Candida Albicans Infection In Mice Research Articles

Effect of Cinnamaldehyde on Systemic Candida albicans Infection in Mice.

To investigate the therapeutic efficacy of cinnamaldehyde (CA) on systemic Candida albicans infection in mice and to provide supportive data for the development of novel antifungal drugs. Ninety BALB/c mice were randomly divided into 3 groups according to a random number table: CA treatment group, fluconazole (positive control) group, and Tween saline (negative control) group, with 30 mice in each group. Initially, all groups of mice received consecutive intraperitoneal injections of cyclophosphamide at 200 mg/kg for 2 days, followed by intraperitoneal injection of 0.25 mL C. albicans fungal suspension (concentration of 1.0 × 107 CFU/mL) on the 4th day, to establish an immunosuppressed systemic Candida albicans infection animal model. Subsequently, the mice were orally administered CA, fluconazole and Tween saline, at 240, 240 mg/kg and 0.25 mL/kg respectively for 14 days. After a 48-h discontinuation of treatment, the liver, small intestine, and kidney tissues of mice were collected for fungal direct microscopic examination, culture, and histopathological examination. Additionally, renal tissues from each group of mice were collected for (1,3)- β -D-glucan detection. The survival status of mice in all groups was monitored for 14 days of drug administration. The CA group exhibited a fungal clearance rate of C. albicans above 86.7% (26/30), significantly higher than the fluconazole group (60.0%, 18/30, P<0.01) and the Tween saline group (30.0%, 9/30, P<0.01). Furthermore, histopathological examination in the CA group revealed the disappearance of inflammatory cells and near-normal restoration of tissue structure. The (1,3)-β-D-glucan detection value in the CA group (860.55 ± 126.73 pg/mL) was significantly lower than that in the fluconazole group (1985.13 ± 203.56 pg/mL, P<0.01) and the Tween saline group (5910.20 ± 320.56 pg/mL, P<0.01). The mouse survival rate reached 90.0% (27/30), higher than the fluconazole group (60.0%, 18/30) and the Tween saline group (30.0%, 9/30), with a significant difference between the two groups (both P<0.01). CA treatment exhibited significant therapeutic efficacy in mice with systemic C. albicans infection. Therefore, CA holds potential as a novel antifungal agent for targeted treatment of C. albicans infection.

Tryptophan metabolites relieve intestinal Candida albicans infection by altering the gut microbiota to reduce IL-22 release from group 3 innate lymphoid cells of the colon lamina propria.

Invasive candidiasis may be caused by Candida albicans (C. albicans) colonization of the intestinal tract. Preventing intestinal damage caused by Candida albicans infection and protecting intestinal barrier function have become a critical issue. Integrated analyses of the microbiome with metabolome revealed a remarkable shift of the gut microbiota and tryptophan metabolites, kynurenic acid (KynA), and indolacrylic acid (IA) in mice infected with C. albicans. The transcriptome sequencing indicated that differentially expressed genes were significantly associated with innate immune responses and inflammatory responses. The results of this study suggest that KynA and IA (KI) can alleviate intestinal damage caused by Candida albicans infection in mice by reducing intestinal permeability, increasing intestinal firmness, alleviating intestinal inflammation, and reducing the secretion of interleukin-22 (IL-22) in the 3 groups of colon innate lymphoid cells (ILC3). We performed a fecal microbiota transplantation (FMT) experiment and found that the intestinal barrier function, inflammation, and IL-22 secretion of ILC3 in the colon lamina propria of the recipient mice subjected to C. albicans infection and KI treatment were consistent with the trends of the donor mice. Our results suggest that tryptophan metabolites may directly regulate colon lamina ILC3 to promote intestinal resistance to C. albicans invasion, or indirectly regulate the ILC3 secretion of IL-22 to play a protective role in the intestinal barrier by affecting intestinal microorganisms, which may become a potential target for alleviating intestine borne C. albicans infection.

A Mouse Model of Candidiasis.

The intravenous challenge model of Candida albicans infection in mice is a well-established procedure that mirrors disseminated candidiasis in humans. In this model, in which the fungus is delivered into the bloodstream causing a systemic infection, the kidneys are the primary target organs. Mice develop renal failure and septic shock that recapitulates the progressive sepsis seen in humans during severe clinical cases. This model is used to study inflammation and the host immune response against fungal infection. This chapter describes the intravenous candidiasis infection protocol, detailing different steps from the preparation of the inoculum, injection of Candida, monitoring of animals, collection of tissue from infected mice, sample preparation and analysis of several parameters related to infection and the inflammatory response.

