Blood, Vol. 95 No. 5 (March 1), 2000:
pp. 1849-1855
Single amino acid substitution in human platelet glycoprotein
Ib
is responsible for the formation of the platelet-specific
alloantigen Iya
Ulrich J. H. Sachs,
Volker Kiefel,
Micaela Böhringer,
Vahid Afshar-Kharghan,
Hartmut Kroll, and
Sentot Santoso
From the Institute for Clinical Immunology and Transfusion Medicine,
Justus Liebig-University, Giessen, Germany; the Department of
Transfusion Medicine, University of Rostock, Rostock, Germany; and
Baylor College of Medicine and Veterans Affairs Medical Center,
Houston, TX.
We recently described a new low-frequency platelet alloantigen on
the human platelet glycoprotein (GP) Ib-IX complex, termed Iya, which was implicated in a severe case of neonatal
alloimmune thrombocytopenia. Immunoprecipitation studies with
trypsin-treated platelets indicated that the Iya
alloantigenic determinants are formed by the membrane-associated remnant moiety of GP Ib
(GP Ibr) together with GP
Ib
and GP IX. To elucidate the molecular basis underlying the
Iya alloantigen, we amplified
GPIbr, GPIb, and
GPIX genes by polymerase chain reaction (PCR).
Nucleotide-sequence analysis of these 3 genes showed a G to A
transition at position 141 on GPIb gene in a subject
positive for Iya. This transition resulted in a
Gly15Glu dimorphism on the N-terminal domain of
GPIb. This finding was confirmed by genotyping analysis of 6 Iya-positive subjects by restriction fragment length
polymorphism (RFLP) studies using NarI endonuclease.
In 300 randomly selected healthy blood donors, one
Iya-positive individual was found. Phenotypes determined by
monoclonal antibody-specific immobilization of platelet antigens assay
and genotypes determined by RFLP were identical in this population. Analysis of Iya-positive platelets showed that the point
mutation affected neither the degree of surface expression nor the
function of the GP Ib-GP Ib-IX complex on the platelet surface.
Transient expression of the GP Ib-IX complex in CHO cells using
wild-type GP Ib (Gly15) or mutant GP Ib
(Glu15) allowed us to demonstrate that this single amino
acid substitution is sufficient to induce Iya epitope(s).
