The influence of defective-interfering particles of the PR-8 strain of influenza A virus on the pathogenesis of pulmonary infection in mice

Homologous autointerference mediated by defective-interfering (DI) particles was first described with the PR-8 strain of influenza virus. However, little is actually known about the influence of DI particles of influenza virus on the pathogenesis of pulmonary infection. The present studies were designed to determine (1) the re-quirements for successful autointerference in vivo with DI particle-enriched PRoS influenza virus and (2) the effects of DI particle-enriched virus on the development and progression of otherwise lethal pulmonary infection in mice. PRoS influenza virus passaged in chicken eggs, but not that passaged in Madin-Darby bovine kidney cells, and enriched in DI particles markedly attenuated pulmonary infection in seven-week-old Swiss and four-week-old C57B 16 / Cr mice but not in three- to four-week-old Swiss mice. In addition, replication of influenza virus, staining of viral anti-gen, and numbers of infiltrates in lungs of mice infected with DI particle-enriched influenza virus were reduced in comparison with values in mice infected with com-parable amounts of wild-type influenza virus. The protection mediated by DI par-ticle-enriched virus appeared to be related to augmented humoral immune re