Hypercholesterolemia exacerbates virus-induced immunopathologic liver disease via suppression of antiviral cytotoxic T cell responses

Common human genetic variants of APOE impact murine COVID-19 mortality

Clinical outcomes of severe acute respiratory syndrome 2 (SARS-CoV-2) infection are highly heterogeneous, ranging from asymptomatic infection to lethal coronavirus disease 2019 (COVID-19). The factors underlying this heterogeneity remain insufficiently understood. Genetic association studies have suggested that genetic variants contribute to the heterogeneity of COVID-19 outcomes, but the underlying potential causal mechanisms are insufficiently understood. Here we show that common variants of the apolipoprotein E (APOE) gene, homozygous in approximately 3% of the world's population1 and associated with Alzheimer's disease, atherosclerosis and anti-tumour immunity2-5, affect COVID-19 outcome in a mouse model that recapitulates increased susceptibility conferred by male sex and advanced age. Mice bearing the APOE2 or APOE4 variant exhibited rapid disease progression and poor survival outcomes relative to mice bearing the most prevalent APOE3 allele. APOE2 and APOE4 mice exhibited increased viral loads as well as suppressed adaptive immune responses early after infection. In vitro assays demonstrated increased infection in the presence of APOE2 and APOE4 relative to APOE3, indicating that differential outcomes are mediated by differential effects of APOE variants on both viral infection and antiviral immunity. Consistent with these in vivo findings in mice, our results also show that APOE genotype is associated with survival in patients infected with SARS-CoV-2 in the UK Biobank (candidate variant analysis, P = 2.6 × 10-7). Our findings suggest APOE genotype to partially explain the heterogeneity of COVID-19 outcomes and warrant prospective studies to assess APOE genotyping as a means of identifying patients at high risk for adverse outcomes.

Low Density Lipoprotein Exposure of Plasmacytoid Dendritic Cells Blunts Toll-like Receptor 7/9 Signaling via NUR77

Background: Pathogens or trauma-derived danger signals induced maturation and activation of plasmacytoid dendritic cells (pDCs) is a pivotal step in pDC-dependent host defense. Exposure of pDC to cardiometabolic disease-associated lipids and proteins may well influence critical signaling pathways, thereby compromising immune responses against endogenous, bacterial and viral pathogens. In this study, we have addressed if hyperlipidemia impacts human pDC activation, cytokine response and capacity to prime CD4+ T cells. METHODS AND RESULTS: We show that exposure to pro-atherogenic oxidized low-density lipoproteins (oxLDL) led to pDC lipid accumulation, which in turn ablated a Toll-like receptor (TLR) 7 and 9 dependent up-regulation of pDC maturation markers CD40, CD83, CD86 and HLA-DR. Moreover, oxLDL dampened TLR9 activation induced the production of pro-inflammatory cytokines in a NUR77/IRF7 dependent manner and impaired the capacity of pDCs to prime and polarize CD4+ T helper (Th) cells. CONCLUSION: Our findings reveal profound effects of dyslipidemia on pDC responses to pathogen-derived signals.

Altered Lipid Profile in COVID-19 Patients and Metabolic Reprogramming

Background

Coronavirus disease 2019 (COVID-19) is a global pandemic. Previous studies have reported dyslipidemia in patients with COVID-19. Herein, we conducted a retrospective study and a bioinformatics analysis to evaluate the essential data of the lipid profile as well as the possible mechanism in patients with COVID-19.

Methods

First of all, the retrospective study included three cohorts: patients with COVID-19, a healthy population, and patients with chronic obstructive pulmonary disease (COPD). For each subject, serum lipid profiles in the biochemical data were compared, including triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C). Furthermore, bioinformatics analyses were performed for exploring the biological or immunological mechanisms.

Results

In line with the biochemical data of the three cohorts, the statistical result displayed that patients with COVID-19 were more likely to have lower levels of TC and HDL-C as compared with healthy individuals. The differential proteins associated with COVID-19 are involved in the lipid pathway and can target and regulate cytokines and immune cells. Additionally, a heatmap revealed that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections were possibly involved in lipid metabolic reprogramming. The viral proteins, such as spike (S) and non-structural protein 2 (Nsp2) of SARS-CoV-2, may be involved in metabolic reprogramming.

Conclusion

The metabolic reprogramming after SARS-CoV-2 infections is probably associated with the immune and clinical phenotype of patients. Hence, metabolic reprogramming may be targeted for developing antivirals against COVID-19.

Multiple aspects of lymphatic dysfunction in an ApoE -/- mouse model of hypercholesterolemia

Introduction: Rodent models of cardiovascular disease have uncovered various types of lymphatic vessel dysfunction that occur in association with atherosclerosis, type II diabetes and obesity. Previously, we presented in vivo evidence for impaired lymphatic drainage in apolipoprotein E null (ApoE ^-/- ) mice fed a high fat diet (HFD). Whether this impairment relates to the dysfunction of collecting lymphatics remains an open question. The ApoE ^-/- mouse is a well-established model of cardiovascular disease, in which a diet rich in fat and cholesterol on an ApoE deficient background accelerates the development of hypercholesteremia, atherosclerotic plaques and inflammation of the skin and other tissues. Here, we investigated various aspects of lymphatic function using ex vivo tests of collecting lymphatic vessels from ApoE ^+/+ or ApoE ^-/- mice fed a HFD. Methods: Popliteal collectors were excised from either strain and studied under defined conditions in which we could quantify changes in lymphatic contractile strength, lymph pump output, secondary valve function, and collecting vessel permeability. Results: Our results show that all these aspects of lymphatic vessel function are altered in deleterious ways in this model of hypercholesterolemia. Discussion: These findings extend previous in vivo observations suggesting significant dysfunction of lymphatic endothelial cells and smooth muscle cells from collecting vessels in association with a HFD on an ApoE-deficient background. An implication of our study is that collecting vessel dysfunction in this context may negatively impact the removal of cholesterol by the lymphatic system from the skin and the arterial wall and thereby exacerbate the progression and/or severity of atherosclerosis and associated inflammation.

Leukocyte Trafficking via Lymphatic Vessels in Atherosclerosis

In recent years, lymphatic vessels have received increasing attention and our understanding of their development and functional roles in health and diseases has greatly improved. It has become clear that lymphatic vessels are critically involved in acute and chronic inflammation and its resolution by supporting the transport of immune cells, fluid, and macromolecules. As we will discuss in this review, the involvement of lymphatic vessels has been uncovered in atherosclerosis, a chronic inflammatory disease of medium- and large-sized arteries causing deadly cardiovascular complications worldwide. The progression of atherosclerosis is associated with morphological and functional alterations in lymphatic vessels draining the diseased artery. These defects in the lymphatic vasculature impact the inflammatory response in atherosclerosis by affecting immune cell trafficking, lymphoid neogenesis, and clearance of macromolecules in the arterial wall. Based on these new findings, we propose that targeting lymphatic function could be considered in conjunction with existing drugs as a treatment option for atherosclerosis.

