Introduction. This article is devoted to determining the level of protective antibodies of the patients at the early and further stages after being suffered from COVID-19. Materials and methods. On the first stage of the research 66 patients of different age  and gender were examined. All patients, with no exception, had positive PCR results on COVID-19. All patients were  relatively divided into two age groups: from  18  to  39   (n = 39) and from 40 to 65 (n = 27). The light form of disease was detected in 40 patients, the moderate form – in 15 and the severe one – in other 3 patients. 8 people  were ill without symptoms. There were 11 patients hospitalized at the department of infectious diseases of the hospital. Afterwards the level of the antibodies was controlled  on the 60th, 90th and 150th day after the onset. All patients were tested for antibodies to COVID-19 by enzyme-linked immunosorbent assay (ELISA) performed on the equip- ment: enzyme-linked immunosorbent assay Tecan (Austria); PW 40 Microplate Washer (France). ELISA set for serology COVID-19 test system IgG SARS-CoV-2 VitroTest (Ukraine). Results. Analyzing the data obtained via laboratory research, it can be seen that the immune response to COVID-19 was formed in 82 % of the examined patients.   The maximum level of antibodies, which remains as such up to 40th day. Results. IgG  increases from 12 to 40 days and then has not changed significantly for 60; 90 and 150 days. Only 4 patients had a noticeable decrease on day 150 (however, they still had a positive level). Conclusion. IgG levels in patients with Sars-Cov2 remain high for at   least 150 days. The formation of antibodies is not affected by the age difference, neither depends on the severity of the disease.

Introduction. This publication describes the continuation of a research to determine the level of specific antibodies in patients in the long term after being suffered from COVID-19. Materials and methods. For this phase of the research, a group of patients who relapsed into a COVID-19 eight months ago (240 days) was examined. The group consists of 42 people. All patients, with no exception, had positive PCR results on COVID-19. Some patients were treated in Hospital № 4 in the infectious department, the other part was treated on an outpatient basis. All patients were relatively divided into two age groups: from 18 to 39 (n = 13) and from 40 to 65 (n = 28). The light form of disease was detected in 29 patients, the moderate form – in 11 and the severe one – in 1 patient. Afterwards the level of the antibodies was controlled on the 60th, 90th, 150th and 240th day after the onset. All patients were tested for antibodies to COVID-19 by enzymelinked immunosorbent assay (ELISA) performed on the equipment: enzyme-linked immunosorbent assay Tecan (Austria); PW 40 Microplate Washer (France). ELISA set for serology COVID-19 test system IgG SARS-CoV-2 VitroTest (Ukraine). Results. According to the first stage of the research, it was recorded that the immune humoral response to Covid-19 was formed in 82 % into the group – in 54 of 66 people. Subsequently, 42 out of 54 individuals with positive antibody levels participated. Analyzing the group of those who have antibodies, we obtained the following results on day 240 from the onset of the disease: IgG levels remain above the threshold level of 80 % (n = 35). It is interesting to note that in 56 % (n = 23) the level of antibodies remains at a very high level. In 20 % (n = 8) into the group, the level of antibodies significantly decreased throughout the research period and became below the threshold by 240 days. Conclusion. Analyzing the data obtained over 8 months (240 days), certain conclusions can be drawn. The maximum level of antibodies was recorded on day 40 from the onset of the disease. It was shown that in the group of patients who had a positive level of specific antibodies to SARS-CoV-2 above the threshold, IgG did not disappear in any patient between 40 and 150 days. However, the downward trend was observed in 20 % of respondents. In this cohort of patients, the antibodies disappeared by day 240. In most patients (80 %) who recover into SARS-CoV-2, IgG levels remain high for at least 240 days.

Background. Our assumption that immunity after COVID-19 will persist has been fully confirmed in the researches already conducted. Our work is a continuation of research that demonstrates the results obtained 12 months of determining the humoral response in patients after COVID-19. Materials and methods. The research involved 42 individuals. All subjects had a positive PCR test for COVID-19. At certain intervals, from 40 to 240 days, individuals in the group were tested for IgG SARS-CoV-2. The last step was to check the level of IgG to the COVID-19 nucleocapsid and spike protein in the research group for 360 days from the onset of the disease. A private certified laboratory in Kyiv, the “DNA Laboratory”, was involved. Patients were tested for antibodies to COVID-19 by ELISA using serology COVID-19 test systems VitroTest (Ukraine). The immunological laboratory of the Institute of Pediatrics, Obstetrics and Gynecology was used in parallel for interlaboratory quality control. The results of the research coincided. Results. The level of class G immunoglobulins to nucleocapsid in the subjects has gradually decreased over 8 months. It is noteworthy that in the period from 40 to 150 days in all 42 patients (100 %) antibodies did not disappear. Decreasing of antibodies occurred between 150 and 240 days. However, the data obtained for 360 days significantly changed the picture. In a certain part of the subjects, who had low or even negative levels of antibodies for 8 months, as of 12 months, the level of immunoglobulin (Ig) class G again rose above the threshold value. Thus, we see that from the group of 42 people 92.8 % have positive antibodies to the nucleocapsid, and 7.2 %. Conclusions. The data obtained illustrate that in the study group within 12 months after SARS-CoV-2, the vast majority of individuals remain with specific antibodies to the nucleocapsid and spike-protein.

Introduction. The CD8αα are present in a subset of T cells and NK cells, but its function is mostly unknown, as well as the role of CD8+ and CD8- NK cell subsets in physiological and pathological environments. Methods. We investigated 130 healthy individuals’ blood samples for the NK cell cytotoxicity against K562 and MOLT4 cell lines. We also analyzed patients after SarsCov2 infection and compared to healthy control. The NK cell phenotype and cytotoxicity were studied by the FACScan flow cytometer using BD monoclonal antibodies. Results. We confirmed that MOLT4 is significantly more resistant to the NK cell cytotoxicity compared to the “classical” K562. CD8+ NK cells are more effective at K562 killing compared to CD8- subsets. The correlation of lymphocyte levels with the specific K562 lysis was weaker for CD8- NK cell subsets (r = 0.37) than CD8+ NK cells (r = 0.45) or whole NK cells population (r = 0.46). However, we found that CD8+ NK cells mostly did not participate in the MOLT-4 killing. CD8- NK cells frequency correlates with MOLT4 lysis more significantly (r = 0.49) than CD8+ NK cells lymphocytes levels (r = 0.27) or whole NK cells population (r = 0.44). Also, we showed that HLA-DR and CD158a positive NK cell levels did not correlate with the MOLT4 and K562 killing, while HLA-DR and CD158a negative subsets levels did with the same significance as the whole NK cells population. Decreased of NK lymphocytes after SarsCov2 infection results to decrease NK population owing to CD8+NK decreased but not CD8neg. Conclusion. NK cell numbers determine NK cell cytotoxicity indirectly through the surface phenotype. CD8 expression on the NK cells is associated with the effective cytotoxicity against K562 but at the same time obstructs a response to MOLT4. CD8αα on NK cells might participate in HLA recognition or enhance response to HLA class-I negative target cells.