Faculty Collaboration Database

O-linked sialic acid residues on platelet membrane glycoprotein IIb mask the human HPA-9b alloepitope. Blood 2023 Nov 30;142(22):1909-1917

Date

09/22/2023

Pubmed ID

37738558

Pubmed Central ID

PMC10731917

DOI

10.1182/blood.2023021122

Scopus ID

2-s2.0-85174357846 (requires institutional sign-in at Scopus site)   1 Citation

Abstract

Sialic acids occupy the terminal position of glycan chains and have the potential to influence the antigenicity of glycoproteins (GP). The polymorphisms of human platelet alloantigens (HPA)-3 and HPA-9, located near the C-terminus of the extracellular domain of platelet membrane GPIIb, are adjacent to sialyl-core 1 O-glycans emanating from serines 845 and 847. Whether the nearby O-glycans affect the antigenicity of HPA-9b or influence the binding of anti-HPA-9b alloantibodies in clinically significant cases of neonatal alloimmune thrombocytopenia is unknown. To address this issue, we generated a series of O-glycan mutant HPA-9 allele-specific induced pluripotent stem cell lines, differentiated them to megakaryocytes (MKs), and examined their ability to bind HPA-9b-specific alloantibodies. We found that both wild-type MKs treated with neuraminidase and those genetically modified to lack the sialidases ST3GAL1 and ST3GAL2 dramatically increased anti-HPA-9b alloantibody binding, indicating that the HPA-9b epitope is partially masked by terminal sialic acids on nearby O-glycans of GPIIb. Interestingly, mutating the serine residues that carry these glycan chains to alanine actually reduced the binding of anti-HPA-9b alloantibodies, indicating that these 2 O-glycan chains contribute to the presentation of the HPA-9b epitope-perhaps by stabilizing the conformation of the GP in this region. Collectively, our data suggest that detection of anti-HPA-9b alloantibodies may be enhanced through the use of HPA-9b-specific MKs that have been genetically altered to lack nearby terminal sialic acid residues but retain the glycan chains to which they are attached.

Author List

Zhang N, Sullivan MJ, Curtis BR, Newman PJ

Author

Brian Curtis PhD Director in the Platelet & Neutrophil Immunology Laboratory department at BloodCenter of Wisconsin

MESH terms used to index this publication - Major topics in bold

Antigens, Human Platelet
Epitopes
Glycoproteins
Humans
Infant, Newborn
Isoantibodies
N-Acetylneuraminic Acid
Platelet Membrane Glycoprotein IIb
Polysaccharides