Silvia Arancia

Evidence that Members of the Secretory Aspartyl Proteinase Gene Family, in Particular SAP2, Are Virulence Factors for Candida Vaginitis

Virulence of Candida albicans strains with targeted disruption of secretory aspartyl proteinase genes (SAP1 to SAP6) was assessed in an estrogen-dependent rat vaginitis model. Null sap1 to sap3 but not sap4 to sap6 mutants lost most of the virulence of their parental strain SC5314. In particular, the sap2 mutant was almost avirulent in this model. Reinsertion of the SAP2 gene into this latter mutant led to the to recovery of the vaginopathic potential. The vaginal fluids of the animals infected by the wild type strain or by the sap1 or sap3 mutants expressed a pepstatin-sensitive proteinase activity in vitro. No traces of this activity were found in the vaginal fluid of rats challenged by the sap2 mutant. All strains were capable of developing true hyphae during infection. Thus, members of SAP family, in particular SAP2, play a clear pathogenic role in vaginitis and may constitute a novel target for chemoimmunotherapy of this infection.

A virosomal vaccine against candidal vaginitis: Immunogenicity, efficacy and safety profile in animal models

A novel vaccine (PEV7) consisting of a truncated, recombinant aspartyl proteinase-2 of Candida albicans incorporated into influenza virosomes was studied. This vaccine candidate generated a potent serum antibody response in mouse and rat following intramuscular immunization. Anti-Sap2 IgG and IgA were also detected in the vaginal fluid of rats following intravaginal or intramuscular plus intravaginal administration. In a rat model of candidal vaginitis, PEV7 induced significant, long-lasting, likely antibody-mediated, protection following intravaginal route of immunization. PEV7 was also found to be safe in a repeated-dose toxicological study in rats. Overall, these data provide a sound basis to envisage the clinical development of this new candidate vaccine against candidal vaginitis.

Phenotypic and Functional Characterization of Vaginal Dendritic Cells in a Rat Model of Candida albicans Vaginitis

ABSTRACT This study analyzes the phenotype of vaginal dendritic cells (VDCs), their antigenic presentation and activation of T-cell cytokine secretion, and their protective role in a rat model of Candida vaginitis. Histological observation demonstrated a significant accumulation of OX62+ VDCs in the mucosal epithelium of Candida albicans-infected rats at the third round of infection. We identified two subsets of OX62+ VDCs differing in the expression of CD4 molecule in both noninfected and Candida-infected rats. The OX62+ CD4+ subset of VDCs displayed a lymphoid cell-like morphology and expressed the T-cell antigen CD5, whereas the OX62+ CD4− VDC subset exhibited a myeloid morphology and was CD5 negative. Candida infection resulted in VDC maturation with enhanced expression of CD80 and CD134L on both CD4+ and CD4− VDC subsets at 2 and 6 weeks after Candida infection. CD5− CD4− CD86− CD80− CD134L+ VDCs from infected, but not noninfected, rats spontaneously released large amounts of interleukin-12 (IL-12) and tumor necrosis factor alpha, whereas all VDC subsets released comparable levels of IL-10 and IL-2 cytokines. Furthermore, OX62+ VDCs from infected rats primed naïve CD4+ T-cell proliferation and release of cytokines, including gamma interferon, IL-2, IL-6, and IL-10, in response to staphylococcal enterotoxin B stimulation in vitro. Adoptive transfer of highly purified OX62+ VDCs from infected rats induced a significant acceleration of fungal clearance compared with that in rats receiving naive VDCs, suggesting a protective role of VDCs in the anti-Candida mucosal immunity. Finally, VDC-mediated protection was associated with their ability to rapidly migrate to the vaginal mucosa and lymph nodes, as assessed by adoptive transfer of OX62+ VDCs labeled with 5 (and 6-)-carboxyfluorescein diacetate succinimidyl ester.

THE MP65 GENE IS REQUIRED FOR CELL WALL INTEGRITY, ADHERENCE TO EPITHELIAL CELLS AND BIOFILM FORMATION IN CANDIDA ALBICANS

BackgroundThe MP65 gene of Candida albicans (orf19.1779) encodes a putative β-glucanase mannoprotein of 65 kDa, which plays a main role in a host-fungus relationship, morphogenesis and pathogenicity. In this study, we performed an extensive analysis of a mp65Δ mutant to assess the role of this protein in cell wall integrity, adherence to epithelial cells and biofilm formation.ResultsThe mp65Δ mutant showed a high sensitivity to a range of cell wall-perturbing and degrading agents, especially Congo red, which induced morphological changes such as swelling, clumping and formation of hyphae. The mp65Δ mutant showed an activation of two MAPKs (Mkc1p and Cek1p), a high level of expression of two stress-related genes (DDR48 and SOD5), and a modulated expression of β-glucan epitopes, but no gross changes in cell wall polysaccharide composition. Interestingly, the mp65Δ mutant displayed a marked reduction in adhesion to BEC and Caco-2 cells and severe defects in biofilm formation when compared to the wild type. All of the mentioned properties were totally or partially recovered in a revertant strain, demonstrating the specificity of gene deletion.ConclusionsWe demonstrate that the MP65 gene of Candida albicans plays a significant role in maintaining cell wall integrity, as well as in adherence to epithelia and biofilm formation, which are major virulence attributes of this fungus.

