Study of Peripheral Blood T-Lymphocytes and Their Subpopulations in COVID-19 Patients.

Objective: To study the characteristic changes in peripheral blood T-lymphocytes and their subpopulations in COVID-19 patients by in-depth characterization of peripheral blood T-lymphocytes and to analyze the changes in the severity of COVID-19 and age factors in relation to changes in T-lymphocytes and their subpopulations. Methods: T-lymphocytes (including Th cells, regulatory T-lymphocytes, CD4+ initial T-lymphocytes, CD4+ memory T-lymphocytes, CD4+ T-lymphocytes functional subsets, Tc cells, CD8+ initial T-lymphocytes, CD8+ memory T-lymphocytes, and CD8+ T-lymphocyte functional subpopulations) were isolated, by flow cytometry, from peripheral blood specimens of 60 COVID-19 patients (experimental group) and 36 healthy controls (control group). The results of the two groups were compared and further analyzed in relation to age and disease severity of COVID-19 patients. Results: The absolute counts of T-lymphocytes and their subpopulations in the peripheral blood of COVID-19 patients were reduced, and the proportions of the cells in each subpopulation were imbalanced, with the absolute counts of T-lymphocytes and their subpopulations in peripheral blood of critically ill patients being lower relative to those of mildly ill patients, and the absolute counts of CD8+ initial T-lymphocytes in the peripheral blood of COVID-19 patients group being negatively correlated with the age of the patients. Conclusion: SARS-CoV-2 infection has an inhibitory effect on the number of T-lymphocytes and the proportion of their subpopulations, especially in critically ill and elderly patients, suggesting that SARS-CoV-2 infection has a serious impact on the cellular immune function of the body, and that in-depth characterization of T-lymphocyte population can more accurately reflect the changes in immune function to assess the state of cellular immune function.