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Biomedical subjects

H Garn

Publications and source records attributed to H Garn.

16 recordsLinked to original sources
PubMed2005

A new approach to an influenza live vaccine: modification of the cleavage site of hemagglutinin.

A promising approach to reduce the impact of influenza is the use of an attenuated, live virus as a vaccine. Using reverse genetics, we generated a mutant of strain A/WSN/33 with a modified cleavage site within its hemagglutinin, which depends on proteolytic activation by elastase. Unlike the wild-type, which requires trypsin, this mutant is strictly dependent on elastase. Both viruses grow equally well in cell culture. In contrast to the lethal wild-type virus, the mutant is entirely attenuated in mice. At a dose of 10(5) plaque-forming units, it induced complete protection against lethal challenge. This approach allows the conversion of any epidemic strain into a genetically homologous attenuated virus.

Animals↗
PubMed2005

Involvement of distal airways in a chronic model of experimental asthma.

BACKGROUND: Bronchial asthma is characterized by chronic airway inflammation and airway remodelling which occurs in both proximal and distal airways. These changes are associated with development of airway hyper-responsiveness and airflow limitation. OBJECTIVE: This study was aimed to analyse whether chronic inhalative allergen challenges in mice lead to morphological and physiological changes comparable with this phenotype. METHODS: For this purpose, BALB/c mice were systemically sensitized to ovalbumin (OVA) followed by aerosol allergen challenges on 2 consecutive days per week for 12 weeks. RESULTS: In chronically challenged mice, tissue inflammation in proximal as well as distal airways was observed with a predominance of lymphocytes within the cellular infiltrate. In contrast, inflammation in the airway lumen decreased over time. These changes were associated by a shift in bronchoalveolar lavage-cytokine levels from IL-4, IL-5 and TNF-alpha production (during the acute phase) towards markedly increased levels of TGF-beta during the chronic phase. Goblet cell hyperplasia and subepithelial fibrosis occurred throughout the airway tree. In terms of lung function, chronically challenged mice developed persistent bronchial hyper-responsiveness and progressive airflow limitation. Six weeks after OVA aerosol discontinuation, airway inflammation still persisted although lung function was normalized. CONCLUSION: These data indicate that our model of chronic aerosol allergen challenges leads to a phenotype of experimental asthma with participation of distal airways and persistence of inflammation thereby resembling many morphological and physiological aspects of human bronchial asthma.

Administration, Inhalation↗
PubMed2003

Impaired recycling of surfactant-like liposomes in type II pneumocytes from injured lungs.

BACKGROUND: Surfactant synthesis and secretion has been shown to be impaired in type II cells from diseased lungs. The mechanism of surfactant lipid recycling, which is an important physiological process in surfactant treatment, was studied in type II cells isolated from injured lungs. METHODS: Different stages of lung injury were induced by exposing rats to 10 ppm nitrogen dioxide (NO(2)) for 3, 20, and 28 days. Type II cells were isolated from these lungs and recycling of (3)H-DPPC labelled surfactant-like liposomes was studied in vitro. RESULTS: Uptake of liposomes (150 micro g/ml) for 20 minutes in the absence and presence of surfactant protein-A (SP-A, 5 micro g/ml) was higher in cells from NO(2) injured lungs (63-78%) than in control cells. There was no difference in liposome uptake between the groups with NO(2) exposure of different duration. After liposome uptake, most of the internalised label remained in the phosphatidylcholine (PC) fraction and increased with duration of exposure to NO(2). After 20 minutes internalisation, cells were allowed to resecrete lipids for a further 20 minute period. In cells from controls and from all stages of lung injury, liposomes that had been internalised in the presence of SP-A were resecreted to a greater extent than those internalised without SP-A. However, cells from lungs exposed to NO(2) resecreted less lipid than cells from control lungs. Again, there was no difference in resecretion between the groups with NO(2) exposure of different duration. CONCLUSION: Type II cells from injured lungs internalise more surfactant-like liposomes than cells from controls, suggesting a putative therapeutic significance to cope with limited alveolar surfactant pools in lung injury.

