Dynamic changes in monocytes subsets in COVID-19 patients.

Background: Coronavirus disease 2019 (COVID-19) is affecting the whole world and threatening human health. We aim to investigate the immunological characteristics of monocytes in critical patients with COVID-19.

Methods: The number and immune status of monocytes were detected by flow cytometry in 32 COVID-19 patients and 18 healthy individuals.

Results: In critical patients with COVID-19, the absolute number of total monocytes and CD16 monocytes was significantly decreased but CD16 pro-inflammatory monocytes was increased compared to healthy controls. Antigen presentation potential of monocytes, as measured by HLA-DR expression, was suppressed, while their inflammatory phenotype (CD38 expression) was enhanced. Cytokine levels showed sustained increases in critical patients. And the levels of IL-6 were positively correlated with CD16 monocytes number. IL-6 and IL-10 levels were negatively correlated with HLA-DR expression of monocytes. During the recovery of COVID-19 patients, the count and immune status of monocyte subsets were restored by degrees. HLA-DR monocytes possessed good sensitivity and specificity for predicting the incidence of critical patients with COVID-19.

Conclusions: In critical patients with COVID-19, decline in number and HLA-DR expression of monocytes might lead to decreased antigen presentation potential and thus immunosuppression, while increased CD16 pro-inflammatory monocytes might mediate hyperinflammation. HLA-DR monocytes might be a meaningful assisted indicator to predict the incidence of critical patients with COVID-19.