Immunologic Aspects of Dyslipidemia: a Critical Regulator of Adaptive Immunity and Immune Disorders

Dyslipidemia is a major cause of cardiovascular diseases which represent a leading cause of death in humans. Diverse immune cells are known to be involved in the pathogenesis of cardiovascular diseases such as atherosclerosis. Conversely, dyslipidemia is known to be tightly associated with immune disorders in humans, as evidenced by a higher incidence of atherosclerosis in patients with autoimmune diseases including psoriasis, rheumatoid arthritis, and systemic lupus erythematosus. Given that the dyslipidemia-related autoimmune diseases are caused by autoreactive T cells and B cells, dyslipidemia seems to directly or indirectly regulate the adaptive immunity. Indeed, accumulating evidence has unveiled that proatherogenic factors can impact the differentiation and function of CD4⁺ T cells, CD8⁺ T cells, and B cells. This review discusses an updated overview on the regulation of adaptive immunity by dyslipidemia and proposes a potential therapeutic strategy for immune disorders by targeting lipid metabolism.

Halted Lymphocyte Egress via Efferent Lymph Contributes to Lymph Node Hypertrophy During Hypercholesterolemia

Dyslipidemia is a central component of atherosclerosis and metabolic syndrome linked to chronic inflammation and immune dysfunction. Previously, we showed that hypercholesterolemic apolipoprotein E knock out (apoE^−/−) mice exhibit systemic effects including skin inflammation and hypertrophic lymph nodes (LNs). However, the mechanisms accounting for LN hypertrophy in these mice remain unknown. Here, we show that hypercholesterolemia led to the accumulation of lymphocytes in LNs. We excluded that the increased number of lymphocytes in expanded LNs resulted from increased lymphocyte proliferation or entry into those LNs. Instead, we demonstrated that the egress of lymphocytes from the enlarged LN of apoE^−/− mice was markedly decreased. Impairment in efferent lymphatic emigration of lymphocytes from LNs resulted from an aberrant expansion of cortical and medullary sinuses that became hyperplastic. Moreover, CCL21 was more abundant on these enlarged sinuses whereas lymph levels of sphingosine 1 phosphate (S1P) were decreased in apoE^−/− mice. Normal LN size, lymphatic density and S1P levels were restored by reversing hypercholesterolemia. Thus, systemic changes in cholesterol can sequester lymphocytes in tissue draining LNs through the extensive remodeling of lymphatic sinuses and alteration of the balance between retention/egress signals leading to LN hypertrophy which subsequently may contribute to poor immunity. This study further illustrates the role of lymphatic vessels in immunity through the regulation of immune cell trafficking.

The lipid-sensor TREM2 aggravates disease in a model of LCMV-induced hepatitis

Lipid metabolism is increasingly being appreciated to affect immunoregulation, inflammation and pathology. In this study we found that mice infected with lymphocytic choriomeningitis virus (LCMV) exhibit global perturbations of circulating serum lipids. Mice lacking the lipid-sensing surface receptor triggering receptor expressed on myeloid cells 2 (Trem2 ^-/-) were protected from LCMV-induced hepatitis and showed improved virus control despite comparable virus-specific T cell responses. Non-hematopoietic expression of TREM2 was found to be responsible for aggravated hepatitis, indicating a novel role for TREM2 in the non-myeloid compartment. These results suggest a link between virus-perturbed lipids and TREM2 that modulates liver pathogenesis upon viral infection. Targeted interventions of this immunoregulatory axis may ameliorate tissue pathology in hepatitis.

Restoration of Declined Immune Responses and Hyperlipidemia by Rubus occidenalis in Diet-Induced Obese Mice

Hyperlipidemia, which is closely associated with a fatty diet and aging, is commonly observed in the western and aged society. Therefore, a novel therapeutic approach for this disease is critical, and an immunological view has been suggested as a novel strategy, because hyperlipidemia is closely associated with inflammation and immune dysfunction. In this study, the effects of an aqueous extract of Rubus occidentalis (RO) in obese mice were investigated using immunological indexes. The mice were fed a high-fat diet (HFD) to induce hyperlipidemia, which was confirmed by biochemical analysis and examination of the mouse physiology. Two different doses of RO and rosuvastatin, a cholesterol synthesis inhibitor used as a control, were orally administered. Disturbances in immune cellularity as well as lymphocyte proliferation and cytokine production were significantly normalized by oral administration of RO, which also decreased the elevated serum tumor necrosis factor (TNF)-α level and total cholesterol. The specific immune-related actions of RO comprised considerable improvement in cytotoxic T cell killing functions and regulation of antibody production to within the normal range. The immunological evidence confirms the significant cholesterol-lowering effect of RO, suggesting its potential as a novel therapeutic agent for hyperlipidemia and associated immune decline.

Aloe QDM complex enhances specific cytotoxic T lymphocyte killing in vivo in metabolic disease mice

We developed spontaneous diet-induced metabolic disease in mice by feeding them a high-fat diet for 23 weeks and administered Aloe QDM complex for 16 weeks to examine its restorative effect on immune disorders and metabolic syndrome. A series of immune functional assays indicated Aloe QDM complex enhanced lymphocyte proliferation and antigen-specific immunity as determined by the restored functions of cytotoxic T lymphocytes (CTL) and IgG production. The elevated serum TNF-α level was also regulated by Aloe QDM complex treatment, which suggested its complex therapeutic potential. As for metabolic phenotypes, oral administration of Aloe QDM complex significantly improved diabetic symptoms, including high fasting glucose levels and glucose tolerance, and distinctly alleviated lipid accumulation in adipose and hepatic tissue. The simultaneous restoration of Aloe QDM complex on metabolic syndrome and host immune dysfunction, especially on the specific CTL killing was first elucidated in our study.

Prolonged Intake of Dietary Lipids Alters Membrane Structure and T Cell Responses in LDLr-/- Mice

Although it is recognized that lipids and membrane organization in T cells affect signaling and T cell activation, to what extent dietary lipids alter T cell responsiveness in the absence of obesity and inflammation is not known. In this study, we fed low-density lipoprotein receptor knockout mice a Western high-fat diet for 1 or 9 wk and examined T cell responses in vivo along with T cell lipid composition, membrane order, and activation ex vivo. Our data showed that high levels of circulating lipids for a prolonged period elevated CD4(+) and CD8(+) T cell proliferation and resulted in an increased proportion of CD4(+) central-memory T cells within the draining lymph nodes following induction of contact hypersensitivity. In addition, the 9-wk Western high-fat diet elevated the total phospholipid content and monounsaturated fatty acid level, but decreased saturated phosphatidylcholine and sphingomyelin within the T cells. The altered lipid composition in the circulation, and of T cells, was also reflected by enhanced membrane order at the activation site of ex vivo activated T cells that corresponded to increased IL-2 mRNA levels. In conclusion, dietary lipids can modulate T cell lipid composition and responses in lipoprotein receptor knockout mice even in the absence of excess weight gain and a proinflammatory environment.

