B-prolymphocytic leukemia cells that form rosettes with sheep red blood cells through monoclonal surface immunoglobulin.

The neoplastic cells from a patient with B-cell prolymphocytic leukemia exhibited sheep red blood cell (SRBC) rosette formation. Immunochemistries revealed no reactivity with T-cell monoclonal antibodies OKT 3, 4, 8, and 11. However, the neoplastic cells expressed characteristics of B-cells including surface IgM and IgD associated with lambda light chains, Ia-like antigenicity, and reactivity to monoclonal antibodies against B-cell antigens B1, B2, and B4. Inhibition procedures revealed that SRBC rosette formation was the result of binding activity of surface immunoglobulin to SRBC. Pretreatment of the leukemic cells with antihuman IgM or lambda antisera, or pronase or trypsin blocked rosette formation with SRBC. Circulating antibody to SRBC was also suspected by the fact that preincubation of SRBC with heat-inactivated patient's serum resulted in agglutination of the SRBC.