IFA on CEF and DF-1 cell cultures infected with MDV, REV, and ALV. Plaques from the isolate GX18NNM5 were evident at 136 h (F2) after inoculation; specific staining of the viral plaques with MDV-1 gB-specific monoclonal antibody BA4 was observed (A, 100 ×), whereas no specific fluorescence was observed in the noninfected cells (D, 100 ×). Positive fluorescence was observed in the GX18NNR1-infected cells by the IFA with REV-specific monoclonal antibody 11B118 (B, 200 ×); no specific fluorescence was observed in the noninfected cells (E, 100 ×). No specific fluorescence was observed in the DF1 cells of both the inoculated cells (C, 200 ×) and the negative control (F, 100 ×) when the IFA was run by using the monoclonal antibody IE5 specific to ALV-p27. Abbreviations: ALV, avian leukosis virus; CEF, chicken embryo fibroblast; IFA, immunofluorescent assay; MDV, Marek's disease virus; REV, reticuloendotheliosis virus.