Preventive measures of Mark's desease (MD) vaccine break caused by very virulent MD virus.

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For prevention of Marek's disease (MD) caused by Marek's disease virus (MDV), monovalent vaccine of herpesvirus of turkey has been widely used for chickens in the field. Recently, however, MD caused by very virulent MDV (vvMDV) was observed in vaccinated chicknes. The final aim of the present study is to develop MD vaccine such as recombiant, polyvalent or component vaccine for controlling the outbreak of MD due to vvMDV. The following results were obtained.1) Arecombinant baculovirus expressing the A antigen (rBV-A) of MDV was constructed. In Spodoptera frugiperda (Sf) cells infectedwith the rBV-A, A antigen (A Ag) expression was localized to the cell surface. By immunoprecipitation of ^<35>S labelled A Ag with a monoclonal antibody to A Ag, a large amount of the A Ag(58-68kDa) was dtected of the rBV-A infected cells but a small amount of the antigen (46-54kDa) was found in the culture supenatant of infected cells. The reconminant A Ag was shown to be reactive with sera of MDV-infected chickens. In sera of chickens immunized with the A Ag, MDV-specific antibody reactive with MDV-infected cells was found.2) A gene encoding a homolog of glycoprotein B of herpes simplex virus (gB homolog) has been identified on the MDV genome. The recombinant baculovirus encoding the gB homolog (rBV-B) of MDV expressed the protein in the cytoplasm and on the surface of Sf cells infected with the rBV-B, when examined by immunofluorescent assay using anti-B sera from chickens or rabbits, and monoclonal antibody against B antigen. The expressed protein had three molecular sized (88/100, 64 and 54kDa).3) Chicks thymectomized and injected with either monoclonal antibody to chicken CD4 of CD8 were infected with vvMDV. The CD8-depleed chcks developed both nerve enlargement and visceral tumor, whereas the CD4-depleted chicks showed only nerve enlargement.