Epitope mapping and binding analysis of insulin-specific monoclonal antibodies using a biosensor approach

Molecular interactions between the human insulin molecule and a panel of seven monoclonal antibodies (mAbs) against insulin were investigated by surface plasmon resonance. Using real-time analysis (BIAcore technology), the antigenic sites recognized on the human insulin molecule by these mAbs were mapped. Three overlapping regions could be defined on the insulin molecule coupled to the dextran matrix on the basis of its recognition by three mAbs groups: group I (mAbs 19, 10), group II (mAbs 13, 5, 25, 15) and group III (mAb P10). The antigenic determinants of the molecule in solution were mapped using a two-site assay in which insulin was presented to each mAb, bound to a rabbit anti-mouse IgG Fc gamma 1 coupled to the dextran. Four antigenic regions were defined: regions I and III were defined by the same antibodies as above whereas region II was recognized differently by mAbs 13, 5 (region IIa) and mAbs 25,15 (region IIb). The Ka value of the mAbs determined using the BIAcore were in the same range (from 3 x 10(7) M-1 to 6.6 x 10(9) M-1) whether insulin was coupled to the dextran matrix or in solution. Furthermore, mAbs 19 and P10, which recognize two distinct regions on the insulin molecule, were selected to develop a highly sensitive immunoassay for measurement of insulin in serum.