Inflammablog6!

RSV in infancy and Asthma

Respiratory Syncytial Virus (RSV) also known as bronchiolitis is an infection in the upper respiratory tract that typically happens before the age of 2. Some children get a more severe form and develop lower airway symptoms as well. Typically only 1-2% of infants are hospitalized with RSV when infection occurs. This disease can leave kids wheezing for several years after the infection has occurred. There is little evidence at this time suggesting if RSV is nonallergenic or if it is an onset of IgE associated asthma. RSV primes the memory T-cells that make Interferon-c (INF-c) and are also associated with IL-4 producing T-cells that are activated during RSV infections. There are many studies that show that there is a strong relationship between RSV and asthma or allergies.

With a normal child a RSV infection is mild and they develop a predominant Th1 antiviral response that clears the infection. The memory T-cells are dominated by IFN-c production rather than IL-4. In children that develop a more severe form of RSV (when hospitalization is needed) a strong INF-c response occurs along with an IL-4 response which leads to the accumulation of antiviral-T cells in the lungs causing an impairment of the respiratory tract. Post infection both IL-4 and IFN-c T-cells are maintained as memory cells that recirculate in the blood. There is some evidence that children who are administered a polyclonal antiviral antibody therapy have a delay in RSV infection and show improved lung function.

There are several different mechanisms that can explain the association between asthma and RSV. Experiments with animals suggest that RSV may contribute to post bronchiolitic symptoms and when inhaled allergens are delivered to these animals the effects are enhanced by a RSV infection. In these studies they link IL-4 production and a type 2 cytokine response with enhanced lung disease during the viral infection--this is also a common feature in asthma and atopy.  This mechanism has yet to be proven in humans.

Results in infant peripheral blood mononuclear cells can be used to show that RSV increases the risk of atopy and provides an IL-4 rich environment in which encountering airborne allergens can create an increased memory T-cell response. Other studies suggest that there is an increase of Th2 response which is medicated by overexpression of the IL-4 which only provides preliminary evidence for a genetic link between RSV and asthma. The last suggestion is that there is a genetic defect that is associated with the delay in postnatal maturation of Th1 function that gives susceptibility to both severe viral infection in the lungs as well as allergies and asthma in childhood.

Eosinophil cationic protein is created in the serum of children with asthma and with children with bronchiolitis. This suggests the degranulation of the eosinophil’s in both conditions. This increase in antigen specific enhancement of IL-4 production may be able to explain the link between RSV and asthma as well as chronic wheezing during childhood.

Referances

Severe Respiratory Syncytial Virus Bronchiolitis in Infancy and Asthma and Allergy at Age 13. http://ajrccm.atsjournals.org/content/171/2/137.full.pdf

 

Enhanced IL-4 responses in children with a history of respiratory

syncytial virus bronchiolitis in infancy P. http://erj.ersjournals.com/content/20/2/376.full.pdf