Immune response to SARS-CoV-2 and mechanisms of immunopathological changes in COVID-19

As a zoonotic disease that has already spread globally to several million human beings and possibly to domestic and wild animals, eradication of coronavirus disease 2019 (COVID-19) appears practically impossible. There is a pressing need to improve our understanding of the immunology of this disease to contain the pandemic by developing vaccines and medicines for the prevention and treatment of patients. In this review, we aim to improve our understanding on the immune response and immunopathological changes in patients linked to deteriorating clinical conditions such as cytokine storm, acute respiratory distress syndrome, autopsy findings and changes in acute-phase reactants, and serum biochemistry in COVID-19. Similar to many other viral infections, asymptomatic disease is present in a significant but currently unknown fraction of the affected individuals. In the majority of the patients, a 1-week, self-limiting viral respiratory disease typically occurs, which ends with the development of neutralizing antiviral T cell and antibody immunity. The IgM-, IgA-, and IgG-type virus-specific antibodies levels are important measurements to predict population immunity against this disease and whether cross-reactivity with other coronaviruses is taking place. High viral load during the first infection and repeated exposure to virus especially in healthcare workers can be an important factor for severity of disease. It should be noted that many aspects of severe patients are unique to COVID-19 and are rarely observed in other respiratory viral infections, such as severe lymphopenia and eosinopenia, extensive pneumonia and lung tissue damage, a cytokine storm leading to acute respiratory distress syndrome, and multiorgan failure. Lymphopenia causes a defect in antiviral and immune regulatory immunity. At the same time, a cytokine storm starts with extensive activation of cytokine-secreting cells with innate and adaptive immune mechanisms both of which contribute to a poor prognosis. Elevated levels of acute-phase reactants and lymphopenia are early predictors of high disease severity. Prevention of development to severe disease, cytokine storm, acute respiratory distress syndrome, and novel approaches to prevent their development will be main routes for future research areas. As we learn to live amidst the virus, understanding the immunology of the disease can assist in containing the pandemic and in developing vaccines and medicines to prevent and treat individual patients.     

Inflammation in COVID-19: from pathogenesis to treatment

The coronavirus disease 2019 (COVID-19) was declared a pandemic in March 2020 by the World Health Organization (WHO). To date, there were > 163 million confirmed cases of COVID-19 and the disease has claimed > 3.3 million lives globally. As with many other diseases, inflammation is a key feature of COVID-19. When inflammation is overwhelming, it may lead to unfavorable outcomes or even death. Scientists all over the world are working tirelessly in search of therapeutic strategies to suppress or modulate inflammation in COVID-19. This review gives an overview of the role of inflammation in COVID-19. It also critically examines the various treatment approaches that target the immune system and inflammation in COVID-19, as well as highlights the key findings in the numerous studies conducted thus far.     

Severity-Adjusted Dexamethasone Dosing and Tocilizumab Combination for Severe COVID-19

PurposeReal-world experience with tocilizumab in combination with dexamethasone in patients with severe coronavirus disease (COVID-19) needs to be investigated.Materials and MethodsA retrospective cohort study was conducted to evaluate the effect of severity-adjusted dosing of dexamethasone in combination with tocilizumab for severe COVID-19 from August 2020 to August 2021. The primary endpoint was 30-day clinical recovery, which was defined as no oxygen requirement or referral after recovery.ResultsA total of 66 patients were evaluated, including 33 patients in the dexamethasone (Dexa) group and 33 patients in the dexamethasone plus tocilizumab (DexaToci) group. The DexaToci group showed a statistically significant benefit in 30-day clinical recovery, compared to the Dexa group (p=0.024). In multivariable analyses, peak FiO₂ within 3 days and tocilizumab combination were consistently significant for 30-day recovery (all p<0.05). The DexaToci group showed a significantly steeper decrease in FiO₂ (-4.2±2.6) than the Dexa group (-2.7±2.6; p=0.021) by hospital day 15. The duration of oxygen requirement was significantly shorter in the DexaToci group than the Dexa group (median, 10.0 days vs. 17.0 days; p=0.006). Infectious complications and cellular and humoral immune responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the convalescence stage were not different between the two groups.ConclusionA combination of severity-adjusted dexamethasone and tocilizumab for the treatment of severe COVID-19 improved clinical recovery without increasing infectious complications or hindering the immune response against SARS-CoV-2.     

