Functional exhaustion of antiviral lymphocytes in COVID-19 patients

Cytotoxic lymphocytes such as Cytotoxic T Lymphocytes (CTLs) and Natural Killer (NK) cells are necessary for the control of viral infection, and the functional exhaustion of cytotoxic lymphocytes is correlated with disease progression.

A new study shows that the total number of NK and CD8+ T cells was decreased markedly in patients with SARS-CoV-2 infection. The function of NK and CD8+ T cells was exhausted with the increased expression of NKG2A in COVID-19 patients. Importantly, in patients convalescing after therapy, the number of NK and CD8+ T cells was restored with reduced expression of NKG2A. These results suggest that the functional exhaustion of cytotoxic lymphocytes is associated with SARS-CoV-2 infection. Hence, SARS-CoV-2 infection may break down antiviral immunity at an early stage.

In the studied cohort of 68 COVID-19 patients admitted to The First Affiliated Hospital (Hefei) and Fuyang Hospital (Fuyang), both of which are part of Anhui Medical University in China, there were 55 cases of Mild Disease (MD) and 13 cases of Severe Disease (SD). Patients were aged 11–84 years, and the median age of patients was 47.13 years. The percentage of male patients was 52.94%. Consistent with previous studies, many patients had fever (80.88%), cough (73.53%), and sputum (32.36%) upon admission. The prevalence of other symptoms (e.g., headache, diarrhea) was relatively low.

Upon admission, the neutrophil count was remarkably higher in SD patients than in MD cases, whereas the lymphocyte count was significantly lower in SD cases than in MD cases. The concentration of Total Bilirubin (TB), D-dimer, and Lactate Dehydrogenase (LDH) in blood was higher in SD patients than that in MD patients. Levels of Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST) were slightly higher in SD cases than those in MD cases. Levels of albumin and hemoglobin were lower in SD patients than those in MD patients. Specifically, T cell and CD8+ T cell counts were decreased significantly in MD and SD patients compared with those in Healthy Controls (HCs). The number of T cells and CD8+ T cells was significantly lower in SD patients than that in MD cases. The counts of NK cells were reduced remarkably in SD patients compared with those in MD cases and HCs.

Link to the paper: https://doi.org/10.1038/s41423-020-0402-2

Editorial Disclaimer: information published during the 2020 COVID-19 pandemic may be updated frequently to reflect the dynamic nature of current understanding.

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