Healthy Human T-Cell Responses to Aspergillus fumigatus Antigens

Aspergillus fumigatus is associated with both invasive and allergic pulmonary diseases, in different hosts. The organism is inhaled as a spore, which, if not cleared from the airway, germinates into hyphal morphotypes that are responsible for tissue invasion and resultant inflammation. Hyphae secrete multiple products that function as antigens, evoking both a protective (T(H)1-T(H)17) and destructive allergic (T(H)2) immunity. How Aspergillus allergens (Asp f proteins) participate in the development of allergic sensitization is unknown.To determine whether Asp f proteins are strictly associated with T(H)2 responses, or represent soluble hyphal products recognized by healthy hosts, human T cell responses to crude and recombinant products were characterized by ELISPOT. While responses (number of spots producing IFN-gamma, IL-4 or IL-17) to crude hyphal antigen preparations were weak, responses to recombinant Asp f proteins were higher. Recombinant allergens stimulated cells to produce IFN-gamma more so than IL-4 or IL-17. Volunteers exhibited a diverse CD4+ and CD8+ T cell antigen recognition profile, with prominent CD4 T(H)1-responses to Asp f3 (a putative peroxismal membrane protein), Asp f9/16 (cell wall glucanase), Asp f11 (cyclophilin type peptidyl-prolyl isomerase) and Asp f22 (enolase). Strong IFN-gamma responses were reproduced in most subjects tested over 6 month intervals.Products secreted after conidial germination into hyphae are differentially recognized by protective T cells in healthy, non-atopic individuals. Defining the specificity of the human T cell repertoire, and identifying factors that govern early responses may allow for development of novel diagnostics and therapeutics for both invasive and allergic Aspergillus diseases

Reevaluation of the Role of HWP1 in Systemic Candidiasis by Use of Candida albicans Strains with Selectable Marker URA3 Targeted to the ENO1 Locus

Previous evaluation of HWP1 in systemic candidiasis in CBA/J mice was done with Candida albicans strains with differing genetic locations of URA3 as a result of Ura-blaster mutagenesis. In this study, the presence of HWP1 and the location of URA3 contributed to the severity of murine systemic candidiasis in BALB/c mice

Emergence of a Candida krusei Isolate with Reduced Susceptibility to Caspofungin during Therapy

Clinical failure associated with reduced susceptibility to caspofungin has been described in Candida albicans and C. parapsilosis. We report a case of Candida krusei infection that progressed despite caspofungin therapy. Reduced microbial susceptibility to all three echinocandins (caspofungin, anidulafungin, and micafungin) was noted but was not associated with mutations in FKS1

A 368-Base-Pair cis-Acting HWP1 Promoter Region, HCR, of Candida albicans Confers Hypha-Specific Gene Regulation and Binds Architectural Transcription Factors Nhp6 and Gcf1p

To elucidate the molecular mechanisms controlling the expression of the hypha-specific adhesin gene HWP1 of Candida albicans, its promoter was dissected and analyzed using a green fluorescent protein reporter gene. A 368-bp region, the HWP1 control region (HCR), was critical for activation under hypha-inducing conditions and conferred developmental regulation to a heterologous ENO1 promoter. A more distal region of the promoter served to amplify the level of promoter activation. Using gel mobility shift assays, a 249-bp subregion of HCR, HCRa, was found to bind at least four proteins from crude extracts of yeasts and hyphae with differing binding patterns dependent on cell morphology. Four proteins with DNA binding activities were identified by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis after separation by anion-exchange and heparin-Sepharose chromatography. One protein with high similarity to Nhp6, an HMG1 family member in Saccharomyces cerevisiae, and another with weak similarity to an HMG-like condensation factor from Physarum polycephalum implicated changes in chromatin structure as a critical process in hypha-specific gene regulation. Proteins with strong homology to histones were also found. These studies are the first to identify proteins that bind to a DNA segment that confers developmental gene regulation in C. albicans and suggest a new model for hypha-specific gene regulation

Niche-Specific Requirement for Hyphal Wall protein 1 in Virulence of <i>Candida albicans</i>

<div><p>Specialized <i>Candida albicans</i> cell surface proteins called adhesins mediate binding of the fungus to host cells. The mammalian transglutaminase (TG) substrate and adhesin, Hyphal wall protein 1 (Hwp1), is expressed on the hyphal form of <i>C. albicans</i> where it mediates fungal adhesion to epithelial cells. Hwp1 is also required for biofilm formation and mating thus the protein functions in both fungal-host and self-interactions. Hwp1 is required for full virulence of <i>C. albicans</i> in murine models of disseminated candidiasis and of esophageal candidiasis. Previous studies correlated TG activity on the surface of oral epithelial cells, produced by epithelial TG (TG1), with tight binding of <i>C. albicans</i> via Hwp1 to the host cell surfaces. However, the contribution of other Tgs, specifically tissue TG (TG2), to disseminated candidiasis mediated by Hwp1 was not known. A newly created <i>hwp1</i> null strain in the wild type SC5314 background was as virulent as the parental strain in C57BL/6 mice, and virulence was retained in C57BL/6 mice deleted for Tgm2 (TG2). Further, the <i>hwp1</i> null strains displayed modestly reduced virulence in BALB/c mice as did strain DD27-U1, an independently created <i>hwp1</i>Δ/Δ in CAI4 corrected for its <i>ura3</i>Δ defect at the <i>URA3</i> locus. Hwp1 was still needed to produce wild type biofilms, and persist on murine tongues in an oral model of oropharyngeal candidiasis consistent with previous studies by us and others. Finally, lack of Hwp1 affected the translocation of <i>C. albicans</i> from the mouse intestine into the bloodstream of mice. Together, Hwp1 appears to have a minor role in disseminated candidiasis, independent of tissue TG, but a key function in host- and self-association to the surface of oral mucosa. </p> </div

