An update on Rodgers and Chido, the antigenic determinants of human C4

Area of Science:

• Immunogenetics
• Complement System Biology
• Molecular Immunology

Background:

• The Rodgers (Rg) and Chido (Ch) blood groups are antigenic determinants associated with the fourth component of human complement (C4).
• Nine distinct C4 determinants have been identified using hemagglutination-inhibition assays with polyspecific human antiserums.
• While C4A isotypes show a strong association with Rg and C4B isotypes with Ch, this link is not absolute.

Purpose of the Study:

• To investigate the structural basis of antigenic determinants within the C4d region.
• To elucidate the complex serologic interrelationships between C4 allotypes and Rg/Ch blood groups.
• To refine a structural model for C4 polymorphic antigenic determinants.

Main Methods:

• Amino acid sequencing of the C4d region from selected C4 allotypes with known antigenic expression.
• Analysis of allotype and Rg/Ch data from diverse donor and patient cohorts, including family studies.
• Development and refinement of a structural model for antigenic determinants at four polymorphic sites.

Main Results:

• Derived amino acid sequences provided support for previously reported complex serologic interrelationships.
• A structural model incorporating sequential and conformational epitopes at four polymorphic sites was proposed.
• Allotype and Rg/Ch data from extensive studies revealed no exceptions to the proposed model.

Conclusions:

• The antigenic determinants of Rg and Ch blood groups contribute significantly to the intricate polymorphism of human complement component 4 (C4).
• The proposed structural model effectively explains the observed serologic associations and antigenic variations within C4.
• Further understanding of C4 polymorphism has implications for complement-mediated diseases and transfusion medicine.