How RSV manipulates the immune response in respiratory cells

Respiratory syncytial virus (RSV) can cause severe lower respiratory tract infections, particularly in newborns and the elderly. How the virus manages to evade the immune system and what changes it triggers in infected cells had not yet been fully understood. Researchers from TWINCORE, Centre for Experimental and Clinical Infection Research, have now, together with interdisciplinary colleagues from Würzburg, Regensburg, Braunschweig and Hannover, demonstrated how the virus interferes with the genetic programme of respiratory cells, inhibits the immune response and disrupts cell function. They have published these findings in the journal Science Advances.

According to estimates by the World Health Organisation (WHO), around 3.6 million children worldwide require hospital treatment for RSV each year. For 100,000 of them, the infection is fatal. “How the virus causes damage in the epithelial cells of the respiratory tract and why the immune response does not keep it better in check has been unclear until now,” says Prof. Thomas Pietschmann, Director of the Institute for Experimental Virology at TWINCORE in Hannover and lead author of the study.

To answer this question, the researchers used a special cell culture model. They cultured respiratory cells from human donors, typically patients receiving a donor lung. “In the laboratory, these cells then grow together to form a lung-like ciliated epithelium, complete with ciliary beating and mucus production,” explains Prof. Bettina Wiegmann from the Department of Cardiac, Thoracic, Transplant and Vascular Surgery at Hannover Medical School and co-author of the study. They then infected this tissue culture with RSV and subsequently analysed gene activity in every single cell using RNA sequencing. “By comparing with uninfected cells, we can identify how thousands of genes are regulated by the infection,” says Prof. Emmanuel Saliba, who heads the research group “Single-Cell Analysis” at the Helmholtz Institute for RNA-based Infection Research (HIRI) in Würzburg, a site of the Helmholtz Centre for Infection Research in Braunschweig in cooperation with the Julius-Maximilians-Universität Würzburg.

“Our data show that only a fraction of the infected cells even realise they have been infected,” says Dr Sibylle Haid, a researcher at Pietschmann’s institute and together with Kevin Berg (University of Regensburg) first author of the study. “This is probably because only some lung cells produce sufficient quantities of virus detectors and thus generate messenger molecules quickly enough to protect themselves and neighbouring cells.” If there are too few of these sensor molecules, the virus gains the upper hand, multiplies and then actively suppresses this protective mechanism. A key messenger substance in the immune system is interferon, which has both a direct antiviral effect and activates the so-called interferon-stimulated genes (ISGs).

“Even treating the cells with interferon cannot eliminate the virus at this stage,” says Haid. With one exception: the team discovered that the antiviral transcription factor IRF1 is not suppressed by RSV and was then able to demonstrate that artificially activating this factor can suppress the RSV infection – at least in the simplified model.

The researchers also found a possible explanation for the cell damage caused by RSV. “In the infected epithelial cells, the genes that control cilia formation were also inhibited,” says Sibylle Haid. Cilia are the tiny hair-like structures on cells that are responsible, among other things, for clearing mucus. If this function is disrupted by the infection, the typical symptoms of the disease arise.

“In this study, we were able to gain important insights into the pathology of RSV infection at the cellular level and also identify IRF1 as a potentially promising candidate for pharmaceutical intervention,” says Thomas Pietschmann. “This would not have been possible without the interdisciplinary collaboration with our partners.” In addition to the research teams led by Thomas Pietschmann, Emmanuel Saliba and Florian Erhard (University of Regensburg), the Helmholtz Centre for Infection Research in Braunschweig and Hannover Medical School were involved. The research project was funded by the RESIST Cluster of Excellence.