Neural crest E-cadherin loss drives cleft lip/palate by epigenetic modulation via pro-inflammatory gene-environment interaction

Gene-environment interactions are believed to play a role in multifactorial phenotypes, although poorly described mechanistically. Cleft lip/palate (CLP), the most common craniofacial malformation, has been associated with both genetic and environmental factors, with little gene-environment interaction experimentally demonstrated. Here, we study CLP families harbouring CDH1/E-Cadherin variants with incomplete penetrance and we explore the association of pro-inflammatory conditions to CLP. By studying neural crest (NC) from mouse, Xenopus and humans, we show that CLP can be explained by a 2-hit model, where NC migration is impaired by a combination of genetic (CDH1 loss-of-function) and environmental (pro-inflammatory activation) factors, leading to CLP. Finally, using in vivo targeted methylation assays, we demonstrate that CDH1 hypermethylation is the major target of the pro-inflammatory response, and a direct regulator of E-cadherin levels and NC migration. These results unveil a gene-environment interaction during craniofacial development and provide a 2-hit mechanism to explain cleft lip/palate aetiology.

Establishment of iPSC lines and zebrafish with loss-of-function AHDC1 variants: models for Xia-Gibbs syndrome

Xia-Gibbs syndrome (XGS) is a syndromic form of intellectual disability caused by heterozygous AHDC1 variants, but the pathophysiological mechanisms underlying this syndrome are still unclear. In this manuscript, we describe the development of two different functional models: three induced pluripotent stem cell (iPSC) lines with different loss-of-function (LoF) AHDC1 variants, derived by reprogramming peripheral blood mononuclear cells from XGS patients, and a zebrafish strain with a LoF variant in the ortholog gene (ahdc1) obtained through CRISPR/Cas9-mediated editing. The three iPSC lines showed expression of pluripotency factors (SOX2, SSEA-4, OCT3/4, and NANOG). To verify the capacity of iPSC to differentiate into the three germ layers, we obtained embryoid bodies (EBs), induced their differentiation, and confirmed the mRNA expression of ectodermal, mesodermal, and endodermal markers using the TaqMan hPSC Scorecard. The iPSC lines were also approved for the following quality tests: chromosomal microarray analysis (CMA), mycoplasma testing, and short tandem repeat (STR) DNA profiling. The zebrafish model has an insertion of four base pairs in the ahdc1 gene, is fertile, and breeding between heterozygous and wild-type (WT) animals generated offspring in a genotypic proportion in agreement with Mendelian law. The established iPSC and zebrafish lines were deposited on the hpscreg.eu and zfin.org platforms, respectively. These biological models are the first for XGS and will be used in future studies that investigate the pathophysiology of this syndrome, unraveling its underlying molecular mechanisms.

DNA methylation of the promoter region at the CREB1 binding site is a mechanism for the epigenetic regulation of brain-specific PKMζ

Protein kinase M zeta, PKMζ, is a brain enriched kinase with a well characterized role in Long-Term Potentiation (LTP), the activity-dependent strengthening of synapses involved in long-term memory formation. However, little is known about the molecular mechanisms that maintain the tissue specificity of this kinase. Here, we characterized the epigenetic factors, mainly DNA methylation, regulating PKMζ expression in the human brain. The PRKCZ gene has an upstream promoter regulating Protein kinase C ζ (PKCζ), and an internal promoter driving PKMζ expression. A demethylated region, including a canonical CREB binding site, situated at the internal promoter was only observed in human CNS tissues. The induction of site-specific hypermethylation of this region resulted in decreased CREB1 binding and downregulation of PKMζ expression. Noteworthy, CREB binding sites were absent in the upstream promoter of PRKCZ locus, suggesting a specific mechanism for regulating PKMζ expression. These observations were validated using a system of human neuronal differentiation from induced pluripotent stem cells (iPSCs). CREB1 binding at the internal promoter was detected only in differentiated neurons, where PKMζ is expressed. The same epigenetic mechanism in the context of CREB binding site was identified in other genes involved in neuronal differentiation and LTP. Additionally, aberrant DNA hypermethylation at the internal promoter was observed in cases of Alzheimer's disease, correlating with decreased expression of PKMζ in patient brains. Altogether, we present a conserved epigenetic mechanism regulating PKMζ expression and other genes enhanced in the CNS with possible implications in neuronal differentiation and Alzheimer's disease.

mir152 hypomethylation as a mechanism for non-syndromic cleft lip and palate

Non-syndromic cleft lip with or without cleft palate (NSCLP), the most common human craniofacial malformation, is a complex disorder given its genetic heterogeneity and multifactorial component revealed by genetic, epidemiological, and epigenetic findings. Epigenetic variations associated with NSCLP have been identified; however, functional investigation has been limited. Here, we combined a reanalysis of NSCLP methylome data with genetic analysis and used both in vitro and in vivo approaches to dissect the functional effects of epigenetic changes. We found a region in mir152 that is frequently hypomethylated in NSCLP cohorts (21-26%), leading to mir152 overexpression. mir152 overexpression in human neural crest cells led to downregulation of spliceosomal, ribosomal, and adherens junction genes. In vivo analysis using zebrafish embryos revealed that mir152 upregulation leads to craniofacial cartilage impairment. Also, we suggest that zebrafish embryonic hypoxia leads to mir152 upregulation combined with mir152 hypomethylation and also analogous palatal alterations. We therefore propose that mir152 hypomethylation, potentially induced by hypoxia in early development, is a novel and frequent predisposing factor to NSCLP.

Neuroprogenitor Cells From Patients With TBCK Encephalopathy Suggest Deregulation of Early Secretory Vesicle Transport

Biallelic pathogenic variants in TBCK cause encephaloneuropathy, infantile hypotonia with psychomotor retardation, and characteristic facies 3 (IHPRF3). The molecular mechanisms underlying its neuronal phenotype are largely unexplored. In this study, we reported two sisters, who harbored biallelic variants in TBCK and met diagnostic criteria for IHPRF3. We provided evidence that TBCK may play an important role in the early secretory pathway in neuroprogenitor cells (iNPC) differentiated from induced pluripotent stem cells (iPSC). Lack of functional TBCK protein in iNPC is associated with impaired endoplasmic reticulum-to-Golgi vesicle transport and autophagosome biogenesis, as well as altered cell cycle progression and severe impairment in the capacity of migration. Alteration in these processes, which are crucial for neurogenesis, neuronal migration, and cytoarchitecture organization, may represent an important causative mechanism of both neurodevelopmental and neurodegenerative phenotypes observed in IHPRF3. Whether reduced mechanistic target of rapamycin (mTOR) signaling is secondary to impaired TBCK function over other secretory transport regulators still needs further investigation.