Animals↗
PubMed2001

Accumulating monocytes in the vasculature of rat renal allografts: phenotype, cytokine, inducible no synthase, and tissue factor mRNA expression.

BACKGROUND: Necrotic patches and hemorrhagic lesions develop in the renal tissue between day 4 and day 5 after transplantation of fully allogeneic DA rat kidneys to LEW recipients. These lesions are at least in part due to destruction and obstruction of blood vessels. Damage of graft endothelial cells and blood coagulation are likely to be mediated by intravascular graft leukocytes. However, this cell population has not been thoroughly characterized before. METHODS: We perfused untreated control kidneys, renal isografts, and allografts on day 4 after transplantation with phosphate-buffered saline/ethylenediaminetetraacetic acid to harvest leukocytes from both the blood stream as well as from the marginal intravascular pool. The mRNA expression of typical products of activated monocytes was analyzed in reverse-transcriptase polymerase chain reaction experiments. Graft monocytes were purified and their immunophenotype was investigated by flow cytometry. RESULTS: Allograft rejection led to a 10-fold increase in the number of intravascular graft leukocytes compared to isografts. A mean number of about 100x10(6) leukocytes was harvested from a single allogeneic kidney, about 73% of these cells were monocytes and most of them displayed an activated phenotype. Compared to isografts, intravascular allograft leukocytes displayed an increased expression of tumor necrosis factor-alpha, inducible NO synthase and tissue factor. CONCLUSIONS: Our study shows that large numbers of activated monocytes accumulate inside allograft vessels. As they express genes the products of which might damage the allograft by inducing cell death or thrombosis, we speculate that they directly participate in allograft destruction.

Animals↗
PubMed2001

Effect of N-acetylcysteine treatment on NO2-impaired type II pneumocyte surfactant metabolism.

Inhalation of nitrogen dioxide (NO2) is known to alter the composition of the bronchoalveolar lavage (BAL) and to impair the surfactant metabolism of type II pneumocytes. However, information is sparse as to whether application of the widely used antioxidant N-acetylcysteine (NAC) is capable of preventing or reducing these alterations. The aim of the study was to investigate if in vivo administration of NAC to NO2-inhaling rats protected BAL parameters and physiology of type II pneumocytes from impairment. For this purpose, rats were exposed to 720 p.p.m. h-1 NO2, that was applied continuously, intermittently or repeatedly. During inhalation one group of rats received saline and the other group received NAC antioxidant (200 mg kg-1, intraperitoneally) once a day. The BAL protein and phospholipid content increased most in the continuously and repeatedly NO2-exposed rats when compared to the controls, while the intermittent exposure did not change these parameters. Application of NAC led to a marked decrease of the protein elevation for the continuously and intermittently exposed groups, but exhibited no influence on the BAL phospholipid. Surprisingly, all NO2 exposure modes elevated the glutathione content (reduced and oxidized) in the BAL. Application of NAC clearly decreased the content of both forms of glutathione in the continuously and the repeatedly NO2-exposed groups. Phospholipid synthesis, measured by choline uptake into type II cells, was increased most after continuous NO2 inhalation. The NAC reduced this increase moderately. Whereas choline uptake by type II cells was obviously stimulated by NO2, the stimulated secretion of phosphatidylcholine from these cells was decreased by this oxidant. Only continuous exposure reduced this activity markedly. The NAC clearly restored the impaired secretion activity in the cells from the continuously NO2-exposed animals. Since the efficacy of NAC in the prevention of NO2-induced impairments in the surfactant system is striking mainly in the continuously exposed group, we suggest that administration of NAC to NO2-induced lung injury partially restores altered BAL components and the impaired physiology of type II pneumocytes.

Acetylcysteine↗
PubMed2000

Chemokine expression during acute rejection of rat kidneys.

