MultiInflammatory Syndrome in Children: A View into Immune Pathogenesis from a Laboratory Perspective

Describing Elephants: An Update on the Immunopathology of Multisystem Inflammatory Syndrome in Children

First described in 2020, multi-system inflammatory syndrome in children (MIS-C) is an, initially life-threatening, disease characterised by severe inflammation and following exposure to SARS-CoV-2. The immunopathology of MIS-C involves a hyperinflammation characterised by a cytokine storm and activation of both the innate and adaptive immune system, eventually leading to multi-organ failure. Several etiological theories are described in literature. Firstly, it is suggested that the gut plays an important role in the translocation of microbial products to the systemic circulation. Additionally, the production of autoantibodies that develop after the initial infection with SARS-CoV-2 might lead to many of its broad clinical symptoms. Finally, the superantigen theory where non-specific binding of the SARS-CoV-2 spike glycoprotein to the T-cell receptor leads to a subsequent activation of T cells, generating a powerful immune response. Despite the sudden outbreak of MIS-C and alarming messages, as of 2024, cases have declined drastically and subsequently show a less severe clinical spectrum. However, subacute cases not meeting current diagnostic criteria might be overlooked even though they represent a valuable research population. In the future, research should focus on adjusting these criteria to better understand the broad pathophysiology of MIS-C, aiding early detection, therapy, and prediction.

Risk of COVID-19 in pediatric population and the effects of COVID-19 vaccination: A retrospective cohort study

OBJECTIVE

Prior studies have demonstrated the adverse effects of upper respiratory infections on the pediatric population, such as increased risk for acute otitis media (AOM). Other studies have noted decreased otitis media complaints during the COVID-19 pandemic. This project aims to identify whether individuals who tested positive for COVID-19 at the Emergency Department (ED) visit had an increased risk of developing severe complications. Additionally, we will study whether vaccination helped decrease following COVID-19 complications.

METHODS

Utilizing the TriNetX database, we obtained de-identified electronic medical records for children under five and 6-10 years old from 2020-2023 in the United States. The study population was propensity-matched for gender, index age, and comorbidities. Complications within eight weeks of the ED visit were compared between COVID-19 vaccinated and unvaccinated children. Risk ratio was used to measure associations between our groups. A p-value less than or equal to 0.05 was considered significant.

RESULTS

After propensity matching, a total of 211,138 children were identified. Within eight weeks after the ED visit, unvaccinated children <5 years old who tested negative for COVID-19 had a 30 % relative risk reduction for AOM, 52 % for sinusitis, 76 % for multisystem inflammatory system (MIS), 17 % for acute respiratory failure, and 37 % for septic shock when compared to those with a positive COVID-19 result (p ≤ 0.05). Unvaccinated 6-10 years old children who tested negative for COVID-19 had an 18 % risk reduction for AOM, 44 % reduction for sinusitis, 63 % reduction for MIS, and 42 % for acute respiratory failure (p ≤ 0.05) compared to those that tested positive for COVID-19. Vaccinated children with positive COVID-19 results have no significant risk of AOM or acute respiratory failure. Additionally, children 6-10 years old with positive COVID-19 results did not have a substantial risk of sinusitis.

CONCLUSION

COVID-19's effects require continued investigation in children. This study showed that there are some increased risks of severe complications following this viral infection.

SARS-CoV-2 serology in pediatrics: Seroprevalence studies in unvaccinated children and humoral antibody response post vaccination

BACKGROUND

Humoral response against SARS-CoV-2 is increasingly accepted as the central correlate of immune protection. Recent pediatric seroprevalence data are extremely limited. Significant knowledge gaps also exist in immune response to mRNA SARS-CoV-2 vaccination in children. As children demonstrate distinct response to naïve infection relative to adults, it is essential to investigate age-specific differences in seroprevalence and antibody response to SARS-CoV-2 vaccination.

METHODS

Seroprevalence was assessed through two cross-sectional serosurveys prior to COVID-19 vaccination approval in children <5 years using residual patient specimens (n = 2902). To assess antibody response post-vaccination, 842 participants (580 children, 262 adults) were prospectively recruited with informed consent. Participation required completion of a health questionnaire and blood donation. Samples were collected at varying times post-vaccination and assayed using the Abbott AdviseDx SARS-CoV-2 IgG II and DiaSorin LIAISON SARS-CoV-2 TrimericS IgG assays.

