Extracellular proteins of Cryptococcus neoformans and host antibody response

Models for Inducing Experimental Cryptococcosis in Mice

Cryptococcus neoformans and Cryptococcus gattii are the predominant etiological agents of cryptococcosis, a particularly problematic disease in immunocompromised individuals. The increased clinical use of immunosuppressive drugs, the inherent ability of Cryptococcus species to suppress and evade host immune responses, and the emergence of drug-resistant yeast support the need for model systems that facilitate the design of novel immunotherapies and antifungals to combat disease progression. The mouse model of cryptococcosis is a widely used system to study Cryptococcus pathogenesis and the efficacy of antifungal drugs in vivo. In this chapter, we describe three commonly used strategies to establish cryptococcosis in mice: intranasal, intratracheal, and intravenous inoculations. Also, we discuss the methodology for delivering drugs to mice via intraperitoneal injection.

Differentiated extracts from freshwater and terrestrial mollusks inhibit virulence factor production in Cryptococcus neoformans

The human fungal pathogen, Cryptococcus neoformans, is responsible for deadly infections among immunocompromised individuals with the evolution of antifungal resistance driving the solution to discover new compounds that inhibit fungal virulence factors rather than kill the pathogen. Recently, exploration into natural sources (e.g., plants, invertebrates, microbes) of antifungal agents has garnered attention by integrating a One Health approach for new compound discovery. Here, we explore extracts from three mollusk species (freshwater and terrestrial) and evaluate effects against the growth and virulence factor production (i.e., thermotolerance, melanin, capsule, and biofilm) in C. neoformans. We demonstrate that clarified extracts of Planorbella pilsbryi have a fungicidal effect on cryptococcal cells comparable to fluconazole. Similarly, all extracts of Cipangopaludina chinensis affect cryptococcal thermotolerance and impair biofilm and capsule production, with clarified extracts of Cepaea nemoralis also conveying the latter effect. Next, inhibitory activity of extracts against peptidases related to specific virulence factors, combined with stress assays and quantitative proteomics, defined distinct proteome signatures and proposed proteins driving the observed anti-virulence properties. Overall, this work highlights the potential of compounds derived from natural sources to inhibit virulence factor production in a clinically important fungal pathogen.

From Naturally-Sourced Protease Inhibitors to New Treatments for Fungal Infections

Proteases are involved in a broad range of physiological processes, including host invasion by fungal pathogens, and enzymatic inhibition is a key molecular mechanism controlling proteolytic activity. Importantly, inhibitors from natural or synthetic sources have demonstrated applications in biochemistry, biotechnology, and biomedicine. However, the need to discover new reservoirs of these inhibitory molecules with improved efficacy and target range has been underscored by recent protease characterization related to infection and antimicrobial resistance. In this regard, naturally-sourced inhibitors show promise for application in diverse biological systems due to high stability at physiological conditions and low cytotoxicity. Moreover, natural sources (e.g., plants, invertebrates, and microbes) provide a large reservoir of undiscovered and/or uncharacterized bioactive molecules involved in host defense against predators and pathogens. In this Review, we highlight discoveries of protease inhibitors from environmental sources, propose new opportunities for assessment of antifungal activity, and discuss novel applications to combat biomedically-relevant fungal diseases with in vivo and clinical purpose.

Predominance of Cryptococcus neoformans Var. grubii in Ahvaz, Molecular Identification and Evaluation of Virulence Factors

Background: Cryptococcus neoformans is an encapsulated yeast pathogen with worldwide distribution, and the highest incidence of cryptococcosis was attributed to C. neoformans (var. grubii. The pathogenicity of Cryptococcus species is associated with several factors, including capsule and melanin production, growth at 37 ºC, and secretion of extracellular enzymes. Objectives: The present study aimed to isolate and identify Cryptococcus species from pigeon guano in Ahvaz, Iran and investigate important virulence factors in the isolates. Methods: Seventy-three isolates of C. neoformans var. grubii were identified based on classical and molecular microbiology methods. Capsule size was measured by the grow yeasts in the presence of 5% CO2. Specific media demonstrated the activity of extracellular enzymes (phospholipase, hemolysin, proteinase, esterase, urease, catalase, and gelatinase). Besides, melanin production was evaluated by the niger seed agar medium. Results: Two hundred and seventeen samples were examined for the presence of Cryptococcus over 165 days in Ahvaz. All tested isolates were contained capsules with variable sizes under 5% CO2 concentration. Moreover, 100% of isolates were produced extracellular enzymes (urease, hemolysin, and catalase), whereas no proteinase and gelatinase activities were observed among isolates. Furthermore, most isolates had phospholipase (93.1%) and esterase activities (86.3%). Also, melanin was produced by all of the isolates. Conclusions: Although two methods were used for recovery of Cryptococcus, only Cryptococcus was isolated from pigeon guano, and swabs from the cage walls were negative. Cryptococcus neoformans var. grubii was the only species from pigeon droppings from Ahvaz with more pathogenic factors. Owing to the high pathogenicity of the isolates, the frequency of the disease is expected to be higher.

