Effect of Fatty Acids on Interleukin 2 Signaling Pathway in Human Lymphocytes

 The effect of palmitic (PA, C16:0), stearic (SA, C18:0), oleic (OA, C18:1, n-9), linoleic (LA, C18:2 n-6), docosahexaenoic (DHA, C22:6 n-3) and eicosapentaenoic (EPA, C20:5 n-3) acids on interleukin -2 (IL-2) signaling pathway in human lymphocytes was investigated. It was also evaluated if these fatty acids at non-toxic concentrations affect IL-2 induced lymphocyte proliferation and cell cycle progression. Human lymphocytes were isolated from normal donors from heparinized venous blood by density-gradient sedimentation using Histopaque. The cells were stimulated with concanavalin A (ConA) and cultured with fatty acids and IL-2 for 24 hours. Lymphocyte proliferation was determined by thymidine incorporation and cell cycle was analyzed by flow cytometry using propidium iodide. Before protein analysis, the cells were stimulated with concanavalin A and treated with IL-2 and fatty acids for one hour. Afterwards, JAK1 and 3, STAT5 a/b and ERK1/2 phosphorylation were analyzed by Western Blotting. PA, SA, DHA and EPA at 50μM decreased the stimulatory effect of IL-2 on lymphocyte proliferation, increasing the percentage of cells in G1 phase and decreasing the proportion of cells in S and G2/M phases. OA and LA at 25μM pronounced the stimulatory effect of IL-2 on lymphocyte proliferation. PA, SA, DHA and EPA decreased JAK1, JAK3 and STAT5 a/b phosphorylation induced by IL-2 but OA and LA did not cause any effect. However, OA and LA increased ERK1/2 phosphorylation and the other fatty acids caused a marked decrease. The total expression of all these proteins was not altered by the fatty acids tested. Therefore, the inhibitory effect of PA, SA, DHA and EPA observed on lymphocyte proliferation was due to a decrease in JAK/STAT and ERK pathways activation. Probably, OA and LA stimulate lymphocyte proliferation by altering ERK 1/2 phosphorylation.