Tocilizumab in patients with severe COVID-19: A single-center observational analysis

Patients with coronavirus disease 2019 (COVID-19) may develop severe respiratory distress, thought to be mediated by cytokine release. Elevated proinflammatory markers have been associated with disease severity. Tocilizumab, an interleukin-6 receptor antagonist, may be beneficial for severe COVID-19, when cytokine storm is suspected. This is a retrospective single-center analysis of the records of patients diagnosed with COVID-19 who received tocilizumab. Outcomes, including clinical improvement, mortality and changes in oxygen-support at 24, 48, and 72 hours, and 7, 14, and 28 days post-tocilizumab, are reported. Patients were evaluated by baseline pre-tocilizumab oxygenation status and changes in proinflammatory markers within 7 days post-tocilizumab are reported. Sixty-six patients received tocilizumab at a mean dose of 724 mg (7.4 mg/kg), 3.7 days from admission. At baseline, 53% of patients were on ventilation support and all had elevated proinflammatory markers, including c-reactive protein (CRP). Common comorbidities were diabetes mellitus (43%) and hypertension (74%). Most patients received concomitant glucocorticoids and hydroxychloroquine. Seven days after tocilizumab, ten patients (15.2%) had clinical improvement in their oxygenation status, and there was a 95% decrease in CRP. Within 14 days of treatment, 29% of patients had clinical improvement, 20% had minimal or no improvement, 17% worsened, 27% died, and 7% were transferred to an outside hospital. Ultimately, 42% of all patients that received tocilizumab expired and 49% were discharged. This study found limited clinical improvement in patients that received tocilizumab in the setting of severe COVID-19. Clinical trials are ongoing to further evaluate tocilizumab's benefit in this patient population.     

Can steroids reverse the severe COVID-19 induced “cytokine storm”?

Severe coronavirus disease (COVID-19) is characterized by an excessive proinflammatory cytokine storm, resulting in acute lung injury and development of acute respiratory distress syndrome (ARDS). The role of corticosteroids is controversial in severe COVID-19 pneumonia and associated hyper-inflammatory syndrome. We reported a case series of six consecutive COVID-19 patients with severe pneumonia, ARDS and laboratory indices of hyper-inflammatory syndrome. All patients were treated early with a short course of corticosteroids, and clinical outcomes were compared before and after corticosteroids administration. All patients evaded intubation and intensive care admission, ARDS resolved within 11.8 days (median), viral clearance was achieved in four patients within 17.2 days (median), and all patients were discharged from the hospital in 16.8 days (median). Early administration of short course corticosteroids improves clinical outcome of patients with severe COVID-19 pneumonia and evidence of immune hyperreactivity.     

The role of HMGB1 in COVID-19-induced cytokine storm and its potential therapeutic targets: A review

Hyperinflammation characterized by elevated proinflammatory cytokines known as ‘cytokine storms’ is the major cause of high severity and mortality seen in COVID-19 patients. The pathology behind the cytokine storms is currently unknown. Increased HMGB1 levels in serum/plasma of COVID-19 patients were reported by many studies, which positively correlated with the level of proinflammatory cytokines. Dead cells following SARS-CoV-2 infection might release a large amount of HMGB1 and RNA of SARS-CoV-2 into extracellular space. HMGB1 is a well-known inflammatory mediator. Additionally, extracellular HMGB1 might interact with SARS-CoV-2 RNA because of its high capability to bind with a wide variety of molecules including nucleic acids and could trigger massive proinflammatory immune responses. This review aimed to critically explore the many possible pathways by which HMGB1-SARS-CoV-2 RNA complexes mediate proinflammatory responses in COVID-19. The contribution of these pathways to impair host immune responses against SARS-CoV-2 infection leading to a cytokine storm was also evaluated. Moreover, since blocking the HMGB1-SARS-CoV-2 RNA interaction might have therapeutic value, some of the HMGB1 antagonists have been reviewed. The HMGB1- SARS-CoV-2 RNA complexes might trigger endocytosis via RAGE which is linked to lysosomal rupture, PRRs activation, and pyroptotic death. High levels of the proinflammatory cytokines produced might suppress many immune cells leading to uncontrolled viral infection and cell damage with more HMGB1 released. Altogether these mechanisms might initiate a proinflammatory cycle leading to a cytokine storm. HMGB1 antagonists could be considered to give benefit in alleviating cytokine storms and serve as a potential candidate for COVID-19 therapy.     