Modeling Early Neural Crest Development via Induction from hiPSC-Derived Neural Plate Border-like Cells

Neural crest cells (NCCs) are a multipotent and transient cell population that gives rise to many important tissues during human embryogenesis. Disturbances that occur during NCCs development may lead to numerous types of diseases and syndromes, which are called neurocristopathies. NCCs in vitro modeling enables the access to cellular, genetic, and biochemical information about the neural crest development and its derivatives. By using cells derived from patients with neurocristopathies it is possible to study the cellular and genetic mechanisms behind each disease in a specific and trustworthy manner, as well as to contribute to the development of prospective treatments. Here, we describe a protocol of 19 days, capable of efficiently generating NCCs from human induced pluripotent stem cells (hiPSCs). This differentiation process recapitulates the intermediate stage of neural plate border-like cells (NBCs), the epithelial to mesenchymal transition (EMT), and enables further generation of NCCs derivatives, such as Schwann cells, smooth muscle cells, melanocytes, peripheral neurons, adipocytes, osteoblasts, and chondrocytes.

A Novel Saliva RT-LAMP Workflow for Rapid Identification of COVID-19 Cases and Restraining Viral Spread

Rapid diagnostics is pivotal to curb SARS-CoV-2 transmission, and saliva has emerged as a practical alternative to naso/oropharyngeal (NOP) specimens. We aimed to develop a direct RT-LAMP (reverse transcription loop-mediated isothermal amplification) workflow for viral detection in saliva, and to provide more information regarding its potential in curbing COVID-19 transmission. Clinical and contrived specimens were used to optimize formulations and sample processing protocols. Salivary viral load was determined in symptomatic patients to evaluate the clinical performance of the test and to characterize saliva based on age, gender and time from onset of symptoms. Our workflow achieved an overall sensitivity of 77.2% (n = 90), with 93.2% sensitivity, 97% specificity, and 0.895 Kappa for specimens containing >102 copies/μL (n = 77). Further analyses in saliva showed that viral load peaks in the first days of symptoms and decreases afterwards, and that viral load is ~10 times lower in females compared to males, and declines following symptom onset. NOP RT-PCR data did not yield relevant associations. This work suggests that saliva reflects the transmission dynamics better than NOP specimens, and reveals gender differences that may reflect higher transmission by males. This saliva RT-LAMP workflow can be applied to track viral spread and, to maximize detection, testing should be performed immediately after symptoms are presented, especially in females.

Novel USP9X variant associated with syndromic intellectual disability in a female: A case study and review

Heterozygous variants in USP9X are associated with female-restricted X-linked mental retardation (MRXS99F), a rare syndrome characterized by neurodevelopmental delay, intellectual disability (ID), and a wide variety of additional congenital anomalies. Here, we report a girl harboring a novel de novo loss-of-function variant in USP9X (c.4091delinsAG, p.Thr1364Lysfs*7), and literature review revealed novel prenatal features associated with MRXS99F, expanding the genotypic and phenotypic landscape of the syndrome. It is important to consider X-linked diseases in girls with ID and perform directed molecular investigation to provide correct diagnosis and prognosis.

Recapitulation of Neural Crest Specification and EMT via Induction from Neural Plate Border-like Cells

Neural crest cells (NCCs) contribute to several tissues during embryonic development. NCC formation depends on activation of tightly regulated molecular programs at the neural plate border (NPB) region, which initiate NCC specification and epithelial-to-mesenchymal transition (EMT). Although several approaches to investigate NCCs have been devised, these early events of NCC formation remain largely unknown in humans, and currently available cellular models have not investigated EMT. Here, we report that the E6 neural induction protocol converts human induced pluripotent stem cells into NPB-like cells (NBCs), from which NCCs can be efficiently derived. NBC-to-NCC induction recapitulates gene expression dynamics associated with NCC specification and EMT, including downregulation of NPB factors and upregulation of NCC specifiers, coupled with other EMT-associated cell-state changes, such as cadherin modulation and activation of TWIST1 and other EMT inducers. This strategy will be useful in future basic or translational research focusing on these early steps of NCC formation.

Discordant congenital Zika syndrome twins show differential in vitro viral susceptibility of neural progenitor cells

Congenital Zika syndrome (CZS) causes early brain development impairment by affecting neural progenitor cells (NPCs). Here, we analyze NPCs from three pairs of dizygotic twins discordant for CZS. We compare by RNA-Seq the NPCs derived from CZS-affected and CZS-unaffected twins. Prior to Zika virus (ZIKV) infection the NPCs from CZS babies show a significantly different gene expression signature of mTOR and Wnt pathway regulators, key to a neurodevelopmental program. Following ZIKV in vitro infection, cells from affected individuals have significantly higher ZIKV replication and reduced cell growth. Whole-exome analysis in 18 affected CZS babies as compared to 5 unaffected twins and 609 controls excludes a monogenic model to explain resistance or increased susceptibility to CZS development. Overall, our results indicate that CZS is not a stochastic event and depends on NPC intrinsic susceptibility, possibly related to oligogenic and/or epigenetic mechanisms.

Zika virus (ZIKV) infection can cause congenital Zika syndrome (CZS), but the underlying mechanisms are poorly understood. Here, the authors generate neural progenitor cells from dizygotic twins with a discordant phenotype regarding CZS and study their response to ZIKV infection.

