Detection and quantitation of IgG on the surface of human lymphoid cells by rosette formation with protein A‐coated sheep red blood cells

Sheep red blood cells coated with protein A of Staphylococcus aureus (SpA) form rosettes with human lymphoid cells with surface‐associated IgG and with cells treated with antibodies of the IgG class against some of the cell membrane antigens. Inhibition of rosette formation by SpA was used for quantitation of immunoglobulins on the cell surface. The sensitivity of the method permits the quantitation of 104 – 105 molecules of IgG receptors and detected less than 104 antibody molecules of the IgG class bound to the surface of IgM‐producing cells. This method seems to be suitable for detection and quantitation of membrane‐associated antigens including immunoglobulins.