A novel pseudopodial component of the dendritic cell anti-fungal response: the fungipod

Model systems for optical trapping: the physical basis and biological applications

The micromechanical methods, among which optical trapping and atomic force microscopy have a special place, are widespread currently in biology to study molecular interactions between different biological objects. Optical trapping is reported to be quite applicable to study the mechanical properties of surface structures onto bacterial (pili and flagella) and eukaryotic (filopodia) cells. The review briefly summarizes the physical basis of optical trapping, as well as the principles of calculating the van der Waals, electrostatic, and donor-acceptor forces when two microparticles or a microparticle and a flat surface are used. Three main types of model systems (abiotic, biotic, and mixed) used in trapping experiments are described, and the peculiarities of manipulation with living (bacteria, fungal spores, etc.) and non-spherical objects (e.g., rod-shaped bacteria) are summarized.

Dectin-1-Mediated DC-SIGN Recruitment to Candida albicans Contact Sites

At host-pathogen contact sites with Candida albicans, Dectin-1 activates pro-inflammatory signaling, while DC-SIGN promotes adhesion to the fungal surface. We observed that Dectin-1 and DC-SIGN collaborate to enhance capture/retention of C. albicans under fluid shear culture conditions. Therefore, we devised a cellular model system wherein we could investigate the interaction between these two receptors during the earliest stages of host-pathogen interaction. In cells expressing both receptors, DC-SIGN was quickly recruited to contact sites (103.15% increase) but Dectin-1 did not similarly accumulate. Once inside the contact site, FRAP studies revealed a strong reduction in lateral mobility of DC-SIGN (but not Dectin-1), consistent with DC-SIGN engaging in multivalent adhesive binding interactions with cell wall mannoprotein ligands. Interestingly, in the absence of Dectin-1 co-expression, DC-SIGN recruitment to the contact was much poorer-only 35.04%. These data suggested that Dectin-1 promotes the active recruitment of DC-SIGN to the contact site. We proposed that Dectin-1 signaling activates the RHOA pathway, leading to actomyosin contractility that promotes DC-SIGN recruitment, perhaps via the formation of a centripetal actomyosin flow (AMF) directed into the contact site. Indeed, RHOA pathway inhibitors significantly reduced Dectin-1-associated DC-SIGN recruitment to the contact site. We used agent-based modeling to predict DC-SIGN transport kinetics with ("Directed + Brownian") and without ("Brownian") the hypothesized actomyosin flow-mediated transport. The Directed + Brownian transport model predicted a DC-SIGN contact site recruitment (106.64%), similar to that we observed experimentally under receptor co-expression. Brownian diffusive transport alone predicted contact site DC-SIGN recruitment of only 55.60%. However, this value was similar to experimentally observed DC-SIGN recruitment in cells without Dectin-1 or expressing Dectin-1 but treated with RHOA inhibitor, suggesting that it accurately predicted DC-SIGN recruitment when a contact site AMF would not be generated. TIRF microscopy of nascent cell contacts on glucan-coated glass revealed Dectin-1-dependent DC-SIGN and F-actin (LifeAct) recruitment kinetics to early stage contact site membranes. DC-SIGN entry followed F-actin with a temporal lag of 8.35 ± 4.57 s, but this correlation was disrupted by treatment with RHOA inhibitor. Thus, computational and experimental evidence provides support for the existence of a Dectin-1/RHOA-dependent AMF that produces a force to drive DC-SIGN recruitment to pathogen contact sites, resulting in improved pathogen capture and retention by immunocytes. These data suggest that the rapid collaborative response of Dectin-1 and DC-SIGN in early contact sties might be important for the efficient acquisition of yeast under flow conditions, such as those that prevail in circulation or mucocutaneous sites of infection.

