Lymphocytes play an important role in cell-mediated immunity and have been implicated in inflammatory and autoimmune diseases. 2. Unsaturated fatty acids, including oleic, linoleic, alpha-linolenic, arachidonic, eicosapentaenoic and docosahexaenoic acids, inhibit mitogen-stimulated lymphocyte proliferation in vitro. The inhibition of proliferation is dependent upon the concentration of fatty acid, the time during culture of fatty acid addition, the duration of exposure of the cells to the fatty acid and the chain length and degree of unsaturation of the fatty acid. 3. Unsaturated fatty acids suppress production of the immunoregulatory cytokine interleukin-2 by lymphocytes in vitro. 4. Triacylglycerols containing unsaturated fatty acids inhibit lymphocyte proliferation and natural killer cell activity in vitro. 5. Feeding weanling rats diets containing olive oil, evening primrose oil or fish oil results in suppression of lymphocyte proliferation. 6. Preliminary studies indicated that supplementation of the diet of healthy humans with fish oil-containing capsules suppresses lymphocyte proliferation and interleukin-2 production. 7. These effects, along with inhibitory effects upon the functions of other cells involved in the immune response, in particular monocytes and macrophages, indicate that certain unsaturated fatty acid-containing oils (particularly evening primrose oil and fish oil) may be of benefit in the treatment of inflammatory and autoimmune diseases.
