Biology subjects

Frischauf, N.

Publications and source records attributed to Frischauf, N..

2 recordsLinked to original sources

bioRxiv2025

A kinetic model of antigen-dependent IgG oligomerization and complement binding

The classical complement pathway (CCP), an important branch of the mammalian immune system, is initiated through multivalent binding of complement protein C1 to Immunoglobulin G (IgG) antibody oligomers assembled on the surface of pathogens, infected or malignant cells, culminating in the formation of the membrane attack complex (MAC) and subsequent cell lysis. IgG oligomers can further engage immune effector cells through Fc{gamma} receptors or complement receptors, facilitating antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP). Detailed knowledge of the factors that drive IgG oligomerization is thus vitally important to establish and improve IgG based therapies. We here focus on the kinetics of antigen-dependent IgG oligomerization and develop a comprehensive model capable of predicting oligomer formation as a function of IgG concentration, antigen density, IgG subclass and Fc point mutants, as well as the presence of Fc-binding and thus oligomerization-inhibiting factors such as staphylococcal protein A (SpA). We characterize the underlying molecular interactions in single molecule force spectroscopy (SMFS) and grating coupled interferometry (GCI) experiments. By fitting experimental data from high-speed atomic force microscopy (HS-AFM) experiments, we further quantify key rate constants and thermodynamic parameters, including free energy changes associated with oligomerization and apply the model to predict complement-mediated lysis in liposomal vesicle-based assays. The presented mechanistic framework may serve as a basis for optimizing antibody engineering and pharmacokinetic/pharmacodynamic modeling in the context of immunotherapies exploiting the CCP.

biophysics↗

bioRxiv2024

Complement activation by IgG subclasses is governed by their ability to oligomerize upon antigen binding

Complement activation through antibody-antigen complexes is crucial in various pathophysiological processes such as infections, inflammation, and autoimmunity, but is also utilized in immunotherapies to eliminate infectious agents, regulatory immune cells, or cancer cells. Although the tertiary structures of the four IgG antibody subclasses are largely identical, complement recruitment and further activation depend strongly on subclass, which is commonly explained by the respective affinity for C1, the first component of the classical complement pathway. Contradicting this established view, we here demonstrate that complement activation by different IgG subclasses is determined by their varying ability to form IgG oligomers on antigenic surfaces large enough to multivalently bind and activate C1. We directly visualize the resulting IgG oligomer structures and characterize their distribution by means of high-speed atomic force microscopy (HS-AFM), quantify their complement recruitment efficiency from quartz crystal microbalance (QCM) experiments, and characterize their ability to activate complement on tumor cell lines as well as in vesicle-based complement lysis assays. We present a mechanistic model of the multivalent interactions that govern C1 binding to IgG oligomers and use this model to extract affinities and kinetic rate constants from real-time interaction QCM data. Together, our detailed characterization yields a comprehensive view on the parameters that govern complement activation by the different IgG subclasses, which may inform the design of future antibody therapies.

immunology↗