Human phagocytic cell responses to Scedosporium apiospermum (Pseudallescheria boydii): variable susceptibility to oxidative injury

Scedosporiosis and lomentosporiosis: modern perspectives on these difficult-to-treat rare mold infections

SUMMARYAlthough Scedosporium species and Lomentospora prolificans are uncommon causes of invasive fungal diseases (IFDs), these infections are associated with high mortality and are costly to treat with a limited armamentarium of antifungal drugs. In light of recent advances, including in the area of new antifungals, the present review provides a timely and updated overview of these IFDs, with a focus on the taxonomy, clinical epidemiology, pathogenesis and host immune response, disease manifestations, diagnosis, antifungal susceptibility, and treatment. An expansion of hosts at risk for these difficult-to-treat infections has emerged over the last two decades given the increased use of, and broader population treated with, immunomodulatory and targeted molecular agents as well as wider adoption of antifungal prophylaxis. Clinical presentations differ not only between genera but also across the different Scedosporium species. L. prolificans is intrinsically resistant to most currently available antifungal agents, and the prognosis of immunocompromised patients with lomentosporiosis is poor. Development of, and improved access to, diagnostic modalities for early detection of these rare mold infections is paramount for timely targeted antifungal therapy and surgery if indicated. New antifungal agents (e.g., olorofim, fosmanogepix) with novel mechanisms of action and less cross-resistance to existing classes, availability of formulations for oral administration, and fewer drug-drug interactions are now in late-stage clinical trials, and soon, could extend options to treat scedosporiosis/lomentosporiosis. Much work remains to increase our understanding of these infections, especially in the pediatric setting. Knowledge gaps for future research are highlighted in the review.

Recurrent Scedosporium apiospermum Cutaneous Infection in a Patient with Rheumatoid Arthritis: The Potent Role of IL-6 Signaling Pathway Blockade: A Case-Based Review

Rheumatoid arthritis (RA) patients deal with a higher risk of bacterial and fungal infections compared to the general population because of their dysregulated immune system as well as the immunosuppressive therapy they usually receive. Scedosporium spp. is a fungal pathogen responsible for cutaneous, lung, central nervous system, and eye infections, mostly in immunocompromised patients, leading to death in disseminated cases. We report the case of an 81-year-old woman with rheumatoid arthritis treated with steroids and an IL-6 inhibitor who was diagnosed with scedosporiosis of the upper limb. She was treated with voriconazole for one month, which was discontinued due to adverse events, and when scedosporiosis relapsed, she switched to itraconazole. We also reviewed the current literature on RA patients presenting with Scedosporium infections. Early and accurate diagnosis of scedosporiosis has therapeutic and prognostic implications, as traditionally this fungus is resistant to commonly used antifungals. Clinical alertness regarding uncommon infections, including fungal, in patients with autoimmune diseases on immunomodulatory agents is essential for effective treatment.

Recent Advances in the Treatment of Scedosporiosis and Fusariosis

Species of Scedosporium and Fusarium are considered emerging opportunistic pathogens, causing invasive fungal diseases in humans that are known as scedosporiosis and fusariosis, respectively. These mold infections typically affect patients with immune impairment; however, cases have been reported in otherwise healthy individuals. Clinical manifestations vary considerably, ranging from isolated superficial infection to deep-seated invasive infection—affecting multiple organs—which is often lethal. While there have been a number of advances in the detection of these infections, including the use of polymerase chain reaction (PCR) and matrix-assisted laser desorption ionization/time-of-flight mass spectrometry (MALDI-TOF MS), diagnosis is often delayed, leading to substantial morbidity and mortality. Although the optimal therapy is controversial, there have also been notable advances in the treatment of these diseases, which often depend on a combination of antifungal therapy, reversal of immunosuppression, and in some cases, surgical resection. In this paper, we review these advances and examine how the management of scedosporiosis and fusariosis may change in the near future.

Stimulation with lysates of Aspergillus terreus, Candida krusei and Rhizopus oryzae maximizes cross-reactivity of anti-fungal T cells

BACKGROUND AIMS

Invasive fungal diseases caused by filamentous fungi and yeasts are significant causes of morbidity and mortality in immunosuppressed hematology patients. We previously published a method to expand Aspergillus fumigatus-specific T cells for clinical cell therapy. In the present study, we investigated expansion of T cells specific for other fungal pathogens and creation of a broadly reactive panfungal T-cell product.