Functional crosstalk between membrane lipids and TLR biology

Toll-like receptors (TLRs) are important transmembrane proteins of the innate immune system that detect invading pathogens and subsequently orchestrate an immune response. The ensuing inflammatory processes are connected to lipid metabolism at multiple levels. Here, we describe different aspects of how membrane lipids can shape the response of TLRs. Recent reports have uncovered the role of individual lipid species on membrane protein function and mouse models have contributed to the understanding of how changes in lipid metabolism alter TLR signaling, endocytosis, and cytokine secretion. Finally, we discuss the importance of systematic approaches to identify the function of individual lipid species or the composition of membrane lipids in TLR-related processes.

Lipoprotein lipase deficiency presenting with neonatal perianal abscesses

Lipoprotein lipase (LPL), a member of the triglyceride lipase gene family, is synthesised by parenchymal cells of the heart, skeletal muscle and adipose tissues before being transported to luminal surfaces of vascular endothelial cells to exert its main physiological function to hydrolyse plasma lipoproteins. LPL deficiency is a rare autosomal recessive disorder, resulting in severe hypertriglyceridaemia from birth. The effect of marked hypertriglyceridaemia on the immune function in children has not been described. We present a case of a neonate with LPL deficiency and grossly elevated plasma triglyceride levels, presenting with recurrent and recalcitrant perianal abscesses suggestive of underlying immunodeficiency. With reduced levels of plasma triglycerides, the recurrent perianal infections resolved. This case report reviews evidence for potential deleterious effects of hypertriglyceridaemia on immune function, however, underlying mechanisms are poorly understood. Whether hypertriglyceridaemia contributes to immune dysfunction in this context is unknown. If there is a pathophysiological link, this may have implications for hypertriglyceridaemia management.

Globosides but not isoglobosides can impact the development of invariant NKT cells and their interaction with dendritic cells

Recognition of endogenous lipid Ag(s) on CD1d is required for the development of invariant NKT (iNKT) cells. Isoglobotrihexosylceramide (iGb3) has been implicated as this endogenous selecting ligand and recently suggested to control overstimulation and deletion of iNKT cells in α-galactosidase A-deficient (αGalA(-/-)) mice (human Fabry disease), which accumulate isoglobosides and globosides. However, the presence and function of iGb3 in murine thymus remained controversial. In this study, we generate a globotrihexosylceramide (Gb3)-synthase-deficient (Gb3S(-/-)) mouse and show that in thymi of αGalA(-/-)/Gb3S(-/-) double-knockout mice, which store isoglobosides but no globosides, minute amounts of iGb3 can be detected by HPLC. Furthermore, we demonstrate that iGb3 deficiency does not only fail to impact selection of iNKT cells, in terms of frequency and absolute numbers, but also does not alter the distribution of the TCR CDR 3 of iNKT cells. Analyzing multiple gene-targeted mouse strains, we demonstrate that globoside, rather than iGb3, storage is the major cause for reduced iNKT cell frequencies and defective Ag presentation in αGalA(-/-) mice. Finally, we show that correction of globoside storage in αGalA(-/-) mice by crossing them with Gb3S(-/-) normalizes iNKT cell frequencies and dendritic cell (DC) function. We conclude that, although detectable in murine thymus in αGalA(-/-)/Gb3S(-/-) mice, iGb3 does not influence either the development of iNKT cells or their interaction with peripheral DCs. Moreover, in αGalA(-/-) mice, it is the Gb3 storage that is responsible for the decreased iNKT cell numbers and impeded Ag presentation on DCs.

Hypercholesterolemic LDL receptor-deficient mice mount a neutrophilic response to tuberculosis despite the timely expression of protective immunity

The prevalence of hypercholesterolemia is rising in industrialized and developing countries. We reported previously that host defense against Mtb was impaired by hypercholesterolemia in ApoE(-/-) mice, raising the possibility that people with HC could be more vulnerable to TB. The present study examined whether TB immunity was similarly impaired in a different hypercholesterolemic model, LDL-R(-/-) mice, which developed comparable elevation of total serum cholesterol as ApoE(-/-)mice when fed HC or LC diets. Like ApoE(-/-) mice, LDL-R(-/-) mice had an exaggerated lung inflammatory response to Mtb with increased tissue necrosis. Inflammation, foamy macrophage formation, and tissue necrosis in LDL-R(-/-) mice increased with the degree of hypercholesterolemia. Unlike ApoE(-/-) mice, LDL-R(-/-) mice fed a HC diet mounted a timely and protective adaptive immune response that restricted mycobacterial replication comparably with WT mice. Thus, ApoE(-/-) and LDL-R(-/-) mice share a cholesterol-dependent hyperinflammatory TB phenotype but do not share the impairment of adaptive immunity found in ApoE(-/-) mice. The impact of hypercholesterolemia on TB immunity is more complex than appreciated by total cholesterol alone, possibly reflecting the different functional effect of specific lipoprotein particles.

Celecoxib, a selective cyclooxygenase-2 inhibitor, lowers plasma cholesterol and attenuates hepatic lipid peroxidation during carbon-tetrachloride-associated hepatotoxicity in rats

Cyclooxygenase-2 (COX-2) expression and prostaglandin production are suggested to play important, complex roles in the pathogenesis of various liver diseases. Studies on the effects of COX-2 inhibitors on the progression of liver fibrosis present controversial results, and the proposed therapeutic potential of these agents in chronic liver disease is predicated largely on their effectiveness in modulating hepatic stellate cell activation in vitro. This study investigated the modulatory effect of celecoxib, a selective COX-2 inhibitor, in CCl(4)-mediated hepatotoxicity in rats. Thirty Wistar albino rats, weighing 120-180 g, were assigned into five groups of 6 rats/group. Groups 1 and 2 received saline (10 mL/kg) and CCl(4) (80 mg/kg), respectively. Group 3 was given celecoxib (5.7 mg/kg), whereas groups 4 and 5 were pretreated with 2.9 and 5.7 mg/kg/day of celecoxib, respectively, 1 hour before CCl(4) treatment. Plasma aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase activities increased significantly by 118.5, 150.0, and 51.3%, respectively, with an accompanying decrease (P < 0.05) in total protein and albumin after CCl(4) treatment. Hepatotoxicity was associated with a significant increase in plasma cholesterol, hepatic lipid peroxidation (LPO), and severe hepatic necrosis with marked fatty and cellular (i.e., mononuclear cells) infiltration. Although celecoxib neither reduced CCl(4)-induced increases in marker enzymes of hepatotoxicity nor significantly attenuated hepatic necrosis, it, however, was effective in reducing elevated cholesterol by 16.5 and 20.8% and LPO by 12.9 and 35.5% at 2.9 and 5.7 mg/kg, respectively. Data suggest that COX-2 inhibitors may be effective in controlling hypercholesterolemia and peroxidative changes associated with liver injury.

