Unravelling the interactions of the environmental host Acanthamoeba castellanii with fungi through the recognition by mannose-binding proteins.

Free-living amoebae (FLAs) are major reservoirs for a variety of bacteria, viruses, and fungi. The most studied mycophagic FLA, Acanthamoeba castellanii (Ac), is a potential environmental host for endemic fungal pathogens such as Cryptococcus spp., Histoplasma capsulatum, Blastomyces dermatitides, and Sporothrix schenckii. However, the mechanisms involved in this interaction are poorly understood. The aim of this work was to characterize the molecular instances that enable Ac to interact with and ingest fungal pathogens, a process that could lead to selection and maintenance of possible virulence factors. The interaction of Ac with a variety of fungal pathogens was analysed in a multifactorial evaluation that included the role of multiplicity of infection over time. Fungal binding to Ac surface by living image consisted of a quick process, and fungal initial extrusion (vomocytosis) was detected from 15 to 80 min depending on the organism. When these fungi were cocultured with the amoeba, only Candida albicans and Cryptococcus neoformans were able to grow, whereas Paracoccidioides brasiliensis and Sporothrix brasiliensis displayed unchanged viability. Yeasts of H. capsulatum and Saccharomyces cerevisiae were rapidly killed by Ac; however, some cells remained viable after 48 hr. To evaluate changes in fungal virulence upon cocultivation with Ac, recovered yeasts were used to infect Galleria mellonella, and in all instances, they killed the larvae faster than control yeasts. Surface biotinylated extracts of Ac exhibited intense fungal binding by FACS and fluorescence microscopy. Binding was also intense to mannose, and mass spectrometry identified Ac proteins with affinity to fungal surfaces including two putative transmembrane mannose-binding proteins (MBP, L8WXW7 and MBP1, Q6J288). Consistent with interactions with such mannose-binding proteins, Ac-fungi interactions were inhibited by mannose. These MBPs may be involved in fungal recognition by amoeba and promotes interactions that allow the emergence and maintenance of fungal virulence for animals.

Disseminated histoplasmosis diagnosed in the bone marrow of an HIV-infected patient: First case imported in Tunisia.

Histoplasmosis is a fungal infection caused by a dimorphic fungus, Histoplasma capsulatum. We report a first case of disseminated histoplasmosis in a 34-year-old woman, infected with human immunodeficiency virus (HIV), originating from Ivory Coast and living in Tunisia for 4 years. She was complaining from fever, chronic diarrhoea and pancytopenia. The Histoplasma capsulatum var. capsulatum was identified by direct microscopic examination of the bone marrow. She was treated by Amphotericin B, relayed by itraconazole. Even though a regression of symptoms and normalization of blood cell count (BCC), the patient died in a respiratory distress related to CMV hypoxemic pneumonia.

Vesicular transport in Histoplasma capsulatum: an effective mechanism for trans-cell wall transfer of proteins and lipids in ascomycetes.

Vesicular secretion of macromolecules has recently been described in the basidiomycete Cryptococcus neoformans, raising the question as to whether ascomycetes similarly utilize vesicles for transport. In the present study, we examine whether the clinically important ascomycete Histoplasma capsulatum produce vesicles and utilized these structures to secrete macromolecules. Transmission electron microscopy (TEM) shows transcellular secretion of vesicles by yeast cells. Proteomic and lipidomic analyses of vesicles isolated from culture supernatants reveal a rich collection of macromolecules involved in diverse processes, including metabolism, cell recycling, signalling and virulence. The results demonstrate that H. capsulatum can utilize a trans-cell wall vesicular transport secretory mechanism to promote virulence. Additionally, TEM of supernatants collected from Candida albicans, Candida parapsilosis, Sporothrix schenckii and Saccharomyces cerevisiae documents that vesicles are similarly produced by additional ascomycetes. The vesicles from H. capsulatum react with immune serum from patients with histoplasmosis, providing an association of the vesicular products with pathogenesis. The findings support the proposal that vesicular secretion is a general mechanism in fungi for the transport of macromolecules related to virulence and that this process could be a target for novel therapeutics.

Human macrophages do not require phagosome acidification to mediate fungistatic/fungicidal activity against Histoplasma capsulatum.

Histoplasma capsulatum (Hc) is a facultative intracellular fungus that modulates the intraphagosomal environment to survive within macrophages (Mphi). In the present study, we sought to quantify the intraphagosomal pH under conditions in which Hc yeasts replicated or were killed. Human Mphi that had ingested both viable and heat-killed or fixed yeasts maintained an intraphagosomal pH of approximately 6.4-6.5 over a period of several hours. These results were obtained using a fluorescent ratio technique and by electron microscopy using the 3-(2,4-dinitroanilo)-3'-amino-N-methyldipropylamine reagent. Mphi that had ingested Saccharomyces cerevisae, a nonpathogenic yeast that is rapidly killed and degraded by Mphi, also maintained an intraphagosomal pH of approximately 6.5 over a period of several hours. Stimulation of human Mphi fungicidal activity by coculture with chloroquine or by adherence to type 1 collagen matrices was not reversed by bafilomycin, an inhibitor of the vacuolar ATPase. Human Mphi cultured in the presence of bafilomycin also completely degraded heat-killed Hc yeasts, whereas mouse peritoneal Mphi digestion of yeasts was completely reversed in the presence of bafilomycin. However, bafilomycin did not inhibit mouse Mphi fungistatic activity induced by IFN-gamma. Thus, human Mphi do not require phagosomal acidification to kill and degrade Hc yeasts, whereas mouse Mphi do require acidification for fungicidal but not fungistatic activity.

