Elucidating T Cell and B Cell Responses to SARS-CoV-2 in Humans: Gaining Insights into Protective Immunity and Immunopathology

Unravelling humoral immunity in SARS-CoV-2: Insights from infection and vaccination

Following infection and vaccination against SARS-CoV-2, humoral components of the adaptive immune system play a key role in protecting the host. Specifically, B cells generate high-affinity antibodies against various antigens of the virus. In this review, we discuss the mechanisms of immunity initiation through both natural infection and vaccination, shedding light on the activation of B cell subsets in response to SARS-CoV-2 infection and vaccination. The innate immune system serves as the initial line of primary and nonspecific defence against viruses. However, within several days following infection or a vaccine dose, a virus-specific immune response is initiated, primarily by B cells that produce antibodies. These antibodies contribute to the resolution of the disease. Subsequently, these B cells transition into memory B cells, which play a crucial role in providing long-term immunity against the virus. CD4+ T helper cells initiate a cascade, leading to B cell somatic hypermutation, germinal center memory B cells, and the production of neutralizing antibodies. B-cell dysfunction can worsen disease severity and reduce vaccine efficacy. Notably, individuals with B cell immunodeficiency show lower IL-6 production. Furthermore, this review delves into several aspects of immune responses, such as hybrid immunity, which has shown promise in boosting broad-spectrum protection. Cross-reactive immunity is under scrutiny as well, as pre-existing antibodies can offer protection against the disease. We also decipher breakthrough infection mechanisms, especially with the novel variants of the virus. Finally, we discuss some potential therapeutic solutions regarding B cells including convalescent plasma therapy, B-1 cells, B regulatory cell (Breg) modulation, and the use of neutralizing monoclonal antibodies in combating the infection. Ongoing research is crucial to grasp population immunity trends and assess the potential need for booster doses in maintaining effective immune responses against potential viral threats.

Sarcoidosis-related autoimmune inflammation in COVID-19 convalescent patients

Currently, there are a large number of reports about the development of autoimmune conditions after COVID-19. Also, there have been cases of sarcoid-like granulomas in convalescents as a part of the post-COVID-19 syndrome. Since one of the etiological theories of sarcoidosis considers it to be an autoimmune disease, we decided to study changes in the adaptive humoral immune response in sarcoidosis and SARS-CoV-2 infection and to find out whether COVID-19 can provoke the development of sarcoidosis. This review discusses histological changes in lymphoid organs in sarcoidosis and COVID-19, changes in B cell subpopulations, T-follicular helper cells (Tfh), and T-follicular regulatory cells (Tfr), and analyzes various autoantibodies detected in these pathologies. Based on the data studied, we concluded that SARS-CoV-2 infection may cause the development of autoimmune pathologies, in particular contributing to the onset of sarcoidosis in convalescents.

Predictors of COVID-19 Severity in Elderly Patients Infected by Omicron in China, 18 December 2022-5 February 2023

Purpose

To analyze the clinical characteristics and prognosis of patients hospitalized with non-severe, severe pneumonia and death in Omicron COVID-19.

Patients and Methods

We collected clinical data from 118 patients with COVID-19 in China from 18 December, 2022 and 5 February, 2023. According to the outcome, the patients were divided into non-severe group, severe group and death group. Subsequently, we statistically analyzed the general condition, clinical manifestations, laboratory parameters, NLR, MLR, PLR and HALP of these groups. We also retrospectively analyzed the possible factors affecting the prognostic regression of patients with COVID-19.

Results

A total of 118 COVID-19 patients were enrolled in this study, including 64 non-severe patients, 38 severe patients and 16 death patients. Compared with the non-severe group, T lymphocytes, B lymphocytes, Th1, Th2, Th17, Treg cells, IgA, IgG, IgM in the severe and death groups decreased more significantly (P<0.05). The levels of myocardial markers, ALT, AST, BUN, Cr, D-dimer, fibrinogen, NLR, MLR and PLR in the severe and death groups were significantly higher than those in the non-severe group (P<0.05). The level of HALP was significantly lower than that of non-severe group (P<0.05). MLR is not only an independent risk factor for the transition from non-severe to severe disease, but also an independent risk factor for predicting the possibility of death in COVID-19 patients.

Conclusion

The analysis of COVID-19 patients in China showed that severe patients were older, more likely to have related complications, lower lymphocyte count, liver and kidney function disorder, glucose and lipid metabolism disorders, myocardial injury, and abnormal coagulation function, suggesting the need for early anticoagulant therapy. In addition, NLR, MLR, PLR and HALP can be used as biomarkers to evaluate the severity and prognosis of COVID-19 patients.

Innate and adaptive immunity to SARS-CoV-2 and predisposing factors

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus (SARS-CoV-2), has affected all countries worldwide. Although some symptoms are relatively mild, others are still associated with severe and even fatal clinical outcomes. Innate and adaptive immunity are important for the control of SARS-CoV-2 infections, whereas a comprehensive characterization of the innate and adaptive immune response to COVID-19 is still lacking and the mechanisms underlying immune pathogenesis and host predisposing factors are still a matter of scientific debate. Here, the specific functions and kinetics of innate and adaptive immunity involved in SARS-CoV-2 recognition and resultant pathogenesis are discussed, as well as their immune memory for vaccinations, viral-mediated immune evasion, and the current and future immunotherapeutic agents. We also highlight host factors that contribute to infection, which may deepen the understanding of viral pathogenesis and help identify targeted therapies that attenuate severe disease and infection.

