SARS-CoV-2 uses ACE2, an inhibitor of the Renin-Angiotensin-Aldosterone System (RAAS), for cellular entry. Studies indicate that RAAS imbalance worsens the prognosis in COVID-19. We present a consecutive retrospective COVID-19 cohort with findings of frequent pulmonary thromboembolism (17%), high pulmonary artery pressure (60%) and lung MRI perfusion disturbances. We demonstrate, in swine, that infusing angiotensin II or blocking ACE2 induces increased pulmonary artery pressure, reduces blood oxygenation, increases coagulation, disturbs lung perfusion, induces diffuse alveolar damage, and acute tubular necrosis compared to control animals. We further demonstrate that this imbalanced state can be ameliorated by infusion of an angiotensin receptor blocker and low-molecular-weight heparin. In this work, we show that a pathophysiological state in swine induced by RAAS imbalance shares several features with the clinical COVID-19 presentation. Therefore, we propose that severe COVID-19 could partially be driven by a RAAS imbalance.

Immunodeficiency disorders have provided much information on the development and interaction of the various B and T lymphoid components in the immune system of man. As the lymphoid system becomes increasingly divided into functional subsets of cells it will be important to find immunodeficiencies affecting newly discovered cell types. Natural killer (NK) cells are a recently described but ill-defined subpopulation of lymphocytes which is thought to play an important part in surveillance against tumour development. Mice homozygous for the beige gene were found to have a selective deficiency in NK function and were more susceptible to transplantation of syngeneic tumours as predicted. We report here that patients carrying the analogous, autosomal recessive Chediak-Higashi (CH) gene have a profound defect in their ability to spontaneously lyse various tumour cells in vitro by either antibody-dependent or independent mechanisms. Since other cell-mediated cytolytic functions were relatively normal, these results suggest that the beige or Chediak-Higashi gene in both man and mouse controls NK function.

We have previously observed that a point mutation on chromosome 13 in the mouse, called beige, leads to a marked, selective impairment in natural-killer (NK) acell function (1). Because beige mice have long been used as an animal model of the Ch~diak-Steinbrinek-Higashi syndrome (C-HS) in man (2) it seemed relevant to assess NK function in humans who bear this rare, autosomal recessive gene. Because of the marked propensity of C-HS patients for developing lymphoproliferative disorders that may be malignant (3) it was predicted that if NK cells in the human were important in immune surveillance, then C-H patients might have low levels of NK activity.In this present paper we show that NK activity in two C-HS donors was profoundly impaired and did not appear to be a result of an alteration of an anti-target selectivity pattern or of the kinetics of lysis, of suppressor cells, of a lack of ability to respond to interferon, or of a lack of target-cell recognition. In the accompanying paper (4) we show that antibody-dependent cell-mediated cytotoxicity against tumor-cell targets is also depressed in C-HS patients with cytolytic activity by monocytes, by polymorphonuclear leukocytes, and by T cells that are relatively normal. Materials and MethodsSubjects. Two male patients, Le. R. (age 26 yr), and La. R. (age: 28 yr), siblings from a consanguinous marriage, and eight different age-and sex-matched normal controls were studied in parallel experiments on three separate occasions over a l-mo period. The detailed clinical history and many previous experiments on these particular patients has been described (5-7). At the time of study the patients were free of overt infections and were not on therapy.

In the preceding (1) paper we showed that human Ch6diak-Steinbrinck-Higashi syndrome (C-HS) 1 donors had a marked impairment in natural-killer (NK)-cell function. It was then relevant to ask whether this defect was selective for NK cells as previously observed in the mouse C-HS model (2) or whether other effector-cell types were also defective. Because the C-HS is thought to involve a single recessive gene (3), it was hoped that these experiments would help clarify the relationship between NK cells and a variety of other cell types capable of lysing tumor-cell targets, including K cells involved in antibody-dependent cell-mediated cytotoxicity (ADCC), T cells, monocytes, and neutrophils. In this paper, we show that lymphocyte-mediated ADCC against tumor-cell targets is also defective, whereas ADCC mediated by both mononuclear cells and polymorphonuclear leukocytes (PMN) against erythrocyte targets is normal. Cytolysis of tumor cells by other effectors (T cells, monocytes, and PMN) was also relatively normal. These results suggest that C-HS patients may have a quite selective impairment in immunologic function. The implication of these findings for immune surveillance is discussed.

