Role of Interferon in the Replication of Human Parainfluenza Virus Type 1 Wild Type and Mutant Viruses in Human Ciliated Airway Epithelium

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Abstract
Human parainfluenza virus type 1 (HPIV1) is a significant cause of pediatric respiratory disease in the upper and lower airways. An in vitro model of human ciliated airway epithelium (HAE), a useful tool for studying respiratory virus-host interactions, was used in this study to show that HPIV1 selectively infects ciliated cells within the HAE and that progeny virus is released from the apical surface with little apparent gross cytopathology. In HAE, type I interferon (IFN) is induced following infection with an HPIV1 mutant expressing defective C proteins with an F170S amino acid substitution, rHPIV1-C F170S , but not following infection with wild-type HPIV1. IFN induction coincided with a 100- to 1,000-fold reduction in virus titer, supporting the hypothesis that the HPIV1 C proteins are critical for the inhibition of the innate immune response. Two recently characterized live attenuated HPIV1 vaccine candidates expressing mutant C proteins were also evaluated in HAE. The vaccine candidates, rHPIV1-C R84G/Δ170 HN T553A L Y942A and rHPIV1-C R84G/Δ170 HN T553A L Δ1710-11 , which contain temperature-sensitive ( ts ) attenuating ( att ) and non- ts att mutations, were highly restricted in growth in HAE at permissive (32°C) and restrictive (37°C) temperatures. The viruses grew slightly better at 37°C than at 32°C, and rHPIV1-C R84G/Δ170 HN T553A L Y942A was less attenuated than rHPIV1-C R84G/Δ170 HN T553A L Δ1710-11 . The level of replication in HAE correlated with that previously observed for African green monkeys, suggesting that the HAE model has potential as a tool for the preclinical evaluation of HPIV1 vaccines, although how these in vitro data will correlate with vaccine virus replication in seronegative human subjects remains to be seen.