Quantitative and qualitative composition of lymphocyte populations and subpopulations in patients with varying severity of a new coronavirus infection

SARS-CoV-2 can cause a decrease in the number of lymphocytes and their functional activity. In patients with COVID-19, especially with a severe course of the disease, a decrease in the quantitative composition of the main populations of lymphocytes is recorded. These indicators do not recover for a long time after recovery. However, it is still not known how long the quantitative and qualitative changes in the composition of lymphocytes will last and whether the severity of the infection affects this process. The aim of our study was to assess the quantitative and qualitative composition of the main populations and subpopulations of lymphocytes in patients with a new coronavirus infection of varying severity. 65 patients with a new coronavirus infection were examined. The average age of the subjects was 47.3±14.5 years. The volunteers were divided into three groups according to the severity of the infection: asymptomatic (n = 21); moderate (n = 32); severe (n = 12). The relative and absolute number of T-lymphocytes (CD3⁺), T-helper cells (CD3⁺CD4⁺), cytotoxic lymphocytes (CD3⁺CD8⁺), natural killers (CD3^–CD16⁺CD56⁺), TNK-lymphocytes (CD3⁺CD16^–CD56⁺) and B-lymphocytes (CD45⁺CD19⁺) were determined. To calculate the percentage of lymphocytes, whole blood was lysed with OPTILYSE C solution (Beckman Coulter, USA) and stained with monoclonal antibodies CD3⁺-FITC/CD8⁺-ECD/CD4⁺-PC5/CD16⁺CD56⁺PE and CD45⁺-Pacific Blue/CD19⁺-PC5 (Beckman Coulter, USA). Cytofluorometry was performed on a flow cytofluorometer “Navios™” (Beckman Coulter, USA). The results of our studies showed that there were no statistically significant changes in the relative and absolute number of immunocompetent cells in asymptomatic patients with a new coronavirus infection, compared with the control group. With an average severity of the disease, a decrease in the relative and absolute content of CD3⁺ and CD8⁺ lymphocytes was revealed, these indicators were restored to control values six months after recovery. In patients with severe infection, there was a decrease in the relative and absolute number of T cells and cytotoxic lymphocytes. These values remained significantly below normal for six months and returned to normal only seven to eight months after recovery. Also, the volunteers of this group were found to have a decrease in the number of natural killers and TNK cells. Thus, the data obtained by us indicate that pathological changes concerning the relative and absolute number of the main populations and subpopulations of lymphocytes in patients with COVID-19 depend on the severity of the disease. The number of T-lymphocytes, cytotoxic lymphocytes, natural killer cells, that is, populations of cells that play a crucial role in effective antiviral protection, has been reduced in those who have undergone a new coronavirus infection in moderate and severe form. This information can be useful for expanding methodological approaches to the diagnosis, treatment of a new coronavirus infection, as well as measures for the rehabilitation of those who have suffered it.