A competitive inhibition assay for gelatin binding fibronectin

A competitive inhibition assay for functional fibronectin (Fn), based on ELISA technology, is described. The assay measures Fn's physiologic ability to bind to denatured collagen (gelatin). Affinity-purified Fn inhibits the binding of alkaline phosphatase coupled Fn to gelatin-coated wells of a microtiter plate in a concentration-dependent manner. The assay range is 50-500 micrograms Fn/ml, which is suitable for the measurement of plasma Fn in both normal and opsonin deficient individuals. It is reproducible over an eightfold dilution of plasma and is resistant to interference by normal plasma proteins. The assay described is quick, quantitative, and reproducible, and satisfies the need for a measure of functional Fn activity in the clinical laboratory.