To discover immune factors that can predict the progression of COVID-19, we evaluated circulating immune cells and plasma cytokines in COVID-19 patients. We found that T cells, including CD4 + T cells and CD8 + T cells, were significantly decreased in severe COVID-19 symptoms but not in mild symptoms, in comparison with healthy people. T cells remained at a low level after recovery from severe COVID-19. CD4 + CD25 + CD127 low Treg-enriched cells were significantly increased in either mild or severe COVID-19 patients, regardless of recovery or not. Moreover, in either mild or severe COVID-19 patients, Treg-enriched cells up-regulated CD25 and down-regulated CD127. After recovery, CD25 was partially down-regulated but still higher than the normal level, while CD127 returned to the normal level in mild patients but not severe patients. B cells were decreased in mild patients and further decreased in severe patients, and remained low after recovery. NK cells were decreased only in severe COVID-19, with a tendency to return to the normal level after recovery. Plasma IL-6 and IL-10 were both elevated in severe patients but not in mild patients. After recovery, IL-6 remained higher than its normal level, while IL-10 returned to the normal level. Binary logistic regression analysis indicated that CD4 + T cells, B cells, IL-6, and IL-10 were significantly associated with COVID-19 severity. Therefore, these parameters are indicators of COVID-19 severity. Dynamic monitoring of these parameters would benefit therapy planning and prognosis evaluation.

Zebrafish have emerged as an attractive animal model for studying nonalcoholic fatty liver disease (NAFLD). However, little is known about the cell types and intercellular interactions in zebrafish liver. Here, we established a liver atlas that consists of 10 cell types using single-cell RNA sequencing. By examining the heterogeneity of hepatocytes and analyzing the expression of NAFLD-associated genes in the specific cluster, we provide a potential target cell model to study NAFLD. Additionally, our analysis identified two distinct resident macrophages with inflammatory and noninflammatory functions and characterized the successive stepwise development of T cell subtypes in the liver. Importantly, we uncovered possible molecular mechanisms and revealed the central regulation of macrophages on target cells of fatty liver by analyzing the cellular interaction between hepatocytes and immune cells. Our data provide valuable information for future research on NAFLD in zebrafish.