Severe COVID-19 induces autoantibodies against angiotensin II that correlate with blood pressure dysregulation and disease severity.

Patients infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can experience life-threatening respiratory distress, blood pressure dysregulation, and thrombosis. This is thought to be associated with an impaired activity of angiotensin-converting enzyme 2 (ACE2), which is the main entry receptor of SARS-CoV-2 and which also tightly regulates blood pressure by converting the vasoconstrictive peptide angiotensin II (AngII) to a vasopressor peptide. Here, we show that a significant proportion of hospitalized patients with COVID-19 developed autoantibodies against AngII, whose presence correlates with lower blood oxygenation, blood pressure dysregulation, and overall higher disease severity. Anti-AngII antibodies can develop upon specific immune reaction to the SARS-CoV-2 proteins Spike or receptor-binding domain (RBD), to which they can cross-bind, suggesting some epitope mimicry between AngII and Spike/RBD. These results provide important insights on how an immune reaction against SARS-CoV-2 can impair blood pressure regulation.

Lymphatic coagulation and neutrophil extracellular traps in lung-draining lymph nodes of COVID-19 decedents.

Clinical manifestations of severe COVID-19 include coagulopathies that are exacerbated by the formation of neutrophil extracellular traps (NETs). Here, we report that pulmonary lymphatic vessels, which traffic neutrophils and other immune cells to the lung-draining lymph node (LDLN), can also be blocked by fibrin clots in severe COVID-19. Immunostained tissue sections from COVID-19 decedents revealed widespread lymphatic clotting not only in the lung, but notably in the LDLN, where the extent of clotting correlated with the presence of abnormal, regressed, or missing germinal centers. it strongly correlated with the presence of intralymphatic NETs. In mice, TNFα induced intralymphatic fibrin clots, and this could be inhibited by DNAse 1, which degrades NETs. In vitro, TNF induced lymphatic endothelial cell upregulation of ICAM-1 and CXCL8 among other neutrophil-recruiting factors as well as thrombomodulin downregulation. Furthermore, in decedents, lymphatic clotting in LDLNs. In a separate cohort of hospitalized patients, serum levels of MPO-DNA (a NET marker) inversely correlated with antiviral antibody titers, but D-dimer levels, indicative of blood thrombosis, did not correlate with either. In fact, patients with high MPO-DNA but low D-dimer levels generated poor anti-viral antibody titers. This study introduces lymphatic coagulation in lungs and LDLNs as a clinical manifestation of severe COVID-19 and suggests the involvement of NETosis of lymphatic-trafficking neutrophils. It further suggests that lymphatic clotting may correlate with impaired formation or maintenance of germinal centers necessary for robust antiviral antibody responses, although further studies are needed to determine whether and how lymphatic coagulation impacts adaptive immune responses.

A series of COVID-19 autopsies with clinical and pathologic comparisons to both seasonal and pandemic influenza.

Autopsies of patients who have died from COVID-19 have been crucial in delineating patterns of injury associated with SARS-CoV-2 infection. Despite their utility, comprehensive autopsy studies are somewhat lacking relative to the global burden of disease, and very few comprehensive studies contextualize the findings to other fatal viral infections. We developed a novel autopsy protocol in order to perform postmortem examinations on victims of COVID-19 and herein describe detailed clinical information, gross findings, and histologic features observed in the first 16 complete COVID-19 autopsies. We also critically evaluated the role of ancillary studies used to establish a diagnosis of COVID-19 at autopsy, including immunohistochemistry (IHC), in situ hybridization (ISH), and electron microscopy (EM). IHC and ISH targeting SARS-CoV-2 were comparable in terms of the location and number of infected cells in lung tissue; however, nonspecific staining of bacteria was seen occasionally with IHC. EM was unrevealing in blindly sampled tissues. We then compared the clinical and histologic features present in this series to six archival cases of fatal seasonal influenza and six archival cases of pandemic influenza from the fourth wave of the 'Spanish Flu' in the winter of 1920. In addition to routine histology, the inflammatory infiltrates in the lungs of COVID-19 and seasonal influenza victims were compared using quantitative IHC. Our results demonstrate that the clinical and histologic features of COVID-19 are similar to those seen in fatal cases of influenza, and the two diseases tend to overlap histologically. There was no significant difference in the composition of the inflammatory infiltrate in COVID-19 and influenza at sites of acute lung injury at the time of autopsy. Our study underscores the relatively nonspecific clinical features and pathologic changes shared between severe cases of COVID-19 and influenza, while also providing important caveats to ancillary methods of viral detection.

Modeling human adaptive immune responses with tonsil organoids.

Most of what we know about adaptive immunity has come from inbred mouse studies, using methods that are often difficult or impossible to confirm in humans. In addition, vaccine responses in mice are often poorly predictive of responses to those same vaccines in humans. Here we use human tonsils, readily available lymphoid organs, to develop a functional organotypic system that recapitulates key germinal center features in vitro, including the production of antigen-specific antibodies, somatic hypermutation and affinity maturation, plasmablast differentiation and class-switch recombination. We use this system to define the essential cellular components necessary to produce an influenza vaccine response. We also show that it can be used to evaluate humoral immune responses to two priming antigens, rabies vaccine and an adenovirus-based severe acute respiratory syndrome coronavirus 2 vaccine, and to assess the effects of different adjuvants. This system should prove useful for studying critical mechanisms underlying adaptive immunity in much greater depth than previously possible and to rapidly test vaccine candidates and adjuvants in an entirely human system.