Rapid platelet turnover in WASP(-) mice correlates with increased ex vivo phagocytosis of opsonized WASP(-) platelets.
OBJECTIVE
Our objective was to determine a mechanism for the thrombocytopenia of murine Wiskott-Aldrich syndrome (WAS).


METHODS
Consumption rates of WAS protein (WASP)(-) and wild-type (WT) platelets were measured by injection of 5-chloromethylfluorescein diacetate (CMFDA)-labeled platelets into WT or WASP(-) recipients, and by in vivo biotinylation. Platelet and reticulated platelet counts were performed using quantitative flow cytometry. Bone marrow megakaryocyte number and ploidy was assessed by flow cytometry. Phagocytosis of CMFDA-labeled, opsonized platelets was assessed using bone marrow-derived macrophages. Serum antiplatelet antibodies were assayed via their binding to WT platelets.


RESULTS
CMFDA-labeled WASP(-) platelets are consumed more rapidly than WT platelets in either WT or WASP(-) recipients. In vivo biotinylation studies corroborate these findings and show a normal consumption rate for WASP(-) reticulated platelets. The number of reticulated platelets is reduced in WASP(-) mice, but a significant number of the mice show an increased proportion of reticulated platelets and more severe thrombocytopenia. Sera from some of the latter group contain antiplatelet antibodies. Compared to WT platelets, WASP(-) platelets opsonized with anti-CD61 or 6A6 antibody are taken up more rapidly by bone marrow-derived macrophages. In vivo consumption rates of WASP(-) platelets are more accelerated by opsonization than are those of WT platelets.


CONCLUSIONS
Both rapid clearance and impaired production contribute to the thrombocytopenia of murine WAS. Increased susceptibility of opsonized WASP(-) platelets to phagocytosis leads to increased in vivo clearance. This correlates with a higher incidence of individuals with an elevated fraction of reticulated platelets, a more severe thrombocytopenia, and antiplatelet antibodies.
Prislovsky
Amanda
A
Department of Pathology and Laboratory Medicine, Memphis Veterans Administration Medical Center, Memphis, TN 38104, USA.
Marathe
Bindumadhav
B
Hosni
Amira
A
Bolen
Alyssa L
AL
Nimmerjahn
Falk
F
Jackson
Carl W
CW
Weiman
Darryl
D
Strom
Ted S
TS
D000818:Animals; D000906:Antibodies / Q000097:blood / Q000276:immunology; D001792:Blood Platelets / Q000276:immunology*; D004195:Disease Models, Animal; D005260:Female; D005434:Flow Cytometry; D005452:Fluoresceins / Q000737:chemistry; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009895:Opsonin Proteins / Q000276:immunology; D010587:Phagocytosis / Q000276:immunology*; D010976:Platelet Count; D013921:Thrombocytopenia / Q000276:immunology*; D013997:Time Factors; D014923:Wiskott-Aldrich Syndrome / Q000235:genetics / Q000276:immunology*; D051316:Wiskott-Aldrich Syndrome Protein / Q000097:blood* / Q000172:deficiency / Q000235:genetics
D000906:Antibodies; D005452:Fluoresceins; D009895:Opsonin Proteins; C495768:Was protein, mouse; D051316:Wiskott-Aldrich Syndrome Protein; C069306:5-chloromethylfluorescein