Infection of hypercholesterolemic mice with Coxsackievirus B

Metabolic syndrome and aberrant immune responses to viral infection and vaccination: Insights from small animal models

This review outlines the propensity for metabolic syndrome (MetS) to induce elevated disease severity, higher mortality rates post-infection, and poor vaccination outcomes for viral pathogens. MetS is a cluster of conditions including high blood glucose, an increase in circulating low-density lipoproteins and triglycerides, abdominal obesity, and elevated blood pressure which often overlap in their occurrence. MetS diagnoses are on the rise, as reported cases have increased by greater than 35% since 1988, resulting in one-third of United States adults currently diagnosed as MetS patients. In the aftermath of the 2009 H1N1 pandemic, a link between MetS and disease severity was established. Since then, numerous studies have been conducted to illuminate the impact of MetS on enhancing virally induced morbidity and dysregulation of the host immune response. These correlative studies have emphasized the need for elucidating the mechanisms by which these alterations occur, and animal studies conducted as early as the 1940s have linked the conditions associated with MetS with enhanced viral disease severity and poor vaccine outcomes. In this review, we provide an overview of the importance of considering overall metabolic health in terms of cholesterolemia, glycemia, triglyceridemia, insulin and other metabolic molecules, along with blood pressure levels and obesity when studying the impact of metabolism-related malignancies on immune function. We highlight the novel insights that small animal models have provided for MetS-associated immune dysfunction following viral infection. Such animal models of aberrant metabolism have paved the way for our current understanding of MetS and its impact on viral disease severity, dysregulated immune responses to viral pathogens, poor vaccination outcomes, and contributions to the emergence of viral variants.

Novel soybean oils differing in fatty acid composition alter immune functions of moderately hypercholesterolemic older adults

Linoleic acid (LA) and α-linolenic acid (ALA) are essential fatty acids that play an important role in modulation of T cell proliferation. The effects of consuming novel soybean oils varying in LA:ALA ratios on T cell proliferation and inflammatory responses were assessed in older adults. Eighteen participants (>50 y old) with elevated cholesterol concentrations (3.37-4.14 mmol/L LDL cholesterol) consumed 5 experimental diets in random order for periods of 35 d. Each diet contained 30% of energy as fat, two-thirds of which was high-oleic acid soybean oil (HiOleic-SO), soybean oil (SO), low-SFA soybean oil (LoSFA-SO), hydrogenated soybean oil (Hydrog-SO), or low-ALA soybean oil (LoALA-SO), resulting in LA:ALA ratios of 2.98, 8.70, 9.69, 15.2, and 18.3, respectively. Participants had higher proliferative responses to phytohemagglutinin (PHA) compared with baseline following consumption of SO (26%; P < 0.05), LoSFA-SO (22%; P < 0.05), or HiOleic-SO (24%; P < 0.05) diets. Proliferative response was similar to the baseline after participants consumed diets with an LA:ALA ratio >10 (Hydrog-SO and LoALA-SO). Post-diet intervention, LA:ALA ratios correlated with proliferative responses to PHA (r = -0.87; P = 0.05). An optimal proliferative response was observed at an LA:ALA ratio of 8.70, with an inverse correlation between proliferative response and LA:ALA ratios >8.70. These effects were independent of changes in the production of PGE(2), inflammatory cytokines, or cytokines involved in growth of lymphocytes. These data suggest that the LA:ALA ratio modulates the proliferative ability of T lymphocytes, which may be due to subtle changes in fatty acid composition of the phospholipids in immune cells.

Interactions among infections, nutrients and xenobiotics

During recent years there have been several incidents in which symptoms of disease have been linked to consumption of food contaminated by chemical substances (e.g., 2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD). Furthermore, outbreaks of infections in food-producing animals have attracted major attention regarding the safety of consumers, e.g., Bovine Spongiform Encephalitis (BSE) and influenza in chicken. As shown for several xenobiotics in an increasing number of experimental studies, even low-dose xenobiotic exposure may impair immune function over time, as well as microorganism virulence, resulting in more severe infectious diseases and associated complications. Moreover, during ongoing infection, xenobiotic uptake and distribution are often changed resulting in increased toxic insult to the host. The interactions among infectious agents, nutrients, and xenobiotics have thus become a developing concern and new avenue of research in food toxicology as well as in food-borne diseases. From a health perspective, in the risk assessment of xenobiotics in our food and environment, synergistic effects among microorganisms, nutrients, and xenobiotics will have to be considered. Otherwise, such effects may gradually change the disease panorama in society.

