Characterization of the antifungal functions of a WGA-Fc (IgG2a) fusion protein binding to cell wall chitin oligomers

Lectibodies as antivirals

Growing concerns regarding the emergence of highly transmissible viral diseases highlight the urgent need to expand the repertoire of antiviral therapeutics. For this reason, new strategies for neutralizing and inhibiting these viruses are necessary. A promising approach involves targeting the glycans present on the surfaces of enveloped viruses. Lectins, known for their ability to recognize specific carbohydrate molecules, offer the potential for glycan-targeted antiviral strategies. Indeed, numerous studies have reported the antiviral effects of various lectins of both endogenous and exogenous origins. However, many lectins in their natural forms, are not suitable for use as antiviral therapeutics due to toxicity, other unfavorable pharmacological effects, and/or unreliable manufacturing sources. Therefore, improvements are crucial for employing lectins as effective antiviral therapeutics. A novel approach to enhance lectins' suitability as pharmaceuticals could be the generation of recombinant lectin-Fc fusion proteins, termed "lectibodies." In this review, we discuss the scientific rationale behind lectin-based antiviral strategies and explore how lectibodies could facilitate the development of new antiviral therapeutics. We will also share our perspective on the potential of these molecules to transcend their potential use as antiviral agents.

Spectroscopic and thermodynamic characterization of the interaction between sugar-stabilised silver nanoparticles and wheat germ agglutinin (WGA), a chitin binding lectin

Nanomaterials have lately been investigated in agriculture as eco-friendly and effective antifungal agents. Many nanomaterials, notably metal nanoparticles, have strong antifungal properties. Among metal nanoparticles, Ag nanoparticles have received the most attention as antifungal agents. Many plant lectins have been identified as antifungal agents. Conjugating AgNPs with antifungal lectins is thus expected to improve Ag nanoparticle antifungal efficacy. Understanding the molecular interactions and physical features of lectin-sugar-stabilised nanoparticle conjugates is critical for future applications. WGA has traditionally been used as an anti-tumor and antifungal agent. To investigate the prospect of developing an effective biocompatible antifungal system with applications in medicine and agriculture, fluorescence spectroscopy was used to investigate the interaction between sugar-stabilised silver nanoparticles and WGA. During the association, protein intrinsic fluorescence emission is suppressed by about ∼15 % at saturation, with no significant shift in fluorescence emission maxima. Binding tests reveal a strong bond. Stern-Volmer analysis of the quenching data indicates that the interaction happens via a static quenching process that induces complex formation. The study of hemagglutination activity and interaction experiments in the presence of particular sugar shows that the lectin's sugar-binding site is separate from the nanoparticle-binding site, and cell recognition is conserved in the lectin-nanoparticle complex. The Van't Hoff plot thermodynamic parameters suggest that the contact is hydrophobic. The fact that ΔGo is negative shows that the binding is a spontaneous process. CD spectroscopy experiments reveal that the lectin's secondary structure is not affected while binding to the nanoparticle. Our findings suggest that a stable WGA-silver nanoparticle combination may emerge for a variety of applications.

Antibody Isolation in C. neoformans

The importance of humoral immunity to fungal infections remains to be elucidated. In cryptococcosis, patients that fail to generate antibodies against antigens of the fungus Cryptococcus neoformans are more susceptible to the disease, demonstrating the importance of these molecules to the antifungal immune response. Historically, antibodies against C. neoformans have been applied in diagnosis, therapeutics, and as important research tools to elucidate fungal biology. Throughout the process of generating monoclonal antibodies (mAbs) from a single B-cell clone and targeting a single epitope, several immunization steps might be required for the detection of responsive antibodies to the antigen of interest in the serum. This complex mixture of antibodies comprises the polyclonal antibodies. To obtain mAbs, B-lymphocytes are harvested (from spleen or peripheral blood) and fused with tumor myeloma cells, to generate hybridomas that are individually cloned and specifically screened for mAb production. In this chapter, we describe all the necessary steps, from the immunization to polyclonal antibody harvesting, hybridoma generation, and mAb production and purification. Additionally, we discuss new cutting-edge approaches for generating interspecies mAbs, such as humanized mAbs, or for similar species in distinct host backgrounds.

