Immunity in SARS-CoV-2 Infection: Clarity or Mystery? A Broader Perspective in the Third Year of a Worldwide Pandemic

COVID-19: from immune response to clinical intervention

The coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has highlighted the pivotal role of the immune response in determining the progression and severity of viral infections. In this paper, we review the most recent studies on the complicated dynamics between SARS-CoV-2 and the host immune system, highlight the importance of understanding these dynamics in developing effective treatments and formulate potent management strategies for COVID-19. We describe the activation of the host's innate immunity and the subsequent adaptive immune response following infection with SARS-CoV-2. In addition, the review emphasizes the immune evasion strategies of the SARS-CoV-2, including inhibition of interferon production and induction of cytokine storms, along with the resulting clinical outcomes. Finally, we assess the efficacy of current treatment strategies, including antiviral drugs, monoclonal antibodies, and anti-inflammatory treatments, and discuss their role in providing immunity and preventing severe disease.

Application of Interferon-γ Release Assay in the Assessment of T-Cell Immunity to SARS-CoV-2 Antigens in the Cohort of Pediatric Patients with Juvenile Idiopathic Arthritis

Background: an accurate assessment of the immunity against SARS-CoV-2 can facilitate a better understanding and management of not only the recent coronavirus but similar pathogens as well. Objective: the aim of this study was to evaluate T-cell immunity with reference to antibody titers in a group of pediatric patients with autoimmune arthritides utilizing the widely known Interferon-γ Release Assay (IGRA). Materials and Methods: This study was conducted in the cohort of 55 children suffering from Juvenile Idiopathic Arthritis (JIA). This research analyzed the SARS-CoV-2 T-cell response measured by a specific quantitative IGRA, followed by a serological ELISA test measuring the presence and quantity of IgG, IgM, and IgA antibodies in serum. Results: The cellular response to SARS-CoV-2 measured by the IGRA test significantly correlated with the antibody titers, IgA (p < 0.00003, R = 0.537), IgG (p < 0.0001, R = 0.668), and IgG nucleocapsid protein (NCP) (p < 0.003, R = 0.0399), with no correlation with IgM levels. The antibody levels in patients receiving biological agents were significantly lower compared to the rest of the cohort (p = 0.0369), while traditional disease-modifying antirheumatic drugs had no such effect. Limitations: the main limitation of the research is the small sample size, mostly due to the specific cohort of patients and the lack of a healthy control. Conclusions: IGRA appears to be a viable tool in the accurate evaluation of T-cell responses to SARS-CoV-2, and serodiagnostics alone is not always sufficient in the assessment of immune responses.

Interferon-γ Release Assay in the Assessment of Cellular Immunity-A Single-Centre Experience with mRNA SARS-CoV-2 Vaccine in Patients with Juvenile Idiopathic Arthritis

Background: As the SARS-CoV-2 virus remains one of the main causes of severe respiratory system infections, the Food and Drug Administration strongly advises the continuation of current vaccination programs, including the distribution of updated boosters, especially in high-risk groups of patients. Therefore, there is an unceasing need for further research on the safety and, no less importantly, the clinical effectivity of the vaccines, with an extra focus on cohorts of patients with underlying health problems. This study aimed to assess the efficacy of the SARS-CoV-2 vaccine in possibly immunocompromised children with rheumatic disease while utilizing the interferon-gamma release assay (IGRA) as a marker for COVID-19 immunity in the study follow-up. Methods: This prospective study was performed in a group of 55 pediatric patients diagnosed with juvenile idiopathic arthritis. Eight participants were immunized with the Comirnaty mRNA vaccine before the research commenced, while the rest of the group (n = 47) had not been vaccinated against SARS-CoV-2. At the study baseline, the cellular response to the virus antigen was measured using a specific quantitative IGRA in whole blood; subsequently, the anti-SARS-CoV-2 test was performed, marking the antibodies' levels in serum. Around four months after the enrollment of the last patient in the study, a follow-up survey regarding the events of COVID-19 infection within the cohort was conducted. Results: The study confirmed that all the vaccinated children developed specific T-cell (p = 0.0016) and humoral (p = 0.001 for IgA antibodies, p = 0.008 for IgG antibodies) responses to the inoculation, including those receiving biological treatment and those on conventional disease-modifying anti-rheumatic drugs. The study also showed the different patterns of immunity elicited both after infection and post-vaccination, with higher levels of antibodies and T-cell response after inoculation than after natural exposure to the pathogen. According to the follow-up survey, six children developed PCR-confirmed SARS-CoV-2 infection, whereas the additional 10 patients admitted to having COVID-like symptoms with no laboratory verification. Conclusions: SARS-CoV-2 vaccinations elicit valid immune responses in pediatric rheumatic patients. Including the assessment of T-cell immunity in the evaluation of inoculation-induced immunization can enhance the accuracy of sole humoral response assays.

