Binding of sheep erythrocytes in chronic lymphocytic leukemias of B-cell origin

Two patients with B chronic lymphocytic leukemia having leukemic cells that bind sheep red blood cells by different mechanisms are described. In the first case, rosette formation was mediated by the anti-sheep erythrocyte activity of a monoclonal surface IgM_k, related to Forssman antigen. In the second, E-rosette formation was found to be independent of both surface immunoglobulins and the classic E-rosette receptor since the leukemic cells were recognized neither by the OKT-11 monoclonal antibody nor by other markers specific for T-cell lineage. Evaluation of these rare cases emphasizes that detection of surface immunoglobulins and spontaneous rosetting are not sufficient for the characterization of leukemic clones and raises some doubts concerning the use of available surface markers in the characterization of lymphoproliferative disorders.