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.

Molecular typing of enteroviruses: current status and future requirements. The European Union Concerted Action on Virus Meningitis and Encephalitis

Human enteroviruses have traditionally been typed according to neutralization serotype. This procedure is limited by the difficulty in culturing some enteroviruses, the availability of antisera for serotyping, and the cost and technical complexity of serotyping procedures. Furthermore, the impact of information derived from enterovirus serotyping is generally perceived to be low. Enteroviruses are now increasingly being detected by PCR rather than by culture. Classical typing methods will therefore no longer be possible in most instances. An alternative means of enterovirus typing, employing PCR in conjunction with molecular genetic techniques such as nucleotide sequencing or nucleic acid hybridization, would complement molecular diagnosis, may overcome some of the problems associated with serotyping, and would provide additional information regarding the epidemiology and biological properties of enteroviruses. We argue the case for developing a molecular typing system, discuss the genetic basis of such a system, review the literature describing attempts to identify or classify enteroviruses by molecular methods, and suggest ways in which the goal of molecular typing may be realized.

Interacting nutritional and infectious etiologies of Keshan disease. Insights from coxsackie virus B-induced myocarditis in mice deficient in selenium or vitamin E

In 1979, Chinese scientists reported that selenium had been linked to Keshan disease, an endemic juvenile cardiomyopathy found in China. However, certain epidemiological features of the disease could not be explained solely on the basis of inadequate selenium nutrition. Fluctuations in the seasonal incidence of the disease suggested involvement of an infectious agent. Indeed, a coxsackievirus B4 isolated from a Keshan disease victim caused more heart muscle damage when inoculated into selenium-deficient mice than when given to selenium-adequate mice. Those results led us to study the relationship of nutritional status to viral virulence. Coxsackievirus B3/0 (CVB3/0), did not cause disease when inoculated into mice fed adequate levels of Se and vitamin E. However, mice fed diets deficient in either Se or vitamin E developed heart lesions when infected with CVB3/0. To determine if the change in viral phenotype was maintained, we passaged virus isolated from Se-deficient hosts, designated as CVB3/0 Se-, back into Se-adequate hosts. The CVB3/0 Se- virus caused disease in Se-adequate mice. To determine if the phenotype change was due to changes in the viral genome, we sequenced viruses isolated from Se-deficient mice and compared them with the input CVB3/0 virus. Six point mutations differed between the parent strain and the recovered CVB3/0 Se- isolates. When the experiment was repeated using vitamin E-deficient mice, the same 6 point mutations were found. This is the first report of a specific host nutritional deficiency altering viral genotype. Keshan disease may be the result of several interacting causes including a dominant nutritional deficiency (selenium), other nutritional factors (vitamin E, polyunsaturated fatty acids), and an infectious agent (virus).

Modulation of coronavirus-mediated cell fusion by homeostatic control of cholesterol and fatty acid metabolism

Cellular susceptibility to fusion mediated by murine coronavirus (mouse hepatitis virus, MHV strain A59) was separated into lipid-dependent and lipid-independent mechanisms with the use of subclones and selected mutants of mouse L-2 fibroblasts. Fusion-resistant L-2 cell mutants had similar cholesterol and fatty acid composition as did their fusion-susceptible parent subclone, and were presumably deficient in a genetically mutable non-lipid, host cell factor (e.g., fusion protein receptor). On the other hand, cellular sensitivity to virus fusion, which is known to be influenced by cell cholesterol content [Daya et al., 1988], was shown further to be modulated by homeostatic alterations in fatty acid metabolism. Cholesterol supplementation of mouse L-2 fibroblasts or of peritoneal macrophages from MHV-susceptible mice elevated susceptibility to viral fusion. Increased fusion susceptibility occurred in cholesterol-supplemented L-2 cells in the absence of any detectable alterations in host cell fatty acid composition, thus demonstrating fusion enhancement by cholesterol alone. L-2 cells cloned by limiting dilution in normal (not cholesterol-supplemented) medium were found to be heterogeneous in cholesterol content. Interestingly, high cholesterol-containing subclones had increased levels of C-18:0, C-18:2, C-20:4, and C-22:6 and markedly reduced levels of C-18:1 fatty acids when compared to low cholesterol-containing subclones. High cholesterol-containing subclones did not show enhanced susceptibility to viral fusion, suggesting that homeostatic alteration of fatty acid metabolism compensated for the increased cholesterol levels and countered the normally fusion-enhancing effect of cholesterol alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical variation in X-linked adrenoleukodystrophy: fatty acid and lipid metabolism in cultured fibroblasts