Traversing the Cell Wall: The Chitinolytic Activity of Histoplasma capsulatum Extracellular Vesicles Facilitates Their Release

Histoplasma capsulatum is the causative agent of histoplasmosis. Treating this fungal infection conventionally has significant limitations, prompting the search for alternative therapies. In this context, fungal extracellular vesicles (EVs) hold relevant potential as both therapeutic agents and targets for the treatment of fungal infections. To explore this further, we conducted a study using pharmacological inhibitors of chitinase (methylxanthines) to investigate their potential to reduce EV release and its subsequent impact on fungal virulence in an in vivo invertebrate model. Our findings revealed that a subinhibitory concentration of the methylxanthine, caffeine, effectively reduces EV release, leading to a modulation of H. capsulatum virulence. To the best of our knowledge, this is the first reported instance of a pharmacological inhibitor that reduces fungal EV release without any observed fungicidal effects.

In vitro and in vivo efficacies of Dectin-1-Fc(IgG)(s) fusion proteins against invasive fungal infections

Fungal infections have increased in the last years, particularly associated to an increment in the number of immunocompromised individuals and the emergence of known or new resistant species, despite the difficulties in the often time-consuming diagnosis. The controversial efficacy of the currently available strategies for their clinical management, apart from their high toxicity and severe side effects, have renewed the interest in the research and development of new broad antifungal alternatives. These encompass vaccines and passive immunization strategies with monoclonal antibodies (mAbs), recognizing ubiquitous fungal targets, such as fungal cell wall β-1,3-glucan polysaccharides, which could be used in early therapeutic intervention without the need for the diagnosis at species-level. As additional alternatives, based on the Dectin-1 great affinity to β-1,3-glucan, our group developed broad antibody-like Dectin1-Fc(IgG)(s) from distinct subclasses (IgG2a and IgG2b) and compared their antifungal in vitro and passive immunizations in vivo performances. Dectin1-Fc(IgG2a) and Dectin1-Fc(IgG2b) demonstrated high affinity to laminarin and the fungal cell wall by ELISA, flow cytometry and microscopy. Both Dectin-1-Fc(IgG)(s) inhibited H. capsulatum and C. neoformans growth in a dose-dependent fashion. For C. albicans, such inhibitory effect was observed with concentrations as low as 0.098 and 0.049 µg/mL, respectively, which correlated with the impairment of the kinetics and lengths of germ tubes in comparison to controls. Previous opsonization with Dectin-1-Fc(IgG)(s) enhanced considerably the macrophage antifungal effector functions, increasing the fungi macrophages-interactions and significantly reducing the intraphagosome fungal survival, as lower CFUs were observed. The administration of both Dectin1-Fc(IgG)(s) reduced the fungal burden and mortality in murine histoplasmosis and candidiasis models, in accordance with previous evaluations in aspergillosis model. These results altogether strongly suggested that therapeutic interventions with Dectin-1-Fc(IgG)(s) fusion proteins could directly impact the innate immunity and disease outcome in favor of the host, by direct neutralization, opsonization, phagocytosis, and fungal elimination, providing interesting information on the potential of these new strategies for the control of invasive fungal infections.

Molecular and Microscopic Methods of Quantifying Candida albicans Cell Wall PAMP Exposure

The cell wall of Candida albicans is a multilayered structure consisting of polysaccharides and proteins. The inner cell wall layer is comprised of chitin and β1-3 and β1-6-glucan which contribute to the overall shape and structure of the cell, while the outer layer of highly glycosylated mannoproteins provides key functional traits such as cell adhesion required for virulence. However, the cell wall is not a static structure but is constantly being remodeled in response to the external environment. Given that all of the cell wall components act as pathogen-associated molecular patterns (PAMPs) that are recognized by a variety of receptors on the surface of innate immune cells, remodeling of the cell wall can have a dramatic impact on the host-pathogen interaction. For example, during growth in standard media, C. albicans shields its major cell wall PAMPs from the innate immune system, but during growth in acidic environments as encountered during colonization of the female reproductive tract, key PAMPs become exposed on the fungal cell surface initiating a strong pro-inflammatory innate immune response. The impact of environmental adaptation on fungal cell wall remodeling, and the subsequent impact this has on the host-pathogen interaction, has been the subject of much research. In this chapter, we outline techniques to assess cell wall components in both resting and environmentally adapted C. albicans cells.

