Development of a monoclonal antibody-based cELISA for the analysis of sulfadimethoxine. 1. Development and characterization of monoclonal antibodies and molecular modeling studies of antibody recognition

Sulfonamide antibiotics are used to treat a variety of bacterial and protoz oan infections in cattle, swine, and poultry. Current residue methods for t he analysis of sulfonamides in animal-based food products include bioassays , chromatographic methods (HPLC, GLC), and immunoassays. Most immunoassays have employed highly specific polyclonal antibodies. In this paper, we desc ribe the isolation of monoclonal antibodies against sulfadimethoxine (SDM) that vary in their sensitivities and cross-reactivities against a large num ber of sulfonamides. The most sensitive monoclonal antibody, designated SDM -18, exhibits an IC50 value for SDM of 1.53 ppb. Another monoclonal antibod y, designated SDM-44, exhibits IC50 values for six sulfonamides well below the established threshold level of 100 ppb for animal tissues. Molecular mo deling studies of the cross-reactive drugs suggest that, depending on the m onoclonal antibody, both steric and electronic features govern antibody bin ding. Due to the diversity of these monoclonal antibodies, it should be pos sible to design both compound- and class-specific monoclonal antibody-based immunoassays.