HN gene C-terminal extension of Newcastle disease virus is not the determinant of the enteric tropism.

The hemagglutinin-neuraminidase (HN) protein of Newcastle disease virus (NDV) plays an important role in virus pathogenicity and tissue tropism. Sequence analysis revealed that the HN gene of many asymptomatic enteric NDV strains encodes a larger open reading frame (616 amino acids, aa) with additional 39 aa at its C-terminus when compared with that (577 aa) of respirotropic NDV strains. Therefore, it has been suspected that the HN C-terminal extension may contribute to the enteric tropism. In the present study, we generated a NDV respirotropic strain LaSota-based recombinant virus with a HN C-terminal extension of 39 aa derived from an enterotropic NDV strain using reverse genetics technology. The biological characterization of the recombinant virus, rLS-HN-ex, showed that the HN C-terminal extension slightly attenuated the virus pathogenicity in embryonated eggs and in day-old chicks when compared to the parental LaSota virus. However, the HN C-terminal extension did not alter virus tissue tropism. In infected chickens, the recombinant virus was detected and re-isolated from the tracheal tissue, but not from the intestinal tissue, exhibiting a similar respirotropic tissue preference as its parental LaSota strain. These results demonstrated that the HN protein C-terminal extension of NDV is not the determinant of the virus enteric tropism.