Immunochemical observations on the human blood group P system

Area of Science:

• Immunology and Serology
• Biochemistry
• Genetics

Background:

• The P blood group system encompasses P1, Pk, and P antigens, with complex serological and genetic relationships that require further elucidation.
• Understanding the chemical structures of these antigens is crucial for deciphering their interactions with corresponding antibodies.

Purpose of the Study:

• To investigate the chemical, genetic, and serological relationships within the P blood group system.
• To identify specific carbohydrate structures responsible for the reactivity of anti-P1, anti-Pk, and anti-P sera.

Main Methods:

• Haemagglutination inhibition experiments were performed using anti-P1, anti-Pk, and anti-P sera.
• Test substances included a glycoprotein with P1 and Pk activity, its hydrolysis fragments, glycolipids, and various saccharides of known structure.

Main Results:

• The trisaccharide alphaGal(1-4)betaGal(1-4)GlcNAc strongly inhibited anti-P1 sera, confirming its role as the P1 determinant.
• A disaccharide alphaGal(1-4)Gal and ceramide trihexoside strongly inhibited anti-Pk sera, suggesting Pk is a precursor to P.
• Globoside strongly inhibited anti-P sera, while alpha-galactosyl residues did not, indicating distinct structural specificities for anti-P antibodies.

Conclusions:

• A close structural relationship exists between P1 and Pk determinants, with anti-Pk sera showing less defined specificity than anti-P1 sera.
• The results support the hypothesis that Pk is a precursor to P, based on inhibition patterns with ceramide trihexoside and globoside.
• The genetic relationship of P1 to P and Pk remains unclear, but potential biosynthetic pathways are discussed to explain antigen absence in the p phenotype.