Fixation with Carnoy's fluid reduces the number of chymase-positive mast cells : not all chymase-positive mast cells are also positive for tryptase

Mast cells in the nasal mucosa can be studied by means of monoclonal antibodies (mAb) against tryptase (T + MC) and chymase (C + MC). Fixation with acetone gives more positive cells than does fixation with Carnoy's fluid. In frozen biopsy specimens of allergic nasal mucosa fixed with acetone, the number of T + MC equals that of C + MC. When fixed with Carnoy's fluid, however, the number of T + MC is larger than the number of C + MC. The decrease in both T + MC and C + MC resulting from fixation with Carnoy's fluid is time-related and depends on the type of mAb used. Carnoy fixation time gives a decrease in the number of C + MC within 1 min, whereas the number of T + MC decreases only after 10 min. Within 1 min, the number of C + MC decreases to a level where continued fixation no longer gives further decreases in the number of cells. Two populations of mast cells can be distinguished here : one sensitive and the other insensitive to Carnoy's fluid. When double-staining is used, fixation with acetone gives three populations of mast cells : one positive for tryptase (T + CMC), another positive for tryptase and chymase (T + C + MC), and a third one positive for chymase (T - C + MC). These three populations were found in lymph node, spleen, thymus, dermis, lung parenchyma, small intestinal submucosa, and nasal mucosa.