Association between the expression of toll-like receptors, cytokines, and homeostatic chemokines in SARS-CoV-2 infection and COVID-19 severity

The recent identification of the involvement of the immune system response in the severity and mortality of acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection highlights the importance of cytokines and chemokines as important factors in the clinical outcomes of COVID-19. However, the impact and roles of the BAFF/APRIL cytokine system, homeostatic chemokines (CXCL12, CXCL13, CCL19, and CCL21), as well as Toll-like receptor (TLR)-3/4 in COVID-19, have not been investigated. We sought to assess the expression levels and roles of TLR3/4, BAFF, APRIL, IFN-β, homeostatic chemokines (CXCL12, CXCL13, CCL19, and CCL21), SARS-CoV-2 IgG and IgM antibodies in patients with critical (ICU) and non-ICU (mild) COVID-19 and their association with mortality and disease severity. Significant high levels of TLR-4 mRNA, IFN-β, APRIL, CXCL13, and IgM and IgG antibodies were observed in ICU patients with severe COVID-19 compared to non-ICU COVID-19 patients and healthy controls. On the other hand, BAFF and CCL21 expression were significantly upregulated in non-ICU patients with COVID-19 compared with that in critical COVID-19 patients. The two groups did not differ in TLR-3, CXCL12, and CCL19 levels. Our findings show high expression levels of some inflammatory chemokines in ICU patients with COVID-19. These findings highlight the potential utility of chemokine antagonists as an immune-based treatment for the severe form of COVID-19. We also believe that selective targeting of TLR/spike protein interactions might lead to the development of a new COVID-19 therapy.