Heavy chain typing in IgG monoclonal gammopathies with special reference to cases of serum hyperviscosity and cryoglobulinaemia.

Heavy chain subclasses of 121 IgG monoclonal proteins were found to be 74% IgG1, 10% IgG2, 12% IgG3 and 4% IgG4. Light chain subclasses showed a slight kappa excess among IgG1 proteins. Electrophoretic studies of these monoclonal proteins and of normal γ-globulin showed IgG1 had a wide range of mobility including the most slow (electronegative) proteins; IgG2 and IgG4 were among the faster moving, while IgG3 showed medium to slow mobility. The above random distribution of IgG subclasses was found in eighteen monoclonal proteins causing hyperviscosity syndrome, whereas among fourteen monoclonal cryoglobulins there was an excess of IgG2 and IgG3 subclasses.