To determine whether the clinical phenotype of ALD correlates with the extent of metabolic abnormality, we investigated VLFA metabolism in cultured fibroblasts from patients with the clinically severe childhood from of ALD and the milder AMN variant. No differences were seen in the content of neutral lipids or phospholipids, in incorporation of [1-14C]lignocerate into cellular lipids, or in the fatty acid composition of fibroblasts from patients with childhood ALD or AMN. [1-14C]Lignocerate oxidation was deficient to a similar extent (35-40% of normal) in both intact fibroblasts and cell homogenates from patients with childhood ALD and AMN. With the use of fibroblast homogenates, oxidation of lignocerate was partially inhibited by various long-chain fatty acids, and residual activity in ALD homogenates was more susceptible to inhibition by palmitate than normal. In the presence of competing palmitate, residual lignocerate oxidative activity in fibroblast homogenates was reduced to 20 +/- 4% of normal in childhood ALD and 24 +/- 2% of normal in AMN. These results indicate that residual VLFA oxidative activity, fatty acid composition, VLFA metabolism, and lipid content of cultured fibroblasts do not correlate with the clinical expression of the ALD gene.

Increased susceptibility to mouse hepatitis virus type 3 (MHV3) infection induced by a hypercholesterolaemic diet with increased adsorption of MHV3 to primary hepatocyte cultures

The administration of a hypercholesterolaemic (HC) diet rendered genetically resistant A/J mice susceptible to mouse hepatitis virus 3 (MHV3) infection. The animals died of acute hepatitis with high viral titres in the liver accompanied by many necrotic foci and high serum transaminase levels. Resistance to virus was re-established by refeeding HC mice with a normal diet for 2 weeks. This modification of pathogenesis was accompanied by an increase in the susceptibility of hepatocyte cultures from HC mice to MHV3 and could be explained by an enhancement in virus adsorption. We hypothesize that the incorporation of cholesterol into the plasma membranes of hepatocytes of HC mice, thereby decreasing the membrane fluidity, may lead to an increase in the availability of virus receptors.

Effect of prolonged modified fasting in obese persons on in vitro markers of immunity: lymphocyte function and serum effects on normal neutrophils

The effects of nutritional manipulation on immune function have been extensively studied in animals, but few studies have examined dietary restriction in humans. Obese patients enrolled in a protein-sparing, calorically restricted diet were monitored over a 3-month period with in vitro examination of mitogen- and antigen-induced lymphocyte blastogenesis. The sera from these patients were evaluated for effects on neutrophil chemotaxis, phagocytosis and microbial killing. Significant changes in body weight, triglycerides and glucose occurred during the diet, and most patients exhibited urinary ketosis. The diet was associated with increased blastogenesis in unstimulated cultures and in varicella and candida antigen-stimulated cultures, but blastogenesis was unchanged for phytohemagglutinin, concanavalin A, SK-SD and histoplasma. In assays of serum effects on neutrophil function, patients with urinary ketosis had depression of chemotaxis and microbial killing but not phagocytosis when compared to baseline or nonketotic patients. This study indicates that long-term caloric restriction is associated with significant effects on in vitro lymphocyte stimulation and with significant serum effects on normal neutrophil function.