Role of Protein Mannosylation in the Candida tropicalis-Host Interaction

Mannans are components of the fungal wall attached to proteins via N- or O-linkages. In Candida albicans, Och1 is an α1,6-mannosyltransferase that adds the first mannose unit to the N-linked mannan outer chain; whereas Pmr1 is an ion pump that imports Mn²⁺ into the Golgi lumen. This cation is the cofactor of Golgi-resident mannosyltransferases, and thus Pmr1 is involved in the synthesis of both N- and O-linked mannans. Since we currently have limited information about the genetic network behind the Candida tropicalis protein mannosylation machinery, we disrupted OCH1 and PMR1 in this organism. The C. tropicalis pmr1Δ and och1Δ mutants showed increased doubling times, aberrant colony and cellular morphology, reduction in the wall mannan content, and increased susceptibility to wall perturbing agents. These changes were accompanied by increased exposure of both β1,3-glucan and chitin at the wall surface of both mutant strains. Our results showed that O-linked mannans are dispensable for cytokine production by human mononuclear cells, but N-linked mannans and β1,3-glucan are key ligands to trigger cytokine production in a co-stimulatory pathway involving dectin-1 and mannose receptor. Moreover, we found that the N-linked mannan core found on the surface of C. tropicalis och1Δ null mutant was capable of inducing cytokine production; and that a mannan-independent pathway for IL-10 production is present in the C. tropicalis-mononuclear cell interaction. Both mutant strains showed virulence attenuation in the Galleria mellonella and the mouse model of systemic candidiasis. Therefore, mannans are relevant for cell wall composition and organization, and for the C. tropicalis-host interaction.

Candida parapsilosis: from Genes to the Bedside

Patients with suppressed immunity are at the highest risk for hospital-acquired infections. Among these, invasive candidiasis is the most prevalent systemic fungal nosocomial infection. Over recent decades, the combined prevalence of non-albicans Candida species outranked Candida albicans infections in several geographical regions worldwide, highlighting the need to understand their pathobiology in order to develop effective treatment and to prevent future outbreaks. Candida parapsilosis is the second or third most frequently isolated Candida species from patients. Besides being highly prevalent, its biology differs markedly from that of C. albicans, which may be associated with C. parapsilosis' increased incidence. Differences in virulence, regulatory and antifungal drug resistance mechanisms, and the patient groups at risk indicate that conclusions drawn from C. albicans pathobiology cannot be simply extrapolated to C. parapsilosis Such species-specific characteristics may also influence their recognition and elimination by the host and the efficacy of antifungal drugs. Due to the availability of high-throughput, state-of-the-art experimental tools and molecular genetic methods adapted to C. parapsilosis, genome and transcriptome studies are now available that greatly contribute to our understanding of what makes this species a threat. In this review, we summarize 10 years of findings on C. parapsilosis pathogenesis, including the species' genetic properties, transcriptome studies, host responses, and molecular mechanisms of virulence. Antifungal susceptibility studies and clinician perspectives are discussed. We also present regional incidence reports in order to provide an updated worldwide epidemiology summary.

Pathology of Neonatal Non- albicans Candidiasis: Autopsy Study and Literature Review

INTRODUCTION/OBJECTIVES

Non- albicans Candida species such as Candida parapsilosis and Candida glabrata have emerged as prevalent pathogens in premature infants. The aim of this study was to systematically delineate the histopathologic findings in neonatal non- albicans candidiasis.

METHODS

We performed a retrospective clinicopathologic analysis of extremely premature (23-28 weeks' gestation) infants diagnosed with invasive candidiasis. Archival autopsy tissues were subjected to periodic acid-Schiff, methenamine-silver and anti- Candida (immuno)histochemical stains, as well as dual anti- Candida and anti-cytokeratin or anti-CD31 immunofluorescence assays. In addition, we studied the prevalence of intestinal Candida colonization in a consecutive autopsy series of extremely premature infants.

RESULTS

Based on positive postmortem blood and/or lung cultures, invasive candidiasis (3 non- albicans and 11 Candida albicans) was diagnosed in 14 of the 187 extremely premature infants examined between 1995 and 2017. In contrast to the well-known inflammatory and tissue-destructive phenotype of congenital C. albicans infection, invasive non- albicans candidiasis/candidemia caused by C. parapsilosis and C. glabrata was inconspicuous by routine hematoxylin-eosin-based histopathologic analysis despite a heavy fungal presence detected in intestines, lungs, and blood by targeted (immuno)histochemical assays. Intestinal colonization by Candida species was identified in 16 of the 26 (61%) extremely premature neonates who had lived for at least 1 week, as assessed by anti- Candida immunostaining.

