The study of fibrin polymerization with monoclonal antibodies.

Three kinds of monoclonal antibody (Mab) of different specificity have been obtained against the N-terminal disulphide knots of fibrinogen and fibrin. Their effects on different phases of fibrin polymerization have been studied. These antibodies were shown to be directed against different epitopes of the B beta(1-53) fragment of the fibrinogen molecule. The different Mab had different effects both on the rate of protofibril lateral aggregation and on the final turbidity of fibrin clots. The Mab were of three specificities: (1) those from clone 2d-2a inhibited the rate of lateral aggregation of protofibrils and decreased the turbidity of the final clot; (2) those from clone B-4C accelerated the polymerization step but did not affect clot turbidity: and (3) those from clone D-IB did not have any effect on either fibrin polymerization or final clot turbidity. The localization of the epitopes recognized by all three kinds of Mab and analysis of our own data and those of others allow us to conclude that one of the active loci involved in protofibril lateral association is situated in the B beta(15-53) fragment of the fibrinogen molecule. Fibrinopeptide B does not need to be split off for this site to function. Fibrin polymerization can occur when one of the two sites of protofibril lateral aggregation in dimeric fibrin molecules is blocked by Mab, and the final clot turbidity is then reduced. The splitting off of one of the two fibrinopeptides B in fibrinogen molecules by thrombin can take place even when the second B beta(Arg14-Gly15) bond is blocked by an antibody molecule.(ABSTRACT TRUNCATED AT 250 WORDS)