Immunomodulatory effects of aerobic training in obesity

Introduction. Physical inactivity and obesity are independent risk factors for atherosclerosis. We analyzed the immunomodulatory capacity of 10-week intensified exercise training (ET) in obese and lean athletes. Markers of the innate immune response were investigated in obese (ONE: ET≤40 km/week) and lean athletes (LNE: ET≤40 km/week and LE: ET≥55 km/week). Methods. Circulating dendritic cells (DC) were analyzed by flow-cytometry for BDCA-1/-2-expression. TLR-2/-4/-7 and MyD88 were analyzed by RT-PCR and Western blot. Circulating oxLDL levels were analyzed by ELISA. Results. BDCA-1 expression at baseline was lower in ONE compared to both other groups (ONE 0.15%; LNE 0.27%; LE 0.33%; P < .05), but significantly increased in ONE after training (+50%; P < .05). In contrast, BDCA-2 expression at baseline was higher in ONE (ONE 0.25%; LNE 0.11%; LE 0.09%; P < .05) and decreased in ONE after the 10-week training period (−27%; P < .05). Gene activations of TLR-4 and TLR-7 with corresponding protein increase were found for all three groups (P < .01/P < .05) compared to pre training. A reduction of oxLDL levels was seen in ONE (−61%; P < .05). Conclusions. Intensified exercise induces an increase of BDCA-1+ DCs and TLR-4/-7 in obese athletes. We hereby describe new immune modulatory effects, which—through regular aerobic exercise—modulate innate immunity and pro-inflammatory cytokines in obesity.

Plasma lipoproteins are important components of the immune system

Plasma lipoproteins (VLDL, LDL, Lp[a] and HDL) function primarily in lipid transport among tissues and organs. However, cumulative evidence suggests that lipoproteins may also prevent bacterial, viral and parasitic infections and are therefore a component of innate immunity. Lipoproteins can also detoxify lipopolysaccharide and lipoteichoic acid. Infections can induce oxidation of LDL, and oxLDL in turn plays important anti-infective roles and protects against endotoxin-induced tissue damage. There is also evidence that apo(a) is protective against pathogens. Taken together, the evidence suggests that it might be valuable to introduce the concept that plasma lipoproteins belong in the realm of host immune response.

Plasma lipoproteins are important components of the immune system

Plasma lipoproteins (VLDL, LDL, Lp[a] and HDL) function primarily in lipid transport among tissues and organs. However, cumulative evidence suggests that lipoproteins may also prevent bacterial, viral and parasitic infections and are therefore a component of innate immunity. Lipoproteins can also detoxify lipopolysaccharide and lipoteichoic acid. Infections can induce oxidation of LDL, and oxLDL in turn plays important anti-infective roles and protects against endotoxin-induced tissue damage. There is also evidence that apo(a) is protective against pathogens. Taken together, the evidence suggests that it might be valuable to introduce the concept that plasma lipoproteins belong in the realm of host immune response.

Epigenetic regulation of dendritic cell differentiation and function by oxidized phospholipids

Dendritic cells (DCs) are the key cell type in the regulation of an adaptive immune response. Under inflammatory conditions monocytes can give rise to immunostimulatory DCs, depending on microenvironmental stimuli. Here we show that oxidized phospholipids (Ox-Pls), which are generated during inflammatory reactions, dysregulate the differentiation of DCs. DCs generated in the presence of Ox-Pls up-regulated the typical DC marker DC-SIGN but did not express CD1a, CD1b, and CD1c. These DCs generated in the presence of Ox-Pls had a substantially diminished T cell-stimulating capacity after stimulation with Toll-like receptor ligands. Toll-like receptor ligand-induced production of interleukin-12 also was strongly diminished, whereas induction of CD83 was not altered. In addition, we found that Ox-Pls strongly inhibit inflammatory stimuli-induced phosphorylation of histone H3, a key step of interleukin-12 production, yet leaving activation of nuclear factor-kappaB unaltered. Taken together, Ox-Pls present during differentiation yielded DCs with a reduced capacity to become immunostimulatory mature DCs. Furthermore, the presence of Ox-Pls blocked histone modifications required for full activation of DCs. Therefore, inflammation-derived Ox-Pls control DC functions in part by epigenetic mechanisms.

Hypercholesterolemic mice exhibit lymphatic vessel dysfunction and degeneration

Lymphatic vessels are essential for lipid absorption and transport. Despite increasing numbers of observations linking lymphatic vessels and lipids, little research has been devoted to address how dysregulation of lipid balance in the blood, ie, dyslipidemia, may affect the functional biology of lymphatic vessels. Here, we show that hypercholesterolemia occurring in apolipoprotein E-deficient (apoE(-/-)) mice is associated with tissue swelling, lymphatic leakiness, and decreased lymphatic transport of fluid and dendritic cells from tissue. Lymphatic dysfunction results in part from profound structural abnormalities in the lymphatic vasculature: namely, initial lymphatic vessels were greatly enlarged, and collecting vessels developed notably decreased smooth muscle cell coverage and changes in the distribution of lymphatic vessel endothelial hyaluronic acid receptor-1 (LYVE-1). Our results provide evidence that hypercholesterolemia in adult apoE(-/-) mice is associated with a degeneration of lymphatic vessels that leads to decreased lymphatic drainage and provides an explanation for why dendritic cell migration and, thus, immune priming, are compromised in hypercholesterolemic mice.

Increased susceptibility to exacerbated liver injury in hypercholesterolemic ApoE-deficient mice: potential involvement of oxysterols

The contribution of metabolic factors to the severity of liver disease is not completely understood. In this study, apolipoprotein E-deficient (ApoE-/-) mice were evaluated to define potential effects of hypercholesterolemia on the severity of carbon tetrachloride (CCl4)-induced liver injury. Under baseline conditions, hypercholesterolemic ApoE-/- mice showed increased hepatic oxidative stress (SOD activity/4-hydroxy-2-nonenal immunostaining) and higher hepatic TGF-beta1, MCP-1, and TIMP-1 expression than wild-type control mice. After CCl4 challenge, ApoE-/- mice exhibited exacerbated steatosis (Oil Red O staining), necroinflammation (hematoxylin-eosin staining), macrophage infiltration (F4/80 immunohistochemistry), and fibrosis (Sirius red staining and alpha-smooth muscle actin immunohistochemistry) and more severe liver injury [alanine aminotransferase (ALT) and aspartate aminotransferase] than wild-type controls. Direct correlations were identified between serum cholesterol and hepatic steatosis, fibrosis, and ALT levels. These changes did not reflect the usual progression of the disease in ApoE-/- mice, since exacerbated liver injury was not present in untreated age-paired ApoE-/- mice. Moreover, hepatic cytochrome P-450 expression was unchanged in ApoE-/- mice. To explore potential mechanisms, cell types relevant to liver pathophysiology were exposed to selected cholesterol-oxidized products. Incubation of hepatocytes with a mixture of oxysterols representative of those detected by GC-MS in livers from ApoE-/- mice resulted in a concentration-dependent increase in total lipoperoxides and SOD activity. In hepatic stellate cells, oxysterols increased IL-8 secretion through a NF-kappaB-independent mechanism and upregulated TIMP-1 expression. In macrophages, oxysterols increased TGF-beta1 secretion and MCP-1 expression in a concentration-dependent manner. Oxysterols did not compromise cell viability. Taken together, these findings demonstrate that hypercholesterolemic mice are sensitized to liver injury and that cholesterol-derived products (i.e., oxysterols) are able to induce proinflammatory and profibrogenic mechanisms in liver cells.

