Immunosuppressive dietary n-3 polyunsaturated fatty acids differentially modulate costimulatory regulation of murine CD4+ T-cell function

Consumption of fish oils (FO) enriched with the n-3 polyunsaturated fatty acids (PUFA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), is beneficial to a variety of inflammatory disorders due, in part, to the alteration of membrane composition of T-lymphocytes and other immune cells. We previously observed that down-regulation of proliferation and cytokine synthesis by CD4+ T-cells in mice fed diets rich in n-3 PUFA was dependent on the involvement of CD28, a co-stimulatory molecule necessary for T-cell activation. Since the co-receptor homologues, CD28 and CTLA-4, have opposing effects on T-cell activation, we hypothesized that the balance of costimulatory and downregulatory properties of CD28 and CTLA-4, respectively, would be altered by diet. A significant increase (p<0.05) in CD28 and CTLA-4 surface expression was observed in CD4+ T-cells post-stimulation with phorbol ester and calcium ionophore (PMA/Iono) or anti-CD3 and anti-CD28 (αCD3/CD28) antibodies in all diet groups. A significant increase (p<0.01; 20%) in the number of CD28 molecules was observed in n-3 PUFA vs. CO-fed mice after 48 h of in vitro CD4+ T-cell activation, and both CTLA-4 mRNA transcript and protein levels were upregulated by 50% at 72 h post-activation (p<0.01). Treatment with anti-CTLA-4 mAb in vivo in Mycobacterium bovis (BCG)-vaccinated mice did not alter the suppressive effects of dietary n-3 PUFA on antigen (PPD)-induced lymphocyte proliferation or delayed hypersensitivity reactions. T-cells from both the C57BL/6 and IL-10mice fed dietary n-3 PUFA after 72 h of in vitro stimulation with αCD3/CD28. CD4T-cells from C57BL/6 mice fed DHA produced significantly less IFNγ and IL-10, while CD4T-cells from IL-10Ligation of CD28 upregulates IL-10 receptor (IL-10R) expression on CD4+ T-cells. Therefore, we hypothesized that dietary n-3 PUFA would suppress T-cell function through the effects of IL-10. Surprisingly, the proliferation of purified splenic CD4+ T-cells activated in vitro with αCD3/CD28 was suppressed by dietary n-3 PUFA in both conventional mice (C57BL/6) and IL-10 gene knockout (IL-10(-/-)) mice. Furthermore, IL-10R cell surface expression was significantly down-regulated on CD4+ T-cells from both the C67BL/6 and IL-10(-/-) mice fed dietary n-3 PUFA produced significantly more IFNγ compared to the CO-fed group.