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Biomedical subjects

Dennis W Metzger

Publications and source records attributed to Dennis W Metzger.

At least 19 recordsLinked to original sources
PubMed2007

Matrix metalloproteinase 9 activity enhances host susceptibility to pulmonary infection with type A and B strains of Francisella tularensis.

A striking feature of pulmonary infection with the Gram-negative intracellular bacterium Francisella tularensis, a category A biological threat agent, is an intense accumulation of inflammatory cells, particularly neutrophils and macrophages, at sites of bacterial replication. Given the essential role played by host matrix metalloproteinases (MMPs) in modulating leukocyte recruitment and the potentially indiscriminate destructive capacity of these cells, we investigated whether MMP-9, an important member of this protease family released by neutrophils and activated macrophages, plays a role in the pathogenesis of respiratory tularemia. We found that F. tularensis induced expression of MMP-9 in FVB/NJ mice and that the action of this protease is associated with higher bacterial burdens in pulmonary and extrapulmonary tissues, development of more extensive histopathology predominated by neutrophils, and increased morbidity and mortality compared with mice lacking MMP-9 (MMP-9(-/-)). Moreover, MMP-9(-/-) mice were able to resolve infection with either the virulence-attenuated type B (live vaccine strain) or the highly virulent type A (SchuS4) strain of F. tularensis. Disease resolution was accompanied by diminished leukocyte recruitment and reductions in both bacterial burden and proinflammatory cytokine production. Notably, neutrophilic infiltrates were significantly reduced in MMP-9(-/-) mice, owing perhaps to limited release of Pro-Gly-Pro, a potent neutrophil chemotactic tripeptide released from extracellular matrix through the action of MMP-9. Collectively, these results suggest that MMP-9 activity plays a central role in modulating the clinical course and severity of respiratory tularemia and identifies MMPs as novel targets for therapeutic intervention as a means of modulating neutrophil recruitment.

Amino Acid Sequence↗
PubMed2007

Interleukin-12 promotes gamma interferon-dependent neutrophil recruitment in the lung and improves protection against respiratory Streptococcus pneumoniae infection.

The ability of exogenous interleukin-12 (IL-12) to elicit protective innate immune responses against the extracellular pathogen Streptococcus pneumoniae was tested by infecting BALB/c mice intranasally (i.n.) with S. pneumoniae after i.n. administration of IL-12. It was found that administration of IL-12 resulted in lower bacterial burdens in the infected mice and significantly improved survival rates. All IL-12-treated mice contained higher levels of pulmonary gamma interferon (IFN-gamma) after infection and significantly more neutrophils than infected mice not treated with IL-12. IFN-gamma was found to be essential for IL-12-induced resistance and for neutrophil influx into the lungs, and the observed changes correlated with increased levels of the IL-8 homologue keratinocyte-derived chemokine (KC). In addition, in vitro tumor necrosis factor alpha (TNF-alpha) production by alveolar macrophages stimulated with heat-killed pneumococci was enhanced by IFN-gamma, and TNF-alpha in turn could enhance production of KC by lung cells. Finally, IL-12-induced protection was dependent upon the presence of neutrophils and the KC receptor CXCR2. Taken together, the results indicate that exogenous IL-12 can improve innate defense in the lung against S. pneumoniae by inducing IFN-gamma production, which in turn enhances chemokine expression, and promotes pulmonary neutrophil recruitment into the infected lung. The findings show that IL-12 and IFN-gamma can mediate a protective effect against respiratory infection caused by extracellular bacterial pathogens.

Animals↗
PubMed2006

Intranasal vaccination of neonatal mice with polysaccharide conjugate vaccine for protection against pneumococcal otitis media.

Streptococcus pneumoniae is the leading bacterial cause of acute otitis media (OM) in young children, and can often produce invasive disease. Typical intramuscular routes of vaccination are poorly protective against development of OM. In the present study, we intranasally (i.n.) inoculated neonatal 1-week-old mice with pneumococcal polysaccharide conjugate vaccine using IL-12 as a mucosal adjuvant. The protective efficacy of this treatment was tested by challenging immunized infant (3-week-old) mice with bacteria to induce OM and invasive disease. i.n. vaccination was found to enhance levels of specific antibodies in middle ear (ME) washes and sera from wild-type (but not IFN-gamma(-/-)) mice. Immunization in the presence of IL-12 resulted in enhanced clearance of S. pneumoniae from the ME. Opsonization of bacteria with ME wash fluids or sera from immunized mice caused increased bacterial clearance from the ME of naïve mice. In addition, immunized mice demonstrated 89% survival after OM-induced invasive pneumococcal infection, compared to 22% survival in unvaccinated mice. These results indicate that i.n. vaccination of neonatal mice in the presence of IL-12 is able to enhance IFN-gamma dependent ME mucosal and systemic immune responses to pneumococci and efficiently protect against both OM and invasive infection.