METHODS

Fungal strains selected were those frequently observed in the clinical hematology setting and included Aspergillus, Candida, Fusarium, Rhizopus and Lomentospora/Scedosporium. Four T-cell cultures specific to each fungus were established. We selected lysates of Aspergillus terreus, Candida krusei and Rhizopus oryzae to expand panfungal T cells. Allelic restriction of anti-fungal activity was determined through the use of specific major histocompatibility complex class II-blocking antibodies.

RESULTS

Individual T-cell cultures specific to each fungus could be expanded in vitro, generating predominantly CD4(+) T cells of which 8% to 20% were fungus-specific. We successfully expanded panfungal T cells from the peripheral blood (n = 8) and granulocyte-colony-stimulating factor-primed stem cell products (n = 3) of normal donors by using a combination of lysates from Aspergillus terreus, Candida krusei and Rhizopus oryzae. Anti-fungal activity was mediated through human leukocyte antigen (HLA)-DR alleles and was maintained when antigen-presenting cells from partially HLA-DRB1-matched donors were used to stimulate T cells.

CONCLUSIONS

We demonstrate a method to manufacture panfungal T-cell products with specificity against a range of clinical fungal pathogens by use of the blood and stem cells of healthy donors as the starting material. The safety and efficacy of these products will need to be tested clinically.

Methylprednisolone impairs conidial phagocytosis but does not attenuate hyphal damage by neutrophils against Exserohilum rostratum

Exserohilum rostratum caused a multistate fungal meningitis outbreak following iatrogenic inoculation of contaminated methylprednisolone in the United States. To gain insight into the immunopathogenesis of this infection, we studied the innate host responses of human neutrophils against E. rostratum conidia and hyphae with or without methylprednisolone. The neutrophil-induced percentage fungal damage against conidia and hyphae was effector-to-target ratio dependent (≤55%). While methylprednisolone did not affect neutrophil-induced fungal damage by treatment of Exserohilum or neutrophils, it compromised phagocytosis of conidia (P < 0.05). These findings suggest that methylprednisolone-treated neutrophils may have altered phagocytic clearance of Exserohilum conidia, reducing host capacity to contain the invasive process.

Proteomic analysis of the secretions of Pseudallescheria boydii, a human fungal pathogen with unknown genome

Pseudallescheria boydii is a filamentous fungus that causes a wide array of infections that can affect practically all the organs of the human body. The treatment of pseudallescheriosis is difficult since P. boydii exhibits intrinsic resistance to the majority of antifungal drugs used in the clinic and the virulence attributes expressed by this fungus are unknown. The study of the secretion of molecules is an important approach for understanding the pathogenicity of fungi. With this task in mind, we have shown that mycelial cells of P. boydii were able to actively secrete proteins into the extracellular environment; some of them were recognized by antibodies present in the serum of a patient with pseudallescheriosis. Additionally, molecules secreted by P. boydii induced in vitro irreversible damage in pulmonary epithelial cells. Subsequently, two-dimensional gel electrophoresis combined with mass spectrometry was carried out in order to start the construction of a map of secreted proteins from P. boydii mycelial cells. The two-dimensional map showed that most of the proteins (around 100 spots) were focused at pH ranging from 4 to 7 with molecular masses ranging from 14 to >117 kDa. Fifty spots were randomly selected, of which 30 (60%) were consistently identified, while 20 (40%) spots generated peptides that showed no resemblance to any known protein from other fungi and/or MS with low quality. Notably, we identified proteins involved in metabolic pathways (energy/carbohydrate, nucleotide, and fatty acid), cell wall remodeling, RNA processing, signaling, protein degradation/nutrition, translation machinery, drug elimination and/or detoxification, protection against environmental stress, cytoskeleton/movement proteins, and immunogenic molecules. Since the genome of this fungus is not sequenced, we performed enzymatic and immunodetection assays in order to corroborate the presence of some released proteins. The identification of proteins actively secreted by P. boydii provides important new information for understanding immune modulation and provides important new perspectives on the biology of this intriguing fungus.

