[Past and present studies on ABO blood group system]

Area of Science:

• Biochemistry
• Immunology
• Genetics

Background:

• Review of three decades of research on the ABO blood group system.
• Classification of progress into five key areas: oligosaccharide structure, enzyme function, immunological profiles, genetic models, and gene transcription.
• Focus on the biochemical and genetic underpinnings of ABO blood group expression.

Discussion:

• Isolation and characterization of H-, A-, and B-active oligosaccharides from human erythrocytes.
• Detailed description of the enzymatic synthesis of A and B antigens, highlighting the role of specific glycosyltransferases (A-enzyme and B-enzyme).
• Explanation of why antigen synthesis is inhibited in Bombay phenotype and non-secretors due to the lack of a fucosyl residue.

Key Insights:

• The A-enzyme (alpha-N-acetyl-galactosaminyltransferase) and B-enzyme (alpha-galactosyltransferase) are responsible for synthesizing blood group A and B antigens, respectively.
• Immunological cross-reactivity exists between A and B enzymes, but not in individuals with blood group O.
• The non-functional nature of the blood group O allele is attributed to a single nucleotide deletion causing a frameshift and truncated peptide.

Outlook:

• The immunological findings align with cDNA structures of human ABO alleles, supporting a gene model where the O allele is non-functional.
• Transcription of the ABO gene can be enhanced by transcription factors binding to upstream sequences.
• Further research into the genetic and biochemical mechanisms of ABO blood group expression is warranted.