In this pilot study, an Italian research team analyzed transcriptional levels of human endogenous retroviruses (HERVs), HERV-related genes, and immune mediators in blood samples from children in the acute or subacute phase of Kawasaki disease (KD), in the acute or subacute phase of multisystem inflammatory syndrome in children (MIS-C), in the acute COVID-19 and in healthy controls. The findings revealed activation of HERVs and inflammatory mediators in pediatric patients with COVID-19, MIS-C, and KD.
Children who are positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are usually asymptomatic or develop mild disease, but, they are at risk of developing a postinfectious complication called multisystem inflammatory syndrome in children (MIS-C). MIS-C is characterized by severe systemic inflammation that affects multiple organs and tissues. Certain clinical characteristics of MIS-C overlap with Kawasaki disease (KD), a febrile systemic vasculitis of the small- and medium-sized arteries that usually affects children under the age of five. Therefore, MIS-C has also been called Kawasaki-like syndrome.
The human endogenous retroviruses (HERVs) are relics of ancient infections, characterized by an RNA intermediate that is reverse-transcribed into a double-stranded DNA. This double-stranded DNA, called a provirus, is capable of integrating into the host cell genome. Because of such a process of endogenization and further fixation in the human population, HERVs have been vertically transmitted to offspring in a Mendelian fashion, constituting up to ~8% of the human genome. HERVs are stable components of the human transcriptome, and exhibit differential expression across a diverse range of human tissues. Particularly, when activated by a specific infectious agent, HERVs with pathogenic effects may cause clinical manifestations that correspond to the tissue in which they are expressed. They are regarded as “dormant enemies within”.
The authors emphasized that their research group and other scientists have demonstrated 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. This suggests that HERVs are contributing factors to the immunopathology of in COVID-19. https://discovermednews.com/sars-cov-2-has-the-ability-to-awaken-ancient-retroviral-genes-and-induce-expression-of-human-endogenous-retroviruses-w-envelope-proteins/
About the study
This multicentre prospective study included 54 children, eight of whom were diagnosed with KD, 17 with MIS-C and 10 with acute COVID-19. Children who tested positive for SARS-CoV-2 RT-PCR in swab samples and reported symptoms compatible with COVID-19 were diagnosed with COVID-19. The diagnosis of KD was made according to the 2017 guidelines of the American Heart Association, and the diagnosis of MIS-C was made according to WHO criteria. The time from disease onset to the 10th day of fever was defined as the “acute phase”, while the time from 11th to 20th day after the fever onset was defined as the “subacute phase”. The healthy controls (n= 19) reported no neurological or psychiatric disorders or the presence of ongoing infections in their medical history.
Transcriptional levels of HERVs, HERV-related genes, syncytin (Syn) 1 and 2, alanine/serine/cysteine/threonine-preferring transporter (ASCT) 1 and 2, and major facilitator superfamily-domain containing 2A (MFSD2A) were analyzed by qRT-PCR in blood samples from children in the acute and subacute phases of KD and MIS-C, in the acute COVID-19 and from healthy controls. In addition, qRT-PCR was employed to assess the mRNA levels of inflammatory and regulatory cytokines: interleukin-1β (IL-1β), IL-6, and IL-10, tumour necrosis factor-α (TNF-α), interferon (INF-γ), monocyte chemoattractant protein 1 (MCP-1), and Toll-like receptors (TLR-3, TLR-4, and TLR-9).
The results showed higher levels of HERV-W, HERV-K, Syncytin (Syn)-1, and ASCT-1 and 2 in blood samples from patients with KD, MIS-C, and COVID-19 compared to healthy controls. Higher levels of Syn-2 and MFSD2A were found only in patients with MIS-C, regardless of the stage of the disease. Moreover, higher levels of HERV-K, Syn-2, and MFSD2A were maintained during the subacute phase of MIS-C in contrast to the subacute phase of KD. Only patients with MIS-C had high values of HERVs, Syn-1, and its putative receptors, but also elevated mRNA levels of Syn-2 and its receptor MFSD2A.
