Enhanced extracellular production of aspartyl proteinase, a virulence factor, by Candida albicans isolates following growth in subinhibitory concentrations of fluconazole

We examined the production of secreted aspartyl proteinase (Sap), a putative virulence factor of Candida albicans, by a series of 17 isolates representing a single strain obtained from the oral cavity of an AIDS patient before and after the development of clinical and in vitro resistance to fluconazole. Isolates were grown in Sap-inducing yeast carbon base-bovine serum albumin medium containing 0, 0.25, 0.5, or 1 MIC of fluconazole, and cultures were sampled daily for 14 days to determine extracellular Sap activity by enzymatic degradation of bovine serum albumin. Extracellular Sap activity was significantly decreased in a dose-dependent manner for the most fluconazole-susceptible isolate (MIC, 1.0 microg/ml) and significantly increased in a dose-dependent manner for the most fluconazole-resistant isolate (MIC, >64 microg/ml). Enhanced extracellular Sap production could not be attributed to cell death or nonspecific release of Sap, because there was no reduction in the number of CFU and no significant release of enolase, a constitutive enzyme of the glycolytic pathway. Conversely, intracellular Sap concentrations were significantly increased in a dose-dependent manner in the most fluconazole-susceptible isolate and decreased in the most fluconazole-resistant isolate. Enhanced Sap production correlated with the overexpression of a gene encoding a multidrug resistance (MDR1) efflux pump occurring in these isolates. These data indicate that exposure to subinhibitory concentrations of fluconazole can result in enhanced extracellular production of Sap by isolates with the capacity to overexpress MDR1 and imply that patients infected with these isolates and subsequently treated with suboptimal doses of fluconazole may experience enhanced C. albicans virulence in vivo.

Comparison of commercial latex agglutination and sandwich enzyme immunoassays with a competitive binding inhibition enzyme immunoassay for detection of antigenemia and antigenuria in a rabbit model of invasive aspergillosis

A commercial latex agglutination assay (LA) and a sandwich enzyme immunoassay (SEIA) (Sanofi Diagnostics Pasteur, Marnes-la-Coquette, France) were compared with a competitive binding inhibition assay (enzyme immunoassay [EIA]) to determine the potential uses and limitations of these antigen detection tests for the sensitive, specific, and rapid diagnosis of invasive aspergillosis (IA). Toward this end, well-characterized serum and urine specimens were obtained by using a rabbit model of IA. Serially collected serum or urine specimens were obtained daily from control rabbits or from rabbits immunosuppressed and infected systemically with Aspergillus fumigatus. By 4 days after infection, EIA, LA, and SEIA detected antigen in the sera of 93, 93, and 100% of A. fumigatus-infected rabbits, respectively, whereas antigen was detected in the urine of 93, 100, and 100% of the rabbits, respectively. False-positive results for non-A. fumigatus-infected rabbits for EIA, LA, and SEIA were as follows: for serum, 14, 11, and 23%, respectively; for urine, 14, 84, and 90%, respectively. Therefore, although the sensitivities of all three tests were similar, the specificity was generally greater for EIA than for LA or SEIA. Infection was also detected earlier by EIA, by which the serum of 53% of A. fumigatus-infected rabbits was positive as early as 1 day after infection, whereas the serum of only 27% of the rabbits tested by LA was positive. Although the serum of 92% of A. fumigatus-infected rabbits was positive by SEIA as early as 1 day after infection, the serum of a high percentage (50%) was false positive before infection. The urine of 21% of A. fumigatus-infected rabbits was positive by EIA as early as 1 day after infection, and the urine of none of the rabbits was false positive before infection. When EIA results for urine specimens were combined with those for serum, sensitivity was improved (i.e., 67% of rabbits were positive by 1 day after infection and only one rabbit gave a false-positive result). A total of 93% of A. fumigatus-infected rabbits were positive for antigen in urine as early as 1 day after infection and the urine of 100% of the rabbits was positive by SEIA. However, before infection, 79% of A. fumigatus-infected rabbits were false positive for antigen in urine by LA and 90% were false positive for antigen in urine by SEIA. These data indicate that the EIA has the potential to be used to diagnose IA with both serum and urine specimens and to detect a greater number of infections earlier with greater specificity than the specificities achieved with the commercial tests.

Candida dubliniensis fungemia: the first four cases in North America

We report the first four North American cases of Candida dubliniensis fungemia, including the first isolation of this organism from the bloodstream of an HIV-infected person. All isolates were susceptible in vitro to commonly used antifungal drugs. This report demonstrates that C. dubliniensis can cause bloodstream infection; however, the incidence of disease is not known.

