We conducted an electrophoretic analysis of monoclonal
gamma-globulin found in the serum of a patient with splenic marginal-zone
lymphoma. This monoclonal
protein showed electrophoretic mobility to the gamma region and reacted with anti-
immunoglobulin (
IgG) antiserum but not with anti-kappa or anti-lambda light chain
antisera.
Sodium dodecyl sulphate-
polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting of the monoclonal
protein-rich
gamma-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-kappa or anti-lambda light chain
antisera. Additionally, an abnormal high-molecular-weight gamma heavy chain was identified by reducing SDS-PAGE. These findings suggest that this monoclonal
protein is composed only of gamma heavy chains of normal and larger size. The presence of abnormal serum
immunoglobulin composed of only gamma heavy chain has been known as a fundamental feature of gamma
heavy chain disease (HCD). However, the unique composition of monoclonal
gamma-globulin makes our case distinct from typical gammaHCD, which is characterized by an abnormal truncated low-molecular-weight gamma heavy chain. Thus, the unusual monoclonal
protein may have been produced by a somatic mutation of IgH gene associated with splenic marginal-zone
lymphoma.