MICROPARTICLE-ENHANCED NEPHELOMETRIC IMMUNOASSAY OF PLASMINOGEN IN BOVINE-MILK

A sensitive microparticle-enhanced nephelometric immunoassay of bovine plasminogen (detection limit in reaction mixture, 4 mu g l(-1)) is de scribed It is based on nephelometric measurement of the light scattere d by microparticle clusters formed during a sandwich assay that uses m icroparticle-anti-plasminogen conjugate and free antibodies from anti- plasminogen rabbit antiserum. This immunoassay was performed in 200-fo ld diluted bovine milk, after release of plasminogen from caseins by e psilon-amino-n-caproic acid treatment and elimination of the caseins. It allowed the quantification of plasminogen in milk for a wide range of concentrations (0.9-14.4 mg l(-1)), with accuracy (linear recovery in overloading assays) and precision (within- and between-run coeffici ents of variation lower than 5%). When it was applied to 106 herd milk samples, this microparticle-enhanced nephelometric immunoassay yielde d milk plasminogen concentrations ranging between 1.1 and 4.9 mg l(-1) , with a mean of 2.0 mg l(-1), and disclosed possible seasonal variati ons.