Acute respiratory failure and a systemic coagulopathy are critical aspects of the morbidity and mortality characterizing infection with severe acute respiratory distress syndrome-associated coronavirus-2, the etiologic agent of Coronavirus disease 2019 (COVID-19). We examined skin and lung tissues from 5 patients with severe COVID-19 characterized by respiratory failure (n= 5) and purpuric skin rash (n = 3). COVID-19 pneumonitis was predominantly a pauci-inflammatory septal capillary injury with significant septal capillary mural and luminal fibrin deposition and permeation of the interalveolar septa by neutrophils. No viral cytopathic changes were observed and the diffuse alveolar damage (DAD) with hyaline membranes, inflammation, and type II pneumocyte hyperplasia, hallmarks of classic acute respiratory distress syndrome, were not prominent. These pulmonary findings were accompanied by significant deposits of terminal complement components C5b-9 (membrane attack complex), C4d, and mannose binding lectin (MBL)-associated serine protease (MASP)2, in the microvasculature, consistent with sustained, systemic activation of the complement pathways. The purpuric skin lesions similarly showed a pauci-inflammatory thrombogenic vasculopathy, with deposition of C5b-9 and C4d in both grossly involved and normally-appearing skin. In addition, there was co-localization of COVID-19 spike glycoproteins with C4d and C5b-9 in the interalveolar septa and the cutaneous microvasculature of 2 cases examined. In conclusion, at least a subset of sustained, severe COVID-19 may define a type of catastrophic microvascular injury syndrome mediated by activation of complement pathways and an associated procoagulant state. It provides a foundation for further exploration of the pathophysiologic importance of complement in COVID-19, and could suggest targets for specific intervention.

Background There are two distinctive acral manifestations of COVID‐19 embodying disparate clinical phenotypes: one is perniosis occurring in mildly symptomatic patients, typically children; the second is the thrombotic retiform purpura of critically ill COVID19 adults. Materials and Methods We compare light‐microscopic, phenotypic, cytokine, and SARS‐CoV‐2 protein and RNA profiles in COVID‐19‐associated perniosis of mildly symptomatic or asymptomatic patients with the thrombotic retiform purpura of critical patients with COVID‐19. Results The COVID‐19‐associated perniosis exhibited vasocentric and eccrinotropic T‐cell and monocyte‐derived CD11c, CD14, and CD123+ dendritic cell infiltrates. Both COVID associated and idiopathic perniosis showed striking expression of the type I interferon‐inducible myxovirus resistance protein‐A (MXA), an established marker for type I interferon signaling in tissue. SARS‐CoV‐2 RNA, IL‐ 6 and caspase 3 were minimally expressed and confined to mononuclear inflammatory cells. The biopsies from livedo/retiform purpura showed pauci‐inflammatory vascular thrombosis without any MXA decoration. Blood vessels exhibited extensive complement deposition with endothelial cell localization of SARS‐CoV‐2 protein, IL6, and caspase 3; SARS CoV‐2 RNA was not seen. Conclusion The COVID‐19‐associated perniosis represents an exaggerated immune reaction to a virus with significant type‐I interferon signaling important to SARS‐CoV‐2 eradication and has implications in regards to a more generalized highly‐inflammatory response. We hypothesize that in the thrombotic retiform purpura of critically ill patients with COVID‐19, the vascular thrombosis in the skin and other organ systems is associated with a minimal interferon response allowing excessive viral replication with release of viral proteins that localize to extrapulmonary endothelium and trigger extensive complement activation.

