Infections with SARS-CoV-2 can be asymptomatic, but they can also be accompanied by a variety of symptoms that result in mild to severe coronavirus disease-19 (COVID-19) and are sometimes associated with systemic symptoms. Although the viral infection originates in the respiratory system, it is unclear how the virus can overcome the alveolar barrier, which is observed in severe COVID-19 disease courses. To elucidate the viral effects on the barrier integrity and immune reactions, we used mono-cell culture systems and a complex human chip model composed of epithelial, endothelial, and mononuclear cells. Our data show that SARS-CoV-2 efficiently infected epithelial cells with high viral loads and inflammatory response, including interferon expression. By contrast, the adjacent endothelial layer was neither infected nor did it show productive virus replication or interferon release. With prolonged infection, both cell types were damaged, and the barrier function was deteriorated, allowing the viral particles to overbear. In our study, we demonstrate that although SARS-CoV-2 is dependent on the epithelium for efficient replication, the neighboring endothelial cells are affected, e.g., by the epithelial cytokines or components induced during infection, which further results in the damage of the epithelial/endothelial barrier function and viral dissemination. IMPORTANCE SARS-CoV-2 challenges healthcare systems and societies worldwide in unprecedented ways. Although numerous new studies have been conducted, research to better understand the molecular pathogen-host interactions are urgently needed. For this, experimental models have to be developed and adapted. In the present study we used mono cell-culture systems and we established a complex chip model, where epithelial and endothelial cells are cultured in close proximity. We demonstrate that epithelial cells can be infected with SARS-CoV-2, while the endothelium did not show any infection signs. Since SARS-CoV-2 is able to establish viremia, the link to thromboembolic events in severe COVID-19 courses is evident. However, whether the endothelial layer is damaged by the viral pathogens or whether other endothelial-independent homeostatic factors are induced by the virus is essential for understanding the disease development. Therefore, our study is important as it demonstrates that the endothelial layer could not be infected by SARS-CoV-2 in our in vitro experiments, but we were able to show the destruction of the epithelial-endothelial barrier in our chip model. From our experiments we can assume that virus-induced host factors disturbed the epithelial-endothelial barrier function and thereby promote viral spread.

Clinical observations indicate that COVID-19 is a systemic disease. An investigation of the viral distribution within the human body and its correlation with tissue damage can aid in understanding the pathophysiology of SARS-CoV-2 infection. We present a detailed mapping of the viral RNA in 61 tissues and organs of 11 deceased patients with COVID-19. The autopsies were performed within the early postmortem interval (between 1.5 and 15 hr, mean: 5.6 hr) to minimize the bias due to viral RNA and tissue degradation. Very high viral loads (>104copies/ml) were detected in most patients' lungs, and the presence of intact viral particles in the lung tissue could be verified by transmission electron microscopy. Interestingly, viral RNA was detected throughout various extrapulmonary tissues and organs without visible tissue damage. The dissemination of SARS-CoV-2-RNA throughout the body supports the hypothesis that there is a maladaptive host response with viremia and multiorgan dysfunction.

AbstractClinical observations indicate that COVID-19 is a systemic disease. An investigation of the viral distribution within the human body in correlation to tissue damage can help understanding the pathophysiology of SARS-CoV-2 infection.We present a detailed mapping of viral RNA in 61 tissues and organs of 11 deceased patients with the diagnosis COVID-19. The autopsies were performed within the (very) early postmortem interval (mean: 5.6 hours) to avoid bias due to viral RNA and tissue degradation. Viral loads, blood levels of cytokines, prothrombotic factors as well as macro- and micro-morphology were correlated.Very high (> 104 copies/ml) viral loads were detected in the lungs of most patients and then correlated to severe tissue damage. Intact viral particles could be verified in the lung tissue by transmission electron microscopy. Viral loads in the lymph nodes were associated with a loss of follicular architecture. Viral RNA was detected throughout further extra-pulmonary tissues and organs without visible tissue damage. Inflammatory cytokines as well as the prothrombotic factors were elevated in all patients.In conclusion, the dissemination of SARS-CoV-2-RNA throughout the body supports the hypothesis of a maladaptive host response with viremia and multi-organ dysfunction.

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With each group was placed one of the nonvaccinated control heifers, each group of three occupying an isolated stall. To test the resistance conferred by the vaccine, virulent bovine tubercle bacilli from cultures were weighed in a fresh state and inoculated into 19 5 ' of the heifers, intravenously, in 5-mg doses with the following results: Group I. Vaccinated heifers 1 and 2 and control No. 13 were inoculated 1 month after vaccination. Control No. 13, killed 60 days after inoculation, showed advanced miliary tuberculosis of the lungs. Vaccinated heifer No.2 died of verminous bronchitis 5 months and 7 days after inoculation. No lesions resembling tuberculosis were found. Guinea pigs, inoculated with portions of, the apparently normal left bronchial lymph node, contracted tuberculosis. Vaccinated heifer No.1 remained in good condition and was butchered 12 months after inoculation. No lesions of tuberculosis could be found. Portions of the left bronchial lymph node were injected into 4 guinea pigs. These were killed but no indication of tuberculosis could be found in them. Group II. Vaccinated heifers 3 and 4 and control No. 14 were inoculated 3 months after vaccination. Control No. 14 died of miliary tuberculosis 44 days after inoculation. Vaccinated heifers 3 and 4 remained in good condition. They were slaughtered 11 months after the test inoculation and no tuberculous lesions could be found. Portions of their bronchial lymph nodes were inoculated into guinea pigs. These pigs were killed 45 days after inoculation. Those that had received tissue from heifer No.4 were tuberculous, but those inoculated from No.3 were free from tuberculosis. Calmette(12) in the latest edition of his book L'Infection Baeillaire ei lao tuberculose chez l.'Homme et chez les Animau.x attributes great importance to the observation that the guinea pigs inoculated from heifers 1 and 3 remained free from tuberculosis. In previous experiments he had observed that calves vaccinated by the intravenous route and later inoculated by the same route with virulent bacilli, remained free from caseous lesions, but their apparently normal lymph-node tissue would retain the bacilli virulent for guinea pigs for at least 18 months. The fact that guinea pigs did not contract tuberculosis when injected with tissues from heifers 1 and 3 was interpreted by Calmette to indicate that the subcutaneous injection of BCG is more efficacious than the intravenous method of vaccination. Group III. Vaccinated heifers Nos. 5 and 6 and control No. 15 were inoculated 6 months after vaccination. Control No. 15 became .very emaciated, was killed 60 days after inoculation and was found to 5 Only 19 heifers are accounted for in their descriptions.