Role of carbohydrate antigens in antifungal glycoconjugate vaccines and immunotherapy

The emergence of fungal infection is a growing public health concern that in the latest years is becoming a serious threat to humans, particularly for immunocompromised individuals. Invasive fungal infections (IFIs), which are associated with significant morbidity and mortality, are on the rise due to the availability of only a few old antifungal agents. In addition to this, the growing use of antibiotics makes the population increasingly susceptible to these infections. Since carbohydrates are the main component of the fungal cell wall, the study of fungal glycans as potential targets for the fight against IFIs has aroused much interest in recent decades. In most fungal species the saccharides of the core are made up of chitin and β-glucans, while the outer layer carbohydrates vary according to the fungal species, such as mannans for Candida albicans, galactomannans for Aspergillus fumigatus hyphae, α-glucans for Aspergillus fumigatus and Cryptococcus neoformans, glucuronoxylomannans (GXM) and galactoxylomannans (GalXM) for Criptococcus neoformans. Being surface antigens, fungal carbohydrates are a logical target for the development of antifungal glycoconjugate vaccines and for immunotherapy with monoclonal antibodies. This review summarizes recent findings on active and passive immunization strategies based on fungal carbohydrates explored preclinically for three of the major fungal pathogens: Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus.

Monoclonal Antibodies against Cell Wall Chitooligomers as Accessory Tools for the Control of Cryptococcosis

Therapeutic strategies against systemic mycoses can involve antifungal resistance and significant toxicity. Thus, novel therapeutic approaches to fight fungal infections are urgent. Monoclonal antibodies (MAbs) are promising tools to fight systemic mycoses. In this study, MAbs of the IgM isotype were developed against chitin oligomers. Chitooligomers derive from chitin, an essential component of the fungal cell wall and a promising therapeutic target, as it is not synthesized by humans or animals. Surface plasmon resonance (SPR) assays and cell-binding tests showed that the MAbs recognizing chitooligomers have high affinity and specificity for the chitin derivatives. In vitro tests showed that the chitooligomer MAbs increased the fungicidal capacity of amphotericin B against Cryptococcus neoformans. The chitooligomer-binding MAbs interfered with two essential properties related to cryptococcal pathogenesis: biofilm formation and melanin production. In a murine model of C. neoformans infection, the combined administration of the chitooligomer-binding MAb and subinhibitory doses of amphotericin B promoted disease control. The data obtained in this study support the hypothesis that chitooligomer antibodies have great potential as accessory tools in the control of cryptococcosis.

Fc-conjugated C-type lectin receptors: Tools for understanding host-pathogen interactions

The use of soluble fusion proteins of pattern recognition receptors (PRRs) used in the detection of exogenous and endogenous ligands has helped resolve the roles of PRRs in the innate immune response to pathogens, how they shape the adaptive immune response, and function in maintaining homeostasis. Using the immunoglobulin (Ig) crystallizable fragment (Fc) domain as a fusion partner, the PRR fusion proteins are soluble, stable, easily purified, have increased affinity due to the Fc homodimerization properties, and consequently have been used in a wide range of applications such as flow cytometry, screening of protein and glycan arrays, and immunofluorescent microscopy. This review will predominantly focus on the recognition of pathogens by the cell membrane-expressed glycan-binding proteins of the C-type lectin receptor (CLR) subgroup of PRRs. PRRs bind to conserved pathogen-associated molecular patterns (PAMPs), such as glycans, usually located within or on the outer surface of the pathogen. Significantly, many glycans structures are identical on both host and pathogen (e.g. the Lewis (Le) X glycan), allowing the use of Fc CLR fusion proteins with known endogenous and/or exogenous ligands as tools to identify pathogen structures that are able to interact with the immune system. Screens of highly purified pathogen-derived cell wall components have enabled identification of many unique PAMP structures recognized by CLRs. This review highlights studies using Fc CLR fusion proteins, with emphasis on the PAMPs found in fungi, bacteria, viruses, and parasites. The structure and unique features of the different CLR families is presented using examples from a broad range of microbes whenever possible.

