High efficiency opsonin-independent phagocytosis ofCandida parapsilosisby human neutrophils

A new PK/PD target for assessing efficacy of micafungin against Candida parapsilosis

BACKGROUND

Pharmacokinetic/pharmacodynamic (PK/PD) targets of echinocandins failed to support current clinical breakpoints of Candida parapsilosis as the PTA is low for susceptible isolates despite the good clinical efficacy of echinocandins against these infections. We therefore investigated the effect of micafungin against C. parapsilosis using an in vitro PK/PD in the presence of 10% human serum.

METHODS

Three susceptible (MIC = 0.5-2 mg/L) and one resistant (MIC > 8 mg/L) C. parapsilosis sensu stricto isolates were tested at two different inocula (104 and 103 cfu/mL) simulating micafungin human exposures in RPMI and in RPMI + 10% pooled human serum. The exposure-effect relationship tAUC0-24/MIC was described and different PK/PD targets were determined in order to calculate the PTA for the standard 100 mg IV q24h dose.

RESULTS

A maximal effect was found at fCmax ≥ 4 mg/L in RPMI and tCmax ≥ 64 mg/L (fCmax = 0.08 mg/L) in the presence of serum for which in vitro PK/PD targets were 50 times lower. Stasis in the presence of serum was found at 272-240 tAUC0-24/MIC, close to the clinical PK/PD target (285 tAUC/MIC), validating the in vitro model. However, the PTA was low for susceptible isolates with EUCAST/CLSI MICs ≤ 2 mg/L. Among the different PK/PD targets investigated, the PK/PD target 28 tAUC/MIC associated with 10% of maximal effect with the low inoculum resulted in PTAs ≥ 95% for susceptible isolates with EUCAST/CLSI MICs ≤ 2 mg/L.

CONCLUSIONS

A new PK/PD target was found for micafungin and C. parapsilosis that supports the current clinical breakpoint. This target could be used for assessing echinocandin efficacy against C. parapsilosis.

From environmental adaptation to host survival: Attributes that mediate pathogenicity of Candida auris

Candida species are a major cause of invasive fungal infections. While Candida albicans, C. glabrata, C. parapsilosis, and C. tropicalis are the most dominant species causing life-threatening candidiasis, C. auris recently emerged as a new species causing invasive infections with high rates of clinical treatment failures. To mimic initial phases of systemic Candida infections with dissemination via the bloodstream and to elucidate the pathogenic potential of C. auris, we used an ex vivo whole blood infection model. Similar to other clinically relevant Candida spp., C. auris is efficiently killed in human blood, but showed characteristic patterns of immune cell association, survival rates, and cytokine induction. Dual-species transcriptional profiling of C. auris-infected blood revealed a unique C. auris gene expression program during infection, while the host response proofed similar and conserved compared to other Candida species. C. auris-specific responses included adaptation and survival strategies, such as counteracting oxidative burst of immune cells, but also expression of potential virulence factors, (drug) transporters, and cell surface-associated genes. Despite comparable pathogenicity to other Candida species in our model, C. auris-specific transcriptional adaptations as well as its increased stress resistance and long-term environmental survival, likely contribute to the high risk of contamination and distribution in a nosocomial setting. Moreover, infections of neutrophils with pre-starved C. auris cells suggest that environmental preconditioning can have modulatory effects on the early host interaction. In summary, we present novel insights into C. auris pathogenicity, revealing adaptations to human blood and environmental niches distinctive from other Candida species.

Immunomodulatory Potential of the Industrialized Houttuynia cordata Fermentation Product In Vitro and in Wistar Rats

Houttuynia cordata fermentation products (HCFPs) are produced and widely used as dietary supplements for health and immune support. However, the effect on immune function for these products has not been clearly demonstrated. In this study, soluble fractions of the selected HCFP were used for determination of the immunomodulatory potential, both in vitro and in animal models. Viability and proliferation of rat splenocytes and phagocytic activity of human neutrophils were evaluated. Studies on immunomodulatory effects, including hematological parameters, mitogen-driven lymphocyte proliferation and hemagglutination, were performed in both healthy and immunosuppressed rats. Soluble fraction of the selected HCFP significantly enhanced phagocytic activity of human neutrophils and tended to stimulate splenocyte viability and proliferation. There was no morbidity or mortality for administration of a 14-day regimen of the selected HCFP in both male and female rats. The healthy rats treated with HCFP gained body weight less than the control group, suggesting a reduction in calorie intake. Moreover, low dose of HCFP caused an increased B cell proliferation in ex-vivo, which was related to the increased antibody titer against SRBC in immunosuppressed rats. Our results indicate that the selected HCFP enhances the phagocytic activity of the neutrophils and augments the antibody production in immunosuppressed rats.

