Antigenic role of stress-induced catalase of Salmonella typhimurium in cell-mediated immunity

Induction of hsp70 in transgenic Drosophila: biomarker of exposure against phthalimide group of chemicals

The expression of stress genes is suggested to be a potentially sensitive indicator of any chemical or physical assault. This led us to explore the possibility of using expression of one of the major stress genes, hsp70, in Drosophila as a biomarker against phthalimide group of chemicals, which may accordingly provide an early indication of exposure to these hazardous chemicals. We exposed third instar larvae of transgenic Drosophila melanogaster (hsp70-lacZ) Bg(9) to different concentrations of the test chemicals (Captan, Captafol and Folpet) for various time intervals (2-48 h) to evaluate expression of hsp70 by X-gal staining, ONPG assay and whole organ in situ immunohistochemistry. The study was further extended to examine the effect of the said chemicals on development of the organism and tissue damage occurring in them, thus raising the possibility of evaluating comparative deleterious effect inducing potential of the test chemicals. Our results showed a strong hsp70 expression in the Captafol-exposed larvae followed by weaker expression in Captan- and Folpet-treated larvae. The effect was further reflected on development as revealed by a delay in emergence of the flies by 3 days in 200 ppm Captafol-exposed group. Hsp70 was found not to be induced at 0.0002 ppm Captafol and at 0.002 ppm Captan and Folpet. The present study suggests that (a). hsp70 induction is sensitive enough to be used as a biomarker against phthalimide group of chemicals, (b). amongst the three test chemicals, Captafol is the most deleterious compound followed by Captan and Folpet, (c). 0.0002 ppm for Captafol and 0.002 ppm for Captan and Folpet, respectively, can be regarded as no observed adverse effect level (NOAEL).

Oxygen free radicals and systemic autoimmunity

Reactive oxygen species generated during various metabolic and biochemical reactions have multifarious effects that include oxidative damage to DNA leading to various human degenerative and autoimmune diseases. The highly reactive hydroxy radical (*OH) can interact with chromatin and result in a wide range of sugar and base-derived products, DNA-protein cross-links and strand breaks. Studies from our laboratory have demonstrated that after modification the DNA becomes highly immunogenic and the induced antibodies exhibit variable antigen-binding characteristics. Systemic lupus erythematosus, a prototype autoimmune disease, is characterized by the presence of autoantibodies to multiple nuclear antigens. The detection of 8-hydroxyguanosine in the immune complex derived DNA of systemic lupus erythematosus patients reinforces the evidence that reactive oxygen species may be involved in its pathogenesis. Increased apoptosis and decreased clearance of apoptotic cells as observed in systemic lupus erythematosus (SLE) might well be a contributory factor in systemic autoimmunity. Clinically, titres of autoantibodies are closely related to the degree of renal inflammation. Anti-DNA antibodies may combine with circulating antigen and contribute to the deposition of immune complexes in renal glomeruli.

Reactive nitrogen and oxygen intermediates and bacterial defenses: unusual adaptations in Mycobacterium tuberculosis

The production of reactive oxygen and reactive nitrogen intermediates is an important host defense mechanism mediated in response to infection by bacterial pathogens. Not surprisingly, intracellular pathogens have evolved numerous defense strategies to protect themselves against the damaging effects of these agents. In enteric bacteria, exposure to oxidative or nitrosative stress induces expression of numerous pathways that allow the bacterium to resist the toxic effects of these compounds during growth in the host. In contrast, members of pathogenic mycobacterial species, including the frank human pathogens Mycobacterium tuberculosis and Mycobacterium leprae, are dysfunctional in aspects of the oxidative and nitrosative stress response, yet they remain able to establish and maintain productive acute and persistent infections in the host. This article reviews the current knowledge regarding reactive oxygen and nitrogen intermediates, and compares the adaptative mechanisms utilized by enteric organisms and mycobacterial species to resist the bactericidal and bacteriostatic effects resulting from exposure to these compounds.

