Comparison of the morphology and enzyme activity of mononuclear cells from Fischer 344 rats with either spontaneous or transplanted leukemia.

Mononuclear cell (MNC) leukemia was identified in 26-month-old F344 rats by splenomegaly, reduced red blood cell counts, and elevated white blood cell counts. Atypical MNC were predominant in spleen and blood with acentric nuclei and red cytoplasmic granules. Pentose shunt, glycolytic, and Krebs cycle enzyme activities were elevated 2- to 11-fold in the enriched MNC fraction (Ficoll-Paque density gradients, 1.077 g/ml) isolated from spleen. A leukemic MNC line was derived from one of the spontaneously leukemic donors and then maintained in vivo by s.c. transfer of 2 X 10(7) spleen cells into 7-8-week-old syngeneic recipients. In these serial transplantation experiments leukemia that was clinically and morphologically indistinguishable from spontaneous leukemia in 104-week-old rats was induced in 22-24-week-old rats. Enhanced enzyme activity in MNC was not essential to maintain the phenotypic expression of Fischer rat leukemia. The pattern of biochemical response in spleen MNC from transplanted cases was the opposite of that previously noted in spontaneously leukemic rats, with 50-70% decreases in the specific activities of pentose shunt enzymes and malate dehydrogenase. Reversal of the expression of these enzymes in MNC may be related to a difference in the growth rate of the tumors or to selective proliferation of the transplanted leukemic cells. In addition acetylcholinesterase activity decreased 35-85% in MNC of spleen and blood. Transplantable MNC from F344 rats provide abundant tumorigenic material with a novel biochemical expression that may be useful in the study of chemotherapeutic intervention.