Neutrophil Extracellular Traps Contribute to COVID-19 Hyperinflammation and Humoral Autoimmunity

Abstract

The coronavirus disease 2019 (COVID-19) is related to enhanced production of NETs, and autoimmune/autoinflammatory phenomena. We evaluated the proportion of low-density granulocytes (LDG) by flow cytometry, and their capacity to produce NETs was compared with that of conventional neutrophils. NETs and their protein cargo were quantified by confocal microscopy and ELISA. Antinuclear antibodies (ANA), anti-neutrophil cytoplasmic antibodies (ANCA) and the degradation capacity of NETs were addressed in serum. MILLIPLEX assay was used to assess the cytokine levels in macrophages’ supernatant and serum. We found a higher proportion of LDG in severe and critical COVID-19 which correlated with severity and inflammatory markers. Severe/critical COVID-19 patients had higher plasmatic NE, LL-37 and HMGB1-DNA complexes, whilst ISG-15-DNA complexes were lower in severe patients. Sera from severe/critical COVID-19 patients had lower degradation capacity of NETs, which was reverted after adding hrDNase. Anti-NET antibodies were found in COVID-19, which correlated with ANA and ANCA positivity. NET stimuli enhanced the secretion of cytokines in macrophages. This study unveils the role of COVID-19 NETs as inducers of pro-inflammatory and autoimmune responses. The deficient degradation capacity of NETs may contribute to the accumulation of these structures and anti-NET antibodies are related to the presence of autoantibodies.

NETosis and Neutrophil Extracellular Traps in COVID-19: Immunothrombosis and Beyond

“…Furthermore, LDGs are prone to NETosis and NET formation, thereby contributing to COVID-19-related immunothrombosis and organ injury ( 26 ). Additional research has shown that a subset of immature (low CD10 expression, CD10 low ) LDGs display reduced capacity to produce NET and robust immunosuppressive capabilities that resemble myeloid-derived suppressor cells ( 27 ). In contrast, mature LDGs with higher CD10 and CD16 expression seem to be preferentially enhanced in COVID-19 and are more prone to NETosis and NET production ( 24 , 27 ).…”

“…Additional research has shown that a subset of immature (low CD10 expression, CD10 low ) LDGs display reduced capacity to produce NET and robust immunosuppressive capabilities that resemble myeloid-derived suppressor cells ( 27 ). In contrast, mature LDGs with higher CD10 and CD16 expression seem to be preferentially enhanced in COVID-19 and are more prone to NETosis and NET production ( 24 , 27 ). For example, a unique LDG subset with intermediate expression of CD16 (CD16 int ) was clearly observed in COVID-19 patients.…”

Low-Density Granulocytes in Immune-Mediated Inflammatory Diseases

“…LDGs have been found to suppress the proliferation of autologous T cells in ex vivo assays and may contribute to lymphopenia and impaired immune response during severe SARS-CoV-2 infection [ 77 , 78 , 80 ]. Nonetheless, LDGs from severe COVID-19 patients, especially LDGs with intermediate CD16 expression (CD16 int LDGs), have been found to be prone to form NETs and aggregate with platelets, which promote alveolar cell apoptosis and thrombogenic coagulopathy [ 81 , 82 ]. Moreover, anti-NET antibodies have been identified in severe COVID-19 patients and display correlation with antinuclear antibody and ANCA positivity, suggesting autoimmune response induced by NETs [ 81 ].…”

“…Nonetheless, LDGs from severe COVID-19 patients, especially LDGs with intermediate CD16 expression (CD16 int LDGs), have been found to be prone to form NETs and aggregate with platelets, which promote alveolar cell apoptosis and thrombogenic coagulopathy [ 81 , 82 ]. Moreover, anti-NET antibodies have been identified in severe COVID-19 patients and display correlation with antinuclear antibody and ANCA positivity, suggesting autoimmune response induced by NETs [ 81 ]. These finds indicate that LDGs impede antiviral responses of T lymphocytes but boost aberrant hyperinflammation and autoimmunity in severe COVID-19 patients.…”

Cellular Immunology and COVID-19

“…A higher proportion of low-density granulocytes in severe and critical COVID-19 and their capacity to produce NETs correlated with severity and inflammatory markers. As defined by Jiram Torres-Ruiz et al, the sera from severe/critical COVID-19 patients had a lower degradation capacity of NETs and anti-NET antibodies and were related to the presence of ANA and ANCA autoantibodies [ 6 ]. Moreover, the cytokine hyper activation in COVID-19 appears to be similar to that seen in rheumatoid arthritis, shedding light on the pathological crosstalk between COVID-19 and rheumatoid arthritis, and the aspects of SARS-CoV-2 infection in RA development [ 7 ].…”