Chemical and biological activity of free radical 'scavengers' in allergic diseases

Reactive oxygen species (ROS) are generated constantly in vivo. They can lead to lipid peroxidation and oxidation of some enzymes, as well as protein oxidation and degradation. Cells possess several biological systems, defined as 'scavengers', to protect themselves from the radical-mediated damage. Immune cells may discharge their arsenal of toxic agents against host tissues, resulting in oxidative damage and inflammation. Therefore, free radical production and disturbance in redox status can modulate the expression of a variety of immune and inflammatory molecules, leading to inflammatory processes, both exacerbating inflammation and effecting tissue damage. Recently, abnormal immunity has been related to oxidative imbalance, and antioxidant functions are linked to anti-inflammatory and/or immunosuppressive properties. Currently, allergy is one of the most important human diseases. We studied the role of the primary antioxidant defence system, constituted by the antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase, protecting cells from toxic oxygen. We analyzed how they are involved in blood cells detoxification, and how the imbalance of reactive oxygen species is related to inflammation in allergic diseases by affecting immune cells. Finally, we discuss the published data that relates anti-free radical therapy to the management of human allergic diseases.

Protection by protein A of apoptotic cell death caused by anti-AIDS drug zidovudine

Zidovudine, the anti-AIDS drug, caused inhibition of mitogen-induced proliferation and perturbation of cell-cycle progression of cultured bone marrow cells of mice. There was significant hypoploidy observed in flow cytometric analysis of AZT-treated bone marrow cells. In apo-direct analysis, cells showed apoptosis in G0/G1 phase. In DNA gel analysis, characteristic laddering of apoptosis was observed in AZT-treated bone marrow cells. We demonstrated that, when the animals were pretreated with protein A (PA) of Staphylococcus aureus, the apoptotic changes could be prevented in bone marrow cells of AZT-treated animals. There is a significant (p < 0.05) increase in proliferation of bone marrow cells subjected to mitogen treatment in PA+AZT-treated animals, compared to only AZT-treated animals. However, cell-cycle phase distribution was not hampered and no laddering in DNA gel analysis was also observed in this group. In apo-direct analysis, PA treatment showed significant (p < 0.001) inhibition of AZT-induced apoptosis. These observations indicate that by using a suitable agent such as protein A the toxic side effects of AZT could be minimized.

Stress genes and species survival

Stress genes can be ascribed to have been generated by the organism for their intrinsic urge to survive against the changing environmental odds, during the evolutionary process. This concept has been supported by a large number of reports describing individual types of phenomena. These have been reconciled and globalised in terms of their relevance in this article. Supporting evidences have been drawn from the literature which indicated that by using different types of inducer one can express heat shock proteins. Similarly, several types of stress inducers, such as calorie restriction, LPS stimulation and Staphylococcal Protein-A stimulation, it was possible to induce a wide array of biological, biochemical and immunological reactions. Such biological reactions rendered protection against toxic, carcinogenic, metabolic, as well as biological stresses induced by microorganisms. Heat shock proteins have been implicated as having a role in providing resistance to the host against different types of stressors. In this article, some mechanistic schemes have been proposed as possible pathways globalising such phenomena. A minute amount of stress inducers has been observed to have helped expression of stress resistance genes, providing increased capability to the host to protect itself against myriads of both biotic and abiotic stressors. More understanding about such phenomena would help in keeping our physiological systems vigilant and our bodies healthy, fighting out the stress-related events effectively.

The Salmonella typhimurium AhpC polypeptide is not essential for virulence in BALB/c mice but is recognized as an antigen during infection

The OxyR regulon is known to mediate protection against oxidizing agents in Salmonella typhimurium. We reported previously that ahp, one of the OxyR-regulated loci, is induced during macrophage interaction (K. P. Francis, P. D. Taylor, C. J. Inchley, and M. P. Gallagher, J. Bacteriol. 179:4046-4048, 1997). We now report on the effects of disrupting ahp or oxyR on virulence in a BALB/c mouse model. Surprisingly, insertion of a Mudlux derivative within ahpC was found to result in attenuation, while irreversible inactivation of the locus through insertion of a cml cassette did not. An SL1344 derivative carrying an oxyR::kan disruption was also found to be as virulent as the parental strain. Moreover, both cell-mediated and humoral responses to AhpC were found to develop during the course of infection, probably through T-helper-cell (type I) activation. These results indicate that, although not essential for virulence, AhpC is expressed by S. typhimurium during infection of BALB/c mice and constitutes a target for the immune system.

