Immunoassay system and procedure based on precipitin-like interaction between immune complex and Clq or other non-immunospecific factor

A process for preparing an assay for quantitatively assaying a biological material for a monovalent bindable substance by means of inhibition of binding of formed complexes to non-immunospecific factor having binding affinity for said complexes, which are composed of a multivalent form of said bindable substance and a multivalent binding partner which binds said bindable substance specifically, the degree of binding of said formed complexes to said non-immunospecific factor being a function of composition of said formed complexes and representable by generally bell-shaped binding curve established over a range of compositions of said formed complexes, said range including compositions in which the amount of said multivalent form of said bindable substance and the amount of said multivalent binding partner are in substantial equivalence, in which the amount of said multivalent form of said bindable substance is in substantial excess of the amount of said multivalent binding partner, and in which the amount of said multivalent binding partner is in substantial excess of the amount of said multivalent form of said bindable substance, said process comprising the steps of:

• a. providing a test device comprising said insolubilized non-immunospecific factor;
• b. establishing selected working limits for said assay within said range of compositions of said formed complexes;
• c. constructing a standard assay curve by plotting relative degree of coupling of said formed complexes to said test device, said formed complexes being formed in a reference system comprising a fixed concentration of said multivalent binding partner, a fixed concentration of said multivalent form of said bindable substance, the composition of complexes resulting from said multivalent binding partner and said multivalent form of said bindable substance being within the selected working limits of step b, and varying concentrations of said bindable substance;
• and
• d. providing a test system comprising said test device, said multivalent binding partner, said multivalent form of said bindable substance and said bindable substance, the respective amounts of said multivalent binding partner and said multivalent form of said bindable substance being substantially equivalent to said fixed concentration thereof, and the amount of said bindable substance being appropriate to produce a known degree of coupling corresponding to a predetermined point on said standard assay curve, thereby enabling quantitative assaying of biological material for said bindable substance.