Chido and Rogers antigenic determinant on the fourth component of human complement

Area of Science:

• Immunogenetics
• Complement System Biology
• Blood Group Serology

Background:

• The Chido (Cha) and Rogers (Rga) blood group antigens are electrophoretic variants of human complement component 4 (C4).
• Previous studies suggested the Cha and Rga antigenic determinants reside on the C4d fragment of C4, based on agglutination of LIS cells.

Purpose of the Study:

• To investigate the precise location of Cha and Rga antigenic determinants on human C4 fragments.
• To clarify the structural basis of Cha and Rga antigenicity in relation to C4 deposition.

Main Methods:

• LIS cells were prepared at 37°C and 4°C with 125I-C4 and analyzed via SDS-PAGE and autoradiography.
• Solubilized cell membranes were examined to identify deposited C4 fragments.
• Purified C4 fragments and chains were used to neutralize anti-Cha and anti-Rga antisera.

Main Results:

• C4d was absent on LIS cells prepared at 37°C, while C4c was present. Cells prepared at 4°C contained both C4d and C4c.
• Anti-Cha and anti-Rga antisera agglutinated both cell types, irrespective of C4d presence.
• Neutralization assays indicated that C4, C4d, and the alpha 4 fragment of C4c neutralized the antisera, but not C4c's alpha 3 fragment or beta/gamma chains.

Conclusions:

• The Cha and Rga antigenic determinants are not located on the C4d fragment as previously assumed.
• Evidence strongly suggests that C4d and the alpha 4 fragment share a common antigenic determinant recognized by anti-Cha and anti-Rga antisera.