Quantitation of ergosterol content: novel method for determination of fluconazole susceptibility of Candida albicans

MIC end points for the most commonly prescribed azole antifungal drug, fluconazole, can be difficult to determine because its fungistatic nature can lead to excessive "trailing" of growth during susceptibility testing by National Committee for Clinical Laboratory Standards broth macrodilution and microdilution methods. To overcome this ambiguity, and because fluconazole acts by inhibiting ergosterol biosynthesis, we developed a novel method to differentiate fluconazole-susceptible from fluconazole-resistant isolates by quantitating ergosterol production in cells grown in 0, 1, 4, 16, or 64 microg of fluconazole per ml. Ergosterol was isolated from whole yeast cells by saponification, followed by extraction of nonsaponifiable lipids with heptane. Ergosterol was identified by its unique spectrophotometric absorbance profile between 240 and 300 nm. We used this sterol quantitation method (SQM) to test 38 isolates with broth microdilution end points of </=8 microg/ml (susceptible), 16 to 32 microg/ml (susceptible dose-dependent [SDD]), or >/=64 microg/ml (resistant) and 10 isolates with trailing end points by the broth microdilution method. No significant differences in mean ergosterol content were observed between any of the isolates grown in the absence of fluconazole. However, 18 susceptible isolates showed a mean reduction in ergosterol content of 72% after exposure to 1 microg of fluconazole/ml, an 84% reduction after exposure to 4 microg/ml, and 95 and 100% reductions after exposure to 16 and 64 microg of fluconazole/ml, respectively. Ten SDD isolates showed mean ergosterol reductions of 38, 57, 73, and 99% after exposure to 1, 4, 16, and 64 microg of fluconazole/ml, respectively. In contrast, 10 resistant isolates showed mean reductions in ergosterol content of only 25, 38, 53, and 84% after exposure to the same concentrations of fluconazole. The MIC of fluconazole, by using the SQM, was defined as the lowest concentration of the drug which resulted in 80% or greater inhibition of overall mean ergosterol biosynthesis compared to that in the drug-free control. Of 38 isolates which gave clear end points by the broth microdilution method, the SQM MIC was within 2 dilutions of the broth microdilution MIC for 33 (87%). The SQM also discriminated between resistant and highly resistant isolates and was particularly useful for discerning the fluconazole susceptibilities of 10 additional isolates which gave equivocal end points by the broth microdilution method due to trailing growth. In contrast to the broth microdilution method, the SQM determined trailing isolates to be susceptible rather than resistant, indicating that the SQM may predict clinical outcome more accurately. The SQM may provide a means to enhance current methods of fluconazole susceptibility testing and may provide a better correlation of in vitro with in vivo results, particularly for isolates with trailing end points.

Molecular diagnosis and epidemiology of fungal infections

A variety of methods are utilized for DNA strain subtyping of Candida spp. because no 'gold standard' exists. Random amplified polymorphic DNA (RAPD) or restriction enzyme analysis (REA) are useful to determine the source of an outbreak, but more reproducible and discriminatory methods such as Southern hybridization and pulsed field gel electrophoresis (PFGE) may be required. When applied to some nosocomial Candida infections, multiple strains and species have been identified. Microevolution of yeast species occurs and epidemiologically related isolates may show minor pattern differences, creating uncertainty as to whether they are distinct strains. Approximately 1000 isolates of Aspergillus fumigatus from environmental and clinical sources were typed by REA probed with an A. fumigatus-specific retrotransposon-like sequence. Patients with no symptom of aspergillosis may carry several strains, whereas patients with pulmonary aspergillosis may carry one or two strains; nocosomial transmission of aspergillosis was proven in 39% of the patients studied; any given environmental strain can be infectious; the environmental population of A. fumigatus is extremely diverse and no specific niche was found in the hospital. A PCR assay was designed to target conserved 18S-ribosomal DNA (rDNA) sequences shared by most fungi and a 687 bp product was amplified from 25 medically important fungal species. Studies with blood, cerebrospinal fluid and sputum specimens from patients with mycoses indicated that the PCR assay is more sensitive in diagnosing invasive fungal infections than blood culture methods. More specific identification is obtainable with genus/species-specif c probes designed from within the PCR-amplified sequences for C. albicans, C. krusei, C. lusitaniae, Pneumocystis carinii, Cryptococcus neoformans, Aspergillus/Penicillium spp. and C. glabrata/Saccharomyces cerevisiae. A. fumigatus and A. niger were differentiated by denaturing gradient gel electrophoresis. In situ hybridization (ISH) detected a 648 bp fragment of the 18S rDNA of C. neoformans and a 568 bp fragment of the alkaline proteinase gene of A. fumigatus in tissues from experimentally infected animals. In ISH, the entire process can be automated, making this procedure rapid and easy. The difficulty in establishing a diagnosis of invasive candidiasis has prompted the quest for a clinically useful PCR test for candidaemia. The universal fungal oligonucleotide primer pair, ITS3 and ITS4, amplifies portions of the 5.8S ad 28S rDNA subunits, and the ITS2 region. Although rRNA genes are highly conserved, the ITS regions are distinctive. DNA probes were designed from ITS2 that were specific for 16 different Candida species. Simple, rapid sample preparation was suitable for PCR analysis of BacT/Alert blood culture bottles. Sample preparation, PCR, and EIA detection of the amplicon from five different Candida species was accomplished in 7 h, 2.5 days sooner than by conventional culture methods. As well as saving time, minor yeast species among a major species, or among bacteria, were simultaneously detected. PCR-EIA using a microtitration plate format had sensitivity 10-times greater than that obtained with ethidium bromide-stained agarose gels. Taqman combines in one step PCR, probe hybridization, and fluorescent signal generation. Taqman PCR had sensitivity equivalent to PCR-EIA and required only 5 h, including sample preparation.

