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Site-directed C3a receptor antibodies from phage display libraries
H Hawlisch1, R Frank, M Hennecke
1Institute of Medical Microbiology, Hannover Medical School, Germany.
Journal of Immunology (Baltimore, Md. : 1950)
|March 24, 1998
Summary
Researchers developed novel single chain Fv fragments (scFvs) targeting the human C3a receptor (C3aR), a key component in immune responses. These scFvs bind specific regions of the C3aR but do not inhibit its ligand-induced signaling.
Area of Science:
- Immunology
- Molecular Biology
- Receptor Signaling
Background:
- The human C3a receptor (C3aR), a rhodopsin-type receptor, plays a role in immune responses.
- C3aR possesses a notably large second extracellular loop, presenting a unique structural feature.
- Understanding C3aR's extracellular domains is crucial for developing targeted therapeutics.
Purpose of the Study:
- To generate and characterize single chain Fv fragments (scFvs) against the human C3a receptor (C3aR).
- To identify immunodominant regions within the C3aR's second extracellular loop.
- To investigate the binding characteristics and functional impact of these scFvs on C3aR.
Main Methods:
- Construction of combinatorial phage antibody libraries from mice immunized with the C3aR's second extracellular loop.
- Selection of anti-C3aR scFvs via panning against purified C3aR loop protein.
- Epitope mapping, flow cytometry, and immunofluorescence assays to characterize scFv binding and C3aR expression.
Main Results:
- A panel of scFvs was generated, binding to specific epitopes within the C3aR's second extracellular loop (residues 185-193 and 218-226).
- scFvs demonstrated specific binding to C3aR-transfected cells and human mast cells (HMC-1), with expression confirmed on granulocytes and monocytes.
- None of the generated scFvs inhibited C3a-induced calcium mobilization, and C3a did not displace scFv binding, indicating ligand-independent binding sites.
Conclusions:
- Novel scFvs targeting distinct immunodominant regions of the C3aR extracellular loop were successfully developed.
- These scFvs provide valuable tools for studying C3aR expression and localization.
- The findings suggest that the N-terminal portion of the second extracellular loop is not involved in C3a binding, offering insights into receptor-ligand interactions.