[The immunoreactivity of IgG and its fragments from ITP patients and their effects on platelet aggregation function].
OBJECTIVE
To prepare ITP plasma IgG and its F(ab')2 fragments and investigate their immunoreactivity to platelet GPIIb/IIIa and/or GPIb/IX and their effects on platelet aggregation function.


METHODS
The ITP patients having inhibitory autoantibody to the platelet aggregation were selected by modified MAIPA and platelet aggregation test with turbidimetry. Plasma IgG and its F(ab')2 fragments were prepared by streptococcal protein A affinity column and pepsin digestion. The immunoreactivity and the effects on platelet aggregation function of the whole antibody and its fragments were detected by modified MAIPA and platelet aggregation test, respectively.


RESULTS
(1) Anti-platelet GPIIb/IIIa and/or GPIb/IX autoantibodies were detected in 34 of 68 (53.6%) ITP patients' plasmas and that from 5 patients significantly inhibited the platelet aggregation induced by ADP or ristocetin. (2) By using protein A column combined with protease digestion, pure IgG and its F(ab')2 fragments were successfully obtained. (3) The purified IgG and its F(ab')2 fragments retained the ability to bind to their respective glycoproteins and inhibited the platelet aggregation function, whereas the IgG depleted plasma lost the ability of binding to the platelet GPs.


CONCLUSIONS
F(ab')2 fragment of the IgG antibody is a functional fragment, which not only has the binding ability to the platelet GPs but also inhibits the platelet aggregation function in a dose-dependent manner.
Chu
Xiao-xia
XX
Hematology Department, Qilu Hospital of Shandong University, Jinan 250012, China.
Hou
Ming
M
Zhu
Yuan-yuan
YY
Peng
Jun
J
Ji
Xue-bin
XB
Wang
Lin
L
Zhang
Feng
F
Ma
Dao-xin
DX
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D005260:Female; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology*; D007074:Immunoglobulin G / Q000276:immunology*; D039661:Integrin beta3 / Q000276:immunology; D008297:Male; D008875:Middle Aged; D010974:Platelet Aggregation; D040201:Platelet Membrane Glycoprotein IIb / Q000276:immunology; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000276:immunology* / Q000503:physiopathology; D055815:Young Adult
D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D039661:Integrin beta3; D040201:Platelet Membrane Glycoprotein IIb