CD105 is regulated by hsa-miR-1287 and its expression is inversely correlated with osteopotential in SHED

A more accurate understanding of the molecular mechanisms and signaling pathways underpinning human mesenchymal stem cell (MSC) plasticity and differentiation properties is pivotal for accomplishing solid and diligent translation of MSC-based experimental therapeutics and clinical trials to broad clinical practice. In addition, this knowledge enables selection of MSC subpopulations with increased differentiation potential and/or use of exogenous factors to boost this potential. Here, we report that CD105 (ENG) is a predictive biomarker of osteogenic potential in two types of MSCs: stem cells from human exfoliated deciduous teeth (SHED) and human adipose-derived stem cells (hASC). We also validate that CD105 can be used to select and enrich for subpopulations of SHED and hASC with higher in vitro osteogenic potential. In addition, we show that hsa-mir-1287 regulates CD105 expression, and propose that fine-tuning hsa-mir-1287 levels could be used to control osteopotential in SHED. These findings provide better discernment of the molecular bases behind MSC osteogenic plasticity and open up new perspectives to leverage osteogenic potential in MSCs by modulation of a specific miRNA.

Rare Variants in the Epithelial Cadherin Gene Underlying the Genetic Etiology of Nonsyndromic Cleft Lip with or without Cleft Palate

Nonsyndromic orofacial cleft (NSOFC) is a complex disease of still unclear genetic etiology. To investigate the contribution of rare epithelial cadherin (CDH1) gene variants to NSOFC, we target sequenced 221 probands. Candidate variants were evaluated via in vitro, in silico, or segregation analyses. Three probably pathogenic variants (c.760G>A [p.Asp254Asn], c.1023T>G [p.Tyr341*], and c.2351G>A [p.Arg784His]) segregated according to autosomal dominant inheritance in four nonsyndromic cleft lip with or without cleft palate (NSCL/P) families (Lod score: 5.8 at θ = 0; 47% penetrance). A fourth possibly pathogenic variant (c.387+5G>A) was also found, but further functional analyses are needed (overall prevalence of CDH1 candidate variants: 2%; 15.4% among familial cases). CDH1 mutational burden was higher among probands from familial cases when compared to that of controls (P = 0.002). We concluded that CDH1 contributes to NSCL/P with mainly rare, moderately penetrant variants, and CDH1 haploinsufficiency is the likely etiological mechanism.

Susceptibility to DNA damage as a molecular mechanism for non-syndromic cleft lip and palate

Non-syndromic cleft lip/palate (NSCL/P) is a complex, frequent congenital malformation, determined by the interplay between genetic and environmental factors during embryonic development. Previous findings have appointed an aetiological overlap between NSCL/P and cancer, and alterations in similar biological pathways may underpin both conditions. Here, using a combination of transcriptomic profiling and functional approaches, we report that NSCL/P dental pulp stem cells exhibit dysregulation of a co-expressed gene network mainly associated with DNA double-strand break repair and cell cycle control (p = 2.88×10(-2)-5.02×10(-9)). This network included important genes for these cellular processes, such as BRCA1, RAD51, and MSH2, which are predicted to be regulated by transcription factor E2F1. Functional assays support these findings, revealing that NSCL/P cells accumulate DNA double-strand breaks upon exposure to H2O2. Furthermore, we show that E2f1, Brca1 and Rad51 are co-expressed in the developing embryonic orofacial primordia, and may act as a molecular hub playing a role in lip and palate morphogenesis. In conclusion, we show for the first time that cellular defences against DNA damage may take part in determining the susceptibility to NSCL/P. These results are in accordance with the hypothesis of aetiological overlap between this malformation and cancer, and suggest a new pathogenic mechanism for the disease.

Human stem cell cultures from cleft lip/palate patients show enrichment of transcripts involved in extracellular matrix modeling by comparison to controls

Nonsyndromic cleft lip and palate (NSCL/P) is a complex disease resulting from failure of fusion of facial primordia, a complex developmental process that includes the epithelial-mesenchymal transition (EMT). Detection of differential gene transcription between NSCL/P patients and control individuals offers an interesting alternative for investigating pathways involved in disease manifestation. Here we compared the transcriptome of 6 dental pulp stem cell (DPSC) cultures from NSCL/P patients and 6 controls. Eighty-seven differentially expressed genes (DEGs) were identified. The most significant putative gene network comprised 13 out of 87 DEGs of which 8 encode extracellular proteins: ACAN, COL4A1, COL4A2, GDF15, IGF2, MMP1, MMP3 and PDGFa. Through clustering analyses we also observed that MMP3, ACAN, COL4A1 and COL4A2 exhibit co-regulated expression. Interestingly, it is known that MMP3 cleavages a wide range of extracellular proteins, including the collagens IV, V, IX, X, proteoglycans, fibronectin and laminin. It is also capable of activating other MMPs. Moreover, MMP3 had previously been associated with NSCL/P. The same general pattern was observed in a further sample, confirming involvement of synchronized gene expression patterns which differed between NSCL/P patients and controls. These results show the robustness of our methodology for the detection of differentially expressed genes using the RankProd method. In conclusion, DPSCs from NSCL/P patients exhibit gene expression signatures involving genes associated with mechanisms of extracellular matrix modeling and palate EMT processes which differ from those observed in controls. This comparative approach should lead to a more rapid identification of gene networks predisposing to this complex malformation syndrome than conventional gene mapping technologies.

Alveolar osseous defect in rat for cell therapy: preliminary report

PURPOSE: To study were to reproduce an alveolar bone defect model in Wistar rats to be used for testing the efficacy of stem cell therapies. Additionally, we also aimed to determine the osteogenesis process of this osseous defect in the 1 month period post-surgery. METHODS: The animals were randomly divided into two groups of 7 animals each. A gingivobuccal incision was made, and a bone defect of 28 mm² of area was performed in the alveolar region. Animals were killed at 2 weeks after surgery (n=7) and 4 weeks after surgery (n=7). RESULTS: The average area of the alveolar defect at time point of 2 weeks was 22.27 ± 1.31 mm² and the average area of alveolar defect at time point of 4 weeks was 9.03 ± 1.17 mm². The average amount of bone formation at time point of 2 weeks was 5.73 ± 1.31 mm² and the average amount of bone formation at time point of 4 weeks was 19 ± 1.17 mm². Statistically significant differences between the amount of bone formation at 2 weeks and 4 weeks after surgery were seen (p=0.003). CONCLUSION: The highest rate of ossification occurred mostly from 2 to 4 weeks after surgery. This observation suggests that 4 weeks after the bone defect creation should be a satisfactory timing to assess the potential of bone inductive stem cells to accelerate bone regeneration in Wistar rats.