Acute Pulmonary Embolism and Immunity in Animal Models

Venous thromboembolism, encompassing acute pulmonary embolism (APE) and deep vein thrombosis (DVT), is a potentially fatal disease with complex pathophysiology. Traditionally, the Virchow triad provided a framework for understanding the pathogenic contributors to thrombus formation, which include endothelial dysfunction, alterations in blood flow and blood hypercoagulability. In the last years, it has become apparent that immunity plays a central role in thrombosis, interacting with classical prothrombotic mechanisms, oxidative stress and vascular factors. Thrombosis amplifies inflammation, and exaggerated inflammatory processes can trigger thrombosis mainly due to the activation of leukocytes, platelets, and endothelial cells. APE-related endothelium injury is a major trigger for immune system activation. Endothelium is also a key component mediating inflammatory reaction and it is relevant to maintain vascular permeability. Exaggerated right ventricular wall stress and overload, with coexisting systemic hypotension and hypoxemia, result in myocardial injury and necrosis. Hypoxia, tissue factor activation and cytokine storm are engaged in the thrombo-inflammatory processes. Thrombus development is characterized by inflammatory state vascular wall caused mainly by an early extravasation of leukocytes and intense selectins and cytokines production. Nevertheless, immunity of DVT is well described, little is known about potential chemokine and cellular differences between thrombus that develops in the vein and thrombus that detaches and lodges in the pulmonary circulation being a cause of APE. There is a paucity of data considering inflammatory state in the pulmonary artery wall during an acute episode of pulmonary embolism. The main aim of this review is to summarize the knowledge of immunity in acute phase of pulmonary embolism in experimental models.

Innate immune responses to SARS-CoV-2

This chapter provides an overview of the innate immune response to SARS-CoV-2, focusing on the recognition, activation, and evasion strategies employed by the virus. The innate immune system plays a crucial role in the early defense against viral infections, and understanding its response to SARS-CoV-2 is essential for developing effective therapeutic approaches. The chapter begins by explaining the basics of the innate immune system, including its components and salient features. It discusses the various pattern recognition receptors involved in recognizing SARS-CoV-2, such as toll-like receptors, RIG-I-like receptors, NOD-like receptors, and other cytosolic sensors. The binding and entry of the virus into host cells and subsequent activation of innate immune cells, including neutrophils, monocytes, macrophages, dendritic cells, NK cells, and ILCs, are explored. Furthermore, the secretion of key cytokines and chemokines, including type I interferons, IL-6, IL-17, and TNF-alpha, is discussed as part of the innate immune response. The concept of PANoptosis, involving programmed cell death mechanisms, is introduced as a significant aspect of the response to SARS-CoV-2. The chapter also addresses the innate immune evasion strategies employed by SARS-CoV-2, which allow the virus to evade or subvert the host immune response, contributing to viral persistence. Understanding these strategies is crucial for developing targeted therapies against the virus.