CONCLUSION

Invasive neonatal non- albicans candidiasis/candidemia appears to have no distinct histopathologic signature. Based on the notoriously low sensitivity of fungal blood cultures and the observed high frequency of Candida intestinal colonization (>50%), it is likely that non- albicans candidiasis/candidemia may be underdiagnosed in (deceased) preterm infants. Routine inclusion of targeted (immuno)histochemical fungal detection strategies in the perinatal autopsy may lead to deeper insight into the prevalence and clinical relevance of neonatal non- albicans candidiasis.

The Interaction of Human Pathogenic Fungi With C-Type Lectin Receptors

Fungi, usually present as commensals, are a major cause of opportunistic infections in immunocompromised patients. Such infections, if not diagnosed or treated properly, can prove fatal. However, in most cases healthy individuals are able to avert the fungal attacks by mounting proper antifungal immune responses. Among the pattern recognition receptors (PRRs), C-type lectin receptors (CLRs) are the major players in antifungal immunity. CLRs can recognize carbohydrate ligands, such as β-glucans and mannans, which are mainly found on fungal cell surfaces. They induce proinflammatory immune reactions, including phagocytosis, oxidative burst, cytokine, and chemokine production from innate effector cells, as well as activation of adaptive immunity via Th17 responses. CLRs such as Dectin-1, Dectin-2, Mincle, mannose receptor (MR), and DC-SIGN can recognize many disease-causing fungi and also collaborate with each other as well as other PRRs in mounting a fungi-specific immune response. Mutations in these receptors affect the host response and have been linked to a higher risk in contracting fungal infections. This review focuses on how CLRs on various immune cells orchestrate the antifungal response and on the contribution of single nucleotide polymorphisms in these receptors toward the risk of developing such infections.

Doxorubicin Hydrochloride Loaded Zymosan-Polyethylenimine Biopolymeric Nanoparticles for Dual 'Chemoimmunotherapeutic' Intervention in Breast Cancer

OBJECTIVE

To utilize nanoparticles produced by condensation of zymosan (an immunotherapeutic polysaccharide) with pegylated polyethylenimine (PEG-PEI) for dual intervention in breast cancer by modulating tumor microenvironment and direct chemotherapy.

METHOD

Positively charged PEG-PEI and negatively charged sulphated zymosan were utilized for electrostatic complexation of chemoimmunotherapeutic nanoparticles (ChiNPs). ChiNPs were loaded with doxorubicin hydrochloride (DOX) for improved delivery at tumor site and were tested for in-vivo tolerability. Biodistribution studies were conducted to showcase their effective accumulation in tumor hypoxic regions where tumor associated macrophages (TAMs) are preferentially recruited.

RESULTS

ChiNPs modulated TAMs differentiation resulting in decrement of CD206 positive population. This immunotherapeutic action was furnished by enhanced expression of Th1 specific cytokines. ChiNPs also facilitated an anti-angiogenetic effect which further reduces the possibility of tumor progression and metastasis.

Specific Human and Candida Cellular Interactions Lead to Controlled or Persistent Infection Outcomes during Granuloma-Like Formation

A delayed type of multicellular process could be crucial during chronic candidiasis in determining the course of infection. This reaction, consisting of organized immune cells surrounding the pathogen, initiates an inflammatory response to avoid fungal dissemination. The goal of the present study was to examine, at an in vitro cellular scale, Candida and human immune cell interaction dynamics during a long-term period. By challenging human peripheral blood immune cells from 10 healthy donors with 32 Candida albicans and non-albicans (C. glabrata, C. tropicalis, C. parapsilosis, C. dubliniensis, C. lusitaniae, C. krusei, and C. kefyr) clinical isolates, we showed that Candida spp. induced the formation of granuloma-like structures within 6 days after challenge, but their sizes and the respective fungal burdens differed according to the Candida species. These two parameters are positively correlated. Phenotypic characteristics, such as hypha formation and higher axenic growth rate, seem to contribute to yeast persistence within granuloma-like structures. We showed an interindividual variability of the human response against Candida spp. Higher proportions of neutrophils and elevated CD4⁺/CD8⁺ T cell ratios during the first days after challenge were correlated with early production of gamma interferon (IFN-γ) and associated with controlled infection. In contrast, the persistence of Candida could result from upregulation of proinflammatory cytokines such as interleukin-6 (IL-6), IFN-γ, and tumor necrosis factor alpha (TNF-α) and a poor anti-inflammatory negative feedback (IL-10). Importantly, regulatory subsets of NK cells and CD4^lo CD8^hi doubly positive (DP) lymphocytes at late stage infiltrate granuloma-like structures and could correlate with the IL-10 and TNF-α production. These data offer a base frame to explain cellular events that guide infection control or fungal persistence.