Rapid identification of up to three Candida species in a single reaction tube by a 5' exonuclease assay using fluorescent DNA probes

We used fungus-specific PCR primers and species-specific DNA probes to detect up to three Candida species in a single reaction tube by exploiting the 5' to 3' exonuclease activity of Taq DNA polymerase. Probes to the internal transcribed spacer region of the rRNA gene were labeled at the 5' end with one of three fluorescent reporter dyes, 6-carboxy-fluorescein (FAM), tetrachloro-6-carboxy-fluorescein (TET), or hexachloro-6-carboxy-fluorescein (HEX), and at the 3' end with a quencher dye, 6-carboxy-tetramethyl-rhodamine. During PCR amplification, each reporter dye emits a characteristic wavelength as it is cleaved from its specific target DNA and from the quencher dye. Therefore, signals from up to three probes can be detected simultaneously during the PCR assay. Six probes were designed for use in this study: CA-FAM, CT-TET, and CP-HEX were added to one tube to simultaneously detect the typically fluconazole-sensitive species C. albicans, C. tropicalis, and C. parapsilosis, respectively. CG-FAM and CK-TET were added to a second tube to simultaneously detect the typically more innately fluconazole-resistant species C. glabrata and C. krusei, respectively. All-CAN-TET, a Candida genus probe, was added to a third tube to detect DNAs from all Candida species tested. DNAs recovered from 61 blood culture bottles, including 23 positive for C. albicans, 18 positive for C. glabrata, 6 positive for C. tropicalis, 6 positive for C. krusei, 5 positive for C. parapsilosis, and 3 positive for mixed fungemias, were tested. Control samples included those from blood culture bottles with no growth (n = 10) or from patients with confirmed bacteremia (n = 10). Probes detected and correctly identified the organisms in 58 of 61 specimens (95.1%) and gave no false-positive results. This method is simple and rapid and does not require post-PCR hybridization and incubation steps. It is sensitive and specific for the detection and identification of Candida species from blood culture bottles, including those containing mixtures of Candida species, and should facilitate an earlier specific diagnosis, leading to more appropriately targeted antifungal drug therapy.

Rapid identification of Candida species with species-specific DNA probes

Rapid identification of Candida species has become more important because of an increase in infections caused by species other than Candida albicans, including species innately resistant to azole antifungal drugs. We previously developed a PCR assay with an enzyme immunoassay (EIA) format to detect amplicons from the five most common Candida species by using universal fungal primers and species-specific probes directed to the ITS2 region of the gene for rRNA. We designed probes to detect seven additional Candida species (C. guilliermondii, C. kefyr, C. lambica, C. lusitaniae, C. pelliculosa, C. rugosa, and C. zeylanoides) included in the API 20C sugar assimilation panel, five probes for species not identified by API 20C (C. haemulonii, C. norvegica, C. norvegensis, C. utilis, and C. viswanathii), and a probe for the newly described species C. dubliniensis, creating a panel of 18 Candida species probes. The PCR-EIA correctly identified multiple strains of each species tested, including five identified as C. albicans by the currently available API 20C database but determined to be C. dubliniensis by genotypic and nonroutine phenotypic characteristics. Species identification time was reduced from a mean of 3.5 days by conventional identification methods to 7 h by the PCR-EIA. This method is simple, rapid, and feasible for identifying Candida species in clinical laboratories that utilize molecular identification techniques and provides a novel method to differentiate the new species, C. dubliniensis, from C. albicans.

The mechanical 'quality' of osteophytes

Intrinsic mechanical properties of osteophytes have been compared with those of normal articular cartilage by obtaining force-indentation curves. The cartilage of the osteophyte was found to be thinner than articular cartilage. The mean stiffness of osteophytes was 272.8 (+/- 78.8) N/mm and the mean stiffness of articular cartilage was 1412 (+/- 917.3) N/mm.

