Effects of purified dietary n-3 ethyl esters on murine T lymphocyte function

To precisely determine the biologic role of fish oil-derived constituents (n-3 polyunsaturated fatty acids), it is imperative that information on highly purified n-3 polyunsaturated fatty acids be evolved. Therefore, we studied the effects of a low dose, short term dietary supplementation with highly purified (n-3) ethyl esters with regard to murine T lymphocyte function. A 10-day dietary supplementation with low dose, highly purified (n-3) fatty acid ethyl esters was examined for effects on murine splenic lymphocyte function and membrane composition. Mice were fed diets containing either 3% safflower oil (SAF) ethyl esters, 2% SAF plus 1% eicosapentaenoic acid ethyl esters (EPA) (99% pure), or 2% SAF plus 1% docosahexaenoic acid ethyl esters (DHA) (97% pure). Fatty acid analysis of the lymphocyte membranes showed that membrane compositions of the EPA- and DHA-fed mice were subsequently enriched with these (n-3) fatty acids. Con A-induced lymphoproliferative assays (Con A, 5 and 10 micrograms/ml) revealed that splenic lymphocytes from the EPA group had significantly higher mitogenic responses relative to lymphocytes from the DHA or SAF groups (p < 0.05). In contrast, DHA splenocytes had the highest level of 3H-labeled diradylglycerol as a percentage of total lipid. Macrophage-lymphocyte co-cultures demonstrated that the dietary effect on proliferation in response to Con A was influenced by lymphocyte source, but apparently not by macrophage source. In addition, cells from Mycobacterium bovis vaccine-vaccinated mice were placed in culture with purified protein derivative (PPD) (10, 20, and 40 micrograms/ml), as well as Con A (5 and 10 micrograms/ml) to allow comparison between mitogenic and antigenic stimulation. No statistically significant differences (p > 0.05) existed between the diet groups upon PPD stimulation. However, lymphocytes from the DHA group exhibited significantly higher proliferative responses to Con A than cells from the EPA and SAF groups (p < 0.05). M. bovis vaccine-immunized EPA and DHA fed mice also exhibited significantly reduced delayed-type hypersensitive reactivity to footpad testing with PPD in comparison to that demonstrated by SAF-fed mice (p < 0.05). EPA-fed mice demonstrated the most decreased response. Overall, this study demonstrates for the first time that: 1) low dose, short term dietary supplementation with highly purified EPA or DHA can modulate select functional and transmembrane signaling responses of murine splenic lymphocytes; and 2) that these dietary agents have differing effects on mitogen vs Ag receptors.