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Human monoclonal IgG isotypes differ in complement activating function at the level of C4 as well as C1q
C I Bindon1, G Hale, M Brüggemann
1Department of Pathology, University of Cambridge, United Kingdom.
The Journal of Experimental Medicine
|July 1, 1988
Summary
Humanized antibodies, like IgG1, are crucial for therapy. IgG1 excels at cell lysis by efficiently activating complement component C4, despite lower initial C1q binding compared to IgG3.
Area of Science:
- Immunology
- Biochemistry
Background:
- Humanized monoclonal antibodies (mAbs) are vital therapeutic agents.
- Understanding their interaction with the complement system is crucial for optimizing efficacy.
Purpose of the Study:
- To investigate the complement-activating properties of different human antibody isotypes (IgG1, IgG2, IgG3, IgG4, IgE) and rat IgG2b.
- To elucidate the mechanisms behind IgG1's superior cell lysis efficiency compared to IgG3.
Main Methods:
- Compared C1q binding, C1 binding and activation, C4 activation, C4b binding, and C3b binding across various antibody isotypes.
- Quantified C4 molecule binding per C1 molecule and assessed C4b attachment sites.
Main Results:
- Human IgG1 demonstrated superior C4 activation and binding efficiency compared to IgG3, despite lower initial C1q and C1 fixation.
- The majority of C4b bound to cells, not the antibody, indicating C4 activation by C1s was key.
- IgG1's efficiency in C4 activation, amplified through the complement cascade, explains its greater cell lysis efficacy.
Conclusions:
- Human IgG1's potent C4 activation is the primary driver of its effectiveness in complement-mediated cell lysis.
- Combining the optimal features of IgG1 and IgG3 could yield enhanced therapeutic antibodies.