Pseudomonas aeruginosa alters inflammatory response of primary bronchial epithelial cells to Rhinovirus infection in vitro

The effects of chronic bacterial infections on susceptibility to and course of viral infections in the lung is still insufficiently understood. Here we investigated whether a co-infection with Pseudomonas aeruginosa (PA) changes the inflammatory response of primary bronchial epithelial cells (pBECS) to rhinovirus infection.

Therefore, pBECs were isolated from explanted lung tissue of lung emphysema patients and cultured in Air-liquid-Interface cell culture for 30 days to obtain a mucociliary differentiated epithelial cell layer. Differentiation was verified by ciliary movement, mucus production and transepithelial electrical resistance measurement. Afterwards a chronic bacterial infection with different clinical strains of PA was emulated during 20 days through repeated addition of PA every four days. Bacterial growth was inhibited by addition of tobramycin (25 µg/ml) to the apical side of the cell cultures. Subsequently, cells were infected with Human Rhinovirus (HRV)-16 or -1B. Interleukin-6 (IL-6) and Interleukin-8 (IL-8) were measured by ELISA, viral RNA was quantified using qPCR.

IL-6 and IL-8 levels were markedly increased in cells infected with HRV-16 (IL6: median 1083 pg/ml, range 660 – 2365 pg/ml; IL8: 141 ng/ml, 120 – 164 ng/ml) as well as HRV-1B (IL6: 1290 pg/ml, 517 – 2492 pg/ml; IL8: 169 ng/ml, 124 – 185 ng/ml).

Concentrations of both cytokines were comparable in cells co-infected with a mucoid PA isolate. Infection with a clinical non-mucoid PA isolate however, completely abrogated IL-6 (HRV-16/-1B: < 6,25 pg/ml), but not IL-8 release (coinfection with HRV-16: 105 ng/ml, 87 – 232 ng/ml; HRV-1B: 115 ng/ml, 61 – 195 ng/ml).

Although the viral load was unaltered there was an increased cytopathic effect visible in the co-infection with the non-mucoid PA strain.

While IL-8 is a potent neutrophil chemoattractant and activator, IL-6 is known to be crucial for orchestrating anti-viral immunity and promoting lung repair after viral-induced lung injury. Thus, our data suggests a potential mechanism through which HRV airway infections could be aggravated in PA-colonized airways.