Roles and Functions of Toll-Like Receptors in Coronavirus Infections: Forthcoming Vaccine and Therapeutic Strategies for Confronting COVID-19

Toll -like receptors (TLRs) are a class of pattern recognition receptors (PRRs) that detect pathogen associated molecular patterns and activate innate and adaptive immune system. Coronaviruses can be detected via TLRs through their biological materials such as ribonucleic acids, glycoproteins and CpG motifs. During COVID -19 pandemic, different strategies have been used for combating SARS -CoV -2 to initiate a proper and balanced immune response through TLRs or other PRRS. Understanding the trigerred TLR signaling pathways during coronavirus infections would assist to understand the control and defense mechanisms against these viral diseases. In this review, we summarize different studies on the use and function of of TLRs and their signaling pathways as vaccines/adjuvants or therapeutic agents against coronavirus infections. Since the pandemic is ongoing and there still many unknowns with respect to COVID -19 immunology, we highlight the role of TLRs and their agonists/antagonists in previous coronavirus infections, and show their potential role in the current SARS -CoV -2 immunopathology.