PROTEIN-A USED IN DELFIA FOR THE DETERMINATION OF SPECIFIC ANTIBODIES

The conditions of protein A labelling with Eu chelates were studied. T he conjugates obtained were compared with those from horseradish perox idase used conventionally in immunochemical practice. Protein A-Eu con jugates were obtained by a method applied previously for antibody labe lling with indium and europium chelates using the bicyclic dianhydride of diethylenetriaminepenta-acetic acid (DADTPA) with some modificatio ns. The Eu-labeled protein A ensured a sensitivity of the IgG determin ation at the level of 2 ng/ml and a dynamic range of the determination from 3 to 1000 ng/ml, which significantly exceed analogous values for the protein A-peroxidase conjugates. The Eu-labeled protein A was use d for the determination of antibodies to Francisella tularensis in the sera of humans vaccinated against tularemia. The assay values exceede d by 10-40-fold the results of an ELISA in sensitivity. It was deduced that the Eu-labeled protein A can be effectively used for the determi nation of antibodies specific to a tularemia causative agent. In parti cular, this compound can be useful for the determination of specific a ntibodies in low immune sera.