Assessment of serological tests for antibodies to different antigens of the SARS-CoV-2 virus: comparison of six immunoassays

The new coronavirus SARS-CoV-2 has become a global challenge to medicine and, in particular, laboratory diagnostics. The study of the antibodies’ level to SARS-CoV-2 can be used as a confirmation test in the diagnosis of a disease, but it becomes of paramount importance in assessing population immunity resulting from a disease or vaccination, as well as in selection of convalescent plasma donors. The kits developed in our country and abroad for detecting antibodies to the SARS-CoV-2 virus differ both in the methods of testing and in the used coronavirus antigens to which the antibodies are directed. The aim of this study was to compare the diagnostic sensitivity and specificity of five kits for the detection of IgG antibodies to the SARS-CoV-2 virus, based on different diagnostic methods. Serum samples from 137 COVID-19 convalescents and 166 donors of blood and its components were examined. The control group consisted of 50 blood sera collected at the beginning of 2019 and 19 sera collected in 2018 (before the advent of the SARS-CoV-2 virus) and stored at -70 °C. Testing was carried out in analytical systems: rapid test “COVID-19 IgM/IgG Rapid Test (Colloidal Gold)” (China), on an automatic immunochemical analyzer Abbott Architect™ i2000 and kit “SARS-CoV2-IgG” (Abbot, Chicago , IL USA), by the chemiluminescence method using an automatic analyzer of the CL series and kits of the “Mindray” company (China) “SARS-CoV-2 IgM” and “SARS-CoV-2 IgG” and by the enzyme immunoassay method on the kits of the companies “Diagnostic Systems” Ltd (Russia, Nizhny Novgorod) “DS-IFA-ANTI-SARS-CoV-2-G”, “Xema” Ltd (Federal State Budgetary Institution “National Medical Research Center of Hematology” of the Ministry of Health of Russia) “SARS-CoV-2-IgG-IFA” and “Vector-Best” CJSC (Russia, Novosibirsk)” SARS-COV-2-IgM-IFA-BEST” and “SARS-COV-2-IgG-IFABEST”. When comparing the results of testing 137 plasma samples on the Vector-Best and Mindray kits for IgG antibodies, 127 samples were positive, 7 samples were negative on both kits, the discrepancy was 2.2%. In the study of IgM antibodies, 32.1% were positive, and 52.6% were negative in both kits. The discrepancy rate was 15.3%. Out of 166 samples, 1 serum (0.6%) was negative in 5 kits. On the Mindray kit, IgG antibodies to the antigens of the SARS-CoV-2 virus were detected in 165 samples (99.4%), on Vector-Best – in 164 sera (98.8%), on Diagnostic systems – in 151 (90.96%), on Xema – in 154 (92.8%), and on Abbott – in 155 samples (93.4%). At the same time, 135 (81.33%) samples were positive in all kits, while 30 samples had discordant results (18.07%), and in 9 sera, specific IgG was not detected in 2 or more kits. ROC analysis revealed a high diagnostic value of all tested kits (AUC from 0.908 to 0.998), which indicates a high quality of the separation model of positive and negative samples (p < 0.001). With the cut-off set by the manufacturers, the sensitivity and specificity ranged from 82.8% and 93.3% for the Diagnostic Systems kit to 99.4% and 95.8% for the VectorBest kit. The calculated correlation coefficients were higher between kits with a similar composition of the antigen used in the kits; therefore, it is better to monitor the dynamics of antibodies by diagnostic kits from the same manufacturer

Anesthesia of laboratory animals in manufacturing of diagnostic and preventive biomedicines

Preparations such as XilaVet, Zoletil 100 as well as Aeranne (Isoflurane) are successfully applied for animal anesthesia in veterinary practice. We assessed a possibility of using parenteral narcosis with Zoletil 100 in combination with muscle relaxant Xila for producer-rabbits involved in manufacturing of natural rabbit serum subsequently deployed for production of diagnostic serum and immunoglobulin preparations. Administration of preparations into auricular vein is easy to do, while animals are sedated immediately allowing for safe fixation on restraining table and causing no additional stress for biomodels. This type of narcosis provides for expected depth of anesthesia and its maintenance until the end of blood-letting procedure. Parameters characterizing the state of cardiovascular system due to anesthetic products remained within the permitted limits. These preparations do not reduce heart beat rate allowing for collecting sufficient blood volumes. Application of inhalation anesthesia with Aeranne in laboratory animals provides for the specified depth of anesthesia and its maintenance until the end of the whole procedure. However, it requires specialized equipment and highly trained personnel with appropriate skills. Usage of Xila as a mono narcosis is not recommended as exhibits weak analgesic effects and strong hypotensive activity by decreasing quantity of collected blood volume. It was found that anesthetics such as Xila, Zoletil 100, Aeranne did not affect specific activity of immune sera in case of total dehematizing procedure. Moreover, antibody titers were not declined throughout entire observation (12 months) period and complied with the requirements of regulatory documentation. In addition, a feasibility of replacing old-fashioned anesthesia method with diethyl ether for a combination of safer contemporary preparations of Zoletil 100 and Xila was demonstrated while manufacturing tableted chemical cholera vaccine in experimental series with suckling rabbits used at diverse stages of raw material verification during surgical interventions. Xila, Zoletil 100, and Aeranne examined by us had no impact on the amount of blood obtained from donor-animals, immunological properties of the sera and ready-to-use diagnostic preparations. Such drugs were safe for all-age animals that comply with the requirements to anesthesia of animal biomodels and producer-animals in manufacturing of immunobiological preparations. Thus, our study allowed to conduct experiments with laboratory animals in a more humane manner