Protection against acute lethal viral infections with the native steroid dehydroepiandrosterone (DHEA)

A significant protective effect of a native adrenal steroid, dehydroepiandrosterone (DHEA), was demonstrated in studies of two lethal viral infection models in mice: systemic coxsackievirus B4 and herpes simplex type 2 encephalitis. The steroid was active either by long-term feeding or by a single subcutaneous injection. A closely related steroid, etiocholanolone, was not protective in these models. Histopathological analysis, leukocyte counts, and numbers of spleen antibody forming cells in the coxsackievirus B4 model suggests that DHEA functions by maintaining or potentiating the immune competence of mice otherwise depressed by viral infection. DHEA was not effective in genetically immunodeficient HRS/J hr/hr mice and did not demonstrate antiviral activity in vitro. While the molecular basis for DHEA's effect on the immune system is not known, studies by others suggest that it may counteract the stress related immunosuppressive effects of glucocorticoids stimulated by viral infection. Because DHEA is a native steroid that has been used clinically with minimal side effects, the utility of DHEA in the therapeutic modulation of acute and chronic viral infections including the acquired immune deficiency syndrome deserves intensive study.

Increased susceptibility of mice to MHV 3 infection induced by hypercholesterolemic diet: impairment of Kupffer cell function

Nutritionally induced hypercholesterolemia in A/J mice causes susceptibility to Mouse Hepatitis type 3 (MHV 3), whereas normal A/J mice are fully resistant. A/J mice fed with a hypercholesterolemic diet for 15 to 60 days develop 5 to 7 days after MHV 3 infection an acute hepatitis which led to high levels of mortality. A direct relationship was found between the high levels of plasma and hepatic cholesterol and the mortality. In attempting to define the dietary-induced physiological changes which led to the loss of resistance, the Kupffer cells were shown to exhibit an impairment of functions in their ability to become activated by LPS in order to take up C3-coated IgM opsonized sheep red blood cells, C3(IgM)SRBC, or 3H-thymidine Escherichia coli, and the susceptibility to interferon (IFN) for the induction of an antiviral state. Peritoneal macrophages which were studied in comparison with the Kupffer cells showed no impaired functions. The findings presented here indicate an inhibition of host resistance, by nutritional hypercholesterolemia, of A/J mice to MHV 3 infection and that, at least one site of impairment occurs specifically at the stage of Kupffer cells function.

Genetic predisposition to diabetes mellitus is associated with impaired humoral immunity to coxsackievirus B4

Experiments were performed to determine whether genetic predisposition to diabetes mellitus (DM) or clinical DM or both exert an influence on the production of neutralization antibodies to coxsackievirus B4 (CB4). The homozygous diabetic mutant mouse db+/db+, on the inbred C57BL/KsJ genetic background, develops a diabetes-like disease when maintained on ad libitum diet but restriction of excess food intake prevents overt disease. The doubly heterozygote db+/+m or the homozygote +m/+m misty coat color mutant, on the C57BL/KsJ genetic background, do not develop DM and served as controls. Animals infected with one-half a previously determined LD50 of CB4 were bled prior to infection and at 3, 5, 7, 14, 21 days and at 1, 2, 3, 4 and 5 months after infection. Serum neutralization antibody (NA) levels were determined from the percent CB4 plaque reduction. Until 2 months following infection, NA levels were not significant in either of the homozygous diabetic mutant groups, db+/db+. In the diabetic mutant group db+/db+, without overt disease, neutralization of CB4 when observed, was low, short-lived, and apparently not specific. However, in the homozygous diabetic mutants with spontaneous diabetes, CB4 NA became evident at 2 months after infection. By 3 months post-infection, serum NA levels were sufficient to cause 90% virus plaque reduction. These observations demonstrate that hereditary DM as characterized by the mutation diabetes, db, in the C57BL/KsJ mouse, is associated with a marked impaired humoral immune response to a diabetogenic human CB4. Specifically, there is an inability to develop an adequate level of anti-CB4 antibodies. The type and degree of immunological impairment are apparently different prior to and after onset of diabetes mellitus.