Effect of testosterone and estrogen supplementation on the resistance to systemic Candida albicans infection in mice

Candida species are the 4th leading cause of nosocomial infections in the US affecting both men and women. Since males of many species can be more susceptible to infections than females, we investigated whether male mice were more susceptible to systemic Candida albicans (C. albicans) infection and if sex hormones were responsible for sex-dependent susceptibility to this infection. Non-gonadectomized or gonadectomized mice were supplemented with sustained release 5α-dihydrotestosterone (5αDHT) or 17-β-estradiol (E2) using subcutaneous pellet implantation. Mice were challenged intravenously with 5 × 105C. albicans/mouse seven days after pellet implantation and monitored for survival and weight change. We observed that male mice were more susceptible to systemic C. albicans infection than female mice while gonadectomized male mice were as resistant to the C. albicans infection as female mice. 5αDHT supplementation of gonadectomized female or male mice increased their susceptibility to the yeast infection while E2 supplementation of gonadectomized male mice did not increase their resistance to the infection. Overall, our results strongly suggest that testosterone plays an important role in decreasing resistance to systemic C. albicans infection.

Endothelial nitric oxide synthase limits host immunity to control disseminated Candida albicans infections in mice.

Three isoforms of nitric oxide synthase (NOS) occur in mammals. High levels of NO produced by NOS2/iNOS can protect against bacterial and parasitic infections, but the role of NOS in fungal innate immunity is less clear. Compared to wild type mice, Nos3-/- mice showed significantly higher survival of candidemia caused by Candida albicans SC5314. NOS3/eNOS is expressed by endothelial cells in the kidney, and colonization of this organ was decreased during the sub-acute stage of disseminated candidiasis. Nos3-/- mice more rapidly eliminated Candida from the renal cortex and exhibited more balanced local inflammatory reactions, with similar macrophage but less neutrophil infiltration than in infected wild type. Levels of the serum cytokines IL-9, IL-12, IL-17 and chemokines GM-CSF, MIP1α, and MIP1β were significantly elevated, and IL-15 was significantly lower in infected Nos3-/- mice. Spleens of infected Nos3-/- mice had significantly more Th2 and Th9 but not other CD4+ T cells compared with wild type. Inflammatory genes associated with leukocyte chemotaxis, IL-1 signaling, TLR signaling and Th1 and Th2 cell differentiation pathways were significantly overexpressed in infected Nos3-/- kidneys, with Nos2 being the most strongly induced. Conversely, the general NOS inhibitor NG-nitro-L-arginine methyl ester increased virulence in the mouse candidemia model, suggesting that iNOS contributes to the protective mechanism in infected Nos3-/- mice. By moderating neutrophil infiltration, the absence of eNOS may reduce the collateral damage to kidney cortex, and Th-9 CD4+ cells may enhance clearance of the infection. These data suggest that selective eNOS inhibition could mitigate candidemia by a combination of systemic and local responses that promote a more effective host immune response.

Glutathione Reductase Promotes Fungal Clearance and Suppresses Inflammation during Systemic Candida albicans Infection in Mice.

Glutathione reductase (Gsr) catalyzes the reduction of glutathione disulfide to glutathione, which plays an important role in redox regulation. We have previously shown that Gsr facilitates neutrophil bactericidal activities and is pivotal for host defense against bacterial pathogens. However, it is unclear whether Gsr is required for immune defense against fungal pathogens. It is also unclear whether Gsr plays a role in immunological functions outside of neutrophils during immune defense. In this study, we report that Gsr-/- mice exhibited markedly increased susceptibility to Candida albicans challenge. Upon C. albicans infection, Gsr-/- mice exhibited dramatically increased fungal burden in the kidneys, cytokine and chemokine storm, striking neutrophil infiltration, histological abnormalities in both the kidneys and heart, and substantially elevated mortality. Large fungal foci surrounded by massive numbers of neutrophils were detected outside of the glomeruli in the kidneys of Gsr -/- mice but were not found in wild-type mice. Examination of the neutrophils and macrophages of Gsr-/- mice revealed several defects. Gsr -/- neutrophils exhibited compromised phagocytosis, attenuated respiratory burst, and impaired fungicidal activity in vitro. Moreover, upon C. albicans stimulation, Gsr -/- macrophages produced increased levels of inflammatory cytokines and exhibited elevated p38 and JNK activities, at least in part, because of lower MAPK phosphatase (Mkp)-1 activity and greater Syk activity. Thus, Gsr-mediated redox regulation is crucial for fungal clearance by neutrophils and the proper control of the inflammatory response by macrophages during host defense against fungal challenge.