Complement cascade in severe forms of COVID-19: Recent advances in therapy

The complement system is an essential component of the innate immune system. The three complement pathways (classical, lectin, alternative) are directly or indirectly activated by the SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). In the most severe forms of COVID-19, overactivation of the complement system may contribute to the cytokine storm, endothelial inflammation (endotheliitis) and thrombosis. No antiviral drug has yet been shown to be effective in COVID-19. Therefore, immunotherapies represent a promising therapeutic in the immunopathological phase (following the viral phase) of the disease. Complement blockade, mostly C5a-C5aR axis blockade, may prevent acute respiratory distress syndrome (ARDS) from worsening or progression to death. Clinical trials are underway.     

Immune dysfunction in COVID-19 and judicious use of antirheumatic drugs for the treatment of hyperinflammation

In the Wuhan province of China, almost two years ago, in December 2019, the novel Coronavirus 2019 has caused a severe involvement of the lower respiratory tract leading to an acute life-threatening respiratory syndrome, coronavirus disease-19 (COVID-19). Subsequently, coronavirus 2 (SARS-CoV-2) rapidly spread to the entire world causing a pandemic and affected every single person on earth either directly or indirectly with destroying all facets of social life and economy. Since the announcement of COVID-19 as a global pandemic, we have witnessed tremendous scientific work on all aspects of COVID-19 across the globe, which has never been witnessed before. The most remarkable achievement would be the introduction of vaccines, which provide protection from the severe infection and is the only premise for the control of disease. However, despite the tremendous work, the number of treatments either antiviral or immunomodulatory for infected patients are considerably limited, yet disease is causing substantial morbidity and mortality. COVID-19 follows heterogenous disease course among infected individuals, and dysregulated immune system is primarily responsible for the worse outcomes. Immune deficiency, being on corticosteroids for inflammatory diseases, delayed interferon response and advanced age adversely influence prognosis with impairing viral clearance. On the other hand, exuberant immune response with features of cytokine storm is the leading cause of death, which can be alleviated by use of either general immunosuppression with corticosteroids or selective neutralization of potent pro-inflammatory cytokines such as interleukin (IL)-1 and IL-6. Herein, we summarized the potential effective immunomodulatory treatments emphasizing in which patient population it is the most suitable, which dose should be administered, and which is the most appropriate timepoint to administer the drug during the course of the disease.     

A sensitive indicator for the severity of COVID-19: thiol

Background/aimThiol status is a good reflector of the cellular redox and have vital roles in various cellular signaling pathways. The purpose of the study was to investigate thiol status in patients with SARS-CoV-2 infection. Materials and methods A total of 587 subjects (517 patients/70 healthy controls) were enrolled in the study.The patients were categorized into the groups regarding to the severity of disease (mild, moderate, severe, and critical).Thiol status of all groups were compared.ResultsThe patients had significantly diminished thiol levels compared to controls. Thiol levels were gradually decreased as the severity of the disease increased. Logistic regression analyses identified that thiol concentrations were an independent risk factor for the disease severity in each phase (mild group OR 0.975, 95%CI 0.965-0.986; moderate group, OR 0.964, 95%CI 0.953-0.976; severe group OR 0.953, 95%CI 0.941-0.965; critical group OR 0.947, 95%CI 0.935-0.960).Thiol test exhibited the largest area under the curve at 0.949, with the highest sensitivity (98.6%) and specificity (80.4%).ConclusionsDepleted thiol status was observed in SARS-CoV-2 infection. Decline of the thiol levels by degrees while the severity of infection increased was closely related to the progression of the disease. This outcome highlights that thiols could be an impressible biomarker for predicting of the severity of COVID-19.     