Enzymatic characterization of clinical and environmental Cryptococcus neoformans strains isolated in Italy

BACKGROUND

Cryptococcus neoformans is an encapsulated yeast causing mainly opportunistic infections. The virulence factors involved in cryptococcosis pathogenesis include the presence and the size of the polysaccharide capsule, the production of melanin by phenoloxidase, the growth at 37°C and the enzyme secretion like proteinase, phospholipase and urease. Many other enzymes are secreted by C. neoformans but their role in the fungus virulence is not yet known.

AIMS

In order to investigate this topic, we compared the phospholipase production between strains from patients and from bird droppings, and we examined its relationship to phenoloxidase production. We further characterized the strains by determining the activity of 19 different extracellular enzymes.

METHODS

Two hundred and five Italian C. neoformans clinical isolates and 32 environmental isolates were tested. Phenoloxidase production was determined by the development of brown colonies on Staib's agar. Extracellular phospholipase activity was performed using the semiquantitative egg-yolk plate method. API ZYM commercial kit was used to observe the production and the activity of 19 different extracellular enzymes.

RESULTS

Statistical analysis of the results showed a significantly higher phospholipase activity in the clinical isolates than in the environmental isolates. No significant difference about the phenoloxidase production between both groups was found. Regarding the 19 extracellular enzymes tested using the API ZYM commercial kit, acid phosphatase showed the highest enzymatic activity in both groups. Concerning the enzyme α-glucosidase, the clinical isolates presented a significantly higher positivity percentage than the environmental isolates. A hundred percent positivity in the enzyme leucine arylamidase production was observed in both groups, but the clinical isolates metabolized a significantly greater amount of substrate.

CONCLUSIONS

The higher phospholipase production in the clinical isolates group confirms the possible role of this enzyme in the cryptococcosis pathogenesis. The extracellular activities of the enzymes acid phosphatase, α-glucosidase and leucine arylamidase, tested by means of the API ZYM commercial kit, appear to be very interesting. Many studies indicate that these enzymes are involved in the virulence of bacteria and parasites; our results suggest their possible role as virulence factors in Cryptococcus infections too.

Virulence-Associated Enzymes of Cryptococcus neoformans

Enzymes play key roles in fungal pathogenesis. Manipulation of enzyme expression or activity can significantly alter the infection process, and enzyme expression profiles can be a hallmark of disease. Hence, enzymes are worthy targets for better understanding pathogenesis and identifying new options for combatting fungal infections. Advances in genomics, proteomics, transcriptomics, and mass spectrometry have enabled the identification and characterization of new fungal enzymes. This review focuses on recent developments in the virulence-associated enzymes from Cryptococcus neoformans. The enzymatic suite of C. neoformans has evolved for environmental survival, but several of these enzymes play a dual role in colonizing the mammalian host. We also discuss new therapeutic and diagnostic strategies that could be based on the underlying enzymology.

Cryptococcus strains with different pathogenic potentials have diverse protein secretomes

Secreted proteins are the frontline between the host and pathogen. In mammalian hosts, secreted proteins enable invasive infection and can modulate the host immune response. Cryptococcosis, caused by pathogenic Cryptococcus species, begins when inhaled infectious propagules establish to produce pulmonary infection, which, if not resolved, can disseminate to the central nervous system to cause meningoencephalitis. Strains of Cryptococcus species differ in their capacity to cause disease, and the mechanisms underlying this are not well understood. To investigate the role of secreted proteins in disease, we determined the secretome for three genome strains of Cryptococcus species, including a hypovirulent and a hypervirulent strain of C. gattii and a virulent strain of C. neoformans. Sixty-seven unique proteins were identified, with different numbers and types of proteins secreted by each strain. The secretomes of the virulent strains were largely limited to proteolytic and hydrolytic enzymes, while the hypovirulent strain had a diverse secretome, including non-conventionally secreted canonical cytosolic and immunogenic proteins that have been implicated in virulence. The hypovirulent strain cannot establish pulmonary infection in a mouse model, but strains of this genotype have caused human meningitis. To directly test brain infection, we used intracranial inoculation and found that the hypovirulent strain was substantially more invasive than its hypervirulent counterpart. We suggest that immunogenic proteins secreted by this strain invoke a host response that limits pulmonary infection but that there can be invasive growth and damage if infection reaches the brain. Given their known role in virulence, it is possible that non-conventionally secreted proteins mediate this process.

