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Effects of Fish Oil and Corn Oil Diets on Prostaglandin-dependent and Myelopoiesis-associated Immune Suppressor Mechanisms of Mice Bearing Metastatic Lewis Lung Carcinoma Tumors¹

Department of Research Services, Edward J. Hines, Jr., Veterans Administration Hospital, Hines, Illinois 60141 [M. R. I. Y., M. E. Y.], and Department of Pathology, Loyola University Stritch School of Medicine, Maywood, Illinois 60153 [M. R. I. Y.]

The effects of a fish oil diet on the myelopoietic and immunological parameters of normal mice and of mice bearing metastatic Lewis lung carcinoma (LLC-C3) tumors were compared to the effects of a corn oil or a mixed-fat rodent chow diet. This was studied soon after tumor appearance, on Day 17, when immune suppression was mediated by prostaglandin E₂ (PGE₂)-producing suppressor cells, and late in tumor development, on Day 28 when immune suppression was associated with myelopoiesis and the appearance of bone marrow-derived suppressor cells whose activity was not dependent on PGE₂. Feeding a fish oil diet from Days 10 to 17 of tumor growth partially restored splenic T-cell blastogenesis, reduced spleen cell secretion of PGE₂, and alleviated splenic suppressor activity. When fed from Days 21 to 28 of tumor growth, a fish oil diet neither restored T-cell blastogenesis nor alleviated suppressor cell activity. The fish oil diet increased the frequency of myeloid progenitor cells in normal mice and in mice bearing small or large tumors. Concurrently, the fish oil diet stimulated the appearance of bone marrow-derived suppressor cells. When administered after the establishment of palpable primary tumors, a fish oil diet also increased the formation of pulmonary lung nodules. In contrast to the fish oil stimulatior of myelopoiesis and the associated suppressor cells, feeding a corn oil diet to tumor-bearing mice during Days 21 to 28 after tumor implantation reduced myelopoiesis and the presence of the associated bone marrow suppressor cells. These data show that a fish oil diet can minimize the immune suppression in tumor bearers when suppression is mediated by PGE₂-producing suppressor cells, but can also induce myelopoietic stimulation leading to the appearance of bone marrow-derived suppressor cells and increased tumor metastasis.

¹ This work was supported in part by the Medical Research Services of the Veterans Administration and by Grant CA-45080 from the NIH.

² To whom requests for reprints should be addressed, at Pathology Research (151Z2), Hines V.A. Hospital, Hines, IL 60141.

Received 9/28/88. Revised 1/ 6/89. Accepted 1/16/89.