Neutrophil extracellular traps, local IL-8 expression, and cytotoxic T-lymphocyte response in the lungs of fatal COVID-19.
Melero I., Villalba-Esparza M., Recalde-Zamacona B., Jiménez-Sánchez D., Teijeira Á., Argueta A., García-Tobar L., Álvarez-Gigli L., Sainz C., Garcia-Ros D., Toledo E., Abengozar-Muela M., Fernández-Alonso M., Rodríguez-Mateos M., Reina G., Carmona-Torre F., Quiroga JA., Del Pozo JL., Cross A., López-Janeiro Á., Hardisson D., Echeveste JI., Lozano MD., Ho L-P., Klenerman P., Issa F., Landecho MF., de Andrea CE.
BACKGROUND: Excessive inflammation is pathogenic in the pneumonitis associated with severe COVID-19. Neutrophils are among the most abundantly present leukocytes in the inflammatory infiltrates and may form neutrophil extracellular traps (NETs) under the local influence of cytokines. NETs constitute a defense mechanism against bacteria but have also been shown to mediate tissue damage in a number of diseases. RESEARCH QUESTION: Could NETs and their tissue-damaging properties inherent to neutrophil-associated functions play a role in the respiratory failure seen in severe COVID-19 patients and how does this relate to the SARS-CoV-2 viral loads, IL-8 (CXCL8) chemokine expression, and cytotoxic T-lymphocytes infiltrates? STUDY DESIGN AND METHODS: Sixteen immediate post-mortem lung biopsies were methodically analyzed as exploratory and validation cohorts. NETs were quantitatively analyzed by multiplexed immunofluorescence and correlated with local levels of IL-8 mRNA and the density of CD8+ T-cell infiltration. SARS-CoV-2 presence in tissue was quantified by RT-PCR and immunohistochemistry. RESULTS: NETs were found in the lung interstitium and surrounding the bronchiolar epithelium with interindividual and spatial heterogeneity. NET density did not correlate with SARS-CoV-2 tissue viral load. NETs were associated with local IL-8 mRNA levels. NETs were also detected in pulmonary thrombi and in only one out of eight liver tissues. NET focal presence negatively correlated with CD8+ T-cell infiltration in the lungs. INTERPRETATION: Abundant neutrophils undergoing NETosis are found in the lungs of patients with fatal COVID-19, but no correlation is found with viral loads. The strong association between NETs and IL-8 points to this chemokine as a potentially causative factor. The function of cytotoxic T-lymphocytes in the immune responses against SARS-CoV-2 may be interfered with the presence of NETs.