RESULTS

Significant increases in seroprevalence were observed between the first and second serosurveys in unvaccinated children <6 months to 5 years (38-75%). In the prospective vaccination cohort, serokinetic response decreased with time post-dose of an mRNA vaccine. Measured IgG titres were significantly higher in children relative to adults across all time points.

CONCLUSIONS

This is the largest evaluation of quantitative SARS-CoV-2 antibody assays in a cohort of Canadian children, adolescents, and adults. Findings suggest high rates of SARS-CoV-2 exposure among unvaccinated young children in the Toronto community. Additional data supports children have higher antibody titres relative to adults post-vaccination.

Mechanisms of redox balance and inflammatory response after the use of methylprednisolone in children with multisystem inflammatory syndrome associated with COVID-19

Background

Multisystem inflammatory syndrome in children (MIS-C) associated with being infected with coronavirus-19 (COVID-19) is a life-threatening condition resulting from cytokine storm, increased synthesis of reactive oxygen species (ROSs), and hyperinflammation occurring in genetically predisposed children following an infection with SARS-CoV-2.

Aim

The primary aims of our study were to identify changes in the activity of antioxidant enzymes in erythrocytes and total oxidative status in plasma after being treated with methylprednisolone (MP).

Methods

A prospective cohort study of 67 children (56.7% male) under 18 with MIS-C being treated with MP was conducted at the Mother and Child Health Institute from January 2021 to April 2022. The impact of the therapy was assessed on the basis of the clinical condition, haematological and biochemical blood parameters, and echocardiographic findings.

Results

59.7% of patients presented cardiovascular (CV) manifestations, while myocardial dysfunction was observed in half of all patients (50.7%). A severe clinical course was observed in 22/67 patients. Children with CV involvement had a significantly higher relative concentration of B lymphocytes and lower relative concentration of NK cells than patients without CV issues (p < 0.001 and p = 0.004, respectively). Patients with severe MIS-C had a lower relative count of NK cells than those with moderate MIS-C (p = 0.015). Patients with myocardial dysfunction had a higher total oxidative plasma status (TOPS) than children without (p = 0.05), which implicates pronounced oxidative stress in the former cohort. In patients with shock, lower erythrocytes superoxide dismutase (SOD) activity was observed on admission compared to patients without shock (p = 0.04). After MP was administered, TOPS was significantly reduced, while catalase (CAT) and SOD activity increased significantly. Treatment failure (TF) was observed in 6 patients, only females (p=0.005). These patients were younger (p=0.05) and had lower CAT activity on admission (p=0.04) than patients with favorable treatment responses. In the group of patients with TF, TOPS increased after treatment (before 176.2 ± 10.3 mV, after 199.0 ± 36.7 mV).

Conclusion

MP leads to rapid modulation of TOPS and increases the activity of antioxidant enzymes in erythrocytes resulting in clinical and echocardiographic improvement. Based on the observed changes in the activity of the antioxidant enzymes, we can conclude that s hydrogen peroxide is the dominant ROS in patients with MIS-C. Patients with TF showed reduced CAT activity, whereas the treatment with MP led to pronounced oxidation. This implies that low CAT activity may be a contraindication for using MP.

Clinical Characteristics and Laboratory Findings in Children with Multisystem Inflammatory Syndrome (MIS-C)-A Retrospective Study of a Tertiary Care Center from Constanta, Romania

A new hyper-inflammatory syndrome in children was identified after SARS-CoV-2 infection as a post-infectious complication that is temporally associated with coronavirus disease (COVID-19). Fever, rash, conjunctival hyperemia, and gastrointestinal problems are all clinical manifestations of multisystem inflammatory syndrome in children. This condition, in some cases, causes multisystem involvement, affecting multiple organ systems and necessitating admission to a pediatric intensive care unit. Due to limited clinical studies, it is necessary to analyze the characteristics of the pathology in order to improve the management and long-term follow-up of high-risk patients. The objective of the study was to analyze the clinical and paraclinical characteristics of children diagnosed with MIS-C. The clinical study is a retrospective, observational, descriptive research work that includes patients diagnosed with MIS-C, temporally associated with coronavirus disease, and it contains clinical characteristics, laboratory data, and demographic information. The majority of patients had normal or slightly increased leukocyte counts, which were associated with neutrophilia, lymphocytopenia, and significantly elevated inflammatory markers, including high levels of C-reactive protein, fibrinogen, the erythrocyte sedimentation rate, serum ferritin, and IL 6 and elevated levels of the cardiac enzymes NT-proBNP and D-dimers, owing to the cardiovascular system involvement in the pro-inflammatory process. At the same time, renal system involvement led to raised creatinine and high proteinuria in association with hypoalbuminemia. This characteristic of the pro-inflammatory status as well as multisystem impairment are highly suggestive of the post-infection immunological reaction of the multisystem syndrome temporally associated with SARS-CoV-2 infection.

