experimental data suggest that mast cell subtypes have different func tions in promoting and modulating inflammation and in remodeling the e xtracellular matrix. Since mast cell tryptase and chymase have differe nt functional properties, these results may clarify the different reac tion patterns observed in various organs and species.