[Dimorphism and pathogenesis of Histoplasma capsulatum]. / Dimorfismo y patogenia de Histoplasma capsulatum.

Dimorphism and pathogenesis of Hisdistoplasma capsulatum is a dimorphic fungal pathogen with worldwide significance, which causes a broad spectrum of disease. In the saprophytic stage, it lives as a mycelial form consisting of hyphae bearing both macro and microconidia. Infection with H. capsulatum occurs by inhalation of microconidia (1-4 x 2-6 microm) or small mycelia fragments (5-8 microm) in the terminal bronchioles and alveoli of the lung. Inhaled conidia then convert into the yeast form that is responsible for the pathogenesis of histoplasmosis. As a soil fungus with no known requirements for interacting with a mammalian host as a necessary stage of its life cycle, the number of its strategies for successful pathogenesis is particularly remarkable. They include dimorphic mould-yeast transition, entry into host macrophages, subcellular localization, intracellular survival and proliferation during clinically unapparent infection with capacity for reactivation. H. capsulatum became the subject of increasing studies concurrently with the rising prevalence of human immunodeficiency. This paper presents an overall view of advances in the investigation of H. capsulatum dimorphic transition and pathogenesis.

Protective antibodies and endemic dimorphic fungi.

The host response to infection is the outcome of a complex interaction between a microbe and a host's innate and adaptive immune system. In this context, the role of antibody in the endemic mycoses is relatively poorly understood. Recently, a monoclonal antibody to a cell surface protein has been shown to be protective in a murine histoplasmosis model. The findings with Histoplasma capsulatum may provide a paradigm for antibody protection against endemic fungi. This paper reviews the recent data on protective antibody in histoplasmosis and previous data supporting a role for antibody in protective responses in other dimorphic fungi.

Histoplasma capsulatum synthesizes melanin-like pigments in vitro and during mammalian infection.

Melanin is made by several important pathogenic fungi and has been implicated in the pathogenesis of a number of fungal infections. This study investigated whether the thermally dimorphic fungal pathogen Histoplasma capsulatum var. capsulatum produced melanin or melanin-like compounds in vitro and during infection. Growth of H. capsulatum mycelia in chemically defined minimal medium produced pigmented conidia. Growth of H. capsulatum yeast in chemically defined minimal medium with L-3,4-dihydroxyphenylalanine (DOPA) or (-)-epinephrine produced pigmented cells. Treatment of the pigmented cells with proteolytic enzymes, denaturant, and hot concentrated acid yielded dark particles that were similar in size and shape to their respective propagules. Melanin-binding monoclonal antibodies (MAb) labeled pigmented conidia, yeast, and the isolated particles as determined by immunofluorescence microscopy. Electron spin resonance spectroscopy revealed that pigmented yeast cells and particles derived from pigmented cells were stable free radicals consistent with their identification as melanins. Tissues from mice infected with H. capsulatum and from biopsy specimens from a patient with histoplasmosis contained fungal cells that were labeled by melanin-binding MAb. Digestion of infected mouse tissues yielded dark particles that reacted with the melanin-binding MAb and were similar in appearance to H. capsulatum yeast cells. Additionally, sera from infected mice contained antibodies that bound melanin particles. Phenoloxidase activity capable of synthesizing melanin from L-DOPA was detected in cytoplasmic yeast cell extracts. These findings indicate that H. capsulatum conidia and yeast can produce melanin or melanin-like compounds in vitro and that yeast cells can synthesize pigment in vivo. Since melanin is an important virulence factor in other pathogenic fungi, this pigment may have a similar role to play in the pathogenesis of histoplasmosis.

Disseminated histoplasmosis in a sea otter (Enhydra lutris).

Disseminated histoplasmosis was diagnosed in a 4.75-year-old, captive female sea otter (Enhydra lutris). At necropsy, the liver was found to be markedly swollen, with many nodules (4-12 mm in diameter). Histologically, macrophages containing numerous intracellular yeast-like organisms were noted in the liver, spleen, lung and kidney. These organisms were labelled immunohistochemically with anti-histoplasma yeast antibody. Ultrastructurally, the yeast-like organisms, 2-4 microm in diameter, were found within membranous structures in the cytoplasm of macrophages. This is the first confirmed report of disseminated histoplasmosis in sea otters.

Histoplasma capsulatum yeasts are phagocytosed via very late antigen-5, killed, and processed for antigen presentation by human dendritic cells.