The fungivorous amoeba Protostelium aurantium targets redox homeostasis and cell wall integrity during intracellular killing of Candida parapsilosis

Predatory interactions among microbes are major evolutionary driving forces for biodiversity. The fungivorous amoeba Protostelium aurantium has a wide fungal food spectrum including foremost pathogenic members of the genus Candida. Here we show that upon phagocytic ingestion by the amoeba, Candida parapsilosis is confronted with an oxidative burst and undergoes lysis within minutes of processing in acidified phagolysosomes. On the fungal side, a functional genomic approach identified copper and redox homeostasis as primary targets of amoeba predation, with the highly expressed copper exporter gene CRP1 and the peroxiredoxin gene PRX1 contributing to survival when encountered with P. aurantium. The fungicidal activity was largely retained in intracellular vesicles of the amoebae. Following their isolation, the content of these vesicles induced immediate killing and lysis of C. parapsilosis in vitro. Proteomic analysis identified 56 vesicular proteins from P. aurantium. Although completely unknown proteins were dominant, many of them could be categorised as hydrolytic enzymes targeting the fungal cell wall, indicating that fungal cell wall structures are under selection pressure by predatory phagocytes in natural environments. TAKE AWAY: The amoeba Protostelium aurantium feeds on fungi, such as Candida parapsilosis. Ingested yeast cells are exposed to reactive oxygen species. A copper exporter and a peroxiredoxin contribute to fungal defence. Yeast cells undergo intracellular lysis. Lysis occurs via a cocktail of hydrolytic enzymes from intracellular vesicles.

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.

Protection of Candida parapsilosis from neutrophil killing through internalization by human endothelial cells

Candida parapsilosis is a fungal pathogen that is associated with hematogenously disseminated disease in premature neonates, acutely ill or immunocompromised patients. In cell culture, C. parapsilosis cells are actively and avidly endocytosed by endothelial cells via actin polymerization mediated by N-WASP. Here we present evidence that C. parapsilosis that were internalized by endothelial cells remained alive, and avoided being acidified or otherwise damaged via the host cell. Internalized fungal cells reproduced intracellularly and eventually burst out of the host endothelial cell. When neutrophils were added to endothelium and C. parapsilosis, they patrolled the endothelial surface and efficiently killed most adherent fungal cells prior to endocytosis. But after endocytosis by endothelial cells, internalized fungal cells evaded neutrophil killing. Silencing endothelial N-WASP blocked endocytosis of C. parapsilosis and left fungal cells stranded on the cell surface, where they were susceptible to neutrophil killing. These observations suggest that for C. parapsilosis to escape from the bloodstream, fungi may adhere to and be internalized by endothelial cells before being confronted and phagocytosed by a patrolling leukocyte. Once internalized by endothelial cells, C. parapsilosis may safely replicate to cause further rounds of infection. Immunosurveillance of the intravascular lumen by leukocytes crawling on the endothelial surface and rapid killing of adherent yeast may play a major role in controlling C. parapsilosis dissemination and infected endothelial cells may be a significant reservoir for fungal persistence.

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.

Candida Immunity

The human pathogenic fungus Candida albicans is the predominant cause of both superficial and invasive forms of candidiasis. C. albicans primarily infects immunocompromised individuals as a result of either immunodeficiency or intervention therapy, which highlights the importance of host immune defences in preventing fungal infections. The host defence system utilises a vast communication network of cells, proteins, and chemical signals distributed in blood and tissues, which constitute innate and adaptive immunity. Over the last decade the identity of many key molecules mediating host defence against C. albicans has been identified. This review will discuss how the host recognises this fungus, the events induced by fungal cells, and the host innate and adaptive immune defences that ultimately resolve C. albicans infections during health.

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.