Immunobiological Characteristics of Cholera Toxin B-Subunit

Carried out was immunobiological evaluation of cholera toxin B subunit preparations obtained using different experimental and production methods. It was demonstrated that B subunit preparations were non-toxic for biomodels and did not cause significant pathological alterations in their organs and tissues. They also did not alter the condition of immunocompetent cells at different stages of their cycle, and promote anti-toxic antibodies production. Thus, B subunit preparations under study can be considered as promising components of cholera vaccine

The Hamburg/ESO R-process Enhanced Star survey (HERES). V. Detailed abundance analysis of the r-process enhanced star HE 2327-5642

We report on a detailed abundance analysis of the strongly r-process enhanced giant star, HE 2327-5642 ([Fe/H] = -2.78, [r/Fe] = +0.99). Determination of stellar parameters and element abundances was based on analysis of high-quality VLT/UVES spectra. The surface gravity was calculated from the NLTE ionization balance between Fe I and Fe II, and Ca I and Ca II. Accurate abundances for a total of 40 elements and for 23 neutron-capture elements beyond Sr and up to Th were determined. The heavy element abundance pattern of HE 2327-5642 is in excellent agreement with those previously derived for other strongly r-process enhanced stars. Elements in the range from Ba to Hf match the scaled Solar r-process pattern very well. No firm conclusion can be drawn with respect to a relationship between the fisrt neutron-capture peak elements, Sr to Pd, in HE 2327-5642 and the Solar r-process, due to the uncertainty of the latter. A clear distinction in Sr/Eu abundance ratios was found between the halo stars with different europium enhancement. The strongly r-process enhanced stars reveal a low Sr/Eu abundance ratio at [Sr/Eu] = -0.92+-0.13, while the stars with 0 < [Eu/Fe] < 1 and [Eu/Fe] < 0 have 0.36 dex and 0.93 dex larger Sr/Eu values, respectively. Radioactive dating for HE 2327-5642 with the observed thorium and rare-earth element abundance pairs results in an average age of 13.3 Gyr, when based on the high-entropy wind calculations, and 5.9 Gyr, when using the Solar r-residuals. HE 2327-5642 is suspected to be radial-velocity variable based on our high-resolution spectra, covering ~4.3 years.Comment: 16 pages, 12 figures, accepted to A&

The Chemical Composition of Two Supergiants in the Dwarf Irregular Galaxy WLM

[Abridged] The chemical composition of two stars in WLM has been determined from high quality UVES data obtained at the VLT UT2 (program 65.N-0375). The model atmospheres analysis shows that they have the same metallicity, [Fe/H] = -0.38 +/-0.20, and [Mg/Fe] = -0.24 +/-0.16. This result suggests that the [alpha(Mg)/Fe] ratio in WLM may be suppressed relative to solar abundances (also supported by differential abundances relative to similar stars in NGC6822 and the SMC). The absolute Mg abundance, [Mg/H] = -0.62 is high relative to what is expected from the nebulae though, where two independent spectroscopic analyses of the HII regions in WLM yield [O/H] = -0.89. Intriguingly, the oxygen abundance determined from the OI 6158 feature in one WLM star is [O/H] = -0.21 +/-0.10, corresponding to five times higher than the nebular oxygen abundance. This is the first time that a significant difference between young stellar and nebular oxygen abundances has been found, and presently, there is no simple explanation for this difference. If the stellar abundances reflect the true composition of WLM, then this galaxy lies well above the metallicity-luminosity relationship for dwarf irregular galaxies. It also suggests that WLM is more chemically evolved than currently interpreted from its color-magnitude diagram.Comment: 27 pages, 7 tables, 10 figures. accepted for publication in the Astronomical Journa