Changes in the cytotoxic and regulatory functions of NK cells in patients with long-COVID under the influence of the human herpesvirus 6 (pilot study)

Long-COVID are often accompanied by the development of autoimmun disorders. Such dysregulation of the immune system can be caused by reactivation of "sluggish" herpesvirus infection in patients after COVID-19. The one of the possible causes of autoimmunization is a change in the cytotoxic functions of NK cells under the influence of HHV6. The aim of research was to study the expression of receptor-ligand Fas-FasL, regulating marker CD38 and inhibitory receptor TIM-3 on NK cells in patients with long-COVID after mild, moderate, and severe stage of COVID-19 in the anamnesis with or without reactivation of HHV-6 and to identify risk factors for the formation of autoimmune disorders in these patients. This study investigated 124 adults (73 female and 51 male) aged 18 to 65 years with long-COVID. The groups of patients with long-COVID were divided depending on mild, moderate, and severe forms of COVID-19 in the anamnesis and with/without reactivation of HHV-6. The control group included 20 healthy participants. Molecular genetic studies (PCR) were performed for all patients to detect the existence of DNA HHV6. Multiparametric flow cytometry was performed on 124 EDTA peripheral blood samples collected from long-COVID patients and 20 healthy controls. There was defined an imbalance between acute antiviral mechanisms, the response contributing to tissue damage and immunopathology, probably autoimmunity in patients with long-COVID after different forms of COVID-19 with reactivation of HHV-6. The presence of HHV-6 in groups with long-COVID was accompanied by higher expression of FasL and CD38, especially in patients, who had a severe form of COVID-19 in the anamnesis. The decrease in TIM-3 in patients with reactivation of HHV-6 compared to patients without HHV-6 puts the preservation of immunological tolerance at risk of Th1-dependent immune responses. The reactivation of HHV-6 is accompanied by higher expression of FasL and CD38, which indicates increased hyperactivation of NK cells, their cytotoxic activity, and subsequent exhaustion. NK cells of these patients lose their immunoregulatory ability, this creates prerequisites for the development of immunopathology, probably autoimmune processes.