Factors affecting early viral load decline of Asian chronic hepatitis C patients receiving pegylated interferon plus ribavirin therapy

Background

Early viral load decline following pegylated interferon-α2a and ribavirin therapy is an important predictor of the treatment responses in chronic hepatitis C (CHC) patients, thus, it is essential to evaluate the influence of host and viral factors on early viral load decline.

Methods

Clinical and serial virological data were collected from 145 consecutive Asian CHC patients with pegylated interferon-α2a plus ribavirin therapy. A dose of pegylated interferon-α2a was administered at week 1 and then weekly with daily oral ribavirin for 24 or 48 weeks. Genotyping and quantification of hepatitis C virus (HCV) RNA were done using molecular methods.

Results

A total of 81 patients were infected with HCV genotype 1, 61 with genotype 2 and 3 with both genotypes 1 and 2. At the end of follow-up, 110 patients attained sustained virological response (SVR). In multivariate analyses, body mass index (BMI) and genotype were related to viral load decline at day 2, baseline viral load and high-density lipoprotein (HDL) cholesterol levels were correlated with viral load decline between days 2 and 28. Genotype, baseline viral load, alanine aminotransferase (ALT) levels and BMI independently predicted rapid virological response, whereas only genotype 2, lower baseline viral load and more substantial viral load decline at day 28 predicted a higher SVR.

Conclusions

HCV genotype, baseline viral load, pretreatment BMI, HDL and ALT levels have a significant effect on early viral load decline of Asian CHC patients with interferon-based therapy. Only HCV genotype, baseline viral load and viral load decline at day 28 can independently predict SVR.

CD11c(+) dendritic cells maintain antigen processing, presentation capabilities, and CD4(+) T-cell priming efficacy under hypercholesterolemic conditions associated with atherosclerosis

Recent reports suggest dyslipidemia impairs dendritic cell (DC) function and adaptive immunity. This study aimed to characterize the effect of hypercholesterolemia on antigen-presenting cell function of DCs and DC-dependent CD4(+) T-cell responses. DCs incubated in vitro with acetylated low-density lipoprotein cholesterol with or without an acyl-coenzyme A:cholesterol acyl-transferase inhibitor maintained their ability to prime CD4(+) T cells. Analysis of T-cell proliferation and interferon-gamma and tumor necrosis factor-alpha production after ex vivo coculture of naïve CD4(+) T cells with splenic, inguinal, or iliac DCs from low-density lipoprotein receptor-deficient (LDLR(-/-)) or apolipoprotein E-deficient (ApoE(-/-)) mice fed an atherogenic diet highlighted DC efficacy in effector T-cell generation under hypercholesterolemic conditions. Adoptive transfer of carboxyfluorescein diacetate, succinimidyl ester (CFSE)-labeled naïve CD4(+) T cells in LDLR(-/-) recipients and subsequent immunization demonstrated effective priming of naïve T cells in hypercholesterolemic mice. CFSE dilution analyses revealed that hypercholesterolemic DCs were equipotent in naïve CD4(+) T-cell priming efficacy with normocholesterolemic DCs. Quantitative real-time PCR and flow cytometric analyses demonstrated that DC expression of multiple molecules involved in antigen processing, presentation, and T-cell stimulation remained unaltered by dyslipidemia. Finally, endogenous antigen-primed CD4(+) T cells responded equivalently to a secondary ex vivo antigenic challenge, regardless of whether they were primed in vivo under hypercholesterolemic or control conditions, demonstrating that all essential steps in CD4(+) T-cell responses remain intact under atherogenic conditions. This study affirms that the adaptive immune response prevails under the hypercholesterolemic conditions present in atherosclerosis. In particular, DCs remain functional antigen-presenting cells and maintain their ability to prime CD4(+) T cells even when cholesterol-loaded.

Hypercholesterolemia impairs immunity to tuberculosis

We demonstrate that apolipoprotein E -deficient (ApoE(-/-)) mice are highly susceptible to tuberculosis and that their susceptibility depends on the severity of hypercholesterolemia. Wild-type (WT) mice and ApoE(-/-) mice fed a low-cholesterol (LC) or high-cholesterol (HC) diet were infected with approximately 50 CFU Mycobacterium tuberculosis Erdman by aerosol. ApoE(-/-) LC mice were modestly more susceptible to tuberculosis than WT LC mice. In contrast, ApoE(-/-) HC mice were extremely susceptible, as evidenced by 100% mortality after 4 weeks with tuberculosis. The lung pathology of ApoE(-/-) HC mice was remarkable for giant abscess-like lesions, massive infiltration by granulocytes, elevated inflammatory cytokine production, and a mean bacterial load approximately 2 log units higher than that of WT HC mice. Compared to WT HC mice, the gamma interferon response of splenocytes restimulated ex vivo with M. tuberculosis culture filtrate protein was delayed in ApoE(-/-) HC mice, and they failed to control M. tuberculosis growth in the lung. OT-II cells adoptively transferred into uninfected ApoE(-/-) HC mice had a weak proliferative response to their antigen, indicating impaired priming of the adaptive immune response. Our studies show that ApoE(-/-) deficiency is associated with delayed expression of adaptive immunity to tuberculosis caused by defective priming of the adaptive immune response and that elevated serum cholesterol is responsible for this effect.

Role of Chlamydia pneumoniae in atherosclerosis

Cardiovascular disease, resulting from atherosclerosis, is a leading cause of global morbidity and mortality. Genetic predisposition and classical environmental risk factors explain much of the attributable risk for cardiovascular events in populations, but other risk factors for the development and progression of atherosclerosis, which can be identified and modified, may be important therapeutic targets. Infectious agents, such as Chlamydia pneumoniae, have been proposed as contributory factors in the pathogenesis of atherosclerosis. In the present review, we consider the experimental evidence that has accumulated over the last 20 years evaluating the role of C. pneumoniae in atherosclerosis and suggest areas for future research in this field.

