A naturally occurring LeuVal mutation in beta3-integrin impairs the HPA-1a epitope: the third allele of HPA-1.
BACKGROUND
Single-amino-acid substitution Leu33Pro in the beta3-integrin is responsible for the formation of the human platelet antigen (HPA)-1. Alloimmunization against HPA-1a (beta3-Leu33) is the most frequent cause of neonatal alloimmune thrombocytopenia and posttransfusion purpura.


METHODS
While HPA-1 genotyping a large cohort of patients with thromboembolic disease with a thermal cycler (LightCycler), one patient was identified with a unique HPA-1a melting curve.


RESULTS
Sequence analysis revealed a C-to-G transversion at nucleotide 175 in the beta3-integrin (ITGB3) gene that alters the Leu33 codon to Val33. Further genotyping of healthy blood donors (n = 2950) identified one nonrelated Pro33Val33-positive individual. To examine whether the presence of Val33 affected the binding pattern of HPA-1 alloantibodies, transfectants were generated expressing recombinant beta3-Leu33 or beta3-Val33. Interestingly, differences in the reactivity of anti-HPA-1a were observed, with some HPA-1a alloantibodies showing diminished reactivity with beta3-Val33 compared to beta3-Leu33 and others reacting equally with both types. Similar findings were observed with recombinant human HPA-1a antibodies, with one of the three not binding to beta3-Val33.


CONCLUSIONS
Our results demonstrate that the naturally occurring Leu33Val mutation in the beta3-integrin can disrupt some HPA-1a epitopes. These findings provide evidence for a heterogeneous humoral response against HPA-1a that may have potential clinical implications for alloimmune thrombocytopenia disorders.
Santoso
Sentot
S
Institute for Clinical Immunology and Transfusion Medicine, Justus Liebig University, Giessen, Germany. sentot.santoso@immunologie.med.uni-giessen.de
Kroll
Hartmut
H
Andrei-Selmer
Cornelia L
CL
Socher
Ines
I
Rankin
Angela
A
Kretzschmar
Evelyne
E
Watkins
Nicholas A
NA
Ouwehand
Willem H
WH