DNA array analysis of altered gene expression in human leukocytes stimulated with soluble and particulate forms of Candida cell wall β-glucan

Multi-step pathogenesis and induction of local immune response by systemic Candida albicans infection in an intravenous challenge mouse model

Different murine species differ in their susceptibility to systemic infection with Candida albicans, giving rise to varied host immune responses, and this is compounded by variations in virulence of the different yeast strains used. Hence, this study was aimed at elucidating the pathogenesis of a clinical C. albicans isolate (HVS6360) in a murine intravenous challenge model by examining the different parameters which included the counts of red blood cells and associated components as well as the organ-specific expression profiles of cytokines and chemokines. Kidneys and brains of infected mice have higher fungal recovery rates as compared to other organs and there were extensive yeast infiltration with moderate to severe inflammation seen in kidney and brain tissues. Red blood cells (RBCs) and haemoglobin (Hb) counts were reduced throughout the infection period. Pattern recognition receptors (PRRs), chemokines and cytokine transcription profiles were varied among the different organs (kidney, spleen and brain) over 72 h post infections. Transcription of most of the PRRs, cytokines and chemokines were suppressed at 72 h post infection in spleen while continuous expression of PRRs, cytokines and chemokines genes were seen in brain and kidney. Reduction in red blood cells and haemoglobin counts might be associated with the action of extracellular haemolysin enzyme and haeme oxygenase of C. albicans in conjunction with iron scavenging for the fungal growth. Renal cells responsible for erythropoietin production may be injured by the infection and hence the combined effect of haemolysis plus lack of erythropoietin-induced RBC replenishment leads to aggravated reduction in RBC numbers. The varied local host immune profiles among target organs during systemic C. albicans infection could be of importance for future work in designing targeted immunotherapy through immunomodulatory approaches.

β-Glucan Derived from Zymosan Acts as an Adjuvant for Collagen-Induced Arthritis

Collagen-induced arthritis (CIA) is an experimental model of rheumatoid arthritis (RA) and has helped researchers to analyze the pathogenesis of inflammatory joint disease. In classical CIA, Freund's complete adjuvant (FCA), which contains heat-killed Mycobacterium tuberculosis, is used as an adjuvant. In our previous study, we reported that particles of beta-glucan, OX-CA, derived from Candida albicans, acted as a proper adjuvant in the CIA model. In this study, to establish pure beta-glucan as an adjuvant for CIA, we tested a commercially available preparation of Zymosan A (ZYM) and modified its products. beta-Glucan fractions of ZYM were prepared by oxidation with various concentrations of NaClO. The oxidized ZYM (OX-ZYM) was mainly composed of beta-glucan. In this study, we examined its effect as an adjuvant for CIA. DBA/1 mice injected with CII and OX-CA developed arthritis 7-10 days after receiving booster injections; the OX-ZYM fractions induced arthritis with the same time course. 0.01% OX-ZYM (oxidized with a 0.01% NaClO solution) caused arthritis faster than 0.1% OX-ZYM or 0.5% OX-ZYM. In conclusion, beta-glucan derived from ZYM by brief oxidation with NaClO is a suitable adjuvant for a CIA model with anti-CII antibody production.

Massive induction of innate immune response to Candida albicans in the kidney in a murine intravenous challenge model

In the experimental Candida albicans intravenous challenge model, the kidney is one of the main organs involved in disease. In progressive infection, fungal burdens are found to increase over time, with rapid increases occurring from 24 h postinfection. Renal transcriptional responses were analyzed at this time in the kidneys of mice infected by either a virulent or an attenuated C. albicans strain, allowing comparison of host responses in progressive and nonprogressive infection. The results of this study demonstrate that both infections share a common transcriptional response, consisting of functions associated with the acute-phase reaction. In addition, challenge with the virulent strain led to a massively increased expression of cytokine genes, other innate response genes and genes suggestive of initiation of the adaptive immune response. This immune response to C. albicans infection, which occurs only in progressive infection, may contribute to development of sepsis and, ultimately, host death.

Toll-like receptor 9-dependent activation of myeloid dendritic cells by Deoxynucleic acids from Candida albicans

The innate immune system of humans recognizes the human pathogenic fungus Candida albicans via sugar polymers present in the cell wall, such as mannan and beta-glucan. Here, we examined whether nucleic acids from C. albicans activate dendritic cells. C. albicans DNA induced interleukin-12p40 (IL-12p40) production and CD40 expression by murine bone marrow-derived myeloid dendritic cells (BM-DCs) in a dose-dependent manner. BM-DCs that lacked Toll-like receptor 4 (TLR4), TLR2, and dectin-1, which are pattern recognition receptors for fungal cell wall components, produced IL-12p40 at levels comparable to the levels produced by BM-DCs from wild-type mice, and DNA from a C. albicans pmr1Delta null mutant, which has a gross defect in mannosylation, retained the ability to activate BM-DCs. This stimulatory effect disappeared completely after DNase treatment. In contrast, RNase treatment increased production of the cytokine. A similar reduction in cytokine production was observed when BM-DCs from TLR9(-/-) and MyD88(-/-) mice were used. In a luciferase reporter assay, NF-kappaB activation was detected in TLR9-expressing HEK293T cells stimulated with C. albicans DNA. Confocal microscopic analysis showed similar localization of C. albicans DNA and CpG-oligodeoxynucleotide (CpG-ODN) in BM-DCs. Treatment of C. albicans DNA with methylase did not affect its ability to induce IL-12p40 synthesis, whereas the same treatment completely eliminated the ability of CpG-ODN to induce IL-12p40 synthesis. Finally, impaired clearance of this fungal pathogen was not found in the kidneys of TLR9(-/-) mice. These results suggested that C. albicans DNA activated BM-DCs through a TLR9-mediated signaling pathway using a mechanism independent of the unmethylated CpG motif.

