ASSOCIATION BETWEEN PRONOUNCED IGA RESPONSE IN RSV BRONCHIOLITIS AND DEVELOPMENT OF ALLERGIC SENSITIZATION

Forty-five children who had been hospitalized with bronchiolitis cause d by respiratory syncytial virus (RSV) at a mean age of 4 months, and 90 matched control children, were tested for occurrence of RSV antibod ies at one year of age. Of the children who had suffered from bronchio litis, forty had demonstrable IgG antibodies, whereas the remaining fi ve only had IgA antibodies against RSV. In the control group, 42% were RSV seropositive. The anti-RSV IgA antibody titres tended to be highe r in patients with bronchiolitis than in controls and a larger proport ion of the seropositive children in the former than in the latter grou p had demonstrable Ige antibodies. These findings suggest that RSV inf ections causing bronchiolitis are more often associated with a strong antibody response than are mild cases of the infection. Follow-up of t he children at 3 years of age showed that allergic sensitization and d evelopment of asthma had occurred much more frequently in children wit h past RSV bronchiolitis than in controls. Children with past RSV bron chiolitis who later developed allergic sensitization had elevated RSV IgA antibody titres at one year of age more frequently than children w ith past RSV-bronchiolitis, who were not sensitized (p=0.015). No sign ificant differences regarding IgG antibody titres were observed. Since IgA, similarly as IgE, antibody formation is strongly Th2 cell depend ent, the results are compatible with other findings suggesting that RV has an unusual propensity to activate the Th2 cell system. This may c ontribute to the pathological picture of bronchiolitis in small childr en and at the same time render the infected child predisposed for late r development of allergic sensitization. RSV bronchiolitis may thus be an important risk factor for later development of atopic disease alth ough it cannot be excluded that the bronchiolitis simply serves as a m arker that predicts later development of atopy.