Summary
Two highly purified neutral proteases from human leukocytes i.e. elastase-like protease
(ELP) and chymotrypsin-like protease (CLP) do not destroy human platelets since no
difference was found in 51Cr liberation from control and enzyme-treated platelets. As with pancreatic chymotrypsin
(α-CT) ELP does not induce the release of 3H-serotonin while CLP provokes 3H- serotonin secretion, in an enzyme concentration and time dependent fashion. The
rate and degree of 3H-serotonin release by CLP is similar to that produced by thrombin. Incubation of
platelets at 37° C for 30 min with α-CT or ELP renders them resistant to thrombin-releasing
activity. Thrombin did not liberate any additional label from platelets which lost
over 60% of serotonin during the preceding incubation with CLP. α-CT and ELP do not
aggregate platelets either in the presence or absence of apyrase. CLP does aggregate
platelets suspended in Tyrode buffer without apyrase but not in the presence of apyrase
(100 mg/1). The action of α-CT, ELP and CLP on washed platelets induces a progressive
prolongation of lag phase and a decrease in changes of light transmission during aggregation
by thrombin. Similarly to α-CT-treated platelets, those subjected to CLP action aggregate
in the presence of human fibrinogen.
It is concluded that: (1) neutral proteases possibly contribute to development of
defects in platelet function in pathological states associated with liberation of
leukocyte content into the circulation, (2) CLP similarly to a-CT, exposes fibrinogen
receptors but in contrast to α-CT, CLP aggregates platelets and stimulates serotonin
secretion.
Keywords
Neutral leukocytic proteases - Human blood platelets