New source of muscle-derived stem cells with potential for alveolar bone reconstruction in cleft lip and/or palate patients

Cleft lip and palate (CLP), one of the most frequent congenital malformations, affects the alveolar bone in the great majority of the cases, and the reconstruction of this defect still represents a challenge in the rehabilitation of these patients. One of the current most promising strategy to achieve this goal is the use of bone marrow stem cells (BMSC); however, isolation of BMSC or iliac bone, which is still the mostly used graft in the surgical repair of these patients, confers site morbidity to the donor. Therefore, in order to identify a new alternative source of stem cells with osteogenic potential without conferring morbidity to the donor, we have used orbicular oris muscle (OOM) fragments, which are regularly discarded during surgery repair (cheiloplasty) of CLP patients. We obtained cells from OOM fragments of four unrelated CLP patients (CLPMDSC) using previously described preplating technique. These cells, through flow cytometry analysis, were mainly positively marked for five mesenchymal stem cell antigens (CD29, CD90, CD105, SH3, and SH4), while negative for hematopoietic cell markers, CD14, CD34, CD45, and CD117, and for endothelial cell marker, CD31. After induction under appropriate cell culture conditions, these cells were capable to undergo chondrogenic, adipogenic, osteogenic, and skeletal muscle cell differentiation, as evidenced by immunohistochemistry. We also demonstrated that these cells together with a collagen membrane lead to bone tissue reconstruction in a critical-size cranial defects previously induced in nonimmunocompromised rats. The presence of human DNA in the new bone was confirmed by PCR with human-specific primers and immunohistochemistry with human nuclei antibodies. In conclusion, we showed that cells from OOM have phenotypic and behavior characteristics similar to other adult stem cells, both in vitro and in vivo. Our findings suggest that these cells represent a promising source of stem cells for alveolar bone grafting treatment, particularly in young CLP patients.

Molecular basis for the selective toxicity of amphotericin B for yeast and filipin for animal cells

Among the polyene antibiotics, many, like filipin, cannot be used clinically because they are toxic; amphotericin B, however, is useful in therapy of human fungal infections because it is less toxic. Both the toxicity of filipin and the therapeutic value of amphotericin B can be rationalized at the cellular and molecular level by the following observations: (i) these polyene antibiotics showed differential effects on cells; filipin was more potent in lysing human red blood cells, whereas amphotericin B was more potent in inhibiting yeast cell growth; and (ii) the effects of filipin were more efficiently inhibited by added cholesterol, the major membrane sterol in human cells, whereas the effects of amphotericin B were more efficiently inhibited by ergosterol, the major membrane sterol in yeast. The simplest inference is that the toxicity and effectiveness of polyenes are determined by their relative avidities for the predominant sterol in cell membranes.

Deuterium NMR investigation of an amphotericin B derivative in mechanically aligned lipid bilayers

The methyl-d(3) amide derivative of the polyene antibiotic amphotericin B was synthesized, assayed for biological activity, incorporated into mechanically aligned bilayers of dipalmitoylphosphatidylcholine (DPPC), and examined by deuterium and phosphorus NMR. The amide derivative has a lesser, but qualitatively similar, biological activity relative to amphotericin B. Incorporation of the amide derivative and ergosterol into aligned DPPC bilayers resulted in a single, stable bilayer phase, as shown by phosphorus NMR of the DPPC headgroups. Deuterium NMR spectra revealed one major (2)H quadrupolar splitting and one major (2)H-(1)H dipolar splitting in the liquid-crystalline phase, consistent with a high degree of alignment and a single, averaged physical state for amphotericin B methyl-d(3) amide in the bilayer. Variations of the quadrupolar and dipolar splittings as a function of macroscopic sample orientation and temperature indicated that the amide derivative undergoes fast rotation about a motional axis that is parallel to the bilayer normal.

Stress proteins in fungal diseases

Heat shock proteins (hsps) are ubiquitous families of proteins, found in all organisms studied so far. They are highly conserved across the species barrier and serve fundamental functions in cell physiology. The term 'heat shock' was adopted because of the early observation of the heat-inducible nature of these proteins, although, as it is now realized that they can be induced by a variety of stressful stimuli, it is probably more appropriate to call them 'stress proteins'. The nomenclature of many hsps, for example hsp90, hsp70 and hsp60, reflects the approximate molecular mass of hsps within each of these families. For many bacterial and parasitic infections, hsps were first recognized as immunodominant antigens on immunoblots of extracts from the organism probed with immune sera, or in T-cell proliferation assays. They have now been identified in a range of fungal pathogens, again often linked to an immune response. In this symposium, we review the association of hsps with humoral immunity to candidosis and aspergillosis, cellular immunity to histoplasmosis, and the identification of hsp70 in another dimorphic fungus, Paracoccidioides brasiliensis. Finally, the crucial role of the membrane in setting the temperature of the heat shock response in yeasts is discussed.

An homologue of the human 100-kDa protein (p100) is differentially expressed by Histoplasma capsulatum during infection of murine macrophages

Using differential display reverse transcription-PCR (DDRT-PCR) we have identified several sequences that are specifically expressed by Histoplasma capsulatum during infection of murine macrophages (MPhi). Here, we report the characterization of a clone, pHc12, identified as a differentially expressed gene 1 hour after infection of MPhi. Screening of a cDNA library of H. capsulatum allowed us to isolate a clone, pHc12-E, that contains the complete coding sequence. We show that after infection the level of transcription of this gene increases about 5 fold. Analysis of its sequence revealed the presence of an open reading frame of 890 aa (ORF890) that shares respectively 30 and 33% identity with human and Caenorhabditis elegans p100 kD and rat p105 kD co-activator proteins. Using the two-dimensional Hydrophobic Cluster Analysis (HCA) method, we showed that H. capsulatum ORF890 and p100 kD co-activator proteins are clearly related. The H. capsulatum protein consists of a four-fold repeated module (domains I to IV) like the p100 kD co-activator proteins, whose three-dimensional (3D) structure is related to staphylococcal thermonuclease, followed by a modified fifth "hybrid" domain which partially resembles the structure of the tudor domain found in multiple copies in the Drosophila melanogaster tudor protein. These data strongly suggest that ORF890 is homologous to human p100 kD and that this protein, named Hcp100, may play an essential role during infection by co-activating the expression of specific genes.

