Biochemical and histochemical evaluation of tryptase in various human tissues

The distribution of tryptase in various human tissue high-salt extracts (skin, lung, pancreas, liver, kidney, and spleen) was studied. Tryptase activity was compared with tissue histamine concentration, chymase activity, and cathepsin D, and histamine-N-methyltransferase (HMT) activities. Tryptase activity, found biochemically in tissue extracts, was localized in tissue sections by an enzyme-histochemical method using peptide 4-methoxy-2-naphthylamide substrates and Fast Garnet GBC as the chromogen. The highest levels of tryptase activity were found in lung and skin extracts. Liver, kidney, and spleen extracts displayed only a little activity. The distribution of histamine was similar to that of tryptase, whereas distributions of cathepsin D and HMT were quite different from that of tryptase. High-salt extracts of lung contained no detectable chymase activity, but in skin extracts this activity was high. Using an enzyme-histochemical method, the tryptase activity in tissue sections seemed solely to be confined to cells, which were granular and Giemsa positive after the red azo dye had been removed with Tween 20. Skin and lung sections contained the highest number of positively stained cells. The inhibition properties of tryptase, found in both tissue extracts and sections, and the substrate profile in tissue sections were identical. Human leukocyte preparation was negative for tryptase when stained enzyme-histochemically. The present results suggest that tryptase in human tissues is found only in the mast cells. The enzyme seems to be identical in the various human tissues studied because the different high-salt extracts were immunologically cross-reactive when tested with a rabbit polyclonal antibody against skin tryptase.