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A new Ser472Asn (Cab2 a+ ) polymorphism localized within the αIIb “thigh” domain is involved in neonatal thrombocytopenia
Author(s) -
Jallu Vincent,
Dusseaux Mathilde,
Kaplan Cecile
Publication year - 2011
Publication title -
transfusion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.045
H-Index - 132
eISSN - 1537-2995
pISSN - 0041-1132
DOI - 10.1111/j.1537-2995.2010.02815.x
Subject(s) - epitope , monoclonal antibody , microbiology and biotechnology , antigen , chemistry , mutation , platelet , antibody , biology , gene , immunology , biochemistry
BACKGROUND: A new platelet antigen, Cab2 a+ , was identified in a case of severe neonatal alloimmune thrombocytopenia (<8 × 10 9 /L) in twins. STUDY DESIGN AND METHODS: Coding sequences of αIIb and β3 genes from parents were amplified and sequenced. CHO cell lines expressing wild‐type or mutated forms of the complex were established to study the role of the mutation in alloimmunization and in αIIbβ3 functions. RESULTS: The father and twins were heterozygous for a single αIIb c.1508G>A mutation leading to a Ser472Asn substitution. Immunologic assays with transfected CHO cells revealed the Asn472 form of αIIbβ3 responsible for the Cab2 a+ epitope but not an Ala472 form. Using these cells lines we demonstrated that both Ser472Asn and Ser472Ala substitutions produced limited structural alteration as revealed by the reactivity of a panel of anti‐αIIbβ3 monoclonal antibodies (MoAbs). Activated Asn472 and Ala472 forms of αIIbβ3 supported 1) binding of soluble fibrinogen and of the ligand mimetic MoAb PAC‐1, 2) ligand‐induced binding site epitopes exposure (MoAbs AP‐5 and D3GP3), and 3) cell aggregation. Adhesion onto adsorbed fibrinogen was conserved and was specifically inhibited by MoAb AP‐2 or peptide RGDS. Finally outside‐in signaling was not affected. CONCLUSION: We have characterized a new low‐frequency alloantigen (<1%) resulting from the Ser472Asn substitution in αIIb and shown this polymorphism to have a limited effect, if any, on the αIIbβ3 complex functions.