Rapid identification of Candida species in blood cultures by a clinically useful PCR method

Widespread use of fluconazole for the prophylaxis and treatment of candidiasis has led to a reduction in the number of cases of candidemia caused by Candida albicans but has also resulted in the emergence of candidemias caused by innately fluconazole-resistant, non-C. albicans Candida species. Given the fulminant and rapidly fatal outcome of acute disseminated candidiasis, rapid identification of newly emerging Candida species in blood culture is critical for the implementation of appropriately targeted antifungal drug therapy. Therefore, we used a PCR-based assay to rapidly identify Candida species from positive blood culture bottles. This assay used fungus-specific, universal primers for DNA amplification and species-specific probes to identify C. albicans, C. krusei, C. parapsilosis, C. tropicalis, or C. glabrata amplicons. It also used a simpler and more rapid (1.5-h) sample preparation technique than those described previously and used detergent, heat, and mechanical breakage to recover Candida species DNA from blood cultures. A simple and rapid (3.5-h) enzyme immunosorbent assay (EIA)-based format was then used for amplicon detection. One hundred fifty blood culture bottles, including 73 positive blood culture bottle sets (aerobic and anaerobic) from 31 patients with candidemia, were tested. The combined PCR and EIA methods (PCR-EIA) correctly identified all Candida species in 73 blood culture bottle sets, including bottles containing bacteria coisolated with yeasts and 3 cultures of samples from patients with mixed candidemias originally identified as single-species infections by routine phenotypic identification methods. Species identification time was reduced from a mean of 3.5 days by routine phenotypic methods to 7 h by the PCR-EIA method. No false-positive results were obtained for patients with bacteremias (n = 18), artificially produced non-Candida fungemias (n = 3), or bottles with no growth (n = 20). Analytical sensitivity was 1 cell per 2-microl sample. This method is simpler and more rapid than previously described molecular identification methods, can identify all five of the most medically important Candida species, and has the potential to be automated for use in the clinical microbiology laboratory.

Analysis of the active site and activation mechanism of the Leishmania surface metalloproteinase GP63

The major surface glycoprotein of Leishmania promastigotes, referred to as GP63, is a zinc metalloproteinase of 63,000 M(r) containing a glycosylphosphatidylinositol (GPI) membrane anchor. Recent studies demonstrated that recombinant GP63 (rGP63) expressed by the baculovirus insect cell system was secreted as a glycosylated latent proteinase that required activation for full proteinase activity (Button et al. (1993) Gene 134, 75-81). To extend these studies, the active site of L. major GP63 was characterized by site-directed mutagenesis and the activation mechanism of latent rGP63 was studied using both secreted and cell surface expression systems. To determine whether the proposed active site of L. major GP63 conforms to other well characterized zinc metalloproteinases, the proposed GP63 catalytic Glu-265, corresponding to catalytic Glu-147 of thermolysin, was changed to Asp-265. Using a transient expression system in COS-7 cells, expression of the Asp-265 mutant GP63 gene resulted in rGP63 with no detectable proteinase activity, whereas expression of the wild-type GP63 gene resulted in rGP63 with a level of proteinase activity similar to native GP63. Thus, the mechanism of GP63 proteinase activity is predicted to be homologous to that of other well characterized zinc metalloproteinases. NH2-Terminal sequence analysis revealed that activation with HgCl2 resulted in removal of the pro region, ultimately generating the mature NH2-terminus. This processing included the removal of a conserved Cys residue (Cys-48) and occurred by a cis mechanism, since the addition of previously activated rGP63 did not lead to an enhancement of latent rGP63 proteinase activation. The mechanism of activation of GP63 is consistent with the cysteine switch mechanism proposed for matrix metalloproteinases and thus has been conserved from protozoa to mammals.

Role of the Leishmania surface protease gp63 in complement fixation, cell adhesion, and resistance to complement-mediated lysis

The Leishmania surface protease gp63 has been identified as a parasite virulence factor. To better define the role of gp63 in Leishmania infectivity, the interaction of recombinant gp63 with complement and complement receptors was examined. On Leishmania, gp63 was not necessary for complement fixation. Complement activation occurred on transfected organisms expressing varying amounts of gp63 and on organisms expressing a mutant form of gp63 devoid of proteolytic activity. However, organisms expressing wild-type gp63 on their surface fixed only small amounts of the terminal complement components and were dramatically more resistant to lysis by complement than were those lacking functional gp63. Organisms expressing wild-type gp63 more rapidly converted C3b on their surface to a form that exhibited the neoantigen of iC3b and interacted avidly with cells expressing Mac-1, the receptor for iC3b. Complement fixation by transfected mammalian cells expressing recombinant Leishmania gp63 on their surface was also examined. The presence of Leishmania gp63 on the surface of these cells converted them into efficient activators of complement. Cells expressing gp63 on their surface fixed complement and bound avidly to the human complement receptors. The proteolytic activity of this molecule was not necessary for complement activation or adhesion to complement receptors. Thus, gp63 may contribute to parasite virulence by exerting a novel type of control over complement fixation. Organisms expressing gp63 can exploit the opsonic properties of complement while avoiding its lytic effects.