Mass cytometry reveals a conserved immune trajectory of recovery in hospitalized COVID-19 patients

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Sepsis of unknown origin with multiorgan failure syndrome: Think of hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis is a clinic pathologic entity characterized by increased proliferation and activation of benign macrophages with hemophagocytosis throughout the reticuloendothelial system. It is a potentially lethal disorder due to an uncontrolled immune response to a triggering agent. HPS may be primary, or secondary to malignancy, infections, auto-immune diseases, and pharmacotherapy. HPS is a rare, but life-threatening complication. Herein, we described a female patient with HPS with secondary sepsis. Our objective was to raise the importance of early diagnosis of HFS by presenting a representative case.     

Dysregulation of the immune response affects the outcome of critical COVID-19 patients

Critical cases of coronavirus disease 2019 (COVID-19) are associated with a high risk of mortality. It remains unclear why patients with the same critical condition have different outcomes. We aimed to explore relevant factors that may affect the prognosis of critical COVID-19 patients. Six critical COVID-19 inpatients were included in our study. The six patients were divided into two groups based on whether they had a good or poor prognosis. We collected peripheral blood samples at admission and the time point of exacerbation to compare differences in the phenotypes and functions of major populations of immune cells between the groups. On admission, compared to patients with poor prognoses, those with good prognoses had significantly higher counts of monocytes (P < .05), macrophages (P < .05), higher frequency of CD3⁺CD4⁺CD45RO⁺CXCR3⁺ subsets (P < .05), higher frequency of CD14⁺CD11C⁺HLA-DR⁺ subset of dendritic cells (P < .05), and a lower count of neutrophils (P < .05). At the time point of exacerbation, the proportions of naïve CD4⁺ T cells (P < .05), Tregs, and Th2 cells in the poor prognosis group were relatively higher than those in the good prognosis group, and CD4⁺ memory T cells were relatively lower (P < .05). According to our results, the poor prognosis group showed a worse immune response than the good prognosis group at the time of admission and at exacerbation. Dysregulation of the immune response affects the outcome of critical COVID-19 patients.     

The role of cytokines and their antagonists in the treatment of COVID-19 patients

The coronavirus disease 2019 (COVID-19) has various presentations, of which immune dysregulation or the so-called cytokine storm syndrome (COVID-CSS) is prominent. Even though cytokines are vital regulators of body immunoinflammatory responses, their exaggerated release can be harmful. This hyperinflammatory response is more commonly observed during severe COVID-19 infections, caused by the excessive release of pro-inflammatory cytokines, such as interleukin-1 (IL-1), IL-6, IL-8, tumour necrosis factor, granulocyte-macrophage colony-stimulating factor, and interferon-gamma, making their blockers and antagonists of great interest as therapeutic options in this condition. Thus, the pathophysiology of excessive cytokine secretion is outlined, and their most important blockers and antagonists are discussed, mainly focussing on tocilizumab, an interleukin-6 receptor blocker approved to treat severe COVID-19 infections.     

Immune repertoire sequencing reveals an abnormal adaptive immune system in COVID-19 survivors

Accumulating evidence suggests that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) impairs the adaptive immune system during acute infection. Still, it remains largely unclear whether the frequency and functions of T and B cells return to normal after the recovery of Coronavirus Disease 2019 (COVID-19). Here, we analyzed immune repertoires and SARS-CoV-2-specific neutralization antibodies in a prospective cohort of 40 COVID-19 survivors with a 6-month follow-up after hospital discharge. Immune repertoire sequencing revealed abnormal T- and B-cell expression and function with large T cell receptor/B cell receptor clones, decreased diversity, abnormal class-switch recombination, and somatic hypermutation. A decreased number of B cells but an increased proportion of CD19⁺CD138⁺ B cells were found in COVID-19 survivors. The proportion of CD4⁺ T cells, especially circulating follicular helper T (cTfh) cells, was increased, whereas the frequency of CD3⁺CD4⁻ T cells was decreased. SARS-CoV-2-specific neutralization IgG and IgM antibodies were identified in all survivors, especially those recorded with severe COVID-19 who showed a higher inhibition rate of neutralization antibodies. All severe cases complained of more than one COVID-19 sequelae after 6 months of recovery. Overall, our findings indicate that SARS-CoV-2-specific antibodies remain detectable even after 6 months of recovery. Because of their abnormal adaptive immune system with a low number of CD3⁺CD4⁻ T cells and high susceptibility to infections, COVID-19 patients might need more time and medical care to fully recover from immune abnormalities and tissue damage.