Monoclonal antibodies for use with 125iodine-labeled radioligands in progesterone radioimmunoassay.

The interactions of heterologous and homologous 125I-iodinated radioligand with polyclonal and monoclonal antibodies directed against 11-hydroxyprogesterone hemisuccinate conjugated to bovine serum albumin were compared. Our data show that, with a polyclonal antibody, the use of the same bridge in the tracer and the antigen results in a low sensitivity while a heterologous tracer can decrease markedly the titer of antibody but increases the sensitivity of the radioimmunoassay. Due to the high specificity of monoclonal antibodies, the interaction with heterologous and homologous iodinated tracers is extremely variable from one antibody to another but the present results demonstrate that radioimmunoassays of very high sensitivity can be obtained with homologous and heterogeneous tracers. However, an appropriate tracer has to be selected to meet the requirement of such an assay.