Characterization of a single group I intron in the 18S rRNA gene of the pathogenic fungus Histoplasma capsulatum

A 425-bp insertion in Histoplasma capsulatum strain G186B, denoted as Hc.SSU.1, was identified as a group I intron, based on the presence of the conserved sequence elements P, Q, R and S and a predicted secondary structure consistent for group I introns. The Hc. SSU.1 sequence from strain G186B was identical to strain G184B but differed from strain FLs1 by five nucleotides. Hc.SSU.1 was most similar to the group I intron from the black mould Exophiala castellanii. Southern blot analysis suggests that the intron is not dispersed in the genome and that most, if not all 18S rRNA genes harbour the intron. Northern blots demonstrated absence of the intron from mature 18S rRNA. A Hc.SSU.1-specific PCR assay detected the intron in six of 37 isolates of Histoplasma. Hc.SSU.1-containing strains exhibited no significant differences in antimicrobial susceptibilities when compared to isolates not containing Hc.SSU.1. This investigation demonstrates the existence of group I intron sequences in the H. capsulatum genome and its evolutionary relationship among other group I intron sequences.

Identification and isolation by DDRT-PCR of genes differentially expressed by Histoplasma capsulatum during macrophages infection

Establishment of infection and disease implies modifications in the genetic programmes of the cell systems that are involved and the differential expression of genes in both parasite and host. In order to identify and isolate relevant genes of the fungus, Histoplasma capsulatum, in which expression is specifically induced during its interaction with murine macrophages (Mphi), we performed a comparative analysis of the pattern of gene expression of the fungus before and after exposure to, and internalization into Mphi by using differential display reverse transcriptase-PCR (DDRT-PCR). Using a limited set of primer combinations, six cDNA fragments of H. capsulatum were identified and isolated; five representing fungal genes in which expressions were enhanced during Mphi infection, whereas one mRNA fragment was down-regulated. Slot blots followed by Northern blot analyses confirmed that the transcripts detected with cDNA clones were over expressed after 1 h of Mphi infection, whereas no transcripts were detected with mRNA purified from H. capsulatum before infection. Sequence analyses and database searches revealed no significant homology to any known sequence for five of these clones. One of the clones showed homology to the rat p105 kD protein, and to the p100 kD co-activator proteins of human and Caenorhabditis elegans. To our knowledge, this is the first experimental evidence that specific genes are differentially expressed by a fungal pathogen when it is exposed to, and phagocytosed by Mphi. Furthermore, these results show that the DDRT-PCR procedure has adequate sensitivity to detect fungal genes induced during parasite-host interaction to identify potential new targets that can be used to develop new antifungal drugs.

Molecular cloning and characterization of a recombinant Histoplasma capsulatum antigen for antibody-based diagnosis of human histoplasmosis

Immunological cross-reactivity among fungi has hampered the development of specific serodiagnostic assays for histoplasmosis. We report the molecular cloning and characterization of a Histoplasma capsulatum cDNA (GH17) that encodes an antigen with immunodiagnostic potential. GH17 is an 810-bp cDNA which encodes a protein of 211 amino acid residues. The GH17 sequence has almost no significant homology with other sequences in GenBank. Southern blot analysis suggests that GH17 is confined to a single location in the genomic DNA of H. capsulatum. Immunoblots indicated that the protein product of GH17 (expressed as a 140-kDa beta-galactosidase fusion protein) was recognized by antibodies in 18 of 18 sera from histoplasmosis patients, but not by antibodies in sera from patients or animals infected with other fungi. GH17 was expressed in a prokaryotic expression vector, pPROEX-1, and recombinant protein was purified by preparative electrophoresis. Antibodies raised to this protein bound to a 60-kDa native antigen in immunoblots of H. capsulatum yeast antigen extract. These results suggest that GH17 encodes an H. capsulatum antigen that may be useful for the diagnosis of histoplasmosis in humans.

An AP1 element is involved in transcriptional regulation of delta9-desaturase gene of Histoplasma capsulatum

We have characterized a region of the promoter of a cloned delta9-desaturase gene (Ole1) of Histoplasma capsulatum, a dimorphic pathogenic fungus of humans. The product of the delta9-desaturase gene is involved in regulating membrane fluid state in animal cells and microorganisms. To identify sequences critical for Ole1 expression in both the saprobic mycelial and parasitic yeast phases of this organism, we performed a deletion analysis. Evidence is presented that a 240 nt region of the proximal promoter is involved in a phase-specific binding in vitro. By sequence analysis we have identified one likely regulatory element that coincides with an AP1 binding site (TGACTAA) that is located at -740 nt of 5'-upstream from the ATG. Using gel mobility shift assays, we show that this cis-acting element binds nuclear proteins extracted from the yeast and mycelial phases of H. capsulatum that may participate in control of expression of the delta9-desaturase gene.

Membrane lipid perturbation modifies the set point of the temperature of heat shock response in yeast

Addition of a saturated fatty acid (SFA) induced a strong increase in heat shock (HS) mRNA transcription when cells were heat-shocked at 37 degrees C, whereas treatment with an unsaturated fatty acid (UFA) reduced or eliminated the level of HS gene transcription at 37 degrees C. Transcription of the delta 9-desaturase gene (Ole1) of Histoplasma capsulatum, whose gene product is responsible for the synthesis of UFA, is up-regulated in a temperature-sensitive strain. We show that when the L8-14C mutant of Saccharomyces cerevisiae, which has a disrupted Ole1 gene, is complemented with its own Ole1 coding region under control of its own promoter or Ole1 promoters of H. capsulatum, the level of HS gene transcription depends on the activity of the promoters. Fluorescence anisotropy of mitochondrial membranes of completed strains corresponded to the different activity of the Ole1 promoter used. We propose that the SFA/UFA ratio and perturbation of membrane lipoprotein complexes are involved in the perception of rapid temperature changes and under HS conditions disturbance of the preexisting membrane physical state causes transduction of a signal that induces transcription of HS genes.

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.

