ALLERGIC SENSITIZATION INCREASES AIRWAY REACTIVITY IN GUINEA-PIGS WITH RESPIRATORY SYNCYTIAL VIRUS BRONCHIOLITIS

Background: Respiratory syncytial virus (RSFT) causes acute bronchioli tis in children and has been implicated in the pathogenesis of recurre nt wheezing and asthma, However, few, children exposed to RSV experien ce acute bronchiolitis or its sequelae, suggesting a subgroup of susce ptible children, An allergic diathesis may predispose children to subs equent airway disease. Objective: This study was carried out to determ ine whether a preexisting allergic state, induced by repeated inhalati onal exposures to ovalbumin, potentiates nonspecific airway responsive ness to acetylcholine and increases airway inflammation during acute R SV bronchiolitis in guinea pigs. Methods: Forty guinea pigs were rando mized into four groups: nonsensitized, noninfected (ovalbumin-, RSV-); sensitized, noninfected (ovalbumin+, RSV-): nonsensitized, infected ( ovalbumin-, RSV+); sensitized, infected (ovalbumin+, RSV+), Depending on grouping, animals were exposed to either repeated aerosols of ovalb umin or saline solution and were subsequently inoculated with either h uman RSV or uninfected culture medium. Six days after inoculation, ani mals underwent acetylcholine challenge, and lung specimens were prepar ed for histologic scoring of airway inflammation. Results: Maximal inc reases in pulmonary resistance (centimeters of water per milliliter pe r second) to acetylcholine were greater for RSV alone (12.4 +/- 3.9) a nd ovalbumin alone (13.7 +/- 3.9) compared with controls (4.3 +/- 1.1) , but significantly greater increases occurred in ovalbumin+, RSV+ ani mals (34.0 +/- 11.0), These ovalbumin+, RSV+ animals demonstrated the combined histologic changes noted with RSV alone and ovalbumin alone i ncluding airway epithelial necrosis, mononuclear and granulocyte infil trates, airway wall edema, hyperplasia of bronchus-associated lymphoid tissue, and goblet cell metaplasia, Conclusion: Prior allergic sensit ization potentiates the physiologic and structural changes induced by acute RSV bronchiolitis. These results suggest that an allergic diathe sis may increase the severity of RSV infections in children.