<p>Normal human tracheobronchial epithelial cells from young healthy non-smokers were pre-exposed to medium (control), e-liquid at an optimized concentration (0.3% v/v) without nicotine (NO-NIC) or with 18 mg/ml of nicotine (NIC-18 mg/ml) for 24 h and then infected with HRV-16 at 10<sup>4</sup> TCID<sub>50</sub>/well or PBS (control) for 6 h (A) and 24 h (B). Viral RNA levels were measured by quantitative real-time RT-PCR. Data (n = 5) are presented as means ± SEM.</p
