II Binding of the Three Ig Classes Found in CLL Cell Lysates by Specific or Nonspecific Immunosorbents

Chronic lymphocytic leukemia (CLL) 1 appears to represent a clonal proliferation of B lymphocytes in that the abnormal cells found in blood and tissues have on their surfaces immunoglobulin (Ig) molecules bearing the same idiotype and light chain type. The expression of more than one heavy chain class is known to be compatible with monoclonality (1). The isotypes found most commonly are IgM and IgD, and such cells presumably reflect a stage of differentiation of normal B lymphocytes. The presence of IgG on such cells has been reported but has often been considered to be of serum origin, possibly at times representing autoantibodies or immune complexes bound to Fc 3, receptors (2). Incubation of the cells at 37°C was then shown to remove such extrinsic IgG, and this has been adopted as a precaution before analysis of surface Ig (3). More recently, however, as detection methods have increased in sensitivity, it has been found that surface IgG is present together with IgM and IgD in some cases of CLL where the intrinsic nature of all classes is suggested by observation of only a single light chain type. In a detailed study of CLL surface isotypes using a sensitive rosette test and observing precautions to remove extrinsic IgG, it was found that out of 24 patients expressing IgM plus IgD on the cell surface, 18 also expressed IgG (4). Similarly, in our smaller study using immunofluorescence, five out of eight patients with surface IgM plus IgD also expressed IgG (5). To investigate the nature of this IgG, anti-idiotypic antibody was raised against the surface IgM on the neoplastic B lymphocytes of the five patients with CLL. By immunosorption studies it has been shown for all five cases that cellular IgM and IgD are idiotypic, but that the IgG is not.