The Sequential Use of Extracorporeal Cytokine Removal Devices in an Adolescent With COVID-19 Receiving Continuous Renal Replacement Therapy

A 14-year-old male developed multisystem inflammatory syndrome in children (MIS-C) after acquiring the SARS-CoV-2 infection. He deteriorated rapidly requiring inotropic and ventilatory support as well as continuous renal replacement therapy (CRRT) due to rhabdomyolysis-associated acute kidney injury. A hemoadsoprtion column Cytosorb® was first incorporated into the CRRT circuit for myoglobin and cytokines removal, which was followed by sequential use of another type of cytokine-removing hemofilter (Oxiris®) (altogether 100 hours of extracorporeal blood purification [EBP] therapy). There was no major complication related to the EBP therapy. Cytokine profile revealed a marked reduction of levels of several cytokines including tumor necrosis factor-α, interleukin (IL)-6, IL-8, and IL-10 after the EBP therapy. It was noted that both pro-inflammatory and anti-inflammatory cytokines were removed, and the removal efficacy varied between different devices. His condition improved and the serum ferritin, C-reactive protein, and procalcitonin levels also dropped gradually, which correlated well with his clinical progress and the trend of cytokine levels. Our case demonstrated that extracorporeal cytokine removal can be safely applied in children with MIS-C and can be considered as adjunctive therapy in selected patients with critically ill conditions.

Nutraceuticals for Complementary Treatment of Multisystem Inflammatory Syndrome in Children: A Perspective from Their Use in COVID-19

Multisystem inflammatory syndrome in children (MIS-C) has been widely reported in some children diagnosed with SARS-CoV-2. Clinical signs of MIS-C are manifested at 2 to 4 weeks after SARS-CoV-2 infection, where elevated biomarkers of inflammation and cardiac dysfunction are the hallmark of this syndrome when infection or exposure to SARS-CoV-2 has been confirmed. However, after two years of acknowledgment, MIS-C treatment is still under research to reach safety and effectiveness in the acute phase in children. Therefore, in this review, we discuss the potential use of natural compounds with antioxidant and anti-inflammatory effects to reduce collateral damage caused by hyperinflammation in MIS-C pathology for new research in treatment and interventions.

Maternal COVID-19 Vaccine May Reduce the Risk of MIS-C in Infants: A Narrative Review

COVID-19 infection in the pediatric population usually leads to a mild illness; however, a rare but serious complication of MIS-C has been seen in children. MIS-C usually presents 2–4 weeks after COVID-19 infection or exposure, and rare reports have been documented in neonates. Vaccinations for COVID-19 have been approved for children aged 6 months and above in the United States, and recent reports suggest significantly low prevalence and risk of complications of Multi-organ Inflammatory Syndrome (MIS-C) in vaccinated children compared to unvaccinated children. Vaccinations for COVID-19 are safe and recommended during pregnancy and prevent severe maternal morbidity and adverse birth outcomes. Evidence from other vaccine-preventable diseases suggests that through passive transplacental antibody transfer, maternal vaccinations are protective against infections in infants during the first 6 months of life. Various studies have demonstrated that maternal COVID-19 vaccination is associated with the presence of anti-spike protein antibodies in infants, persisting even at 6 months of age. Further, completion of a 2-dose primary mRNA COVID-19 vaccination series during pregnancy is associated with reduced risk for COVID-19–associated hospitalization among infants aged 6 months or less. Therefore, it can be hypothesized that maternal COVID-19 vaccination can reduce the risk of and severity of MIS-C in infants. In this article, we review the literature to support this hypothesis.

