Large granular lymphocyte leukemia/lymphoma in six cats

This report describes six cases of feline large granular lymphocyte lymphom a identified by light microscopy on the basis of their characteristic azuro philic granulation in Giemsa-stained plastic sections and by electron micro scopy on the basis of their typical granules. Although the granules of all the tumor cells were negative for peroxidase activity, they all demonstrate d chloroacetate-esterase and acid phosphatase activity. All the tumors reac ted with cross-reacting antibodies against the CD3 antigen (epsilon chain) and did not react with a cross-reacting monoclonal antibody directed agains t epitopes on cytoplasmic domains of the CD20 antigen. Three tumors had a p ositive reaction with a monoclonal human CD57-like antibody. This is highly suggestive of either a cytotoxic T cell or a natural killer cell origin of the: neoplasias. In three cats, although other abdominal organs were affec ted to a variable extent, the main neoplastic lesions were localized in the gastrointestinal tract anti the jejunal lymph nodes. In contrast, in the o ther three cats, organ involvement was more widespread, affecting the lung (two), myocardium (two), precardiac mediastinum (one), salivary gland (one) , and spinal cord (one); in addition, leukemia was present in two of these cats. The data presented indicate that tumors made up of large granular lym phocytes occur more frequently in cats than previously assumed and that the y share many characteristic features with specific subtypes of clonal disor ders of large granular lymphocytes in humans.