Abstract/Summary

Polyunsaturated fatty acids (PUFA) have been shown to suppress immune cell functions in vitro. Dietary studies investigating the effects of PUFA-containing oils on lymphocyte functions have yielded contradictory findings; such studies are difficult to compare since there are many variations in protocols. The present study investigated the effects of exogenously added fatty acids on proliferation of leucocytes to whole blood in vitro and the effects of feeding diets containing oils rich in saturated fatty acids, monounsaturated fatty acids, n-6 PUFA or n-3 PUFA on rat leucocyte proliferation in whole blood and on receptor and surface marker expression by peripheral blood leucocytes. When added exogenously to whole blood all fatty acids tested, except myristic acid, inhibited leucocyte proliferation; the greatest inhibition of proliferation was seen with arachidonic and eicosapentaenoic acids. To investigate the effects of dietary lipids on proliferation and surface marker expression by leucocytes, rats were fed for ten weeks on a low fat (LF) diet (approximately 2% fat by weight) or on one of five high fat diets, which contained 20% (by weight) hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), evening primrose oil (EPO) or menhaden (fish) oil (MO). Compared with feeding the LF, SO or EPO diets, the HCO, OO and MO diets suppressed the proliferation of leucocytes in whole blood at low concentrations of Con A. High fat feeding decreased the sensitivity of B-cells to LPS, but had no effect on the magnitude of the response to this mitogen. Dietary lipid manipulation had no effect on leucocyte subpopulations (T-cells, B-cells, CD4+ cells, CD8+ cells, monocytes/macrophages, natural killer cells) or on the expression of adhesion molecules (LFA-1, ICAM, CD2). The effects of dietary lipid manipulation on leucocyte proliferation are clearly very different from the effects of addition of single fatty acids to whole blood in vitro. This is likely to be due to alterations in blood triacylglycerol and cholesterol concentrations brought about by different dietary lipids, suggesting that dietary lipids have marked effects on leucocyte proliferation and that the use of the whole blood system may be a more physiological way of determining the effects of dietary lipids on immune function than the use of single exogenously added fatty acids with purified cells.