The effect of quality and quantity of dietary fat on the immune system.

The effect of the quality and quantity of dietary fats on the morphology and function of the immune system of Sprague-Dawley rats fed either 5% mixed fat, 24% saturated fat, 24% polyunsaturated fat, or 24% partially saturated fat was examined. After 2.5 months of dietary treatment high fat groups showed evidence of splenic hyperplasia, however, no consistent morphologic changes were seen in the mesenteric lymph nodes (MLN). Splenocytes from rats fed the 24% polyunsaturated fat diet were cultured in fetal bovine serum (FBS) and had a depressed lymphocyte transformation response, which persisted after 5 months of dietary treatment. Supplementing the culture medium with 10% rat serum altered the transformation response profile, but high fat serum did not have an immunosuppressive effect. MLN lymphocytes from rats fed the 24% partially saturated diet for 2.5 months had an enhanced response to concanavalin A; at five months the response was elevated in the groups fed saturated as well as partially saturated fat diets. These results suggest that the modulating effect of fat on the immune system depends on the duration of feeding, the type of fat consumed and the organ examined.