Impaired function of immune reactivity to Listeria monocytogenes in diet-fed mice

Mice fed a diet high in cholesterol, lard, and sucrose were shown to exhibit an impairment of specific immunity to Listeria monocytogenes. Whereas titers of L. monocytogenes in livers of normal mice decreased rapidly after 6 days of infection, L. monocytogenes persisted in livers of diet-fed mice. Adoptive transfer experiments indicated that L. monocytogenes-immune spleen cells are generated in diet-fed mice. However, the function of immune spleen cells from donors of either nutritional status was impaired in diet-fed recipients. The results indicate that the site(s) of impairment of specific immunity to L. monocytogenes in diet-fed mice occurs at a stage beyond the generation of immune T-cells.

Dietary hepatic cholesterol elevation: effects on coxsackievirus B infection and inflammation

Mice made hypercholesterolemic (HC) by diet are highly susceptible to coxsackievirus (CV) B5, whereas normal adult animals remain resistant. In attempting to define those dietary-induced physiological changes which contribute to altered resistance, a strong association between accumulation of intrahepatic cholesterol and increased CV B5-induced mortality was demonstrated, with maximum susceptibility to CV coinciding with a 2.5-fold increase in the ratio of hepatic cholesterol to protein. This metabolic imbalance was associated with a lower clearance rate of CV from the blood and liver of C57BL/6 mice, although virus-specific neutralizing antibody production was unaltered. In addition to CV, HC mice were more susceptible to an intravenous inoculation of Listeria monocytogenes in comparison to controls. The macrophage stimulant Corynebacterium parvum failed to increase resistance of HC mice to a high dose of CV B4 and L. monocytogenes and failed to induce the hepatomegaly, splenomegaly, and cellular infiltrate seen in the liver and spleen of normal animals. Furthermore, the peritoneal monocytic infiltrate induced by thioglycolate in normal animals was absent in HC mice. Results from these experiments suggest that decreased resistance to CV in the HC host is attributed to a defect in the nonspecific immune responses of macrophages and monocytes which are of primary importance in resistance to this virus and other infectious agents.

Resistance to bacterial and parasitic infections in the nutritionally compromised host

Over the past few years the relationships and interactions of diet, disease, and immunology are becoming better defined with the development and understanding of host defenses. Nutritional state, immunity, and disease all influence each other in the hospitalized patient, the elderly, and the young. Disease can alter nutritional needs and immune responses to antigens. The roles of both dietary excesses and deficiencies on cellular, secretory, and humoral immune responses are related to diseases and disease incidence in humans and experimental animals. Malnutrition alters incidence and severity of fungal, bacterial, viral, and parasitic pathogens. The mechanisms of altered disease resistance in nutritionally stressed animal models occurs via changes in the lymphoreticular endothelial system. The effects of common nutritional deficiencies, low protein, and low carbohydrate diets on antibody production, macrophage function, secretory IgA synthesis, and T-cell functions. Nutritional supplementation can increase lymphocyte function and decrease growth of some pathogens and tumors. Alternatively, obesity and high fat have roles in infectious disease and immunity.

Suppression of aortic elastic tissue autofluorescence for the detection of viral antigen

Suppression of aortic elastic tissue autofluorescence was achieved by employing a modification of Verhoeff's elastic tissue staining procedure. Consquently, coxsackievirus B antigen present in the aortic media was detected by conventional fluorescent antibody staining.

Coxsackievirus B cardiopathy and angiopathy in the hypercholesterolemic host

Studies on the pathogenic potential of the human cardiotropic enterovirus, coxsackievirus B5, show that this agent localizes and replicates in the aorta of mice. Nutritionally-induced hypercholesterolemia leads to an increased replication and persistence of virus in tissues, specifically the aorta. Coxsackievirus B cardiopathy is markedly augmented in the hypercholesterolemic host, resulting in a persistent cardiomyolysis which is not evident in virus-infected animals with normal cholesterol levels. Pathological changes in the aorta become evident only months after the acute infection, and only in hypercholesterolemic animals previously infected with coxsackievirus B5. Our findings of coxsackievirus B-induced angiopathy and cardiopathy in the hypercholesterolemic host extend the known pathogenic range of these human viruses, and further emphasizes their potential as etiological agents of cardiovascular disease.