Synthetic conjugate peptide Fba-Met6 (MP12) induces complement-mediated resistance against disseminated Candida albicans

The fungal genus Candida includes common commensals of the human mucosal membranes, and the most prevalently isolated species, C. albicans, poses a threat of candidemia and disseminated infection associated with an unacceptably high mortality rate and an immense $4 billion burden (US) yearly. Nevertheless, the demand for a vaccine remains wholly unfulfilled and increasingly pressing. We developed a double-peptide construct that is feasible for use in humans with the intention of preventing morbid infection by targeting epitopes derived from fructose bisphosphate aldolase (Fba) and methionine synthase (Met6) which are expressed on the C. albicans cell surface. To test the applicability of the design, we vaccinated mice via the intramuscular (IM) route with the conjugate denoted Fba-Met6 MP12 and showed that the vaccine enhanced survival against a lethal challenge. Because overall endpoint IgG1 and IgG2a antibody titers were robust and these mouse subclasses are associated with protective functionality, we investigated the potential of Fba and Met6 specific antibodies to facilitate the well-defined anti-Candida response by complement, which opsonizes fungi for degradation by primary effectors. Notably, reductions in the fungal burdens and enhanced survival were both abrogated in MP12-vaccinated mice that were pre-challenge dosed with cobra venom factor (CVF), a complement depleting factor. Altogether, we demonstrated that complement is relevant to MP12-based protection against disseminated C. albicans, delineating that a novel, multivalent targeted vaccine against proteins on the surface of C. albicans can enhance the natural response to infection.

Comparative Proteomic Analysis of Histoplasma capsulatum Yeast and Mycelium Reveals Differential Metabolic Shifts and Cell Wall Remodeling Processes in the Different Morphotypes

Histoplasma capsulatum is a thermally dimorphic fungus distributed worldwide, but with the highest incidence in the Americas within specific geographic areas, such as the Mississippi River Valley and regions in Latin America. This fungus is the etiologic agent of histoplasmosis, an important life-threatening systemic mycosis. Dimorphism is an important feature for fungal survival in different environments and is related to the virulence of H. capsulatum, and essential to the establishment of infection. Proteomic profiles have made important contributions to the knowledge of metabolism and pathogenicity in several biological models. However, H. capsulatum proteome studies have been underexplored. In the present study, we report the first proteomic comparison between the mycelium and the yeast cells of H. capsulatum. Liquid chromatography coupled to mass spectrometry was used to evaluate the proteomic profile of the two phases of H. capsulatum growth, mycelium, and yeast. In summary, 214 and 225 proteins were only detected/or preferentially abundant in mycelium or yeast cells, respectively. In mycelium, enzymes related to the glycolytic pathway and to the alcoholic fermentation occurred in greater abundance, suggesting a higher use of anaerobic pathways for energy production. In yeast cells, proteins related to the tricarboxylic acid cycle and response to temperature stress were in high abundance. Proteins related to oxidative stress response or involved with cell wall metabolism were identified with differential abundance in both conditions. Proteomic data validation was performed by enzymatic activity determination, Western blot assays, or immunofluorescence microscopy. These experiments corroborated, directly or indirectly, the abundance of isocitrate lyase, 2-methylcitrate synthase, catalase B, and mannosyl-oligosaccharide-1,2-alpha-mannosidase in the mycelium and heat shock protein (HSP) 30, HSP60, glucosamine-fructose-6-phosphate aminotransferase, glucosamine-6-phosphate deaminase, and N-acetylglucosamine-phosphate mutase in yeast cells. The proteomic profile-associated functional classification analyses of proteins provided new and interesting information regarding the differences in metabolism between the two distinct growth forms of H. capsulatum.

