Infection and the development of allergic disease.

Persistent allergic diseases exemplified by atopic asthma frequently begin during very early life. Epidemiological findings indicate that progression from allergic sensitization to atopic asthma occurs most frequently when atopy is accompanied by early respiratory viral infections. The underlying mechanism appears to involve recruitment of atopy-associated effector mechanisms into the host response to the virus. This has the dual effect of antagonising anti-viral immunity and amplifying inflammation in the infected airway mucosa, driving asthma pathogenesis. Immune responses underlying the allergic state are uniquely plastic during childhood. Alleviating specific allergy during this period may reduce risk of subsequent asthma development.