Serological characteristics of a membrane glycoprotein gp82 of Marek's disease virus

Marek's disease virus (MDV) is a cell-associated herpesvirus of gallinaceous fowl. Glycoproteins of herpesviruses have been reported to be important in stimulating humoral and cell-mediated immune responses against viral infection. At least eight glycoproteins of MDV have been identified, and glycoprotein B (gB) has been reported to produce protective immunity. In addition to glycoproteins, other cell membrane proteins may also be important for engendering immunity. In an attempt to determine whether the protein is involved in immune responses, we developed three monoclonal antibodies (Mabs) and rabbit polyclonal antibodies specific for MDV membrane protein gp82. Three Mabs (Mab2.1, 3.7, and 5.7) were produced by using TrpEgp82 fusion protein as the immunogen that was expressed by recombinant pATH expression vector pATHgp82 in Escherichia coli. Indirect immunofluorescence assay (IFA), immunoprecipitation, and Western blot analysis were used to determine the characteristics of gp82. All of the Mabs reacted with gp82 protein irrespective of its conformation. The gp82 protein was predominantly anchored on the surface membrane of a chicken embryo fibroblast (CEF) infected with serotype 1 MDV (MDV-1). There was no detectable immunofluorescence staining in the cytoplasm or nucleus in the MDV-1-infected CEFs. These results indicate that gp82 is a membrane protein. The distribution pattern of immunofluorescence staining of gp82 varies between CEFs infected with the low passage MDV-1 isolate Md11, and those infected with a high passage derivative, Md11/75c. In SB-1 (Serotype 2 MDV [MDV-2]) and Turkey herpesvirus (HVT) (serotype 3 MDV [MDV-3]) infected CEFs, gp82 was not detected by immunoprecipitation, Western blot, or IFA using both monoclonal and polyclonal antibodies. These results suggest that gp82 in serotype 2 or 3 has a modified epitope, or that the gene is permanently repressed.