Alarmins and innate lymphoid cells 2 activation: a common pathogenetic
link connecting RSV bronchiolitis and later wheezing/asthma?
Abstract
Severe RSV infection in infancy is associated with increased risk of
recurrent wheezing in childhood. Both acute and long-term alterations in
airway functions are thought to be related to inefficient anti-viral
immune response. The airway epithelium, the first target of respiratory
syncytial virus (RSV), normally acts as an immunological barrier able to
elicit an effective immune reaction but may also be programmed to
directly promote a Th2 response, independently from Th2 lymphocyte
involvement. Recognition of RSV transcripts and viral replication
intermediates by bronchial epithelial cells brings about release of
TSLP, IL-33, HMGB1 and IL-25, dubbed “alarmins”. These epithelial
cell-derived proteins are particularly effective in stimulating innate
lymphoid cells 2 (ILC2) to release IL-4, IL-5, and IL-13. ILC2, reflect
the innate counterparts of Th2 cells and, when activate, are potent
promoters of airway inflammation and hyperresponsiveness in RSV
bronchiolitis and childhood wheezing/asthma. Long-term epithelial
progenitors or persistent epigenetic modifications of the airway
epithelium following RSV infection, may play a pathogenetic role in the
short and long-term increased susceptibility to obstructive lung
diseases in response to RSV in the young. Additionally, ILC2 function
may be further regulated by RSV-induced changes in gut microbiota
community composition that can be associated with disease severity in
infants. A better understanding of the alarmin-ILC interactions in
childhood might provide insights into the mechanisms characterizing
these immune-mediated diseases and indicate new targets for prevention
and therapeutic interventions.