LAUSR

Background Since Dec. 2019, the COVID-19 pandemic has been an outbreak. T cells play an important role in dealing with various disease-causing pathogens. However, the role of T cells played in COVID-19 patients is still unknown. Our study aimed to describe the immunologic state of the critically ill COVID-19 patients. Methods A total of 63 patients with confirmed COVID-19 pneumonia were admitted to the Department of Intensive Care Unit of the First Affiliated Hospital of Harbin Medical University. The immunologic characteristics (lymphocyte apoptosis, the expression of PD-1 and HLA-DR in T cells, T cell subset levels, redistribution and the production of inflammatory factors) as well as their laboratory parameters were compared between severe group and critical group. Results The level of T cells in peripheral blood was decreased in critical patients compared with that in severe patients, but the expression levels of PD-1 (CD4+: 24.71% VS 30.56%; CD8+: 33.05% VS 32.38%) and HLA-DR (T cells: 36.28% VS 27.44%; monocytes: 20.58% VS 23.83%) in T cells were not significantly changed, and apoptosis and necrosis were not different in lymphocytes (apoptosis: 1.04% VS 1.27%; necrosis: 0.67% VS 1.11%), granulocytes, or monocytes between those two groups. Conclusion There is severe immunosuppression in critically ill COVID-19 patients. Redistribution of T cells might be the main reason for lymphocytic decline. Decreasing the infiltration of T lymphocytes in the lung may be beneficial for the treatment of COVID-19.