A Modified ELISA Method to Evaluate the Interaction of Schistosoma mansoni Proteins with Plasminogen

An important aspect of host-pathogen interactions is the interference of secreted proteins with the fibrinolytic system. Herein, we describe a modified ELISA method used to evaluate the interaction of a recombinant Schistosoma mansoni protein with plasminogen (PLG). Using this protocol, we demonstrated that a secreted protein, recombinant venom allergen-like protein 18 (rSmVAL18) acts as a plasminogen receptor increasing its activation into plasmin in the presence of the urokinase-type plasminogen activator (uPA). PLG binding was determined by immobilizing human PLG in the plate and incubating with the recombinant protein; competitive binding with a lysine analog demonstrated the interaction of the protein lysine residues with PLG Kringle domains. To assess the activation of S. mansoni recombinant protein-bound PLG, the amidolytic activity of generated plasmin was measured using the D-Val-Leu-Lys 4-nitroanilide dihydrochloride substrate.