Utilization of fish meal and fish oil for production of Cryptococcus sp. MTCC 5455 lipase and hydrolysis of polyurethane thereof

Fish meal has been used as an additional nitrogen source and fish oil as inducer for the growth and production of lipase from Cryptococcus sp. MTCC 5455. A response surface design illustrated that the optimum factors influencing lipase production were fish meal, 1.5 %, w/v, Na2HPO4, 0.2 %, w/v, yeast extract, 0.25 %, w/v and sardine oil, 2.0 %, w/v with an activity of 71.23 U/mL at 96 h and 25 °C, which was 48.39 % higher than the conventional one-factor-at-a-time method. The crude concentrated enzyme hydrolyzed polyurethane (PUR) efficiently and hydrolysis was 94 % at 30 °C and 96 h. The products, diethylene glycol and adipic acid were quantified by HPLC and scanning electron microscopic studies of the degraded polymer showed significant increase in size of the holes from 24 to 72 h of incubation. Hydrolysis of PUR within 96 h makes the lipase novel for disposal of PUR and provides an innovative solution to the problems created by plastic wastes.

Deletion of the CAP10 gene of Cryptococcus neoformans results in a pleiotropic phenotype with changes in expression of virulence factors

The human pathogen Cryptococcus neoformans causes meningo-encephalitis. The polysaccharide capsule is an important virulence factor for this yeast-like fungus. Previously, we had shown that disruption of the CAP10 gene, encoding a putative xylosyltransferase, results in mutant cells that lack most of the capsular polysaccharides on the cell surface, but do not show a typical acapsular phenotype. In contrast to the acapsular cap59 mutant, cap10 did not induce maturation of dendritic cells when exposed to components of the immune system. In order to gain further insight into the causes of this phenotype displayed by the cap10 mutant, we performed a more in-depth phenotypic analysis of the cell wall and surface structures of this mutant compared to the wild type strain and acapsular mutant cap59. Moreover, we analyzed the cap10 mutant and the wild type strain for differential gene expression of, amongst others, enzymes that are involved in biogenesis of cell wall and capsule components. We conclude that a mutation in the CAP10 gene results in a pleiotropic phenotype with effects on different cellular processes affecting, amongst others, cell size, expression of virulence factors and size of extracellular vesicles.

Antifungal susceptibility, enzymatic activity, PCR-fingerprinting and ITS sequencing of environmental Cryptococcus laurentii isolates from Uberaba, Minas Gerais, Brazil

Cryptococcus laurentii has been classically considered a saprophytic species, although several cases of human infection have been already reported. This study aimed to evaluate the phospholipase, proteinase and hemolysins activity, the antifungal susceptibility profile, the genetic variability by M13 and (GACA)(4) fingerprinting and the internal transcribe spacer (ITS) sequencing of 38 C. laurentii isolates recovered from captive bird droppings and surrounding hospital areas. All of them exhibited phospholipase activity, while the hemolytic activity was evidenced in 34 (89.4%) isolates. None of them exhibited proteinase activity. Twenty-seven isolates (71.1%) presented susceptibility dose dependent to fluconazole. Most isolates (94.7%) were susceptible to voriconazole, while one (2.65%) was resistant to this drug. Twenty-one (55.3%) isolates showed reduced susceptibility to itraconazole while nine (23.7%) were resistant. Three (7.9%) and five (13.1%) isolates exhibited resistance to ketoconazole and amphotericin B, respectively. Most C. laurentii fingerprinting obtained with M13 and (GACA)(4) showed high heterogeneity. By using the two primers, seven (18.4%) isolates grouped as A (CL2, CL7, and CL8), B (CL35, CL38) and C (CL29, CL30) with 100% similarity. Different from most variable surrounding hospital isolates, all but one of the pet shops strains clustered with the two primers, although they had been recovered from different neighborhoods. All isolates were identified as C. laurentii phylogenetic group I by ITS sequencing. Thus, the presence of virulence factors, a decreased antifungal susceptibility and a heterogeneous molecular pattern of the C. laurentii isolates here described suggests this species can be a potential pathogen in the context of the immunocompromised population.

The fatal fungal outbreak on Vancouver Island is characterized by enhanced intracellular parasitism driven by mitochondrial regulation

In 1999, the population of Vancouver Island, Canada, began to experience an outbreak of a fatal fungal disease caused by a highly virulent lineage of Cryptococcus gattii. This organism has recently spread to the Canadian mainland and Pacific Northwest, but the molecular cause of the outbreak remains unknown. Here we show that the Vancouver Island outbreak (VIO) isolates have dramatically increased their ability to replicate within macrophages of the mammalian immune system in comparison with other C. gattii strains. We further demonstrate that such enhanced intracellular parasitism is directly linked to virulence in a murine model of cryptococcosis, suggesting that this phenotype may be the cause of the outbreak. Finally, microarray studies on 24 C. gattii strains reveals that the hypervirulence of the VIO isolates is characterized by the up-regulation of a large group of genes, many of which are encoded by mitochondrial genome or associated with mitochondrial activities. This expression profile correlates with an unusual mitochondrial morphology exhibited by the VIO strains after phagocytosis. Our data thus demonstrate that the intracellular parasitism of macrophages is a key driver of a human disease outbreak, a finding that has significant implications for a wide range of other human pathogens.

