Antigenic determinants of C3 and C4 complement components on washed erythrocytes from normal persons

Area of Science:

• Immunology
• Hematology

Background:

• Complement system proteins, specifically C3 and C4, play crucial roles in immune responses.
• Antigenic determinants of C3 and C4 are present on erythrocytes, influencing diagnostic assays.

Purpose of the Study:

• To investigate the presence and significance of C3 and C4 antigenic determinants on normal erythrocytes.
• To evaluate their impact on direct and indirect antiglobulin tests.

Main Methods:

• Agglutination assays using antisera against C3, C3d, and C4.
• Testing erythrocytes from 16 normal individuals.
• Assessing the effect of anticoagulants (EDTA, heparin, ACD, CPD) and storage conditions.

Main Results:

• Erythrocytes showed agglutination with anti-C3, anti-C3d, and anti-C4, inhibited by corresponding proteins.
• C3/C4 determinants were found on erythrocytes regardless of anticoagulant.
• Storage at 4°C for two weeks did not significantly alter agglutination.
• Significant variations in agglutination intensity were observed among individuals.
• Anti-C3c did not cause agglutination, suggesting C3d carries the detected antigens.
• Dilute antibody concentrations were required for direct antiglobulin tests to prevent false positives.

Conclusions:

• Normal erythrocytes possess C3 and C4 antigens, primarily on the C3d fragment.
• These antigens can interfere with direct antiglobulin tests, necessitating careful reagent dilution.
• Understanding these findings is crucial for accurate interpretation of antiglobulin test results in clinical diagnostics.