The Role of NETosis and Complement Activation in COVID-19-Associated Coagulopathies

Neutrophils and COVID-19

Neutrophils are the first line of defense against pathogens, most effectively by forming Neutrophil Extracellular Traps (NETs). Neutrophiles are further classified into several subpopulations during their development, eliminating pathogens through various mechanisms. However, due to the chaotic and uncontrolled immune response, NETs are often severely resulting in tissue damage and lung infections. The uncontrolled and poorly acknowledged host response regarding the cytokine storm is one of the major causes of severe COVID-19 conditions. Specifically, the increased formation of low-density neutrophils (LDNs), together with neutrophil extracellular traps (NETs) is closely linked with the severity and poor prognosis in patients with COVID-19. In this review, we discuss in detail the ontogeny of neutrophils at different stages and their recruitment and activation after infections, focusing on SARS-CoV-2. In addition, this chapter summarized the research progress on potential targeted drugs (NETs and Cytokine inhibitors) for neutrophil medical therapy and hoped to provide reference for the development of related therapeutic drugs for critically ill COVID-19 patients.

The association between mortality due to COVID-19 and coagulative parameters: a systematic review and meta-analysis study

AIMS AND OBJECTIVES

This systematic review and meta-analysis study evaluated the association between mortality due to COVID-19 and coagulative factors.

METHODS

A systematic search was conducted on electronic databases including PubMed, Scopus, and the Web of Science from the beginning of the pandemic until October 2024 to identify relevant studies on COVID-19 patients and their laboratory findings related to coagulation markers and mortality outcome. Eligibility criteria were defined based on the PICO framework, and data extraction was performed by two authors independently using a standardized sheet. Statistical analysis was accomplished using the random effects model, and heterogeneity among studies was assessed using the I2 test. R and RStudio were used for statistical analysis and visualization.

RESULTS

Our systematic literature search yielded 6969 studies, with 48 studies meeting the inclusion criteria for our meta-analysis. The mean platelet count was significantly lower in deceased COVID-19 patients compared to survivors (20.58), while activated partial thromboplastin time (aPTT) and fibrinogen levels did not show significant differences. The pooled mean difference of D-Dimer, International Normalized Ratio (INR), and prothrombin time (PT) were significantly lower in survived patients (-2.45, -0.10, and -0.84, respectively). These findings suggest that platelet count, D-Dimer, INR, and PT may serve as potential indicators of mortality in COVID-19 patients.

CONCLUSION

The results of our systematic review and meta-analysis revealed a significant reduction in the pooled platelet count among deceased individuals when compared to survivors. However, no significant distinctions were observed in the pooled mean activated aPTT and fibrinogen levels between the deceased and survivor groups. On the other hand, there were noticeable variations in the pooled estimated mean of INR, PT, and D-Dimer levels, with significantly higher values in the deceased group compared to those who survived.

Immunity and Coagulation in COVID-19

Discovered in late 2019, the SARS-CoV-2 coronavirus has caused the largest pandemic of the 21st century, claiming more than seven million lives. In most cases, the COVID-19 disease caused by the SARS-CoV-2 virus is relatively mild and affects only the upper respiratory tract; it most often manifests itself with fever, chills, cough, and sore throat, but also has less-common mild symptoms. In most cases, patients do not require hospitalization, and fully recover. However, in some cases, infection with the SARS-CoV-2 virus leads to the development of a severe form of COVID-19, which is characterized by the development of life-threatening complications affecting not only the lungs, but also other organs and systems. In particular, various forms of thrombotic complications are common among patients with a severe form of COVID-19. The mechanisms for the development of thrombotic complications in COVID-19 remain unclear. Accumulated data indicate that the pathogenesis of severe COVID-19 is based on disruptions in the functioning of various innate immune systems. The key role in the primary response to a viral infection is assigned to two systems. These are the pattern recognition receptors, primarily members of the toll-like receptor (TLR) family, and the complement system. Both systems are the first to engage in the fight against the virus and launch a whole range of mechanisms aimed at its rapid elimination. Normally, their joint activity leads to the destruction of the pathogen and recovery. However, disruptions in the functioning of these innate immune systems in COVID-19 can cause the development of an excessive inflammatory response that is dangerous for the body. In turn, excessive inflammation entails activation of and damage to the vascular endothelium, as well as the development of the hypercoagulable state observed in patients seriously ill with COVID-19. Activation of the endothelium and hypercoagulation lead to the development of thrombosis and, as a result, damage to organs and tissues. Immune-mediated thrombotic complications are termed "immunothrombosis". In this review, we discuss in detail the features of immunothrombosis associated with SARS-CoV-2 infection and its potential underlying mechanisms.

The Roles of Neutrophil-Derived Myeloperoxidase (MPO) in Diseases: The New Progress

Myeloperoxidase (MPO) is a heme-containing peroxidase, mainly expressed in neutrophils and, to a lesser extent, in monocytes. MPO is known to have a broad bactericidal ability via catalyzing the reaction of Cl- with H2O2 to produce a strong oxidant, hypochlorous acid (HOCl). However, the overproduction of MPO-derived oxidants has drawn attention to its detrimental role, especially in diseases characterized by acute or chronic inflammation. Broadly speaking, MPO and its derived oxidants are involved in the pathological processes of diseases mainly through the oxidation of biomolecules, which promotes inflammation and oxidative stress. Meanwhile, some researchers found that MPO deficiency or using MPO inhibitors could attenuate inflammation and tissue injuries. Taken together, MPO might be a promising target for both prognostic and therapeutic interventions. Therefore, understanding the role of MPO in the progress of various diseases is of great value. This review provides a comprehensive analysis of the diverse roles of MPO in the progression of several diseases, including cardiovascular diseases (CVDs), neurodegenerative diseases, cancers, renal diseases, and lung diseases (including COVID-19). This information serves as a valuable reference for subsequent mechanistic research and drug development.