During acute rejection of fully allogeneic rat renal allografts, few neutrophil granulocytes are detected, whereas an abundant infiltrate of macrophages and T lymphocytes becomes apparent. The mechanisms leading to this specific pattern of infiltration are not understood. We performed a sequential daily Northern blot analysis of the mRNA expression of the CC-chemokines MCP-1, MIP-1alpha and RANTES and of the CXC-chemokines GRO/KC and MIP-2 in rat renal isografts (LEW --> LEW, n = 1 per day) and allografts during acute rejection (DA --> LEW, n = 3 per day). MCP-1 gene expression strongly increased on days 3-4 after allotransplantation and returned to control levels on day 6. The expression of MIP-1alpha and RANTES continuously rose until day 3-4 and remained stable thereafter. Isografts displayed minor changes in CC-chemokine expression. In contrast to CC-chemokines, GRO/KC was expressed in low amounts during rejection and MIP-2 mRNA remained undetectable. In conclusion, the expression of the CC-chemokines MCP-1, MIP-1 and RANTES was clearly upregulated during rejection, whereas the mRNA of the CXC-chemokines MIP-2 and GRO/KC was not detected at all or remained at low levels. This pattern of chemokine gene expression is in good accordance with the predominant mononuclear leukocyte infiltrate in allografts.

Animals↗
PubMed2000

Experimental silicosis: a shift to a preferential IFN-gamma-based Th1 response in thoracic lymph nodes.

In chronic silicosis, mechanisms leading to lymphocyte activation are still poorly understood, although it is well known that not only the lung but also the draining lymph nodes are affected. In the present study, we investigated T-cell activation by analysis of cytokine expression in the enlarged thoracic lymph nodes of rats 2 mo after an 8-day silica aerosol exposure. In the case of helper T cell (Th) type 1 cytokines, we found a significant increase in interferon (IFN)-gamma mRNA expression, whereas interleukin (IL)-2 expression remained unchanged. In contrast, gene transcription for the Th2-type cytokines IL-4 and IL-10 was diminished. In addition, with use of an in vitro lymphocyte-macrophage coculture system, an enhanced IFN-gamma and a reduced IL-10 release were shown with cells from silicotic animals. With regard to IFN-gamma-inducing cytokines, we observed enhanced IL-12 mRNA levels in vivo, whereas IL-18 gene expression was slightly decreased. These data indicate that a persistent shift toward an IFN-gamma-dominated type 1 (Th1/cytotoxic T cell type 1) T-cell reaction pattern occurred within the thoracic lymph nodes of silicotic animals. Thus a mutual activation of lymphocytes and macrophages may maintain the chronic inflammatory changes that characterize silicosis.

Animals↗
PubMed1999

Differential expression of monocyte chemotactic protein-1 (MCP-1) in transforming rat hepatic stellate cells.

BACKGROUNDS/AIMS: Hepatic stellate cells and infiltrating leukocytes play a key role in the pathogenesis of liver fibrosis. The chronic phase of liver inflammation is characterized by immigrating mononuclear cells. To understand the underlying mechanisms responsible for the attraction of mononuclear cells in the pathogenesis of liver fibrosis, we investigated the inducible production of chemotactic activities in hepatic stellate cells. METHODS: Cultured hepatic stellate cells of different transformation grades and after in vitro transformation to myofibroblast-like cells were stimulated with tumor necrosis factor-a or bacterial lipopolysaccharide. Mononuclear cell attracting chemotactic activities were evaluated by chemotaxis assays, ELISA, and Northern blot analysis. RESULTS: We observed a transformation grade-dependent differential responsiveness of hepatic stellate cells and myofibroblast-like cells. Monocyte chemotactic protein-1 was inducible by tumor necrosis factor-alpha in non-transformed hepatic stellate cells. In contrast, monocyte chemotactic protein-1 was not inducible by bacterial lipopolysaccharide until the cells were fully transformed into myofibroblast-like cells. Despite a delayed onset, the bacterial lipopolysaccharide-inducible monocyte chemotactic protein-1 expression did not depend on an endogenous production of tumor necrosis factor-alpha. CONCLUSIONS: Our results indicate that the tumor necrosis factor-alpha and bacterial lipopolysaccharide-inducible production of chemokines plays a central role in the pathogenesis of liver fibrosis. These data suggest that when hepatic stellate cells have been transformed to a myofibroblast-like cells phenotype, e.g. by chronic injury, the cells become more sensitive to bacterial lipopolysaccharide, which may potentiate the production of chemotactic and fibrogenic mediators. A strong secretion of monocyte chemotactic protein-1 may contribute to the maintenance of an inflammatory infiltrate dominated by mononuclear cells.

