title: A "silent" nucleotide substitution in exon 4 is responsible for the "alternative expression" of HLA-A*01:01:38L through aberrant splicing.
abstract: A Welsh Bone Marrow Donor Registry donor was serologically typed, using both alloantisera and monoclonal antibodies, as human leukocyte antigen (HLA)-A2, A-, but typed by polymerase chain reaction sequence-specific priming as HLA-A*01, A*02. Full gene sequencing of the A*01 separated allele indicated an apparently normal A*01:01:01:01 apart from a silent change at nucleotide 705 in exon 4, codon 211 (alanine: normally GCG but GCA in this donor). Sequence analysis of the amplified A*01 allele in cDNA synthesized from RNA indicated that exons 1, 2, 3, and 5 had typical A*01:01 sequences. However, exon 4 was truncated in this allele (87 nucleotides shorter), beginning just after the single nucleotide polymorphism (SNP) identified in genomic DNA sequencing. The nucleotide sequence up to, and 1 nucleotide after, the SNP is homologous with the 3' end of human leukocyte antigen (HLA)-A intron 3 and thus resembles a splice site. However, a small amount of "normal" HLA-A1 was detected on the surface of cells from an Epstein-Barr virus transformed B-cell line (BCL), but not on peripheral blood mononuclear cells, by flow cytometry. Additionally, a trace amount of "normal sized" A*01 was amplified from cDNA. We suggest that in this A*01 variant allele (A*01:01:38L) intron 3 is largely spliced out with a part of exon 4; exon 4 is still in-frame but the protein is smaller than the wild type. This is likely to affect folding and assembly of the "wild type" mature protein on the cell surface, thus explaining the apparent null phenotype when assayed by conventional serology. However, a small amount of A1 protein is made from correctly spliced A*01 mRNA and is detectable on BCLs using flow cytometry.
authors: Tissue Typing Laboratory, New Zealand Blood Service, Auckland, New Zealand. paul.dunn@nzblood.co.nz
authors: Paul P J
authors: PP
authors: Dunn
authors: Laura
authors: L
authors: Hammond
authors: Ernest
authors: E
authors: Coates
authors: Jane
authors: J
authors: Street
authors: Leon
authors: L
authors: Griner
authors: Christopher
authors: C
authors: Darke
mesh_terms: D017398:Alternative Splicing / Q000276:immunology; D000911:Antibodies, Monoclonal / Q000378:metabolism; D001402:B-Lymphocytes / Q000166:cytology / Q000378:metabolism*; D001788:Blood Grouping and Crossmatching; D016026:Bone Marrow Transplantation; D002461:Cell Line, Transformed; D002469:Cell Separation; D005091:Exons / Q000235:genetics; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000276:immunology; D015788:HLA-A1 Antigen / Q000235:genetics / Q000378:metabolism*; D006650:Histocompatibility Testing; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000378:metabolism*; D009711:Nucleotides / Q000235:genetics; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide; D017384:Sequence Deletion / Q000235:genetics
chemical_list: D000911:Antibodies, Monoclonal; C506470:HLA-A*01:01 antigen; D015788:HLA-A1 Antigen; D009711:Nucleotides