The role of pattern recognition receptors in the innate recognition of Candida albicans

Candida albicans is both a commensal microorganism in healthy individuals and a major fungal pathogen causing high mortality in immunocompromised patients. Yeast-hypha morphological transition is a well known virulence trait of C. albicans. Host innate immunity to C. albicans critically requires pattern recognition receptors (PRRs). In this review, we summarize the PRRs involved in the recognition of C. albicans in epithelial cells, endothelial cells, and phagocytic cells separately. We figure out the differential recognition of yeasts and hyphae, the findings on PRR-deficient mice, and the discoveries on human PRR-related single nucleotide polymorphisms (SNPs).

Silenced suppressor of cytokine signaling 1 (SOCS1) enhances the maturation and antifungal immunity of dendritic cells in response to Candida albicans in vitro

Dendritic cells (DCs) are known to play an important role in initiating and orchestrating antimicrobial immunity. Given the fact that candidiasis appears often in immunocompromised patients, it seems plausible that DCs hold the key to new antifungal strategies. One possibility to enhance the potency of DC-based immunotherapy is to silence the negative immunoregulatory pathways through the ablation suppressor of cytokine signaling suppressor 1 (SOCS1). Here, we deliver small interfering RNA (siRNA) against SOCS1 into murine bone marrow DCs, and as a consequence, we investigate the maturation/action of DCs and the subsequent T cell response after exposure to C. albicans. Our results show that the maturation of DCs (i.e., expressions of CD80, CD40, CD86, and MHC II) are significantly increased in the silenced SOCS1 treatment group after exposure to C. albicans. As a result, suppression of the SOCS1 promotes the greatest expression of IFN-γ and IL-12, and reduces IL-4 secretions, which induce CD4⁺ cell Th1 differentiation but inactivate Th2 cell development. The responses of IL-6 and TNF-β consist of up-regulation in the presence of C. albicans, but this is not specific to SOCS1 silencing, suggesting that these cytokines are not regulated by the SOCS1 gene in fungal infections. We find Th17 differentiation is unchanged regardless of SOCS1 inhibition. The increase in phagocytosis and killing of C. albicans in SOCS1 gene-treated DCs indicate a role for this cytokine suppressor in innate immunity as well. In conclusion, our findings support the view that SOCS1 protein is a critical inhibitory molecule for controlling cytokine response and antigen presentation by DCs, thereby regulating the magnitude of innate and adaptive immunities by generating IFN-γ-production T cells (Th1)—but not Th17—from naïve CD4⁺ T cells. Our study demonstrates that SOCS1 siRNA can serve as a useful vehicle to modulate the function of DCs against C. albicans infection.

Beyond Candida albicans: Mechanisms of immunity to non-albicans Candida species

The fungal genus Candida encompasses numerous species that inhabit a variety of hosts, either as commensal microbes and/or pathogens. Candida species are a major cause of fungal infections, yet to date there are no vaccines against Candida or indeed any other fungal pathogen. Our knowledge of immunity to Candida mainly comes from studies on Candida albicans, the most frequent species associated with disease. However, non-albicans Candida (NAC) species also cause disease and their prevalence is increasing. Although research into immunity to NAC species is still at an early stage, it is becoming apparent that immunity to C. albicans differs in important ways from non-albicans species, with important implications for treatment, therapy and predicted demographic susceptibility. This review will discuss the current understanding of immunity to NAC species in the context of immunity to C. albicans, and highlight as-yet unanswered questions.

