Human parathyroid antigen: characterization and localization with monoclonal antibodies.

A cell surface antigen on human parathyroid cells was identified by monoclonal antibodies. The antigen, called parathyroid antigen (PTA), is found on both of two major polypeptides (190 kDa and 160 kDa) apparently associated exclusively with parathyroid cells. To determine whether PTA was a suitable target for in vivo imaging, 125I-labeled anti-PTA was injected into nude mice bearing human parathyroid xenografts. IgG1 anti-PTA antibody showed excellent radiolocalization of the grafts, whereas IgM anti-PTA, containing the same variable domains as the IgG1 antibody, showed little specific binding. These results suggest that antibody isotype is an important parameter for the in vivo immunoscintigraphy of specific cellular antigens.