The physical characterization of an aggregating IgG heteropolymer containing rheumatoid factor

An IgG heteropolymer containing rheumatoid factor activity was isolated from the serum of a patient with the polyclonal hyperviscosity syndrome. This aggregating system was characterized using ultracentrifugation, classical light scattering, and rheological methods. The degree of polymerization is shown to be reversible and dependent on both pH and concentration. Light-scattering studies show a minimum stable intermediate consisting of four IgG monomers to exist at pH 7.4. The theoretical intrinsic viscosity and radius of gyration for the feasible configurations of such a tetramer were calculated. These models were compared to the experimental values. A cyclic structure is shown to be most compatible with the experimental data. Immunochemical analysis suggests that each tetramer contains two IgG1 rheumatoid factors binding to determinants on IgG3 Fc regions.