Differential course of HIV-1 infection and apolipoprotein E polymorphism

We studied the course of infection with human immunodeficiency virus type 1 (HIV-1) in relation to apolipoprotein E (APOE) polymorphism found for 209 Italians treated at Infectious Disease Clinics in Rome and Modena. Clinically, patients were classified into four groups according to the yearly rate of decline in CD4+ cell count (LTNP: long-term non-progression; SLOW, ’NORMAL’ or RAPID). Patients at both extremes of the clinical spectrum, i.e. those who rapidly progressed to AIDS and those with stable high CD4 cell counts, had few APOE ɛ4 and ɛ2 alleles (P = 0.04). Detailed clinical information was then used to construct four model-based clinical profiles using grade-of-membership analysis (GoM), predictive of APOE genotypic frequencies: 1. The clinical profile associated with good long-term prognosis lacked ɛ2 (P=0.01); 2. Disease progression to AIDS was associated with ɛ4 and ɛ2, most evident for zidovudine-lamivudine regimens without a protease inhibitor (P = 0.03); and, 3. AIDS patients had low ɛ4 and ɛ2 frequencies, consistent with a high mortality rate among ɛ4+ and ɛ2+ AIDS patients. These findings suggest allele-specific immunomodulatory effects involving inherited APOE isoform important enough to alter the clinical course of HIV infection and, possibly, drug efficacy. They imply a connection between lipid metabolism and immunity potentially relevant to common disorders.

Proatherogenic immune responses are regulated by the PD-1/PD-L pathway in mice

T lymphocyte responses promote proatherogenic inflammatory events, which are influenced by costimulatory molecules of the B7 family. Effects of negative regulatory members of the B7 family on atherosclerosis have not been described. Programmed death-ligand 1 (PD-L1) and PD-L2 are B7 family members expressed on several cell types, which inhibit T cell activation via binding to programmed death-1 (PD-1) on T cells. In order to test whether the PD-1/PD-L pathway regulates proatherogenic T cell responses, we compared atherosclerotic lesion burden and phenotype in hypercholesterolemic PD-L1/2(-/-)LDLR(-/-) mice and LDLR(-/-) controls. PD-L1/2 deficiency led to significantly increased atherosclerotic burden throughout the aorta and increased numbers of lesional CD4(+) and CD8(+) T cells. Compared with controls, PD-L1/2(-/-)LDLR(-/-) mice had iliac lymphadenopathy and increased numbers of activated CD4(+) T cells. Serum levels of TNF-alpha were higher in PD-L1/2(-/-)LDLR(-/-) mice than in controls. PD-L1/2-deficient APCs were more effective than control APCs in activating CD4(+) T cells in vitro, with or without cholesterol loading. Freshly isolated APCs from hypercholesterolemic PD-L1/2(-/-)LDLR(-/-) mice stimulated greater T cell responses than did APCs from hypercholesterolemic controls. Our findings indicate that the PD-1/PD-L pathway has an important role in downregulating proatherogenic T cell response and atherosclerosis by limiting APC-dependent T cell activation.

Predictors of viral kinetics to peginterferon plus ribavirin combination therapy in Japanese patients infected with hepatitis C virus genotype 1b

For chronic hepatitis C virus (HCV) infection, evaluation of response to peginterferon (PEG-IFN) plus ribavirin (RBV) therapy based on viral kinetics is useful as an early predictor of treatment efficacy, but the underlying mechanisms of the different viral kinetics to treatment are still unclear. The response to 48-week PEG-IFN-RBV combination therapy was evaluated in 160 Japanese adult patients infected with HCV genotype 1b and determined the rapid virological response (at 4 weeks), early virological response (at 12 weeks), end-of treatment response, and sustained virological response (6 months after end of treatment). The proportion of patients who showed rapid, early and sustained virological, and end-of treatment responses were 50%, 73%, 47%, and 71%, respectively. Furthermore, 66% of patients who achieved early virological response also showed sustained virological response. Multivariate analysis identified substitutions of amino acid (aa) 70 and 91 in the HCV core region (double-wild-type) as a predictor of early HCV-RNA negativity, rapid, early, and sustained virological responses and end-of treatment response, and lipid metabolic factors (high levels of LDL cholesterol and total cholesterol) as predictors of early and rapid virological responses and end-of treatment response. Male sex and low levels of alpha-fetoprotein were other predictors of sustained virological response. Furthermore, female sex and severity of liver fibrosis were determinants of lack of sustained virological response in spite of early virological response. This study identified predictors of efficacy of PEG-IFN-RBV therapy based on viral kinetics in Japanese patients infected with HCV genotype 1b.

Chronic Immune Reactivity Against Persisting Microbial Antigen in the Vasculature Exacerbates Atherosclerotic Lesion Formation

Objective— The purpose of this study was to examine the relative contribution of different immunopathological mechanisms during murine cytomegalovirus (MCMV)-mediated acceleration of atheroma formation in apolipoprotein E–deficient (apoE −/− ) mice.

Methods and Results— To distinguish between the effects of systemic activation and cognate immune reactivity against a pathogen-derived persisting antigen in the vasculature, we used hypercholesterolemic transgenic mice constitutively expressing the β-galactosidase (β-gal) transgene in the cardiovascular system (apoE −/− ×SM-LacZ). After infection with β-gal–recombinant MCMV-LacZ, apoE −/− , and apoE −/− ×SM-LacZ mice mounted comparable cellular immune responses against the virus. β-gal–specific CD8 + T cells expanded rapidly and remained detectable for at least 100 days in both mouse strains. However, compared with apoE −/− mice, apoE −/− ×SM-LacZ mice developed drastically accelerated atherosclerosis. Moreover, atherosclerotic lesions in MCMV-LacZ–infected apoE −/− ×SM-LacZ but not apoE −/− mice were associated with pronounced inflammatory infiltrates.

Conclusions— Taken together, our data indicate that chronic immune reactivity against pathogen-derived antigens persisting in the vasculature significantly exacerbates atherogenesis.

Predictive factors of early and sustained responses to peginterferon plus ribavirin combination therapy in Japanese patients infected with hepatitis C virus genotype 1b: amino acid substitutions in the core region and low-density lipoprotein cholesterol levels

BACKGROUND/AIMS

We showed previously that amino acid (aa) substitutions in the HCV core region (HCV-CR) are predictors of non-virological response (NVR) to peginterferon (PEG-IFN) plus ribavirin (RBV) therapy. Here, we determined the predictive factors of sustained virological response (SVR) and early virologic response (EVR) to this treatment.

METHODS

We evaluated the response to 48-week PEG-IFN-RBV therapy in 114 Japanese adults infected with HCV genotype 1b and determined the predictors of EVR and SVR.

