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2-Deoxy-2-[18F]fluoro-d-glucose positron emission tomography (FDG-PET) is widely used to study cerebral glucose metabolism. Here, we investigated whether the FDG-PET signal is directly influenced by microglial glucose uptake in mouse models and patients with neurodegenerative diseases. Using a recently developed approach for cell sorting after FDG injection, we found that, at cellular resolution, microglia displayed higher glucose uptake than neurons and astrocytes. Alterations in microglial glucose uptake were responsible for both the FDG-PET signal decrease in Trem2-deficient mice and the FDG-PET signal increase in mouse models for amyloidosis. Thus, opposite microglial activation states determine the differential FDG uptake. Consistently, 12 patients with Alzheimer’s disease and 21 patients with four-repeat tauopathies also exhibited a positive association between glucose uptake and microglial activity as determined by 18F-GE-180 18-kDa translocator protein PET (TSPO-PET) in preserved brain regions, indicating that the cerebral glucose uptake in humans is also strongly influenced by microglial activity. Our findings suggest that microglia activation states are responsible for FDG-PET signal alterations in patients with neurodegenerative diseases and mouse models for amyloidosis. Microglial activation states should therefore be considered when performing FDG-PET.

SummaryThe costimulatory molecule CD70 is expressed on activated immune cells and is known to modulate responses of T, B, and NK cells via its receptor CD27. Until now, there is only limited data describing the role of CD70 in atherosclerosis. We observed that ruptured human carotid atherosclerotic plaques displayed higher CD70 expression than stable carotid atherosclerotic plaques, and that CD70 expression in murine atheroma localized to macrophages. Lack of CD70 impaired the inflammatory capacity (e. g. reactive oxygen species and nitric oxide production) of bone marrow-derived macrophages, increased both M1-like and M2-like macrophage markers, and rendered macrophages meta-bolically inactive and prone to apoptosis. Moreover, CD70-deficient macrophages expressed diminished levels of scavenger receptors and ABC-transporters, impairing uptake of oxidised low-density lipoprotein (oxLDL) and cholesterol efflux, respectively. Hyperlipidaemic Apoe −/− mice reconstituted with CD70-deficient bone marrow displayed a profound increase in necrotic core size, plaque area, and number of lesional macrophages as compared to mice receiving control bone marrow. Accordingly, 18 week-old, chow diet-fed CD70-deficient Apoe−/−mice displayed larger atheroma characterised by lower cellularity and more advanced plaque phenotype than Apoe−/− mice. In conclusion, CD70 promotes macrophage function and viability and is crucial for effective phagocytosis and efflux of oxLDL. Deficiency in CD70 results in more advanced atheroma. Our data suggest that CD70 mitigates atherosclerosis at least in part by modulating macrophage function.Note: The review process for this manuscript was fully handled by G. Y. H. Lip, Editor in Chief.Supplementary Material to this article is available online at www.thrombosis-online.com.

Atherosclerosis is a chronic inflammatory disease that is mediated by innate and adaptive immune responses. The disease is characterized by sub-endothelial accumulation and modification of lipids in the artery wall triggering an inflammatory reaction which promotes lesion progression and eventual plaque rupture, thrombus formation, and the respective clinical sequelae such as myocardial infarction or stroke. During the past decade, T-cell-mediated immune responses, especially control of pro-inflammatory signals by regulatory T cells (Tregs), have increasingly attracted the interest of experimental and clinical researchers. By suppression of T cell proliferation and secretion of anti-inflammatory cytokines, such as interleukin-10 (IL-10) and transforming growth factor-β, Tregs exert their atheroprotective properties. Atherosclerosis-prone, hyperlipidemic mice harbor systemically less Tregs compared to wild-type mice, suggesting an imbalance of immune cells which affects local and systemic inflammatory and potentially metabolic processes leading to atherogenesis. Restoring or increasing Treg frequency and enhancing their suppressive capacity by various modulations may pose a promising approach for treating inflammatory conditions such as cardiovascular diseases. In this review, we briefly summarize the immunological basics of atherosclerosis and introduce the role and contribution of different subsets of T cells. We then discuss experimental data and current knowledge pertaining to Tregs in atherosclerosis and perspectives on manipulating the adaptive immune system to alleviate atherosclerosis and cardiovascular disease.

