Natural killer T cells are required for lipopolysaccharide-mediated enhancement of atherosclerosis in apolipoprotein E-deficient mice.

Lipopolysaccharide (LPS) has been shown to accelerate atherosclerosis and to increase the prevalence of IL-4-producing natural killer T (NKT) cells in various tissues. However, the role of NKT cells in the development of LPS-induced atherosclerotic lesions has not been fully tested in NKT cell-deficient mice. Here, we examined the lesion development in apolipoprotein E knockout (apoE-KO) mice and apoE-KO mice on an NKT cell-deficient, CD1d knockout (CD1d-KO) background (apoE-CD1d double knockout; DKO). LPS (0.5 µg/g body weight/wk) or phosphate-buffered saline (PBS) was intraperitoneally administered to apoE-KO and DKO mice (8-wk old) for 5 wk and atherosclerotic lesion areas were quantified thereafter. Consistent with prior reports, NKT cell-deficient DKO mice showed milder atherosclerotic lesions than apoE-KO mice. Notably, LPS administration significantly increased the lesion size in apoE-KO, but not in DKO mice, compared to PBS controls. Our findings suggest that LPS, and possibly LPS-producing bacteria, aggravate the development of atherosclerosis primarily through NKT cell activation and subsequent collaboration with NK cells.

Type II NKT cells stimulate diet-induced obesity by mediating adipose tissue inflammation, steatohepatitis and insulin resistance.

The progression of obesity is accompanied by a chronic inflammatory process that involves both innate and acquired immunity. Natural killer T (NKT) cells recognize lipid antigens and are also distributed in adipose tissue. To examine the involvement of NKT cells in the development of obesity, C57BL/6 mice (wild type; WT), and two NKT-cell-deficient strains, Jα18(-/-) mice that lack the type I subset and CD1d(-/-) mice that lack both the type I and II subsets, were fed a high fat diet (HFD). CD1d(-/-) mice gained the least body weight with the least weight in perigonadal and brown adipose tissue as well as in the liver, compared to WT or Jα18(-/-) mice fed an HFD. Histologically, CD1d(-/-) mice had significantly smaller adipocytes and developed significantly milder hepatosteatosis than WT or Jα18(-/-) mice. The number of NK1.1(+)TCRß(+) cells in adipose tissue increased when WT mice were fed an HFD and were mostly invariant Vα14Jα18-negative. CD11b(+) macrophages (Mφ) were another major subset of cells in adipose tissue infiltrates, and they were divided into F4/80(high) and F4/80(low) cells. The F4/80(low)-Mφ subset in adipose tissue was increased in CD1d(-/-) mice, and this population likely played an anti-inflammatory role. Glucose intolerance and insulin resistance in CD1d(-/-) mice were not aggravated as in WT or Jα18(-/-) mice fed an HFD, likely due to a lower grade of inflammation and adiposity. Collectively, our findings provide evidence that type II NKT cells initiate inflammation in the liver and adipose tissue and exacerbate the course of obesity that leads to insulin resistance.

Natural killer T cells are involved in adipose tissues inflammation and glucose intolerance in diet-induced obese mice.

BACKGROUND: Macrophage and lymphocyte infiltration in adipose tissue may contribute to the pathogenesis of obesity-mediated metabolic disorders. Natural killer T (NKT) cells, which integrate proinflammatory cytokines, have been demonstrated in the atherosclerotic lesions and in visceral adipose tissue. OBJECTIVE: To determine whether NKT cells are involved in glucose intolerance and adipose tissue inflammation in diet-induced obese mice. METHODS AND RESULTS: Male beta(2)-microglobulin knockout (KO) mice lacking NKT cells and C57BL/6J (wild-type) mice were fed with a high-fat diet (HFD) for 13 weeks [corrected]. Body weight and visceral obesity were comparable between wild-type and KO mice. However, macrophage infiltration was reduced in adipose tissue and glucose intolerance was significantly ameliorated in KO mice. To further confirm that NKT cells are involved in these abnormalities, alpha-galactosylceramide, 0.1 microg/g body weight, which specifically activates NKT cells, was administered after 13 weeks of HFD feeding. alpha-Galactosylceramide significantly exacerbated glucose intolerance and macrophage infiltration as well as cytokine gene expression in adipose tissue. CONCLUSIONS: NKT cells play a crucial role in the development of adipose tissue inflammation and glucose intolerance in diet-induced obesity.

Allograft inflammatory factor-1 augments macrophage phagocytotic activity and accelerates the progression of atherosclerosis in ApoE-/- mice.