MBL-mediated opsonophagocytosis of Candida albicans by human neutrophils is coupled with intracellular Dectin-1-triggered ROS production

Mannan-binding lectin (MBL), a lectin homologous to C1q, greatly facilitates C3/C4-mediated opsonophagocytosis of Candida albicans (C. albicans) by human neutrophils, and has the capacity to bind to CR1 (CD35) expressed on circulating neutrophils. The intracellular pool of neutrophil Dectin-1 plays a critical role in stimulating the reactive oxygen species (ROS) generation through recognition of β-1,3-glucan component of phagocytized zymosan or yeasts. However, little is known about whether MBL can mediate the opsonophagocytosis of Candida albicans by neutrophils independent of complement activation, and whether MBL-mediated opsonophagocytosis influence the intracellular expression of Dectin-1 and ROS production. Here we showed that the inhibited phagocytic efficiency of neutrophils as a result of blockage of Dectin-1 was compensated by exogenous MBL alone in a dose-dependent manner. Furthermore, the expressions of Dectin-1 at mRNA and intracellular protein levels were significantly up-regulated in neutrophils stimulated by MBL-pre-incubated C. albicans, while the expression of surface Dectin-1 remained almost unchanged. Nevertheless, the stimulated ROS production in neutrophils was partly and irreversibly inhibited by blockage of Dectin-1 in the presence of exogenous MBL. Confocal microscopy examination showed that intracellular Dectin-1 was recruited and co-distributed with ROS on the surface of some phagocytized yeasts. The β-1,3-glucanase digestion test further suggested that the specific recognition and binding site of human Dectin-1 is just the β-1,3-glucan moiety on the cell wall of C. albicans. These data demonstrate that MBL has an ability to mediate the opsonophagocytosis of Candida albicans by human neutrophils independent of complement activation, which is coupled with intracellular Dectin-1-triggered ROS production.

Candida albicans biofilms do not trigger reactive oxygen species and evade neutrophil killing

Neutrophils are found within Candida albicans biofilms in vivo and could play a crucial role in clearing the pathogen from biofilms forming on catheters and mucosal surfaces. Our goal was to compare the antimicrobial activity of neutrophils against developing and mature C. albicans biofilms and identify biofilm-specific properties mediating resistance to immune cells. Antibiofilm activity was measured with the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)2H-tetrazolium-5-carboxanilide assay and a molecular Candida viability assay. Reactive oxygen species generation was assessed by measuring fluorescence of 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester in preloaded neutrophils. We found that mature biofilms were resistant to leukocytic killing and did not trigger reactive oxygen species, even though neutrophils retained their viability and functional activation potential. Beta-glucans found in the extracellular matrix negatively affected antibiofilm activities. We conclude that these polymers act as a decoy mechanism to prevent neutrophil activation and that this represents an important innate immune evasion mechanism of C. albicans biofilms.

Leukotrienes target F-actin/cofilin-1 to enhance alveolar macrophage anti-fungal activity

Candida albicans is the most common opportunistic fungal pathogen and causes local and systemic disease in immunocompromised patients. Alveolar macrophages (AMs) are pivotal for the clearance of C. albicans from the lung. Activated AMs secrete 5-lipoxygenase-derived leukotrienes (LTs), which in turn enhance phagocytosis and microbicidal activity against a diverse array of pathogens. Our aim was to investigate the role of LTB(4) and LTD(4) in AM antimicrobial functions against C. albicans and the signaling pathways involved. Pharmacologic and genetic inhibition of LT biosynthesis as well as receptor antagonism reduced phagocytosis of C. albicans when compared with untreated or WT controls. Conversely, exogenous LTs of both classes augmented base-line C. albicans phagocytosis by AMs. Although LTB(4) enhanced mainly mannose receptor-dependent fungal ingestion, LTD(4) enhanced mainly dectin-1 receptor-mediated phagocytosis. LT enhancement of yeast ingestion was dependent on protein kinase C-δ (PKCδ) and PI3K but not PKCα and MAPK activation. Both LTs reduced activation of cofilin-1, whereas they enhanced total cellular F-actin; however, LTB(4) accomplished this through the activation of LIM kinases (LIMKs) 1 and 2, whereas LTD(4) did so exclusively via LIMK-2. Finally, both exogenous LTB(4) and LTD(4) enhanced AM fungicidal activity in an NADPH oxidase-dependent manner. Our data identify LTB(4) and LTD(4) as key mediators of innate immunity against C. albicans, which act by both distinct and conserved signaling mechanisms to enhance multiple antimicrobial functions of AMs.