Generation And Characterization Of Monoclonal Antibodies Against The N-Terminus Of Alpha-2-Antiplasmin

Around 70% of circulating alpha-2-antiplasmin (alpha 2AP), the main natural plasmin inhibitor, is N-terminally cleaved between residues Pro12 and Asn13 by antiplasmin-cleaving enzyme. This converts native Met-alpha 2AP into the more potent fibrinolysis inhibitor Asn-alpha 2AP. The Arg6Trp (R6W) polymorphism affects the N-terminal cleavage rate of Met-alpha 2AP in a purified system, with similar to 8-fold faster conversion of Met(R6)-alpha 2AP than Met(W6)-alpha 2AP. To date, assays to determine N-terminally intact Met-alpha 2AP in plasma have been limited to an ELISA that only measures Met(R6)-alpha 2AP. The aim of this study was to generate and characterize monoclonal antibodies (mAbs) against Met(R6)-alpha 2AP, Met(W6)-alpha 2AP and all alpha 2AP forms (total-alpha 2AP) in order to develop specific Met(R6)-alpha 2AP and Met(W6)-alpha 2AP ELISAs. Recombinant Met(R6)-alpha 2AP, Met(W6)-alpha 2AP and Asn-alpha 2AP were expressed in Drosophila S2 cells. Using hybridoma technology, a panel of 25 mAbs was generated against a mixture of recombinant Met(R6)-alpha 2AP and Met(W6)-alpha 2AP. All mAbs were evaluated for their specific reactivity using the three recombinant alpha 2APs in one-site non-competitive ELISAs. Three mAbs were selected to develop sandwich-type ELISAs. MA-AP37E2 and MAAP34C4 were selected for their specific reactivity against Met(R6)-alpha 2AP and Met(W6)-alpha 2AP, respectively, and used for coating. MA-AP15D7 was selected for its reactivity against total-alpha 2AP and used for detection. With the novel ELISAs we determined Met(R6)-alpha 2AP and Met(W6)-alpha 2AP levels in plasma samples and we showed that Met(R6)-alpha 2AP was converted faster into Asn-alpha 2AP than Met(W6)-alpha 2AP in a plasma milieu. In conclusion, we developed two specific ELISAs for Met(R6)-alpha 2AP and Met(W6)-alpha 2AP, respectively, in plasma. This will enable us to determine N-terminal heterogeneity of alpha 2AP in plasma samples.