Novel insights into host-fungal pathogen interactions derived from live-cell imaging

The theoretical physicist and Nobel laureate Richard Feynman outlined in his 1959 lecture, “There’s plenty of room at the bottom”, the enormous possibility of producing and visualising things at smaller scales. The advent of advanced scanning and transmission electron microscopy and high-resolution microscopy has begun to open the door to visualise host-pathogen interactions at smaller scales, and spinning disc confocal and two-photon microscopy has improved our ability to study these events in real time in three dimensions. The aim of this review is to illustrate some of the advances in understanding host-fungal interactions that have been made in recent years in particular those relating to the interactions of live fungal pathogens with phagocytes. Dynamic imaging of host-pathogen interactions has recently revealed novel detail and unsuspected mechanistic insights, facilitating the dissection of the phagocytic process into its component parts. Here, we will highlight advances in our knowledge of host-fungal pathogen interactions, including the specific effects of fungal cell viability, cell wall composition and morphogenesis on the phagocytic process and try to define the relative contributions of neutrophils and macrophages to the clearance of fungal pathogens in vitro and the infected host.

Human dendritic cell subsets display distinct interactions with the pathogenic mould Aspergillus fumigatus

The mould Aspergillus fumigatus is primarily an opportunistic pathogen of immunocompromised patients. Once fungal spores have been inhaled they encounter cells of the innate immune system, which include dendritic cells (DCs). DCs are the key antigen-presenting cells of the immune system and distinct subtypes, which differ in terms of origin, morphology and function. This study has systematically compared the interactions between A. fumigatus and myeloid DCs (mDCs), plasmacytoid DCs (pDCs) and monocyte-derived DCs (moDCs). Analyses were performed by time-lapse video microscopy, scanning electron microscopy, plating assays, flow cytometry, 25-plex ELISA and transwell assays. The three subsets of DCs displayed distinct responses to the fungus with mDCs and moDCs showing the greatest similarities. mDCs and moDCs both produced rough convolutions and occasionally phagocytic cups upon exposure to A. fumigatus whereas pDCs maintained a smooth appearance. Both mDCs and moDCs phagocytosed conidia and germ tubes, while pDCs did not phagocytose any fungi. Analysis of cytokine release and maturation markers revealed specific differences in pro- and anti-inflammatory patterns between the different DC subsets. These distinct characteristics between the DC subsets highlight their differences and suggest specific roles of moDCs, mDCs and pDCs during their interaction with A. fumigatus in vivo.

Super-resolution imaging of C-type lectin spatial rearrangement within the dendritic cell plasma membrane at fungal microbe contact sites

Dendritic cells express DC-SIGN and CD206, C-type lectins (CTLs) that bind a variety of pathogens and may facilitate pathogen uptake for subsequent antigen presentation. Both proteins form punctate membrane nanodomains (∼80 nm) on naïve cells. We analyzed the spatiotemporal distribution of CTLs following host-fungal particle contact using confocal microscopy and three distinct methods of cluster identification and measurement of receptor clusters in super-resolution datasets: DBSCAN, Pair Correlation and a custom implementation of the Getis spatial statistic. Quantitative analysis of confocal and super-resolution images demonstrated that CTL nanodomains become concentrated in the contact site relative to non-contact membrane after the first hour of exposure and established that this recruitment is sustained out to 4 h. DC-SIGN nanodomains in fungal contact sites exhibit a 70% area increase and a 38% decrease in interdomain separation. Contact site CD206 nanodomains possess 90% greater area and 42% lower interdomain separation relative to non-contact regions. Contact site CTL clusters appear as disk-shaped domains of approximately 150-175 nm in diameter. The increase in length scale of CTL nanostructure in contact sites suggests that the smaller nanodomains on resting membranes may merge during fungal recognition, or that they become packed closely enough to achieve sub-resolution inter-domain edge separations of <30 nm. This study provides evidence of local receptor spatial rearrangements on the nanoscale that occur in the plasma membrane upon pathogen binding and may direct important signaling interactions required to recognize and respond to the presence of a relatively large pathogen.

