Search PubMed⌕ Search

Biomedical subjects

Martin Schaller

Publications and source records attributed to Martin Schaller.

45 records · Page 3Linked to original sources
PubMed2002

Individual acid aspartic proteinases (Saps) 1-6 of Candida albicans are not essential for invasion and colonization of the gastrointestinal tract in mice.

In order to investigate whether there is a role for individual secreted aspartic proteinases (Saps) of Candida albicans in gastrointestinal infection of mice we compared the differential expression of SAP1-6 genes and production of Sap1-6 proteins with invasion and persistence of SAP knockout strains in the gastrointestinal tract. Using an in vivo expression technology (IVET) we found a high percentage of expression of SAP4-6 genes which increased steadily in the course of infection. Expression of SAP1-3 genes was detected occasionally and in lower percentages than that of SAP4-6 genes. With reverse transcriptase-polymerase chain reaction (RT-PCR), mRNA for SAP 4 and SAP6 were detected in the stomach of all mice, whereas SAP2, SAP3 and SAP5 mRNA were detected not in all animals and SAP1 mRNA was not detectable. Also with immunoelectron microscopy we demonstrated production of Saps1-3 as well as Saps4-6 with antibodies cross-reacting with either Saps1-3 or Saps4-6. In contrast to the fact that gene expression and production of Saps were readily detectable, we were unable to demonstrate differences in the ability to invade the stomach, to disseminate to the brain as well as in the duration of faecal shedding and the number of fungi persisting in the faeces of mice infected with SAP knockout strains in comparison to control strains. We conclude that although Saps were produced, individual Saps were not indispensable factors for virulence during gastrointestinal infection of mice.

Animals↗
PubMed2002

Infection of human oral epithelia with Candida species induces cytokine expression correlated to the degree of virulence.

A defined and balanced immunomodulatory response is crucial for the protection of mucosal surfaces being in contact with pathogenic microorganisms. This study examined the local host response mechanisms of epithelial cells in experimental Candida albicans, C. tropicalis, and C. glabrata infections by measuring the expression of cytokines at the mRNA and protein level. During the course of infection with active but not with heat-killed C. albicans stimulation of the gene expression levels for interleukin-1alpha, interleukin-1beta, tumor necrosis factor, Exodus-2, P-selectin ligand, granulocyte-monocyte colony-stimulating factor, and interleukin-8 was observed by standard and quantitative reverse transcription-polymerase chain reaction. This cytokine pattern may favor a chemotactic and a T helper 1 response. Initial moderate or weak upregulation of these cytokine genes by reverse transcription-polymerase chain reaction was also observed in epithelial infection with the less virulent species C. tropicalis and C. glabrata. Heat-killed C. albicans failed to induce an epithelial immune response. At the protein level, expression of interleukin-8 protein was strongly enhanced during the course of C. albicans infection, whereas lower levels were seen with C. tropicalis and C. glabrata. The different expression patterns of cytokines were associated with differences in virulence of the Candida strains. This study's data, therefore, show a correlation between the virulence potential of pathogenic fungi, possibly mediated by specific virulence factors (such as proteinases), and the secretion of epithelial cytokines and chemokines, which may initiate in vivo a protective T helper 1 immunologic response and contribute to the recruitment of activated leukocytes and lymphocytes to the site of mucosal infection.

Candida albicans↗
PubMed2002

Long-lasting "christmas tree rash" in an adolescent: isotopic response of indeterminate cell histiocytosis in pityriasis rosea?

A 13-year-old girl developed a non-pruritic pityriasis rosea-like rash, which did not respond to topical corticosteroids or UV therapy but persisted for 2 years. The lymphohistiocytic infiltrate in the upper dermis showed mononuclear cells immunoreactive with S100, CD68, factor XIIIa and CD1a. Electron microscopic evaluation of these cells demonstrated lamellated dense bodies but no Birbeck granules, lipid vacuoles or cholesterol crystals. Two diagnoses were made: a primarily clinical diagnosis of generalized eruptive histiocytosis and a more cell-biology-based diagnosis of an indeterminate cell histiocytosis. Three years later, the lesions are showing spontaneous resolution, with loss of erythema and flattening. Our patient's indeterminate cells fulfil Rowden's classical definition (dendritically shaped epidermal non-keratinocytes without identifying cytoplasmic features), as well as Zelger's newer definition (cells with features of both macrophages and dendritic cells). A Christmas tree pattern has not been previously described in indeterminate cell histiocytosis. Development of indeterminate cell histiocytosis in the lesions of a healing pityriasis rosea might explain the unusual distribution pattern. The development of a skin disorder at the site of an unrelated, already healed skin disease is known as an isotopic response. Key

Adolescent↗
PubMed2002

Cytokine expression induced by Candida albicans in a model of cutaneous candidosis based on reconstituted human epidermis.