The increase in transcriptional activity of Syn-2 and MFSD2A was detected only in the peripheral blood of MIS-C patients. This expression profile was maintained in patients with MIS-C throughout the subacute phase. But, HERVs, Syn-1 and its receptors decreased during the subacute phase of MIS-C, likely due to the reduction of the infectious stimulus.
As MIS-C develops after the COVID-19, researchers compared the transcriptional activity in blood samples from children with MIS-C and children with COVID-19. The findings revealed higher levels of HERV-W, Syncytins (Syn-1 and Syn-2) ASCT-1 and 2, and MFSD2A in children with MIS-C.
Also, children in the acute phase of MIS-C had higher mRNA levels of HERV-W, HERV-K, Syn-1, Syn-2, ASCT-1, and MFSD2A compared to children in the acute phase of KD. Children in the subacute phase of KD had higher levels of HERV-K than children in the acute phase of KD. The authors noted that they have shown for the first time that HERVs, Syn-1, and its putative receptors are highly expressed in patients with KD, although the levels observed do not reach those observed in MIS-C patients. Given the inflammatory nature of KD and the ability of HERVs to modulate the inflammatory response, they speculated that HERVs may also contribute to the immunopathogenesis of KD.
The mRNA levels of cytokines IL-1β, IL-6, IL-10, TNF-α, MCP-1, IFN-γ, and Toll-like receptors TLR-3, TLR-4, and TLR-9 were also assessed in the same samples by quantitative RT real-time PCR analysis. Compared to healthy controls, all the three diseases were characterized by significant increase in the mRNA levels of the cytokines.
Increased mRNA levels of TLRs were found in children with acute COVID-19, in children in the acute phase of MIS-C, and in children in the subacute phase of MIS-C. These results show that an increase in the mRNA levels of TLRs parallels with HERVs activation in children with COVID-19 and children with MIS-C. The authors stated that these findings could be attributed to the ability of HERVs to activate pattern-recognition receptors, evoking the production of proinflammatory mediators.
In pediatric patients with COVID-19 the levels of IL-6, IL-10, MCP-1, TLR-3, and TLR-9 were higher than in patients with MIS-C. The levels of TNF-α were higher in patients in the acute phase of MIS-C.
The comparison of transcriptional activity in blood samples from children in the acute phase of KD and those in the acute phase of MIS-C revealed that the expression levels of TNF-α were higher in the latter group, whereas the levels of IL-10 were higher in the former group. Patients in the subacute phase of MIS-C had higher levels of IL-10 and MCP-1 than patients in the subacute phase of KD.
The progression of KD revealed lower levels of IL-10, TNF-α, and MCP-1 in the subacute phase compared with the acute phase of the disease. During the progression of MIS-C, lower levels of TNF-α, TLR-3, TLR-4, TLR-7, and TLR-9 were found during the subacute phase compared with the acute phase. Only IL-6 and IL-10 were found to be higher in the subacute phase compared to the acute phase of MIS-C. It is interesting that correlation analysis demonstrated an association between HERVs and cytokine expression only in patients with MIS-C. Negative correlations have been found between HERV-W mRNA levels and IL-10 and between Syn-2 and IL-10, whereas positive correlations have been found between HERV-K mRNA levels and IL-10 and between HERV-W mRNA levels and C-reactive protein.
In conclusion, these findings revealed the activation of HERVs, syncytin, and its putative receptors, as well as inflammatory mediators in pediatric patients with COVID-19, MIS-C, and KD. These results support the role of HERVs in inflammatory diseases, and their interaction with the immune system. In particular, the increased mRNA levels of Syn-2 and MFSD2A seem to be a characteristic feature of MIS-C patients at the transcriptional level.
This article was published in the International Journal of Molecular Sciences.
Balestrieri, E et al. Preliminary Evidence of the Differential Expression of Human Endogenous Retroviruses in Kawasaki Disease and SARS-CoV-2-Associated Multisystem Inflammatory Syndrome in Children. Int. J. Mol. Sci. 2023, 24, 15086. https://doi.org/10.3390/ijms242015086