Chronic lymphocytic leukaemia and IgG heavy chain disease

A 64-year-old woman who has suffered from chronic lymphocytic leukaemia since 1976 is discussed. In 1978, an abnormal protein component was found in her serum by means of immunoelectrophoresis. Using the techniques of immunoselection of the serum immunoglobulins and immunofluorescence of the bone marrow cells, it was demonstrated that this component consists of IgG1 heavy chains only. The native protein, COL, consisted of a dimer linked by disulphide bonds of a molecular weight of 80 000 daltons. Its monomeric unit had a molecular weight of 40 000 daltons, as determined by SDS-polyacrylamide gel electrophoresis after reduction with 2-mercaptoethanol. Protein COL was not produced by the leukaemic cells (which bore IgM-lambda on their membrane) but by a morphologically distinct clone of lymphoid cells. After therapy with chlorambucil, the level of the heavy chain disease protein in the serum decreased substantially.