Animals↗
PubMed1999

Occupational exposure to high frequency electromagnetic fields and its effect on human immune parameters.

The present study recorded a considerable excess of recommended exposure limits in the vicinity of shortwave diathermy devices used for medical treatment of patients. Different kinds of field probes were used to measure electric and magnetic field strength and the whole body exposure of medical personnel operating shortwave, decimeter wave and microwave units was calculated. To investigate the influence of chronic exposure on the immune system of operators, blood was sampled from physiotherapists working at the above mentioned devices. Eighteen exposed and thirteen control persons, matched by sex and age, were examined. Total leucocyte and lymphocyte counts were performed and leucocytic subpopulations determined by flow cytometry and monoclonal antibodies against surface antigens. In addition, to quantify subpopulations of immunocompetent cells, the activity of lymphocytes was measured. Lymphocytes were stimulated by mitogen phytohemagglutinin and their proliferation measured by a flow cytometric method. No statistically significant differences between the control and exposed persons were found. In both study groups all immune parameters were within normal ranges.

Adult↗
PubMed1998

Histopathological changes in enlarged thoracic lymph nodes during the development of silicosis in rats.

Silicosis is primarily a fibrotic lung disease which also affects the draining lymph nodes. In the present study, we examined the lymph nodes of rats from 2 weeks to 52 weeks after an 8-day silica aerosol exposure. Parallel to the typical silicotic changes in the lungs, profound alterations occurred in both posterior mediastinal lymph nodes. The weight of the lymph nodes progressively increased from 3.5-fold to 35-fold at 52 weeks after silica exposure. The weight increase was accompanied by an early increase of T cells and preferentially of CD4+ cells at 2 weeks, which converted into a B cell increase at 6 weeks. Histologically, a leukocyte influx without apparent structural changes was noted at 2 weeks whereas at 6 weeks, germinal centers and T cell regions were disappearing and macrophages accumulated in granuloma-like structures which were randomly scattered throughout the lymphoid tissue. Within the granulomas, macrophages were detected that carried ingested silica particles without apparent signs of degeneration or apoptosis. At 52 weeks after silica exposure, macrophage granulomas persisted without induction of fibrosis in both lymph nodes, and T and B cells were now evenly distributed within the tissue. These data extend our previous findings on lymphocyte and macrophage activation and indicate that the early and marked disorganization of draining lymph node structures may contribute to the immune abnormalities in silicosis.

Animals↗
PubMed1997

Induction of neutrophil-attracting chemokines in transforming rat hepatic stellate cells.

BACKGROUND & AIMS: Hepatic stellate cells (HSCs) play a key role in the pathogenesis of liver fibrosis. Immigrating leukocytes can potentiate the progression of liver fibrosis by release of fibrogenic mediators and cytotoxic actions. The inducible production of neutrophil chemotactic activities in HSCs was investigated to understand the underlying mechanisms responsible for the attraction of leukocytes in the pathogenesis of liver fibrosis. METHODS: Cultured HSCs of different transformation grades and after transformation to myofibroblasts (MFBs) were stimulated with tumor necrosis factor (TNF)-alpha and lipopolysaccharide (LPS), respectively. Induced leukocyte chemotactic activities were evaluated by chemotaxis assays, enzyme-linked immunosorbent assay, and Northern blot analysis. RESULTS: A transformation grade-dependent differential responsiveness of HSCs and MFBs was observed. TNF-alpha-inducible production of chemotactic mediators increased substantially with advancing transformation. Only transformed MFBs were LPS responsive. Macrophage inflammatory protein 2 was identified as one of the inducible chemokines. CONCLUSIONS: The results suggest that chemokines play an important role in the pathogenesis of liver fibrosis. Proinflammatory cytokines can initiate the production of chemotactic activities. The more HSCs are transformed to MFBs, e.g., by chronic injury, the more sensitive the cells become to LPS, which may lead to a vicious circle of enhanced fibrogenic and chemotactic mediator production.

