[Europium-labelled Staphylococcus aureus protein A as a reagent for determining specific antibodies]. / Belok A Staphylococcus aureus, mechennyi evropiem, kak reagent dlia opredeleniia spetsificheskikh antitel.

In this work the conditions of labeling protein A with europium ions were studied and the conjugates obtained in this study were compared with traditional peroxidase conjugates currently used in immunochemistry. The conjugates of protein A with Eu3+ chelate were obtained with the use of cyclic dianhydride of diethylenetriaminepentaacetic acid (DADETPA). Conjugation methods with the use of DADETPA was shown to permit obtaining high-quality conjugates with europium chelates. Europium-labeled protein A ensured the sensitivity of the determination of adsorbed IgG at a level of 2 ng/ml and the dynamic analytical range within 3-1,000 ng/ml, which essentially exceeded similar characteristics of peroxidase conjugates with protein A. Europium-labeled protein A was used for the detection of antibodies to Francisella tularensis in the sera of humans immunized against tularemia. The sensitivity of this assay exceeded that of the enzyme immunoassay 10- to 40-fold. A conclusion was made on the possibility of using europium labelled protein A for the determination of specific antibodies to F.tularensis. This preparation may be useful in the determination of specific antibodies in low-immune sera.

Protein A used in DELFIA for the determination of specific antibodies.

The conditions of protein A labelling with Eu chelates were studied. The conjugates obtained were compared with those from horseradish peroxidase used conventionally in immunochemical practice. Protein A-Eu conjugates were obtained by a method applied previously for antibody labelling with indium and europium chelates using the bicyclic dianhydride of diethylenetriaminepenta-acetic acid (DADTPA) with some modifications. The Eu-labeled protein A ensured a sensitivity of the IgG determination 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 used for the determination of antibodies to Francisella tularensis in the sera of humans vaccinated against tularemia. The assay values exceeded 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 determination of antibodies specific to a tularemia causative agent. In particular, this compound can be useful for the determination of specific antibodies in low immune sera.