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Specific inhibition of the classical complement pathway by C1q-binding peptides
1Department of Nephrology, Leiden University Medical Center, Leiden, The Netherlands. A.Roos@LUMC.NL
Insights
A novel peptide, 2J, effectively inhibits the classical complement pathway by targeting C1q binding. This specific inhibition prevents complement-mediated damage in diseases like xenograft rejection without compromising essential antimicrobial functions.
Area of Science:
- Immunology
- Biochemistry
- Drug Discovery
Background:
- Complement system activation drives immune complex diseases and xenograft rejection.
- Targeting the classical complement pathway offers therapeutic potential without impairing innate immunity.
Purpose of the Study:
- To identify and characterize peptide inhibitors of the C1q-mediated classical complement pathway.
- To develop a therapeutic agent for preventing complement-mediated pathological conditions.
Main Methods:
- Synthesis and screening of 42 peptides for C1q inhibitory activity.
- Assessing peptide inhibition of C1q hemolytic activity and alternative pathway function.
- ELISA and cell-based assays to evaluate C1q binding, complement activation, and deposition.
Main Results:
- Peptide 2J demonstrated potent inhibition of C1q hemolytic activity across multiple species.
- 2J binds to the globular head of C1q, inhibiting C1q-IgG interaction and downstream classical pathway activation (C4, C3, C5b-9).
- 2J significantly reduced C4 and C3 deposition on xenogeneic cells.
Conclusions:
- Peptide 2J is a potent inhibitor of the classical complement pathway's initiation step.
- 2J shows promise as a therapeutic agent for complement-mediated diseases, including hyperacute xenograft rejection.
Abstract:
Undesired activation of the complement system is a major pathogenic factor contributing to various immune complex diseases and conditions such as hyperacute xenograft rejection. We aim for prevention of complement-mediated damage by specific inhibition of the classical complement pathway, thus not affecting the antimicrobial functions of the complement system via the alternative pathway and the lectin pathway. Therefore, 42 peptides previously selected from phage-displayed peptide libraries on basis of C1q binding were synthesized and examined for their ability to inhibit the function of C1q. From seven peptides that showed inhibition of C1q hemolytic activity but no inhibition of the alternative complement pathway, one peptide (2J) was selected and further studied. Peptide 2J inhibited the hemolytic activity of C1q from human, chimpanzee, rhesus monkey, rat, and mouse origin, all with a similar dose-response relationship (IC(50) 2-6 microM). Binding of C1q to peptide 2J involved the globular head domain of C1q. In line with this interaction, peptide 2J dose-dependently inhibited the binding of C1q to IgG and blocked activation of C4 and C3 and formation of C5b-9 induced via classical pathway activation, as assessed by ELISA. Furthermore, the peptide strongly inhibited the deposition of C4 and C3 on pig cells following their exposure to human xenoreactive Abs and complement. We conclude that peptide 2J is a promising reagent for the development of a therapeutic inhibitor of the earliest step of the classical complement pathway, i.e., the binding of C1q to its target.