A simple radioimmunoassay for the enumeration of rosette-forming cells

A simple radioimmunoassay for the enumeration of Ig bearing (Ig+) lymphocytes by rosette formation with anti-Ig, antibody coated erythrocytes (Ab-E) is described. The method is based upon labeling lymphocyte populations with 51Cr, rosetting them with Ab-E, separating the rosetted from unrosetted cells by centrifugation through a Ficoll-Hypaque layer, counting the radioactivity of the unrosetted cells, and counting the radioactivity of the unrosetted cells in a rosetting system with unreactive uncoated-E. This permits the calculation of the percentage of rosette-forming Ig+ cells. The assay eliminates the subjectivity and tediousness of counting and distinguishing between rosetted and unrosetted cells under the microscope. Being also sensitive and reliable, this radioimmunoassay may, after suitable modifications, replace the conventional counting of other types of rosettes.