Respiratory Syncytial Virus Increases the Virulence of Streptococcus pneumoniae by Binding to Penicillin Binding Protein 1a. A New Paradigm in Respiratory Infection

Abstract

Rationale: Respiratory syncytial virus (RSV) and Streptococcus pneumoniae are major respiratory pathogens. Coinfection with RSV and S. pneumoniae is associated with severe and often fatal pneumonia but the molecular basis for this remains unclear.Objectives: To determine if interaction between RSV and pneumococci enhances pneumococcal virulence.Methods: We used confocal microscopy and Western blot to identify the receptors involved in direct binding of RSV and pneumococci, the effects of which were studied in both in vivo and in vitro models of infection. Human ciliated respiratory epithelial cell cultures were infected with RSV for 72 hours and then challenged with pneumococci. Pneumococci were collected after 2 hours exposure and changes in gene expression determined using quantitative real-time polymerase chain reaction.Measurements and Main Results: Following incubation with RSV or purified G protein, pneumococci demonstrated a significant increase in the inflammatory response and bacterial adherence to human ciliated epithelial cultures and markedly increased virulence in a pneumonia model in mice. This was associated with extensive changes in the pneumococcal transcriptome and significant up-regulation in the expression of key pneumococcal virulence genes, including the gene for the pneumococcal toxin, pneumolysin. We show that mechanistically this is caused by RSV G glycoprotein binding penicillin binding protein 1a.Conclusions: The direct interaction between a respiratory virus protein and the pneumococcus resulting in increased bacterial virulence and worsening disease outcome is a new paradigm in respiratory infection.Keywords: respiratory syncytial virus; pneumococcus; cilia; virulence; G protein Respiratory syncytial virus (RSV) and Streptococcus pneumoniae, also known as the pneumococcus, are major respiratory pathogens causing a huge global healthcare burden, predominantly in young children and the elderly (1). Global RSV disease burden is estimated at 64 million cases and 160,000 deaths every year (2). Pneumococcal pneumonia results in more than 1 million deaths each year worldwide with approximately half a million in children younger than 5 years (3). There is increasing evidence that RSV and the pneumococcus interact to increase the severity of respiratory disease (4-6). Seasonal increases in infections This article has an online supplement, which is accessible from this issue's table of contents at www.atsjournals.org This article has embedded videos, which play in place from both the online PDF or HTML versions. If you cannot view Flash videos on your device, please try playing the videos in the online PDF, or access the original uncompressed videos at http://www.atsjournals.org/doi/suppl/10.1164/rccm.201311-2110OC. To play, mouse over the image and click on the arrow that will appear in the center or on the lower left.

Viral–bacterial interactions in the respiratory tract

“…3). Direct binding of the RSV G protein to pneumococci induces changes to the bacterial transcriptome and renders bacterial strains more virulent by increasing the expression of virulence genes such as pneumolysin (Smith et al, 2014b). Additionally, structural modifications might influence pathogenicity of bacteria.…”

Viral/bacterial respiratory tract co-infections in children

“…In the lungs of mice, neutrophils, other inflammatory infiltrates and pro-inflammatory cytokines have been observed during IAV or RSV and bacterial co-infection (124)(125)(126)(127)(128). RSV has also been shown to augment the inflammatory response of PRRs upon recognition of Gram positive bacterial cell wall components (129).…”

“…pneumoniae and S. pneumoniae after direct binding to RSV, both of which were associated with increased pneumococcal virulence in mice (128,134). …”

“…Viral infection of airway epithelial cells has been found to aid bacterial adherence to the URT by a number of mechanisms, although the effect differs between viruses, bacterial strains and experimental models. Free RSV virions have been shown to bind directly to H. influenzae and S. pneumoniae (128,136,137), which could through proximity augment each pathogen's binding to their respective host cell receptors ( Figure 1.2A). There is also some evidence that the RSV G glycoprotein, localised at the host cell membrane of virus infected cells, can act as a receptor for bacteria (Figure 1.2B) (136,137).…”

“…pneumoniae membrane-associated enzyme penicillin binding protein 1a (PBP1a) has recently been identified as one of the binding partners of RSV G (128).…”