Dermal mast cells in mastocytosis: fixation, distribution and quantitation

The mast cell distribution and number were studied in skin biopsies of 18 mastocytosis patients and 10 controls. The biopsies were stained for mast cells with toluidine blue at pH 0.5. The number in the upper dermis of lesional abdominal skin was at least twice as high as that of normal adjacent skin. Fixation in iso-osmotic 0.6% formaldehyde and 0.5% acetic acid, revealed more mast cells than conventional 4% formaldehyde fixation. Staining for 5 days, when compared to the normal for 30 min, increased the number of demonstrable mast cells just as did the change in fixation. Conventional formaldehyde fixation thus partially blocks the dye-binding of cutaneous mast cells, about 20% of the cells escaping detection. The degree of aldehyde blocking was similar in lesional and normal skin. A more pronounced blocking of dye-binding has been demonstrated previously in gut mucosal mast cells. Whether the blocking of dye-binding is an expression of heterogeneity in dermal mast cells remains to be determined.