Background: The hemostasis system has been extensively investigated in patients in the acute phase of coronavirus disease 2019 (COVID-19). In contrast, the post-COVID syndrome is a poorly known entity, and there is a lack of information on the mechanisms underlying the hemostasis abnormalities in the post-COVID period. Aim: To analyze the potential changes in the parameters of the hemostasis system in the post-COVID period in the plasma of donors with different titers of anti-SARS-CoV-2 IgG. Methods: The plasma from 160 donors who had recovered from COVID infection was used in the study. Based on the results of the Abbott SARS-CoV-2 IgG serological assay, all donors were divided into several groups: 5 ± 3 (n=20); 55 ± 5 (n=20); 65 ± 5 (n=20); 75 ± 5 (n=20); 85 ± 5 (n=20); 95 ± 5 (n=20); 125 ± 5 (n=20); 175 ± 5 (n=20) Index (S/C). A total of 20 healthy individuals without anti-SARS-CoV-2 IgG constituted the control group. Key laboratory parameters, such as fibrinogen concentrations, soluble fibrin monomer complex (SFMCs), and D-dimer, were investigated. In addition, the qualitative composition of the fraction of SFMCs was analyzed. Results: The slight increase in the concentration of fibrinogen, SFMCs, and D-dimers in some donor groups have been found, which could cause the development of hemostasis disorders. In the fraction of SFMCs, the increase in the number of protein fragments with a molecular weight of less than 250 kDa and an increase in the level of proteins with a molecular weight of more than 270 kDa was revealed. Conclusion: The obtained results indicated the relationship between the changes in the parameters of the hemostasis system and the titers of anti-SARS-CoV-2 IgG in donors in the post-COVID period. It can be assumed that donors with higher titers of anti-SARS-CoV-2 IgG (>55 ± 5 Index (S/C)) are more prone to hemostasis abnormalities in the post-COVID period since a pronounced imbalance in the levels of SFMCs and D-dimer characterizes them. The appearance of protein fragments of different molecular weights in the fraction of SFMC points to uncontrolled activation of biochemical processes involving molecules of fibrinogenic origin. Additional studies are required to elucidate the role of anti-SARS-CoV-2 IgG in the post-COVID period.

The fibrinolytic system plays an important role in controlling blood coagulation at each stage, from thrombin generation to fibrin clot cleavage. Currently, long-term multiorgan dysfunction post-coronavirus disease 2019 (COVID-19) may include coagulation disorders. Little information is available about the potential causes of post-COVID-19 coagulopathy, but one of them may be subpopulation IgG produced by the immune system against SARS-CoV-2. This article describes the changes in the main parameters of the fibrinolytic system in donors with various titers of anti-SARS-CoV-2 IgG, which is part of a complex study of the hemostasis system in these donor groups. We determined the most significant parameters of the fibrinolytic system, such as potential activity and amount of plasminogen and tissue plasminogen activator (tPA), amount of plasminogen activator inhibitor-1 (PAI-1), inhibitory potentials of α-2-antiplasmin, α-1-antitrypsin, α-2-macroglobulin in the blood plasma of donor groups. The obtained results represent the maximum and minimum values of measurement parameters among donor groups with titers of anti-SARS-CoV-2 IgG at least 10 ± 3 Index (S/C), and their statistical differences from the reference point [donor group with titer of anti-SARS-CoV-2 IgG 0 Index (S/C)]. We established the changes in fibrinolytic parameters depending on the titers of anti-SARS-CoV-2 IgG. One conclusion can be drawn from this: anti-SARS-CoV-2 IgG population may influence coagulation in the post-COVID-19 period. Further research in-vitro and in-vivo experimental models using selected and purified IgG may confirm our previous findings.