Characterization of Native Reversible Self-Association of a Monoclonal Antibody Mediated by Fab-Fab Interaction.

The native reversible self-association of monoclonal antibodies has been associated with high viscosity, liquid-liquid, and liquid-solid phase separation. We investigated the native reversible self-association of an IgG1, which exerts this association even at low protein concentrations, in detail to gain further understanding of this phenomenon by extensive characterization of the association as a function of multiple factors, namely pH, temperature, salt concentration, and protein concentration. The nature of the self-association of the full-length IgG1 as well as the corresponding Fab and Fc fragment was studied by viz. size exclusion chromatography combined with multiangle light scattering, batch dynamic and static light scattering, analytical ultracentrifugation, small angle X-ray scattering, asymmetric flow field flow fractionation coupled with multiangle light scattering, and intrinsic fluorescence. We rationalized the self-association as a combination of hydrophobic and electrostatic interactions driven by the Fab fragments. Finally, we investigated the long-term stability of the IgG1 molecule.