AN AVIAN HEPATOMA-CELL LINE FOR THE CULTIVATION OF INFECTIOUS LARYNGOTRACHEITIS VIRUS AND FOR THE EXPRESSION OF FOREIGN GENES WITH A MAMMALIAN PROMOTOR

Infectious laryngotracheitis virus (ILTV) is the causative agent of a highly infectious upper respiratory tract disease in chickens. Vaccine development and basic studies on ILTV have been hampered by the lack of a cell line for the cultivation of this herpesvirus which was ident ified in 1930. Four different avian cell lines were tested for their s uitability to propagate ILTV. Here we report the successful growth of ILTV with a chemically-induced avian hepatoma cell line, while retrovi rus transformed cell lines derived from permissive primary cells, were found to be non-permissive for ILTV. After multiple passaging of ILTV in the hepatoma cells, the virus could be grown up to a titre of 1 X 10(7) EID50 per ml with a replication cycle comparable to that in prim ary hepatocytes. Methods of plaque assay, DNA-transfection, and expres sion of a reporter gene were established. The gene coding for the bact erial beta-galactosidase gene under the control of the cytomegalovirus (CMV) immediate-early promotor was transiently expressed, indicating that a mammalian herpesvirus promotor was recognized by this avian cel l line. Infectious ILTV virions were produced after transfecting this cell-line with purified ILTV DNA. The results indicated that the cell line is suitable for the construction of recombinant ILTV and for the molecular biological study of this important avian pathogen.