Highly pathogenic H5N1 influenza virus alters pH-mediated fusion properties, overcomes blocks to lysosome escape and replication, and impairs macrophage function

Abstract

Highly pathogenic H5N1 influenza virus infections are associated with severe respiratory damage and high morbidity and mortality in infected humans. Due to the critical role that macrophages play in response to respiratory pathogens, investigating such viruses’ ability to evade or exploit the innate immune response can provide greater insight into macrophage function at the host-pathogen interface. Unlike H5 viruses, we found that all non-H5 influenza virus strains including the 2009 H1N1 pandemic virus experience a block upstream of nuclear entry and escape and are unable to replicate in macrophages. However, only highly pathogenic H5N1 strains could successfully produce new viral protein synthesis and progeny release. Furthermore, it was found that the pH of fusion of the hemagglutinin (HA) protein, not sialic acid receptor binding, influenced replication. On a functional level, it was shown that while reactive oxygen species (ROS) were not produced during viral infection, macrophage phagocytosis was significantly impaired by productive viral replication. Future studies will focus on elucidating the molecular mechanism(s) of these blocks in differential H5 virus-specific replication, and the overall effect of viral replication in in vivo model systems.