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BackgroundIt is well established that adaptive immune responses induced by hypercholesterolemia play an important role in the development of atherosclerosis, but the pathways involved remain to be fully characterized. In the present study we assessed immune responses to hypercholesterolemia induced by feeding Apoe-/- mice a high-fat diet for 4 or 8 weeks.ResultsThe primary immune response in lymph nodes draining the aortic root was an increased expression of interferon (IFN)-γ in CD8+CD28+ T cells, while an activation of IFN-γ expression in CD4+ T cells was observed only after 8 weeks of high-fat diet. Contrarily, spleen CD4+ T cells responded with a higher expression of IL-10. Spleen CD8+ T cells expressed both IFN-γ and IL-10 and showed enhanced proliferation when exposed to Concanavalin A. Plasma levels of IgG and IgM against oxidized LDL did not change, but the level of apolipoprotein B/IgM immune complexes was increased.ConclusionHypercholesterolemia leads to unopposed activation of Th1 immune responses in lymph nodes draining atherosclerotic lesions, whereas Th1 activation in the spleen is balanced by a concomitant activation of Th2 cells. The activation of CD8+ T cells implies that hypercholesterolemia is associated with formation of cell autoantigens.

Interleukin (IL) 27 is an interesting cytokine as it has both pro- and anti-inflammatory properties. IL-27 binds to cytokine receptor WSX-1 to activate cells. In this experiment we determined the effect of IL-27 on atherosclerosis and blocked the function of IL-27 in vivo. This was achieved by injecting a lentivirus encoding the WSX-1 receptor lacking the intracellular domain with a human IgG2 tag (sWSX-1) in female LDL receptor deficient mice. The sWSX-1 protein was continuously released into the blood for at least 10 weeks and the responders (n=11) had a high serum hIgG level in comparison to the mice which received an empty virus (n=10), whereas the non-responders (n=9) did not show an increased hIgG level. After 10 weeks of atherogenic diet, mice were sacrificed . In vitro sWSX-1 was able to inhibit the IL-27-mediated IL-2 secretion in spleen cells. The in vivo blockade of IL-27 via the soluble receptor sWSX-1 resulted in a 31 % reduction in aortic lesion size in the responder group (2,7 x 10 5 μm 2 ± 2,2 x 10 4 ) compared to the control group (3,7 x 10 5 μm 2 ± 3,5 x 10 4 ). No change was measured in the non-responders (3,4 x 10 5 μm 2 ± 2,5 x 10 4 ) The lesion size negatively correlated with the concentration of the soluble receptor in the serum. sWSX-1 production did not affect the collagen content of the lesion, while there was a trend towards an increased macrophage content. FACS analysis showed that blockade of IL-27 increased the circulating T helper cell and cytotoxic T cell population by 2-fold. Surprisingly, no changes were detected in the Th1 and Th17 populations. There was a 5-fold increase in the percentage circulating regulatory T cells in the presence of sWSX-1. Furthermore, CCR2 expression on circulating Ly6C low monocytes was reduced by 44 %. The proliferation of spleen cells showed no change between the control and mice with overexpression of sWSX-1. Taken together these results indicate that blockade of interleukin 27 reduces lesion formation by inducing a less inflammatory immune status.