RESULTS

EVR was achieved by 70% and SVR by 45% of patients. 64% of patients who achieved EVR also showed SVR, while none of non-EVR achieved SVR. Multivariate analysis identified low-density lipoprotein cholesterol (LDL-C) (>or=86 mg/dl), aa substitutions in HCV-CR (double-wild-type; arginine at aa 70/leucine at aa 91), gamma-glutamyl transpeptidase (GGT) (<109 IU/l), RBV dose (>or=11.0mg/kg), and leukocyte count (>or=4500/mm3) as significant determinants of EVR, and aa substitutions in HCV-CR (double-wild-type), LDL-C (>or=86 mg/dl), male gender, ICG R15 (<10%), GGT (<109 IU/l), and RBV dose (>or=11.0 mg/kg) as determinants of SVR. Prediction of response to therapy based on combination of these factors had high sensitivity, specificity, positive, and negative predictive values.

CONCLUSIONS

Our study identified aa substitutions in the core region and serum LDL-C as predictors of response to PEG-IFN-RBV therapy in Japanese patients infected with HCV genotype 1b.

Dyslipidemia inhibits Toll-like receptor-induced activation of CD8alpha-negative dendritic cells and protective Th1 type immunity

Environmental factors, including diet, play a central role in influencing the balance of normal immune homeostasis; however, many of the cellular mechanisms maintaining this balance remain to be elucidated. Using mouse models of genetic and high-fat/cholesterol diet–induced dyslipidemia, we examined the influence of dyslipidemia on T cell and dendritic cell (DC) responses in vivo and in vitro. We show that dyslipidemia inhibited Toll-like receptor (TLR)–induced production of proinflammatory cytokines, including interleukin (IL)-12, IL-6, and tumor necrosis factor-α, as well as up-regulation of costimulatory molecules by CD8α⁻ DCs, but not by CD8α⁺ DCs, in vivo. Decreased DC activation profoundly influenced T helper (Th) cell responses, leading to impaired Th1 and enhanced Th2 responses. As a consequence of this immune modulation, host resistance to Leishmania major was compromised. We found that oxidized low-density lipoprotein (oxLDL) was the key active component responsible for this effect, as it could directly uncouple TLR-mediated signaling on CD8α⁻ myeloid DCs and inhibit NF-κB nuclear translocation. These results show that a dyslipidemic microenvironment can directly interfere with DC responses to pathogen-derived signals and skew the development of T cell–mediated immunity.

Role of apolipoproteins in gammadelta and NKT cell-mediated innate immunity

Recent findings reveal unanticipated connections between the fields of lipid metabolism and immunology. They concern gammadelta and NKT cells, nonconventional T cell populations that do not recognize protein antigens and are involved in immunity against cancer, defense against infections, or in regulation of classical immune responses. In this review, we summarize data linking perturbations of apolipoprotein levels and nonconventional T cells with inflammatory processes such as autoimmune diseases or atherosclerosis. We integrate and discuss recent findings on the implication of apolipoproteins in antigen recognition by gammadelta and NKT cells, with emphasis on apolipoproteins A-I and E. These findings also provide indications that apolipoproteins influence antitumor immunosurveillance.

Heat shock protein 60 autoimmunity and early lipid lesions in cholesterol-fed C57BL/6JBom mice during Chlamydia pneumoniae infection

Chronic Chlamydia pneumoniae infection and autoimmunity to heat shock protein 60 (Hsp60) have both been documented to be associated with atherosclerosis. Herein, we studied the effects of C. pneumoniae infection and a diet with a low-cholesterol supplement on the development of autoantibodies to mouse Hsp60 and early lipid lesions in the aortic valve of C57BL/6JBom mice. In addition, pulmonary infection was investigated. C57BL/6JBom mice were given one to three C. pneumoniae inoculations and fed either a regular diet or a diet enriched with 0.2% cholesterol. Autoantibody responses against mouse Hsp60 developed in both diet groups when the mice were infected with C. pneumoniae and in uninfected mice fed a cholesterol-enriched diet. C. pneumoniae infections increased subendothelial foam cell accumulation in mice on a 0.2% cholesterol-enriched diet (p = 0.022), without apparent hypercholesterolemia. These in vivo data suggest that autoantibodies against mouse Hsp60 develop as a consequence of cholesterol feeding and repeated C. pneumoniae infections. Further, infectious burden increased early lipid lesions in C57BL/6JBom mice fed a cholesterol-enriched diet.

Dyslipidemia associated with atherosclerotic disease systemically alters dendritic cell mobilization

High LDL and/or low HDL are risk factors for atherosclerosis and are also a common clinical feature in systemic lupus erythematosus, rheumatoid arthritis, and psoriasis. Here, we show that changes in lipid profiles that reflect atherosclerotic disease led to activation of skin murine dendritic cells (DCs) locally, promoted dermal inflammation, and induced lymph node hypertrophy. Paradoxically, DC migration to lymph nodes was impaired, suppressing immunologic priming. Impaired migration resulted from inhibitory signals generated by platelet-activating factor (PAF) or oxidized LDL that acts as a PAF mimetic. Normal DC migration and priming was restored by HDL or HDL-associated PAF acetylhydrolase (PAFAH), which mediates inactivation of PAF and oxidized LDL. Thus, atherosclerotic changes can sequester activated DCs in the periphery where they may aggravate local inflammation even as they poorly carry out functions that require their migration to lymph nodes. In this context, HDL and PAFAH maintain a normally functional DC compartment.

Increased susceptibility to experimental autoimmune neuritis after upregulation of the autoreactive T cell response to peripheral myelin antigen in apolipoprotein E-deficient mice

Experimental autoimmune neuritis (EAN), an acute demyelinating inflammatory disease of the peripheral nervous system (PNS), is a good model for the human counterpart, Guillain-Barré syndrome. Apolipoprotein E (ApoE), a 34 kDa glycosylated protein with multiple biological properties, has been linked both with the innate immune response of mice and with neurological disease. The present study investigated the previously unexplored role of ApoE in autoimmune-mediated demyelination. ApoE-deficient (apoE -/-) mice exhibited a greater susceptibility to EAN induced by the PNS myelin P0 protein peptide 180-199, as compared to wild type (apoE +/+) mice. The augmented susceptibility seen in apoE -/- mice was associated with increased inflammatory cell infiltrates in the PNS during the effector phase. Although the 2 groups of mice exhibited no quantitative or proportional differences in splenic lymphocyte populations, the apoE -/- mice showed enhanced antigen-specific proliferation of T cells of spleen, which is related to modified macrophage function, upregulation of Th1 and downregulation of Th2-autoreactive responses to P0 peptide. These effects were shown as increased numbers of IFN-gamma expressing cells in the spleen and of IFN-gamma, IL-12 and TNF-alpha expressing cells in the PNS, as well as a decreased IL-10 production by splenic cells in apoE -/- mice. In addition, apoE -/- mice had enhanced antigen-specific antibody responses, which might have contributed to their aggravated EAN. These data provide strong evidence that apoE acts as an inhibitor of this inflammatory and demyelinating disease by upregulating IL-10, as well as by inhibiting Th1 responses and antigen-specific antibody formation. These data may aid the development of new and more effective therapeutic strategies for inflammatory and demyelinating diseases such as Guillain-Barré syndrome.

