Dietary n-3 PUFA affect TcR-mediated activation of purified murine T cells and accessory cell function in co-cultures

Abstract

Diets enriched in n-3 polyunsaturated fatty acids (PUFA) suppress several functions of murine splenic T cells by acting directly on the T cells and/or indirectly on accessory cells. In this study, the relative contribution of highly purified populations of the two cell types to the dietary suppression of T cell function was examined. Mice were fed diets containing different levels of n-3 PUFA; safflower oil (SAF; control containing no n-3 PUFA), fish oil (FO) at 2% and 4%, or 1% purified docosahexaenoic acid (DHA) for 2 weeks. Purified (>90%) T cells were obtained from the spleen, and accessory cells (>95% adherent, esterase-positive) were obtained by peritoneal lavage. Purified T cells or accessory cells from each diet group were co-cultured with the alternative cell type from every other diet group, yielding a total of 16 different co-culture combinations. The T cells were stimulated with either concanavalin A (ConA) or antibodies to the T cell receptor (TcR)/CD3 complex and the costimulatory molecule CD28 (alphaCD3/alphaCD28), and proliferation was measured after four days. Suppression of T cell proliferation in the co-cultures was dependent upon the dose of dietary n-3 PUFA fed to mice from which the T cells were derived, irrespective of the dietary treatment of accessory cell donors. The greatest dietary effect was seen in mice consuming the DHA diet (P = 0.034 in the anova; P=0.0053 in the Trend Test), and was observed with direct stimulation of the T cell receptor and CD28 costimulatory ligand, but not with ConA. A significant dietary effect was also contributed accessory cells (P = 0.033 in the Trend Test). We conclude that dietary n-3 PUFA affect TcR-mediated by T cell activation by both direct and indirect (accessory cell) mechanisms.

Fig. 1

The in vitro proliferative response to αCD3/αCD28 of co-cultures of purified T lymphocytes (L) and purified accessory cells (M) isolated from mice fed diets containing different levels of n-3 PUFA for two weeks; lymphocytes from each diet source (LS, LD, LF2, LF4) were co-cultured with accessory cells from each diet source (▪ (M)S, (M)D, (M)F2, □ (M)F4) in a 4 × 4 factorial design; S, Safflower oil diet; F2, 2% Fish oil diet; F4, 4% Fish oil diet; D, DHA-enriched diet; Mean ± SEM (n = 3–5 mice).

Fig. 2

Lymphocyte diet source as a determinant of lymphoproliferation induced by αCD3/αCD28 in cultures of purified T cells from mice fed four different levels of n-3 PUFA in co-culture with purified accessory cells from all four diet sources; Saff, safflower oil diet; Fish2, 2% fish oil diet; Fish4, 4% fish oil diet; DHA DHA-enriched diet; mean ± SEM for n = 12–18 mice; values identified by a different letter are significantly different (P_TREND < 0·05).

Fig. 3

Accessory cell diet source as a determinant of lymphoproliferation induced by αCD3/αCD28 in cultures of accessory cells from mice fed four different levels of n-3 PUFA in co-culture with purified T lymphocytes from all four diet groups; Saff, safflower oil diet; Fish2, 2% fish oil diet; Fish4, 4% fish oil diet; DHA, DHA-enriched diet; mean ± SEM for 12–18 mice; values identified by a different letter are significantly different (P_TREND < 0·05).

Fig. 4

The in vitro proliferative response to ConA of co-cultures of purified T lymphocytes (L) and purified accessory cells (M) isolated from mice fed diets containing different levels of n-3 PUFA for two weeks; lymphocytes from each diet source (LS, LD, LF2, LF4) were co-cultured with accessory cells from each diet source (▪ (M)S, (M)D, (M)F2, □ (M)F4) in a 4 × 4 factorial design; S, Safflower oil diet; F2, 2% Fish oil diet; F4, 4% Fish oil diet; D, DHA-enriched diet; Mean ± SEM (n = 3–5 mice); no statistically significant dietary effects were detected.