Characterization of immunoglobulin structures from the surface of chronic lymphocytic leukemia cells.

Chronic lymphocytic leukemia cells with relatively large amounts of mu and kappa immunoglobulin structures on the surface, and apparently very small amounts intracellularly, were subjected to homogenization or washing after freezing and thawing. After a light centrifugation, which sedimented the nuclei and unbroken cells, most of the immunoglobulin structures were found in the supernatant. Ultracentrifugation, which was performed to remove the membranes from the supernatant, sedimented only half the amount of the immunoglobulin structures. By sucrose density gradient ultracentrifugation and Sephadex G-200 filtration, the unsedimented immunoglobulin structures were shown to consist of 7S IgM and free kappa chains. About 80,000 7S IgM molecules were calculated to be present on each cell. The amount of kappa chains not associated with IgM was estimated to be equal to the amount of kappa chains in IgM. Inhibition of passive hemagglutination was used to detect and quantitate the immunoglobulin structures.