Severe Hypercholesterolaemia Leads to Strong Th2 Responses to an Exogenous Antigen

Severe hypercholesterolaemia is associated with decreased levels of immunoglobulin G2a (IgG2a) antibodies [T-helper 1 (Th1) response] to modified malondialdehyde-modified low-density lipoprotein (MDA-LDL) and increased levels of Th2-dependent IgG1 antibodies in apolipoprotein E-deficient (apoE(-/-)) mice. To investigate whether this reflects a general pattern of metabolic regulation of the humoral immune response, apoE(-/-) mice were fed diets resulting in different degrees of hypercholesterolaemia and immunized with keyhole limpet haemocyanin (KLH) in aluminium hydroxide. Cholesterol levels for different treatment groups ranged from 14 to 77 mmol/l in serum and from 10 to 39 mmol/g in liver. Mice with severe hypercholesterolaemia had increased IgG1 antibodies to MDA-LDL and decreased IgG2a anti-MDA-LDL. Importantly, titres of IgG2a antibodies to KLH were also decreased, while IgE anti-KLH was increased, with a corresponding induction of interleukin-4 (IL-4) and IL-10 and a decrease in interferon-gamma (IFN-gamma) in KLH-stimulated spleen cells in vitro. Thus, hypercholesterolaemia clearly affects antibody production both to the autoantigen MDA-LDL and to the exogenous antigen KLH, favouring antibody isotypes (IgG1 and IgE) that are dependent on Th2 help to B cells. Nuclear receptors ligated by oxidized lipid derivatives modulate T-cell responses, and it is speculated that this mechanism may cause the switch to Th2 in severe hypercholesterolaemia.

Effect of a therapeutic lifestyle change diet on immune functions of moderately hypercholesterolemic humans

Hypercholesterolemia is a risk factor for coronary heart disease (CHD) and also could contribute to impaired immune response. The National Cholesterol Education Program Expert Panel recommends a therapeutic lifestyle change (TLC) diet to reduce the risk for CHD. We investigated the effects of changing from a high-fat Western diet to a low-fat diet in accordance with a TLC diet on immune functions of older adults with hypercholesterolemia to determine whether improving the lipid profile via dietary intervention would have beneficial effects on immune functions. In a double-blind study, 18 subjects consumed both a Western diet (38% fat) and a TLC diet (28% fat) for 32 days in a randomized order. Measures of cellular immune responses, including delayed-type hypersensitivity (DTH) response, in vitro lymphocyte proliferation, and interleukin (IL)-2 production, and production of proinflammatory mediators, including tumor necrosis factor-alpha, IL-6, IL-1beta, and prostaglandin E2, were determined. DTH response and lymphocyte proliferative response increased significantly (29% and 27%, respectively) after consumption of a TLC diet. Our results indicate that consumption of a TLC diet enhances T cell-mediated immune functions in older adults with elevated cholesterol level. This might be a clinically important benefit, considering the decline of T cell-mediated immune functions with aging and evidence of impaired immune function associated with hypercholesterolemia.

Cellular cholesterol depletion triggers shedding of the human interleukin-6 receptor by ADAM10 and ADAM17 (TACE)

Interleukin-6 (IL-6) activates cells by binding to the membrane-bound IL-6 receptor (IL-6R) and subsequent formation of a glycoprotein 130 homodimer. Cells that express glycoprotein 130, but not the IL-6R, can be activated by IL-6 and the soluble IL-6R which is generated by shedding from the cell surface or by alternative splicing. Here we show that cholesterol depletion of cells with methyl-beta-cyclodextrin increases IL-6R shedding independent of protein kinase C activation and thus differs from phorbol ester-induced shedding. Contrary to cholesterol depletion, cholesterol enrichment did not increase IL-6R shedding. Shedding of the IL-6R because of cholesterol depletion is highly dependent on the metalloproteinase ADAM17 (tumor necrosis factor-alpha-converting enzyme), and the related ADAM10, which is identified here for the first time as an enzyme involved in constitutive and induced shedding of the human IL-6R. When combined with protein kinase C inhibition by staurosporine or rottlerin, breakdown of plasma membrane sphingomyelin or enrichment of the plasma membrane with ceramide also increased IL-6R shedding. The effect of cholesterol depletion was confirmed in human THP-1 and Hep3B cells and in primary human peripheral blood monocytes, which naturally express the IL-6R. For decades, high cholesterol levels have been considered harmful. This study indicates that low cholesterol levels may play a role in shedding of the membrane-bound IL-6R and thereby in the immunopathogenesis of human diseases.

Association of low-density lipoprotein receptor polymorphisms and outcome of hepatitis C infection

The low-density lipoprotein receptor (LDLR) has been proposed to promote hepatitis C virus endocytosis and the cell membrane protein CD81 may also promote HCV host cell entry. The CD81 gene was sequenced to screen for novel polymorphisms, but no SNPs were identified. Polymorphisms within the LDLR gene are associated with the pathogenesis of familial hypercholesterolemia, atherosclerosis and obesity. We therefore studied genetic variation within the LDLR gene and clinical features of hepatitis C infection. An amino acid change in exon 8 was associated with severity of fibrosis; a SNP in exon 10 correlated with viral clearance and overall inflammation, and a SNP in the 3'UTR appeared to influence treatment response. There were no other significant associations between any of the SNPs studied and the clinical measures of hepatitis C infection. We furthermore report on linkage disequilibrium within the gene and haplotype frequencies in our population. Our findings support a possible role for the LDLR in the modulation of disease progression by affecting immune responses, rather than functioning as receptor for HCV.

Evidence for infectious agents in cardiovascular disease and atherosclerosis

During the past decade, several novel risk factors for atherosclerosis, including inflammation and infections, have been reported. Seroepidemiological studies suggest an association between several microbes and coronary heart disease. Microbes or their structural components are found in atherosclerotic plaques, but the only intact microbes commonly present are herpes viruses and Chlamydia pneumoniae. These agents are able to initiate and accelerate atherosclerosis in animal models. If they cause persistent infection in the vessel wall, they can directly promote a proinflammatory, procoagulant, and proatherogenic environment. Microbes could also have a remote effect--e.g., bacterial heat shock proteins with high sequence homology with human counterpart could, in the presence of a chronic infection, induce autoimmunity against vascular cells, and lead to an atherosclerotic process. Several intervention trials with antibiotics are underway, and will hopefully shed new light on the role of bacteria in atherosclerosis. The causal relationship can be proved by use of vaccination to prevent infections.