Mechanism of IL-6 expression in SARS-CoV-2 infected peripheral monocyte-derived macrophages

In a recent study posted on Research Square* Preprint server. Scientific ReportsResearchers investigated the detailed mechanism of’Cytokine storm‘This induces acute respiratory distress syndrome (ARDS) and often leads to the death of patients with severe coronavirus disease 2019 (COVID-19).

Previous studies have shown the involvement of cytokines such as interleukin (IL) -6 in ARDS by SARS-CoV-2 infection with severe acute respiratory syndrome. In addition, studies have shown the presence of IL-6-producing CD14 + CD16 + monocytes in the peripheral blood of COVID-19 patients in the intensive care unit compared to COVID-19 patients who do not require hospitalization. ..

Monocytes are often the first cells of the immune system to come into contact with viral pathogens, including SARS-CoV-2. However, the detailed mechanism of IL-6 expression in SARS-CoV-2 infected peripheral monocyte-derived macrophages (MDM) is unknown.

About research

In this study, researchers added frozen / thawed lysates of SARS-CoV-2 infected cells to cultured macrophages (MDM) or pluripotent bone marrow cells to mimic SARS-CoV-2 infection in the alveoli. And then these cells secreted IL-6. They studied the underlying mechanisms that regulate IL-6 expression in SARS-CoV-2 infected peripheral monocyte-derived macrophages (MDM). They also showed that anti-nucleocapsid (N) antibodies enhance the induction of IL-6 via nucleocapsid (N) proteins.

Survey results

Transmembrane serine protease 2 (TMPRSS2) / VeroE6 cells infected with SARS-CoV-2 while investigating the effects of SARS-CoV-2 infected cells on MDM (as a model of SARS-CoV-2 infection in the alveolar) The lysate was added to MDM along with SARS-CoV-2.

Despite the fact that SARS-CoV-2 RNA levels decreased over time, the authors found that IL-6 in the supernatant of MDM incubated with SARS-CoV-2 infected cytolysis. We focused on increasing levels, but not for non-infected cells. Lysate. Interestingly, three different strains of SARS-CoV-2 isolates were able to induce IL-6 production by MDM.

Testing myelomonocyte leukemia cells (K-ML2) cells as an alternative to MD, the authors found that SARS-CoV-2 infected cell lysates induce IL-6 production from K-ML2 cells and SARS- We noted that it suggests a specific component of CoV-2. -Infected cells stimulated MDM and K-ML2 cells to produce IL-6.

By screening for SARS-CoV-2 protein expression plasmid transfected into a derivative of human fetal kidney 293 cells containing SV40 T antigen (293T cells), SARS-CoV-2N protein containing recombinant N protein produces IL-6. It was found to be more efficient than the SARS_CoV-2 spike (S) protein. In addition, using a plasmid encoding a shortened version of the N protein, the authors were able to identify that the C-terminal domain (CTD) of the N protein is responsible for IL-6-induced activity.

In both culture supernatants of granulocyte macrophage colony stimulating factor (GM-CSF) stimulating factor and macrophage colony stimulating factor (M-CSF) stimulated MDM, after 2 days of N protein stimulation, the assay results show elevated levels of multiple cytokines. Was shown. All these cytokines, including IL-6, IL-8, tumor necrosis factor (TNF-α), macrophage inflammatory protein-1 beta (MIP-1β), pentraxin-3, thymic stromal phosphopoietin (TSLP), Rise during severe COVID-19.

In GM-CSF-stimulated MDM, an increase in N-protein-induced increase in IP-10, a predictor of severe disease of COVID-19, was observed, and even if MDM was not productive, cytokines in COVID-19 patients were observed. Infection with SARS-CoV-2 indicates that it can be a source.

Transfection of K-ML2 cells containing N protein with serially diluted patient sera from actual SARS-CoV-2 patients enhanced IL-6 production, although 0.01-10% of COVID-19 patient sera enhanced IL-6 production. Serum from 5 healthy donors does not enhance IL-6 production.

In addition, when researchers evaluated 203 serum samples from mild, moderate, and severe COVID-19 cases, the serum of severe patients induced significantly more IL-6 than other patients. Was observed. Similarly, anti-N antibody levels also increased.

Conclusion

This study showed that SARS-CoV-2 infected epithelial cells induce IL-6 production via bystander macrophages or bone marrow cells (due to the presence of the SARS-CoV-2 N protein). therefore, COVID19 Symptoms It may worsen rapidly 5 to 8 days after the onset of symptoms, and anti-N antibodies enhance this phenomenon.

The results showed that the proposed mechanism of antibody-dependent enhancement (ADE) of IL-6 production from macrophages could occur without actual productive SARS-CoV-2 infection.Therefore, this study provided relatively little evidence. Effectiveness of An all-virus-based COVID-19 vaccine that is more inactivated than the widely used messenger ribonucleic acid (mRNA) -based vaccines such as the Moderna vaccine.

For COVID-19 treatment, steroids and anti-IL-6 receptor antibodies are recommended to suppress the excessive immune response. Five anti-N antibodies, including N1, N4, N5, N9, and N12, may serve as a new therapeutic strategy for COVID-19, which will be treated in future studies based on IL-6 suppression. Only possible if is established.

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