[In vitro determination of virulence factors activity associated with several Cryptococcus neoformans clinical isolates]

Different phenotypic characteristics associated with virulence of the Cryptococcus neoformans species complex have shown an important role in their pathogenicity. In this study we have determined the role of phenotypically and genotypically factors of some virulence factors from clinical isolates in the two species of the complex; 35 C. neoformans and 19 Cryptococcus gattii. Growth at 37 degrees C, macroscopic and microscopic morphology, switching phenomenon, activity of 23 extracellular enzymes, variability of the colonies in agar with phloxin B; phospholipase B gene, and the mating type were determined by PCR; the molecular pattern was determined by URA5 RFLP. All isolates grew at 37 degrees C, the capsular size was greater in C. gattii (1.87 microm -/+1.47 microm) than in C. neoformans (0.83 microm -/+0.15 microm). Switching was observed mainly in isolates of C. gattii. All isolates expressed the enzyme urease, a lower activity of the proteases (Pz= 0.54), but a higher activity of the phospholipase (Pz=0.43) and phenoloxidase (Pz=0.003) was determined for C. gattii.

Therapeutic efficacy of a conjugate vaccine containing a peptide mimotope of cryptococcal capsular polysaccharide glucuronoxylomannan

Vaccination with P13, a peptide mimotope of the cryptococcal capsular polysaccharide glucuronoxylomannan (GXM), has been shown to confer protection against a subsequent lethal Cryptococcus neoformans challenge. In this study, we sought to investigate whether P13-based vaccines could be effective in an already-established infection. To address this question, we developed a systemic chronic cryptococcal infection model. We vaccinated chronically infected mice with P13-protein conjugates and monitored their survival. Compared to the controls, the conjugates prolonged the survival of chronically infected mice. The degree of protection was a function of the mouse strain (BALB/c or C57BL/6), the carrier protein (tetanus toxoid or diphtheria toxoid), and the route of infection (intraperitoneal or intravenous). Serum GXM levels were correlated with the day of death, but the correlation was driven by the carrier protein and mouse strain. The passive transfer of heat-treated sera from P13 conjugate-vaccinated mice conferred protection to naïve BALB/c mice, indicating that antibody immunity could contribute to protection. The measurement of peripheral blood cytokine (gamma interferon [IFN-gamma], interleukin-10 [IL-10], and IL-6) gene expression showed that P13 conjugate-vaccinated BALB/c and C57BL/6 mice mounted a strong Th2 (IL-10)-like response relative to the Th1 (IFN-gamma)-like response, with the degree depending on the mouse strain and carrier protein. Taken together, our data suggest that a vaccine could hold promise in the setting of chronic cryptococcosis, and that vaccine efficacy could depend on immunomodulation and augmentation of the natural immune response of the host.

Extracellular glycosylphosphatidylinositol-anchored mannoproteins and proteases of Cryptococcus neoformans

Extracellular proteins of Cryptococcus neoformans are involved in the pathogenesis of cryptococcosis, and some are immunoreactive antigens that may potentially serve as candidates for vaccine development. To further study the extracellular proteome of the human fungal pathogen Cry. neoformans, we conducted a proteomic analysis of secreted and cell wall-bound proteins with an acapsular strain of Cry. neoformans. Proteins were identified from both intact cells and cell walls. In both cases, extracellular proteins were removed with trypsin or beta-glucanase, and then all proteins/peptides were purified by solid-phase extraction, spin dialysis, and HPLC, and identified by liquid chromatography-mass spectrometry. This study identified 29 extracellular proteins with a predicted N-terminal signal sequence and also a predicted glycosylphosphatidylinositol anchor motif in more than half. Among the novel proteins identified were five glycosylphosphatidylinositol-anchored proteins with extensive Ser/Thr-rich regions but no apparent functional domains, a glycosylphosphatidylinositol-anchored aspartic protease, and a metalloprotease with structural similarity to an elastinolytic metalloprotease of Aspergillus fumigatus. This study suggests that Cry. neoformans has the machinery required to target glycosylphosphatidylinositol-anchored proteins to the cell wall, and it confirms the extracellular proteolytic ability of Cry. neoformans.

