Mechanism of autoimmune hemolytic anemia in chronic lymphocytic leukemia.

Chronic lymphocytic leukemia (CLL) is a malignant clonal expansion of CD5+B lymphocytes. The CD5+B lymphocytes have been postulated to produce autoantibodies. CLL patients may demonstrate features of autoimmunity including autoimmune hemolytic anemia. However, the origin of the autoantibodies causing the hemolysis is not clear. The present studies were performed to determine whether these autoantibodies are the products of the neoplastic B-CLL clones. Immunoglobulins (Ig) were eluted from washed red blood cells (RBC) obtained from two CLL patients at the time they had autoimmune (DAT-direct antiglobulin test-positive) hemolytic anemia. The light chain phenotypes of these eluted autoantibodies were determined and found to be monotypic with exact correlation to the light chain expressed on the surface of the B-CLL clones. Elutions from RBC of DAT negative patients or normal volunteers failed to demonstrate measurable amounts of Ig. In contrast, Ig eluted from RBC obtained from SLE patients with DAT positive hemolytic anemia found to be polyclonal autoantibodies exhibiting both light chain types. Furthermore, CD5+B lymphocytes obtained from the same two CLL patients (DAT+) produce, in vitro understimulation with phorbal myristate acetate (PMA), monoclonal antibodies which react and bind to RBC. Thus these studies provide direct evidence demonstrating that the antibodies causing the autoimmune hemolytic anemia in our two CLL patients are the products of the B-CLL neoplastic clones.