Human blood-group MN and precursor specificities: structural and biological aspects

Area of Science:

• Biochemistry
• Immunology
• Glycobiology

Background:

• Human blood group MM and NN antigens possess distinct immunodominant groupings.
• These antigens differ by a single sialic acid residue, crucial for their specificities.

Purpose of the Study:

• To elucidate the biochemical relationship between M and N blood group antigens.
• To investigate the structural basis of M and N specificities and their genetic determination.
• To explore the role of MN antigens and their precursors in human breast cancer.

Main Methods:

• Mild acid treatment to alter M specificity.
• Enzymatic inactivation using beta-D-galactosidase.
• Chemical removal of N-acetylneuraminic acid.
• Analysis of antigen structures and reactivities.

Main Results:

• M specificity can be converted to N specificity by mild acid treatment, indicating N is a precursor to M.
• Enzymatic and chemical treatments revealed the roles of sialic acid and beta-D-galactopyranosyl groups in antigenicity.
• The Thomsen-Friedenreich T antigen is uncovered upon sialic acid depletion, and beta-D-galactosidase treatment yields Tn activity.
• MN antigens and precursors are found in benign and malignant human breast glands, with altered precursors in cancerous tissue.

Conclusions:

• M and N blood group specificities are not determined by two allelic genes as previously thought.
• The structural relationship between M and N antigens is biochemical, with N preceding M.
• Blood group MN active substances and their precursors have implications in human breast cancer.