Actividad enzimática extracelular en Cryptococcus neoformans en diferentes países

Three hundred and ten Cryptococcus neoformans strains isolated from AIDS patients in five different countries (151 from Brazil, 23 from Italy, 28 from Spain, 104 from Thailand and four from Turkey) were tested by the API-ZYM kit to detect their extracellular enzymatic activity. The enzymes esterase (C4) (no 3), esterase lipase (C8) (no 4), leucine arylamidase (no 6) and acid phosphatase (no 11) were commonly positive in most of the strains (more than 95%). These enzymes could be considered a useful tool not only for C. neoformans identification, but in particular for their possible relationship to new C. neoformans virulence factors and also for epidemiological research. Interestingly, it is also the high positive percentage of alpha-glucosidase and beta-glucosidase detected in all isolates. The serotype A was the most predominant serotype in all countries, except for Italy where the serotype D was predominant. Further studies are needed to draw a clear correlation between the API-ZYM profile and serotype.

Identification of major proteins secreted by Cryptococcus neoformans

The characterization of proteins secreted by Cryptococcus neoformans is of relevance to the identification of vaccine candidates, because concentrated supernatants from the fungus have been shown to be immunoprotective in previous studies. After fractionation of supernatants by anion exchange chromatography and preparative electrophoresis, we obtained the N-terminal amino acid sequences of 13 major proteins. Using a C. neoformans nucleotide database, we were able to clone and sequence the ORFs coding for 12 of these proteins. Some of the genes are identical to previously described ones, while six encode novel proteins, including four putative mannoproteins. The molecular characterization of these and other secreted products may provide useful information in the development of immune-based strategies to control cryptococcosis.

Feasibility and prospects for a vaccine to prevent cryptococcosis

Cryptococcosis is a relatively common fungal disease caused by Cryptococcus neoformans that has high morbidity and mortality. Numerous studies have established the feasibility of enhancing host immunity to C neoformans in naive immunocompetent animal models by vaccination. Several antigens have been identified that appear to be suitable vaccine candidates. Induced immune responses can mediate protection through both humoral and cellular immunity. Hence, a vaccine against cryptococcosis in humans is probably feasible but there are significant obstacles to vaccine development that range from uncertainties about the pathogenesis of infection to economic considerations.

Characterization of two novel cryptococcal mannoproteins recognized by immune sera

Host defenses against the encapsulated yeast Cryptococcus neoformans involve both humoral and cell-mediated immunity. Mannoproteins (MPs) are a heterogeneous class of immunodominant glycoproteins which have been only incompletely characterized. In this study, we report on the molecular features of two novel MPs that are recognized by serum antibodies during cryptococcosis. After fractionation of extracellular cryptococcal products, MPs reacted more strongly than other components with sera from C. neoformans-infected AIDS patients. Further fractionation and Western blot analysis of MPs evidenced the presence of highly reactive bands with molecular masses of 250, 125, 115, and 84 kDa. The 115- and 84-kDa bands contained significant amounts of N-linked oligosaccharides, as shown by decreased molecular mass after peptide-N-glycosidase F treatment. N-terminal amino acid sequences of the two bands were used to search C. neoformans nucleotide databases. Homologous genomic sequences were used to synthesize DNA probes and isolate cDNA clones containing the full-length genes, which were designated MP84 and MP115. Both genes showed the presence of a serine/threonine-rich region, a potential site for heavy glycosylation. MP84 and MP115 showed homology with, respectively, polysaccharide deacetylases and carboxylesterases from other organisms. Recombinant, deglycosylated proteins expressed in Escherichia coli still reacted with sera from patients, albeit more weakly than natural MPs, indicating that at least some of the reactive epitopes were retained in the recombinant forms. In conclusion, we identified two novel MPs that are important targets of antibody responses during cryptococcosis. These data may be useful to devise alternative immunity-based strategies to control the disease.

Isolation and Characterization of Cryptococcus neoformans from Environmental Sources in Busan

Twenty nine samples of pigeon droppings (n = 12) and soil contaminated with avian excreta (n = 19), collected from different sites in Busan, were examined for isolation and characterization of Cryptococcus neoformans. Of these samples, 5 strains of C. neoformans were recovered from pigeon droppings (5/12 : 41.7%). All isolates were belonged to C. neoformans var. grubii (serotype A). The extracellular enzyme activities of the strains by using the API-ZYM system showed two different enzymatic patterns. The genetic variability among C. neoformans isolates was analyzed by random amplified polymorphic DNA (RAPD) using three 10-mer primers. Two different RAPD patterns, which clearly distinguished the isolates, were identified. Analysis of RAPD patterns provided a good characterization of environmental strains of C. neoformans serotype A as a heterogeneous group and were in good agreement with enzymatic profiles.

