Preliminary Evidence of the Differential Expression of Human Endogenous Retroviruses in Kawasaki Disease and SARS-CoV-2-Associated Multisystem Inflammatory Syndrome in Children

Abstract

Multisystem inflammatory syndrome in children (MIS-C) is a postinfectious sequela of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with some clinical features overlapping with Kawasaki disease (KD). Our research group and others have highlighted that the spike protein of SARS-CoV-2 can trigger the activation of human endogenous retroviruses (HERVs), which in turn induces inflammatory and immune reactions, suggesting HERVs as contributing factors in COVID-19 immunopathology. With the aim to identify new factors involved in the processes underlying KD and MIS-C, we analysed the transcriptional levels of HERVs, HERV-related genes, and immune mediators in children during the acute and subacute phases compared with COVID-19 paediatric patients and healthy controls. The results showed higher levels of HERV-W, HERV-K, Syn-1, and ASCT-1/2 in KD, MIS-C, and COV patients, while higher levels of Syn-2 and MFSD2A were found only in MIS-C patients. Moreover, KD and MIS-C shared the dysregulation of several inflammatory and regulatory cytokines. Interestingly, in MIS-C patients, negative correlations have been found between HERV-W and IL-10 and between Syn-2 and IL-10, while positive correlations have been found between HERV-K and IL-10. In addition, HERV-W expression positively correlated with the C-reactive protein. This pilot study supports the role of HERVs in inflammatory diseases, suggesting their interplay with the immune system in this setting. The elevated expression of Syn-2 and MFSD2A seems to be a distinctive trait of MIS-C patients, allowing to distinguish them from KD ones. The understanding of pathological mechanisms can lead to the best available treatment for these two diseases, limiting complications and serious outcomes.

Keywords: COVID-19; HERVs; Kawasaki disease; human endogenous retroviruses; inflammation; multisystem inflammatory syndrome in children.

Figure 1

The mRNA levels of the ENV gene of HERVs, HERV-related sequences, and their putative receptors in blood samples from paediatric patients with Kawasaki disease, COVID-19, multisystem inflammatory syndrome, and healthy controls. The expression levels of (A) the env gene of HERV-W and HERV-K, (B) syncytin-1 (Syn-1), alanine/serine/cysteine/threonine-preferring transporter 1 and 2 (ASCT-1, ASCT-2), and (C) syncytin-2 (Syn-2), and the major facilitator superfamily-domain-containing 2A (MFSD2A) were analysed by qRT-PCR in blood samples from children during the acute and subacute phase of Kawasaki disease (KDa and KDsa), multisystem inflammatory syndrome (MIS-Ca and MIS-Csa), paediatric COVID-19 patients (COV) during the acute phase, and healthy controls (HCs). The results are represented as box plots depicting mild (black dot) and extreme outliers (asterisk) for each group. (D) The p-values for groupwise differences examined by the nonparametric Mann–Whitney U-test (statistical significance is defined when p < 0.050).

Figure 2

The mRNA levels of inflammatory and regulatory cytokines and interferon-gamma and Toll-like receptors in blood samples from paediatric patients with Kawasaki disease, COVID-19, multisystem inflammatory syndrome, and healthy controls. The mRNA levels of (A) inflammatory and regulatory cytokines: interleukin-1β (IL-1β), IL-6, and IL-10, (B) tumour necrosis factor-α (TNF-α), interferon (INF-γ), and monocyte chemoattractant protein 1 (MCP-1), and (C) Toll-like receptors (TLR-3, TLR-4, and TLR-9) were analysed by qRT-PCR in blood samples from children during the acute and subacute phase of Kawasaki disease (KDa and KDsa), multisystem inflammatory syndrome (MIS-Ca and MIS-Csa), paediatric COVID-19 patients (COV) during the acute phase, and healthy controls (HCs). The results are represented as box plots depicting mild (black dot) and extreme outliers (asterisk) for each group. (D) The p-values for groupwise differences examined by the nonparametric Mann–Whitney U-test (statistical significance is defined when p < 0.050).

Figure 3

Scatter plots of HERVs expression levels (X-axis) versus cytokines and CRP levels (Y-axis) in MIS-Ca and COV patients. Pairwise associations between continuous variables were tested through the Spearman correlation test. The Rho coefficients and p-values were reported.