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The MDTC-RP30 lymphoblastoid cell line established from Marek's disease (MD) tumors in turkeys consisted of a heterogeneous population of cells 10 to 25 micron in diameter. Large-cell fractions obtained from a bovine fetal serum gradient had a higher titer of cell-associated MD virus (MDV) than the small-cell fractions. Seven single-cell clones were established from MDTC-RP30 cell line: two consisted of large cells, and the other clones consisted of small cells. Infectious MDV was rescued from large-cell clones in chicken embryo fibroblast cultures but not from small-cell clones. All clones contained MDV DNA sequences when hybridized against cloned MDV DNA. All clones were positive for a Marek's-disease-tumor-associated surface antigen and surface immunoglobulins. All but two small-cell clones caused MD in susceptible chickens. The two large-cell-type clones were uniformly tetraploid, whereas one small-cell clone was diploid and the four others were a mixture of diploid and tetraploid, with an occasional triploid cell. Evidence of translocation involving the male (Z) chromosome and the chromosome #3 was seen in one clone. These results suggest that MDV transforms different subpopulations of lymphocytes.

The major immunogenic viral proteins of Marek's disease virus (MDV) and turkey herpesvirus (HVT) share antigenic determinants. The polyacrylamide gel electrophoresis pattern of five viral polypeptides immunoprecipitated with homologous convalescent chicken plasma was identical with the pattern obtained after immunoprecipitation with heterologous convalescent chicken plasma. A panel of monoclonal antibodies was used to identify MDV and HVT polypeptides. Sixteen monoclonal antibodies were positive in an immunofluorescence assay. However, only eight monoclonal antibodies immunoprecipitated a total of seven distinct viral proteins from MDV- and HVT-infected cells. Six of these monoclonals immunoprecipitated multiple viral proteins. None of the monoclonal antibodies recognized the common A antigen of MDV or HVT. Monoclonal antibodies immunoprecipitated three glycoproteins (100,000, 60,000, and 49,000 Da) that comigrate in polyacrylamide gels with three of the five common polypeptides obtained with the convalescent chicken plasma. In addition, a 79,000-Da protein was common to all MDV- and HVT-infected cells. Competition immunoprecipitation and peptide mapping by limited proteolysis confirmed that the three glycoproteins and the 79,000-Da protein contain MDV-HVT common epitopes. MDV-specific antigenic determinants were detected on the three remaining viral proteins (41,000, 38,000, and 24,000 Da).