Human respiratory syncytial virus A2 strain replicates and induces innate immune responses by respiratory epithelia of neonatal lambs

Abstract

Summary Human respiratory syncytial virus (RSV) is a pneumovirus that causes significant respiratory disease in pre-mature and full-term infants. It was our hypothesis that a common strain of RSV, strain A2, would infect, cause pulmonary pathology, and alter respiratory epithelial innate immune responses in neonatal lambs similarly to RSV infection in human neonates. Newborn lambs between 2 and 3 days of age were inoculated intrabronchially with RSV strain A2. The lambs were sacrificed at days 3, 6, and 14 days post-inoculation. Pulmonary lesions in the 6-day post-inoculation group were typical of RSV infection including bronchiolitis with neutrophils and mild peribronchiolar interstitial pneumonia. RSV mRNA and antigen were detected by qPCR and immunohistochemistry respectively with peak mRNA levels and antigen at day 6. Expression of surfactant proteins A and D, sheep beta-defensin-1 and thyroid transcription factor 1 mRNA were also assessed by real-time qPCR. There was a significant increase in surfactant A and D mRNA expression in RSV-infected animals at day 6 post-inoculation. There were no significant changes in sheep beta-defensin-1 and thyroid transcription factor-1 mRNA expression. This study shows that neonatal lambs can be infected with RSV strain A2 and the pulmonary pathology mimics that of RSV infection in human infants thereby making the neonatal lamb a useful animal model to study disease pathogenesis and therapeutics. RSV infection induces increased expression of surfactant proteins A and D in lambs, which may also be an important feature of infection in newborn infants.

Respiratory syncytial virus is associated with an inflammatory response in lungs and architectural remodeling of lung-draining lymph nodes of newborn lambs

“…In some experiments, we used banked lung samples from lambs that were used in another study to characterize hRSV infection in the lamb model (26). Briefly, healthy lambs 2-3 days of age were sedated with an intramuscular injection of xylazine (0.1 mg/kg), and a sterile bronchoscope was used to instill hRSV strain A2 (5 ml at 2.0 ϫ 10 7 pfu/ml) or sterile cell growth media (5 ml) in the right mainstem bronchus.…”

“…Lambs are susceptible to infection by both ovine and bovine strains of RSV, and can be experimentally infected with the human RSV A2 strain (hRSV). In fact, infection of neonatal lambs with hRSV results in pathology resembling infection in human infants, as evidenced by mild peribronchiolar infiltrates of lymphocytes and plasma cells, and bronchiolitis characterized by epithelial cell degeneration, sloughing of degenerating cells, and intraluminal infiltrates of neutrophils (26). These symptoms of hRSV disease are not observed in hRSV-infected rodents.…”

Animal Models of Respiratory Syncytial Virus Pathogenesis and Vaccine Development: Opportunities and Future Directions

“…Neonatal (2-3 days of age) lambs were given a high dose of intrabronchial HRSV A2 infection (Olivier et al, 2009). Clinically, the lambs exhibited fever and, and some had a moderate cough (Olivier et al, 2009).…”

“…Clinically, the lambs exhibited fever and, and some had a moderate cough (Olivier et al, 2009). Histopathology showed suppurative bronchiolitis with epithelial desquamation and cellular debris and neutrophils in airway lumina.…”

“…Histopathology showed suppurative bronchiolitis with epithelial desquamation and cellular debris and neutrophils in airway lumina. HRSV antigen was detected by IHC, and it was fairly extensive in the bronchiolar epithelium and in alveolar regions where syncytia were evident (Olivier et al, 2009). In a second study from the Ackermann group, immune responses of newborn lambs infected with HRSV A2 were examined (Sow et al, 2011).…”