Abdominal aortic aneurysm (AAA) is characterized by a prominent inflammatory cell infiltrate and local destruction of extracellular matrix. Following the acute phase, the inflammatory infiltrate is predominately composed of T lymphocytes and macrophages. We have previously reported that inhibition of Th1 or Th2 cell responses had no effect on the development or the complications of experimental murine AAA. We hypothesized that another subset of T cell, natural Treg cells (Tregs), plays a role in the pathophysiology of AAA. Male C57Bl/6 mice were infused with Angiotensin II (1μg/kg/mn) for 28 days using osmotic pumps. A control group received non-immune isotype-matched IgG antibody (n=20) and a group received anti-CD25 antibody (n=20) every 10 days that depleted more than 95% of Tregs in lymphoid organs. Treg depletion induced AAA rupture (15% vs 0%, P<0.05) and more severe AAA stages compared to control mice (P<0.01). Histological analysis showed an increase of elastin degradation (mean layer number 2.5 vs 5.6, P=0.01) and an increase of T cell accumulation in the adventitia of Treg-depleted mice (2816 vs 330 μm2, P<0.01). CD28 or B7 deficiency leads to a profound reduction in Treg cells. We infused Angiotensin II into C57Bl/6 CD28+/+ (n=17), CD28 -/- mice (n=11) or B7 -/- mice (n=16). CD28 or B7 deficiency did not alter the pressor response to Angiotensin II. CD28 and B7 deficiency induced an increase of AAA incidence compared to control mice, respectively 68%, 72%, and 10%, P<0.001. Moreover, CD28 and B7 deficiency induced 20% of AAA rupture whereas no rupture was observed in control mice. In another set of experiments, transfer of Tregs (3x106 cells) into CD28 -/- mice abolished AAA rupture (0% vs 15%, P<0.05) and significantly reduced AAA severity (P<0.01). Moreover, Treg transfer decreased elastin degradation (mean layer number 3.7 vs 2.5, P=0.04) and T cell infiltration in the adventitia (390 vs 2747 μm2, P<0.01). Conclusion: We have shown for the first time that natural regulatory T cell protected against AAA development and rupture.
Inflammatory cell infiltration is a feature of postischemic neovascularization. However, mechanisms leading to leukocyte attraction to the site of neovascularization are still undefined. We hypothesized that the CXC chemokine receptor 3 (CXCR3) may contribute to leukocyte accumulation and subsequently to blood vessel growth in the ischemic area. Ischemia induced by femoral artery ligature improved the number of CXCR3-expressing cells and the level of its ligand, CXCL10. Angiographic score, blood flow recovery measurement, and capillary density analysis showed a significant decrease of ischemic/nonischemic leg ratio in CXCR3-deficient mice when compared with controls ( P <0.05), at day 21 after ischemia. Interestingly, this impairment was as important as that observed in mice deficient for the well known CC-chemokine monocyte chemoattractant protein-1 (MCP-1). At day 7 of ischemic injury, the number of CD3-positive T cells and Mac-3–positive monocytes/macrophages was 38% and 45% lower, respectively, in the ischemic leg of CXCR3-deficient mice compared with the control group ( P <0.05), suggesting an important role for CXCR3 in leukocyte recruitment into the ischemic area. VEGF protein content, a classical proangiogenic factor, was also markedly reduced (80% reduction) in ischemic leg of CXCR3-deficient mice ( P <0.01). Injection of bone marrow–derived mononuclear cells (BM-MNCs) isolated from wild-type animals restored the neovascularization reaction in CXCR3-deficient mice whereas BM-MNCs from CXCR3-deficient mice was ineffective. In conclusion, CXCR3 plays a key role in neovascularization and provides novel information on the mechanisms leading to leukocyte infiltration in the vessel growth area.
Experimental models of atherosclerosis suggest that recruitment of monocytes into plaques drives the progression of this chronic inflammatory condition. Cholesterol-lowering therapy leads to plaque stabilization or regression in human atherosclerosis, characterized by reduced macrophage content, but the mechanisms that underlie this reduction are incompletely understood. Mice lacking the gene Apoe (Apoe–/– mice) have high levels of cholesterol and spontaneously develop atherosclerotic lesions. Here, we treated Apoe–/– mice with apoE-encoding adenoviral vectors that induce plaque regression, and investigated whether macrophage removal from plaques during this regression resulted from quantitative alterations in the ability of monocytes to either enter or exit plaques. Within 2 days after apoE complementation, plasma cholesterol was normalized to wild-type levels, and HDL levels were increased 4-fold. Oil red O staining and quantitative mass spectroscopy revealed that esterified cholesterol content was markedly reduced. Plaque macrophage content decreased gradually and was 72% lower than baseline 4 weeks after apoE complementation. Importantly, this reduction in macrophages did not involve migratory egress from plaques or CCR7, a mediator of leukocyte emigration. Instead, marked suppression of monocyte recruitment coupled with a stable rate of apoptosis accounted for loss of plaque macrophages. These data suggest that therapies to inhibit monocyte recruitment to plaques may constitute a more viable strategy to reduce plaque macrophage burden than attempts to promote migratory egress.
