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PubMed1996

Skin and serum reactivity among humans to histoplasmin in the vicinity of a natural focus of Histoplasma capsulatum var. duboisii.

The epidemiology of histoplasmosis duboisii (African histoplasmosis) is not well understood. The present study was carried out to investigate the prevalence of skin sensitivity and to determine by immunodiffusion the presence of antibodies among humans to histoplasmin around a recently discovered natural focus of Histoplasma capsulatum var. duboisii in a bat cave in Ogbunike in the Anambra State of Nigeria. Out of the 40 subjects, all young adults aged 18-30 years, comprising cave guides, traders and farmers examined in the immediate vicinity of the cave, 14 (35.0%) gave a positive skin test. In another population of the same age group, comprising 620 persons, viz. traders, farmers, palm oil workers and some patients attending rural clinics, examined in other nearby areas in Anambra State, 55 (8.8%) reacted positively to histoplasmin. In the immunodiffusion tests, 2 (2.08%) of the 96 school children and 17 (9.4%) of the 181 young adults, including farmers, palm oil workers and traders tested amongst the population around the cave, demonstrated precipitating antibodies to histoplasmin in their sera. Only 5 (0.79%) of the 630 adults of the same age group with similar occupations examined from other areas in Anambra State had precipitating antibodies. Out of another 50 subjects examined, viz.; wood workers, traders, farmers, and school teachers in Nsukka in the Enugu State, two (4.0%) demonstrated antibodies. It is suggested that asymptomatic infections due to the duboisii variety of H. capsulatum may be common in the human population around the cave. A diligent search with the help of local hospitals and public health officials may reveal clinical cases of histoplasmosis duboisii with cutaneous and systemic lesions.

Adolescent↗
PubMed1990

Modifications of the immune response induced by Histoplasma capsulatum products.

To understand the host-parasite relationship in histoplasmosis, mice were inoculated with histoplasmin (HP), the filtrate of aged cultures of Histoplasma capsulatum, and the immune response of these mice towards sheep red blood cells (SRBC) and to trinitrophenyl hapten was studied. The filtrate abrogated completely the primary antibody response to both antigens as measured by the number of spleen hemolytic plaque forming cells when HP was administered at doses greater than 200 micrograms two days before the antigen. Suppression was elicited by HP when it was injected either intravenously, intraperitoneally, or subcutaneously. Inoculation with HP and antigen on the same day did not result in suppression. The secondary antibody response was not modified at any dose. Variation of the response with time was determined by counting the number of rosette forming cells (RFC) to SRBC every two days for a total of 21 days. Antibody-mediated RFC ('B' rosettes) were depressed throughout the experiment, while the number of non 'B', presumably T, RFC did not vary from control values. In animals inoculated with HP alone, high number of RFC were detected on day 11 after HP inoculation, suggesting that HP may have polyclonal activation effects. These results support the possibility that H. capsulatum evades the immune defenses by induction of a suppressive phenomenon in which the afferent limb of the immune response is not involved. This effect appeared to be induced directly by a product of the fungus, instead of by factors generated during the immune response to this microorganism.

Animals↗
PubMed1988

Paraquat induced thiol modulation of Histoplasma capsulatum morphogenesis.

Cysteine metabolism with the subsequent release of anionic thiols has been shown to be involved in yeast cell morphogenesis of the dimorphic, pathogenic fungus Histoplasma capsulatum. Following transfer to fresh medium, intracellular thiol levels during the initial 2-4 h appear to determine the eventual growth form. Mild oxidative stress induced by paraquat (methyl viologen) caused enhanced intracellular and extracellular thiol production and an increase in protein thiol formation. Mildly stressed cells continued to grow in the yeast form. Severe oxidative stress induced by high concentrations of paraquat resulted in lowered thiol production as well as reversion to the alternate mycelial morphology. These results suggest that thiol modulation of intracellular protein status may be involved in morphogenesis of H. capsulatum.

Cysteine↗
PubMed1982

Cysteine-independent and cysteine-requiring yeast-strains of Histoplasma capsulatum.

Recently we described a strain of Histoplasma capsulatum, designated H-35, which is able to grow as yeast on a minimal medium consisting of inorganic salts, glucose and a trace of biotin. Using this strain as a prototrophic wild type we sought auxotrophic mutants. Mutagenized yeast-cells were starved for inorganic sulfate in sulfur-free minimal medium. Sulfate was then added, and growing prototrophic cells were killed by addition of amphotericin B. After 24 hours non-growing auxotrophs were 'rescued' by removal of amphotericin and addition of yeast extract. This 'mutant enrichment' cycle was repeated two additional times, after which the cells were plated on blood agar and 800 yeast-colonies were picked. Seventeen of these yeast-strains required cysteine for growth, as compared with strain H-35, which grew as yeast on minimal medium.

