Immunization against a low-frequency human platelet alloantigen in fetal alloimmune thrombocytopenia is not a single event: characterization by the combined use of reference DNA and novel allele-specific cell lines expressing recombinant antigens.
BACKGROUND
Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is caused by maternal immunization against a fetal platelet (PLT) alloantigen. In cases of FNAIT attributed to low-frequency PLT alloantigens, the laboratory diagnosis is often hampered by the lack of adequate PLTs.


METHODS
Three families with maternal immunization against fetal PLT antigens were analyzed. In Family 1, previous immunization of another female or woman has been observed. In Families 2 and 3, newborns presented with the typical clinical picture of FNAIT. Genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism and direct sequencing with reference to DNA from Epstein-Barr virus-transformed B-lymphoblastoid cell lines. Antibodies were characterized by glycoprotein (GP)-specific immunoassay with a panel of stable Chinese hamster ovary cell lines expressing low-frequency alloantigens.


RESULTS
In three families, maternal immunization associated with the low-frequency alloantigens human PLT antigen (HPA)-8bw (Sra), HPA-11bw (Groa), and HPA-13bw (Sita) was identified. Maternal serum samples showed positive reactions in an antigen capture assay with cell lines carrying recombinant GP IIb/IIIa (HPA-8bw and -11bw) or GPIa/IIa (HPA-13bw), respectively. These results could be confirmed by genotyping analysis of fathers and newborns.


CONCLUSIONS
This study demonstrates that cases of FNAIT attributed to low-frequency PLT alloantigens cannot be regarded as single events. The availability of reference DNA and cell lines expressing recombinant PLT alloantigens can facilitate their identification.
Kroll
Hartmut
H
Institute for Clinical Immunology and Transfusion Medicine, Justus Liebig University Giessen, Germany. Hartmut.Kroll@immunologie.med.uni-giessen.de
Yates
Julie
J
Santoso
Sentot
S
D016824:Antigens, Human Platelet / Q000235:genetics / Q000276:immunology*; D002461:Cell Line, Transformed; D004247:DNA; D005260:Female; D005315:Fetal Diseases / Q000276:immunology* / Q000628:therapy; D005838:Genotype; D006680:HLA Antigens / Q000235:genetics / Q000276:immunology; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008431:Maternal-Fetal Exchange / Q000276:immunology*; D010375:Pedigree; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D011247:Pregnancy; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000276:immunology*; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology
D016824:Antigens, Human Platelet; D006680:HLA Antigens; D011994:Recombinant Proteins; D004247:DNA