The value of the Premier enzyme immunoassay for diagnosing Blastomyces dermatitidis infections

One hundred and three sera drawn from 20 proven and 65 suspected cases of blastomycosis were examined concurrently with the enzymes immunoassay and microimmunodiffusion tests for the 'A' antibody specific for Blastomyces dermatitidis. Results indicated that all 20 proven sera were positive by both these tests. Thirteen of the 65 sera from suspected blastomycosis cases were positive by the enzyme immunoassay only, whereas none reacted positively in the micro-immunodiffusion test. Eighteen sera from apparently normal subjects, and patients with heterologous fungal and HIV infections were also tested by both tests. The sensitivity and specificity of the enzyme immunoassay test was 100% and 85.6%, respectively. The micro- immunodiffusion test was 100% sensitive and specific. In light of the fact that the enzyme immunoassay test is not entirely specific, a positive result should be confirmed by either a positive culture, histopathology or micro-immunodiffusion test.

Hsp70 in parasites: as an inducible protective protein and as an antigen

The heat shock (HS) response is a general homeostatic mechanism that protects cells and the entire organism from the deleterious effects of environmental stresses. It has been demonstrated that heat shock proteins (HSP) play major roles in many cellular processes, and have a unique role in several areas of cell biology, from chronic degenerative diseases to immunology, from cancer research to interaction between host and parasites. This review deals with the hsp70 gene family and with its protein product, hsp70, as an antigen when pathogens infect humans. Members of HSP have been shown to be major antigens of many pathogenic organisms when they experience a major temperature shift upwards at the onset of infection and become targets for host B and T cells.

Comparative evaluation of the Premier enzyme immunoassay, micro-immunodiffusion and complement fixation tests for the detection of Histoplasma capsulatum var. capsulatum antibodies

A total of 178 sera, including 68 from proven cases of histoplasmosis (65 positive for the presence of Histoplasma capsulatum var. capsulatum antibodies and three positive for antigen), 93 from patients with suspected histoplasmosis but with no laboratory evidence of H. capsulatum var. capsulatum infection, 14 from humans with heterologous fungal and non-fungal infections and three from normal individuals, were tested for IgG H. capsulatum antibodies and M or M and H precipitins by enzyme immunoassay (EIA) (Meridian Diagnostics, Cincinnati, OH, USA) and microimmunodiffusion (MID) respectively. Sixty-three of the 68 histoplasmosis case sera demonstrated IgG antibody, and 65 of 68 demonstrated the presence of specific precipitins in the MID test. Nine positive case sera, when tested with the Laboratory Branch complement fixation (LBCF) test, reacted positively to whole yeast and histoplasmin antigens (titres 1:8 to 1:512). Three histoplasmosis case sera repeatedly tested negative for IgG, specific precipitins and complement-fixing antibodies, whereas they were positive for Histoplasma antigen. Eighteen of 95 sera from patients without evidence of histoplasmosis demonstrated IgG antibody in the EIA only. Among these positive sera, three out of three cases of aspergillosis and three out of five cases of blastomycosis were confirmed. Sera from HIV-infected and healthy individuals did not show IgG or M and/or H antibodies to H. capsulatum. Ninety-three sera were negative by both EIA and MID. The EIA for IgG was less sensitive (97%) than MID (100%). The specificity of EIA and MID was 84% and 100% respectively.

Morphological transition in the human fungal pathogen Histoplasma capsulatum

Considerable information has accumulated recently about specific genes of Histoplasma capsulatum that are expressed during the process of adaptation when the organism undergoes morphological transition at the onset of infection. The study of these genes is crucial to identify targets for the development of novel antifungal agents.

Treatment of murine candidiasis and cryptococcosis with amphotericin B incorporated into egg lecithin-bile salt mixed micelles

Amphotericin B (AmB) with deoxycholate (Fungizone) and AmB incorporated into mixed micelles (AmB-mixMs) composed of egg lecithin with glycocholate, deoxycholate, or taurocholate were compared as treatments for murine infections. For mice infected with Candida albicans, treatment consisted of a single intravenous injection; for mice infected with Cryptococcus neoformans, treatment consisted of two intravenous injections. The maximal tolerated doses of AmB as Fungizone were 1.25 mg/kg of body weight in mice with candidiasis and 2.5 mg/kg of body weight in mice with cryptococcosis. The AmB-mixMs were nontoxic to mice at doses of 80 and 100 mg/kg of body weight and were therapeutically more active than the maximal tolerated dose of Fungizone in both models of infection. However, when Fungizone or AmB-mixMs were administered at equivalent doses of AmB, AmB-mixMs were more active in treating murine candidiasis, whereas Fungizone was more active in treating murine cryptococcosis.

Amphotericin B incorporated into egg lecithin-bile salt mixed micelles: molecular and cellular aspects relevant to therapeutic efficacy in experimental mycoses

The cellular activities of amphotericin B (AmB) used as Fungizone were compared with those of AmB complexed to either egg lecithin and glycocholate (Egam) or egg lecithin and deoxycholate (Edam). Under conditions in which leakage of K+ from erythrocytes and cultured L cells treated with Fungizone was almost complete, Egam and Edam containing concentrations of AmB severalfold greater than the concentration of AmB in Fungizone had no effect but retained the ability to decrease the level of retention of K+ in fungal cells. Analysis by absorption and circular dichroism spectroscopy demonstrated that when these formulations containing AmB at concentrations of less than 10(-5) M were added to buffer, the AmB dissociated slowly as monomers from Egam or Edam and dissociated rapidly as a mixture of monomers and self-associated species from Fungizone. We propose that in Egam and Edam, the absence of free AmB in the self-associated form reduces the toxicity of AmB to mammalian cells, whereas the presence of monomeric AmB results in the retention of the antifungal activities of these complexes.

Evaluation of a commercial enzyme immunoassay for the detection of cryptococcal antigen

A total of 143 cerebrospinal and serum samples, from proven and suspected cases of cryptococcosis, were concurrently examined using a recently introduced enzyme immunoassay (EIA Premier, Meridian Diagnostics, Inc., Cincinnati, OH, USA) and three latex agglutination (LA) procedures (Immunomycologics, Inc., Norman, OK, USA; IBL, Inc., Cranbury, NJ, USA and a non-commercial LA test). Of these 143 specimens, 115 were negative for cryptococcal antigen (CrAg) with the EIA and LA tests. The remaining 28 specimens were evaluated by the LA tests, and all were positive for CrAg (with titres ranging from 1:2 to 1:8192). Of these 28 LA-positive specimens, 26 were also tested by the EIA. This procedure detected CrAg in 23 specimens (88.5%), with antigen levels ranging from 1:4 to 1:266,857. There were 3 LA-positive specimens (tires 1:4 to 1:32) which were negative by the EIA procedure (10.7%). One LA-negative specimen demonstrated CrAg (titre 1:30) by the EIA procedure. The sensitivity of the EIA and LA tests was 85.2 and 100%, respectively. The specificity of the LA test was 100%, whereas that of the EIA was 97%. The agreement among laboratories for testing the specimens with the three LA tests was 100%.