Amphotericin B↗
PubMed1984

Ultrastructural aspects of cytoplasmic ribosomes from Histoplasma capsulatum and Blastomyces dermatitidis as revealed by heavy metal staining.

Cytoplasmic ribosomes were isolated and purified from sonicates of the mycelial and yeastlike growth forms of the pathogenic dimorphic fungi, Histoplasma capsulatum and Blastomyces dermatitidis. Similar ribosomal fractions were prepared from Neurospora crassa and Saccharomyces cerevisiae. These latter organisms were selected as typical filamentous and yeastlike monophasic fungi, and their ribosomes were used as reference standards. High resolution electron microscopy permitted a comparison of both positively and negatively-stained ribosomes to those dehydrated without heavy metal salt. Such studies revealed statistically significant differences in physical dimensions. Cautious interpretations of substructural detail of the various ribosomal preparations suggested both interphasic and interspecies differences.

Blastomyces↗
PubMed1978

Migration inhibition factor study in Histoplasma capsulatum.

Mice sublethally infected with viable Histoplasma capsulatum or immunized with merthiolate-killed yeast phase cells showed decreased mortality on subsequent challenge infection as compared to controls. Migration inhibition (MI) assays using peritoneal and spleen cells from immunized but unchallenged mice showed no parallel correlation with percent mortality. MI assay indices fluctuated without concomitant changes in resistance to challenge injection with live yeast phase cells. Viable vaccines induced greater resistance to challenge infection than killed cells, although both were comparable in sensitizing ability as measured by MI assay techniques with this mouse model.

Animals↗
PubMed1985

Distribution of Histoplasma capsulatum in Amazonian wildlife.

In a survey of 296 sylvatic animals captured from virgin forests in the north-eastern and south-western Amazon of Brazil, Histoplasma capsulatum was isolated, via the indirect hamster inoculation method, from the liver and spleen of four common opossums Didelphis marsupialis and two pacas Agouti paca. The infected animals did not show any clinical symptoms or histopathology. The known Amazonian mammalian species with natural histoplasmosis now total five, the previously reported species being the spiny rat Proechimys guyannensis, the two-toed sloth Choloepus didactylus and the nine-banded armadillo Dasypus novemcinctus.

Animals↗
PubMed1988

Immunosuppression transfer by spleen cells from young to adult mice previous to Histoplasma capsulatum infection.

The passive transfer of spleen cells from 1 month old mice into adult syngeneic mice, abrogates their resistance to histoplasmal infection. This suppressive state was detected in two cell populations, one non-adherent and another adherent with radioresistant characteristics. The transferred spleen cells were treated by different anti-sera: anti-theta, anti-adherent cells (produced in rabbits) and monoclonal anti-Thy 1.2 respectively. The irradiated and non-irradiated adult recipient mice were infected with Histoplasma yeasts utilizing the Lethal Dose50 for 1 month old mice. The infection course was determined by death percentage, the histoplasmosis murine signs and the number of the fungal colony forming units (CFU) from the infected spleens. The results of the anti-sera treatment suggest that non-adherent as well as adherent cells participate in the suppressive phenomena. A lower number of CFU was identified in infected animals which received cells treated with anti-Thy 1.2 anti-sera.

Agglutination Tests↗
PubMed1991

Resistance of Histoplasma capsulatum to killing by human neutrophils. Evasion of oxidative burst and lysosomal-fusion products.

The basis for resistance of yeast form of Histoplasma capsulatum to antifungal activity of human neutrophils was studied. In limiting dilution assays and short term coculture assays human neutrophils were ineffective in killing H. capsulatum whereas Candida albicans was readily killed. By contrast, in a cell free hydrogen peroxide-peroxidase-halide system H. capsulatum was as sensitive to killing as C. albicans. Moreover, lysate of human neutrophils effectively substituted for horse-radish peroxidase in a cell free system for killing H. capsulatum. H. capsulatum elicited significant products of the oxidative burst in human neutrophils as detected by luminol-enhanced chemiluminescence. However, the response was two-fold less (p less than 0.05) than that induced by C. albicans. Transmission electron microscopy studies showed that phagosome-lysosome fusion took place when neutrophils phagocytosed C. albicans or H. capsulatum. Taken together, these findings indicate that, even though H. capsulatum elicits an oxidative burst and phagosome-lysosome fusion within the phagosome, it is capable of evading damage in short term assays.

