Cutaneous tumor of northern pike, Esox lucius L. I. In vitro mitogenic responses of mononuclear cells from lymphoid tissues and tumor.

To evaluate functional characteristics of lymphocytes from the northern pike, Esox lucius L., mononuclear cells were isolated by Ficoll-Isopaque gradients from lymphoid organs and cutaneous tumors of normal and tumor bearing pikes. The cells were tested in a lymphocyte proliferation assay in medium supplemented with fetal calf serum or autologous plasma using three concentrations of PHA, Con A, tuberculin PPD, and LPS. Lymphocytes of northern pike could be triggered to DNA synthesis in vitro. However, no clearcut anatomical partitioning of mitogen responses was found, since the mean optimal proliferation indices for each mitogen were similar in blood, head kidney, and spleen, while cells from head kidney, the equivalent of bone marrow, were stimulated as well with the murine T cell mitogens PHA and Con A as with the B cell mitogens PPD and LPS. Tumorous pikes seemed to have an apparently normal lymphocyte population since they responded by blastogenesis as well as normal pikes. Tumor cells exhibited a high basic metabolic rate and reactivity to mitogens was largely lacking.