Skin equivalents based on reconstituted human epidermis have been used recently to establish models for allergic/irritant contact dermatitis and cutaneous candidosis. In the present study the cytokine expression pattern and the morphological alterations in experimental cutaneous candidosis were investigated by RT-PCR and histological analysis. In experimental cutaneous C albicans infection the mRNA expression levels of interleukin (IL)-1a, IL-1beta, IL-8, GM-CSF, Exodus-2, tumour necrosis factor-alpha and PSL (P-selectin ligand) were upregulated. Cytokine profile and histological features of infected skin (separation of keratinocytes, oedema, vacuolisation) were comparable to that seen in experimental contact dermatitis. These immunomodulatory and morphological similarities might reflect a common pathogenesis factor in both diseases.

Candida albicans↗
PubMed2002

Candida albicans hyphal formation and the expression of the Efg1-regulated proteinases Sap4 to Sap6 are required for the invasion of parenchymal organs.

The ability to change between yeast and hyphal cells (dimorphism) is known to be a virulence property of the human pathogen Candida albicans. The pathogenesis of disseminated candidosis involves adhesion and penetration of hyphal cells from a colonized mucosal site to internal organs. Parenchymal organs, such as the liver and pancreas, are invaded by C. albicans wild-type hyphal cells between 4 and 24 h after intraperitoneal (i.p.) infection of mice. In contrast, a hypha-deficient mutant lacking the transcription factor Efg1 was not able to invade or damage these organs. To investigate whether this was due to the inability to undergo the dimorphic transition or due to the lack of hypha-associated factors, we investigated the role of secreted aspartic proteinases during tissue invasion and their association with the different morphologies of C. albicans. Wild-type cells expressed a distinct pattern of SAP genes during i.p. infections. Within the first 72 h after infection, SAP1, SAP2, SAP4, SAP5, SAP6, and SAP9 were the most commonly expressed proteinase genes. Sap1 to Sap3 antigens were found on yeast and hyphal cells, while Sap4 to Sap6 antigens were predominantly found on hyphal cells in close contact with host cells, in particular, eosinophilic leukocytes. Mutants lacking EFG1 had either noticeably reduced or higher expressed levels of SAP4 to SAP6 transcripts in vitro depending on the culture conditions. During infection, efg1 mutants had a strongly reduced ability to produce hyphae, which was associated with reduced levels of SAP4 to SAP6 transcripts. Mutants lacking SAP1 to SAP3 had invasive properties indistinguishable from those of wild-type cells. In contrast, a triple mutant lacking SAP4 to SAP6 showed strongly reduced invasiveness but still produced hyphal cells. When the tissue damage of liver and pancreas caused by single sap4, sap5, and sap6 and double sap4 and -6, sap5 and -6, and sap4 and -5 double mutants was compared to the damage caused by wild-type cells, all mutants which lacked functional SAP6 showed significantly reduced tissue damage. These data demonstrate that strains which produce hyphal cells but lack hypha-associated proteinases, particularly that encoded by SAP6, are less invasive. In addition, it can be concluded that the reduced virulence of hypha-deficient mutants is not only due to the inability to form hyphae but also due to modified expression of the SAP genes normally associated with the hyphal morphology.

Animals↗
PubMed2002

The siderophore iron transporter of Candida albicans (Sit1p/Arn1p) mediates uptake of ferrichrome-type siderophores and is required for epithelial invasion.