MOLECULAR MIMICRY OF SARS-COV-2 SPIKE PROTEIN IN THE NERVOUS SYSTEM: A BIOINFORMATICS APPROACH

Introduction

The development of vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in record time to cope with the ongoing coronavirus disease 2019 (COVID-19) pandemic has led to uncertainty about their use and the appearance of adverse neurological reactions. The SARS-CoV-2 spike protein (SP) is used to produce neutralizing antibodies and stimulate innate immunity. However, considering the alterations in the nervous system (NS) caused by COVID- 19, cross-reactions are plausible.

Objective

To identify peptides in Homo sapiens SP-like proteins involved in myelin and axon homeostasis that may be affected due to molecular mimicry by antibodies and T cells induced by interaction with SP.

Materials and methods

A bioinformatics approach was used. To select the H. sapiens proteins to be studied, related biological processes categorized based on gene ontology were extracted through the construction of a protein–protein interaction network. Peripheral myelin protein 22, a major component of myelin in the peripheral nervous system, was used as the query protein. The extracellular domains and regions susceptible to recognition by antibodies were extracted from UniProt. In the study of T cells, linear sequence similarity between H. sapiens proteins and SP was assessed using BLASTp. This study considered the similarity in terms of biochemical groups per residue and affinity to the human major histocompatibility complex (human leukocyte antigen I), which were evaluated using Needle and NetMHCpan 4.1, respectively.

Results

A large number of shared pentapeptides between SP and H. sapiens proteins were identified. However, only a small group of 39 proteins was linked to axon and myelin homeostasis. In particular, some proteins, such as phosphacan, attractin, and teneurin-4, were susceptible targets of B and T cells. Other proteins closely related to myelin components in the NS, such as myelin-associated glycoprotein, were found to share at least one pentamer with SP in extracellular domains.

Conclusion

Proteins involved in the maintenance of nerve conduction in the central and peripheral NS were identified in H. sapiens. Based on these findings, re-evaluation of the vaccine composition is recommended to prevent possible neurological side effects.

T cells in SARS-CoV-2 infection and vaccination

While antibodies garner the lion’s share of attention in SARS-CoV-2 immunity, cellular immunity (T cells) may be equally, if not more important, in controlling infection. Both CD8⁺ and CD4⁺ T cells are elicited earlier and are associated with milder disease, than antibodies, and T-cell activation appears to be necessary for control of infection. Variants of concern (VOCs) such as Omicron have escaped the neutralizing antibody responses after two mRNA vaccine doses, but T-cell immunity is largely intact. The breadth and patient-specific nature of the latter offers a formidable line of defense that can limit the severity of illness, and are likely to be responsible for most of the protection from natural infection or vaccination against VOCs which have evaded the antibody response. Comprehensive searches for T-cell epitopes, T-cell activation from infection and vaccination of specific patient groups, and elicitation of cellular immunity by various alternative vaccine modalities are here reviewed. Development of vaccines that specifically target T cells is called for, to meet the needs of patient groups for whom cellular immunity is weaker, such as the elderly and the immunosuppressed. While VOCs have not yet fully escaped T-cell immunity elicited by natural infection and vaccines, some early reports of partial escape suggest that future VOCs may achieve the dreaded result, dislodging a substantial proportion of cellular immunity, enough to cause a grave public health burden. A proactive, rather than reactive, solution which identifies and targets immutable sequences in SARS-CoV-2, not just those which are conserved, may be the only recourse humankind has to disarm these future VOCs before they disarm us.

Cellular immunity in patients with COVID-19: molecular biology, pathophysiology, and clinical implications

The COVID-19 pandemic is caused by the SARS-CoV-2 coronavirus. From the viewpoint of factors critical to contain the virus, the neutralizing antibodies to SARS-CoV-2 garner most of the attention, however, it is essential to acknowledge that it is the level of the virus-specific T cell and B cell response that forms a basis for an effective neutralizing antibody response. T cell responses develop early and correlate with the protection, but they are relatively attenuated in the severe disease, in part due to lymphopenia. Understanding the role of different T cell subpopulations in the protection or the COVID-19 pathogenesis is critical to the prevention and treatment. The expression profile of different T cell subpopulations varies with the COVID-19 severity and is associated with the degree of T cell responses and the disease outcome. The structural changes in the genome, transcriptome, and proteome of SARS-CoV-2 promote the emergence of new variants of the virus and can reduce its interaction with antibodies and result in avoiding the neutralization. There is a strong correlation between the number of virus-specific CD4 T cells and neutralizing IgG antibody titers against SARS-CoV-2. During the primary viral infection, there is a wide variation in the cellular and humoral immune responses, patients with severe and prolonged symptoms showing highly imbalanced cellular and humoral immune responses. This review focuses on the generation and clinical significance of cellular immunity in the protection against severe acute infection and reinfection, as well as the potential involvement of seasonal coronavirus-specific cross-reactive T cells in response to SARS-CoV-2.

The role of antigen-presenting cells in the pathogenesis of COVID-19

Coronavirus Disease 2019 (COVID-19) is one of the three lethal coronavirus outbreaks in the recent two decades and a serious threat to global health all over the world. The principal feature of the COVID-19 infection is the so-called "cytokine storm" exaggerated molecular response to virus distribution, which plays massive tissue and organ injury roles. Immunological treatments, including monoclonal antibodies and vaccines, have been suggested as the main approaches in treating and preventing this disease. Therefore, a proper investigation of the roles of antigen-presenting cells (APCs) in the aforementioned immunological responses appears essential. The present review will provide detailed information about APCs' role in the infection and pathogenesis of SARS-CoV-2 and the effect of monoclonal antibodies in diagnosis and treatment.