SUMMARY
Immunohistochemical detection of Marek’s disease virus-EcoRI-Q (Meq) in tumor cells is one of the most accurate methods for the definitive diagnosis of Marek’s disease (MD). We previously generated several anti-Meq monoclonal antibodies for immunohistochemistry (IHC) to detect Meq expressed in experimentally induced MD lymphomas in formalin-fixed, paraffin-embedded sections. Here we evaluated the usefulness of anti-Meq monoclonal and cocktail antibodies (mix of three anti-Meq monoclonal antibodies: 3A3-112, 5F7-82, and 6B5-128) for the immunohistochemical diagnosis of MD in 104 field cases of chicken lymphoma that occurred in Japan between 1976 and 2023. Results revealed 100 cases of T-cell lymphoma, of which 99 cases were Meq+ with the cocktail antibody. Two distinct histological subtypes have been identified in MD tumors, suggesting that the morphological diagnosis of MD is complex and emphasizing the need for immunohistochemical detection. For the diagnosis of chicken B-cell lymphoma, detection of B cell-activating factor belonging to the tumor necrosis factor family receptor (BAFF-R) by IHC was found to be useful. Four cases of B-cell lymphoma consistently grew uniformly, and Meq was undetectable. In conclusion, Meq detection using IHC is valuable for the pathological diagnosis of field MD cases.