AN IMMUNOHISTOCHEMICAL STUDY OF AN EQUINE B-CELL LYMPHOMA

The tissues of an 8-year-old thoroughbred castrated male horse with eq uine lymphoma were examined immunohistochemically. Neoplastic masses w ere observed in the mediastinum, mesenteric lymph nodes, gastric mucos a and serosa, liver capsule, and spleen capsule with associated lymph nodes. Histopathologically, the neoplastic cells were seen to consist predominantly of a mixture of well differentiated small and large type s. Immunohistochemically, the small lymphoid cells were MHC class IIlo w+ and PanT(-) and the large lymphoid cells were MHC class IIhigh+ and PanT(-). These findings revealed that the neoplastic cells were of B- lymphocyte lineage.