MOLECULAR-BASIS FOR SPECIES AND LIGAND SPECIFICITY OF A MONOCLONAL-ANTIBODY RAISED AGAINST HUMAN IGF-I

The anti-hIGF-I monoclonal antibody, alpha-sm1.2, was found to have su bstantial crossreactivity with human and rat IGF-II, but recognized ra t IGF-I only when this ligand was present at very high concentration. (E-50 for hIGF-I similar to 3.5 ng/tube vs. similar to 12,000 ng/tube for rat IGF-I). In the context of previous studies to define the epito pe(s) of alpha-sm1.2, these findings point to the critical importance of aspartic acid at residue 20 in the B domain in determining the spec ies and ligand specificity of this antibody. Previous studies using th is antibody in rodent tissues may require reinterpretation in the ligh t of these findings.