Patients
Fifty confirmed COVID-19 patients including 8 severe patients on ventilation, 29 severe non-ventilated and 13 moderate patients were participated into the study upon admission to the Masih Daneshvari Hospital of Shahid Beheshti Medical University (Tehran-Iran) b etween 10th April 2020- 9th March, 2021. All patients were diagnosed as stated by World Health Organization interim guidance (17). The patients with severe COVID-19 was confirmed by at least one of the following creteria: respiratory rate≥30/min; blood oxygen saturation ≤93%; ratio of partial pressure of oxygen in arterial blood to the inspired oxygen fraction (PaO2FiO2) < 300; lung infiltrates present on>50% of the lung field (18). Eight healthy age-matched controls were also recruited. This study was approved by Masih Daneshvari Hospital ethical committee (IR.SBMU.NRITLD.REC.1399.122).
Data collection
The clinical records of patients were collected from electronic medical records from Masih Daneshvari Hospital. The information recorded included demographic data, medical history, underlying comorbidities, symptoms, signs, laboratory findings; chest computed tomographic (CT) scans, and treatment measures including antiviral therapy, corticosteroid therapy, respiratory support and kidney replacement therapy.
Laboratory examination of blood samples
Whole blood samples containing anti-coagulant EDTA (3ml) and with citrate (3ml) or no anticoagulant (3ml) were obtained from all participants upon admission. Tubes containing blood without anticoagulant were centrifuged, the serum separated and stored at -80°C for IL-8 measurement. Serum tests including kidney and liver function tests: creatinine kinase-muscle/brain activity (CK-MB), lactate dehydrogenase (LDH), C-reactive protein (CRP), ferritin, creatine phosphokinase (CPK), and the international normalized ratio (INR) were also performed. The erythrocyte sedimentation ratio was determined in citrate-treated whole blood samples.
Cell staining and flow cytometry
Three ml whole blood in EDTA were obtained from all participants and MDSCs were analysed by flow cytometry (FACS Calibour, BD, USA). Briefly, blood samples were then stained with anti-CD11b APC (BD Biosciences, CA, USA), anti-HLA-DR PE (eBioscience, San Diego, CA, USA), anti-CD14 PerCP-cy5.5 (eBioscience) and anti-CD15 FITC (BD Biosciences) for 30 min in the dark as described before (19, 20). Cells were then washed and suspended in FACS buffer before 20,000 events were analysed by FACS. The gating strategy was CD11b+/HLA-DR-/dim and within this population CD14+/CD15- cells and CD14-/CD15+ were identified as described previously (19, 20). Flow cytometry data was subsequently analysed by FlowJO-V10 software (USA) and reported as the frequency (percentage) of the respective subset of leukocytes.
Measurement of IL-8
Serum concentrations of IL-8 were measured by linked immunosorbent assay (ELISA) (BD Biosciences, CA, USA) as described in manufacturer data sheet.
Statistical analysis
Data analysis was performed using the SPSS software version 16.0 and Graph Pad Prism software version 6 . Results were reported as the mean ± standard deviation (SD). The measurement data between two groups were analyzed using Student’s t-test. The non-parametric Mann-Whitney U test was used for non-normally distributed variables. Difference among multiple groups was compared using one‑way analysis of variance (ANOVA), p<0.05 was considered as statistically significant.