Cells, Cultured↗
PubMed1981

Selenocystine-resistant mutants of Histoplasma capsulatum.

Cysteine metabolism has been thought to be important to the phenomenon of dimorphism in Histoplasma capsulatum. We sought mutants with genetic blocks in the metabolism of cysteine by selection of colonies resistant to the toxic analogue, selenocystine. The 22 resistant strains thus obtained were all deficient in uptake of cystine from the surrounding medium but were normally able to convert from mycelium to yeast and back again. Furthermore, they had normal quantities of NADH-dependent cystine reductase when this enzyme was measured. We conclude that mutants defective in cystine uptake can be readily obtained by selection of colonies resistant to selenocystine, and that a lesion in cystine-uptake does not appear to affect the phenomenon of dimorphism in this organism.

Cystine↗
PubMed1981

Electron cytochemical evidence for lysosomal-like equivalents in Histoplasma capsulatum.

Electron cytochemical localizations of acid phosphatase, aryl sulfatase, deoxyribonuclease, adenylate cyclase, and c-AMP phosphodiesterase activity sites in thin sections of cells of the two growth phases of the zoopathogenic Histoplasma capsulatum are described and illustrated by transmission electron micrographs. Various activity sites of these enzymes included the cytomembranes of the nucleus, mitochondria, and endoplasmic reticulum. At the same time, electron opaque reaction products were sequestered within membrane-bound, vacuolar regions of the cytosol. These vacuoles may be ontogenically related to membranous or vesicular inclusions commonly seen in thin sections of glutaraldehyde osmium tetroxide-fixed cells. These enzymatically-active vacuoles are believed consistent with previous descriptions of fungal lysosomal-like structures found in certain other fungi. Lysosomal-like vacuoles of H. capsulatum may provide a means of compartmentalization of various hydrolytic enzymes involved in catabolism and mobilization of storage reserves, and perhaps to function as well in other aspects of the life cycle of this important pathogenic dimorphic fungus.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1995

Epididymal histoplasmosis diagnosed by isolation of Histoplasma capsulatum from semen.

An autochthonous case of epididymal histoplasmosis masquerading as tuberculosis in a 55-year-old male patient is reported from India. It was diagnosed by culture of Histoplasma capsulatum from semen and by demonstration of the fungus upon re-examination of epididymal biopsy sections previously misinterpreted as tuberculous granuloma. The patient's main complaints were painful epididymal swelling, occasional fever and cough. He was treated successfully by excision of epididymis and vas deferens combined with amphotericin B therapy. This is believed to be the first case of epididymal histoplasmosis to be reported outside the American continent and the fourth of its type reported in the English literature. The case is also noteworthy in that H. capsulatum was isolated for the first time from semen, and it underlines the importance of mycological culture of semen specimens for diagnosis of genitourinary infections of obscure etiology.

Biopsy↗
PubMed1995

Induction of novel protein synthesis by opsonized Histoplasma capsulatum ingested by murine peritoneal macrophages.

It is known that Histoplasma capsulatum can resist the intraphagolysosomal environment and multiply inside macrophages. This resistance can be closely related to its pathogenicity. The mechanism of this resistance has been investigated, but it has not been clarified as yet. To learn about the metabolic condition of the yeast-form of H. capsulatum (isolates G217B and CDC 105) when ingested by macrophages, we investigated protein synthesis by ingested H. capsulatum with [35S]-methionine labeling. Cycloheximide at 5 to 10 micrograms/ml was used to preferentially inhibit macrophage uptake of [35S]-methionine without affecting H. capsulatum uptake. Protein synthesis by H. capsulatum in medium alone served as a positive control. The negative control consisted of macrophages with ingested heat-killed H. capsulatum. Analysis of cytosols with SDS-PAGE and fluorography disclosed that, respectively for G217B and CDC 105, ingested H. capsulatum synthesized 4 and 5 novel proteins, increased the synthesis of 9 and 17 proteins and decreased the synthesis of 9 and 10 constitutive proteins. Ten of these novel or increased proteins were apparently common to both strains. These metabolic changes in ingested H. capsulatum could reflect its adaptation to the intraphagolysosomal environment of macrophages and its ability to multiply there.

