Anti-glycoprotein IIb/IIIa autoantibodies are reversibly internalized into platelets in idiopathic (autoimmune) thrombocytopenic purpura.
We used flow cytometry to investigate the binding of platelet-binding IgG (PBIgG) to unfixed platelets in idiopathic thrombocytopenic purpura (ITP), including that of anti-glycoprotein (GP) IIb/IIIa antibodies. Anti-GPIIb/IIIa antibodies were detected in 13/64 ITP patients using antigen-capture ELISA and immunoblotting. When unfixed platelets were incubated with ITP plasma, the PBIgG level was significantly higher than after incubation with normal plasma. When 1 microM ADP was added to unfixed platelets, which were incubated with ITP plasma and washed, the PBIgG level increased additively. GMP-140 is a constituent of platelet alpha-granules, and a monoclonal antibody directed against this protein showed weak binding to platelets after 1 microM ADP stimulation. The increase of PBIgG produced by ADP was significantly greater when ITP plasma positive for anti-GPIIb/IIIa antibody was used compared with that obtained using antibody-negative ITP plasma. This increase of PBIgG was markedly inhibited by the removal of extracellular calcium with EDTA or the dissociation of the GPIIb/IIIa complex by EDTA treatment at 37 degrees C. These results suggest that anti-GPIIb/IIIa autoantibodies are internalized by unfixed ITP platelets and stored somewhere other than the alpha-granules. This stored antibody pool can be reversibly redistributed on the platelet surface by weak stimulants such as ADP and a functional GPIIb/IIIa complex appears to be necessary for this to occur.
Nomura
S
S
First Department of Internal Medicine, Kansai Medical University, Osaka, Japan.
Yanabu
M
M
Fukuroi
T
T
Kido
H
H
Kawakatsu
T
T
Yamaguchi
K
K
Suzuki
M
M
Kokawa
T
T
Yasunaga
K
K
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000937:Antigen-Antibody Reactions; D016824:Antigens, Human Platelet / Q000276:immunology*; D001323:Autoantibodies / Q000276:immunology*; D001327:Autoimmune Diseases / Q000276:immunology*; D001692:Biological Transport; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D008297:Male; D008875:Middle Aged; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000276:immunology*; D013921:Thrombocytopenia / Q000276:immunology
D016824:Antigens, Human Platelet; D001323:Autoantibodies; D007074:Immunoglobulin G