Background: Adaptive immunity and co-stimulatory signals are pivotal to all stages of atherosclerosis. CD40-CD40L (CD154) co-stimulatory molecules are central mediators of disease progression. However, it remains undetermined whether platelet- or T cell-specific CD40L contributes to its pro-atherogenic function. Method: We generated mice carrying a mutated allele of the CD40L gene flanked by loxp-sites sensitive to cre-mediated inactivation. We crossed these to Apoe -/- -deficient mice which also expressed Cre specifically in T cells ( Cd4Cre tg ) or platelets (Pf4Cre tg ) to generate Apoe -/- Cd40lg fl/fl -Cd4Cre tg , -Cd4Cre wt , -Pf4Cre tg , or -Pf4Cre wt mice. After consuming chow diet for 28 weeks the immune status and atherosclerosis was assessed by flow cytometry, RNA expression analysis and histology of the ascending aorta, blood, draining lymph nodes, and spleen. Results: Specific deletion of CD40L on T cells leads to decreased atherosclerotic lesion size in the ascending aorta while plaque size in Apoe -/- Cd40lg fl/fl -Pf4Cre tg or -Pf4Cre wt mice did not differ. Furthermore, platelet-specific ablation of CD40L did not results in changes of immune cells distribution. In contrast, cytokine and RNA analysis data pointed to a less inflammatory phenotype in Apoe -/- Cd40lg fl/fl Cd4Cre tg mice compared to Apoe -/- Cd40lg fl/fl Cd4Cre wt controls. Interestingly, T cell-specific inactivation of CD40L also caused a systemic decrease of Tregs in draining lymph nodes, spleen, blood, and thymus. Conclusion: Taken together our data confirm that CD40L expressed on T cells but not on platelets contributes to the disease-aggravating role of the CD40/CD40L dyad in atherosclerosis. Thus, T cell-expressed CD40L may provide a promising candidate for further investigation in atherosclerosis and other inflammatory diseases.

Aims The co-stimulatory receptor CD27 modulates responses of T cells, B cells, and NK cells. Various T cell subsets participate in atherogenesis. However, the role of CD27 in atherosclerosis remains unexplored.Methods and results Here we investigated the effect of bone marrow-derived and systemic CD27 deficiency in Apolipoprotein E-deficient (Apoe(-/-)) mice in early and advanced stages of atherosclerosis. Lethally-irradiated Apoe(-/-) mice reconstituted with Cd27(-/-)Apoe(-/-) bone marrow and consuming an atherogenic diet displayed a markedly increased plaque size and lesional inflammation compared to mice receiving Cd27(+/+)Apoe(-/-) bone marrow. Accordingly, chow diet-fed Cd27(-/-)Apoe(-/-) mice showed exacerbated lesion development and increased inflammation at the age of 18 weeks. At a more advanced stage of atherosclerosis (28 weeks), lesion size and phenotype did not differ between the two groups. Systemic and bone marrow-derived CD27 deficiency reduced the abundance of regulatory T cells (Treg) in blood, lymphoid organs, and the aorta. Numbers of other immune cells were not affected while expression of inflammatory cytokine genes (e.g. IL-1 beta and IL-6) was increased in the aorta when haematopoietic CD27 was lacking. In vitro, Tregs of CD27-deficient mice showed similar suppressive capacity compared with their wild-type controls and migrated equally towards CCL19 and CCL21. However, thymic Cd27(-/-) Tregs underwent increased apoptosis and expressed fewer markers of proliferation in vivo. Reconstitution of Cd27(-/-)Apoe(-/-) mice with Cd27(+/+)Apoe(-/-) Tregs reversed the increase in atherosclerosis.Conclusion We demonstrate that CD27 co-stimulation increases the number of Tregs and limits lesion development and inflammation in experimental atherosclerosis, particularly during early stages of disease. Thus, our study suggests that promotion of CD27 function may mitigate atherosclerosis.

Atherosclerosis, an inflammatory disease of large arteries, is - through its clinical manifestations stroke and myocardial infarction - the leading cause of morbidity and mortality in the industrialized world. Adaptive immunity and co-stimulatory signals play a pivotal role during all stages of the disease. Recently, regulatory T cells (Treg) were attributed an anti-inflammatory and anti-atherogenic role. The interaction of CD70, a member of the tumor necrosis factor super family with its receptor CD27 modulates Treg development but also affects T cell proliferation, differentiation, and activation at the sites of antigen priming and at effector function. We hypothesized an increased atherosclerotic burden and an exacerbation of disease upon CD27 deficiency. Cd27+/+Apoe-/- or Cd27-/-Apoe-/- bone marrow was transplanted into Apoe-/- recipient mice. After reconstitution, mice were fed a 0.15% high fat/cholesterol diet for 6 weeks. Plaque area at the aortic sinus was increased 2.3-fold in Cd27-/-Apoe-/- chimeras. Plaques contained high amounts of macrophages, which was accompanied by a reduced frequency of aortic (54.1%) and splenic (17.7%) Tregs. Similar results were obtained in 18 wk old Cd27-/-Apoe-/- on a normal chow diet, that also displayed an increase in atherosclerotic plaque area and a 2.5-fold higher plaque macrophage content. In addition, Cd27-/-Apoe-/-mice showed a significant decrease in the abundance of splenic (26%) and aortic (27%) Tregs. Remarkably, 28 week-old Cd27-/-Apoe-/- mice did not exhibit this phenotype, suggesting that CD27 only plays a role in earlier stages of atherosclerosis. Although Cd27-/-Apoe-/- Tregs did not show changes in suppressive or migratory capacity compared to Cd27+/+Apoe-/-, Cd27-deficiency did result in a marked increase in thymic Treg apoptosis. Taken together, our data reveal that deficiency for CD27 impairs thymic Treg development, which thereby exacerbates early and intermediate atherosclerosis by increasing plaque inflammation.