Protein kinase C-delta (PKC\u03b4), a marker of inflammation and tuberculosis disease progression in humans, is important for optimal macrophage killing effector functions and survival in mice

We previously demonstrated that protein kinase C-δ (PKCδ) is critical for immunity against Listeria monocytogenes, Leishmania major, and Candida albicans infection in mice. However, the functional relevance of PKCδ during Mycobacterium tuberculosis (Mtb) infection is unknown. PKCδ was significantly upregulated in whole blood of patients with active tuberculosis (TB) disease. Lung proteomics further revealed that PKCδ was highly abundant in the necrotic and cavitory regions of TB granulomas in multidrug-resistant human participants. In murine Mtb infection studies, PKCδ−/− mice were highly susceptible to tuberculosis with increased mortality, weight loss, exacerbated lung pathology, uncontrolled proinflammatory cytokine responses, and increased mycobacterial burdens. Moreover, these mice displayed a significant reduction in alveolar macrophages, dendritic cells, and decreased accumulation of lipid bodies (lungs and macrophages) and serum fatty acids. Furthermore, a peptide inhibitor of PKCδ in wild-type mice mirrored lung inflammation identical to infected PKCδ−/− mice. Mechanistically, increased bacterial growth in macrophages from PKCδ−/− mice was associated with a decline in killing effector functions independent of phagosome maturation and autophagy. Taken together, these data suggest that PKCδ is a marker of inflammation during active TB disease in humans and required for optimal macrophage killing effector functions and host protection during Mtb infection in mice.

Inhibiting the immunoproteasome exacerbates the pathogenesis of systemic Candida albicans infection in mice.

Apart from its role in MHC class I antigen processing, the immunoproteasome has recently been implicated in the modulation of T helper cell differentiation under polarizing conditions in vitro and in the pathogenesis of autoimmune diseases in vivo. In this study, we investigated the influence of LMP7 on T helper cell differentiation in response to the fungus Candida albicans. We observed a strong effect of ONX 0914, an LMP7-selective inhibitor of the immunoproteasome, on IFN-γ and IL-17A production by murine splenocytes and human peripheral blood mononuclear cells (PBMCs) stimulated with C. albicans in vitro. Using a murine model of systemic candidiasis, we could confirm reduced generation of IFN-γ- and IL-17A-producing cells in ONX 0914 treated mice in vivo. Interestingly, ONX 0914 treatment resulted in increased susceptibility to systemic candidiasis, which manifested at very early stages of infection. Mice treated with ONX 0914 showed markedly increased kidney and brain fungal burden which resulted in enhanced neutrophil recruitment and immunopathology. Together, these results strongly suggest a role of the immunoproteasome in promoting proinflammatory T helper cells in response to C. albicans but also in affecting the innate antifungal immunity in a T helper cell-independent manner.

6-O-Branched Oligo-β-glucan-Based Antifungal Glycoconjugate Vaccines.

With the rapid growth in fungal infections and drug-resistant fungal strains, antifungal vaccines have become an especially attractive strategy to tackle this important health problem. β-Glucans, a class of extracellular carbohydrate antigens abundantly and consistently expressed on fungal cell surfaces, are intriguing epitopes for antifungal vaccine development. β-Glucans have a conserved β-1,3-glucan backbone with sporadic β-1,3- or β-1,6-linked short glucans as branches at the 6-O-positions, and the branches may play a critical role in their immunologic functions. To study the immunologic properties of branched β-glucans and develop β-glucan-based antifungal vaccines, three branched β-glucan oligosaccharides with 6-O-linked β-1,6-tetraglucose, β-1,3-diglucose, and β-1,3-tetraglucose branches on a β-1,3-nonaglucan backbone, which mimic the structural epitopes of natural β-glucans, were synthesized and coupled with keyhole limpet hemocyanin (KLH) to form novel synthetic conjugate vaccines. These glycoconjugates were proved to elicit strong IgG antibody responses in mice. It was also discovered that the number, size, and structure of branches linked to the β-glucan backbone had a significant impact on the immunologic property. Moreover, antibodies induced by the synthetic oligosaccharide-KLH conjugates were able to recognize and bind to natural β-glucans and fungal cells. Most importantly, these conjugates elicited effective protection against systemic Candida albicans infection in mice. Thus, branched oligo-β-glucans were identified as functional epitopes for antifungal vaccine design and the corresponding protein conjugates as promising antifungal vaccine candidates.

