Long COVID-19/post-COVID condition in children: do we all speak the same language?

Post-COVID condition is a new and highly debated entity that is still to be outlined in its complexity, especially in the pediatric population. In response to the article by Trapani and colleagues, we report the results of a long-term follow-up conducted in the outpatient clinic of the Pediatric Infectious Diseases Unit on children admitted to our hospital with SARS-CoV-2 infection.

Multicenter analysis of neutrophil extracellular trap dysregulation in adult and pediatric COVID-19.

Dysregulation in neutrophil extracellular trap (NET) formation and degradation may play a role in the pathogenesis and severity of COVID-19; however, its role in the pediatric manifestations of this disease, including multisystem inflammatory syndrome in children (MIS-C) and chilblain-like lesions (CLLs), otherwise known as "COVID toes," remains unclear. Studying multinational cohorts, we found that, in CLLs, NETs were significantly increased in serum and skin. There was geographic variability in the prevalence of increased NETs in MIS-C, in association with disease severity. MIS-C and CLL serum samples displayed decreased NET degradation ability, in association with C1q and G-actin or anti-NET antibodies, respectively, but not with genetic variants of DNases. In adult COVID-19, persistent elevations in NETs after disease diagnosis were detected but did not occur in asymptomatic infection. COVID-19-affected adults displayed significant prevalence of impaired NET degradation, in association with anti-DNase1L3, G-actin, and specific disease manifestations, but not with genetic variants of DNases. NETs were detected in many organs of adult patients who died from COVID-19 complications. Infection with the Omicron variant was associated with decreased NET levels when compared with other SARS-CoV-2 strains. These data support a role for NETs in the pathogenesis and severity of COVID-19 in pediatric and adult patients.

Autoantibodies Against Proteins Previously Associated With Autoimmunity in Adult and Pediatric Patients With COVID-19 and Children With MIS-C.

The antibody profile against autoantigens previously associated with autoimmune diseases and other human proteins in patients with COVID-19 or multisystem inflammatory syndrome in children (MIS-C) remains poorly defined. Here we show that 30% of adults with COVID-19 had autoantibodies against the lung antigen KCNRG, and 34% had antibodies to the SLE-associated Smith-D3 protein. Children with COVID-19 rarely had autoantibodies; one of 59 children had GAD65 autoantibodies associated with acute onset of insulin-dependent diabetes. While autoantibodies associated with SLE/Sjögren's syndrome (Ro52, Ro60, and La) and/or autoimmune gastritis (gastric ATPase) were detected in 74% (40/54) of MIS-C patients, further analysis of these patients and of children with Kawasaki disease (KD), showed that the administration of intravenous immunoglobulin (IVIG) was largely responsible for detection of these autoantibodies in both groups of patients. Monitoring in vivo decay of the autoantibodies in MIS-C children showed that the IVIG-derived Ro52, Ro60, and La autoantibodies declined to undetectable levels by 45-60 days, but gastric ATPase autoantibodies declined more slowly requiring >100 days until undetectable. Further testing of IgG and/or IgA antibodies against a subset of potential targets identified by published autoantigen array studies of MIS-C failed to detect autoantibodies against most (16/18) of these proteins in patients with MIS-C who had not received IVIG. However, Troponin C2 and KLHL12 autoantibodies were detected in 2 of 20 and 1 of 20 patients with MIS-C, respectively. Overall, these results suggest that IVIG therapy may be a confounding factor in autoantibody measurements in MIS-C and that antibodies against antigens associated with autoimmune diseases or other human proteins are uncommon in MIS-C.

Immunopathological signatures in multisystem inflammatory syndrome in children and pediatric COVID-19.

Pediatric Coronavirus Disease 2019 (pCOVID-19) is rarely severe; however, a minority of children infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) might develop multisystem inflammatory syndrome in children (MIS-C), with substantial morbidity. In this longitudinal multi-institutional study, we applied multi-omics (analysis of soluble biomarkers, proteomics, single-cell gene expression and immune repertoire analysis) to profile children with COVID-19 (n = 110) and MIS-C (n = 76), along with pediatric healthy controls (pHCs; n = 76). pCOVID-19 was characterized by robust type I interferon (IFN) responses, whereas prominent type II IFN-dependent and NF-κB-dependent signatures, matrisome activation and increased levels of circulating spike protein were detected in MIS-C, with no correlation with SARS-CoV-2 PCR status around the time of admission. Transient expansion of TRBV11-2 T cell clonotypes in MIS-C was associated with signatures of inflammation and T cell activation. The association of MIS-C with the combination of HLA A*02, B*35 and C*04 alleles suggests genetic susceptibility. MIS-C B cells showed higher mutation load than pCOVID-19 and pHC. These results identify distinct immunopathological signatures in pCOVID-19 and MIS-C that might help better define the pathophysiology of these disorders and guide therapy.

Detection of faecal SARS-CoV-2 RNA in a prospective cohort of children with multisystem inflammatory syndrome (MIS-C).