Protective role of stress genes

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Pathogenicity and protective effect of rough mutants of Salmonella species in germ-free piglets

In this study, two stable, rough, streptomycin-sensitive Salmonella mutants with different types of genetic defects were used to colonize groups of germ-free (GF) piglets. The lipopolysaccharide (LPS) of Salmonella typhimurium SF 1591 was of the Ra chemotype (complete core), whereas the LPS of the S. minnesota mR 595 deep-rough mutant contained only lipid A and 2-keto-3-deoxyoctulosonic acid (Re chemotype). Both strains readily colonized the intestinal tracts of GF piglets and were stable during the whole experiment. All animals survived, and only transient fever was observed in some piglets colonized with the SF 1591 strain. Finally, streptomycin and virulent, smooth, streptomycin-resistant S. typhimurium LT2 were administered perorally 1 week later. All piglets colonized previously with the deep-rough mutant mR 595 died of sepsis, in contrast to piglets infected with the LT2 strain and colonized with the SF 1591 mutant, all of which survived. This difference is explained by the penetration of the mesenteric lymph nodes, spleen, and liver by great numbers of live bacteria in the latter case, resulting in prominent systemic and local immune responses. On the other hand, live bacteria were found only rarely in the mesenteric lymph nodes of animals colonized with the mR 595 strain and a negligible antibody response was observed.

Intracellular survival and multiplication of virulent and less virulent strains of Streptococcus bovis in pigeon macrophages

The intracellular fate of pigeon S. bovis strains ingested by macrophages was studied in vivo and in vitro. During in vivo experiments, histological and electron microscopical examinations demonstrated numerous cocci, which appeared to be actively multiplying, within splenic macrophages of pigeons experimentally inoculated with a highly virulent S. bovis serotype 1 strain. In pigeons inoculated with a low virulence serotype 3 strain, intracellular cocci were only occasionally observed. For in vitro experiments, pigeon peritoneal macrophages were inoculated with a S. bovis serotype 1 or serotype 3 strain and incubated. Following an initial decrease, an increase in the number of intracellular bacteria was observed in tests performed with the S. bovis serotype 1 strain, demonstrating intracellular multiplication. Macrophages in these experiments had all died after 7 h of incubation, possibly indicating that the intracellular replication of S. bovis resulted in the release of substances toxic for macrophages. In experiments performed with the S. bovis serotype 3 strain, the number of intracellular bacteria continuously decreased, reflecting killing of organisms. Significant changes in the number of adhering macrophages in S. bovis serotype 3 inoculated cultures were not observed. These results indicate S. bovis in pigeons is a facultative intracellular bacterium and intracellular multiplication may be involved in virulence.

Effects of ethanol on cellular immunity to facultative intracellular bacteria

Alcohol abuse has been associated with an increase in infectious diseases caused by pathogenic and opportunistic microorganisms. Study results obtained from this laboratory and other laboratories have shown that consumption of large amounts of ethanol is associated with numerous changes in the immune system. The purpose of this article is to report findings obtained from this laboratory, as well as review those obtained from other laboratories, from experiments designed to evaluate the effects of ethanol on various components of antimicrobial host-defense mechanisms. The effects of ethanol on various aspects of immunity obtained with the use of in vivo and in vitro model systems are reviewed as they pertain to antimicrobial defenses. All current data would support the suggestion that ethanol affects both the development of an antigen-specific immune response and the effector mechanisms of the cellular immune response. Findings obtained from animal models show that ethanol prevents the formation of granulomas in infected tissues, perhaps by inhibiting the response of macrophages to T-cell cytokines. Data obtained from this laboratory also support the suggestion that the inability of the immune system to control the intracellular growth of microorganisms results in an exaggerated inflammatory response that is responsible for at least a part of the tissue damage.

Light emission from a Mudlux transcriptional fusion in Salmonella typhimurium is stimulated by hydrogen peroxide and by interaction with the mouse macrophage cell line J774.2

Hydrogen peroxide is known to induce a multigenic response in Salmonella typhimurium cells. We have used a Mudlux transcriptional reporter system to identify and isolate fusions in the virulent strain SL1344 which respond to hydrogen peroxide in vitro by light production, and one of these fusions, MPG203, has been further characterized. Transient light production was observed from MPG203 at levels of hydrogen peroxide as low as 10 microM. However, high levels of this toxic oxidizing agent resulted in light suppression, particularly at low bacterial densities. This fusion was also shown to produce light following adhesion to cells of the mouse macrophage cell line J774.2. Furthermore, the response was greatly reduced in the presence of catalase, directly implicating hydrogen peroxide as the eliciting agent and suggesting the involvement of the hydrogen peroxide-induced bacterial stress response in the infection process. Chemiluminescence studies also indicated that inhibition of the respiratory burst may occur as the infection ratio is increased. In addition, the level of light produced from bacteria within individual macrophage cells was shown to vary.