Southern blot analysis in a case of Richter's syndrome. Evidence for a postrearrangement heavy chain gene deletion associated with the altered phenotype.

Richter's syndrome (RS) can be defined as the emergence of an aggressive lymphoma in patients suffering from chronic lymphocytic leukemia (CLL). The authors performed immunophenotypic and Southern blot analysis of the peripheral blood and tissue specimen of a patient with RS. Using immunoperoxidase and immunogold-silver staining techniques and a panel of monoclonal antibodies, the authors found that the large cells characteristic of RS showed an altered immunophenotype as compared with the CLL cells and did not express mu heavy chain. Southern blot analysis revealed identical kappa light chain rearrangements in both tumoral cell populations consistent with a common clonal origin. Using the JH probe and several restriction enzymes, the authors also found evidence for a postrearrangement deletion of the heavy chain mu gene. These findings suggest that in this case of RS, a deletion of the heavy chain mu gene resulted in loss of mu expression by the larger cells that were characteristic of RS and was associated with their altered phenotype.