Immunodominant epitopes on glycoprotein IIb-IIIa recognized by autoreactive T cells in patients with immune thrombocytopenic purpura.
It was recently reported that autoreactive CD4(+) T cells to glycoprotein IIb-IIIa (GPIIb-IIIa) mediate antiplatelet autoantibody production in patients with immune thrombocytopenic purpura (ITP). To further examine the antigenic specificity of the GPIIb-IIIa-reactive T cells, 6 recombinant fragments encoding different portions of GPIIbalpha or GPIIIa were generated and tested for their ability to stimulate antigen-specific T-cell proliferation and anti-GPIIb-IIIa antibody production in vitro. T cells from the peripheral blood of 25 patients with ITP and 10 healthy donors proliferated in response to recombinant GPIIb-IIIa fragments in various combinations. The amino-terminal portions of both GPIIbalpha and GPIIIa (IIbalpha18-259 and IIIa22-262) were frequently recognized (60% and 64%, respectively) compared with other fragments (4%-28%) in patients with ITP, but this tendency was not detected in healthy donors. In subsequent analyses in patients with ITP, T-cell reactivities to IIbalpha18-259 and IIIa22-262 were consistently detected, whereas those to other fragments were sometimes lost. In vitro antigenic stimulation of peripheral blood mononuclear cells with IIbalpha18-259 or IIIa22-262 promoted the synthesis of anti-GPIIb-IIIa antibodies in patients with ITP, but not in healthy donors. Of 15 CD4(+) T-cell lines specific for platelet-derived GPIIb-IIIa generated from 5 patients with ITP, 13 lines recognized IIbalpha18-259, IIIa22-262, or both. T-cell lines reactive to IIbalpha18-259 or IIIa22-262 promoted the production of anti-GPIIb-IIIa antibodies that were capable of binding to normal platelet surfaces. These results indicate that the immunodominant epitopes recognized by pathogenic CD4(+) T cells in patients with ITP are located within the amino-terminal portions of both GPIIbalpha and GPIIIa.
Kuwana
M
M
Institute for Advanced Medical Research and the Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan. kuwanam@sc.itc.keio.ac.jp
Kaburaki
J
J
Kitasato
H
H
Kato
M
M
Kawai
S
S
Kawakami
Y
Y
Ikeda
Y
Y
D000328:Adult; D000368:Aged; D000906:Antibodies; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D016022:Case-Control Studies; D018929:Cell Culture Techniques; D018604:Epitope Mapping; D005260:Female; D006801:Humans; D016056:Immunodominant Epitopes / Q000097:blood*; D008213:Lymphocyte Activation; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000276:immunology / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000276:immunology*; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000097:blood*; D011993:Recombinant Fusion Proteins / Q000276:immunology / Q000494:pharmacology
D000906:Antibodies; D016056:Immunodominant Epitopes; D010446:Peptide Fragments; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011993:Recombinant Fusion Proteins