Extracellular enzymatic activity and serotype of Cryptococcus neoformans strains isolated from AIDS patients in Brazil

One hundred and fifty-one Cryptococcus neoformans strains isolated from AIDS patients in Brazil and maintained in the Adolfo Lutz Institute (São Paulo, Brazil) were tested for phospholipase, protease and other extracellular enzymatic activities and their serotypes determined. Production of extracellular phospholipase and protease was tested by the agar plate methods. Determination of extracellular enzyme profile of the strains was performed by using the API-ZYM kit system, which can test 19 different enzymes. The serotypes were determined by cell agglutination using the Crypto-check method. Among the 151 strains, 147 were identified as serotype A and four strains were serotype AD. Production of extracellular phospholipase and protease was extensive and observable at early stages of incubation. All of the tested strains were positive for the production of both enzymes. In the API-ZYM tests, more than 90 % of the 151 tested strains were positive for esterase C4 (No. 3), esterase lipase C8 (No. 4), leucine arylamidase (No. 6), phosphatase acid (No. 11), naphtol-AS-BI-phosphohydrolase (No. 12), alpha-glucosidase (No. 16) and beta-glucosidase (No. 17). Differences in enzymatic activities between the Brazilian strains and strains isolated in other countries were observed. The phospholipase, protease and other enzyme activities may play a role in host tissue invasion by C. neoformans.

Purification and characterization of a 43-kilodalton extracellular serine proteinase from Cryptococcus neoformans

An extracellular proteinase was purified from culture filtrates of Cryptococcus neoformans NHPY24 by DEAE ion-exchange chromatography and gelatin affinity column chromatography with azoalbumin as the substrate. The molecular mass of the purified enzyme was 43 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, its pH optimum was 7.0 to 8.0, and maximal activity was obtained at pH 7.5 and 37 degrees C. By isoelectric focusing, the purified enzyme had a pI of 4.77. Enzyme activity was inhibited by serine proteinase inhibitors such as phenylmethylsulfonyl fluoride and diisopropylfluorophosphate. The purified enzyme was thus a serine proteinase. It hydrolyzed natural substrates including hemoglobin, beta-casein, and gamma globulin.

Humoral response against Cryptococcus neoformans mannoprotein antigens in HIV-infected patients

Twenty-four sera from healthy donors, 18 from HIV-positive patients (< 200 CD4+/mm3) and 18 sera collected before and during cryptococcosis from HIV-positive patients were analysed for the presence of humoral response to C. neoformans mannoproteins. Our results show that samples from healthy subjects and from HIV-positive patients had one of three antibody response profiles: (i) presence of reactive antibodies against both 105 and 80 kilodalton mannoproteins; (ii) presence of reactive antibodies against one of the two mannoproteins; or (iii) absence of reactive antibodies. Importantly the percentage of unreactive sera increased 6-fold in HIV-positive patients and more than 10-fold in patients with cryptococcosis. In addition, in the latter patients no variation of humoral response before and during cryptococcosis was observed. These results suggest that HIV-positive patients show a marked difficulty in mounting or maintaining antibody response to mannoprotein and this could contribute to predisposition to cryptococcosis.

Budding of melanized Cryptococcus neoformans in the presence or absence of L-dopa

Cryptococcus neoformans is a pathogenic fungus that produces melanin when incubated in the presence of certain phenolic substrates such as L-3,4-dihydroxyphenylalanine (L-dopa). Melanin is an enigmatic polymer that is deposited in the cell wall and contributes to virulence. Substantial progress has been made in understanding the synthesis of melanin and the mechanisms by which it contributes to virulence, but relatively little is known about how melanin is rearranged during growth and budding. In this study we used transmission and scanning electron microscopy and immunofluorescence of melanized cells and melanin 'ghosts' to study the process of melanization during replication. Budding in melanized C. neoformans results in focal disruption of cell-wall melanin at the bud site. In the presence of L-dopa, bud-related melanin defects are repaired and daughter cells are melanized. However, in the absence of substrate, mother cells cannot repair their melanin defects and daughter cells are non-melanized. Hence, melanin in the parent cell is not carried to the daughter cells, but rather is synthesized de novo in buds. These results imply that melanin remodelling occurs during cell growth in a process that involves degradation and synthesis at sites of budding.

An ecto-protein tyrosine phosphatase of Entamoeba histolytica induces cellular detachment by disruption of actin filaments in HeLa cells

Actin cytoskeleton disruption in host cells has been demonstrated for PTPases from pathogenic microorganisms. In this work, we analysed whether the secreted acid phosphatase from Entamoeba histolytica has phosphotyrosine phosphatase activity and the possibility that this activity may participate in damaging host cells. The secreted acid phosphatase of E. histolytica, which catalyses p-nitrophenyl phosphate hydrolysis at acid pH values, was found to have phosphotyrosine phosphatase activity. The enzymatic properties of phosphotyrosine phosphatase and acid phosphatase were virtually identical and included: Km values of 10 x 10(-4) M, no requirement for divalent cations, and sensitivity to molybdate, vanadate, and tungstate. The phosphotyrosyl phosphatase activity caused significant levels of cell rounding and detachment correlating with disruption of the actin stress fibres in HeLa cells. Thus, our data suggest that secreted phosphotyrosine phosphatase could play a cytotoxic role during amoebic infection.

