Monoclonal antibodies to rat calcitonin: their use in antigenic mapping and immunohistochemistry

A library of monoclonal antibodies (mAbs) to rat calcitonin (rCT) was raised from several fusions. Antibodies were screened by enzyme-linked immunosorbent assay with solid phase rCT. Affinities for rCT ranged from 10(9)-10(11) M(-1). Some mAbs reacted preferentially with solid phase rCT, but not with liquid phase, 125I-labeled rCT. Cross-reactivity with human CT (hCT) was assessed using solid phase hCT. Although there are only two amino acid differences, at least nine of the mAbs do not cross-react with solid phase hCT. Several cross-reactive mAbs were chosen for immunohistochemical studies of human medullary thyroid carcinoma samples and showed strong positive staining. A 33 x 33 matrix solid-liquid mAb inhibition assay was carried out to probe the rCT molecule. Five different clusters of mAb were distinguished and interpreted as reflecting five distinct antigenic regions on the surface of the rCT molecule.