Characterization of monoclonal antibodies against bovine insulin.

Six different monoclonal antibodies (IgG1 and IgG2a) were obtained after fusions of X63-Ag8-6.5.3 myeloma cells with spleen cells from BALB/c mice immunized with bovine insulin. Definition of binding determinants was attempted by competitive binding studies with insulins, proinsulins and modified insulins from various species. The monoclonal antibodies OXI-001 and OXI-004 were inferred to react with a region including residue A10, OXI-002 with an antigenic determinant in the B26-30 region, OXI-005 with a region including B30 and OXI-006 with a tertiary structure near the N-terminus of the B chain, possibly including B3 and A10. The equilibrium binding constants for these antibodies were calculated by three different methods (Scatchard, Langmuir and non-linear regression) and were found to be in the range of 2 X 10(7)-8 X 10(9), with good agreement between the different methods of calculation. As expected for a given monoclonal antibody, the heterogeneity index was close to 1.0, as calculated from Sip's logarithmic transformation of the binding equation. These parameters were compared to those of a mixture of the six different monoclonal antibodies and those of a conventional hyperimmune anti-insulin serum (guinea-pig). The half-dissociation times (t1/2) of complexes of antibody and bovine insulin ranged from 35 min to 38 h.