Standardized susceptibility testing of fluconazole: an international collaborative study

An international collaborative study of broth dilution (MIC) and disk diffusion susceptibility testing of fluconazole was conducted by using a chemically defined medium (High-Resolution Antifungal Assay Medium; Oxoid Ltd., Basingstoke, United Kingdom) and standard test methods performed in eight reference laboratories. Ten yeast isolates were tested by each test method in duplicate on each of 3 separate days. The intralaboratory reproducibility of the MIC test was excellent; 95.7% of the replicate tests (n = 220) were within 2 doubling dilutions of the other values in the set for the eight laboratories. The intralaboratory reproducibility of the disk test was also good, with 91% of the replicate tests (n = 234) agreeing with each other within an arbitrarily chosen value of 4 mm. Interlaboratory agreement of MIC test results was acceptable, with 84% of the MICs agreeing within 2 doubling dilutions. In contrast, the interlaboratory agreement of the disk test was not good, with only 59% of test results agreeing within 4 mm. Comparison of the rank order of MICs obtained in each laboratory with the reference rank order gave an agreement of 70 to 80% (median, 80%) with the MIC test and 70 to 90% (median, 80%) with the disk test. These preliminary results are encouraging for the development of standardized testing methods for testing fluconazole.

4-oxatetradecanoic acid is fungicidal for Cryptococcus neoformans and inhibits replication of human immunodeficiency virus I

Candida albicans and Cryptococcus neoformans are major causes of systemic fungal infections, particularly in patients with acquired immunodeficiency syndrome. Metabolic labeling studies revealed that these organisms synthesize a small number of N-myristoylproteins, the most prominent being 20-kDa ADP-ribosylation factors (Arfs). C. albicans Arf has approximately 80% identity with the essential Arf1 and Arf2 proteins of Saccharomyces cerevisiae. [3H]Myristic acid analogs with oxygen for -CH2- substitutions at C4, C6, C11, and C13 are incorporated into cellular N-myristoylproteins, phospholipids, and neutral lipids produced by these three yeasts during exponential growth at 30 degrees C in complex media. Analog- and organism-specific differences in the efficiency of labeling of proteins and lipid classes were observed. The effects of oxatetradecanoic acids with oxygen for -CH2- substitutions at C3-C13 on C. neoformans, C. albicans, and S. cerevisiae were assessed during mid-log phase growth at 30 degrees C. A single dose of 3-oxa-, 4-oxa-, 5-oxa- or 6-oxatetradecanoic acid (O3-O6, final concentration = 300 microM) was able to inhibit growth of C. neoformans in the order O4 greater than O5 greater than O3 approximately O6. The other compounds were inactive. 4-Oxatetradecanoic acid was fungicidal, producing a 10,000-fold reduction in viable cell number 1 h after administration and continued suppression of cell growth for 7 h. A clear dose response was observed over a concentration range of 100-300 microM. 4-Oxatridecanoic acid was 100-fold less potent in reducing cell viability than 4-oxatetradecanoic acid but more potent than 5-oxatridecanoic acid. O4 produced approximately 10-100-fold reductions in the viability of C. albicans and S. cerevisiae at 300-500 microM, respectively, whereas O5 and O6 were less active. Since N-myristoylation of the Pr55gag polyprotein precursor produced by human immunodeficiency virus I (HIV-I) is essential for its assembly, we also assessed the antiviral effects of 4-oxatetradecanoic acid. O4 is able to produce a 50% reduction in the replication of HIV-I in acutely infected human T-lymphocyte cell lines at a concentration of 18 microM. Together, these data suggest that (i) the position of the oxygen for methylene substitution is a critical determinant of the fungicidal activity of O4 and (ii) NMT may be an attractive therapeutic target for treating opportunistic fungal infections in patients infected with HIV-I.

Typing of Histoplasma capsulatum by restriction fragment length polymorphisms in a nuclear gene

We previously described yps-3, a Histoplasma-specific nuclear gene probe useful in the identification of Histoplasma capsulatum. By using restriction fragment length polymorphisms (RFLPs) of DNA detected by the yps-3 gene and mitochondrial DNA, 76 clinical and soil isolates of H. capsulatum were classified. The majority of North American isolates obtained from endemic regions of the midwestern United States were members of the previously characterized class 2, although four clinical isolates from different patients with AIDS from that region were grouped in class 1 with the temperature-sensitive Downs strain. A Florida soil isolate (FLS1) was placed in class 4 on the basis of RFLP with both probes. Two American Type Culture Collection strains (G184B and G186B) from Panama were grouped into class 3 by this analysis. A group of five H. capsulatum isolates obtained from patients with AIDS in New York City were typed into a new class 5 on the basis of yps-3 polymorphisms; those organisms fell into two broad mitochondrial DNA patterns, designated 5b and 5c. Two new isolates from Panama were also members of this broad yps-3 class 5 group, but they exhibited a distinct mitochondrial DNA profile (class 5a). A sixth class was detected in DNA obtained from a patient with AIDS from Panama; that DNA had unique RFLP profiles with respect to both probes. These observations suggest that the Histoplasma-specific yps-3 gene probe is a sensitive tool for typing H. capsulatum in clinical specimens. Additionally, these studies provide molecular support for the hypothesis that AIDS-associated histoplasmosis in nonendemic areas is due to reactivation of a previously acquired infection.