Administration, Intranasal↗
PubMed2006

Superoxide dismutase B gene (sodB)-deficient mutants of Francisella tularensis demonstrate hypersensitivity to oxidative stress and attenuated virulence.

A Francisella tularensis live vaccine strain mutant (sodB(Ft)) with reduced Fe-superoxide dismutase gene expression was generated and found to exhibit decreased sodB activity and increased sensitivity to redox cycling compounds compared to wild-type bacteria. The sodB(Ft) mutant also was significantly attenuated for virulence in mice. Thus, this study has identified sodB as an important F. tularensis virulence factor.

Animals↗
PubMed2005

Mucosal B cell deficiency in IgA-/- mice abrogates the development of allergic lung inflammation.

We have investigated the consequence of lack of IgA on host immunity using a murine model of allergic lung inflammation. Mice with a targeted disruption of the alpha-switch region and 5' H chain gene (IgA(-/-) mice), which lack total IgA, developed significantly reduced pulmonary inflammation with fewer inflammatory cells in lung tissue and bronchoalveolar lavage fluids, as well as reduced levels of total and IgG1 OVA-specific Abs and decreased IL-4 and IL-5 in bronchoalveolar lavage fluids compared with IgA(+/+) controls, following allergen sensitization and challenge. This defect was attributable to fewer B cells in the lungs of IgA(-/-) mice. Polymeric IgR-deficient (pIgR(-/-)) mice, which lack the receptor that transports polymeric IgA across the mucosal epithelium where it is cleaved to form secretory IgA, were used to assess the contribution of secretory IgA vs total IgA in the induction of allergic lung inflammation. pIgR(-/-) and pIgR(+/+) mice had comparable levels of inflammation, demonstrating that IgA bound to secretory component is not necessary for the development of allergic lung inflammation, although this does not necessarily rule out a role for transudated IgA in lung secretions because of "mucosal leakiness" in these mice. The results indicate that Ag-specific B cells are required at mucosal surfaces for induction of inflammation and likely function as major APCs in the lung for soluble protein Ags.

Administration, Intranasal↗
PubMed2005

Early activation of NK cells after lung infection with the intracellular bacterium, Francisella tularensis LVS.

Francisella tularensis is a gram-negative intracellular bacterium that has been classified as a Category A biothreat because of its ability to induce deadly pneumonic tularemia when inhaled. In the present study, an experimental model of F. tularensis LVS intranasal infection was used to study the immune cells involved in cytokine secretion in the lungs after infection. Dramatic increases in the numbers of cells secreting IFN-gamma were observed 72 h after intranasal infection of BALB/c and C57BL/6 mice with sublethal (1000 CFU) or lethal (10,000 CFU) doses of F. tularensis LVS and the cells primarily responsible for this IFN-gamma expression were identified as CD11b+ DX5+ NK cells. The findings were further confirmed in C57BL/6 mice showing that cells responsible for IFN-gamma secretion in the lungs were CD11b+ DX5+ NK1.1+. NK cell depletion studies showed a decrease in the percentage of IFN-gamma secreting cells, due not only to a diminished proportion of IFN-gamma secreting NK cells, but also to a reduced percentage of T cells secreting IFN-gamma. The results indicate that IFN-gamma is secreted in response to respiratory infection with F. tularensis LVS, and that NK cells are the early responders responsible for IFN-gamma secretion.

Administration, Intranasal↗
PubMed2005

Intranasal interleukin-12 treatment for protection against respiratory infection with the Francisella tularensis live vaccine strain.

Francisella tularensis is a gram-negative intracellular bacterium that can induce lethal respiratory infection in humans and rodents. However, little is known about the role of innate or adaptive immunity in protection from respiratory tularemia. In the present study, the role of interleukin-12 (IL-12) in inducing protective immunity in the lungs against intranasal infection of mice with the live vaccine strain (LVS) of F. tularensis was investigated. It was found that gamma interferon (IFN-gamma) and IL-12 were strictly required for protection, since mice deficient in IFN-gamma, IL-12 p35, or IL-12 p40 all succumbed to LVS doses that were sublethal for wild-type mice. Furthermore, exogenous IL-12 treatment 24 h before intranasal infection with a lethal dose of LVS (10,000 CFU) significantly decreased bacterial loads in the lungs, livers, and spleens of wild-type BALB/c and C57BL/6 mice and allowed the animals to survive infection; such protection was not observed in IFN-gamma-deficient mice. The resistance induced by IL-12 to LVS infection was still observed in NK cell-deficient beige mice but not in CD8-/- mice. These results demonstrate that exogenous IL-12 delivered intranasally can prevent respiratory tularemia through a mechanism that is at least partially dependent upon the expression of IFN-gamma and CD8 T cells.