Animals↗
PubMed1997

T-lymphocyte activation in the enlarged thoracic lymph nodes of rats with silicosis.

Silicosis is primarily a mononuclear cell inflammatory and fibrotic disease of the pulmonary parenchyma. It is known that lung-associated lymph nodes are also affected. To study the involvement of lymphocytes in silicosis, we examined lymph nodes of rats 12 months after an 8-day silica aerosol exposure. We found that 2 thoracic lymph nodes close to the thymus were enormously enlarged in silicotic rats and contained a 49-fold higher cell number than control lymph nodes. The higher cell number was caused by parallel increases in T- and B-lymphocytes, natural killer (NK) cells, and macrophages without change in the relative proportions when compared with control thoracic lymph nodes. By examining interleukin-2 (IL-2) receptor and intercellular adhesion molecule-1 expression, we detected a significantly higher percentage of activated CD8+ T cells and, to a lower degree, of CD4+ T cells in thoracic lymph nodes of silicotic animals. In contrast, no differences in the activation state were found in T cells obtained from cervical or mesenteric lymph nodes of silicotic and control rats. The occurrence of activated T cells in thoracic lymph nodes of silicotic rats was documented further by selectively enhanced interferon-gamma (IFN-gamma) mRNA expression in the absence of IL-2 and IL-4 mRNA changes. These data show that T-lymphocytes of thoracic lymph nodes have become activated with an enhanced IFN-gamma gene transcription which may be an important cause of macrophage activation during silicosis.

Animals↗
PubMed1995

Present knowledge about specific absorption rates inside a human body exposed to radiofrequency electromagnetic fields.

We have compiled results of scientific investigations about the relationship between external field-strengths and specific absorption rates inside the human body. The data were normalized to SAR-values that form the basis for current safety standards. Results were compared to exposure limits given in these standards. This comparison should serve as a reference for the selection of reliable reference levels for personal protection against thermal effects in radiofrequency electromagnetic fields. The need to measure and monitor ankle/wrist currents to protect some exposed workers is explained. The study has also highlighted a scarcity of dosimetric data at frequencies below 3 MHz.

Dose-Response Relationship, Radiation↗
PubMed1994

An improved MTT assay using the electron-coupling agent menadione.

A modification of the MTT based tetrazolium colorimetric assay is described. Using the electron-coupling agent menadione formazan formation by murine splenocytes and P-815 cells was significantly increased whereas dye reduction by macrophages was hardly influenced. These observations suggest that it should be possible to improve the tetrazolium based cytotoxicity assays of murine macrophages against cells of the syngeneic tumour cell line P-815.

Animals↗
PubMed1991

Inhibition of cellular immune reactions by zymosan.

Mice treated intraperitoneally with zymosan showed a strong inhibition of the DTHR (delayed-type hypersensitivity reaction) against sheep erythrocytes (SE), ovalbumin (OA), and alloantigen. Furthermore, the rejection time of skin transplants was nearly doubled while antibody formation against SE was significantly enhanced. When a DTHR against OA and an antibody formation against SE were induced at the same time in the same animals, than the suppressive and stimulating effects cancelled each other. These results are discussed with regard to the sensitivity of lymphocyte subpopulations, which may be different if exposed to phagocytosis-induced oxygen radicals.

Animals↗