Isolation, characterization, and sequencing of Candida albicans repetitive element 2

A 1059-bp Sau3A fragment, designated Candida albicans repetitive element 2 (CARE-2), was isolated from the genome of the pathogenic yeast, C. albicans. CARE-2 DNA was detected on several C. albicans chromosomes separated by transverse alternating-field electrophoresis. A high degree of interstrain variation in the pattern of hybridizing bands were observed by Southern blot analysis, with a minimum of 10-14 copies of CARE-2 per strain. A low frequency of new CARE-2 polymorphisms was observed over time for three strains grown at 25 degrees C or 37 degrees C. No new CARE-2 polymorphisms were observed from two naturally occurring switch phenotypes. To localize repeated DNA, oligodeoxyribonucleotide probes, each representing a different region of CARE-2, were hybridized to genomic blots. A lower number of copies were observed 5' and 3' to a 600-bp region of CARE-2. Nucleotide (nt) sequence analysis of CARE-2 DNA shows the element is characterized by six perfect direct repeats 6 bp in length and shows no significant DNA similarity with any known nt sequence.

Mitochondrial activity and heat-shock response during morphogenesis in the pathogenic fungus Histoplasma capsulatum

Changes in temperature and a variety of other stimuli coordinately induce transcription of a specific set of heat-shock genes in all organisms. In the human fungal pathogen Histoplasma capsulatum, a temperature shift from 25 to 37 degrees C acts not only as a signal that causes transcription of heat-shock genes, but also triggers a morphological mycelium- to yeast-phase transition. The temperature-induced morphological transition may be viewed as a heat-shock response followed by cellular adaptation to a higher temperature. We have found that by inducing thermotolerance, i.e., an initial incubation at 34 degrees C, the thermosensitive attenuated Downs strain of H. capsulatum can be made to resemble those of the more temperature-tolerant G222B strain with respect to mitochondrial ATPase activity and electron transport efficiency at elevated temperatures. Furthermore, if the heat-shock response is first elicited by preincubation at milder temperatures or stress, transcription of heat-shock mRNA in mycelial cells of Downs strain that shifted to 37 degrees C proceeds at rates comparable to those of the virulent strains.

Characterization of CARE-1: Candida albicans repetitive element-1

A middle repetitive DNA element, Candida albicans repetitive element-1 (CARE-1) has been isolated from the pathogenic yeast C. albicans. CARE-1 appears to be species-specific and constitutes approx. 0.045% of total C. albicans DNA, or a reiteration frequency of about two to twelve copies per haploid genome. The CARE-1 element has been detected on several C. albicans chromosomes separated by field-inversion gel electrophoresis, suggesting that the element is dispersed. Interstrain variation was observed in the number and distribution of hybridizing bands. The element is well conserved, since no nucleotide (nt) heterogeneity was observed when the sequences of two CARE-1 family members isolated from two different chromosomes (A and B) of C. albicans were compared. CARE-1 possesses 467 bp and is characterized by several stretches of A's and T's, short direct repeats and shows no significant homology to any known nt sequence.

Systemic fungal infections: an overview

Increasingly more common, these infections pose diagnostic and therapeutic problems. The distinction between primary infection in healthy hosts and opportunistic infection in the immunocompromised remains clinically useful. Three major diseases in each category are discussed. A promising therapeutic advance is the introduction of orally administered azoles.

Structure-activity study of inhibition of amphotericin B (Fungizone) binding to sterols, toxicity to cells, and lethality to mice by esters of sucrose

The effects of four monoesters of sucrose with different acyl chain lengths (palmitate, C16; myristate, C14; laurate, C12; and caprate, C10) on the aggregation state of amphotericin B (AmB), its binding to cholesterol and ergosterol, its toxicity to cells, and its lethality to mice were determined. In solution, all four of these esters inhibited AmB binding to cholesterol more than to ergosterol; this effect correlated with the ester-induced shift from the mainly aggregated form of AmB to the mainly monomeric form. In experiments with cells, the esters inhibited the toxicity of AmB to mouse erythrocytes and cultured mouse fibroblast L-929 cells more than its toxicity to Candida albicans cells. When injected intravenously with AmB, these esters decreased AmB lethality to mice. In all of these assays, the ester with the shortest chain length (caprate) was much less potent than the other three esters. Our results indicate a correlation between in vitro and in vivo assays and suggest that the in vitro and in vivo selectivity of AmB may be enhanced by surface-active agents which modulate the aggregation state of AmB.

Inhibition of amphotericin B (Fungizone) toxicity to cells by egg lecithin-glycocholic acid mixed micelles

Mixed micelles prepared from egg lecithin and the sodium salt of glycocholic acid markedly inhibited amphotericin B toxicity to mammalian cells without significantly affecting the antifungal effects of the drug.

Temperature-sensitive variants of Histoplasma capsulatum isolated from patients with acquired immunodeficiency syndrome

Histoplasma capsulatum isolates from three St. Louis area AIDS patients with disseminated histoplasmosis were found to be closely related to the temperature-sensitive, previously unique, Downs strain based on growth phenotype and restriction fragment length polymorphisms (RFLP) involving mitochondrial DNA, ribosomal DNA, and the yps-3 gene. H. capsulatum isolates from five non-AIDS patients in the St. Louis area with disseminated histoplasmosis or chronic pulmonary histoplasmosis had the growth phenotype and RFLP pattern characteristic of most strains isolated from other regions of the USA.

In vitro and in vivo activities of Sch 39304, fluconazole, and amphotericin B against Histoplasma capsulatum

The antifungal activities of amphotericin B and two triazoles, Sch 39304 and fluconazole, were tested against Histoplasma capsulatum. In this study Sch 39304 compared favorably with amphotericin B in treating histoplasmosis in normal and leukopenic mice, whereas fluconazole was much less active. The differences in the efficacies of the triazoles appeared to be due to differences in their pharmacokinetics and the dosage schedule that was used. For amphotericin B there was a good correlation between in vitro and in vivo efficacy, but this was not true of the triazole derivatives. These results further demonstrate that, with the methods used in this study, in vitro susceptibility testing of triazoles may not be predictive of in vivo activity against isolates of H. capsulatum.

Comparison of fluconazole with amphotericin B in treatment of histoplasmosis in normal and immunosuppressed mice

The activities of fluconazole and amphotericin B against Histoplasma capsulatum were investigated. The minimum inhibitory concentrations ranged from 0.12 to 0.47 microgram/mL for amphotericin B and from 16 to 250 micrograms/mL for fluconazole. Fluconazole given orally twice a day for 6 consecutive days compared favorably with amphotericin B given intraperitoneally once every other day for a total of six doses in the treatment of histoplasmosis in normal and leukopenic mice.