Role of the Leishmania surface protease gp63 in complement fixation, cell adhesion, and resistance to complement-mediated lysis

The Leishmania surface protease gp63 has been identified as a parasite virulence factor. To better define the role of gp63 in Leishmania infectivity, the interaction of recombinant gp63 with complement and complement receptors was examined. On Leishmania, gp63 was not necessary for complement fixation. Complement activation occurred on transfected organisms expressing varying amounts of gp63 and on organisms expressing a mutant form of gp63 devoid of proteolytic activity. However, organisms expressing wild-type gp63 on their surface fixed only small amounts of the terminal complement components and were dramatically more resistant to lysis by complement than were those lacking functional gp63. Organisms expressing wild-type gp63 more rapidly converted C3b on their surface to a form that exhibited the neoantigen of iC3b and interacted avidly with cells expressing Mac-1, the receptor for iC3b. Complement fixation by transfected mammalian cells expressing recombinant Leishmania gp63 on their surface was also examined. The presence of Leishmania gp63 on the surface of these cells converted them into efficient activators of complement. Cells expressing gp63 on their surface fixed complement and bound avidly to the human complement receptors. The proteolytic activity of this molecule was not necessary for complement activation or adhesion to complement receptors. Thus, gp63 may contribute to parasite virulence by exerting a novel type of control over complement fixation. Organisms expressing gp63 can exploit the opsonic properties of complement while avoiding its lytic effects.

Microtitration plate enzyme immunoassay to detect PCR-amplified DNA from Candida species in blood

We developed a microtitration plate enzyme immunoassay to detect PCR-amplified DNA from Candida species. Nucleotide sequences derived from the internal transcribed spacer (ITS) region of fungal rDNA were used to develop species-specific oligonucleotide probes for Candida albicans, C. tropicalis, C. parapsilosis, and C. krusei. No cross-hybridization was detected with any other fungal, bacterial, or human DNAs tested. In contrast, a C. (Torulopsis) glabrata probe cross-reacted with Saccharomyces cerevisiae DNA but with no other DNAs tested. Genomic DNA purified from C. albicans blastoconidia suspended in blood was amplified by PCR with fungus-specific universal primers ITS3 and ITS4. With the C. albicans-specific probe labeled with digoxigenin, a biotinylated capture probe, and streptavidin-coated microtitration plates, amplified DNA from a few as two C. albicans cells per 0.2 ml of blood could be detected by enzyme immunoassay.

Mutational and functional analysis of the Leishmania surface metalloproteinase GP63: similarities to matrix metalloproteinases

The major surface glycoprotein of Leishmania, referred to as GP63, is a zinc metalloproteinase of 63,000 M(r) present on promastigotes and amastigotes from diverse species of Leishmania. GP63 shares several characteristics with the members of the matrix metalloproteinase family including degradation of at least one component of the extracellular matrix, location at the cell surface, requirement for Zn2+ for proteinase activity and inhibition of the proteinase activity by chelating agents and alpha 2-macroglobulin. Site-directed mutagenesis of the cloned L. major GP63 genes was carried out to determine whether the proposed active site of Leishmania GP63 was homologous to those of other zinc metalloproteinases. The codon encoding the catalytic glutamic acid was modified to encode an aspartic acid and when expressed in COS-7 cells the resulting mutant GP63 had no demonstrable proteinase activity compared to wild type GP63. GP63 was predicted to be synthesized as a precursor protein containing a pro region at the NH2-terminus of GP63 implicated to be involved with the regulation of proteinase activity. As with many other proteinases, including matrix metalloproteinases, these enzymes are synthesized as latent proteinases that require activation for full proteinase activity. L. major recombinant GP63 (rGP63) has been produced in the baculovirus expression system where rGP63 was secreted as a latent proteinase. To study the activation of baculovirus rGP63, purified rGP63 was incubated with the mercurial compound, HgCl2, at concentrations previously shown to result in activation of other latent matrix degrading metalloproteinases and resulted in a significant enhancement of GP63 proteinase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonculture methods for diagnosis of disseminated candidiasis

Two of the nonculture approaches to the diagnosis of DC, enzymatic-fluorometric determination of serum D-arabinitol and detection of marker antigens in antigenemia (enolase and CWMP), have been commercialized and have shown promise in limited clinical trials. These approaches are not new but are the culmination of efforts made over 10 or more years. Clearly, further fine-tuning of both metabolite and antigen detection is needed to simplify the methods and to improve their sensitivity and specificity so that they will be valuable in guiding clinical treatment decisions. An alternative approach, detection of DC by DNA amplification methods such as PCR, is a special case of a compelling technology and one that is capable of standardization across microbial genera. The availability of simplified PCR diagnostic methods for DC remains a tantalizing prospect. Nevertheless, the development of methods to release DNA from very small numbers of Candida organisms in the blood in a form that is sufficiently free of inhibitors of PCR will require further intensive effort. The maturation of these converging laboratory approaches to nonculture diagnosis of DC leads to more optimism about the eventual use of these methods in clinical laboratories.

