Two-dimensional electrophoretic analysis of immunoglobulin patterns in monoclonal gammopathies

Two-dimensional (2-D) electrophoresis was performed on 24 serum samples from patients diagnosed with monoclonal gammopathies. These samples had been shown to have a homogeneous immunoglobulin (M component) by zone electrophoresis and immunofixation. Using 2-D electrophoresis, the nature of this aberrant protein was further analyzed. It has been presumed that the sharp, dark stained band identified by immunofixation was the production of a monoclonal immunoglobulin. The increased resolution afforded by 2-D methodology reveals several different patterns. On 2-D electrophoresis, a monoclonal antibody has a unique pattern. It consists of 3 to 6 strong, restricted heavy chain bands and a single distorted light chain spot. The 3-6 bands are microheterogeneity of the isoelectric point, attributed to posttranslational glycosylation and/or amidation/deamidation. Analysis by 2-D electrophoresis indicated only 5 samples with a true monoclonal pattern. All but 2 of the samples clearly had aberrant immunoglobulin, but interpretation of the pattern would suggest the protein is other than a fully synthesized monoclonal antibody. The samples showed the following: a monoclonal heavy chain pattern with multiple distorted light chain spots, only an aberrant light chain area, only an aberrant heavy chain, and only a polyclonal increase. Several IgG gammopathies had, in addition, concentrations of gamma heavy chain at a reduced size (34 kDa).