The long-known phenomenon of individual antigenic specificity of myeloma proteins, which suggested unique abnormalities, is now readily explainable on the basis of the homogeneity of these proteins. Isolated antibodies of similar homogeneity have been obtained which show the same individual specificity. All currently available criteria, including a large number of genetic markers, indicate the extreme similarity of myeloma proteins to individual normal γ-globulins and individual antibodies. Evidence is accumulating that they may actually represent antibodies for which in most instances the antigen is unknown.
The major protein defect thus far found for the malignant plasma cell involves asynchronous polypeptide chain synthesis. Decreased heavy chain synthesis is frequently observed, leading to an excess of uncombined light chains which is manifest as Bence Jones proteinuria. Light chain synthesis is only rarely affected.