DIFFERENTIAL TITRATION OF PLASMIN AND PLASMINOGEN IN MILK USING SANDWICH ELISA WITH MONOCLONAL-ANTIBODIES

Two sandwich enzyme-linked immunosorbent assays (ELISA) have been deve loped for quantitation of bovine milk plasminogen and plasmin. The ass ays used two monoclonal antibodies, one specific for plasminogen and t he other specific for plasminogen plus plasmin. Plasmin concentration was obtained by subtracting the first concentration from the second. T he assays were sensitive (linear range, 5-75 ng/ml), repeatable (CV, 8 and 5% for plasmin and plasminogen titration respectively), specific (no cross reactivity with the major milk proteins) and directly applic able to skimmed milk with no particular pretreatment of the sample. Ho wever, ELISA did not permit complete titration of milk plasminogen and plasmin (only 60-90% could be quantified). This lack of accuracy was due to casein interfering with the plasmin-plasminogen titration bg EL ISA. Results obtained with ELISA or an enzymic technique on 20 milk sa mples collected from individual cows milked throughout pregnancy showe d that the ELISA was particularly suitable for analysis of late lactat ion or mastitic milk where proteinase inhibitors interfered with enzym ic quantitation.