An enzyme-linked antiglobulin test to quantify nanogram quantities of IgG on polystyrene microspheres

A method is described in which polystyrene latex beads are used for constructing standard curves to estimate the number of protein molecules on cell surfaces by an enzyme-liked immunoassay test (ELAT). A series of immune globulin (IgG) dilutions in pH 9.8 carbonate buffer were coated on 3-microns microbeads by incubation overnight at 4 degrees C and subjected to ELAT. The r value of the curve derived from four assays was 0.9991. This standard curve applied to previously recorded ELAT data resulted in estimating that normal RBC have 63 +/- 19 (SD) IgG molecules and that the lower level of sensitivity of the antiglobulin test is 155 IgG molecules per RBC. The method should be useful for more precise standardization of procedures for measuring proteins on cell surfaces.