A novel immunoassay for the quantitation of human C4 gene products

Area of Science:

• Immunology
• Biochemistry
• Genetics

Background:

• Complement component 4 (C4) exists as two main forms, C4A and C4B, crucial for immune response.
• Accurate quantitation of C4A and C4B is essential for understanding immune function and diagnosing deficiencies.
• Existing methods for C4 quantitation have limitations in specificity and ability to differentiate C4A/C4B.

Purpose of the Study:

• To develop and validate a novel immunoassay for the precise quantitation of total C4, C4A, and C4B.
• To assess the assay's reproducibility, specificity, and comparison with existing methods.
• To evaluate the assay's utility in detecting heterozygous C4 null states.

Main Methods:

• Development of an immunoassay using mouse monoclonal antibodies targeting Rodgers 1 and Chido 1 epitopes on C4A and C4B.
• Activation of the complement system component C1 using heat-aggregated IgG.
• Quantitation of total C4, C4A, and C4B, with interassay variation assessed.
• Comparison with radial immunodiffusion for total C4 quantitation in 103 individuals.

Main Results:

• The developed immunoassay demonstrated high specificity and reproducibility with low interassay variation (10.8-12.4%).
• A strong correlation (Pearson's r = 0.81) was observed when comparing the immunoassay to radial immunodiffusion for total C4.
• The assay successfully identified three individuals with genetic total-C4 deficiency as nonreactive.
• The assay proved superior to existing methods for C4A and C4B quantitation and detection of C4 null states.

Conclusions:

• A novel, activated immunoassay provides accurate and reproducible quantitation of C4A, C4B, and total C4.
• This assay surpasses current methods for detecting C4A/C4B levels and identifying heterozygous C4 null states.
• The developed method offers significant improvements for clinical diagnostics and research in complement system disorders.