Effects of IgG and its F(ab')2 fragments of some patients with idiopathic thrombocytopenic purpura on platelet aggregation.
OBJECTIVE
To make humanized monoclonal antibodies by phage surface display technology, we screened out the specific anti-platelet glycoproteins (GPs) IgG antibody from patients with chronic idiopathic thrombocytopenic purpura (ITP), which can inhibit platelet aggregation.


METHODS
We studied plasmas from 68 patients with ITP for the presence of IgG antibodies specific for GPIIb/IIIa and/or GPIb/IX using modified monoclonal antibody immobilization of platelet antigen assays. The IgG antibody and its F(ab')(2) fragments of the positive plasmas which could inhibit platelet aggregation function were prepared and purified. Their immunoreactivity to platelet GPs and effects on platelet function were further analyzed.


RESULTS
GPIIb/IIIa- and GPIb/IX-specific antibodies were found in 21 and 19 patients, respectively. Six of them had antibodies against both GP complexes. Among the 34 positive plasmas, four with positive anti-GPIIb/IIIa autoantibody showed significant inhibition of platelet aggregation induced by adenosine diphosphate (ADP), whereas one with GPIb/IX-specific antibody inhibited ristocetin-induced platelet aggregation. The purified IgG and its F(ab')(2) fragments from two patients not only retained the ability to bind to platelet GPs but also impaired the in vitro ADP-induced platelet aggregation.


CONCLUSIONS
F(ab')(2) portion of the IgG is a functional fragment, which is responsible for the autoantibody interaction with platelet GPs in ITP, and some of them also affect platelet function, which can be used to develop completely humanized anti-GPIIb/IIIa small molecular phage antibody.
Chu
Xiao Xia
XX
Hematology Oncology Center, Qilu Hospital of Shandong University, Jinan, Shandong, China.
Hou
Ming
M
Peng
Jun
J
Zhu
Yuan Yuan
YY
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; D002908:Chronic Disease; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology / Q000627:therapeutic use*; D007074:Immunoglobulin G / Q000494:pharmacology / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D010974:Platelet Aggregation / Q000187:drug effects*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000188:drug therapy*
D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D010980:Platelet Membrane Glycoproteins