Adaptation, Biological↗
PubMed1993

Two-dimensional immunoelectrophoresis of histoplasmin and a purified polysaccharide-protein antigen of Histoplasma capsulatum.

Crude histoplasmin and a polysaccharide-protein complex (PPC-histo) antigens obtained from culture filtrates of Histoplasma capsulatum were analyzed by single and tandem two-dimensional immunoelectrophoresis (TD-IEP) using a rabbit hyperimmune anti-histoplasmin polyvalent serum. Single TD-IEP showed 14 arc precipitates for histoplasmin. Continuity of arcs 2, 6, and 7, and 9 and 10 was observed, suggesting a different polymeric configuration of the same antigen. This was also confirmed in tandem TD-IEP of histoplasmin with homologous (PPC-histo) and heterologous PPC's from Blastomyces dermatitidis, Paracoccidioides brasiliensis and Coccidioides immitis. Tandem TD-IEP of histoplasmin and PPC-histo displayed a similar antigenic pattern to histoplasmin alone, being arcs 1 and 3 more evident and apparently present only in histoplasmin and PPC-histo. Tandem TD-IEP showed common antigens among the other heterologous fungal purified antigens, and seems useful to observe the multiplicity of antigens present in fungal preparations and to identify those precipitates (arcs 1 and 3) that are predominant in the purified preparation.

Animals↗
PubMedDate not supplied

Deactivation of macrophage oxidative burst in vitro by different strains of Histoplasma capsulatum.

It was previously reported that Histoplasma capsulatum (Hc) yeast not only failed to stimulate a murine macrophage oxidative burst (OB), but they also blunted or abolished OB stimulation by a subsequent encounter with potent stimuli such as zymosan or phorbol 12-myristate 13-acetate (PMA). The present studies show that macrophage deactivation is proportional to the time of incubation and the dose of Hc yeast that induce the deactivated state. Hc yeast derived from a virulent strain (G217B) are more efficient inducers of macrophage deactivation than similar preparations derived from the avirulent Downs Hc strain. Yeast cells of two other pathogenic fungi, Candida albicans and Cryptococcus neoformans are shown to stimulate rather than deactivate a macrophage OB.

Animals↗
PubMed1996

Extracellular proteolytic enzyme activity of Histoplasma capsulatum var. duboisii.

Histoplasma capsulatum var. duboisii is the etiological agent of African histoplasmosis, an important deep mycosis in West Africa. Not much is known about the physiological properties of this fungus. This communication reports on the extracellular proteolytic enzyme activity of this fungus. Five isolates of this fungus tested hydrolyzed azocasein and bovine serum albumin at pH 6.8 and 8.0. Assay of the crude enzyme showed that proteolytic activity increased with age and peaked on the 10th day and then again on the 13th day for the yeast form, and on the 11th day of growth for the mycelial form. The optimum temperature and pH for maximum enzyme activity were 35 degrees C and 6.8 respectively. The proteinase activity was more pronounced with the yeast form than with the mycelial form. The action of enzyme inhibitors suggested the presence of an aspartyl proteinase.

Animals↗
PubMed1995

A temperature-sensitive strain of Histoplasma capsulatum has an altered delta 9-fatty acid desaturase gene.

We have isolated and characterized the delta 9-desaturase gene (Ole1), which codes for a key enzyme involved in regulating membrane fluidity in animal cells and microorganisms, from two strains of Histoplasma capsulatum, one that is temperature-tolerant (G217B) and the other temperature-susceptible (Downs). These pathogenic fungi are dimorphic in that they undergo a morphologic transition from the mycelial to yeast-like form when the temperature of incubation is switched from 25 to 37 degrees C or when they infect a susceptible host. The coding sequences of the two genes, both containing an intron of 93 nucleotides, are virtually identical and analogous to the delta 9-desaturase gene of Saccharomyces cerevisiae and those of the rat, mouse and human. Ole1 transcription of the thermotolerant G217B and thermosensitive Downs strains is similar in yeast phase cells and during the temperature shift down from 34, 37, or 40 to 25 degrees C (yeast-to-mycelia transition). Nevertheless, the delta 9-desaturase gene is transcriptionally inactive in mycelia of G217B at 25 degrees C while it is actively transcribed in the Downs strain at the same temperature. These results are in agreement with the finding that membranes of the Downs strain have a higher level of oleic acid. The differential expression of delta 9-desaturase genes is discussed in relationship to differences in thermosensitivity in the fungal isolates and in regulating the level of expression of heat shock genes.

Amino Acid Sequence↗