Recurring viral infection triggers asthma attack

Recurring viral infections in early months of life can make babies prone to asthma attacks in the later stages of life, a new study has found.

In a new finding, a husband-wife researcher duo of Indian origin claimed that repeated attacks by common virus known as respiratory syncytial virus (RSV), could cripple a portion of a child's own immune system triggering asthma attacks in adulthood. Repeated infection breaches the natural protective barrier from breast milk.

RSV is a common cause of lower respiratory tract infection. It is one of the major causes of such infections among children in India accounting for almost one-third of cases. RSV is common in the US and Europe. Now experimenting with mice in the laboratory, Anuradha Ray and Prabir Ray from the University of Pittsburgh and their colleagues mapped the way how RSV infection in early years of life increased the risk of asthma in adults.

“The babies are the most vulnerable up to two years of age and there is no good vaccine against RSV,” the couple told Deccan Herald in an email interview. Previous studies demonstrated newborns could be protected from developing allergies through proteins transferred in breast milk. Scientists had also shown how exposure of nursing mice to low doses of allergens protected the newborns from asthma.

But the new research published in the September 9 issue of ‘Nature Medicine’ found that protection provided by breast milk wean away after some time if the virus continue to strike at the babies repeatedly. If breastfed newborn mice protected from asthma were repeatedly infected with RSV, they no longer exhibit the protective effect and become susceptible to asthma later in life.

The virus overcomes the natural immune system by inducing an inflammatory response in the lung that impairs the function of a set of protective immune cells termed regulatory T cells, which in turn, produce inflammatory mediators to promote allergic responses. RSV cripples the function of those protective cells in such a way that they behave like pro-inflammatory cells.

Asthma is caused when allergens irritate the airways of a person. As a result, the airways become tightened and inflamed producing lots of sticky mucous, which make breathing difficult. The new research explains the how and why of the attack. “It is now well-accepted that in both humans and mice, regulatory T cells in our immune system suppress allergic and auto-immune diseases. We feel that the mechanism of virus-induced dysfunction of these regulatory cells identified in our study is also relevant in humans,” the duo said.