Prospects for the application of recombinant antigens Treponema pallidum TР0163 and TР0971 in enzyme-linked immunosorbent assay for the detection of immunoglobulin M in the serum of syphilis patients: A pilot observational study

Background. The enzyme-linked immunosorbent assay based on recombinant analogues of Treponema pallidum immunogenic proteins enables the diagnosis of syphilis by determining immunoglobulin G and immunoglobulin M. The detection of specific immunoglobulin M is considered an important criterion in diagnostics of syphilis at early stages. The efficiency of the assay depends on the antigens used to detect antitreponemal antibodies and the clinical stage of the infection. No consensus exists on which antigens exhibit the best characteristics for serodiagnosis of syphilis, and no test systems can differentiate between various forms of the infection or assess treatment efficacy. This highlights the need for new antigens or combinations thereof that can identify antibodies characteristic of specific clinical forms of the disease. Objective. To evaluate the diagnostic potential of recombinant Treponema pallidum proteins TР0163 and TР0971 as candidate antigens for detecting immunoglobulin M in serum samples from patients with primary, secondary, early latent, and late latent syphilis using the enzyme-linked immunosorbent assay. Methods. A pilot observational study was carried out with a control group of blood serum samples from 10 healthy donors and 45 blood serum samples from patients with a confirmed diagnosis of the following forms of syphilis: primary (n = 12), secondary (n = 6), early latent (n = 13), and late latent (n = 14). Diagnosis and classification of the disease were determined by a dermatovenereologist according to clinical guidelines. The primary endpoint of the study was to assess the diagnostic capability of recombinant Treponema pallidum proteins TР0163 and TР0971 for detecting immunoglobulin M using enzyme-linked immunosorbent assay. Data processing was carried out by means of Microsoft Excel 2017 (Microsoft, USA). A statistical level was considered statistically significant at p < 0.05. Results. The diagnostic sensitivity of detection immunoglobulin M with recombinant antigen TР0971 accounted for 91.7%, 83.3%, 84.6%, and 7.7% for patients in the primary, secondary, early latent, and late latent syphilis groups, respectively. For recombinant antigen TР0163, statistically significant detection of immunoglobulin M was observed for secondary and early latent syphilis, with diagnostic sensitivities of 66.7% and 53.8%, respectively. In primary and late latent syphilis, immunoglobulin M to TР0163 were not revealed. Conclusion. TР0971 represents a promising antigenic marker for early stages of syphilis. Antigen TР0163 is characterized by low diagnostic sensitivity for detecting immunoglobulin M to Treponema pallidum.

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