Antiplatelet antibodies in WASP(−) mice correlate with evidence of increased in vivo platelet consumption

Objective

To study the role of antiplatelet antibodies in the thrombocytopenia of murine Wiskott-Aldrich syndrome (WAS).

Materials and Methods

A flow cytometric method was developed for detection of serum antiplatelet antibodies via their binding to intact target platelets lacking surface antibodies. Platelets were labeled with 5-chloromethylfluorescein diacetate (CMFDA) in order to track their clearance from the circulation. WASP(−)μMT(−/−) mice were generated by standard breeding methods.

Results

Serum antiplatelet antibodies were detected in approximately 40% of WASP(−) males. The mean level of reticulated platelets is significantly increased in these antibody(+) males. While WASP(−) males show an approximately 50% reduction in platelet counts, 5% to 10% show a more severe thrombocytopenia associated with increased reticulated platelets, suggesting the presence of clearance-inducing antiplatelet antibodies. In support of that inference, 90% of the latter mice show detectable serum antiplatelet antibodies. The antibodies are primarily immunoglobulin G, and are also detected in >30% of CD47(−/−) males. WASP(−)μMT(−/−) males, which demonstrate no serum- or platelet-associated antibodies, show a degree of thrombocytopenia similar to that of WASP(−) males. Their platelet clearance rates remain accelerated—more so in WASP(−)μMT(−/−) than WASP(+)μMT(−/−) recipients.

Conclusions

These findings suggest that platelet WASP deficiency results in an increase in platelet clearance rates by two mechanisms: an antibody-independent mechanism that largely requires WASP deficiency in trans, and an antibody-dependent mechanism that does not. Both an increased incidence of antiplatelet antibodies and an increased susceptibility to their effects contribute to antibody-dependent clearance of WASP(−) platelets.