Administration, Intranasal↗
PubMed2004

Azithromycin modulates murine immune responses to pneumococcal conjugate vaccine and inhibits nasal clearance of bacteria.

Macrolide antibiotics, including azithromycin, have been implicated in the modulation of host immune responses, independently of their antimicrobial properties. The present work was designed to study the effect that azithromycin has on protective humoral immune responses induced by a 7-valent, polysaccharide, pneumococcal conjugate vaccine (PCV7). By use of a murine vaccination/challenge model, it was found that inoculation with azithromycin led to significantly lower primary antibody responses, decreased recall proliferative responses, and, in nasal cavities, impaired clearance of Streptococcus pneumoniae serotype 14 from the nasal cavities. The results demonstrate that azithromycin can be inhibitory with regard to protective immune responsiveness.

Animals↗
PubMed2004

An important role for polymeric Ig receptor-mediated transport of IgA in protection against Streptococcus pneumoniae nasopharyngeal carriage.

The importance of IgA for protection at mucosal surfaces remains unclear, and in fact, it has been reported that IgA-deficient mice have fully functional vaccine-induced immunity against several bacterial and viral pathogens. The role of respiratory Ab in preventing colonization by Streptococcus pneumoniae has now been examined using polymeric IgR knockout (pIgR(-/-)) mice, which lack the ability to actively secrete IgA into the mucosal lumen. Intranasal vaccination with a protein conjugate vaccine elicited serotype-specific anti-capsular polysaccharide Ab locally and systemically, and pIgR(-/-) mice produced levels of total serum Ab after vaccination that were similar to wild-type mice. However, pIgR(-/-) mice had approximately 5-fold more systemic IgA and 6-fold less nasal IgA Ab than wild-type mice due to defective transport into mucosal tissues. Wild-type, but not pIgR(-/-) mice were protected against infection with serotype 14 S. pneumoniae, which causes mucosal colonization but does not induce systemic inflammatory responses in mice. The relative importance of secretory IgA in host defense was further shown by the finding that intranasally vaccinated IgA gene-deficient mice were not protected from colonization. Although secretory IgA was found to be important for protection against nasal carriage, it does not appear to have a crucial role in immunity to systemic pneumococcus infection, because both vaccinated wild-type and pIgR(-/-) mice were fully protected from lethal systemic infection by serotype 3 pneumococci. The results demonstrate the critical role of secretory IgA in protection against pneumococcal nasal colonization and suggest that directed targeting to mucosal tissues will be needed for effective vaccination in humans.

Administration, Intranasal↗
PubMed2003

Delivery of IL-12 intranasally leads to reduced IL-12-mediated toxicity.

Interleukin-12 (IL-12) is a heterodimeric cytokine that enhances immune responses to bacterial, parasitic, and viral pathogens, and leads to tumor regression in animal models. For this reason, the use of IL-12 as a vaccine adjuvant and as a therapeutic agent for the treatment of cancer is being investigated. Unfortunately, the extreme toxicity of this molecule observed during clinical trials has limited its use. This toxicity correlates with increased IFN-gamma expression, decreased glucose levels, and altered histological responses in the spleen and duodenum. In this study, we show that intranasal (i.n.) delivery of IL-12 is a less toxic route of inoculation compared to the commonly employed subcutaneous route. When delivered i.n., IL-12 induces less systemic IFN-gamma production and fewer pathological tissue changes, yet is efficacious, as indicated by enhanced CD3(+) T cell activation and increased production of Th1-associated immunoglobulins (i.e., serum IgG2a). Thus, IL-12 can be delivered safely and effectively by the i.n. route, a finding which may allow IL-12 to fulfill its clinical potential.

Adjuvants, Immunologic↗
PubMed2003

Cyclic pressure affects osteoblast functions pertinent to osteogenesis.

