Rapid immunomagnetic phenotyping of cells.

A new method for immunophenotyping of cells in suspension has been developed. The method is based on identification of cells that have formed rosettes with superparamagnetic particles (Dynabeads) conjugated with monoclonal antibodies directed against cell-surface antigens. The method is extremely simple. Twenty-five microliters of cells are mixed with 5 microliters of Dynabeads in U-bottom microtitre wells. Following a 1-min centrifugation step, rosette formation can be inspected in the microscope. Staining of the cells before rosetting with acridine orange/ethidium bromide allows direct quantification of viable cells carrying a given marker. The method is limited to detection of cell-surface antigens, and the results obtained are comparable to those seen with indirect immunofluorescence. The method may be used for phenotyping of leukaemia and other cancer cells, and can also be used for phenotyping of cells that can only be obtained in small numbers, such as spinal fluid cells.