Purification and characterization of the extracellular aspartyl proteinase of Candida albicans: removal of extraneous proteins and cell wall mannoprotein and evidence for lack of glycosylation

Aspartyl proteinase (AP) is an extracellular enzyme of Candida albicans implicated as a pathogenic factor. Previous reports on the purification and characterization of AP suggested that a single DEAE-Sephadex chromatographic step was sufficient for the removal of extraneous proteins and that the final product was glycosylated. We purified AP using a chromatographic series consisting of DEAE-Sephadex A25, Sephadex G75 and rechromatography on DEAE-Sephadex A25. Use of DEAE-Sephadex alone did not remove extraneous proteins and removed little contaminating mannoprotein (MP). The addition of a Sephadex G75 column to the purification scheme removed the majority of contaminating MP and proteins. The final DEAE-Sephadex A25 chromatographic step resulted in (a) removal of detectable extraneous proteins, (b) removal of immunologically detectable MP by dot blot and Western blot enzyme immunoassay, (c) loss of periodic acid-silver stain positivity, and (d) a high AP yield (1295 U l-1) and specific activity (1749 U mg-1). We conclude that a single DEAE-Sephadex A25 purification step is insufficient to remove extraneous proteins and MP, which could interfere with the production of AP-specific antibodies and the dissection of moieties responsible for immune reactivity. Reports of periodic acid-Schiff or anthrone positivity of AP preparations may reflect the presence of extraneous MP, which can be removed by the chromatographic series we describe.

Heterogeneity of the purified extracellular aspartyl proteinase from Candida albicans: characterization with monoclonal antibodies and N-terminal amino acid sequence analysis

Three dominant proteins (41, 48, and 49 kDa) were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in purified preparations of the extracellular aspartyl proteinase (AP) of Candida albicans. All three proteins bound to the specific carboxyl proteinase ligand, pepstatin A, and were associated with maximum AP activity. The N-terminal amino acid sequence for the 48- and 49-kDa proteins matched that reported by others for AP, whereas the sequence for the 41-kDa protein was unique and was not homologous to any known protein. Time course studies demonstrated the simultaneous presence of all three proteins, supporting evidence that the 41- and 48-kDa proteins were not breakdown products of AP. Previous studies did not detect carbohydrate in SDS-polyacrylamide gels of purified AP preparations stained with periodic acid and silver, making glycosylation an unlikely explanation for the observed differences in the molecular masses of the proteins. Some monoclonal antibodies directed against the 49-kDa protein reacted with the 41- and 48-kDa proteins, indicating cross-reactive epitopes. Other monoclonal antibodies, however, reacted only with the 49-kDa protein. We conclude that three pepstatin A-binding proteins occur in purified AP preparations: two have the same amino acid N terminus as that reported for AP, whereas the third has a unique sequence. All three proteins should be considered when undertaking studies to determine the role of AP in candidal pathogenesis or when preparing specific antibodies for antigen capture assays.

Humanization of a mouse monoclonal antibody by CDR-grafting: the importance of framework residues on loop conformation

A mouse monoclonal antibody (mAb 425) with therapeutic potential was 'humanized' in two ways. Firstly the mouse variable regions from mAb 425 were spliced onto human constant regions to create a chimeric 425 antibody. Secondly, the mouse complementarity-determining regions (CDRs) from mAb 425 were grafted into human variable regions, which were then joined to human constant regions, to create a reshaped human 425 antibody. Using a molecular model of the mouse mAb 425 variable regions, framework residues (FRs) that might be critical for antigen-binding were identified. To test the importance of these residues, nine versions of the reshaped human 425 heavy chain variable (VH) regions and two versions of the reshaped human 425 light chain variable (VL) regions were designed and constructed. The recombinant DNAs coding for the chimeric and reshaped human light and heavy chains were co-expressed transiently in COS cells. In antigen-binding assays and competition-binding assays, the reshaped human antibodies were compared with mouse 425 antibody and to chimeric 425 antibody. The different versions of 425-reshaped human antibody showed a wide range of avidities for antigen, indicating that substitutions at certain positions in the human FRs significantly influenced binding to antigen. Why certain individual FR residues influence antigen-binding is discussed. One version of reshaped human 425 antibody bound to antigen with an avidity approaching that of the mouse 425 antibody.