Identification and cloning of a cryptococcal deacetylase that produces protective immune responses

Cell-mediated immunity plays a crucial role in host defenses against Cryptococcus (Filobasidiella) neoformans. Therefore, the identification of cryptococcal antigens capable of producing T-cell-mediated responses, such as delayed-type hypersensitivity (DTH) reactions, may be useful in the development of immune-based strategies to control cryptococcosis. In order to characterize DTH-producing antigens, culture supernatants from the unencapsulated Cap-67 strain were separated by anion-exchange chromatography. After further fractionation by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a purified protein with an apparent molecular mass of 25 kDa was found to produce DTH, as evidenced by increased footpad swelling in mice immunized with culture supernatants, relative to unimmunized mice. The 20-amino-acid N-terminal sequence of the 25-kDa protein was used to search data of the C. neoformans Genome Project. Based on the genomic DNA sequence, a DNA probe was used to screen a lambda cDNA library prepared from strain B3501. Clones were isolated containing the full-length gene (d25), which showed homology with a number of polysaccharide deacetylases from fungi and bacteria. The recombinant d25 protein expressed in Escherichia coli was similar to the natural one in DTH-producing activity. Moreover, immunization with either the natural or the recombinant protein prolonged survival and decreased fungal burden in mice challenged with the highly virulent C. neoformans strain H99. In conclusion, we have described the first cryptococcal gene whose product, a 25-kDa extracellular polysaccharide deacetylase, has been shown to induce protective immunity responses.

Do kinetics of the humoral response to Cryptococcus neoformans proteins during murine cryptococcosis reflect outcome?

The kinetics of the humoral response to Cryptococcus neoformans proteins were studied in outbred mice infected with isolate NIH52D. Future nonsurvivors had earlier and stronger (i.e., more bands recognized) humoral responses than survivors. In addition, antibodies to a 56- to 60-kDa membrane antigen and to a 39- to 40-kDa cytosolic antigen were detected more frequently in samples from future nonsurvivors and from survivors, respectively (P < 0.05).

Analysis of the enzymatic activity of mycelial and yeast phases of Penicillium marneffei

The cell-associated and extracellular enzymatic activities were examined in a total of 10 Penicillium marneffei isolates. Both mycelia and yeast expressed alkaline phosphatase, acid phosphatase and naphthol-AS-BI-phosphohydrolase activities, whereas a variety of other enzyme activities, including trypsin, chymotrypsin and alpha-fucosidase were absent. There was some inter-isolate variation in both mycelia and yeast in the activities of other enzymes such as esterases and galactosidases. Enzyme activities did not change significantly over the course of culturing in three representative isolates.

Antioxidant systems in the pathogenic fungi of man and their role in virulence

In the last two decades, a variety of fungal antioxidants have attracted considerable interest, largely arising from their hypothetical role as virulence determinants. Melanin is a potent free radical scavenger and in Cryptococcus neoformans, there is now good evidence that the production of melanin is a significant virulence determinant. There is also recent evidence linking melanin biosynthesis to the virulence of Aspergillus fumigatus conidia. Superoxide dismutases are important housekeeping antioxidants and have an additional hypothetical role in virulence; however, although these enzymes have been biochemically characterized from Aspergillus and Cryptococcus, there is as yet no firm evidence that these enzymes are involved in pathogenicity. Catalase production may play some role in the virulence of Candida albicans but this enzyme has not been shown, as yet, to influence the virulence of A. fumigatus. There are some data supporting an antioxidant function for the acyclic hexitol mannitol in C. neoformans, but further investigations are required in this area. Research into the putative antioxidant activities of a range of other fungal enzymes, such as acid phosphatases, remains limited at this time.

An opsonizing monoclonal antibody that recognizes a noncapsular epitope expressed on Cryptococcus neoformans

A mouse hybridoma secreting a monoclonal antibody (MAb) that bound a noncapsular epitope expressed on C. neoformans was developed by immunizing BALB/c mice with formalin-killed serotype A yeasts. The hybridoma, designated CSFi, secreted an immunoglobulin G2b MAb that reacted with all C. neoformans serotypes tested, including the acapsular mutant ATCC 52817 (Cap67). Postsectioned immune electron microscopy revealed extensive binding of the MAb to the cell walls of both encapsulated and acapsular yeasts. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis of secreted antigens recovered from concentrated culture supernatants from both encapsulated and acapsular strains was conducted. The results showed that this MAb bound predominantly to antigens with molecular masses of approximately 75 and 100 kDa. A competitive enzyme-linked immunosorbent assay was used to demonstrate that the MAb was not cross-reactive with purified glucuronoxylomannan derived from either serotypes A or D. Experiments conducted with mouse peritoneal phagocytes and the mouse phagocyte-like cell line, J774A.1, demonstrated that the CSFi MAb opsonized the yeasts and increased their adherence to both types of phagocytic cells. We conclude, therefore, that antibodies directed at noncapsular epitopes can serve as opsonins and may have a role in modulating cryptococcal infection.

