Immune system status of healthcare professionals after high-risk exposure to SARS-CoV-2

Abstract Background The immunological background responsible for the severe course of COVID-19 and the immune factors that protect against SARS-CoV-2 infection are still unclear. The aim of this study was to investigate immune system status in people with high exposure to SARS-CoV-2 infection. Methods Seventy-one people employed in the observation and infectious diseases unit were qualified for the study between November 2020 and October 2021. Symptomatic COVID-19 was diagnosed in 35 people. Anti-SARS-CoV-2 antibodies were also found in 8 people. Peripheral blood mononuclear cells (PBMCs) and plasma were obtained from all participants (in symptomatic COVID-19 patients approximately one month after infection). PBMC subpopulations were analyzed by flow cytometry, and the concentrations of cytokines and anti-SARS-CoV-2 antibodies were determined by ELISA. Results The percentages of cytotoxic T lymphocytes (CTLs), CD28 + and T helper (Th) cells with invariant T-cell receptors were significantly higher in persons with symptomatic COVID-19 than in those who did not develop symptoms. The following percentages of PBMC populations were significantly lower in symptomatic COVID-19 patients than in asymptomatic people: CTLs in the late stage of activation (CD8 + /CD95 + ), NK cells, regulatory-like Th cells (CD4 + /CTLA-4 + ), and Th17-like cells (CD4 + /CD161 + ). Additionally, persons with anti-SARS-CoV-2 antibodies had a significantly higher lymphocyte count and IL-6 concentration than persons without these antibodies. Conclusion Numerous lymphocyte populations are permanently altered by SARS-CoV-2 infection, and they contribute to the severity of COVID-19. Understanding the immune background of COVID-19 may improve the prevention of this disease by identifying people at risk of a severe course of infection. Trial registration This is a retrospective observational study without a trial registration number.