Immunological classification of a pike lymphoma.

Monoclonal and polyclonal antibodies against mammalian intermediate filament (IF) proteins were used to demonstrate IF expression in tissues and lymphoma tumors of northern pikes, Esox lucius L., from the Aland Islands of Finland by indirect immunofluorescence microscopy. Frozen sections of pike tissues demonstrated IFs in a manner confirming their evolutionary conservation and subclass specificity. Tumor cells showed morphological resemblance to head kidney cells and were positive for vimentin while negative for cytokeratin, desmin, neurofilament proteins, and glial fibrillary acidic protein. The results show that the neoplasm is a mesenchymal as opposed to an epithelial, muscle, neural, or glial tumor, and is probably hemic cell derived. A rabbit anti-pike IgM antiserum showed that up to 90% of mononuclear (MN) cells isolated on Ficoll-Isopaque gradients from peripheral blood, spleen and head kidney were surface- and cytoplasmic-immunoglobulin positive by indirect immunofluorescence, while a maximum of 5% of tumor cells were positive. A maximum of 5% of MN cells from hemic tissues exhibited rosettes when incubated with AET-treated sheep red blood cells; however, only 1% of cells in the tumor formed rosettes. Lymphocyte proliferation assays were performed on MN cells from hemic tissues and tumor using phytohemagglutinin P, concanavalin A, tuberculin purified protein derivative and lipopolysaccharide W in medium supplemented with fetal calf serum or autologous pike plasma. Proliferation indices in hemic tissues were similar in the groups. However, all proliferation indices in tissues were significantly higher than corresponding values in the tumor. These assays show that pike MN cells respond when stimulated by T and B cell mitogens, but that this reactivity is lacking in the tumor.