Abstract Aims: Myeloid inflammatory cells are recruited to the tumor microenvironment and subsequently educated in situ to acquire a pro-invasive, pro-angiogenic and immunosuppressive phenotype. Components of the metabolic syndrome are known to aggravate tumorigenesis in part through myeloid cell activation. We hypothesized that consumption of a high fat/high cholesterol pro-atherogenic diet and its associated low-grade inflammation would accelerate the initiation of solid tumors. Methods and results: Here, we show that two-week feeding of wildtype C57BL/6J mice with a pro-atherogenic diet increases the pool of circulating inflammatory Ly-6C hi monocytes available for initial melanoma development and amplifies the accumulation of myeloid cells within the tumor microenvironment, in an IL-1β-dependent manner. Under pro-atherogenic diet feeding, myeloid cells display heightened pro-angiogenic, pro-inflammatory and immunosuppressive activities. Within the first days after tumor implantation, myeloid cells become the main producer of VEGF-A in the tumor. Depletion of Ly-6C hi monocytes in mice fed with a pro-atherogenic diet limits immune cell infiltration in the tumor, and inhibits tumor growth. IL-1β deficiency or specific inhibition of VEGF-A in myeloid cells recapitulates the beneficial effect of Ly-6C hi monocyte depletion, suggesting their complementary roles in tumorigenesis in the context of mild hyperlipidemia. Conclusion: Our study shows that dyslipidemia provide high amounts of activated myeloid cells with pro-tumoral activity and shed light on cross-disease communication between cardiovascular pathologies and cancer. Translational Perspective: In this study we demonstrate that dyslipidemia accelerates the development of solid tumors through the increased infiltration of Ly6C hi monocytes that differentiate into pro-tumoral myeloid cells. These findings demonstrate that dyslipidemia can silently boost tumor development in normal-weight individuals through the action of IL-1β and VEGF-A. Our work sheds light on the potential benefit of targeting IL-1β and VEGF-A in cancer patients with moderate dyslipidemia.
Background: Innate immune responses activated through myeloid cells contribute to the initiation, progression and complications of atherosclerosis in experimental models. However, the critical upstream pathways that link innate immune activation to foam cell formation are still poorly identified. We hypothesized that activation of TREM (Triggering Receptor Expressed on Myeloid cells)-1 plays a determinant role in macrophage atherogenic responses. Methods and Results: Ldlr-/- mice reconstituted with bone marrow deficient for Trem-1 (Trem-1-/-) showed a strong reduction of atherosclerotic plaque size in both the aortic sinus and the thoraco-abdominal aorta, and displayed a less inflammatory plaque phenotype compared to Trem-1+/+ chimeric mice. Genetic invalidation of Trem-1 led to alteration of monocyte recruitment into atherosclerotic lesions and inhibited Tlr4-initiated pro-inflammatory macrophage responses. Furthermore, we identified a critical role for Trem-1 in the upregulation of Cd36, thereby promoti...
Several chemokines or chemokine receptors are involved in atherogenesis. CCR1 is expressed by macrophages and lymphocytes, two major cell types involved in the progression of atherosclerosis, and binds to lesion-expressed ligands. We examined the direct role of the blood-borne chemokine receptor CCR1 in atherosclerosis by transplanting bone marrow cells from either CCR1+/+ or CCR1−/− mice into low-density lipoprotein-receptor (LDLr)-deficient mice. After exposure to an atherogenic diet for 8 weeks, no differences in fatty streak size or composition were detected between the 2 groups. After 12 weeks of atherogenic diet, however, an unexpected 70% increase in atherosclerotic lesion size in the thoracic aorta was detected in the CCR1−/− mice, accompanied by a 37% increase in the aortic sinus lesion area. CCR1−/− mice showed enhanced basal and concanavalin A-stimulated IFN-γ production by spleen T cells and enhanced plaque inflammation. In conclusion, blood-borne CCR1 alters the immuno-inflammatory response in atherosclerosis and prevents excessive plaque growth and inflammation.
