Monoclonal antibodies directed against human tissue-type plasminogen activator: a characterization of their species specificity, affinity and heavy-chain binding.

Six monoclonal antibodies (mIgG) and a polyclonal antibody (pIgG) directed against human tissue-type plasminogen activator (t-PA) were tested for their species specificity towards human or murine t-PA. Whereas pIgG as well as several mIgGs discriminated poorly between these two t-PA species, one mIgG (clone E3) was highly specific for human t-PA. Inhibition and binding studies of human t-PA by mIgGs revealed high affinity-high inhibitory (E3) as well as high affinity-poor inhibitory (B1) mIgGs. The relative affinity of two mIgGs for human t-PA was found to be equal or even superior to that of pIgG. Immunoblotting of reduced two-chain t-PA and of an isolated heavy chain of t-PA prepared by recombinant DNA technology, showed that the E3 antibody was directed against the heavy chain of t-PA.