Binding properties of a monoclonal antibody directed toward lead-chelate complexes

A monoclonal antibody (2C12) that recognizes a Pb(II)-cyclohexyldiethylenet riamine pentaacetic acid complex was produced by the injection of BALB/c mi ce with a Pb(II)-chelate complex covalently coupled to a carrier protein. T he ability of purified antibody to interact with a variety of metal-free ch elators and metal-chelate complexes was assessed by measuring equilibrium d issociation constants. The antibody bound to metal-free trans-cyclohexyldie thylenetriamine pentaacetic acid (CHXDTPA) with an equilibrium dissociation constant of 2.3 x 10(-7) M. Addition of Pb(II) increased the affinity of t he antibody for the complex by 25-fold; Pb(II) was the only metal. cation ( of 15 different di-, tri-, and hexavalent metals tested) that increased the affinity of the antibody for CHXDTPA. The increased affinity was due prima rily to an increase in the association rate constant. The antibody also had the ability to interact with ethylenediamine tetraacetic acid (EDTA), diet hylenetriamine pentaacetic acid (DTPA), and structurally related derivative s, but with affinities from 50- to 10000-fold less than that determined for CHXDTPA. Addition of metals to EDTA-based chelators reduced the affinity o f the antibody for these ligands. However, when DTPA was used as the chelat or, addition of Pb(IT) increased the affinity of the antibody for the compl ex by 200-fold. The sensitivity of prototype immunoassays for Pb(II) could be modulated by changing the structure of the immobilized metal-chelate com plex and/or the soluble chelator used to complex Pb(II) in the test solutio n.