Mechanisms of fungal pathogenicity: correlation of virulence in vivo, susceptibility to killing by polymorphonuclear neutrophils in vitro, and neutrophil superoxide anion induction among Blastomyces dermatitidis isolates

Seven Blastomyces dermatitidis isolates varying in virulence for mice were compared for susceptibility to polymorphonuclear neutrophil (PMN) killing and the ability to induce superoxide anion (O2-) production by PMNs in vitro. In vitro killing of six B. dermatitidis isolates by murine peripheral blood PMNs or by PMNs elicited from the peritoneal cavity by a local immune reaction (B. dermatitidis-immune mice given killed B. dermatitidis intraperitoneally 24 h earlier) inversely correlated with in vivo virulence (most to least virulent) isolates: VV, V, V40, KL-1, A2, and GA-1). The capacity of isolates to induce O2- production by PMNs also inversely correlated with in vivo virulence. Isolate A, of intermediate in vivo virulence, was a good inducer of O2- production in vitro but was no more susceptible to in vitro killing by PMNs than isolate V, VV, or V40. Fungal intracellular superoxide dismutase or catalase content did not correlate with in vivo virulence or in vitro killing by PMNs. Isolate A, however, had two to four times the intracellular catalase activity as did other B. dermatitidis isolates, suggesting a possible mechanism for its enhanced resistance to in vitro killing by PMNs. Therefore, while in vitro killing by PMNs and the capacity to induce O2- production by PMNs inversely correlated with virulence for six B. dermatitidis isolates, isolate A was an exception: its resistance to killing by PMN-generated oxygen metabolites in vitro but its susceptibility to killing in vivo suggest that its in vivo killing occurs by other, perhaps nonoxidative, mechanisms.

Comparative effects of cilofungin and amphotericin B on experimental murine candidiasis

The effectiveness of cilofungin (LY121019, referred to hereafter as LY), a lipopeptide, was studied in a murine candidiasis model. CD-1 mice (5 weeks old) were injected intravenously with 3 x 10(5) Candida albicans yeast cells. Intraperitoneal LY or amphotericin B (AmB) therapy was begun 4 days after infection and was continued daily for 2 weeks. LY and AmB were compared at 62.5, 6.25, and 0.625 mg/kg per day, with the LY dose split into two treatments per day. Mice were observed for 30 days postinfection, and survivors were necropsied. AmB at 62.5 mg/kg per day was lethal in the absence of infection. Cumulative mortality for infected controls was 94% (17 of 18). Survival of mice treated with the control diluent for LY was the same as survival with no treatment. Survival after 0.625 mg of LY per kg per day was the same as that of the controls, and 6.25 or 62.5 mg of LY per kg per day was significantly superior. AmB treatment at 0.625 or 6.25 mg/kg per day was protective and superior to the same LY doses. Atrophied kidneys were common in AmB-treated mice, and mice treated with 6.25 mg of AmB per kg per day appeared ill during therapy. The number of CFU recovered from kidneys and spleens of surviving mice reflected the same relationships between drugs and doses as those described for mortality. C. albicans was not cleared from the kidneys of mice in any group, and only in the 6.25-mg/kg-per-day AmB treatment group was not detectable C. albicans found in the spleens. These data indicate that LY or AmB suppresses candida infection but neither is curative in this model.

In vivo activation of peripheral blood polymorphonuclear neutrophils by gamma interferon results in enhanced fungal killing

The effect of in vivo administration of murine recombinant gamma interferon (IFN) on the fungicidal activity of murine peripheral blood polymorphonuclear neutrophils (PB-PMNs) was studied. Mice were injected intramuscularly with 250, 2,500, 25,000 or 250,000 U of IFN 5 h before collection of peripheral blood. Purified PB-PMNs were cocultured in vitro with Blastomyces dermatitidis yeast cells for 2 h. PB-PMNs from untreated mice killed 44.5 +/- 12.5% of the fungal inoculum, whereas PB-PMNs from mice treated with 25,000 or 250,000 U of IFN showed significantly enhanced in vitro killing (68.0 +/- 9.4% [P less than 0.005] and 72.3 +/- 1.1% [P less than 0.001], respectively). Treatment with 250 or 2,500 U of IFN or 25,000 U of heated (100 degrees C, 15 min) IFN had no effect. The IFN-induced activation of PB-PMNs was transitory. Significant enhancement of PB-PMN killing activity occurred 1, 2, or 5 h after in vivo IFN administration, but no enhancement was observed 16 or 24 h after IFN treatment. Enhanced fungicidal activity by PB-PMNs from mice treated for 5 h with 25,000 U of IFN correlated with an increased release of superoxide anion (O2-) in vitro after stimulation of PB-PMNs with phorbol ester; normal PB-PMNs and IFN-activated PB-PMNs, respectively, produced 2.2 +/- 2.5 and 23.5 +/- 4.8 nmol of O2- per 10(6) PB-PMNs per 30 min (P less than 0.005). The exogenous addition of compounds that antagonize or inhibit the formation of oxygen radicals (superoxide dismutase, catalase, dimethyl sulfoxide, or sodium azide) significantly inhibited fungal killing by both normal and IFN-activated PB-PMNs. In addition to the enhanced microbicidal activity and superoxide generation demonstrated in vitro with constant cell numbers, there was a transient leukocytosis (particularly neutrophilia) in peripheral blood at doses of IFN and at times after IFN administration where enhanced activity was also demonstrated. In summary, our results indicate that PB-PMNs can be activated in vivo for enhanced killing of a fungal target. The enhanced killing capacity of IFN-activated PB-PMNs is due at least in part to the enhancement of oxidative killing mechanisms.

