[Immunosuppressive effect of parenteral fat emulsions in defined immunostimulation].

Background: In the heterotopic rat heart allotransplant model we have previously shown that intravenous fat emulsions are to a various extent immunosuppressive or immunoneutral, dependent on their n-3/n-6 fatty acid ratio. Safflower oil (n-3: n-6 = 1:370), fish oil (7.6:1) and soybean oil (1:6.5) prolonged the transplant survival time to 13.3, 12.3 and 10.4 days compared to 6.7 days (oil control group; 1.2.1) and 7.8 days (saline control group) (p < 0.01), respectively. This study presents a correlation of graft survival to immunohistological, cell biological and biochemical parameters.

Materials and methods: 20% emulsions of safflower oil, fish oil, soybean oil and a 1:1 mixture of safflower and fish oil (oil control group) were continuously infused (9 g fat/kg body weight/day; n = 10 each group) after transplantation. Subpopulations of infiltrating and circulating immunocompetent cells and leukotriene B4 and B5 release of circulating mononuclear cells were analyzed (on the 4th postoperative day).

Results: In the 2 groups with the highest prolongation of graft survival the number of infiltrating cells was reduced by up to 40% and the peripheral blood mononuclear cell interleukin-6 release by up to 45%. Beyond that, circulating T cells were reduced in the fish oil group. Leukotriene B4 was released in all groups to the same extent, leukotriene B5 exclusively in the fish oil group.

Conclusions: Intravenous fat emulsions show a varying immunomodulatory effect in dependence of the n-3/n-6 fatty acid ratio. Both n-6 and n-3 fatty acids, if applied as main fatty acid source, exert immunosuppressive effects by a diminished infiltration and mobilisation of immunocompetent cells. Soybean oil with a more balanced n-3/n-6 fatty acid ratio than safflower oil is significantly less immunosuppressive than safflower oil, and fat emulsions with a n-3/n-6 fatty acid ratio of 1:2 are immunologically neutral.