Monoclonal antibodies against different antigenic determinants of a protein molecule (human serum albumin) as detected after labeling the antigen with two different markers.

By using FITC- and 125I-labeled human serum albumin (HSA) the reactivity of anti-HSA hybridoma antibodies was compared in solid-phase immunofluorescence assay (SIFA) and radioimmunoassay (SRIA). A considerable number of hybridoma antibodies had been detected which are positive in SIFA but not in SRIA. Since this cannot be explained by a difference in the sensitivity of the assays it seems likely that these monoclonal antibodies detect antigenic determinants which contain tyrosine as an essential part.