The Pathogenesis of Aspergillus fumigatus, Host Defense Mechanisms, and the Development of AFMP4 Antigen as a Vaccine

Aspergillus fumigatus is one of the ubiquitous fungi with airborne conidia, which accounts for most aspergillosis cases. In immunocompetent hosts, the inhaled conidia are rapidly eliminated. However, immunocompromised or immunodeficient hosts are particularly vulnerable to most Aspergillus infections and invasive aspergillosis (IA), with mortality from 50% to 95%. Despite the improvement of antifungal drugs over the last few decades, the therapeutic effect for IA patients is still limited and does not provide significant survival benefits. The drawbacks of antifungal drugs such as side effects, antifungal drug resistance, and the high cost of antifungal drugs highlight the importance of finding novel therapeutic and preventive approaches to fight against IA. In this article, we systemically addressed the pathogenic mechanisms, defense mechanisms against A. fumigatus, the immune response, molecular aspects of host evasion, and vaccines' current development against aspergillosis, particularly those based on AFMP4 protein, which might be a promising antigen for the development of anti-A. fumigatus vaccines.

Wheat Germ Agglutinin—From Toxicity to Biomedical Applications

Wheat germ agglutinin is a hevein class N-Acetylglucosamine–binding protein with specific toxicity and biomedical potential. It is extractable from wheat germ—a low-value byproduct of the wheat industry—using well–established extraction methods based on salt precipitation and affinity chromatography. Due to its N-Acetylglucosamine affinity, wheat germ agglutinin exhibits antifungal properties as well as cytotoxic properties. Its anticancer properties have been demonstrated for various cancer cells, and toxicity mechanisms are well described. Wheat germ agglutinin has been demonstrated as a viable solution for various biomedical and therapeutic applications, such as chemotherapy, targeted drug delivery, antibiotic-resistant bacteria monitoring and elimination. This is performed mostly in conjunction with nanoparticles, liposomes, and other carrier mechanisms via surface functionalization. Combined with abundant wheat byproduct sources, wheat germ agglutinin has the potential to improve the biomedical field considerably.

Protective Efficacy of Lectin-Fc(IgG) Fusion Proteins In Vitro and in a Pulmonary Aspergillosis In Vivo Model

Aspergillosis cases by Aspergillus fumigatus have increased, along with fungal resistance to antifungals, urging the development of new therapies. Passive immunization targeting common fungal antigens, such as chitin and β-glucans, are promising and would eliminate the need of species-level diagnosis, thereby expediting the therapeutic intervention. However, these polysaccharides are poorly immunogenic. To overcome this drawback, we developed the lectin-Fc(IgG) fusion proteins, Dectin1-Fc(IgG2a), Dectin1-Fc(IgG2b) and wheat germ agglutinin (WGA)-Fc(IgG2a), based on their affinity to β-1,3-glucan and chitooligomers, respectively. The WGA-Fc(IgG2a) previously demonstrated antifungal activity against Histoplasma capsulatum, Cryptococcus neoformans and Candida albicans. In the present work, we evaluated the antifungal properties of these lectin-Fc(s) against A. fumigatus. Lectin-Fc(IgG)(s) bound in a dose-dependent manner to germinating conidia and this binding increased upon conidia germination. Both lectin-Fc(IgG)(s) displayed in vitro antifungal effects, such as inhibition of conidia germination, a reduced length of germ tubes and a diminished biofilm formation. Lectin-Fc(IgG)(s) also enhanced complement deposition on conidia and macrophage effector functions, such as increased phagocytosis and killing of fungi. Finally, administration of the Dectin-1-Fc(IgG2b) and WGA-Fc(IgG2a) protected mice infected with A. fumigatus, with a 20% survival and a doubled life-span of the infected mice, which was correlated to a fungal burden reduction in lungs and brains of treated animals. These results confirm the potential of lectin-Fc(IgGs)(s) as a broad-spectrum antifungal therapeutic.