Peptides of the Constant Region of Antibodies Display Fungicidal Activity

Synthetic peptides with sequences identical to fragments of the constant region of different classes (IgG, IgM, IgA) of antibodies (Fc-peptides) exerted a fungicidal activity in vitro against pathogenic yeasts, such as Candida albicans, Candida glabrata, Cryptococcus neoformans, and Malassezia furfur, including caspofungin and triazole resistant strains. Alanine-substituted derivatives of fungicidal Fc-peptides, tested to evaluate the critical role of each residue, displayed unaltered, increased or decreased candidacidal activity in vitro. An Fc-peptide, included in all human IgGs, displayed a therapeutic effect against experimental mucosal and systemic candidiasis in mouse models. It is intriguing to hypothesize that some Fc-peptides may influence the antifungal immune response and constitute the basis for devising new antifungal agents.

Identification of inhibitors of drug-resistant Candida albicans strains from a library of bicyclic peptidomimetic compounds.

The screening of a library of small molecule peptidomimetics toward secreted aspartic proteinase-2 (SAP2) of Candida albicans allowed us to identify two compounds that showed in vitro inhibitory potency comparable to pepstatin A. In an experimental model of vaginal candidiasis, the two candidate compounds were as active as a therapeutic dose of fluconazole. Importantly, this activity was fully preserved when the challenger was a fluconazole-resistant strain of the fungus. Altogether, our data demonstrate SAP2 as a valid C. albicans target for the development of new drugs against this important human pathogen.

Rapid, simple, and low-cost identification of Candida species using high-resolution melting analysis

The feasibility of using high-resolution melting analysis (HRMA) was examined for its rapid and simple detection of 5 clinically relevant Candida species (C. albicans, C. glabrata, C. kefyr, C. parapsilosis, and C. guilliermondii). HRMA was able to differentiate clinical Candida species and resulted in being sensitive, reproducible, and inexpensive.

Generation of a highly immunogenic recombinant enolase of the human opportunistic pathogen Candida albicans

Enolase, a 46 kDa glycolytic enzyme, is an immunodominant antigen of Candida albicans, an important human opportunistic pathogen. The full‐length coding sequence of C. albicans enolase gene was subcloned into the prokaryotic expression vector pDS56/RBSII, His6/E− under the control of an inducible promoter to produce a His6‐tagged enolase. The recombinant protein was purified to homogeneity by one‐step nickel‐chelate affinity chromatography. It was recognized by a monoclonal antibody specific for C. albicans enolase, as well as by anti‐enolase antibodies present in human sera (IgG). The recombinant protein promptly elicited antibody in mice and detected immune responses in normal human subjects that were comparable to those generated by the native C. albicans enolase. Thus this new recombinant enolase constitutes a valuable reagent for studying the possible role of this protein in anti‐Candida immune response.

Studies of Immune Responses in Candida vaginitis

The widespread occurrence of vaginal candidiasis and the development of resistance against anti-fungal agents has stimulated interest in understanding the pathogenesis of this disease. The aim of our work was to characterize, in an animal model of vaginal candidiasis, the mechanisms that play a role in the induction of mucosal immunity against C. albicans and the interaction between innate and adaptive immunity. Our studies evidenced the elicitation of cell-mediated immunity (CMIs) and antibody (Abs)-mediated immunity with a Th1 protective immunity. An immune response of this magnitude in the vagina was very encouraging to identify the proper targets for new strategies for vaccination or immunotherapy of vaginal candidiasis. Overall, our data provide clear evidence that it is possible to prevent C. albicans vaginal infection by active intravaginal immunization with aspartyl proteinase expressed as recombinant protein. This opens the way to a modality for anti-Candida protection at the mucosa. The recombinant protein Sap2 was assembled with virosomes, and a vaccine PEVION7 (PEV7) was obtained. The results have given evidence that the vaccine, constituted of virosomes and Secretory aspartyl proteinase 2 (Sap2) (PEV7), has an encouraging therapeutic potential for the treatment of recurrent vulvovaginal candidiasis.

Protection against rat vaginal candidiasis by adoptive transfer of vaginal B lymphocytes

Vulvovaginal candidiasis is a mucosal infection affecting many women, but the immune mechanisms operating against Candida albicans at the mucosal level remain unknown. A rat model was employed to further characterize the contribution of B and T cells to anti-Candida vaginal protection. Particularly, the protective role of vaginal B cells was studied by means of adoptive transfer of vaginal CD3(-) CD5(+) IgM(+) cells from Candida-immunized rats to naïve animals. This passive transfer of B cells resulted into a number of vaginal C. albicans CFU approximately 50% lower than their controls. Sorted CD3(-) CD5(+) IgM(+) vaginal B lymphocytes from Candida-infected rats proliferated in response to stimulation with an immunodominant mannoprotein (MP) antigen of the fungus. Importantly, anti-MP antibodies and antibody-secreting B cells were detected in the supernatant and cell cultures, respectively, of vaginal B lymphocytes from infected rats incubated in vitro with vaginal T cells and stimulated with MP. No such specific antibodies were found when using vaginal B cells from uninfected rats. Furthermore, inflammatory and anti-inflammatory cytokines, such as interleukin-2 (IL-2), IL-6 and IL-10, were found in the supernatant of vaginal B cells from infected rats. These data are evidence of a partial anti-Candida protective role of CD3(-) CD5(+) IgM(+) vaginal B lymphocytes in our experimental model.