Evaluation of recombinant proteins T. pallidum Тр0163 and Тр0971 as antigens for the diagnosis of syphilis using enzyme immunoassay

Background. With the deciphering of the T. pallidum genome and the application of bioinformatics and immunoproteomics, many recombinant T. pallidum proteins have emerged that have been evaluated for their diagnostic value, some of which are used as diagnostic antigens in commercial tests. In practice, however, there are often significant difficulties in diagnosing asymptomatic forms of syphilis, especially late forms, when the sensitivity of serologic methods may vary considerably. Therefore, the search for more sensitive and specific antigens for the serological diagnosis of syphilis continues.

Aims. To evaluate the potential of recombinant proteins T. pallidum Тр0163 and Тр0971 as candidate antigens for the determination of IgG in the sera of syphilis patients using enzyme immunoassay.

Methods. Recombinant T. pallidum proteins Тр0163 and Тр0971 were produced by Cusabio (China). Serum samples from patients with a confirmed diagnosis of primary, secondary, early latent and late latent syphilis, as well as serum samples from healthy individuals as controls, were used for the indirect enzyme-linked immunosorbent assay. To characterize the antibody concentration, a positivity coefficient was determined as the ratio of the optical density obtained for each sample to the critical optical density. The positivity coefficient was used to determine the difference between groups of syphilis patients and healthy individuals using the Mann-Whitney test for unpaired samples, as well as to assess the clinical informativeness of the laboratory test. The diagnostic efficiency of the enzyme immunoassay was assessed by calculating the indices in the groups of patients with established syphilis diagnosis and in the group of healthy individuals, in accordance with the standard for assessing the diagnostic informativeness of laboratory tests.

Results. The overall diagnostic efficiency of the study of recombinant proteins for the determination of IgG class antibodies by enzyme immunoassay is 65.4 and 66.7% for Тр0163 and Тр0971 respectively, demonstrating the specificity and positive predictive value of the study. The sensitivity of ELISA in relation to the study of forms of syphilis was not 68.8%.

Conclusions. In order to improve the treponema-specific diagnosis of syphilis, we believe it is important to continue working with these antigens to determine the effectiveness of ELISA to detect IgG, IgM or IgM/ IgG antibodies with a large number of clinical serum samples from syphilis patients, patients with non-syphilitic pathology and healthy individuals.