Local innate host response and filamentous fungi in patients with cystic fibrosis

Filamentous fungi especially Aspergillus spp. and Scedosporium spp. can colonize the lungs of cystic fibrosis (CF) patients. Persistent infection by these organisms may cause deterioration of lung function, mycetomas or local invasive disease. Although CF patients exert an excessive inflammatory response to inhaled bacteria, very little is known about the local innate immune response to filamentous fungi. In this paper, we review the innate immune response of respiratory tract of healthy individuals to filamentous fungi with some inference to CF patients and link the latter to existing data. We also report some preliminary findings on the in vitro antifungal responses of human phagocytes against Aspergillus spp. isolated from CF patients. Translation of these in vitro findings to appropriate in vivo systems and into clinical trials of immunomodulatory treatments may lead to improved strategies for appropriate innate host defenses in CF patients persistently infected with filamentous fungi.

Biochemical characterization of potential virulence markers in the human fungal pathogen Pseudallescheria boydii

The ubiquitous Pseudallescheria boydii (anamorph Scedosporium apiospermum) is a saprophytic filamentous fungus recognized as a potent etiologic agent of a wide variety of infections in immunocompromised as well as in immunocompetent patients. Very little is known about the virulence factors expressed by this fungal pathogen. The present review provides an overview of recent discoveries related to the identification and biochemical characterization of potential virulence attributes produced by P. boydii, with special emphasis on surface and released molecules. These structures include polysaccharides (glucans), glycopeptides (peptidorhamnomannans), glycolipids (glucosylceramides) and hydrolytic enzymes (proteases, phosphatases and superoxide dismutase), which have been implicated in some fundamental cellular processes in P. boydii including growth, differentiation and interaction with host molecules. Elucidation of the structure of cell surface components as well as the secreted molecules, especially those that function as virulence determinants, is of great relevance to understand the pathogenic mechanisms of P. boydii.

Host immune response against Scedosporium species

Scedosporium apiospermum and Scedosporium prolificans cause therapy-refractory infections in immunocompromised and immunocompetent hosts. While innate immune response is believed to be critical for the host defense against these fungi, its role has only recently been elucidated. Undefined pathogen-associated molecular patterns on the surface of conidia and hyphae are recognized by pattern-recognition receptors (PRRs) on the membrane of phagocytes, and the signal is transmitted intracellularly. PRRs that are important in the recognition of both fungal species are human Toll-like receptors (or Toll receptors in Drosophila melanogaster) and dectin-1. These induce signals responsible for the activation of genes leading to an effective host defense, especially those encoding pro-inflammatory cytokines. Both species are efficiently phagocytosed and elicit an oxidative burst by neutrophils and monocytes. While cytokines, such as interleukin-15, granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor and interferon-gamma, have been found in vitro to variably modulate antifungal activity of human phagocytes, cytokines in vivo activities are less well documented. Certain antifungal agents exert immunopharmacological effects on phagocytes against S. apiospermum and S. prolificans. Translation of these in vitro findings to appropriate in vivo systems and into clinical trials may lead to improved strategies for augmenting innate host defenses in patients infected with these emerging pathogens.

Infections caused by Scedosporium spp

Scedosporium spp. are increasingly recognized as causes of resistant life-threatening infections in immunocompromised patients. Scedosporium spp. also cause a wide spectrum of conditions, including mycetoma, saprobic involvement and colonization of the airways, sinopulmonary infections, extrapulmonary localized infections, and disseminated infections. Invasive scedosporium infections are also associated with central nervous infection following near-drowning accidents. The most common sites of infection are the lungs, sinuses, bones, joints, eyes, and brain. Scedosporium apiospermum and Scedosporium prolificans are the two principal medically important species of this genus. Pseudallescheria boydii, the teleomorph of S. apiospermum, is recognized by the presence of cleistothecia. Recent advances in molecular taxonomy have advanced the understanding of the genus Scedosporium and have demonstrated a wider range of species than heretofore recognized. Studies of the pathogenesis of and immune response to Scedosporium spp. underscore the importance of innate host defenses in protection against these organisms. Microbiological diagnosis of Scedosporium spp. currently depends upon culture and morphological characterization. Molecular tools for clinical microbiological detection of Scedosporium spp. are currently investigational. Infections caused by S. apiospermum and P. boydii in patients and animals may respond to antifungal triazoles. By comparison, infections caused by S. prolificans seldom respond to medical therapy alone. Surgery and reversal of immunosuppression may be the only effective therapeutic options for infections caused by S. prolificans.

