The role of effector T cells in the course of COVID-19 in different waves of the pandemic

The coronavirus pandemic has become the most serious global health threat and greatest challenge to the human population this century. The search for simple and quick diagnostic methods to assess immunological status of patients infected with the SARS-CoV-2 virus is ongoing. The aim of our study was to evaluate lymphocyte subpopulations with determination of their effector and memory nature in patients from the 1st coronavirus disease 2019 (COVID-19) wave (n = 23) and the 5th COVID-19 wave (n = 38) and to compare them with a healthy control group (HC) (n=20), using panel of monoclonal antibodies by multiparameter flow cytometry methods. We determined lymphocytes population (lymphocytes T, B and NK cells), and subpopulation of CD4 and CD8 lymphocytes T (effector, central memory and effector memory) in patients with COVID-19 and HC. Compared to the control group, profound lymphopenia was observed in both groups of patients with COVID-19. Additionally, both the percentages and absolute numbers of CD4 and CD8 cells were decreased. The percentages of effector and central memory T CD4 and CD8 cells did not differ between the study groups. The effector memory CD4 and CD8 cells was the highest in the 5th wave in relation to 1st wave group as well as HC (for CD4 cells respectively, 14.1 vs. 23,2 vs. 12,5%, p< 0.05 and CD8 cells respectively, 18.1 vs. 35.1 vs. 19.3%, p< 0.05). Our results showed a marked increase in the number of effector memory T cells in the fifth wave of COVID-19. Monitoring effector lymphocytes during infection allows the assessment of the patient's immune status, the readiness of lymphocytes for an immune response, and may be necessary to improve clinical outcomes.