Effect Of PB2 E627K On The Pathogenicity Of H3N2 Canine Influenza Virus In Mice

Canine influenza virus?CIV?is pathogen in dogs.Dogsshow mild clinical signs after infecting with CIV.Since the first isolationof CIV H3N2 in C hina in 2006,the virus is only prevalent in Asia.However,in 2015,the outbreak and spreadof CIV H3N2 in American indicating that CIV H3N2 have the potential risk for spreading to other regions.CIVH3N2have received more attention in recent studies after reporting the virus spread to American and causing the outbreak of dog flu.Due to close contact between dogs and humans,the dogs might be a mammalian influenza virus"mixer"that highlights the significance of the study of this virus.Pathogenicity of influenza virus involves polygenic traits.The PB2 627K not only closely related to the pathogenicity of influenza virus,but also have important effects on influenza virus replication and virulence.The r GD02 and rGD02-E627K were rescued by the GD02 reverse genetic system and site-directed mutation technology.Then evaluated the pathogenicity ofr GD02 and GD02 in mice.The results showed that both r GD02 and GD02were not fatal inmice and had similar effects on mice body weight,indicating that the rGD02 and GD02 pathogenicity of mice was no signi ficant difference and reverse genetic technology does not enhance the virulence.The pathogenicity were compared between the reconstituted wild-type rGD02 and rGD02-E627K in mice.The results showed that rGD02and r GD02-E627K were not fatal in mice(MLD₅₀>10⁶EID₅₀);the change rate of body weight showed that both rGD02 and r GD02-E627K could slow the weight gain of mice,but there was no significant difference between the two groups.The viral titer of the lungs and tracheas of the rGD02-E627K group was higher than the r GD02 group,but there was no significant difference between the two groups.There was no significant difference in histopathologyof mice's lungs and tracheas between the two groups.Studies on viral pathogenicity revealed that a single amino acid substitution of E627K in PB2 couldn't remarkably enhance the virulence of CIV H3N2 in mice.The constructionof CIV H3N2 reverse genetic system and the evolution of the pathogenicity of PB2 E627K mutation of CIV H3N2 in mice provide foundations for further studies on the pathogenesis,gene function and vaccine development of H3N2 CIV.