Deleted IgG1 and IgG2 H chains in a patient with an IgG subclass imbalance

The serum of a female patient studied over 7 months initially showed, in addition to normal residual IgG, two abnormal IgG proteins and in the last 3 months of the disease showed only one abnormal IgG protein. Gm typing and serological subclass determinations revealed an imbalance of allelic forms within the IgG1 subclass during the disease. The IgG2 level remained markedly elevated throughout the study. The two abnormal IgG-related proteins were devoid of light chains. The abnormal gamma cathodic immunoglobulin and the abnormal beta 2-immunoglobulin were Fc-like and covalently disulphide linked, with molecular weights of 60,000 daltons (N terminal, SER) and 72,000 daltons (N terminal, GLY) respectively. The first belonged to the IgG1 subclass and the second to the IgG2 subclass. No abnormal proteolytic activity was noted and plasma cells reacted with anti-gamma-chain antisera only. We hypothesize that the molecular defect leading to the deleted chains was an early event, preceding the differentiation into plasma cells which produced the two IgG1 and IgG2 deleted H chains.