Introduction Respiratory syncytial virus (RSV) leads to serious lower respiratory tract disease and prolonged periods of symptoms in cystic fibrosis (CF) patients. This study aims to determine whether RSV viral burden and the level of cytopathic effect (CPE) is higher in CF bronchial epithelial cells.

Methods Paired immortalised bronchial epithelial cell lines, CFBE41o-, expressing either wild type (WT) or Phe508del CFTR were infected with RSV A2 at an MOI of 0, 0.01, 0.1 and 1.0. Cell viability was measured daily by Resazurin assay, and viral burden by plaque assay in HEp-2 cells and RT-PCR. Viral attachment was determined by PCR after incubating RSV with the cells for 2 hrs at 4°C. Intracellular RSV proteins were measured by western blot.

Results Phe508del CFTR cells showed significantly greater and more rapid CPE by RSV (0.1 and 1 MOI) compared to WT cells. Viral burden was increased in the Phe508del cells each day up to 7 days post infection. The levels of intracellular RSV genetic material determined by PCR were also increased by 4.0 ± 0.2 (mean of MOIs ± SD) fold at 12 hours post infection in CF cells compared to WT. It was confirmed that increased levels of viral RNA led to increased intracellular viral proteins. Virus shedding determined by PCR in the supernatant at 24 hours post infection was also increased by 10.7 ± 5.0 fold in CF cells. There was no evidence of increased RSV attachment to CF cells.

Conclusion RSV causes CPE in bronchial epithelial cells expressing Phe508del CFTR more rapidly than in WT cells. This increased CPE was associated with an increased viral burden, which occurs despite similar levels of cell attachment and is therefore likely due to increased viral replication or transcription within the cell, which led to increased levels of intracellular RSV proteins. The mechanism for this is under investigation.