A Kinetic Model of Antigen-Dependent IgG Oligomerization and Complement Binding

Area of Science:

• Immunology
• Biophysics
• Biochemistry

Background:

• The classical complement pathway (CCP) is vital for immunity, activated by IgG antibody oligomers binding to pathogens or abnormal cells.
• IgG oligomers also mediate effector functions like antibody-dependent cellular cytotoxicity and phagocytosis via Fcγ receptors.
• Optimizing IgG-based therapies necessitates a deep understanding of IgG oligomerization dynamics.

Purpose of the Study:

• To develop a kinetic model predicting IgG oligomer formation.
• To characterize molecular interactions governing IgG oligomerization.
• To apply the model for predicting complement-mediated cell lysis.

Main Methods:

• Development of a kinetic model incorporating IgG concentration, antigen density, subclass, Fc mutants, and inhibitors.
• Characterization of molecular interactions using single molecule force spectroscopy and grating coupled interferometry.
• Fitting experimental data from high-speed atomic force microscopy to quantify kinetic and thermodynamic parameters.

Main Results:

• A predictive kinetic model for IgG oligomer formation was successfully developed.
• Key rate constants and thermodynamic parameters, including free energy changes, were quantified.
• The model accurately predicted complement-mediated lysis in liposomal vesicle assays.

Conclusions:

• The developed mechanistic framework provides insights into IgG oligomerization.
• This framework can optimize antibody engineering for improved immunotherapies.
• It also aids in pharmacokinetic/pharmacodynamic modeling for therapies utilizing the CCP.