In an attempt to elucidate the cellular/molecular correlations between mechanical stimuli and new bone formation, the present in vitro study used a custom-made laboratory setup and examined the effects of cyclic pressure on select functions of osteoblasts pertinent to osteogenesis. The results demonstrated that, compared to controls (no pressure), mRNA expression for type-I collagen (the main constituent of the organic phase of bone) was enhanced when osteoblasts were exposed to cyclic pressure (10-40 kPa at 1.0 Hz) for 1 h daily for up to 19 consecutive days. In addition, compared to controls, both deposition of collagen and accumulation of calcium (one of the major components of the inorganic phase of bone) increased significantly (p<0.05) following exposure of osteoblast cultures to cyclic pressure for 19 days. Since the amounts of total DNA in controls and in osteoblast cultures exposed to cyclic pressure were similar at all time points tested, it was concluded that increased collagen and calcium concentrations in cultures resulted from enhanced osteoblast function (and not from increased number of cells); the presence of increased amounts of collagen affected the subsequent increased accumulation of calcium. These results provide evidence that daily exposure to cyclic pressure for various time periods (up to 19 days) affect osteoblast functions pertinent to bone formation.

Animals↗
PubMed2003

Increased protection against pneumococcal disease by mucosal administration of conjugate vaccine plus interleukin-12.

Streptococcus pneumoniae is a common cause of respiratory tract infections, its main entry route being the nasal mucosa. The recent development of pneumococcal polysaccharide conjugate vaccines has led to a dramatic improvement in protection against invasive disease in infants and children, but these vaccines have been found to be only 50 to 60% protective against bacterial carriage. In this study, we investigated the efficacy of intranasal (i.n.) conjugate vaccine delivery using interleukin-12 (IL-12) as a mucosal adjuvant. Immunized mice treated with IL-12 demonstrated increased expression of lung and splenic gamma interferon and IL-10 mRNAs; high levels of antibody, particularly serum immunoglobulin G2a (IgG2a) and respiratory IgA; and significantly increased opsonic activity. After intraperitoneal challenge with type 3 pneumococci, there was 75% survival of i.n. vaccinated mice compared to 0% survival of unvaccinated mice. In addition, after i.n. challenge with type 14 pneumococci, vaccinated mice possessed fewer bacterial colonies in the upper respiratory tract than unvaccinated mice. However, no significant difference in type 14 carriage was observed between vaccinated and unvaccinated groups following intramuscular vaccination, the typical route of vaccination in humans. Using mice with a genetic disruption in IgA expression, it was found that pneumococcus-specific IgA played a significant role in the clearance of bacteria from the upper respiratory tract. We conclude that i.n vaccination in the presence of IL-12 is able to enhance systemic and mucosal immune responses to pneumococci and efficiently protect against both invasive infection and bacterial carriage.

Adjuvants, Immunologic↗
PubMed2003

Intranasal vaccination using interleukin-12 and cholera toxin subunit B as adjuvants to enhance mucosal and systemic immunity to human immunodeficiency virus type 1 glycoproteins.

We have investigated the induction of protective mucosal immunity to human immunodeficiency virus type 1 (HIV-1) isolate 89.6 by intranasal (i.n.) immunization of mice with gp120 and gp140 together with interleukin-12 (IL-12) and cholera toxin subunit B (CTB) as adjuvants. It was found that both IL-12 and CTB were required to elicit mucosal antibody responses and that i.n. immunization resulted in increased total, immunoglobulin G1 (IgG1), and IgG2a anti-HIV-1 antibody levels in serum; increased total, IgG1, IgG2a, and IgA antibody expression in bronchoalveolar lavage fluids; and increased IgA antibody levels in vaginal washes. Levels of anti-HIV-1 antibodies in both sera and secretions were higher in groups immunized with gp140 than in those immunized with gp120. However, only gp120-specific mucosal antibodies demonstrated neutralizing activity against HIV-1 89.6. Taken together, the results show that IL-12 and CTB act synergistically to enhance both systemic and local mucosal antibody responses to HIV-1 glycoproteins and that even though gp140 induces higher antibody titers than gp120, only gp120-specific mucosal antibodies interfere with virus infectivity.

AIDS Vaccines↗
PubMed2003

Exogenous interleukin-12 protects against lethal infection with coxsackievirus B4.

