The kallikrein-kinin system in bronchoalveolar lavage fluid from patients with COVID-19

Background : Markers of both inflammation and coagulation are linked to clinical outcome in coronavirus disease 2019 (COVID-19). Binding of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to the angiotensin-converting enzyme 2 receptor, which is involved in kinin breakdown, interferes with the kallikreinkinin pathway. This could result in increased vascular permeability, fluid excess in the lungs and pulmonary edema. Furthermore, the kallikrein-kinin pathway links coagulation and inflammation through its interactions with the contact activation pathway of coagulation via factor XII and with neutrophil extracellular traps (NETs). These insights could help to explain the clinical presentation of COVID-19 pneumonia with pulmonary coagulopathy and the high incidence of thromboembolic complications in COVID-19. Aims : Given the lack of clinical evidence to support this hypothesis, we studied the kallikrein-kinin system in bronchoalveolar lavage (BAL) fluid. Methods : In BAL fluid samples from patients with or without COVID-19, we performed in-depth analyses of kinin peptides (bradykinin, Lys-bradykinin, Lys-bradykinin-(1-8), bradykinin-(1-8), bradykinin-(1-7), and bradykinin-(1-5)) using a liquid chromatography with tandem mass spectrometry assay, along with measurements of plasma and tissue kallikrein hydrolytic activity and myeloperoxidase (MPO)-DNA complexes as a biomarker for NETs. Informed consent and ethical approval were obtained. Results : We observed higher levels of the most downstream kinin peptide bradykinin-(1-5) (Figure 1), higher tissue kallikrein activity (Figure 2), and higher levels of MPO-DNA complexes (699.0 ng/mL [66.0-142621.0], median [range], n = 21 vs 70.5 [9.9-960.0], n = 19;P < 0.001) in BAL fluid from patients with COVID-19 compared to those in BAL fluid from patients without COVID-19. Conclusions : Our data support the hypothesis that SARS-CoV-2 induces dysregulation of the kallikrein-kinin system, which contributes to thromboinflammation in COVID-19. These findings encourage the investigation of drugs that target the kallikrein-kinin system as a potential treatment option for patients with COVID-19.

Monocyte-driven atypical cytokine storm and aberrant neutrophil activation as key mediators of COVID-19 disease severity.

Epidemiological and clinical reports indicate that SARS-CoV-2 virulence hinges upon the triggering of an aberrant host immune response, more so than on direct virus-induced cellular damage. To elucidate the immunopathology underlying COVID-19 severity, we perform cytokine and multiplex immune profiling in COVID-19 patients. We show that hypercytokinemia in COVID-19 differs from the interferon-gamma-driven cytokine storm in macrophage activation syndrome, and is more pronounced in critical versus mild-moderate COVID-19. Systems modelling of cytokine levels paired with deep-immune profiling shows that classical monocytes drive this hyper-inflammatory phenotype and that a reduction in T-lymphocytes correlates with disease severity, with CD8+ cells being disproportionately affected. Antigen presenting machinery expression is also reduced in critical disease. Furthermore, we report that neutrophils contribute to disease severity and local tissue damage by amplification of hypercytokinemia and the formation of neutrophil extracellular traps. Together our findings suggest a myeloid-driven immunopathology, in which hyperactivated neutrophils and an ineffective adaptive immune system act as mediators of COVID-19 disease severity.