Quantitative and qualitative alterations of circulating myeloid cells and plasmacytoid DC in SARS‐CoV‐2 infection

Abstract

SARS-CoV-2 is responsible for a new infectious disease (COVID-19) in which individuals can either remain asymptomatic or progress from mild to severe clinical conditions including acute respiratory distress syndrome and multiple organ failure. The immune mechanisms that potentially orchestrate the pathology in SARS-CoV-2 infection are complex and only partially understood. There is still paucity of data on the features of myeloid cells involved in this viral infection. For this reason, we investigated the different activation status profiles and the subset distribution of myeloid cells and their correlation with disease progression in 40 COVID-19 patients at different stages of disease. COVID-19 patients showed a decrease in the absolute number of plasmacytoid and myeloid dendritic cells, different subset distribution of monocytes and different activation patterns of both monocytes and neutrophils, coupled to a significant reduction of HLA-DR monocyte levels. We found that some of these alterations are typical of all COVID-19 patients, while some others vary at different stages of the disease and correlate with biochemical parameters of inflammation. Collectively, these data suggest that not only the lymphoid, but also the myeloid compartment, is severely affected by SARS-CoV-2 infection.

Monocyte HLA‐DR Measurement by Flow Cytometry in COVID‐19 Patients: An Interim Review

“…We identified four additional articles specifically reporting on mHLA‐DR measurement at hospital admission (23–26). Patients presented with various levels of severity, and routine flow cytometry was performed and results were expressed as means of fluorescence intensities (for the total CD14+ monocyte population) meaning that results cannot be strictly compared between centers.…”

“…Moreover, Moratto et al also observed that, among severe patients, those who progressed to a critical status (admission to ICU) had the lowest expression (23). In addition, as mentioned above, in COVID-19 patients, the proportion of non-classical monocytes (CD14 low CD16+) was lower than in controls (23,25).…”

“…We identified four additional articles specifically reporting on mHLA-DR measurement at hospital admission (23)(24)(25)(26).…”

The central role of the nasal microenvironment in the transmission, modulation, and clinical progression of SARS-CoV-2 infection

“…The proportions of these three subsets in the circulation of healthy individuals are well defined, although an expansion of inflammatory monocytes has been described in autoimmunity and chronic inflammation. 82 Accumulating data have shown that proportions of monocyte subsets are altered in COVID-19, 83,84 together with a significant downregulation of monocyte HLA-DR expression. 83,85,86 In addition to monocytes, DCs are another innate cell population with a crucial role in nasal immunity.…”

“…82 Accumulating data have shown that proportions of monocyte subsets are altered in COVID-19, 83,84 together with a significant downregulation of monocyte HLA-DR expression. 83,85,86 In addition to monocytes, DCs are another innate cell population with a crucial role in nasal immunity. 87 Two subsets of DCs have been described: plasmacytoid DCs (pDCs), which rapidly respond to viral infections secreting high amounts of type I and III IFNs, and myeloid DC (mDC), which act as sentinels ready to stimulate T cells.…”