Labeling of proteins with [35S]methionine and/or [35S]cysteine in the absence of cells

Incubation of [35S]methionine and [35S]cysteine with bovine albumin, globulin, catalase, hemoglobin, or human globulin resulted in incorporation of the 35S label into each of these proteins. Trichloroacetic acid (TCA) precipitation revealed that the percentage of label incorporated ranged from 1 to 15%. The 35S labeling was resistant to dissociation by reducing SDS-PAGE, prolonged dialysis against 4 M urea, heating, TCA precipitation, and dilution by gel filtration. The labeling effect was more efficient with [35S]cysteine than [35S]methionine. Incubation of 35S label with proteins differing in methionine and cysteine content revealed no requirement for sulfur-containing amino acids in the target protein. Protein carboxymethylation reduced but did not prevent 35S label incorporation. Amino acid analysis of labeled proteins revealed that the radioactive label was not consistently associated with an individual amino acid. Differences in the ability of various proteins to spontaneously label with these amino acids suggest caution in the interpretation of metabolic labeling experiments and the necessity for inclusion of additional controls. Alternatively, our experience indicates a potentially useful method for labeling proteins in the absence of cells.

Heat shock protein 70 (hsp70) as a major target of the antibody response in patients with pulmonary cryptococcosis

Cryptococcus neoformans causes infection in individuals with defective T cell function, such as AIDS, as well as without underlying disease. It has been suggested that humoral as well as cellular immunity might play an important role in the immune response to C. neoformans infection. We have recently shown, using immunoblotting, that the 70-kD hsp family of C. neoformans was the major target molecule of the humoral response in murine pulmonary cryptococcosis. In this study we also used immunoblotting to define the antibody responses in the sera of 24 patients with pulmonary cryptococcosis: 21 proven and three suspected diagnoses. Anti-C. neoformans hsp70 antibody was detected in 16 of 24 (66.7%) patients with pulmonary cryptococcosis. Fourteen of 17 (82.3%) patients with high antigen titres (> or = 1:8) and two of seven (28.6%) patients with low titres (< or = 1:4) had detectable levels of anti-hsp70 antibody. Sera from patients positive for anti-hsp70 antibody showed high titres in the Eiken latex agglutination test for the detection of serum cryptococcal antigen. Our results indicate that the 70-kD hsp family from C. neoformans appears to be a major target molecule of the humoral response, not only in murine pulmonary cryptococcosis, but also in human patients with pulmonary cryptococcosis.

Variants of a Cryptococcus neoformans strain elicit different inflammatory responses in mice

The virulence of Cryptococcus neoformans isolates with high and low extracellular proteolytic activity was investigated in mice. No consistent relationship between proteolytic activity and virulence was observed, but isolates derived from one strain were shown to elicit different inflammatory responses.

Microevolution of a standard strain of Cryptococcus neoformans resulting in differences in virulence and other phenotypes

Cryptococcus neoformans is a major fungal pathogen for patients with debilitated immune systems. However, no information is available on the stability of virulence or of phenotypes associated with virulence for C. neoformans laboratory strains. A serendipitous observation in our laboratory that one isolate of C. neoformans ATCC 24067 (strain 52D) became attenuated after continuous in vitro culture prompted us to perform a comparative study of nine strain 24067 isolates obtained from six different research laboratories. Each isolate was characterized by DNA typing, virulence for mice, proteinase production, extracellular protein synthesis, melanin synthesis, carbon assimilation pattern, antifungal drug susceptibility, colony morphology, growth rate, agglutination titers, phagocytosis by murine macrophages, capsule size, and capsular polysaccharide structure. All isolates had similar DNA typing patterns consistent with their assignment to the same strain, although minor chromosome size polymorphisms were observed in the electrophoretic karyotypes of two isolates. Several isolates had major differences in phenotypes that may be associated with virulence, including growth rate, capsule size, proteinase production, and melanization. These findings imply that C. neoformans is able to undergo rapid changes in vitro, probably as a result of adaptation to laboratory conditions, and suggest the need for careful attention to storage and maintenance conditions. In summary, our results indicate that C. neoformans (i) can become attenuated by in vitro culture and (ii) is capable of microevolution in vitro with the emergence of variants exhibiting new genotypic and phenotypic characteristics.