Molecular cloning and biochemical characterization of a Cu,Zn-superoxide dismutase from Scedosporium apiospermum

A Cu,Zn-superoxide dismutase has been characterized from Scedosporium apiospermum, a fungus which often colonizes the respiratory tract of patients with cystic fibrosis. Enzyme production was stimulated by iron starvation. Purification was achieved from mycelial extract from 7-day-old cultures on Amberlite XAD-16. The purified enzyme presented a relative molecular mass of 16.4 kDa under reducing conditions and was inhibited by potassium cyanide and diethyldithiocarbamate, which are two known inhibitors of Cu,Zn-SODs. Its optimum pH was 7.0 and the enzyme retained full activity after pretreatment at temperatures up to 50 degrees C. Moreover, a 450-bp fragment of the gene encoding the enzyme was amplified by PCR using degenerate primers designed from sequence alignment of four fungal Cu,Zn-SODs. Sequence data from this fragment allowed us to design primers which were used to amplify by walking-PCR the flanking regions of the known fragment. SaSODC gene (890 bp) corresponded to a 154 amino acid polypeptide with a predicted molecular mass of 15.9 kDa. A database search for sequence homology revealed for the deduced amino acid sequence 72 and 83% identity rate with Cu,Zn-SODs from Aspergillus fumigatus and Neurospora crassa, respectively. To our knowledge, this enzyme is the first putative virulence factor of S. apiospermum to be characterized.

An α-Glucan of Pseudallescheria boydii Is Involved in Fungal Phagocytosis and Toll-like Receptor Activation

The host response to fungi is in part dependent on activation of evolutionarily conserved receptors, including toll-like receptors and phagocytic receptors. However, the molecular nature of fungal ligands responsible for this activation is largely unknown. Herein, we describe the isolation and structural characterization of an alpha-glucan from Pseudallescheria boydii cell wall and evaluate its role in the induction of innate immune response. These analyses indicate that alpha-glucan of P. boydii is a glycogen-like polysaccharide consisting of linear 4-linked alpha-D-Glcp residues substituted at position 6 with alpha-D-Glcp branches. Soluble alpha-glucan, but not beta-glucan, led to a dose-dependent inhibition of conidia phagocytosis. Furthermore, a significant decrease in the phagocytic index occurred when alpha-glucan from conidial surface was removed by enzymatic treatment with alpha-amyloglucosidase, thus indicating an essential role of alpha-glucan in P. boydii internalization by macrophages. alpha-Glucan stimulates the secretion of inflammatory cytokines by macrophages and dendritic cells; again this effect is abolished by treatment with alpha-amyloglucosidase. Finally, alpha-glucan induces cytokine secretion by cells of the innate immune system in a mechanism involving toll-like receptor 2, CD14, and MyD88. These results might have relevance in the context of infections with P. boydii and other fungi, and alpha-glucan could be a target for intervention during fungal infections.

Pseudallescheriasis in the 21st century

Since its discovery as an agent of mycetoma nearly a century ago, Pseudallescheria boydii with its asexual (synanamorphic) form, Scedosporium apiospermum, is now recognized as an important emerging opportunistic pathogen causing invasive mycosis in immunocompromised patients. The clinical spectrum of pseudallescheriasis is wide. Invasive disease of the lung, CNS and dissemination are serious manifestations in immunocompromised patients. This organism responds poorly to amphotericin B, and its histopathologic resemblance to aspergillosis often results in a delay in diagnosis. In vitro data, animal models and accumulating clinical experience support the use of voriconazole as a primary treatment for pseudallescheriasis. This paper reviews the microbiology, ecology, epidemiologic trends, clinical manifestations and current treatment options of pseudallescheriasis.

Generation of highly purified and functionally active human TH1 cells against Aspergillus fumigatus

Invasive aspergillosis remains a serious complication in patients undergoing allogeneic stem cell transplantation (SCT). Since it became clear that lymphocytes provide a critical secondary defense against fungi, adoptive transfer of functionally active anti-Aspergillus T cells might be an option to restore adaptive immune effector mechanisms. Using the interferon (IFN)-γ secretion assay, we isolated human activated T cells upon stimulation with a cellular extract of Aspergillus fumigatus. Culturing this cell population for 14 days, we obtained an average of 1.1 × 107 cells from a single 100-mL blood draw in 7 of 7 healthy individuals. Within another 14 days, these cells were expanded to an average number of 2.0 × 108 T-helper 1 (TH1) cells secreting IFN-γ on stimulation with Aspergillus antigens. Testing various fungal antigen extracts, similar proportions of IFN-γ-producing CD3+/CD4+ cells were obtained upon activation with antigen extracts of A fumigatus, A flavus, A niger, and Penicillium chrysogenum, whereas no significant IFN-γ production was observed upon activation with antigen extracts of Alternaria alternata and Candida albicans. In addition, generated T cells were able to induce damage to A fumigatus hyphae, and significantly increased hyphal damage induced by human neutrophils. CD4+ T-cell-mediated alloreactivity of generated anti-Aspergillus T cells was clearly reduced compared with that of the original cell population. In conclusion, we present a simple and feasible strategy for rapid generation of a high number of functional active T cells against Aspergillus from a single blood draw. Our data suggest that functionally active T cells against Aspergillus could be a promising treatment option for patients undergoing allogeneic SCT. (Blood. 2006;107: 2562-2569)