BACKGROUND: Multisystem Inflammatory Syndrome in Children (MIS-C) is a rare but severe illness associated with SARS-CoV-2 infection. A dysregulated immune response is recognized as the main pathogenic mechanism. Previous studies demonstrated the presence of SARS-CoV-2 RNA in faeces of almost one-third of patients with COVID-19, while data are currently missing about MIS-C. OBJECTIVES: to evaluate faecal sample positivity to SARS-CoV-2 in MIS-C and to compare the positivity rate between MIS-C and COVID-19 hospitalised children.  DESIGN: observational descriptive study with prospective patient enrollment. SETTING AND PARTICIPANTS: the SARS-CoV-2 positivity was evaluated in stool samples obtained in a prospective series of 63 paediatric patients admitted to Regina Margherita Children's Hospital (Azienda Ospedaliero Universitaria - Città della Salute e della Scienza, Turin, Northern Italy) with diagnosis of MIS-C (N. 31) or COVID-19 (N. 32), during the first year of pandemic emergency. The real-time reverse transcription polymerase chain reaction (real-time RT-PCR), was performed using a validated kit measuring 3 target SARS-CoV-2 genes: E gene, N gene, and ORF1ab gene MAIN OUTCOME MEASURES: SARS-CoV-2 stool positivity and concomitant gastrointestinal symptoms. RESULTS: overall, 16/63 (25%) stool samples revealed the presence of SARS-CoV-2 mRNA. In patients with COVID-19, faecal samples were collected 8 days as median (IQR 7) after the presumed viral exposure and were positive in 12/31 (39%; 95%CI 23.2-56.2); among children with MIS-C, stools were collected 27.5 days as median (IQR 26.25) after presumed contact and the positivity rate was 12.5% (95%CI 4.4-27.0) (4/32). More than 80% of the children with MIS-C presented gastrointestinal symptoms, but the frequency of gastrointestinal symptoms in patients with positive stools for SARS-CoV-2 RNA is not higher than patients tested negative (p=0.092). CONCLUSIONS: MIS-C patients frequently experienced gastrointestinal symptoms, confirming the intestinal involvement in MIS-C already described in the literature. The presence of SARS-CoV-2 mRNA in faecal samples is confirmed in more than 10% of MIS-C patients and stool positivity was also detected many days after presumed first contact with the virus. This data suggests the possibility of tracing SARS-COV-2 also in faeces for a better description of its circulation and spread in the environment.

COVID-19 in Children: Expressions of Type I/II/III Interferons, TRIM28, SETDB1, and Endogenous Retroviruses in Mild and Severe Cases.

Children with the new coronavirus disease 2019 (COVID-19) have milder symptoms and a better prognosis than adult patients. Several investigations assessed type I, II, and III interferon (IFN) signatures in SARS-CoV-2 infected adults, however no data are available for pediatric patients. TRIM28 and SETDB1 regulate the transcription of multiple genes involved in the immune response as well as of human endogenous retroviruses (HERVs). Exogenous viral infections can trigger the activation of HERVs, which in turn can induce inflammatory and immune reactions. Despite the potential cross-talks between SARS-CoV-2 infection and TRIM28, SETDB1, and HERVs, information on their expressions in COVID-19 patients is lacking. We assessed, through a PCR real time Taqman amplification assay, the transcription levels of six IFN-I stimulated genes, IFN-II and three of its sensitive genes, three IFN-lIIs, as well as of TRIM28, SETDB1, pol genes of HERV-H, -K, and -W families, and of env genes of Syncytin (SYN)1, SYN2, and multiple sclerosis-associated retrovirus (MRSV) in peripheral blood from COVID-19 children and in control uninfected subjects. Higher expression levels of IFN-I and IFN-II inducible genes were observed in 36 COVID-19 children with mild or moderate disease as compared to uninfected controls, whereas their concentrations decreased in 17 children with severe disease and in 11 with multisystem inflammatory syndrome (MIS-C). Similar findings were found for the expression of TRIM-28, SETDB1, and every HERV gene. Positive correlations emerged between the transcriptional levels of type I and II IFNs, TRIM28, SETDB1, and HERVs in COVID-19 patients. IFN-III expressions were comparable in each group of subjects. This preserved induction of IFN-λs could contribute to the better control of the infection in children as compared to adults, in whom IFN-III deficiency has been reported. The upregulation of IFN-I, IFN-II, TRIM28, SETDB1, and HERVs in children with mild symptoms, their declines in severe cases or with MIS-C, and the positive correlations of their transcription in SARS-CoV-2-infected children suggest that they may play important roles in conditioning the evolution of the infection.

Sequelae of COVID-19 in Hospitalized Children: A 4-Months Follow-Up.

Little is known about the sequelae of SARS-CoV-2 infection in children. In a COVID-19 dedicated clinic, we followed-up for 4 months 25 children previously hospitalized for COVID-19, performing clinical, laboratory, and lung ultrasound evaluation. Mid-term sequelae were rarely observed in our COVID-19 children's cohort.