Remodeling of the Histoplasma Capsulatum Membrane Induced by Monoclonal Antibodies

Antibodies play a central role in host immunity by directly inactivating or recognizing an invading pathogen to enhance different immune responses to combat the invader. However, the cellular responses of pathogens to the presence of antibodies are not well-characterized. Here, we used different mass spectrometry techniques to study the cellular responses of the pathogenic fungus Histoplasma capsulatum to monoclonal antibodies (mAb) against HSP60, the surface protein involved in infection. A proteomic analysis of H. capsulatum yeast cells revealed that mAb binding regulates a variety of metabolic and signaling pathways, including fatty acid metabolism, sterol metabolism, MAPK signaling and ubiquitin-mediated proteolysis. The regulation of the fatty acid metabolism was accompanied by increases in the level of polyunsaturated fatty acids, which further augmented the degree of unsaturated lipids in H. capsulatum's membranes and energy storage lipids, such as triacylglycerols, phosphatidylcholines, phosphatidylethanolamines and phosphatidylinositols. MAb treatment also regulated sterol metabolism by increasing the levels of cholesterol and ergosterol in the cells. We also showed that global changes in the lipid profiles resulted in an increased susceptibility of H. capsulatum to the ergosterol-targeting drug amphotericin B. Overall, our data showed that mAb induction of global changes in the composition of H. capsulatum membranes can potentially impact antifungal treatment during histoplasmosis.

Monoclonal Antibodies as Tools to Combat Fungal Infections

Antibodies represent an important element in the adaptive immune response and a major tool to eliminate microbial pathogens. For many bacterial and viral infections, efficient vaccines exist, but not for fungal pathogens. For a long time, antibodies have been assumed to be of minor importance for a successful clearance of fungal infections; however this perception has been challenged by a large number of studies over the last three decades. In this review, we focus on the potential therapeutic and prophylactic use of monoclonal antibodies. Since systemic mycoses normally occur in severely immunocompromised patients, a passive immunization using monoclonal antibodies is a promising approach to directly attack the fungal pathogen and/or to activate and strengthen the residual antifungal immune response in these patients.

Demonstration and Characterization of Cyst-Like Structures in the Life Cycle of Trichomonas vaginalis

Trichomonas vaginalis is the parasitic protozoan residing in human urogenital tract causing trichomoniasis, which is the leading non-viral sexually transmitted disease. It has cosmopolitan distribution throughout the globe and affects both men and women. Lifecycle of the parasite has been traditionally described as consisting of motile and symptom-causing trophozoites. Chemical and temperature perturbations in trophozoites have been shown to aid conversion to pseudocysts, which is poorly investigated. In the current study, we show the formation of viable cyst-like structures (CLS) in stationary phase of T. vaginalis axenic culture. We used a fluorescent stain called calcofluor white, which specifically binds to chitin and cellulose-containing structures, to score for T. vaginalis CLS. Using flow cytometry, we demonstrated and quantitated the processes of encystation as well as excystation; thus, completing the parasite's lifecycle in vitro without any chemical/temperature alterations. Like cysts from other protozoan parasites such as Entamoeba histolytica and Giardia lamblia, T. vaginalis CLS appeared spherical, immotile, and resistant to osmotic lysis and detergent treatments. Ultrastructure of CLS demonstrated by Transmission Electron Microscopy showed a thick electron-dense deposition along its outer membrane. To probe the physiological role of CLS, we exposed parasites to vaginal pH and observed that trophozoites took this as a cue to convert to CLS. Further, upon co- culturing with cells of cervical origin, CLS rapidly excysted to form trophozoites which abrogated the cervical cell monolayer in a dose-dependent manner. To further corroborate the presence of two distinct forms in T. vaginalis, we performed two-dimensional gel electrophoresis and global, untargeted mass spectrometry to highlight differences in the proteome with trophozoites. Interestingly, CLS remained viable in chlorinated swimming pool water implicating the possibility of its role as environmentally resistant structures involved in non-sexual mode of parasite transmission. Finally, we showed that symptomatic human patient vaginal swabs had both T. vaginalis trophozoites and CLS; thus, highlighting its importance in clinical infections. Overall, our study highlights the plasticity of the pathogen and its rapid adaption when subjected to stressful environmental cues and suggests an important role of CLS in the parasite's life cycle, pathogenesis and transmission.

