Further research is necessary to delineate the role of Cu in immune system activities. Zn and Cu are antagonistic with one another: Zn deficiency leads to an increase in Cu levels in liver and bone Burch et al. Conversely, excess Zn leads to Cu deficiency. Under certain conditions, Zn wrlting Cu can inhibit one another's absorption. For example, Zn servie in Zn-adequate rats is decreased with excess Cu, but not in Zn-deficient rats Evans et al. Both Cu and Zn absorption are increased with a Zn deficiency. However, only Cu absorption is increased with a Cu deficiency.

Selenium Se is an essential component of glutathione peroxidase, an antioxidant enzyme that plays an important role in removing hydrogen peroxide and organic hydroperoxides Chaudiere et al. A deficiency in Se can induce a state of oxidative stress in the host. Oxidative stress is a term used to describe the overabundance of the production of free radicals and other oxidants in comparison with antioxidant defenses.

Thus, oxidative stress describes a situation in which prooxidants are favored over antioxidants. Oxidative stress can affect host cells in a number of ways. Beckman and Ames 1997 have suggested that oxygen free radicals damage on the order of 10,000 DNA bases per cell per day, of which a small percentage are not repaired. Membrane integrity of cells becomes impaired due to oxygen free radical-mediated lipid peroxidation, leading to the decrease or loss of cellular function.

Proteins are also susceptible to free-radical damage. For example, hydroxy radicals modify amino acid residues at metal-binding sites of proteins Stadtman, 1992. The increased susceptibility to infectious pathogens in Se deficiency may be due to decreased antibody production and impaired servvice responses Chandra and Chandra, 1986. Se deficiency has also been associated with an endemic cardiomyopathy in China known as Keshan disease.

Essay writing service wiki disease KD is characterized by acute or chronic heart conditions affecting heart function such as cardiac insufficiency, enlargement of the heart, arrhythmia, atrial fibrillation, and tachycardia Li essay writing service wiki al. Histologically, KD is characterized by multiple focal necrosis and myocardial parenchymatous degeneration Gu, 1983. Epidemiologists in China found that the disease occurred only in areas with low Se soil content. Subsequently, it was found that individuals residing in KD endemic areas were of low Se status.

Supplementation with Se to normal nutritional levels has prevented the widespread occurrence of KD wiik endemic areas of China. However, the Se deficiency alone did not explain all aspects of the disease. The seasonal and annual incidence of KD suggested that an infectious cofactor may play an etiological role in the development of the disease.

Indeed, virologists in China have isolated several enterovirus strains from blood and essay writing service wiki specimens of KD victims Su et al. One of the enteroviruses, Coxsackievirus B4 CVB4recovered from a blood sample of a KD patient, caused a higher incidence and more severe myocarditis in neonatal mice born to Se-deficient dams than in neonates born to dams that were fed a diet containing adequate levels of Se Bai et al. Coxsackieviruses, and particularly CVB viruses, are etiological agents of viral-induced myocarditis and are suspected agents of dilated cardiomyopathy DCM Fuster et al.

DCM is the second leading indication for heart transplantation in this country O'Connell and Robinson, sefvicewhich suggests that infections with CVB viruses are responsible for a great deal of servixe and mortality. Coxsackieviruses are nonenveloped RNA viruses in the Picornaviridae family, subgroup enterovirus of which the most commonly known enterovirus is poliovirus.

The genome consists of approximately 7,500 base pairs in an open reading frame, flanked by both 3' and 5' nontranslated regions. With over 3 decades of research, the mouse model of CVB-induced myocarditis is widely accepted as an appropriate animal model for human myocarditis Woodruff, 1980. Although the response is initiated by the viral infection, the heart pathology is widely believed to be due to an immunopathological process. Evidence for an immunopathological basis for enterovirus-induced cardiomyopathy is provided by the lack of or diminished disease in CVB3-infected athymic nude mice and lack of disease in writint adult mice that were not reconstituted with T-cells Woodruff and Woodruff, 1974.

In addition, essay writing service wiki the peak period of cardiac inflammation, virus is not generally detectable in mouse heart tissue Woodruff, 1980. Although the immune system clearly contributes to the pathology, it also performs a protective function. Strains of mice that can clear virus from the heart more rapidly and rapidly produce neutralizing antibody develop only a mild myocarditis. However, strains of mice fssay have delayed viral clearance and delayed production of neutralizing antibody develop severe myocarditis Herskovitz et al.

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