IMMUNOHISTOCHEMICAL IDENTIFICATION OF B-LYMPHOCYTES AND T-LYMPHOCYTESIN FORMALIN-FIXED, PARAFFIN-EMBEDDED FELINE LYMPHOSARCOMAS - RELATIONTO FELINE LEUKEMIA-VIRUS STATUS, TUMOR SITE, AND PATIENT AGE

The lymphocyte phenotype of 70 formalin-fixed, paraffin-embedded felin e lymphosarcomas (LSAs) was determined immunohistochemically using a T cell polyclonal antibody, and a B cell monoclonal antibody. Forty-sev en of 70 (67%) tumors were T cell, 19/70 (27%) were B cell, and 4/70 ( 6%) did not stain with either marker. Thirty-eight of 70 (54%) tumors were positive for feline leukemia virus (FeLV) antigen by immunohistoc hemistry (IHC), and 52/70 (74%) tumors were positive for FeLV DNA usin g the polymerase chain reaction (PCR). B cell tumors were as frequentl y FeLV-positive as T cell tumors using either IHC or PCR. Intestinal t umors were more likely to be B cell than T. The incidence of B and T c ell tumors was not different among young (less than or equal to 3 y), middle-aged (> 3 y to less than or equal to 8 y), and old (> 8 y) cats . Both B and T cell tumors from old cats were FeLV-positive more often by PCR than by IHC. Feline leukemia virus DNA but not antigen, was de tected in B cell tumors and intestinal tumors from cats > 8 y as often as it was detected in B cell tumors and intestinal tumors from cats l ess than or equal to 8 y. Previously, most B cell and intestinal tumor s from old cats were considered to be negative for FeLV. Here, the res ults suggest involvement of latent or replication-defective forms of t he virus in such tumors from old cats. This study supports a role for FeLV in feline B cell as well as T cell tumorigenesis.