Infections with the group B coxsackieviruses either can be asymptomatic or can lead to debilitating chronic diseases. To elucidate the mechanism by which these viruses cause chronic disease, we developed a mouse model of chronic pancreatitis by using a virulent variant of coxsackievirus B4, CVB4-V. Infection with CVB4-V results in an early, severe pancreatitis, which can lead to mortality or progress to chronic pancreatitis. Chronic pancreatitis, in this model, is due to immunopathological mechanisms. We investigated whether interleukin-12 (IL-12) could modulate the outcome of CVB4-V infection. Eighty-five percent of the infected mice treated with 500 ng of IL-12 survived, whereas all untreated mice succumbed. To understand the mechanism underlying the beneficial effect of IL-12, we investigated the role of gamma interferon (IFN-gamma). Three lines of evidence suggest that the protective effect of IL-12 is due to IFN-gamma. First, administration of IL-12 increased the production of endogenous IFN-gamma in CVB4-V-infected mice. Both NK and NKT cells were identified as the source of IFN-gamma. Second, IFN-gamma knockout mice treated with IL-12 succumbed to infection with CVB4-V. Third, wild-type mice treated with IFN-gamma survived infection with CVB4-V. Due to the antiviral effects of IFN-gamma, we examined whether IL-12 treatment affected viral replication. Administration of IL-12 did not decrease viral replication in the pancreas, but it did prevent extensive tissue damage and the subsequent development of chronic pancreatitis. The data suggest that IL-12 treatment during CVB4-V infection is able to suppress the immunopathological mechanisms that lead to chronic disease.

Animals↗
PubMed2002

Natural anti-galactose alpha1,3 galactose antibodies delay, but do not prevent the acceptance of extracellular matrix xenografts.

Naturally occurring antibodies to the galactose alpha1,3 galactose (alpha gal) epitope expressed on xenogeneic grafts are a major barrier to organ transplantation in humans. Porcine small intestinal submucosa (SIS) expresses the alpha gal epitope and is currently being used as a bioscaffold for tissue remodeling. To examine in detail the potential role of the alpha gal epitope in immune recognition of this acellular, avascular biomaterial, we have used mice which have a genetic disruption in the alpha1,3 galactosyltransferase gene (alpha gal(-/-)mice) and thus express natural anti-alpha gal antibodies in a manner similar to humans. It was found that alpha gal(-/-)mice produced IgM anti-alpha gal antibodies in addition to IgG1 SIS-specific antibodies, which did not bind to the alpha gal epitope. Histological examination of implant sites demonstrated an early inflammatory response that consisted predominantly of neutrophils in both alpha gal(+/+) and alpha gal(-/-)mice. However, while alpha gal(+/+)mice completely remodeled SIS implants by day 25, alpha gal(-/-)mice still exhibited some visible SIS together with inflammatory cellular infiltrates at this time point. Nevertheless, by day 35, the implant site in alpha gal(-/-)mice appeared to be entirely remodeled although a few acute inflammatory cells were still present. Immunization of alpha gal(-/-)mice with sheep erythrocytes to enhance anti-alpha gal antibody levels led to a more robust early inflammatory response following implantation but did not change the ultimate fate of the graft. We conclude that, in contrast to xenotransplantation of whole organs, naturally-occurring anti-alpha gal antibodies do not influence the ability of xenogeneic extracellular matrices to serve as bioscaffolds for tissue remodeling.

Animals↗
PubMed2002

The Th2-restricted immune response to xenogeneic small intestinal submucosa does not influence systemic protective immunity to viral and bacterial pathogens.

Implantation of mice with xenogeneic extracellular matrix (ECM) not only results in tissue remodeling but also elicits a strong Th2 immune response. It is possible that the Th2 cytokines induced by ECM act systemically and result in immune suppression to unrelated antigens. In this case, the recipient would be predisposed to immune dysfunction and have increased susceptibility to various pathogens. The purpose of this study was to determine if ECM implantation does, in fact, influence the immune response to other antigens. Four models were examined to determine the effects of ECM implantation on systemic immunity. In the first model, mice were subcutaneously implanted with porcine small intestinal submucosa (SIS) and immunized with a T-dependent subunit vaccine against influenza virus. The antibody response and protection against lethal infection were then measured. The second model consisted of similar experiments performed using a T-independent polysaccharide vaccine against S. pneumoniae. In the third model, mice were implanted and the cell-mediated response to dinitrofluorobenzene (DNFB) challenge was determined. The fourth model involved examining the influence of SIS implantation on rejection of xenogeneic skin grafts. We found that antibody levels of mice vaccinated against influenza virus or S. pneumoniae were not affected by SIS implantation and these mice did not exhibit increased or decreased susceptibility to either infectious agent. Similarly, mice implanted with ECM showed no cell-mediated immune dysfunction upon challenge with DNFB or xenogeneic skin grafts. The results of this study demonstrate that the Th2-restricted response induced by xenogeneic ECM implantation does not cause generalized immune suppression. Therefore, SIS implantation does not increase susceptibility to viral or bacterial pathogenic agents.

Animals↗