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. [ABSTRACT FROM AUTHOR]