Accelerated bone resorption leading to osteopenia and osteoporosis has been noted in human immunodeficiency virus (HIV) seropositive, treatment-naive patients, but it may be greatly increased in incidence in those receiving highly active anti-retroviral therapies that incorporate certain protease inhibitors (PI). The pathophysiology of these processes is unclear. We have documented the induction of the primary cytokine responsible for osteoclast differentiation and bone resorption, the receptor activator of nuclear factor B ligand (RANKL), in T cells exposed to soluble HIV-1 envelope glycoprotein gp120. Using a murine osteoclast precursor cell line as well as primary human osteoclast precursors, we demonstrate that pharmacologic levels of two PIs that are linked clinically to osteopenia, ritonavir and saquinavir, abrogate a physiological block to RANKL activity, interferon-␥-mediated degradation of the RANKL signaling adapter protein, TRAF6 (tumor necrosis factor receptor-associated protein 6) in proteasomes. In contrast, indinavir and nelfinavir, PIs that may promote or stabilize bone formation in vivo, had no impact on this system. These findings offer a molecular basis for the acceleration of bone resorption by certain PIs and provide the first example of clinically useful drugs that can interfere with the cross-talk between RANKL and interferon-␥ via the proteasome. They also suggest a novel therapeutic approach to HIV osteopenia through modulation of these two molecules. Loss of bone mineral density (BMD)1 leading to osteopenia has been observed among HIV seropositive patients naive to antiretroviral therapy, but it is infrequent and of unclear clinical significance (1-3). However, certain antiretroviral therapy regimens may accelerate bone resorption in HIV ϩ adults and children (4 -8). For example, in a survey of 112 homosexual HIV ϩ men, the relative risk for bone resorption in those receiving highly active antiretroviral therapy treatment incorporating a protease inhibitor (PI) was 2.19 (1.13-4.23, p ϭ 0.02) (5). In another recent longitudinal evaluation of BMD in HIV ϩ individuals, there was only a weak association between BMD and PI treatment, but there were too few patients to distinguish among different type of PIs (9). Indeed, in one study the PIs indinavir and nelfinavir were associated with augmented or stable bone resorption, respectively (10). A satisfactory pathophysiological mechanism for HIV-linked bone resorption must be able to account for all of these findings. We focused on a T cell cytokine linked to acceleration of bone resorption in vitro and in vivo, the receptor activator of nuclear factor B ligand (RANKL) (11), and its interaction with a signaling pathway that is altered by therapeutic levels of certain PIs.Specifically, RANKL activity is modulated through interferon (IFN)-␥-coupled proteasomal degradation of TNF receptor-associated factor 6 (TRAF6) (12). RANKL recruits TRAF6 to the cytoplasmic tail of RANK, resulting in the activation of NF-B and certain mitogen-activated protein ...

The objective of this study was to elucidate the pathophysiology that underlies severe COVID-19 by assessing the histopathology and the in situ detection of infectious SARS-CoV-2 and viral capsid proteins along with the cellular target(s) and host response from twelve autopsies. There were three key findings: 1) high copy infectious virus was limited mostly to the alveolar macrophages and endothelial cells of the septal capillaries; 2) viral spike protein without viral RNA localized to ACE2+ endothelial cells in microvessels that were most abundant in the subcutaneous fat and brain; 3) although both infectious virus and docked viral spike protein was associated with complement activation, only the endocytosed pseudovirions induced a marked up-regulation of the key COVID-19 associated proteins IL6, TNF alpha, IL1 beta, p38, IL8, and caspase 3. Importantly, this microvasculitis was associated with characteristic findings on hematoxylin and eosin examination that included endothelial degeneration and resultant basement membrane zone disruption and reduplication. It is concluded that serious COVID-19 infection has two distinct mechanisms: 1) a microangiopathy of pulmonary capillaries associated with a high infectious viral load where endothelial cell death releases pseudovirions into the circulation, and 2) the pseudovirions dock on ACE2+ endothelial cells most prevalent in the skin/subcutaneous fat and brain that activates the complement pathway/coagulation cascade resulting in a systemic procoagulant state as well as the expression of cytokines that produce the cytokine storm. The data predicts a favorable response to therapies based on either removal of circulating viral proteins and/or blunting of the endothelial-induced response.

Respiratory failure and acute kidney injury (AKI) are associated with high mortality in SARS-CoV-2-associated Coronavirus disease 2019 (COVID-19). These manifestations are linked to a hypercoaguable, pro-inflammatory state with persistent, systemic complement activation. Three critical COVID-19 patients recalcitrant to multiple interventions had skin biopsies documenting deposition of the terminal complement component C5b-9, the lectin complement pathway enzyme MASP2, and C4d in microvascular endothelium. Administration of anti-C5 monoclonal antibody eculizumab led to a marked decline in D-dimers and neutrophil counts in all three cases, and normalization of liver functions and creatinine in two. One patient with severe heart failure and AKI had a complete remission. The other two individuals had partial remissions, one with resolution of his AKI but ultimately succumbing to respiratory failure, and another with a significant decline in FiO 2 requirements, but persistent renal failure. In conclusion, anti-complement therapy may be beneficial in at least some patients with critical COVID-19.