Schinus terebinthifolia leaf lectin (SteLL) has anti-infective action and modulates the response of Staphylococcus aureus-infected macrophages

Staphylococcus aureus is recognized as an important pathogen causing a wide spectrum of diseases. Here we examined the antimicrobial effects of the lectin isolated from leaves of Schinus terebinthifolia Raddi (SteLL) against S. aureus using in vitro assays and an infection model based on Galleria mellonella larvae. The actions of SteLL on mice macrophages and S. aureus-infected macrophages were also evaluated. SteLL at 16 µg/mL (8 × MIC) increased cell mass and DNA content of S. aureus in relation to untreated bacteria, suggesting that SteLL impairs cell division. Unlike ciprofloxacin, SteLL did not induce the expression of recA, crucial for DNA repair through SOS response. The antimicrobial action of SteLL was partially inhibited by 50 mM N-acetylglucosamine. SteLL reduced staphyloxathin production and increased ciprofloxacin activity towards S. aureus. This lectin also improved the survival of G. mellonella larvae infected with S. aureus. Furthermore, SteLL induced the release of cytokines (IL-6, IL-10, IL-17A, and TNF-α), nitric oxide and superoxide anion by macrophagens. The lectin improved the bactericidal action of macrophages towards S. aureus; while the expression of IL-17A and IFN-γ was downregulated in infected macrophages. These evidences suggest SteLL as important lead molecule in the development of anti-infective agents against S. aureus.

Modulation of the fungal mycobiome is regulated by the chitin-binding receptor FIBCD1

In the present study, Moeller et al. identify a previously unrecognized pathway through which intestinal epithelial cells expressing the novel chitin-binding receptor FIBCD1 can recognize and control intestinal fungal colonization, limit fungal dysbiosis, and dampen intestinal inflammation.

Host–microbiota interactions are critical in regulating mammalian health and disease. In addition to bacteria, parasites, and viruses, beneficial communities of fungi (the mycobiome) are important modulators of immune- and tissue-homeostasis. Chitin is a major component of the fungal cell wall, and fibrinogen C containing domain 1 (FIBCD1) is a chitin-binding protein; however, the role of this molecule in influencing host–mycobiome interactions in vivo has never been examined. Here, we identify direct binding of FIBCD1 to intestinal-derived fungi and demonstrate that epithelial-specific expression of FIBCD1 results in significantly reduced fungal colonization and amelioration of fungal-driven intestinal inflammation. Collectively, these results identify FIBCD1 as a previously unrecognized microbial pattern recognition receptor through which intestinal epithelial cells can recognize and control fungal colonization, limit fungal dysbiosis, and dampen intestinal inflammation.

Difficult but Not Impossible: in Search of an Anti-Candida Vaccine

Purpose of Review

Pervasive fungal infection among the immunocompromised population, in conjunction with a lack of effective treatment options, has demanded further scrutiny. Millions of people are still dying annually from fungal infections. While existing treatment for these fungal infections exists, it is difficult to administer without adverse effects in the immunocompromised and is slowly becoming obsolete due to varying mutation rates and rising resistance in multiple species. Thus, vaccines may be a viable target for preventing and treating fungal infections and addressing the critical challenge of such infections.

Recent Findings

Candida albicans, along with other non-albicans Candida species, is among the more virulent class of fungal specimens considered for vaccine development. C. albicans is responsible for a large percentage of invasive fungal infections among immunocompromised and immunocompetent populations and carries a relatively high mortality rate. In the last decade, a recent increase in infective capacity among Candida species has shed light on the lack of adequate fungal vaccine choices. While roadblocks still exist in the development of antifungal vaccines, several novel targets have been examined and proposed as candidates.

Summary

Success in vaccine development has universal appeal; an anti-Candida vaccine formulation could be modified to work against other fungal infections and thus bolster the antifungal pipeline.

Immunization Strategies for the Control of Histoplasmosis

Histoplasmosis is an infection caused by the dimorphic fungus Histoplasma capsulatum. Histoplasmosis is typically self-limited and presents asymptomatically in most people. Nevertheless, histoplasmosis can cause severe pulmonary disease and death. Histoplasmosis is increasingly found worldwide; however, it is best documented in the endemic region of the Mississippi river valley system in the Eastern part of the United States (US). Epidemiological studies from the US detailing the morbidity, mortality, and cost associated with histoplasmosis underscore the need to develop a vaccine.

Purpose of review

This review will detail some of the major developments in potential vaccines against histoplasmosis, with particular emphasis on those that could be used to immunize immunocompromised hosts. Additionally, this review will highlight some non-traditional vaccine-like ideas for the prevention of diverse mycoses.

