Pneumonia is the leading cause of death in patients with COVID-19 infection and disproportionately affects older individuals. In addition to the diffuse patchy alveolar infiltrates and acute hypoxemic respiratory failure typical of viral pneumonia, patients with COVID-19 often develop hypotension requiring alpha-adrengergic agonists, very high serum levels of IL-6 and its transcriptional target C-Reactive Protein (CRP) and display evidence of intravascular coagulation. This is accompanied by the death of cells in multiple tissues including the kidney, muscle, liver and occasionally the heart. This end-organ injury is an important driver of morbidity and perhaps mortality in COVID-19 patients. These unusual clinical features suggest a virus-induced cytokine storm, but the underlying mechanisms are unknown and these clinical features are not recapitulated in rodent or primate models of the disease.Our early analysis of bronchoalveolar lavage fluid collected from the alveolar space of patients with severe COVID-19 pneumonia requiring mechanical ventilation challenge the existing paradigm that IL-6 originates in immune cells within the alveolar space. Specifically, we found that at the time of intubation, the alveolar space in the majority of patients with severe COVID-19-induced ARDS harbors mature alveolar macrophages and lymphocytes none of which produce IL-6. Instead, a subset of resident alveolar macrophages produce IL-1? and appear to support replication of SARS-CoV-2.We hypothesize that disordered proteostasis in alveolar macrophages from aged individuals prevents viral killing after uptake of SARS- CoV-2. Replicating virus activates the inflammasome to induce IL-1? release in the lung, which in turn induces the release of IL-6 from endothelial cells in the lung and distant organs. We will test this hypothesis in two related experiments. Experiment 1. To determine whether activation of the inflammasome in response to COVID- 19 infection is necessary for the release of IL-6 from the lung endothelium. We will infect lung slices from normal human donors with SARS-CoV-2 in the presence or absence of an IL-1? inhibitor that is under evaluation as a therapy for patients with COVID-19 associate pneumonia (canakinumab). We will examine the lung slices after infection using single cell RNA-Seq and RNAscope. Experiment 2. To determine whether endothelial cells in tissues outside the lung express IL6 in patients with severe COVID-19. We will perform RNAscope on fixed tissues harvested from 9 patients who have undergone autopsy after COVID-19 at Northwestern and RNAscope plus single cell RNA-Seq on lung, kidney, spleen and lymph nodes from 5 patients who undergo post- mortem biopsy in our ICU.
Pneumonia is the leading cause of death in patients with COVID-19 infection and disproportionately affects older individuals. Increased levels of inflammatory biomarkers, such as IL-6, are causally linked to mortality and morbidity in patients with severe COVID-19 and are actively being targeted in clinical trials. In this application using samples from patients with COVID-19 we will identify cellular sources of these cytokines in the lung and distant organs and evaluate the role of age-related proteostatic dysfunction in macrophage activation in response to SARS-CoV-2 infection.
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