Allograft inflammatory factor (AIF)-1, originally cloned from a rat heart allograft under chronic rejection, is induced in various inflammatory conditions including atherosclerosis. Using mouse AIF-1 transfected macrophages and AIF-1 transgenic (AIF-1 Tg) mice, we analyzed the influence of AIF-1 overexpression on macrophage phagocytosis and the development of atherosclerosis. The AIF-1 transfectants showed significantly increased phagocytosis of latex beads and E. coli BioParticles as well as incorporation of acetylated low-density lipoprotein (LDL) compared to those of vector controls. Concordant results were obtained with elicited peritoneal exudate cells from AIF-1 Tg mice. When AIF-1 Tg mice were crossbred with apolipoprotein E knockout mice (ApoE-/-), these AIF-1 Tg ApoE-/- mice developed significantly increased atherosclerotic lesions compared to ApoE-/- mice. These results suggest that enhanced AIF-1 expression leads to augmented incorporation of degenerated LDL by macrophages and promotes development of atherosclerotic vasculopathy.

Platelet aggregability in patients with hypertension treated with angiotensin II type 1 receptor blockers.

AIM: Cardiovascular events associated with hypertension often involve thrombosis. Increased platelet activity is one of the risk factors of cardiovascular diseases. Antithrombotic properties of antihypertensive agents are not fully characterized. Angiotensin II type 1 receptor blockers (ARBs) are widely used for the treatment of hypertension. Some ARBs can provoke antiaggregatory effects on platelets in vitro. Whether ARBs can inhibit platelet aggregation was tested in hypertensive patients in vivo. METHODS: Platelet aggregation was assessed by the highly sensitive particle counting method using laser-light scattering. RESULTS: Large platelet aggregation induced by adenosine diphosphate (ADP, 3 microM) was 2.6+/-0.4 (x10(7)) (SE) in hypertensive patients treated with losartan (72+/-3 years old, n=10) while it was 3.9+/-0.6 in hypertensive patients treated with candesartan (70+/-5 years old, n=6; p=0.056). Large platelet aggregation induced by thromboxane A2 receptor agonist, U46619 (10 microM), was 2.8+/-0.5 (x10(7)) in hypertensive patients treated with losartan while it was 5.1+/-0.9 in hypertensive patients treated with candesartan (p=0.033). Clinical characteristics including the control of blood pressure did not differ between the two groups (losartan 136+/-5/73+/-3 mmHg vs. candesartan 135+/-4/76+/-5). CONCLUSION: Thus, losartan may have the possibility to inhibit platelet activation in patients with hypertension independent of blood pressure reduction. Antiaggregatory properties may be independent of angiotensin II type 1 receptor or of antihypertensive actions. The favorable effects of losartan on reduction of adverse cardiovascular events among hypertensive patients may be at least partly mediated by inhibition of platelet activation.

Lower prevalence of circulating natural killer T cells in patients with angina: a potential novel marker for coronary artery disease.

OBJECTIVE: Atherosclerosis is an inflammatory disease. Natural killer T cells are a unique lymphocyte subset that can recognize lipid antigens presented by CD1d and secrete copious amounts of pro-atherogenic cytokines such as interferon-gamma. We have previously shown that natural killer T cells accelerate atherosclerosis in mice and macrophages incubated with oxidized low-density lipoproteins induce natural killer T cells to produce interferon-gamma. Thus, whether the prevalence of natural killer T cells in peripheral blood is altered in patients with angina pectoris and its correlation with coronary risk factors was determined. METHOD: Cell profiling was performed using flow cytometry in patients with stable angina, unstable angina (Braunwald IIIB), and healthy controls. Natural killer T cells in peripheral blood were identified by the expression of natural killer T specific invariant T cell receptor alpha-chain (Valpha24) and T cell receptor beta-chain (Vbeta11). RESULTS: Prevalence of natural killer T (Valpha24-Vbeta11 double positive) cells was significantly decreased in patients with unstable angina and stable angina compared with that in controls. No significant differences were observed in the prevalence between unstable and stable angina. Reduction of natural killer T cells was independently associated with the presence of angina. CONCLUSIONS: Lower prevalence of circulating natural killer T cells is related to the presence of coronary artery disease. As T cell receptor down-regulation or apoptosis after natural killer T cell activation and subsequent interferon-gamma release may contribute to atherogenesis, natural killer T cells can become a novel therapeutic target for the prevention and treatment of atherosclerotic vascular diseases.