Assessment of neutrophil degranulation intensity and changes in neutrophil phenotype by FCᵧRIIIB expression level in blood of patients with COVID-19 and convalescents

Abstract

Introduction. Disease severity in hospitalized COVID-19 patients correlates with the relative content in the blood of a specific low-density neutrophilic granulocyte (NG) population, whose cells are characterized by reduced granularity, high heterogeneity in the expression of FcᵧRIIIb (CD16) and a tendency to spontaneous autolysis (netosis).The aim of the study was to compare the intensity of NG degranulation and the FcᵧRIIIb expression by these cells in blood of patients with COVID-19 and convalescents.Materials and methods. The blood leukocytes of 40 patients diagnosed with COVID-19, 33 convalescents and 20 healthy donors (control) were examined using flow cytometry. To identify NG (CD16+-granulocytes) and to assess the surface expression of the netosis molecular trigger (FcᵧRIIIb), a single-color reagent of labeled monoclonal antibodies CD16-FITC was used. Immunophenotyping of lymphocytes was performed using two four-color reagents. In addition, cell debris content was determined in each Lyse/No-Wash-stained whole blood sample. The presence of neutrophils at the stage of netosis was confirmed by microscopy. Cytokine production was determined on an automatic enzyme immunoassay analyzer.Results. Against the background of characteristic changes in the lymphocyte subpopulation composition and cytokine production, in blood of COVID-19 patients with acute pneumonia, hypoxia and tachycardia a more intense degranulation of NG (2.6 times), higher degree of CD16 expression heterogeneity (1.8 times) and an increased leukocytolysis intensity (1.6 times) were observed compared to convalescents who have undergone severe and moderate forms of the disease. In convalescents, the degree of differences of these indicators compared to control values varied in concordance with the disease severity.Conclusion. The nature of changes in the parameters studied in COVID-19 patients in the acute phase of the disease and during the period of convalescence confirms the possible mechanism of the development of complications due to an imbalance between the activity of elastase released from NG granules and its plasma inhibitor α1 -antitrypsin.