Background: Using A549 alveolar epithelial type II-like cells, we investigated the effects of cigarette smoke on the expression of rhinovirus (RV)-induced Toll-like receptor (TLR) 3, interleukin (IL)-6, and IL-8 secretion and viral replication.
Methods: Cigarette smoke extract (CSE) was prepared by smoking two commercial cigarettes with filters (0.9-mg of nicotine and 8.5-mg of tar per cigarette). Cells were infected with RV serotype 16 (RV-16) and cultured for 2 days (RV group), pretreated with 1, 2.5, or 5% CSE for 1 day before RV infection, and culture with CSE for 2 days after infection (RV plus CSE group), or were cultured in medium for 3 days (control group), treated with 1, 2.5, or 5% CSE for 3 days (CSE group). Changes in TLR3, IL-6, and IL-8 mRNA expression were assayed by real-time polymerase chain reaction and TLR3 protein expression were assessed by flow cytometry; IL-6 and IL-8 secretions were measured by ELISA; and RV replication was assessed by viral culture.
Results: CSE increased RV-induced TLR3 expression and RV-induced IL-8 secretion at lower concentrations in A549 cells. On the contrary, CSE dose dependently inhibited RV-induced IL-6 secretions and had no effect on RV replications.
Conclusion: Our results suggest that cigarette smoke may potentiate viral common cold symptoms by enhancing IL-8 secretion at lower concentrations, but not by increasing viral replication.