23 hybridomas secreting monoclonal antibodies against human α2, the fast-acting inhibitor of plasmin present in plasma, have been produced by the cell-fusion technique. Isotyping of the monoclonal antibodies has revealed that 14 monoclonal antibodies belong to the class IgG1, 6 to the class IgG2a, and 3 to the class tgG2b. All light chains belong to the κ group. The specificity and relative avidity of these monoclonals have been determined Using an indirect enzyme-linked immunosorbent assay. 13 monoclonals exhibit a relatively high avidity for α2, 5 are of intermediate avidity, and 5 of low avidity. The epitope specificity of these 23 rnonoclonal antibodies, originating from a single mouse, have been examined in inhibition experiments. A group of 10 monoclonal antibodies exhibit a very similar inhibition pattern. Partial inhibition effects displayed by 10 other antibodies define partially overlapping antigenic regions. The binding of these antibodies seems to produce a conformational change in the α2 molecule, reducing the binding of two other antibodies. The last antibody defines an independent epitope.

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