Immunological and ultrastructural characterization of true histiocytic lymphoma in the northern pike, Esox lucius L.

An epidemic of a malignant neoplasm occurs in northern pike, Esox lucius L., from the Aland Islands of Finland. The neoplasm is morphologically similar to other pike hemic tumors reported in other areas of the world. Pike normal tissues showed evolutionary conservation with the mammalian intermediate filament proteins cytokeratin, desmin, vimentin, neurofilament protein, and glial fibrillary acidic protein; tumor cells are positive for vimentin, suggesting that the neoplasm is of mesenchymal origin. Hemic tissue mononuclear cells undergo polyclonal stimulation by the known mammalian T- and B-lymphocyte mitogens phytohemagglutinin P, concanavalin A, tuberculin-purified protein derivative, and lipopolysaccharide W; pike tumor cells are nonreactive. Pike normal hemic tissue mononuclear cells are variously positive for surface and cytoplasmic immunoglobulins, using rabbit anti-pike immunoglobulin M and cross-reactive mouse anti-carp immunoglobulin M antibodies; tumor cells, however, are not positive. The tumor cells were also diffusely stained with sodium fluoride-sensitive nonspecific esterase. The foregoing suggest that the neoplasm is not of B-lymphocytic or plasmacytic derivation, while the T-lymphocytic as opposed to monocytic derivation cannot be excluded on the basis of marker studies. The ultrastructural studies, however, suggest a neoplasm of histiomonocytic derivation, while the absence of sinusoidal infiltration of tumor cells to head kidney, spleen, liver, or peripheral blood suggests that it is a piscine analogue of human true histiocytic lymphoma. Population dynamics studies indicate that the neoplasm affects primarily sexually mature males 5 to 6 yr of age, but does not at present appear to be a major factor affecting Aland pike populations.