SARS-CoV-2 enters the cell through the ACE2 receptor, which is considered one of the main inhibitors in the Renin-Angiotensin-Aldosterone System (RAAS).1​ ,2 The virus has been shown to downregulate the ACE2 receptor, leading to a subsequent increase in the vasopressoragentangiotensinII.3​ Evidently,criticalcoronavirusdisease2019(COVID-19)is thought to be due to a dysregulated immune response, causing a cytokine-release syndrome eventually leading to acute respiratory distress syndrome (ARDS).4​ ,5 ​However, several reports on clinical laboratory features and case-descriptions of critically ill patients with COVID-19 show discrepancies compared to typical ARDS. Here, we show that infusing swines with angiotensin II induces a pathophysiological syndrome closely resembling that of patients with RT-PCR-positive COVID-19. By using multimodal clinical imaging of patients, comparing laboratory data and translational histological features, we show that it is highly likely that an increase in RAAS is one, if not the main, pathogenic feature in critical COVID-19. Furthermore, it is plausible that this large animal model can be used to screen for potential new treatments for patients with severe COVID-19 and that MRI lung perfusion can be used to evaluate the outcome of potential treatments targeting the pathophysiological syndrome.

SARS-CoV-2 enters the cell through the ACE2 receptor, which is considered one of the main inhibitors in the Renin-Angiotensin-Aldosterone System (RAAS).1​ ,2 The virus has been shown to downregulate the ACE2 receptor, leading to a subsequent increase in the vasopressoragentangiotensinII.3​ Evidently,criticalcoronavirusdisease2019(COVID-19)is thought to be due to a dysregulated immune response, causing a cytokine-release syndrome eventually leading to acute respiratory distress syndrome (ARDS).4​ ,5 ​However, several reports on clinical laboratory features and case-descriptions of critically ill patients with COVID-19 show discrepancies compared to typical ARDS. Here, we show that infusing swines with angiotensin II induces a pathophysiological syndrome closely resembling that of patients with RT-PCR-positive COVID-19. By using multimodal clinical imaging of patients, comparing laboratory data and translational histological features, we show that it is highly likely that an increase in RAAS is one, if not the main, pathogenic feature in critical COVID-19. Furthermore, it is plausible that this large animal model can be used to screen for potential new treatments for patients with severe COVID-19 and that MRI lung perfusion can be used to evaluate the outcome of potential treatments targeting the pathophysiological syndrome.

No abstract

Dibutyryl cAMP (dB-cAMP) and the cAMP elevating agents, prostaglandin E1, theophylline, and histamine markedly suppressed NK cytolytic function in a dose-and rate-dependent manner. The inhibition was rapidly induced and persisted in the presence of the drugs. Separate pretreatment of targets and highly purified NK cells, isolated by a target binding and velocity sedimentation technique, revealed that PGE1 and dB-cAMP acted at the level of the effector cell in a short-term cytolytic assay. In contrast to the inhibitory effects of cAMP elevating agents, dB-cGMP and carbamylcholine caused a small but significant acceleration in the rate of lysis and could compete with inhibitory doses of dB-cAMP to reduce the level of suppression thereby suggesting that the cAMP-cGMP ratio might be important in NK-mediated lysis. Insulin had no effect on NK activity, whereas T cell-mediated cytolysis was augmented by insulin and cGMP if the effector cells were taken early after alloimmunization but not later. Neither cAMP- nor cGMP-elevating agents affected the frequency of NK-target cell conjugates. These results are compatible with the hypothesis that cyclic nucleotides may be involved in triggering the lytic event within NK cells.