Production of prostaglandins and leukotrienes by Paracoccidioides brasiliensis

Paracoccidioides brasiliensis is the causative agent of paracoccidioidomycosis, the most prevalent deep mycosis in Latin America. Production of eicosanoids, including prostaglandins and leukotrienes, during fungal infections is theorized to play a critical role on fungal survival and/or growth as well as on host immune response modulation. Host cells are one source of these mediators; however another potential source may be the fungus itself. The purpose of our study was to assess whether P. brasiliensis strains with different degree of virulence (Pb18, Pb265, PbBT79, Pb192) produce both, prostaglandin E(2) (PGE(2)) and leukotriene B(4) (LTB(4)). Moreover, we asked if P. brasiliensis can use exogenous sources of arachidonic acid (AA), as well as metabolic pathways dependent on cyclooxygenase (COX) and lipoxygenase (5-LO) enzymes, for PGE(2) and LTB(4) production, respectively. Finally, a possible association between these eicosanoids and fungus viability was assessed. We demonstrated, using ELISA assays, that all P. brasiliensis strains, independently of their virulence, produce high PGE(2) and LTB(4) levels after a 4-hour culture, which were reduced after 8 hours. However, in both culture times, higher eicosanoids levels were detected when culture medium was supplemented with exogenous AA. Differently, treatment with indomethacin, a COX inhibitor, or MK886, a 5-LO inhibitor, induces a reduction on PGE(2) and LTB(4) levels, respectively, as well as in fungus viability. The data provide evidence that P. brasiliensis is able to metabolize either endogenous or exogenous AA by pathways that depend on COX and 5-LO enzymes for producing, respectively, PGE(2) and LTB(4) that are critical for its viability.

Clues to the presence of pathogenic fungi in certain environments

The presence of various pathogenic fungi in rather unsuspected hosts and environments has always attracted the attention of the scientific community. Reports on the putative role of animals in fungal infections of humans bear important consequences on public health as well as on the understanding of fungal ecology. Fungi are ubiquitous in nature and their great capacity for adaptation allows them to survive and indeed, to thrive, in plants, trees and other natural substrata. Nonetheless, we are just beginning to learn the significance that these diverse fungal habitats have on the increasing number of immunosuppressed individuals. The accidental or permanent presence of fungi in animals, plants, soils and watercourses should not be taken too lightly because they constitute the source where potential pathogens will be contracted. If those fungal habitats that carry the largest risks of exposure could be defined, if seasonal variations in the production of infectious propagules could be determined, and if their mode of transmission were to be assessed, it would be possible to develop protective measures in order to avoid human infection. Additionally, unsuspected avenues for the exploration of fungal survival strategies would be opened, thus enhancing our capacity to react properly to their advancing limits. This paper explores several ecological connections between human pathogenic fungi and certain animals, trees, waterways and degraded organic materials. The occurrence of such connections in highly endemic areas will hopefully furnish more precise clues to fungal habitats and allow the design of control programs aimed at avoiding human infection.

Prostaglandin E-2 production by high and low virulent strains of Paracoccidioides brasiliensis

The production of prostaglandins (PGs) during fungal infections could be an important suppressor factor of host immune response. Host cells are one source of prostaglandin E-2 (PGE(2)); however another potential source of PGE(2) is the fungal pathogen itself. Thus, both host and fungal PGE2 production is theorized to play a role in pathogenesis, being critical for growth of the fungus and to modulate the host immune response. The purpose of this work was to investigate if high and low virulent strains of Paracoccidioides brasiliensis have the capacity to produce PGE(2) in vitro, and if this production was related to the fungal growth. The results demonstrated that both strains of P. brasiliensis produce high levels of PGE(2) and the treatment with indomethacin, a cyclooxygenase inhibitor, significantly reduced the production of this mediator, as well as the viability of the fungus. Thus, our data indicate that PGE(2) is produced by P. brasiliensis by a cyclooxygenase-dependent metabolic pathway, and its production is required for fungal survival. This discovery reveals an important factor that has potentially great implications for understanding the mechanisms of immune deviation during infection.

Paracoccidioides brasiliensis Uses Endogenous and Exogenous Arachidonic Acid for PGE(x) Production

Paracoccidioides brasiliensis is the agent of paracoccidioidomycosis, the most prevalent deep mycosis in Latin America. Production of eicosanoids during fungal infections plays a critical role on fungal biology as well as on host immune response modulation. The purpose of our study was to assess whether P. brasiliensis strains with different degree of virulence (Pb18, Pb265, Bt79, Pb192) produce prostaglandin E-x (PGE(x)). Moreover, we asked if P. brasiliensis could use exogenous sources of arachidonic acid (AA), as well as metabolic pathways dependent on cyclooxygenase (COX) enzyme, as reported for mammalian cells. A possible association between this prostanoid and fungus viability was also assessed. Our results showed that all strains, independently of their virulence, produce high PGE(x) levels on 4 h culture that were reduced after 8 h. However, in both culture times, higher prostanoid levels were detected after supplementation of medium with exogenous AA. Treatment with indomethacin, a COX inhibitor, induced a reduction on PGEx, as well as in fungus viability. The data provide evidence that P. brasiliensis produces prostaglandin-like molecules by metabolizing either endogenous or exogenous AA. Moreover, the results suggest the involvement of these mediators on fungal viability.