Dectin-1 is not required for the host defense to Cryptococcus neoformans

Dectin-1 is known as a sole receptor for beta-glucan, a major cell wall component of fungal microorganisms. In the current study, we examined the role of this molecule in the host defense to Cryptococcus neoformans, an opportunistic fungal pathogen in AIDS patients. There was no significant difference in the clinical course and cytokine production between dectin-1 gene-deficient and control mice. These results indicate that dectin-1 is not likely essential for the development of host protective responses to C. neoformans.

Deoxynucleic acids from Cryptococcus neoformans activate myeloid dendritic cells via a TLR9-dependent pathway

The mechanism of host cell recognition of Cryptococcus neoformans, an opportunistic fungal pathogen in immunocompromised patients, remains poorly understood. In the present study, we asked whether the DNA of this yeast activates mouse bone marrow-derived myeloid dendritic cells (BM-DCs). BM-DCs released IL-12p40 and expressed CD40 upon stimulation with cryptococcal DNA, and the response was abolished by treatment with DNase, but not with RNase. IL-12p40 production and CD40 expression were attenuated by chloroquine, bafilomycin A, and inhibitory oligodeoxynucleotides (ODN) that suppressed the responses caused by CpG-ODN. Activation of BM-DCs by cryptococcal DNA was almost completely abrogated in TLR9 gene-disrupted (TLR9(-/-)) mice and MyD88(-/-) mice, similar to that by CpG-ODN. In addition, upon stimulation with whole yeast cells of acapsular C. neoformans, TLR9(-/-) BM-DCs produced a lower amount of IL-12p40 than those from wild-type mice, and TLR9(-/-) mice were more susceptible to pulmonary infection with this fungal pathogen than wild-type mice, as shown by increased number of live colonies in lungs. Treatment of cryptococcal DNA with methylase resulted in reduced IL-12p40 synthesis by BM-DCs. Furthermore, using a luciferase reporter assay, cryptococcal DNA activated NF-kappaB in HEK293 cells transfected with the TLR9 gene. Finally, confocal microscopy showed colocalization of fluorescence-labeled cryptococcal DNA with CpG-ODN and the findings merged in part with the distribution of TLR9 in BM-DCs. Our results demonstrate that cryptococcal DNA causes activation of BM-DCs in a TLR9-dependent manner and suggest that the CpG motif-containing DNA may contribute to the development of inflammatory responses after infection with C. neoformans.

Contribution of dectin-1 and granulocyte macrophage-colony stimulating factor (GM-CSF) to immunomodulating actions of beta-glucan

beta-Glucans are major cell wall structural components in fungi. As they are not found in animals, these carbohydrates are considered to be classic pathogen-associated molecular patterns (PAMPs), and are recognized by the innate immune system. Although their immunomodulating activities have been shown to be associated with the recognition of some fungi, and with their medicinal properties in the field of cancer immunotherapy, it is still unclear how beta-glucans mediate their effects. Recent studies have started to shed some light on their cellular receptors, such as dectin-1, and their molecular mechanisms of action. We have extensively investigated the response of leukocytes to beta-glucan, focusing on cytokine induction by SCG, which is a major 6-branched 1,3-beta-d-glucan in Sparassis crispa Fr. There is a strain difference in the reactivity of mice to SCG, and DBA/1 and DBA/2 mice are highly sensitive strains. In the process of research on cytokine induction by SCG in DBA/2 mice, we found that GM-CSF plays a key biological role in this activity. Cytokine induction by SCG was completely abolished in dendritic cells from dectin-1 knockout mice. On the other hand, controlling the level of endogenous GM-CSF production and/or dectin-1 expression could regulate the reactivity to beta-glucan. These results indicate that the key factors in the responsiveness to beta-glucan are GM-CSF production and dectin-1 expression. In this review, we describe how the key molecules related to the expression of the immunomodulating activities of beta-glucan were identified, and how the response to beta-glucan is controlled.

Effect of Candida albicans cell wall glucan as adjuvant for induction of autoimmune arthritis in mice

Collagen-induced arthritis (CIA) is an experimental model of rheumatoid arthritis (RA) and has aided research into the pathogenesis of inflammatory joint disease. Typically, Type II collagen (CII) emulsified with Freund's complete adjuvant (FCA) is injected into DBA/1 mice. After a booster injection, the mice develop inflammation of the paws. But the fact that the immunization of CII alone does not induce arthritis suggests that activation of the immune system by an adjuvant is necessary for induction of the arthritis. In the present study, we investigated the ability of beta-glucans derived from Candida albicans to act as an adjuvant to induce autoimmune arthritis. DBA/1 mice were injected with CII emulsified with FCA or particulate beta-glucan, OX-CA, on day 0 and given a booster at day 21. Mice immunized with CII plus OX-CA developed arthritis at around 7-10 days after the booster injection. Similarly, mice administered CII emulsified with FCA developed arthritis with the same time course. The mice immunized with CII and OX-CA had a more severe arthritis than those immunized with CII and FCA. Histological changes and production of anti-CII antibody were observed regardless of the type of injection. In addition, components of C. albicans were also tested for their ability to induce arthritis as an adjuvant. The results showed that CSBG, which is a soluble beta-glucan, acted as an adjuvant for CIA but CAWS, which is a mannoprotein-beta-glucan complex, did not. In conclusion, beta-glucan derived from C. albicans acted as an adjuvant and the injection with CII resulted in arthritis with the production of anti-CII autoantibody. The results strongly suggested that fungal metabolites such as beta-glucans have the capacity to induce and exacerbate autoimmune diseases such as RA.