#Synergy between HA #cleavage site #sequence and NA-mediated #plasminogen recruitment as a virulence mechanism for low-pathogenic avian #influenza
ABSTRACT An outbreak of H3N1 low-pathogenic avian influenza virus (LPAIV) in Belgium in 2019 caused unexpected levels of mortality and morbidity in poultry . These viruses possess an NA polymorphism associated with plasminogen (PLG) binding , as well as an atypical sequence around the HA cleavage site ; accordingly, HA cleavage mediated by NA-driven PLG recruitment has been proposed to underlie their systemic spread and pathogenicity. To test this, we established a reverse genetics system for A/chicken/Belgium/460/2019 and created single mutations in HA (K345R) and NA (S122N) that restored the viruses to normal consensus, as well as an HA/NA double mutant. Confirming previous work, trypsin-independent spread and HA cleavage of wild-type Ck/Belgium were observed in the presence of fetal bovine serum containing PLG in vitro. Dose-dependent HA cleavage and trypsin-independent spread were also observed in the presence of purified chicken PLG . Compared to the wild-type virus, both HA...