Aspergillus Section Fumigati Typing by PCR-Restriction Fragment Polymorphism▿

Recent studies have shown that there are multiple clinically important members of the Aspergillus section Fumigati that are difficult to distinguish on the basis of morphological features (e.g., Aspergillus fumigatus, A. lentulus, and Neosartorya udagawae). Identification of these organisms may be clinically important, as some species vary in their susceptibilities to antifungal agents. In a prior study, we utilized multilocus sequence typing to describe A. lentulus as a species distinct from A. fumigatus. The sequence data show that the gene encoding β-tubulin, benA, has high interspecies variability at intronic regions but is conserved among isolates of the same species. These data were used to develop a PCR-restriction fragment length polymorphism (PCR-RFLP) method that rapidly and accurately distinguishes A. fumigatus, A. lentulus, and N. udagawae, three major species within the section Fumigati that have previously been implicated in disease. Digestion of the benA amplicon with BccI generated unique banding patterns; the results were validated by screening a collection of clinical strains and by in silico analysis of the benA sequences of Aspergillus spp. deposited in the GenBank database. PCR-RFLP of benA is a simple method for the identification of clinically important, similar morphotypes of Aspergillus spp. within the section Fumigati

Differential Aspergillus lentulus Echinocandin Susceptibilities Are Fksp Independent ▿

The recently described species Aspergillus lentulus exhibits differential and reduced susceptibilities to echinocandins and other antifungal drugs in vitro. A. lentulus isolates overall are less susceptible to caspofungin, although they maintain susceptibility to anidulafungin and micafungin. Mutations or polymorphisms in fks, the gene encoding the catalytic subunit of β-1,3-glucan synthase, are known to confer decreased susceptibility to echinocandins in Candida spp. and Aspergillus fumigatus. The analysis of the A. lentulus fks sequence did not reveal a polymorphism at any of the known hot-spot regions of the gene. Caspofungin and micafungin kinetic inhibition profiles of the A. lentulus glucan synthase were comparable to those from susceptible A. fumigatus enzymes. Although the basal cell wall chitin levels in A. lentulus averaged 60% of those in A. fumigatus, echinocandin treatment promoted the increase of cell wall chitin in both organisms, indicating that A. lentulus displays a compensatory chitin response similar to that of A. fumigatus. The data suggest that differential echinocandin susceptibilities in A. lentulus are independent of the echinocandin target, Fksp, and they emphasize the potential that the drugs' capacity to inhibit the target enzyme is unequal at the cellular level

Hwp1 is required for full virulence in an animal model of gut translocation candidiasis.

<p>C57BL/6 mice were fed <i>C. albicans</i> in their drinking water to establish GI colonization followed by immunosuppression to induce neutropenia and intestinal mucosa damage. (<b>A</b>) Gut colonization levels are independent upon <i>HWP1</i> expression. Colonization levels in mice were assessed by measuring the fungal burden in the stools (CFU/g) of individual mice. Mean CFU/g of stool of mice fed SCH1211 (n=8) or HR615 (n=7) were not statistically different relative to SC5314 (WT, n=7). (<b>B</b>) Survival of mice post immunosuppression with cyclophosphamide. Mice colonized with the <i>hwp1</i> null strain SCH1211 were less virulent relative to SC5314 (P=0.003). Single expression of <i>HWP1</i> (HR615) did not restore wild type survival kinetics in mice (P=0.035), although none of the mice colonized with HR615 survived to the end of the observation period. <i>C. albicans</i> was recovered from the livers of all the mice at the time of sacrifice (data not shown), indicating translocation from the GI tract.</p

<i>hwp1</i> null strains display attenuated virulence in BALB/c mice.

<p>BALB/c mice infected with <i>hwp1</i>Δ/Δ strains SCH1211 (n=11) or DD27-U1 (n=6) were attenuated in virulence in intravenously infected BALB/c mice. Reintroducing <i>HWP1</i> at its native site in SCH1211 (HR615, n=7) did not restore full virulence of the strain to wild type levels (SC5314, n=13). The rate of survival among the strains deleted for <i>HWP1</i> (SCH1211 and DD27-U1) or expressing a single allele (HR615) was statistically different (P<0.05) relative to the wild type SC5314. </p