Recent findings

Historically, immunization strategies against histoplasmosis have largely focused on identifying immunogenic proteins that confer protection in animal models. More recently, novel active, therapeutic, and immunomodulatory strategies have been explored as potential alternatives for those with various immune-deficiencies.

Summary

The studies summarized in this review demonstrate that more research is needed to clarify the immunobiology, clinical role and efficacy of each candidate vaccine in the ever-expanding potential armamentarium against histoplasmosis.

Current trends to control fungal pathogens: exploiting our knowledge in the host-pathogen interaction

Human fungal infections remain a major challenge in medicine. Only a limited number of antifungal drugs are available, which are often related to severe adverse effects. In addition, there is an increased emergence related to resistant strains, which makes imperative to understand the host-pathogen interactions as well as to develop alternative treatments. Host innate and adaptive immunity play a crucial role controlling fungal infections; therefore, vaccines are a viable tool to prevent and treat fungal pathogens. Innate immunity is triggered by the interaction between the cell surface pattern recognition receptors (PRRs) and the pathogen-associated molecular patterns (PAMPs). Such an initial immunological response is yet little understood in fungal infections, in part due to the complexity and plasticity of the fungal cell walls. Described host cell-fungus interactions and antigenic molecules are addressed in this paper. Furthermore, antigens found in the cell wall and capsule, including peptides, glycoproteins, glycolipids, and glycans, have been used to trigger specific immune responses, and an increased production of antibodies has been observed when attached to immunogenic molecules. The recent biotechnological advances have allowed the development of vaccines against viral and bacterial pathogens with positive results; therefore, this technology has been applied to develop anti-fungal vaccines. Passive immunization has also emerged as an appealing alternative to treat disseminated mycosis, especially in immunocompromised patients. Those approaches have a long way to be seen in clinical cases. However, all studies discussed here open the possibility to have access to new therapies to be applied alone or in combination with current antifungal drugs. Herein, the state of the art of fungal vaccine developments is discussed in this review, highlighting new advances against Candida albicans, Aspergillus fumigatus, Cryptococcus neoformans, Paracoccidioides brasiliensis, and Sporothrix spp.

Lack of chitin synthase genes impacts capsular architecture and cellular physiology in Cryptococcus neoformans

Cryptococcus neoformans mutants lacking each of the eight putative chitin synthase genes (CHS) have been previously generated. However, it is still unclear how deletion of chitin synthase genes affects the cryptococcal capsule. Since the connections between chitin metabolism and capsular polysaccharides in C. neoformans are numerous, we analyzed the effects of deletion of CHS genes on capsular and capsule-related structures of C. neoformans. CHS deletion affected capsular morphology in multiple ways, as determined by scanning electron microscopy and immunofluorescence analysis. Molecular diameter, serological reactivity and export of capsular polysaccharide were also affected in most of the chsΔ mutants, but the most prominent alterations were observed in the chs3Δ strain. C. neoformans cells lacking CHS genes also had altered formation of extracellular vesicles and variable chitinase activity under stress conditions. These results reveal previously unknown functions of CHS genes that greatly impact the physiology of C. neoformans.

The status of cryptococcosis in Latin America

Cryptococcosis is a life-threatening fungal infection caused by the encapsulated yeasts Cryptococcus neoformans and C. gattii, acquired from the environment. In Latin America, as occurring worldwide, C. neoformans causes more than 90% of the cases of cryptococcosis, affecting predominantly patients with HIV, while C. gattii generally affects otherwise healthy individuals. In this region, cryptococcal meningitis is the most common presentation, with amphotericin B and fluconazole being the antifungal drugs of choice. Avian droppings are the predominant environmental reservoir of C. neoformans, while C. gattii is associated with several arboreal species. Importantly, C. gattii has a high prevalence in Latin America and has been proposed to be the likely origin of some C. gattii populations in North America. Thus, in the recent years, significant progress has been made with the study of the basic biology and laboratory identification of cryptococcal strains, in understanding their ecology, population genetics, host-pathogen interactions, and the clinical epidemiology of this important mycosis in Latin America.