Abstract: Ligand having at least two determinant or binding sites is contacted with a labeled first binder, an unlabeled second binder different than the first binder and a precipitating binder specific for the second binder, with such contacting precipitating a complex of the ligand and the first and second binders to thereby separate bound labeled binder from unbound labeled binder. The bound and/or unbound labeled binder is determined as a measure of the ligand.

Abstract: A set of four cell suspensions containing erythrocytes monospecifically sensitized with IgG, IgM, C3, and C4. The suspensions provide control cells to determine the purity and strength of the antibodies to these immunoglobins or complement components contained in antisera used for clinical testing. Strict control of the pH, temperature, and EDTA concentration of a solution to which blood is added allows for the elective production of C3- or C4-sensitized cells. Selecting a serum with IgG or IgM antibodies and inactivating undesired proteins permits the production IgG- or IgM-sensitized cells. The resultant cells have agglutination reaction strengths of about 2-4+. Erythrocytes from humans or other animals may undergo the monospecific sensitization. Other human proteins, such as IgA or C5, and plasma proteins from other animals may similarly be attached monospecifically to red blood cells.