A functional platelet fibrinogen receptor with a deletion in the cysteine-rich repeat region of the beta(3) integrin: the Oe(a) alloantigen in neonatal alloimmune thrombocytopenia.
This report describes a new low-frequency alloantigen, Oe(a), responsible for a case of neonatal alloimmune thrombocytopenia (NAIT). In a population study none of 600 unrelated blood donors was an Oe(a) carrier. By immunochemical studies the Oe(a) antigen could be assigned to platelet glycoprotein (GP) IIIa. Sequencing of GPIIIa complementary DNA from an Oe(a) (+) individual showed deletion of a lysine residue at position 611 (DeltaLys(611)). Analysis of 20 Oe(a) (-) and 3 Oe(a) (+) individuals showed that the DeltaLys(611) form of GPIIIa was related to the phenotype. Anti-Oe(a) reacted with the DeltaLys(611), but not with the wild-type isoforms on stable transfectants expressing GPIIIa, indicating that DeltaLys(611) directly induces the expression of Oe(a) epitopes. Under nonreducing conditions the Pro(33)DeltaLys(611) variant migrated with a slightly decreased molecular weight compared to the Pro(33)Lys(611) isoform suggesting that DeltaLys(611) has an influence on the disulfide bonds of GPIIIa. The Pro(33)DeltaLys(611) GPIIIa could undergo conformational changes and bind to fibrinogen in a similar manner as the Pro(33)Lys(611) isoform. No difference was found in the tyrosine phosphorylation of pp125(FAK), suggesting that DeltaLys(611) has no effect on integrin function. In contrast to all other low-frequency antigens, the DeltaLys(611) isoform was associated with the HPA-1b, but not with the high frequency HPA-1a allele. Comparison with GPIIIa DNA from nonhuman primates indicated that the HPA-1a allele represents the ancestral form of GPIIIa. It can be assumed that the Oe(a) form did arise as a result of a mutational event from an already mutated GPIIIa allele.
Santoso
Sentot
S
Institute for Clinical Immunology and Transfusion Medicine, Justus Liebig University Giessen, Germany. sentot.santoso@immunologie.med.uni-giessen.de
Kiefel
Volker
V
Richter
Ina G
IG
Sachs
Ulrich J H
UJ
Rahman
Abdul
A
Carl
Bettina
B
Kroll
Harmut
H
D000328:Adult; D015703:Antigens, CD / Q000235:genetics / Q000276:immunology / Q000502:physiology; D016824:Antigens, Human Platelet / Q000235:genetics* / Q000276:immunology / Q000502:physiology; D003545:Cysteine; D004252:DNA Mutational Analysis; D005260:Female; D014644:Genetic Variation / Q000235:genetics / Q000276:immunology; D006801:Humans; D007231:Infant, Newborn; D039661:Integrin beta3; D007518:Isoantibodies / Q000009:adverse effects / Q000276:immunology; D007519:Isoantigens / Q000235:genetics / Q000276:immunology; D008297:Male; D008431:Maternal-Fetal Exchange / Q000276:immunology; D010375:Pedigree; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics* / Q000276:immunology* / Q000502:physiology; D010980:Platelet Membrane Glycoproteins / Q000235:genetics / Q000276:immunology / Q000502:physiology; D011247:Pregnancy; D011250:Pregnancy Complications, Hematologic / Q000209:etiology / Q000276:immunology; D020449:Repetitive Sequences, Amino Acid; D017384:Sequence Deletion; D013921:Thrombocytopenia / Q000209:etiology / Q000235:genetics / Q000276:immunology*
D015703:Antigens, CD; D016824:Antigens, Human Platelet; D039661:Integrin beta3; D007518:Isoantibodies; D007519:Isoantigens; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins; D003545:Cysteine