Proteases of polymorphonuclear neutrophils: influence of different salts and buffers on pericellular lysis

Polymorphonuclear neutrophils (PMN) contain neutral proteases which are cytochemically detectable on blood smears. The activity of these proteases can be visualized by pericellular lysis, i.e. through a disk like degradation of plasma and erythrocytes around centrally located neutrophils. This degradation is inhibited by protease inhibitors in a concentration-dependent manner. Striking differences in halo formation were found depending on the type of buffer and salt used and change of temperature. A halo formation was obtained in Tris-HCl buffer, pH 7.5 without salt, at room temperature (22 degrees C), and with short incubation periods (30 min). Borate buffer, pH 8.5, showed a comparable halo formation only at 37 degrees C, after addition of salts, and after longer incubation times (180 min). When different alkali chlorides were used, halo size increased with molecular mass. Optimum halo size was achieved at a concentration of 250 mM. Addition of MgCl2 and CaCl2 (250 mM) resulted in a small halo formation at 22 degrees C, but inhibited halo formation at 37 degrees C. The present study shows that the pericellular lysis caused around neutrophils by the release of proteases is affected by a complex interaction of salts, temperature, buffers and thermodynamic aspects, all of which should be evaluated carefully in these kinds of experiments.