Identification of novel factors associated with severe respiratory syncytial virus disease in infants

Almost all infants are infected with RSV by 2 years. 1–3 % of RSV-infected infants are hospitalised with severe disease. Reasons for susceptibility to severe disease remain obscure. We aimed to identify factors that might explain such susceptibility.

We generated well-differentiated primary nasal epithelial cell (WD-PNEC) cultures from infants with histories of severe or mild RSV disease. Following infection with RSV BT2a (clinical isolate), virus growth kinetics, cytopathogenesis, chemokines, and IL-29/IFNλ1 responses and differential gene expression were determined. In an exciting development, 1 differentially expressed gene, ptn, encodes pleiotrophin (PTN), which interacts with nucleolin (NCL), an RSV entry co-factor. The PTN antiviral activity was determined in BEAS-2B cells and WD-PBECs (where B=bronchial).

Viral growth kinetics, cell tropism, IP-10/CXCL10, TRAIL and RANTES/CCL5 responses did not differ significantly between cohorts. However, apical cell sloughing and IL-29/IFNλ1 were diminished in severe WD-PNECs following infection, while expression of isg15, ifi6, irf9, duox2 and tap1 was also reduced. Interestingly, diminished ptn expression was evident in severe WD-PNECs, irrespective of RSV infection. Furthermore, pre-treatment with PTN blocked RSV infection in BEAS-2B cells and WD-PBECs, while neutralisation of PTN with either antibodies or siRNAs resulted in increased RSV replication.

Diminished apical cell sloughing and expression/secretion of IL-29/IFNλ1 and specific interferon stimulated genes in WD-PNECs were associated with severe RSV. Importantly, PTN was identified as a novel endogenously expressed RSV antiviral protein in human airway epithelium. Lower expression of PTN in paediatric airway epithelium may explain, in part, increased susceptibility to severe disease.