Effects of high levels of dietary oils on autoimmune responses.

Arguments for the cardiovascular benefits of increased consumption of polyunsaturated fats (PUFAs) compared to saturated fats ignore the possibility that long term exposure to this type of fat may affect immune competence. The profile of inflammatory and immunoregulatory mediators produced by metabolism of PUFAs of the w-3 and w-6 series differ [ 11. Our studies examined the effect of high levels of dietary oils on autoimmunity. Dietary oils were chosen that contained high levels of PUFAs of the w-3 series (fish oil [Maxepa]) and 0-6 series (corn oil), monounsaturated fats of the 0-9 series (olive oil) and saturated fats (SFA [hydrogenated coconut oil]). To meet specification for other parts of the study, the corn oil included 25% olive oil. The effect of dietary oils was examined using a mouse model of autoimmune haemolytic anaemia [2]. This involves the injection of mice with rat red blood cells (RRBC). Certain antigenic determinants on the red cell surface are common between the two species. In addition to producing antibodies against the foreign RRBC the mice also produce antibodies against their own RBC, an anti-self or autoimmune response. Groups of 8 Balb/c mice were fed either control diet (SDS rat and mouse Nol) or semi-synthetic diets containing 25 % oil for 28 days prior to i.p. injection with 2 x 10" rat red blood cells once a week for 5 weeks. In a second experiment mice were fed diets containing 20% oil for 63 days and received 2 x lo7 RRBC i.p. on day 28. The presence of anti-RRBC and anti-mouse (self) red blood cell (MRBC) antibody on the surface of the MRBC was assessed using haemagglutination techniques. The lowest dilution at which agglutination occurred was recorded as the end point titre. Results were analysed using a two way analysis of variance. Comparisons were made using either the Least Significant Difference test (LSD) or Mann-Whitney (MW) according to data distribution. Reduced anti-RRBC responses in mice fed 25% diet that received multiple injections could be observed in all diets on day 42 (Table 1). At day 35 this was only present in the Maxepa and coconut groups. Similarly in mice receiving a single injection and fed 20% diet reduced anti-RRBC responses were observed only in the Maxepa and coconut groups. Although all diets reduced the titres of anti-MRBC antibody, particulary on day 63 (Table 2.). the Maxepa and Coconut oils had the most consistent effect. No significant changes in anti-MRBC titre was detected in mice fed the 20% diet (results not shown). These results were consistent with the observation that antibody responses in mice fed diets with a high PUFA to SFA (PIS) ratio were down regulated compared to diets with a low P/S ratio [3]. The use of two treatment regimes showed that both the anti-RRBC and MRBC responses from mice fed Maxepa and coconut oils diets were most consistently reduced.The effect of the SFA coconut oil may be related to the medium chain length of its fatty acids and their influence on membrane fluidity. Autoimmune diseases are produced by the presence anti-self antibodies. A reduced response could reflect a general effect on regulation of antibody production. Dietary fat has been reported to reduce the level of Ia expression on the surface of antigen presenting cells in rats and mice, which may in turn affect antigen presentation [4,5]. In conclusion high levels of the Maxepa (w-3) and coconut oils (SFA) in the diet appear to inhibit antibody production and the Table 1 . Anti-rat red blood cell responses