Toll-Like Receptors and Emerging Viral Infections

Abstract

Emerging viral infections are considered a global threat, and they have gained more importance after the coronavirus outbreak in 2019, which affected the whole world. The innate immune system recognizes invading pathogens via pattern recognition receptors (PRRs) expressed on different immune cells extracellularly and intracellularly. Out of several PRRs, Toll-like receptors (TLRs) are one of the critical PRRs recognizing diverse pathogen-associated molecular patterns (PAMPs) varying from viruses, bacteria, and fungi. Viral pathogens possess specific molecular signatures such as dsRNA and high CpG content that differentiate them from mammalian cells. TLRs play their role in innate immunity against pathogenic viruses by producing antiviral cytokines and chemokines. Most emerging viral pathogens are RNA viruses including severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome-related coronavirus (MERS-CoV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). These viruses are recognized by TLR 2, TLR 3, TLR 4, TLR7, and TLR8 with the coordination of other PRR members resulting in the activation of costimulatory molecules that initiate immune response. This chapter provides insights into the TLRs’ role in developing and regulating the immune response against emerging viral pathogens. It exploits their roles in innate immunity to develop treatment strategies against deadly emerging viral pathogens.