Regulatory CD4 and CD8 T cells are negatively correlated with CD4 /CD8 T cell ratios in patients acutely infected with SARS-CoV-2.

Regulatory T cell can protect against severe forms of coronaviral infections attributable to host inflammatory responses. But its role in the pathogenesis of COVID-19 is still unclear. In this study, frequencies of total and multiple subsets of lymphocytes in peripheral blood of COVID-19 patients and discharged individuals were analyzed using a multicolor flow cytometry assay. Plasma concentration of IL-10 was measured using a microsphere-based immunoassay kit. Comparing to healthy controls, the frequencies of total lymphocytes and T cells decreased significantly in both acutely infected COVID-19 patients and discharged individuals. The frequencies of total lymphocytes correlated negatively with the frequencies of CD3 CD56 NK cells. The frequencies of regulatory CD8 CD25 T cells correlated with CD4 /CD8 T cell ratios positively, while the frequencies of regulatory CD4 CD25 CD127 T cells correlated negatively with CD4 /CD8 T cell ratios. Ratios of CD4 /CD8 T cells increased significantly in patients beyond age of 45 years. And accordingly, the frequencies of regulatory CD8 CD25 T cells were also found significantly increased in these patients. Collectively, the results suggest that regulatory CD4 and CD8 T cells may play distinct roles in the pathogenesis of COVID-19. Moreover, the data indicate that NK cells might contribute to the COVID-19 associated lymphopenia.