Syk signaling in dendritic cells orchestrates innate resistance to systemic fungal infection.

Host protection from fungal infection is thought to ensue in part from the activity of Syk-coupled C-type lectin receptors and MyD88-coupled toll-like receptors in myeloid cells, including neutrophils, macrophages and dendritic cells (DCs). Given the multitude of cell types and receptors involved, elimination of a single pathway for fungal recognition in a cell type such as DCs, primarily known for their ability to prime T cell responses, would be expected to have little effect on innate resistance to fungal infection. Here we report that this is surprisingly not the case and that selective loss of Syk but not MyD88 in DCs abrogates innate resistance to acute systemic Candida albicans infection in mice. We show that Syk expression by DCs is necessary for IL-23p19 production in response to C. albicans, which is essential to transiently induce GM-CSF secretion by NK cells that are recruited to the site of fungal replication. NK cell-derived-GM-CSF in turn sustains the anti-microbial activity of neutrophils, the main fungicidal effectors. Thus, the activity of a single kinase in a single myeloid cell type orchestrates a complex series of molecular and cellular events that underlies innate resistance to fungal sepsis.

Evaluation of an extract of North American ginseng (Panax quinquefolius L.) in Candida albicans-infected complement-deficient mice

Ethnopharmacological relevanceGinseng is a widely consumed aromatic herb that is purported to have health benefits. Several studies report a beneficial impact of ginseng or its derivatives on Candida albicans infection in mice and suggest that its immune-modulatory properties contribute to this effect. However, these studies generally administered ginseng to experimental animals by injection, whereas people typically ingest ginseng. Furthermore, although disseminated candiasis is typically a disease of immune-impaired hosts, previous studies have generally used immune competent host species in the assessments. Materials and methodsWe evaluated the efficacy of an ingested extract of ginseng against Candida albicans infection in DBA/2J mice, which are highly susceptible to Candida albicans infection. A ginseng extract was added to the drinking water for two days before and for the remainder of the study after intravenous inoculation of mice with Candida albicans. Mice were evaluated for morbidity, mortality, Candida albicans titers, and concentrations of inflammatory cytokines and chemokines. ResultsIngestion of the ginseng extract did not significantly affect overall morbidity or mortality. However, ingestion of the extract was associated with significantly lower renal titers of Candida albicans and with significantly lower concentrations of some inflammatory cytokines in kidney and/or serum. ConclusionsAssessment of morbidity, mortality, inflammatory markers, and renal titers after spontaneous ingestion of ginseng by susceptible hosts represents a comprehensive approach to characterizations of therapeutic efficacy against infectious agents. Our findings extend previous reports of the efficacy of ginseng against Candida albicans by demonstrating significant reductions in infectious load and some markers of inflammation in susceptible mice. Our data therefore support further assessment of the immune-modulatory properties of this widely consumed herb and its components.

Blue Dye and Red Light, a Dynamic Combination for Prophylaxis and Treatment of Cutaneous Candida albicans Infections in Mice

The objective of this study was to investigate photodynamic therapy (PDT), using blue dye and red light, for prophylaxis and treatment of cutaneous Candida albicans infections in mice. A mouse model of skin abrasion infected with C. albicans was developed by inoculating wounds measuring 1.2 cm by 1.2 cm with 10(6) or 10(7) CFU. The use of a luciferase-expressing strain of C. albicans allowed real-time monitoring of the extent of infection in mice noninvasively through bioluminescence imaging. The phenothiazinium salts toluidine blue O (TBO), methylene blue (MB), and new methylene blue (NMB) were compared as photosensitizers (PS) for the photodynamic inactivation of C. albicans in vitro. PDT in vivo was initiated either at 30 min or at 24 h after fungal inoculation to investigate the efficacies of PDT for both prophylaxis and treatment of infections. Light at 635 ± 15 nm or 660 ± 15 nm was delivered with a light dose of 78 J/cm(2) (for PDT at 30 min postinfection) or 120 J/cm(2) (for PDT at 24 h postinfection) in multiple exposures with bioluminescence imaging taking place after each exposure of light. In vitro studies showed that NMB was superior to TBO and MB as the PS in the photodynamic inactivation of C. albicans. The efficacy of PDT was related to the ratio of PS concentration to fungal cell density. PDT in vivo initiated either at 30 min or at 24 h postinfection significantly reduced C. albicans burden in the infected mouse skin abrasion wounds. These data suggest that PDT is a viable approach for prophylaxis and treatment of cutaneous C. albicans infections.