Bacterial subversion of host cytoskeletal machinery: hijacking formins and the Arp2/3 complex

The host actin nucleation machinery is subverted by many bacterial pathogens to facilitate their entry, motility, replication, and survival. The majority of research conducted in the past primarily focused on exploitation of a host actin nucleator, the Arp2/3 complex, by bacterial pathogens. Recently, new studies have begun to explore the role of formins, another family of host actin nucleators, in bacterial pathogenesis. This review provides an overview of recent advances in the study of the exploitation of the Arp2/3 complex and formins by bacterial pathogens. Secreted bacterial effector proteins seem to manipulate the regulation of these actin nucleators or functionally mimic them to drive bacterial entry, motility and survival within host cells. An enhanced understanding of how formins are exploited will provide us with greater insight into how a fundamental eurkaryotic cellular process is utilized by bacteria and will also advance our knowledge of host-pathogen interactions.

A new tool to quantify receptor recruitment to cell contact sites during host-pathogen interaction

To understand the process of innate immune fungal recognition, we developed computational tools for the rigorous quantification and comparison of receptor recruitment and distribution at cell-cell contact sites. We used these tools to quantify pattern recognition receptor spatiotemporal distributions in contacts between primary human dendritic cells and the fungal pathogens C. albicans, C. parapsilosis and the environmental yeast S. cerevisiae, imaged using 3D multichannel laser scanning confocal microscopy. The detailed quantitative analysis of contact sites shows that, despite considerable biochemical similarity in the composition and structure of these species' cell walls, the receptor spatiotemporal distribution in host-microbe contact sites varies significantly between these yeasts. Our findings suggest a model where innate immune cells discriminate fungal microorganisms based on differential mobilization and coordination of receptor networks. Our analysis methods are also broadly applicable to a range of cell-cell interactions central to many biological problems.

Evaluation of in vivo pathogenicity of Candida parapsilosis, Candida orthopsilosis, and Candida metapsilosis with different enzymatic profiles in a murine model of disseminated candidiasis

Six isolates of the Candida parapsilosis complex with different enzymatic profiles were used to induce systemic infection in immunocompetent BALB/c mice. Fungal tissue burden was determined on days 2, 5, 10, and 15 post challenge. The highest fungal load irrespective of post-infection day was detected in the kidney, followed by the spleen, lung, and liver, with a tendency for the fungal burden to decrease by day 15 in all groups. Significant differences among the strains were not detected, suggesting that the three species of the "psilosis" group possess a similar pathogenic potential in disseminated candidiasis regardless of their enzymatic profiles.

Whole Pichia pastoris yeast expressing measles virus nucleoprotein as a production and delivery system to multimerize Plasmodium antigens

Yeasts are largely used as bioreactors for vaccine production. Usually, antigens are produced in yeast then purified and mixed with adjuvants before immunization. However, the purification costs and the safety concerns recently raised by the use of new adjuvants argue for alternative strategies. To this end, the use of whole yeast as both production and delivery system appears attractive. Here, we evaluated Pichia pastoris yeast as an alternative vaccine production and delivery system for the circumsporozoite protein (CS) of Plasmodium, the etiologic agent of malaria. The CS protein from Plasmodium berghei (Pb) was selected given the availability of the stringent C57Bl/6 mouse model of infection by Pb sporozoites, allowing the evaluation of vaccine efficacy in vivo. PbCS was multimerized by fusion to the measles virus (MV) nucleoprotein (N) known to auto-assemble in yeast in large-size ribonucleoprotein rods (RNPs). Expressed in P. pastoris, the N-PbCS protein generated highly multimeric and heterogenic RNPs bearing PbCS on their surface. Electron microscopy and immunofluorescence analyses revealed the shape of these RNPs and their localization in peripheral cytoplasmic inclusions. Subcutaneous immunization of C57Bl/6 mice with heat-inactivated whole P. pastoris expressing N-PbCS RNPs provided significant reduction of parasitemia after intradermal challenge with a high dose of parasites. Thus, in the absence of accessory adjuvants, a very low amount of PbCS expressed in whole yeast significantly decreased clinical damages associated with Pb infection in a highly stringent challenge model, providing a proof of concept of the intrinsic adjuvancy of this vaccine strategy. In addition to PbCS multimerization, the N protein contributed by itself to parasitemia delay and long-term mice survival. In the future, mixtures of whole recombinant yeasts expressing relevant Plasmodium antigens would provide a multivalent formulation applicable for antigen combination screening and possibly for large-scale production, distribution and delivery of a malaria vaccine in developing countries.

