Decreased T cell populations contribute to the increased severity of COVID-19

Background: We observe changes of the main lymphocyte subsets (CD16(+)CD56.CD19, CD3, CD4, and CD8) in COVID-19-infected patients and explore whether the changes are associated with disease severity. Methods: One-hundred and fifty-four cases of COVID-19-infected patients were selected and divided into 3 groups (moderate group, severe group and critical group). The flow cytometry assay was performed to examine the numbers of lymphocyte subsets. Results: CD3(+), CD4(+) and CD8(+) T lymphocyte subsets were decreased in COVID-19-infected patients. Compared with the moderate group and the sever group, CD3(+), CD4(+) and CD8(+) T cells in the critical group decreased greatly (P < 0.001, P = 0.005 or P = 0.001). Conclusions: Reduced CD3(+), CD4(+), CD8(+) T lymphocyte counts may reflect the severity of the COVID-19. Monitoring T cell changes has important implications for the diagnosis and treatment of severe patients who may become critically ill.