COVID-19 and Myocarditis: Review of Clinical Presentations, Pathogenesis and Management

There are four main myocarditis presentations identified in the context of severe acute respiratory coronavirus 2 (SARS-CoV-2): myocarditis associated with acute coronavirus disease 2019 (COVID-19) infection, post-acute COVID-19 syndrome, multisystem inflammatory syndrome, and vaccination-associated myocarditis. This article reviews the clinical features and current management strategies for each of these presentations. The overall prevalence of myocarditis is considered to be rare, although accurate estimation is affected by heterogeneity in diagnostic criteria and reporting, as well as infrequent use of gold-standard diagnostic endomyocardial biopsy. Severity of disease can range from mild symptoms to fulminant myocarditis. Therapeutic interventions are typically supportive and extrapolated from treatment for non-COVID-19 viral myocarditis. Several pathogenic mechanisms for the development of myocarditis have been proposed, and ongoing research is critical for elucidating disease pathogenesis and potentially identifying therapeutic targets. The long-term cardiovascular sequelae of SARS-CoV-2 infections and associated myocarditis require further elucidation and understanding.

Cardiac Complications Associated with COVID-19, MIS-C, and mRNA COVID-19 Vaccination

The COVID-19 vaccine is now approved for individuals greater than 5 years of age, but vaccination rates remain lower than expected in the pediatric age group. Misinformation and widespread reporting of vaccine-related myocarditis are contributing to vaccine hesitancy. When compared to severe cardiac complications that are associated with COVID-19, vaccine-related myocarditis has a milder presentation, is easily treated, and has a good prognosis. Acute COVID-19 has been associated with higher rates of myocarditis and myocardial injury. Multisystem inflammatory syndrome in children occurs weeks after initial infection with SARS-CoV-2 and can be associated with severe cardiovascular complications and death. Cardiac complications associated with acute COVID-19 and MIS-C are more severe and occur more frequently than myocarditis after mRNA COVID-19 vaccination. Furthermore, some of the academic and social disruptions caused by the pandemic expect to be eased by widespread vaccination. For all these reasons, COVID-19 vaccination is strongly recommended for all eligible age groups.

Clinical characteristics of children with MIS-C fulfilling classification criteria for macrophage activation syndrome

BACKGROUND

Macrophage activation syndrome (MAS) is a potentially life-threatening complication of various inflammatory disorders, including multisystem inflammatory syndrome in children (MIS-C). MIS-C refractory to treatment should raise suspicion of MAS, which can be fatal if a definitive diagnosis is delayed. Unfortunately, there is a lack of data on MAS in children with MIS-C.

OBJECTIVE

Our study aims to analyze the risk factors for the development of MAS in MIS-C, its clinical course and response to treatment, and identify predictive factors for pediatric intensive care.

MATERIAL AND METHODS

We analyzed data from the Polish MIS-C registry of the MultiOrgan Inflammatory Syndromes COVID-19 Related Study. Patients were diagnosed according to the WHO MIS-C definition and treated according to national guidelines (Polish Pediatric Society) based on international consensus. MAS definition was based on 2016 Classification Criteria for Macrophage Activation Syndrome Complicating Systemic Juvenile Idiopathic Arthritis.

RESULTS

Two-hundred and seventy four children met the study inclusion criteria. Fifty-nine patients fulfilled MAS classification criteria, nine of which required admission to the pediatric intensive care unit (PICU). MIS-C patients with MAS were significantly older than patients without MAS (median 11.2 vs. 8.1 years). Multivariable analysis showed that age, symptoms characteristic of atypical Kawasaki disease, and skin erosions were significant factors associated with MAS in MIS-C patients. Analysis of laboratory parameters showed that on admission, MIS-C patients with MAS had significantly lower median lymphocyte and platelet counts, albumin and sodium levels, and higher median levels of C-reactive protein, procalcitonin, ferritin, D-dimers, triglycerides, serum creatinine, urea, and γ-glutamyl transpeptidase, and neutrophil count. Multivariate analysis showed that higher procalcitonin, ferritin, and fibrinogen levels at admission were predictive of MAS. Only elevated troponin level was a factor indicating a requirement of PICU hospitalization for children with MAS. MIS-C patients fulfilling MAS criteria were treated more often with intravenous immunoglobulins and steroids than children without MAS. Children with MAS more often required mechanical ventilation. None of the patients required biological agents.

CONCLUSIONS

The clinical course of MAS in MIS-C seems milder, treatment less aggressive, and the prognosis better than expected based on the current knowledge on MAS complicating other rheumatological diseases.