The immune response against Candida spp. and Sporothrix schenckii

Candida albicans is the main causative agent of systemic candidiasis, a condition with high mortality rates. The study of the interaction between C. albicans and immune system components has been thoroughly studied and nowadays there is a model for the anti-C. albicans immune response; however, little is known about the sensing of other pathogenic species of the Candida genus. Sporothrix schenckii is the causative agent of sporotrichosis, a subcutaneous mycosis, and thus far there is limited information about its interaction with the immune system. In this paper, we review the most recent information about the immune sensing of species from genus Candida and S. schenckii. Thoroughly searches in scientific journal databases were performed, looking for papers addressing either Candida- or Sporothrix-immune system interactions. There is a significant advance in the knowledge of non-C. albicans species of Candida and Sporothrix immune sensing; however, there are still relevant points to address, such as the specific contribution of pathogen-associated molecular patterns (PAMPs) for sensing by different immune cells and the immune receptors involved in such interactions. This manuscript is part of the series of works presented at the "V International Workshop: Molecular genetic approaches to the study of human pathogenic fungi" (Oaxaca, Mexico, 2012).

Candida parapsilosis and the neonate: epidemiology, virulence and host defense in a unique patient setting

Invasive candidiasis is a common problem in premature infants that leads to high morbidity and mortality. Although Candida albicans has historically been the most prominent species involved in these infections and has therefore been the subject of the most study, Candida parapsilosis is increasing in frequency, and neonates are disproportionately affected. This article reviews unique aspects of the epidemiology of this organism as well as strategies for prophylaxis against invasive candidiasis in general. Additionally, important differences between C. parapsilosis and C. albicans are coming to light related to virulence determinants and interactions with components of host immunity. These developments are reviewed while highlighting the significant gaps in our understanding that remain to be elucidated.

The role of galectin-3 in phagocytosis of Candida albicans and Candida parapsilosis by human neutrophils

Candida albicans causes the majority of invasive candidiasis in immunocompromised adults while Candida parapsilosis is a leading cause of neonatal candidiasis. While much work has focused on how the immune system recognizes and responds to C. albicans, less is known about host interaction with C. parapsilosis. This study investigates the human neutrophil phagocytic response to these species. Neutrophils underwent phagocytosis of C. parapsilosis yeast and C. albicans hyphae much more efficiently than C. albicans yeast. Treatment of neutrophils with a galectin-3 (gal3) blocking antibody inhibited phagocytosis of C. parapsilosis yeast and C. albicans hyphae, but not C. albicans yeast. The majority of neutrophil gal3 was expressed intracellularly and was secreted from neutrophils after treatment with C. parapsilosis mannan. When neutrophils were treated with exogenous gal3, phagocytosis of both C. albicans and C. parapsilosis yeast increased. Exposure of neutrophils to C. parapsilosis yeast increased phagocytosis of C. albicans yeast and was inhibited by gal3 blocking antibody. Taken together, these data indicate that gal3 secreted from neutrophils may act as a pro-inflammatory autocrine/paracrine signal in neutrophil phagocytosis and suggest that gal3 has a unique role in neutrophil response to C. parapsilosis yeast and C. albicans hyphae distinct from C. albicans yeast.

Dendritic cells in antifungal immunity and vaccine design

Life-threatening fungal infections have increased in recent years while treatment options remain limited. The development of vaccines against fungal pathogens represents a key advance sorely needed to combat the increasing fungal disease threat. Dendritic cells (DC) are uniquely able to shape antifungal immunity by initiating and modulating naive T cell responses. Targeting DC may allow for the generation of potent vaccines against fungal pathogens. In the context of antifungal vaccine design, we describe the characteristics of the varied DC subsets, how DC recognize fungi, their function in immunity against fungal pathogens, and how DC can be targeted in order to create new antifungal vaccines. Ongoing studies continue to highlight the critical role of DC in antifungal immunity and will help guide DC-based vaccine strategies.