Histoplasma capsulatum (Hc) is a facultative, intracellular parasite of world-wide importance. As the induction of cell-mediated immunity to Hc is of critical importance in host defense, we sought to determine whether dendritic cells (DC) could function as a primary APC for this pathogenic fungus. DC obtained by culture of human monocytes in the presence of GM-CSF and IL-4 phagocytosed Hc yeasts in a time-dependent manner. Upon ingestion, the intracellular growth of yeasts within DC was completely inhibited compared with rapid growth within human macrophages. Electron microscopy of DC with ingested Hc revealed that many of the yeasts were degraded as early as 2 h postingestion. In contrast to macrophages, human DC recognized Hc yeasts via the fibronectin receptor, very late Ag-5, and not via CD18 receptors. DC stimulated Hc-specific lymphocyte proliferation in a concentration-dependent manner after phagocytosis of viable and heat-killed Hc yeasts, but greater proliferation was achieved after ingestion of viable yeasts. These data demonstrate that human DC can phagocytose and degrade a fungal pathogen and subsequently process the appropriate Ags for stimulation of lymphocyte proliferation. In vivo, such interactions between DC and Hc may facilitate the induction of cell-mediated immunity.

Inmunolocalización del complejo polisacárido-proteína en ultraestructuras de la fase micelial y levaduriforme de Histoplasma capsulatum / Immunolocalization of the polysaccharide-protein complex (PPCD-Histo) in the Histoplasma capsulatum mycelium and yeast phase ultrastructures

Introducción: El empleo de un antígeno parcialmente purificado denominado complejo polisacárido-proteína desproinizado de Histoplasma capsulatum (CPPD-Histo), utilizado para discriminar la histoplasmosis de diversas micosis pulmonares y otras enfermedades respiratorias en métodos inmunodiagnósticos de alta sensibilidad, ha sido motivo de estudio desde hace años por nuestro grupo de investigación: Objetivo: En este trabajo se planteó conocer la ubicación celular preferencial del antígeno CPPD-Histo, en las diferentes formas y estructuras de las fases micelial y levaduriforme del hongo. Material y métodos: El estudio se desarrolló mediante inmunolocalización con marcaje de oro coloidal para microscopia electrónica, usando anticuerpos primarios CPPD-Histo específicos. Resultados y discusión: La localización en microscopia electrónica mostró mayor concentración del CPPD-Histo en las zonas de mayor grosor de la capa externa de la pared celular de las proyecciones digitiformes de macroconidios, poco marcaje en pared celular de hifas, y una distribución dispersa de la marca en las levaduras. Conclusión: La pared celular de los macroconidios de la fase micelial del hongo es la estructura fúngica con mayor concentración del antígeno CPPD-Histo

Organización de la colección de cepas de Histoplasma capsulatum del Laboratorio de Inmunología de Hongos, Facultad de Medicina, UNAM / Organization of the Histoplasma capsulatum strains collection from the laboratorio de Inmunologia de Hongos, Facultad de Medicina, UNAM

Objetivo: El presente trabajo muestra la organización, los lineamientos y las particularidades de la colección de cepas de Histoplasma capsulatum del laboratorio de Inmunología de Hongos del Departamento de Microbiología y parasitología, de la Facultad de medicina, UNAM. Características de la colección: Está formada por primoaislamientos del hongo a partir de diversas fuentes y distintas procedencias geográficas dentro de la República Mexicana, además de cepas de la república Mexicana, además de cepas de referencia de otros países, características que destacan el aspecto especial y selecto de esta colección

Alterations to the cell wall of Histoplasma capsulatum yeasts during infection of macrophages or epithelial cells.

Many Histoplasma capsulatum strains have alpha-(1,3)-glucan in their cell walls and spontaneously produce variants that lack this polymer. The variants, in contrast to the parents, exist in aberrant shapes within macrophages. Here, the ultrastructure of the parental and variant cell walls was examined. All yeasts had identical electron-lucent, thick walls when grown in broth culture. However, ingestion by either macrophages or hamster trachea epithelial (HTE) cells caused the walls of variants to become electron-dense, thin, and sinuous. Parental strains remained unchanged in macrophages. Within HTE cells inoculated with parental strains, some organisms retained a thick wall and alpha-(1,3)-glucan but appeared to be degrading. In contrast, apparently intact intracellular yeasts had thin, wavy walls lacking alpha-(1,3)-glucan. A microenvironment within HTE cells that is unfavorable for the parental phenotype may trigger this ultrastructural change, potentially explaining why only variant yeasts are harvested from such cultures.

A universal post-embedding protocol for immunogold labelling of osmium-fixed, epoxy resin-embedded tissue.

The authors have found that double etching of epoxy-embedded, ultrathin sections with 3% sodium metaperiodate rendered epitope expression comparable to that obtained with either saturated or half-saturated sodium metaperiodate solutions. In contrast to either of the two more concentrated oxidizing solutions, double etching with 3% sodium metaperiodate neither bleached the specimens nor generated holes in the plastic resin.