A single-nucleotide polymorphism in the human ITGB3 gene is associated with the platelet-specific alloantigen Va (HPA-17bw) involved in fetal maternal alloimmune thrombocytopenia.
BACKGROUND
The previously reported platelet (PLT)-specific antigen, Va(a), was defined by an alloantibody detected in the serum sample of a mother who delivered an infant displaying symptoms of severe fetal maternal alloimmune thrombocytopenia (FMAIT). This PLT antigen was localized to the integrin alphaIIbbeta3 (GPIIbIIIa) but its genetic basis was not defined.


METHODS
Genomic ITGA2B (alphaIIb) and ITGB3 (beta3) DNA from a Va(a)-positive individual were sequenced to identify potential polymorphisms underlying the Va(a) antigen. Recombinant beta3 integrin carrying the putative mutation was then used to assess serologic reactivity with the original maternal Va(a) antiserum.


RESULTS
A single-nucleotide polymorphism (SNP; C622>T) in exon 5 of ITGB3 resulting in the replacement of threonine with methionine at residue 195 of the mature beta3 was identified. Calmodulin-tagged soluble recombinant beta3 encoding Met195 was produced in S2 cells and found to react specifically with the Va(a) antiserum.


CONCLUSIONS
With the use of a combination of DNA sequencing and recombinant antigen expression, the molecular basis of the PLT-specific Va(a) antigen (HPA-17bw), a low-frequency antigen implicated in FMAIT, has been resolved. These data further demonstrate the value of using recombinant beta3 peptides for the detection of rare but clinically relevant antibodies.
Stafford
Prachi
P
The Department of Haematology, University of Cambridge and NHS Blood and Transplant, Cambridge, UK.
Garner
Stephen F
SF
Rankin
Angela
A
Kekomaki
Riitta
R
Watkins
Nicholas A
NA
Ouwehand
Willem H
WH
D016824:Antigens, Human Platelet / Q000097:blood / Q000276:immunology*; D005091:Exons / Q000235:genetics; D005260:Female; D005315:Fetal Diseases / Q000235:genetics* / Q000276:immunology; D006801:Humans; D039661:Integrin beta3 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008431:Maternal-Fetal Exchange; D008954:Models, Biological; D040201:Platelet Membrane Glycoprotein IIb / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide; D011247:Pregnancy; D011248:Pregnancy Complications; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013921:Thrombocytopenia / Q000235:genetics* / Q000276:immunology
D016824:Antigens, Human Platelet; C061248:ITGB3 protein, human; D039661:Integrin beta3; D040201:Platelet Membrane Glycoprotein IIb; D011994:Recombinant Proteins