Detection of B virus antibody in monkey sera using glycoprotein D expressed in mammalian cells

The gene encoding glycoprotein D (gD) of the monkey B virus (Cereopithecine herpesvirus 1) was cloned into a mammalian expression vector, pcDNA3.1(-), and the recombinant plasmid DNA was transfected into COS7 cells. The expre ssion of gD in transfected COS7 cells was detected by indirect immunofluore scence assay or radioimmunoprecipitation analysis (RIPA). Although the expr essed gD protein was revealed to react well with sera from monkeys naturall y infected with B virus by RIPA, some sera showed reduced reactivity when a nalyzed by the Western blotting (WB) method. Some sera also showed relative ly high background when the WB was performed using gD, expressed from recom binant plasmid. The mutant gD, protein lacking the transmembrane domain (TM ) and cytoplasmic tail (CT) was next expressed in COS7 cells. The mutant pr otein was secreted into culture medium without apparent loss of the antigen icity. Using the secretory form of the gD protein as antigen in dot blot an alysis, sera from B virus-infected monkeys were shown to react with the mut ant protein without nonspecific reaction. Since the recombinant gD or its d erivative lacking TM and CT could be expressed in mammalian cells with prop er antigenicity, these antigens appeared to be useful for serological detec tion of B virus infection in monkeys.