DC-SIGN and influenza hemagglutinin dynamics in plasma membrane microdomains are markedly different

DC-SIGN, a Ca(2+)-dependent transmembrane lectin, is found assembled in microdomains on the plasma membranes of dendritic cells. These microdomains bind a large variety of pathogens and facilitate their uptake for subsequent antigen presentation. In this study, DC-SIGN dynamics in microdomains were explored with several fluorescence microscopy methods and compared with dynamics for influenza hemagglutinin (HA), which is also found in plasma membrane microdomains. Fluorescence imaging indicated that DC-SIGN microdomains may contain other C-type lectins and that the DC-SIGN cytoplasmic region is not required for microdomain formation. Fluorescence recovery after photobleaching measurements showed that neither full-length nor cytoplasmically truncated DC-SIGN in microdomains appreciably exchanged with like molecules in other microdomains and the membrane surround, whereas HA in microdomains exchanged almost completely. Line-scan fluorescence correlation spectroscopy indicated an essentially undetectable lateral mobility for DC-SIGN but an appreciable mobility for HA within their respective domains. Single-particle tracking with defined-valency quantum dots confirmed that HA has significant mobility within microdomains, whereas DC-SIGN does not. By contrast, fluorescence recovery after photobleaching indicated that inner leaflet lipids are able to move through DC-SIGN microdomains. The surprising stability of DC-SIGN microdomains may reflect structural features that enhance pathogen uptake either by providing high-avidity platforms and/or by protecting against rapid microdomain endocytosis.

Innate antifungal immunity: the key role of phagocytes

Fungal diseases have emerged as significant causes of morbidity and mortality, particularly in immune-compromised individuals, prompting greater interest in understanding the mechanisms of host resistance to these pathogens. Consequently, the past few decades have seen a tremendous increase in our knowledge of the innate and adaptive components underlying the protective (and nonprotective) mechanisms of antifungal immunity. What has emerged from these studies is that phagocytic cells are essential for protection and that defects in these cells compromise the host's ability to resist fungal infection. This review covers the functions of phagocytes in innate antifungal immunity, along with selected examples of the strategies that are used by fungal pathogens to subvert these defenses.

In vitro interactions of Candida parapsilosis wild type and lipase deficient mutants with human monocyte derived dendritic cells

Background

Candida parapsilosis typically is a commensal of human skin. However, when host immune defense is compromised or the normal microflora balance is disrupted, C. parapsilosis transforms itself into an opportunistic pathogen. Candida-derived lipase has been identified as potential virulence factor. Even though cellular components of the innate immune response, such as dendritic cells, represent the first line of defense against invading pathogens, little is known about the interaction of these cells with invading C. parapsilosis. Thus, the aim of our study was to assess the function of dendritic cells in fighting C. parapsilosis and to determine the role that C. parapsilosis-derived lipase plays in the interaction with dendritic cells.

Results

Monocyte-derived immature and mature dendritic cells (iDCs and mDCs, respectively) co-cultured with live wild type or lipase deficient C. parapsilosis strains were studied to determine the phagocytic capacity and killing efficiency of host cells. We determined that both iDCs and mDCs efficiently phagocytosed and killed C. parapsilosis, furthermore our results show that the phagocytic and fungicidal activities of both iDCs and mDCs are more potent for lipase deficient compared to wild type yeast cells. In addition, the lipase deficient C. parapsilosis cells induce higher gene expression and protein secretion of proinflammatory cytokines and chemokines in both DC types relative to the effect of co-culture with wild type yeast cells.

Conclusions

Our results show that DCs are activated by exposure to C. parapsilosis, as shown by increased phagocytosis, killing and proinflammatory protein secretion. Moreover, these data strongly suggest that C. parapsilosis derived lipase has a protective role during yeast:DC interactions, since lipase production in wt yeast cells decreased the phagocytic capacity and killing efficiency of host cells and downregulated the expression of host effector molecules.

Understanding lipid rafts and other related membrane domains

Evidence in support of the classical lipid raft hypothesis has remained elusive. Data suggests that transmembrane proteins and the actin-containing cortical cytoskeleton can organize lipids into short-lived nanoscale assemblies that can be assembled into larger domains under certain conditions. This supports an evolving view in which interactions between lipids, cholesterol, and proteins create and maintain lateral heterogeneity in the cell membrane.