title: Identification of the Molecular and Genetic Basis of PX2, a Glycosphingolipid Blood Group Antigen Lacking on Globoside-deficient Erythrocytes.
abstract: The x2 glycosphingolipid is expressed on erythrocytes from individuals of all common blood group phenotypes and elevated on cells of the rare P/P1/P(k)-negative p blood group phenotype. Globoside or P antigen is synthesized by UDP-N-acetylgalactosamine:globotriaosyl-ceramide 3-β-N-acetylgalactosaminyltransferase encoded by B3GALNT1. It is the most abundant non-acid glycosphingolipid on erythrocytes and displays the same terminal disaccharide, GalNAcβ3Gal, as x2. We encountered a patient with mutations in B3GALNT1 causing the rare P-deficient P1 (k) phenotype and whose pretransfusion plasma was unexpectedly incompatible with p erythrocytes. The same phenomenon was also noted in seven other unrelated P-deficient individuals. Thin-layer chromatography, mass spectrometry, and flow cytometry were used to show that the naturally occurring antibodies made by p individuals recognize x2 and sialylated forms of x2, whereas x2 is lacking on P-deficient erythrocytes. Overexpression of B3GALNT1 resulted in synthesis of both P and x2. Knockdown experiments with siRNA against B3GALNT1 diminished x2 levels. We conclude that x2 fulfills blood group criteria and is synthesized by UDP-N-acetylgalactosamine: globotriaosylceramide 3-β-N-acetylgalactosaminyltransferase. Based on this linkage, we proposed that x2 joins P in the GLOB blood group system (ISBT 028) and is renamed PX2 (GLOB2). Thus, in the absence of a functional P synthase, neither P nor PX2 are formed. As a consequence, naturally occurring anti-P and anti-PX2 can be made. Until the clinical significance of anti-PX2 is known, we also recommend that rare P1 (k) or P2 (k) erythrocyte units are preferentially selected for transfusion to P(k) patients because p erythrocytes may pose a risk for hemolytic transfusion reactions due to their elevated PX2 levels.
authors.affiliation: From the Division of Hematology and Transfusion Medicine, Department of Laboratory Medicine, Lund University, SE-22184 Lund, Sweden.
authors.forename: Julia S
authors.identifier: http://orcid.org/0000-0002-5506-1543
authors.initials: JS
authors.lastname: Westman
authors.affiliation: the Institute of Biomedicine, The Sahlgrenska Academy, Gothenburg University, SE-40530 Gothenburg, Sweden.
authors.forename: John
authors.initials: J
authors.lastname: Benktander
authors.affiliation: From the Division of Hematology and Transfusion Medicine, Department of Laboratory Medicine, Lund University, SE-22184 Lund, Sweden, the Clinical Immunology and Transfusion Medicine, Laboratory Medicine, Office of Medical Services, Region Skåne, SE-22185 Lund, Sweden.
authors.forename: Jill R
authors.identifier: http://orcid.org/0000-0003-2940-2604
authors.initials: JR
authors.lastname: Storry
authors.affiliation: the Institut National de la Transfusion Sanguine (INTS), Département Centre National de Référence pour les Groupes Sanguins, F-75015 Paris, France, and the Laboratory of Excellence GR-Ex, F-75015 Paris, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Peyrard
authors.affiliation: From the Division of Hematology and Transfusion Medicine, Department of Laboratory Medicine, Lund University, SE-22184 Lund, Sweden, the Clinical Immunology and Transfusion Medicine, Laboratory Medicine, Office of Medical Services, Region Skåne, SE-22185 Lund, Sweden.
authors.forename: Annika K
authors.initials: AK
authors.lastname: Hult
authors.affiliation: From the Division of Hematology and Transfusion Medicine, Department of Laboratory Medicine, Lund University, SE-22184 Lund, Sweden, the Clinical Immunology and Transfusion Medicine, Laboratory Medicine, Office of Medical Services, Region Skåne, SE-22185 Lund, Sweden.
authors.forename: Åsa
authors.initials: Å
authors.lastname: Hellberg
authors.affiliation: the Institute of Biomedicine, The Sahlgrenska Academy, Gothenburg University, SE-40530 Gothenburg, Sweden, Susann.Teneberg@medkem.gu.se.
authors.forename: Susann
authors.identifier: http://orcid.org/0000-0003-1957-9553
authors.initials: S
authors.lastname: Teneberg
authors.affiliation: From the Division of Hematology and Transfusion Medicine, Department of Laboratory Medicine, Lund University, SE-22184 Lund, Sweden, the Clinical Immunology and Transfusion Medicine, Laboratory Medicine, Office of Medical Services, Region Skåne, SE-22185 Lund, Sweden, Martin_L.Olsson@med.lu.se.
authors.forename: Martin L
authors.identifier: http://orcid.org/0000-0003-1647-9610
authors.initials: ML
authors.lastname: Olsson
mesh_terms: D000906:Antibodies / Q000235:genetics / Q000276:immunology; D001789:Blood Group Antigens / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D004187:Disaccharides / Q000235:genetics*; D004912:Erythrocytes / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D005915:Globosides / Q000378:metabolism; D006028:Glycosphingolipids / Q000096:biosynthesis / Q000235:genetics*; D006801:Humans; D009154:Mutation; D017350:N-Acetylgalactosaminyltransferases / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype
chemical_list: D000906:Antibodies; D001789:Blood Group Antigens; D004187:Disaccharides; D005915:Globosides; D006028:Glycosphingolipids; C000602104:N-acetylgalactosaminyl-1-3-galactose; C585979:B3GALNT1 protein, human; D017350:N-Acetylgalactosaminyltransferases
keywords: blood; blood group; erythrocyte; glycolipid; glycolipid structure; glycosphingolipid; glycosyltransferase; transfusion medicine