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Alteration in H chain V region affects complement activation by chimeric antibodies.
C Horgan1, K Brown, S H Pincus
1National Institutes of Health, National Institute of Allergy and Infectious Diseases, Rocky Mountain Laboratories, Hamilton, MT 59840.
Journal of Immunology (Baltimore, Md. : 1950)
|October 15, 1990
Summary
Differences in the variable (V) regions of chimeric antibodies significantly impact their ability to activate complement (C) by human immunoglobulin G1 (IgG1). This suggests V region variations influence C activation pathways.
Area of Science:
- Immunology
- Molecular Biology
- Complement System
Background:
- Human IgG1 antibodies are crucial in immune responses, mediating effector functions like complement activation.
- The variable (V) regions of antibodies are responsible for antigen binding, but their role in downstream effector functions like complement activation is less understood.
- Chimeric antibodies, combining elements from different species, allow for the dissection of antibody structure-function relationships.
Purpose of the Study:
- To investigate the role of antibody variable (V) regions in complement (C) activation mediated by human IgG1.
- To compare the C activation capabilities of two IgG1 antibodies that differ solely in their VH domains.
Main Methods:
- Synthesis of chimeric IgG1 antibodies with identical constant (C) domains but differing V domains.
- Analysis of antigen (Ag) binding using Enzyme-Linked Immunosorbent Assay (ELISA).
- Assessment of complement activation by measuring the binding of complement components C1q and C3d via ELISA.
Main Results:
- While initial antigen binding assays suggested potential epitope differences, competitive inhibition assays indicated similar binding affinities for the synthetic polypeptide (Tyr, Glu)-Ala-Lys ((T,G)-A-L).
- Crucially, antibodies with different V regions demonstrated significant variations in binding complement components C1q and C3d after binding immobilized antigen.
- Antibody 10B, compared to antibody B11, exhibited enhanced complement activation and greater binding of C1q and C3d when present at equal concentrations.
Conclusions:
- Variable (V) region differences in IgG1 antibodies can substantially influence their capacity to activate the complement system.
- These findings highlight the importance of antibody V regions beyond antigen specificity in determining effector functions.
- The study provides evidence that subtle structural variations in antibody V regions can lead to distinct downstream immune signaling.