Abstract
We conducted an electrophoretic analysis of monoclonal γ-globulin found in the serum of a patient with splenic marginal-zone lymphoma. This monoclonal protein showed electrophoretic mobility to the γ region and reacted with antii-mmunoglobulin (IgG) antiserum but not with anti-κ or anti-λ light chain antisera. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting of the monoclonal protein-rich γ-globulin fraction extracted from the sliced gel revealed the presence of two types of abnormal IgG molecule, low- and high-molecular-weight IgG, neither of which reacted with anti-κ or anti-λ light chain antisera. Additionally, an abnormal high-molecular-weight γ heavy chain was identified by reducing SDS-PAGE. These findings suggest that this monoclonal protein is composed only of γ heavy chains of normal and larger size. The presence of abnormal serum immunoglobulin composed of only γ heavy chain has been known as a fundamental feature of γ heavy chain disease (HCD). However, the unique composition of monoclonal γ-globulin makes our case distinct from typical γHCD, which is characterized by an abnormal truncated low-molecular-weight γ heavy chain. Thus, the unusual monoclonal protein may have been produced by a somatic mutation of IgH gene associated with splenic marginal-zone lymphoma.