EFFECTS OF DIETARY-LIPID MANIPULATION UPON GRAFT-VS-HOST AND HOST VS GRAFT RESPONSES IN THE RAT

The popliteal lymph node (PLN) assay was used to establish whether die tary lipids with differing fatty acid compositions could affect cell-m ediated immunity in the rat. Weanling rats were fed for 4 weeks on a l owfat (2.5% by weight; LF) diet or on diets containing 20% (by weight) hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), e vening primrose oil (EPO), or menhaden (fish) oil (MO). Feeding the MO diet suppressed the graft vs host response compared with feeding the LF, HCO, SO, or EPO diets, while feeding the OO diet suppressed this r esponse compared with feeding the LF or EPO diets. Feeding the MO diet suppressed the host vs graft response compared with feeding each of t he other diets. Following the graft vs host reaction, PLN lymphocytes from animals fed the MO diet had significantly lower levels of express ion of LFA-1 and CD2 compared with PLN lymphocytes from animals fed th e LF diet; furthermore, they had lower levels of expression of T-cell receptor (TcR), CD4, CD8, LFA-1, and CD2 compared with lymphocytes fro m animals fed some, and in the case of CD2 each, of the other high-fat diets. Feeding the MO diet resulted in a lower proportion of cells ex pressing the interleukin-2 receptor, indicating an inhibition of lymph ocyte activation, and a lower proportion of CD16(+)/CD3(-) cells, indi cating a decrease in the proportion of NK cells within the PLN. Follow ing the host vs graft reaction, PLN lymphocytes from animals fed the M O diet had significantly lower levels of expression of TcR and CD8 com pared with lymphocytes from animals fed each of the other diets; furth ermore, they had lower levels of expression of CD4, CD2, and LFA-1 com pared with lymphocytes from animals fed the LF, HCO, OO, or SO diets. These observations indicate that the smaller PLN size of animals fed t he MO diet results from an inhibition of activation and subsequent pro liferation of cells within the node and perhaps also a suppression of movement of cells from the bloodstream to the PLN, due to decreased le vel of expression of adhesion molecules. These lowered levels of expre ssion might be due to an inhibitory effect of the n-3 polyunsaturated fatty acids found in MO upon components of the signal transduction pat hways involved in lymphocyte activation or upon expression of the gene s for the surface molecules or both. (C) 1995 Academic Press, Inc.