Enhanced killing of Blastomyces dermatitidis by gamma interferon-activated murine peripheral blood polymorphonuclear neutrophils

Normal peripheral blood polymorphonuclear neutrophils (PB-PMNs), challenged in vitro with yeast form Blastomyces dermatitidis, reduced inoculum colony-forming units of a virulent strain by 37.5 +/- 9.5%. Pre-incubation of PB-PMNs with 10-100,000 U/ml of purified recombinant murine gamma-interferon (IFN) for 1 h prior to challenge with fungi resulted in significant enhancement of PB-PMN fungicidal activity. No direct fungicidal activity by IFN alone was observed. Pretreatment of selected concentrations of IFN shown to have PMN-enhancing activity (100 or 1000 U/ml) with rabbit hyperimmune anti-IFN antiserum for 1 h before addition to PB-PMNs abrogated the enhancement of fungicidal activity. Isolated peripheral blood mononuclear cells failed to kill B. dermatitidis, even when mononuclear cells were present at a concentration ten times greater than that normally used in killing assays, and failed to be activated by IFN. Treatment of unstimulated or IFN-activated PB-PMNs with complement and hybridoma-derived monoclonal antibody specific for PMNs eliminated PB-PMN fungicidal activity. Exogenously added lipopolysaccharide (0.0005-50,000 ng/ml) did not activate PB-PMNs, whether added alone or in conjunction with IFN. The PB-PMN activating capacity of IFN could be destroyed by heat treatment (100 degrees C, 15 min) or by acid treatment with HCl (pH 2). These results demonstrate that recombinant gamma-interferon can stimulate PB-PMNs to kill B. dermatitidis, that the PB-PMN activating moiety is IFN and that PB-PMNs are responsible for fungal killing in this assay system.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced oxidative mechanisms in immunologically activated versus elicited polymorphonuclear neutrophils: correlations with fungicidal activity

Peritoneal polymorphonuclear neutrophils (PMN) from mice were tested for their ability to kill the yeast form of Blastomyces dermatitidis (Bd) in vitro and for their fungicidal mechanisms. PMN elicited from immune mice by the intraperitoneal injection of non-viable Bd (referred to as immunologically activated PMN or ActPMN) showed significantly enhanced fungicidal activity in comparison with PMN elicited with thioglycollate medium (ThioPMN) [means = 44.7% (SD 12.8%) and 16.4% (SD 9.2%) killed; n = 14; p less than 0.001]. Production of superoxide anion (O2-) by ActPMN after stimulation with phorbol myristate acetate was enhanced in comparison with production by ThioPMN. Superoxide dismutase, which removes O2-, inhibited ActPMN killing by 75% (p less than 0.001) when added to cultures immediately before challenge with Bd (optimal concentration: 6000 U/ml). Sodium azide, which inhibits myeloperoxidase and scavenges singlet oxygen (1O2), and catalase, which breaks down hydrogen peroxide (H2O2), inhibited ActPMN killing by 64% (p less than 0.001) and 52% (p less than 0.001), with optimal concentrations of 1 mM and 10,000 U/ml, respectively. Two agents that both scavenge 1O2 and antagonise hypochlorous acid (HOCl-), histidine and tryptophan, were also powerful inhibitors of ActPMN killing. Quenchers of hydroxyl radical (.OH), dimethylsulfoxide and sodium benzoate, had less effect, and required higher concentrations. These data suggest that the enhanced killing of Bd by ActPMN involves one or more oxidative mechanisms, and that there is a prominent role for O2-, either directly or as a precursor of other active oxygen species, a probable role for H2O2, and possible roles for 1O2, HOCl-, and .OH.