Myeloid-derived suppressor cells in the blood of COVID-19 patients

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<b>Background:</b> The pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains unknown but may be associated with a cytokine storm and inflammatory cell defects. Myeloid-derived suppressive cells (MDSCs) exist in two forms, granulocyte (G-MDSCs) and monocytic (M-MDSCs) that both suppress T-cell function. <b>Objective:</b> To determine serum MDSCs in severe and mild COVID-19 patients and correlate this with levels of the chemoattractant CXCL-8. <b>Methods:</b> 31 confirmed COVID-19 patients: 29 with severe disease including 4 on a ventilator, and 8 healthy control subjects were enrolled at Masih Daneshvari Hospital, Tehran between 10th April- 9th May 2020. Standard clinical and biochemical features, serum and peripheral blood mononuclear cells (PBMCs) were collected. The surface expression of CD14, CD15, CD11b and HLA-DR on MDSCs was measured by flow cytometry. <b>Results:</b> The percentage of M-MDSCs and G-MDSCs was higher in COVID-19 subjects than in healthy control subjects (P≤0.0001) with no difference between COVID-19 severity or ventilator status. Serum CXCL-8 levels were greater in patients with COVID-19 than in healthy control subjects and greater in ventilated compared with non-ventilated patients (P=0.012). Serum CXCL-8 levels were similar in mild and severe COVID-19 patients. G-MDSC percentages correlated positively with CRP levels (r=0.44, P=0.01) but negatively with internal normalized ratio and age (r=-0.47, P=0.006; r=-0.36, P=0.03). The frequency of M-MDSCs was negatively correlated with O2 saturation (r = -0.54, P = 0.002). <b>Conclusion:</b> Increased serum CXCL-8 levels in COVID-19 patients may lead to the expansion and recruitment of MDSC cells in blood and be associated with poor clinical outcomes.