Scedosporium apiospermum: changing clinical spectrum of a therapy-refractory opportunist*

Current knowledge on the opportunist Scedosporium apiospermum (teleomorph: Pseudallescheria boydii), generated over a period of more than 120 years, is reviewed. The natural environmental habitat of the fungus is unknown; nutrient-rich, brackish waters like river estuaria have been suggested. The fungus is strongly promoted by agricultural and particularly by industrial pollution.

Effects of interleukin-15 on antifungal responses of human polymorphonuclear leukocytes against Fusarium spp. and Scedosporium spp

Fusarium spp. and Scedosporium spp. have emerged as important fungal pathogens that are frequently resistant to antifungal compounds. We investigated the effects of human interleukin-15 (IL-15) on human polymorphonuclear leukocyte (PMNL) activity against Fusarium solani and Fusarium oxysporum as well as Scedosporium prolificans and Scedosporium apiospermum. IL-15 (100 ng/ml) significantly enhanced PMNL-induced hyphal damage of both Fusarium spp. and S. prolificans after incubation for 22 h (P < 0.01) but not S. apiospermum. In addition, IL-15 enhanced PMNL oxidative respiratory burst evaluated as superoxide anion production in response to S. prolificans but not to the other fungi after 2 h incubation. IL-15 increased interleukin-8 (IL-8) release from PMNLs challenged with hyphae of F. solani and S. prolificans (P< or = 0.04). Release of tumor necrosis factor-alpha was not affected. The species-dependent enhancement of hyphal damage and induction of IL-8 release suggest that IL-15 plays an important role in the immunomodulation of host response to these emerging fungal pathogens.

TLRs govern neutrophil activity in aspergillosis

Polymorphonuclear neutrophils (PMNs) are essential in initiation and execution of the acute inflammatory response and subsequent resolution of fungal infection. PMNs, however, may act as double-edged swords, as the excessive release of oxidants and proteases may be responsible for injury to organs and fungal sepsis. To identify regulatory mechanisms that may balance PMN-dependent protection and immunopathology in fungal infections, the involvement of different TLR-activation pathways was evaluated on human PMNs exposed to the fungus Aspergillus fumigatus. Recognition of Aspergillus and activation of PMNs occurred through the involvement of distinct members of the TLR family, each likely activating specialized antifungal effector functions. By affecting the balance between fungicidal oxidative and nonoxidative mechanisms, pro- and anti-inflammatory cytokine production, and apoptosis vs necrosis, the different TLRs ultimately impacted on the quality of microbicidal activity and inflammatory pathology. Signaling through TLR2 promoted the fungicidal activity of PMNs through oxidative pathways involving extracellular release of gelatinases and proinflammatory cytokines while TLR4 favored the oxidative pathways through the participation of azurophil, myeloperoxidase-positive, granules and IL-10. This translated in vivo in the occurrence of different patterns of fungal clearance and inflammatory pathology. Both pathways were variably affected by signaling through TLR3, TLR5, TLR6, TLR7, TLR8, and TLR9. The ability of selected individual TLRs to restore antifungal functions in defective PMNs suggests that the coordinated outputs of activation of multiple TLRs may contribute to PMN function in aspergillosis.

Micafungin enhances neutrophil fungicidal functions against Candida pseudohyphae

We evaluated the effect of the combination of micafungin and polymorphonuclear leukocytes (PMN) against hyphae of Candida albicans and Candida dubliniensis. Micafungin enhanced the PMN oxidative burst dose dependently. The combination was synergistic (C. albicans) or additive (C. dubliniensis); when PMN were pretreated with granulocyte-macrophage colony-stimulating factor, the combination was more effective.