The human fungal pathogen Candida albicans contains a close homologue of yeast siderophore transporters, designated Sit1p/Arn1p. We have characterized the function of SIT1 in C. albicans by constructing sit1 deletion strains and testing their virulence and ability to utilize a range of siderophores and other iron complexes. sit1 mutant strains are defective in the uptake of ferrichrome-type siderophores including ferricrocin, ferrichrysin, ferrirubin, coprogen, and triacetylfusarinine C. A mutation of FTR1 did not impair the use of these siderophores but did affect the uptake of ferrioxamines E and B, as well as of ferric citrate, indicating that their utilization was independent of Sit1p. Hemin was a source of iron for both sit1 and ftr1 mutants, suggesting a pathway of hemin uptake distinct from that of siderophores and iron salts. Heterologous expression of SIT1 in the yeast Saccharomyces cerevisiae confirmed the function of Sit1p as a transporter for ferrichrome-type siderophores. The sit1 mutant was defective in infection of a reconstituted human epithelium as a model for human oral mucosa, while the SIT1 strain was invasive. In contrast, both sit1 and SIT1 strains were equally virulent in the mouse model of systemic infection. These results suggest that siderophore uptake by Sit1p/Arn1p is required in a specific process of C. albicans infection, namely epithelial invasion and penetration, while in the blood or within organs other sources of iron, including heme, may be used.

Animals↗
PubMed2001

Different isoforms of secreted aspartyl proteinases (Sap) are expressed by Candida albicans during oral and cutaneous candidosis in vivo.

Distinct isoforms of secreted aspartyl proteinases (Sap) of Candida albicans are important virulence factors for different types of candidosis. Predominant expression of Sap1-3 has been shown to be crucial for superficial infections in experimental mucosal and cutaneous candidosis, whereas Sap4-6 might be important for systemic disease. This in-vivo study investigated Sap expression in two samples from patients with oral candidosis and from cutaneous infection. Two different polyclonal antibodies directed against Sap1-3 and Sap4-6 were used for ultrastructural characterisation of protein localisation and expression. Post-embedding immuno-electron microscopy revealed Sap1-3 and Sap4-6 immunoreactivity in all samples. All C. albicans cells expressed predominantly the proteinases Sap1-3 which were evenly distributed within the cell wall and cytoplasmic membrane. In contrast, Sap4-6 labelling was only evident in a few fungal cells. In particular it was localised at the tips of hyphal cells during invasion. These data suggest a different pathogenetic role for Sap1-3 and Sap4-6 during host-fungal interaction.

Adult↗
PubMed2001

The role and relevance of phospholipase D1 during growth and dimorphism of Candida albicans.

The phosphatidylcholine-specific phospholipase D1 (PLD1) in Saccharomyces cerevisiae is involved in vesicle transport and is essential for sporulation. The gene encoding the homologous phospholipase D1 from Candida albicans (PLD1) was used to study the role of PLD1 in this pathogenic fungus. In vitro and in vivo expression studies using Northern blots and reverse transcriptase-PCR showed low PLD1 mRNA levels in defined media supporting yeast growth and during experimental infection, while enhanced levels of PLD1 transcripts were detected during the yeast to hyphal transition. To study the relevance of PLD1 during yeast and hyphal growth, an essential part of the gene was deleted in both alleles of two isogenic strains. In vitro PLD1 activity assays showed that pld1 mutants produced no detectable levels of phosphatidic acid, the hydrolytic product of PLD1 activity, and strongly reduced levels of diacylglycerol, the product of lipid phosphate phosphohydrolase, suggesting no or a negligible background PLD1 activity in the pld1 mutants. The pld1 mutants showed no growth differences compared to the parental wild-type in liquid complex and minimal media, independent of the growth temperature. In addition, growth rates of pld1 mutants in media with protein as the sole source of nitrogen were similar to growth rates of the wild-type, indicating that secretion of proteinases was not reduced. Chlamydospore formation was normal in pld1 mutants. When germ tube formation was induced in liquid media, pld1 mutants showed similar rates of yeast to hyphal transition compared to the wild-type. However, no hyphae formation was observed on solid Spider medium, and cell growth on cornmeal/Tween 80 medium indicated aberrant morphogenesis. In addition, pld1 mutants growing on solid media had an attenuated ability to invade the agar. In a model of oral candidosis, pld1 mutants showed no attenuation of virulence. In contrast, the mutant was less virulent in two different mouse models. These data suggest that PLD1 is not essential for growth and oral infections. However, they also suggest that a prominent part of the phosphatidic acid and diacylglycerol pools is produced by PLD1 and that the level of these components is important for morphological transitions under certain conditions in C. albicans.

Animals↗