Immunisation with the glycolytic enzyme enolase confers effective protection against Candida albicans infection in mice

Candida albicans is an opportunistic human fungal pathogen that continues to be a leading cause of candidal infections in immunocompromised hosts. Enolase, an important glycolytic enzyme located on the cell wall of C. albicans, was cloned, purified, and characterized by molecular cloning, affinity chromatography and Western blotting. C57BL/6J mice were immunized with recombinant enolase subcutaneously every two weeks, and the protective effect against systemic challenge evaluated by fungal burdens in target organs, titres of specific antibodies to enolase, and by levels of Th1/2 cytokines in serum. After challenge with C. albicans strains SC5314 and 3630, fungal burdens in the liver, kidney, brain, spleen and lung were significantly decreased in immunized mice. Histopathological assessment demonstrated that enolase protected the tissue structure, and decreased the infiltration of inflammatory cells. The titres of enolase-specific IgG1 and IgG2a in the immune serum reached up to 1:51200. Furthermore, opsonization with immune serum resulted in enhanced killing of both 3630 and SC5314 by murine neutrophils. Levels of IL-12 and IL-8 in the immune serum increased, whereas the concentration of the Th2 cytokine, IL-10, was significantly higher in immunized mice compared to the control group. It was concluded that recombinant enolase effectively protected mice against disseminated candidiasis, and may be a promising target for vaccination against different strains of C. albicans.

CD4+CD25+Foxp3+ Regulatory T Cells Promote Th17 Cells In Vitro and Enhance Host Resistance in Mouse Candida albicans Th17 Cell Infection Model

Th17 cells and CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells are thought to promote and suppress inflammatory responses, respectively. Here we explore why under Th17 cell polarizing conditions, Treg cells did not suppress, but rather upregulated, the expression of interleukin-17A (IL-17A), IL-17F, and IL-22 from responding CD4(+) Tcells (Tresp cells). Upregulation of IL-17 cytokines in Tresp cells was dependent onconsumption of IL-2 by Treg cells, especially at early time points both invitro and invivo. During an oral Candida albicans infection in mice, Treg cells induced IL-17 cytokines in Tresp cells, which markedly enhanced fungal clearance and recovery from infection. These findings show how Treg cells can promote acute Th17 cell responses to suppress mucosal fungus infections and reveal that Treg cellshave a powerful capability to fight infections besides their role in maintaining tolerance or immune homeostasis.

Dual roles of CD4+CD25+Foxp3+ Tregs in regulating Th17 cells and promoting host resistance to Candida albicans (137.7)

Abstract Th17 cells and CD4+CD25+Foxp3+ regulatory T cells (Tregs) are thought to promote and suppress inflammatory responses, respectively. However, their direct interaction in the context of an inflammation is unclear. Here we show that under Th17 conditions, Tregs suppress late but not early Th17 responses. Moreover, Tregs boost IL-17A, IL-17F and IL-22 in Th17 cells at early time-points. Transient up-regulation of Th17 cytokines by Tregs plays a protective role in clearing Candida albicans infection in mice. However, Tregs regain their suppressive functions over time and suppress Th17 cell mediated inflammation in Candida infected mice. Thus, Tregs play dual roles by initially promoting protective Th17 cells, but subsequently reducing the pathology of Th17 driven inflammation.

Therapeutic effect of cinnamon oil on gastric candida albicans infection in mice

Therapeutic effect of cinnamon oil on gastric candida albicans infection in mice

Host-Pathogen Interactions and the Pathological Consequences of Acute Systemic Candida albicans Infections in Mice

Candida albicans is a commensal organism that lives as benign member of the microflora of healthy individuals. In response to changes in the host immune status or microflora, C. albicans ceases to be a commensal organism and infects a variety of host tissues. The capacity to shift from a commensal to pathogenic state requires a coordinated metabolic response that triggers discrete developmental programs and that induce the expression of specific virulence traits. Several virulence traits have been described in C. albicans including adhesion, morphological and phenotypic switching, and the production of secreted hydrolytic enzymes. These attributes contribute to host tissue recognition, tissue invasion and colonization, as well as evasion of the host immune response. Recent experimental progress has illuminated some of the cellular processes that enable Candida cells to sense and respond to changes in the host environment. Similarly, cells of the host innate immune system are able to recognize invading C. albicans cells and induce a complex immune response that ultimately determines the clinical outcome of the infection. In this review we describe the current understanding of the events taking place during systemic infections of C. albicans. The interplay between defined pathogen and host specific responses are discussed. Additionally, we provide experimental data on the pathological consequences resulting from acute systemic infections of C. albicans in mice.

