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(-)mu MT(-/-) 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(-mu MT(-/-) 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(-)mu MT(-/-) than WASP(+)mu MT(-/-) 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 anti body-dependent mechanism that does not. Both an increased incidence of antiplatelet antibodies and an increased susceptibility to their effects contribute to anti body-dependent clearance of WASP(-) platelets. (C) 2009 ISEH - Society for Hematology and Stem Cells. Published by Elsevier Inc.