Establishment of an immortal turkey turbinate cell line for propagation of avian metapneumovirus

Avian metapneumovirus (AMPV) is an upper respiratory viral pathogen that causes turkey rhinotracheitis. In most studies, the African monkey kidney derived Vero cell line has been widely used for the propagation of AMPV. Until recently, there has not been a homologous avian cellular substrate which could continuously produce high titer AMPV. Of the primary cell substrates tested of avian origin, primary turkey turbinate and kidney cells produced AMPV titers equal to or greater than Vero cells. When compared to Vero propagated AMPV, both turkey turbinate and kidney cell propagated AMPV generated larger fluorescent plaques. Furthermore, turkey turbinate propagated AMPV showed 11 amino acid differences in fusion (F) protein gene of the AMPV genome, suggesting that AMPV propagated in homologous avian cellular substrates may produce more infectious virus with possibly more effective fusion activity.; Efforts to generate a continuously growing homologous cell line, resulted in the establishment of the first known spontaneously immortalized line of embryonic turkey turbinate cells, designated as the TT-1 cell line. Rapidly growing TT-1 cells propagated sufficiently high AMPV titers, suggesting that a non-tumorigenic, reverse transcriptase negative TT-1 cell line can serve as an excellent homologous cellular substrate for virus propagation.; The TT-1 cell line produced an AMPV negative sense single stranded RNA genome that contains 1.8kb attachment glycoprotein (G) gene, which is a hypervariable gene that enables virus subtypes to be distinguished. Surprisingly, Vero cell propagated AMPV revealed an essentially deleted G gene in the viral genome, resulting in no G gene mRNA expression. In addition, no splicing mRNA variants of the G gene were detected from either mammalian or avian propagated AMPV. The G gene deletion might be caused by subcellular molecular mechanisms that are species-specific, suggesting that the antigenic changes together with the lack of viral gene deletions found in avian cell propagated AMPV could serve as an alternative approach for live vaccine development.