The following is a summary of “Cold exposure impairs extracellular vesicle swarm–mediated nasal antiviral immunity,” published in the FEBRUARY 2023 issue of Allergy & Immunology by Huang, et al.

The human upper respiratory tract has a variety of innate immune responses and is the initial site where inhaled respiratory viruses come into contact with humans. It was well known that respiratory viral infections vary seasonally and that ambient temperature significantly impacts how the immune system reacts to infections; nevertheless, the molecular processes that underlie these phenomena were still poorly understood. Therefore, extracellular vesicles (EVs) generated from nasal epithelium were examined for innate Toll-like receptor 3 (TLR3)-dependent antiviral immunity.

Researchers examined the production and composition of nasal epithelial EVs after TLR3 stimulation in fresh human nasal mucosal surgical tissues and human autologous cells. In addition, they investigated the mechanisms behind TLR3-stimulated EVs’ antiviral efficacy against respiratory viruses and the impact of cool ambient temperature on TLR3-dependent antiviral immunity.

They discovered that exposure to poly (I:C), also known as polyinosinic: polycytidylic acid, caused a swarm-like increase in the release of nasal epithelial EVs via the TLR3 signaling. EVs took involvement in TLR3-dependent antiviral defense, defending the host against viral infections through EV-mediated functional miR-17 distribution and direct virion neutralization upon binding to virus ligands via surface receptors such as LDLR and ICAM-1. Cold exposure compromised the powerful antiviral immune defense capabilities mediated by TLR3-stimulated EVs by reducing total EV secretion and individual EV microRNA packing and antiviral binding affinity.

Nasal epithelial EVs that are TLR3-dependent had a variety of intrinsic antiviral defenses that helped to prevent respiratory viral infections. The seasonal change in the frequency of upper respiratory tract infections was further explained by the work in a direct quantitative mechanistic manner.