Production of leukotriene B4 by Paracoccidioides brasiliensis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Produção de prostaglandinas e leucotrienos por Paracoccidioides brasiliensis

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Pathogenesis II: Fungal responses to host responses: interaction of host cells with fungi

Most of our knowledge concerning the virulence determinants of pathogenic fungi comes from the infected host, mainly from animal models and more recently from in vitro studies with cell cultures. The fungi usually present intra- and/or extracellular host-parasite interfaces, with the parasitism phenomenon dependent on complementary surface molecules. Among living organisms, this has been characterized as a cohabitation event, where the fungus is able to recognize specific host tissues acting as an attractant, creating stable conditions for its survival. Several fungi pathogenic for humans and animals have evolved special strategies to deliver elements to their cellular targets that may be relevant to their pathogenicity. Most of these pathogens express surface factors that mediate binding to host cells either directly or indirectly, in the latter case binding to host adhesion components such as extracellular matrix (ECM) proteins, which act as 'interlinking' molecules. The entry of the pathogen into the host cell is initiated by fungal adherence to the cell surface, which generates an uptake signal that may induce its cytoplasmic internalization. Once this is accomplished, some fungi are able to alter the host cytoskeletal architecture, as manifested by a rearrangement of microtubule and microfilament proteins, and this can also induce epithelial host cells to become apoptotic. It is possible that fungal pathogens induce modulation of different host cell pathways in order to evade host defences and to foster their own proliferation. For a number of pathogens, the ability to bind ECM glycoproteins, the capability of internalization and the induction of apoptosis are considered important factors in virulence. Furthermore, specific recognition between fungal parasites and their host cell targets may be mediated by the interaction of carbohydrate-binding proteins, e.g., lectins on the surface of one type of cell, probably a parasite, that combine with complementary sugars on the surface of host-cell. These interactions supply precise models to study putative adhesins and receptor-containing molecules in the context of the fungus-host interface. The recognition of the host molecules by fungi such as Aspergillus fumigatus, Paracoccidioides brasiliensis and Histoplasma capsulatum, and their molecular mechanisms of adhesion and invasion, are reviewed in this paper.

Survival of Atta sexdens workers on different food sources

Leaf-cutting ants belonging to the tribe Attini are major herbivores and important agriculture pests in the neotropics, these ants being thought to feed on the sap which exudes from the plant material which they cut and also on the mycelium of a symbiotic fungus that grows on plant material inside their nests in what is called 'the fungus garden'. However, we have found that the survival of Atta sexdens worker ants on leaves, on mycelium. of the ants' symbiotic fungus, Leucoagaricus gongylophorus, or on plant polysaccharides was the same as that of starved A. sexdens, while, conversely, significantly longer survival was achieved by ants fed on the fungus garden material or on some of the products (especially glucose) of the hydrolysis of plant polysaccharides. We found that the fungus garden contained glucose at a higher concentration than that found in leaves or fungal mycelium, and that this glucose was consumed by the ant to the extent that it was probably responsible for up to 50% of the nutritional needs of the workers. The fungus garden contained polysaccharide degrading enzymes (pectinase, amylase, xylanase and cellulase) in proportions similar to that observed in laboratory cultures of L. gongylophorus. It thus appears that A. sexdens workers obtain a significant part of their nutrients from plant polysaccharide hydrolysis products produced by the action of extracellular enzymes released by L. gongylophorus. In this paper we discuss the symbiotic nutrition strategy of A. sexdens workers and brood and the role played by plant polysaccharides in the nutrition of attine ants. (C) 2003 Elsevier B.V. Ltd. All rights reserved.

PATTERNS OF COLONIZATION AND INCIPIENT NEST SURVIVAL IN ACROMYRMEX-NIGER AND ACROMYRMEX-BALZANI (HYMENOPTERA, FORMICIDAE)

Patterns of colonization by queens and incipient nest survival of the leaf-cutting ants Acromyrmex niger and Acromyrmex balzani were studied by means of belt transects and individually marked incipient nests. No relation was found between colony density and the number of colonization attempts. Both species are not claustral, and high rates of queen mortality were attributed to conspecific executions and predation. of other discernable mortality factors, failure of fungal garden establishment was the most important. Only 34 of 296 A. balzani and 13 of 154 A. niger marked colonies were alive at the end of one year. These figures are higher than those reported for species of Atta. These results are contrasted with those of claustral-founding Atta species. Small colonies are occasionally raided by larger colonies which robbed brood.

Differential gene expression by Paracoccidioides brasiliensis in host interaction conditions: Representational difference analysis identifies candidate genes associated with fungal pathogenesis

Paracoccidioides brasiliensis causes infection by the host inhalation of airborne propagules of the mycelia phase of the fungus. These particles reach the lungs, and disseminate to virtually all organs. Here we describe the identification of differentially expressed genes in studies of host-fungus interaction. We analyzed two cDNA populations of P. brasiliensis, one obtained from infected animals and the other an admixture of fungus and human blood thus mimicking the hematologic events of the fungal dissemination. Our analysis identified transcripts differentially expressed. Genes related to iron acquisition, melanin synthesis and cell defense were specially upregulated in the mouse model of infection. The upregulated transcripts of yeast cells during incubation with human blood were those predominantly related to cell wall remodeling/synthesis. The expression pattern of genes was independently confirmed in host conditions, revealing their potential role in the infection process. This work can facilitate functional studies of novel regulated genes that may be important for the survival and growth strategies of P. brasiliensis in humans. (c) 2006 Elsevier Masson SAS. All rights reserved.

Sporothrix schenckii complex biology: environment and fungal pathogenicity

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)