Immune interaction between respiratory syncytial virus infection and allergen sensitization critically depends on timing of challenges

Severe respiratory syncytial virus (RSV) infection has been hypothesized to be a risk factor for the development of allergy and asthma, but epidemiologic studies in humans have been inconclusive. By use of a well-characterized murine model of RSV infection and allergic sensi-tization with ovalbumin, the effect of a preceding severe RSV infection on the development of the pulmonary allergic inflammatory response and airway hyperresponsiveness (AHR) was tested. The impact of prior allergic sensitization on RSV-induced illness, as measured by weight loss, also was evaluated. RSV infection before allergic sensitization decreased allergen-induced AHR, production of interleukin-13 in lung tissue, and lung eosinophilia. In contrast, allergic sensitization before RSV infection increased AHR and decreased RSV-related weight loss and lung levels of interferon-g but did not alter viral clearance. These data provide evi-dence that RSV-associated AHR occurs in hosts with allergic responses and that allergic inflammation is diminished when preceded by RSV infection. In some studies, respiratory syncytial virus (RSV) infection is highly associated with the development of asthma and allergic sensitization in children [1, 2]. Severe RSV bronchiolitis durin