Virus replication and cytokine production in primary alveolar macrophages and airway epithelial cells induced by emerging canine H3N8 influenza virus (LB510)

Canine H3N8 influenza virus was first recognized as a serious infectious pulmonary disease in racing greyhound dogs in 2004. Disease resulted from direct transmission of commonly circulating equine H3N8 virus to dogs. We hypothesized that transmission of equine influenza virus to dogs was characterized by mutations in one or more genes that allowed the virus to replicate more efficiently in dog airway epithelial cells and/or alveolar macrophages and induce higher levels of proinflammatory cytokines. Primary alveolar macrophages and airway epithelial cells were isolated from dogs and inoculated with emergent and endemic canine H3N8 influenza viruses A/canine/Florida /43/2004 (canine/FL/04), canine/FL/05, canine/PA/09 as well as early and more recent equine viruses equine/KY/91, equine/NY/99 and equine/OH/03. Cytokines responses were measured by multiplex protein assay and/or quantitative PCR. Emergent and endemic canine viruses replicated to higher titers in dog macrophages than did the equine viruses from 1999 and 2003. Only endemic canine viruses from 2005 and 2009 replicated to a higher titer in isolated dog airway epithelial cells than did equine viruses from 1999 and 2005. Induction of TNF‐alpha in macrophages by equine and canine viruses was highly variable among macrophage isolates from different dogs. No significant differences were measured in epithelial cell production of IL‐8 in response to canine or equine H3N8 virus inoculation. Although small differences in productive virus replication were detected for canine influenza virus isolates compared to equine influenza virus isolates in macrophages and epithelial cells, differences in cytokine production were not detected. Grant Funding Source : Supported by NIH AI101625