Interventions for prevention of respiratory syncytial virus bronchiolitis and sequelae in guinea pigs
Creators: name: Sutton, Troy C.
Publisher: name: University of British Columbia
Year: 2009

description: Respiratory syncytial virus (RSV) is the leading cause of infant hospitalization and children who recover from RSV bronchiolitis often develop episodes of recurrent wheezing and "asthma"-like symptoms. Despite considerable research, the mechanisms causing both RSV bronchiolitis and its sequelae are poorly understood. Recent clinical studies suggest a T helper 2 (Th2) immune response may be involved in the pathogenesis of RSV bronchiolitis. By applying the T helper 1 (Thl)/T helper 2 (Th2) paradigm, we examined the effects of two interventions, (administration of "low" dose RSV or CpGODN) designed to shift the Thl/Th2 balance towards a Thl response, on the development of RSV bronchiolitis and post-bronchiolitis sequelae in a guinea pig model of experimental RSV infection. There were four groups of animals: a Sham-Inoculated Group, a Challenge Dose RSV Group (receiving ~10⁴ syncytial forming units (s.f.u.)), an Intervention Dose RSV (~10² s.f.u.) + Challenge Dose RSV Group, and a CpG-ODN + Challenge Dose RSV Group. We compared the four groups (n =11-12) during acute and chronic (days 7 and 60 post-challenge dose inoculation, respectively) RSV infection. Airway hyperresponsiveness (AHR) was measured using an acetylcholine challenge method in a whole body plethysmograph. Airway infiltration by T cells and eosinophils was assessed by point counting stained lung sections. Using a semi-quantitative RT-PCR method we compared lung IFN-ɣ/IL-5 mRNA ratios as an index of the Thl/Th2 balance and, using a RSV immunostaining technique, we assessed the proportion of animals in each group with RSV antigens in the lungs. Results on day 7 showed that the Challenge Dose RSV Group developed AHR, increased levels of airway T cells and eosinophils, a Th2 shift in lung IFN-ɣ/IL-5 mRNA ratio and showed 9/11 animals with RSV positive immunostaining. The Intervention Dose Group differed from the Challenge Dose Group in that it had a significantly lower proportion of animals with RSV positive immunostaining (1/11) and had an intermediate level of eosinophils compared to the Sham-Inoculated and Challenge Dose RSV Groups. The CpG-ODN Group did not develop AHR, a Th2 shift, or increased levels of eosinophils, but did develop an intermediate level of T cells. The CpG-ODN Group, like the Intervention Dose Group, had a significantly lower proportion of animals with RSV positive immunostaining (3/12) compared to the Challenge Dose RSV (positive control) Group, suggesting that both interventions prevented RSV infection and/or enhanced viral clearance. On day 60, the Challenge Dose RSV Group maintained AHR, elevated levels of airway T cells and eosinophils, and a Th2 shift observed on day 7, and 7/12 animals had RSV positive immunostaining. The Intervention Dose Group, on the other hand, did not maintain AHR and increased levels of T cells and eosinophils seen on day 7 and had a Thl/Th2 ratio that was not significantly different from the Sham-Inoculated or Challenge Dose RSV Group. The CpG-ODN Group was unaltered with respect to AHR, airway eosinophils, or a Th2 shift, but did have a decrease in airway T cells to a level similar to that seen in the Sham-Inoculated Group. In both the Intervention Dose Group and CpGODN Group no animals (0/12 and 0/11 respectively) had RSV positive immunostaining, suggesting that the interventions prevented the development of a persistent RSV infection. In conclusion, CpG-ODN immunotherapy protected against the development of RSV bronchiolitis, while the "low" dose intervention did not, and both interventions provided protection against the development of post-bronchiolitis sequelae in guinea pigs.