Host resistance to Candida albicans infection of mice with collagen-induced arthritis treated with leflunomide

The dehydro-orotate dehydrogenase inhibitor leflunomide is used for the treatment of rheumatoid arthritis. In the present study, its influence on host resistance to Candida albicans infection in mice with collagen-induced arthritis (CIA) was investigated. Leflunomide administered at a dose of 5 mg/kg for 5 consecutive days in mice with CIA inhibited collagen-specific cellular and humoral responses. The drug did not change the severity of primary C. albicans infection evaluated by kidney and liver colonization. At the early stage of infection leflunomide inhibited IFN-γ production and enhanced IL-4 secretion. The effect of the drug on IL-4 production was less pronounced at the late phase of infection. Leflunomide enhanced anti- Candida IgM antibody production and diminished anti- Candida IgG antibody synthesis. This correlated with impaired resistance to reinfection. Results demonstrate that leflunomide administration to mice with collagen-induced arthritis might affect mechanisms of the late immune response to C. albicans infection.

Detection of Fungal Infections Using Radiolabeled Antifungal Agents

The outcome of antifungal therapy depends on the progression of the infection at the start of therapy. Unfortunately, most patients are diagnosed once the fungal infection has progressed considerably as a result of the non-specific clinical signs of fungal infections in immunocompromised patients and the poor sensitivity of current mycological diagnostic tests. This review will highlight current fungal diagnostic techniques and will focus on scintigraphic methods for the specific detection of fungal infections in mice. For this purpose, antifungal components (e.g. fluconazole and antifungal peptides) are radiolabeled e.g. with technetium-99m ((99m)Tc) and their in vivo distribution is monitored in infected mice. It has been demonstrated that (99m)Tc-fluconazole is an excellent tracer to detect Candida albicans infections in mice as it distinguishes these infections from bacterial infections and sterile inflammations. However, this radiopharmaceutical only poorly detects infections with Aspergillus fumigatus in mice. (99m)Tc-peptides derived from antifungal peptides/proteins, such as human ubiquicidin and lactoferrin, can distinguish C. albicans and A. fumigatus infections from sterile inflammations, but not from bacterial infections, in mice. Furthermore, the efficacy of fluconazole in C. albicans-infected mice could be successfully monitored using (99m)Tc-ubiquicidin. In conclusion, neither (99m)Tc-fluconazole nor the (99m)Tc-peptides tested are optimal tracers for fungal infections. Nonetheless, since early initiation of antifungal therapy for candidemia reduces its high mortality rate, a positive result with (99m)Tc-fluconazole scintigraphy is of clinical relevance. Finally, the possibility that other (radiolabeled) antifungal agents, e.g. voriconazole, caspofungin, antifungal plant or insect defensins, can be useful for detection of fungal infections should be considered.

Protective effects of a protein-bound polysaccharide, PSK, on Candida albicans infection in mice via tumor necrosis factor-α induction

We investigated the protective mechanism of a protein-bound polysaccharide, PSK, against lethal infection with Candida albicans ( C. albicans) in mice. (1) In BALB/c mice inoculated intravenously with C. albicans, the intraperitoneal (ip) administration of PSK increased survival rates and prolonged the survival period depending on the time of administration, the dosage, and the size of fungal inoculum; the maximal effect was obtained when PSK 250 mg/kg was ip administered to mice 24 h before inoculation of 1×10 6 C. albicans (30 days survivors showed 60% and the mean survival period of mice with fatal infection increased 209%). (2) The protective effect of PSK was significantly decreased in mice treated with cyclophosphamide or carrageenan, or in mice treated previously with anti-tumor necrosis factor-α (TNF-α) antibody. (3) The administration of PSK significantly enhanced the expression of TNF-α gene in spleen and increased leukocyte functions from 6 h to 1 day after inoculation. (4) When the PSK fraction subjected to hydrolysis with β1–3 glucanase or hydrazine was used instead of PSK, the anti-fungal activities were significantly decreased. These findings suggested that the protective effect of PSK on lethal C. albicans infection in mice was mainly produced via TNF-α functions, and that β1–3 glucan and protein moiety in PSK molecule were involved in the expression of the activities.