An Insight into the Role of Postmortem Immunohistochemistry in the Comprehension of the Inflammatory Pathophysiology of COVID-19 Disease and Vaccine-Related Thrombotic Adverse Events: A Narrative Review

Von Willebrand factor and the thrombophilia of severe COVID-19: in situ evidence from autopsies

Background

COVID-19 is accompanied by a hypercoagulable state and characterized by microvascular and macrovascular thrombotic complications. In plasma samples from patients with COVID-19, von Willebrand factor (VWF) levels are highly elevated and predictive of adverse outcomes, especially mortality. Yet, VWF is usually not included in routine coagulation analyses, and histologic evidence of its involvement in thrombus formation is lacking.

Objectives

To determine whether VWF, an acute-phase protein, is a bystander, ie, a biomarker of endothelial dysfunction, or a causal factor in the pathogenesis of COVID-19.

Methods

We compared autopsy samples from 28 patients with lethal COVID-19 to those from matched controls and systematically assessed for VWF and platelets by immunohistochemistry. The control group comprised 24 lungs, 23 lymph nodes, and 9 hearts and did not differ significantly from the COVID-19 group in age, sex, body mass index (BMI), blood group, or anticoagulant use.

Results

In lungs, assessed for platelets by immunohistochemistry for CD42b, microthrombi were more frequent in patients with COVID-19 (10/28 [36%] vs 2/24 [8%]; P = .02). A completely normal pattern of VWF was rare in both groups. Accentuated endothelial staining was found in controls, while VWF-rich thrombi were only found in patients with COVID-19 (11/28 [39%] vs 0/24 [0%], respectively; P < .01), as were NETosis thrombi enriched with VWF (7/28 [25%] vs 0/24 [0%], respectively; P < .01). Forty-six percent of the patients with COVID-19 had VWF-rich thrombi, NETosis thrombi, or both. Trends were also seen in pulmonary draining lymph nodes (7/20 [35%] vs 4/24 [17%]; P = .147), where the overall presence of VWF was very high.

Conclusion

We provide in situ evidence of VWF-rich thrombi, likely attributable to COVID-19, and suggest that VWF may be a therapeutic target in severe COVID-19.

Autopsy Findings and Inflammatory Markers in SARS-CoV-2: A Single-Center Experience

Purpose

The systemic inflammatory response related to COVID-19 can be easily investigated in living patients. Unfortunately, not every biomarker is suitable for postmortem analysis since several factors may interfere. The aim of this study was to summarize key histopathological findings within each organ system due to COVID-19 and to assess if serological inexpensive and widely available biomarkers such as CRP, IL-6, fibrinogen and d-Dimers, associated with adverse outcomes in COVID-19, can be implemented in a post-mortem assessment.

Patients and Methods

A total of 60 subjects divided in 2 groups were included. All subjects died outside a hospital setting and therefore did not receive specific or symptomatic therapies that could have modulated the inflammatory response. The first group included 45 subjects in which mandatory autopsy was performed in order to establish the cause of death and macroscopic examination of the lungs was highly suggestive of SARS-CoV-2 infection. As controls (Group 2), 20 subjects who died from polytrauma in high velocity car accidents and suicide were selected. Bronchial fluids collected during the autopsy procedure were used for the RT-PCR diagnosis of SARS-CoV-2 and serum samples were sent for analysis of IL-6, CRP, d-Dimers and fibrinogen.

Results

Compared with the control group, the subjects of the COVID-19 group were older (59±19.5 vs.38±19.15 years, p=0.0002) and had more underlying comorbidities such as hypertension (60% vs 35%, p=0.06) or were overweight (53.3% vs 30%, p=0.08). The levels of CRP, IL-6, fibrinogen and d-Dimers in postmortem plasma samples were significantly higher in COVID-19 subjects than in control group (p< 0.0001). Moreover, the level of IL-6 was significantly higher in overweight patients (r=0.52, P<0.001). In all COVID-19 subjects, the histological examination revealed features corresponding to the exudative and/or proliferative phases of diffuse alveolar damage. Large pulmonary emboli were observed in 7 cases. Gross cardiac enlargement with left ventricular hypertrophy was observed in 19 cases. The most frequent pathological finding of the central nervous system was acute/early-subacute infarction.

Conclusion

Due to the complexity of the inflammatory response, we postulate that a combination of biomarkers, rather than a single laboratory parameter, might be more effective in obtaining a reliable postmortem COVID-19 diagnosis.

How the Innate Immune System of the Blood Contributes to Systemic Pathology in COVID-19-Induced ARDS and Provides Potential Targets for Treatment

Most SARS-CoV-2 infected patients experience influenza-like symptoms of low or moderate severity. But, already in 2020 early during the pandemic it became obvious that many patients had a high incidence of thrombotic complications, which prompted treatment with high doses of low-molecular-weight heparin (LMWH; typically 150-300IU/kg) to prevent thrombosis. In some patients, the disease aggravated after approximately 10 days and turned into a full-blown acute respiratory distress syndrome (ARDS)-like pulmonary inflammation with endothelialitis, thrombosis and vascular angiogenesis, which often lead to intensive care treatment with ventilator support. This stage of the disease is characterized by dysregulation of cytokines and chemokines, in particular with high IL-6 levels, and also by reduced oxygen saturation, high risk of thrombosis, and signs of severe pulmonary damage with ground glass opacities. The direct link between SARS-CoV-2 and the COVID-19-associated lung injury is not clear. Indirect evidence speaks in favor of a thromboinflammatory reaction, which may be initiated by the virus itself and by infected damaged and/or apoptotic cells. We and others have demonstrated that life-threatening COVID-19 ARDS is associated with a strong activation of the intravascular innate immune system (IIIS). In support of this notion is that activation of the complement and kallikrein/kinin (KK) systems predict survival, the necessity for usage of mechanical ventilation, acute kidney injury and, in the case of MBL, also coagulation system activation with thromboembolism. The general properties of the IIIS can easily be translated into mechanisms of COVID-19 pathophysiology. The prognostic value of complement and KKsystem biomarkers demonstrate that pharmaceuticals, which are licensed or have passed the phase I trial stage are promising candidate drugs for treatment of COVID-19. Examples of such compounds include complement inhibitors AMY-101 and eculizumab (targeting C3 and C5, respectively) as well as kallikrein inhibitors ecallantide and lanadelumab and the bradykinin receptor (BKR) 2 antagonist icatibant. In this conceptual review we discuss the activation, crosstalk and the therapeutic options that are available for regulation of the IIIS.

Medico-legal analysis of cases of children who died suddenly due to pneumonia undiagnosed in their lifetime

Pneumonia is one of the most common causes of children's hospitalization and death. The aim of the study was a medico-legal analysis of children who died suddenly due to pneumonia undiagnosed in their lifetime. The research was of a retrospective character and consisted in an analysis of prosecution files. The study included 47 children who died between 2011-2018 in whom pneumonia after post-mortem examination was indicated as the cause of death, as well as children in whom the cause of death, despite additional post-mortem examinations, including histopathological tests, was not established. In some cases, under additional post-mortem examinations, additional targeted immunohistochemical staining of selected lung sections was performed to establish the diagnosis. In children with prodromal symptoms, histopathological examination showed significantly more frequent atelectasis than in children without prodromal symptoms. Pneumonia is a significant clinical problem. Especially in young children, it may proceed with- out any symptoms that would cause such a diagnosis to be made. A properly conducted post-mortem diagnosis supplemented by immunohistochemical examinations allows to reduce the number of unexplained deaths in children.