Inhibition of human endothelial cell chemokine production by the opportunistic fungal pathogen Cryptococcus neoformans

Host Sensing by Pathogenic Fungi

The ability to cause disease extends from the ability to grow within the host environment. The human host provides a dynamic environment to which fungal pathogens must adapt to in order to survive. The ability to grow under a particular condition (i.e., the ability to grow at mammalian body temperature) is considered a fitness attribute and is essential for growth within the human host. On the other hand, some environmental conditions activate signaling mechanisms resulting in the expression of virulence factors, which aid pathogenicity. Therefore, pathogenic fungi have evolved fitness and virulence attributes to enable them to colonize and infect humans. This review highlights how some of the major pathogenic fungi respond and adapt to key environmental signals within the human host.

The impact of the host on fungal infections

Outcomes of fungal infections in immunocompromised individuals depend on a complex interplay between host and pathogen factors, as well as treatment modalities. Problems occur when host responses to an infection are either too weak to effectively help eradicate the pathogen, or when they become too strong and are associated with host damage rather than protection. Immune reconstitution syndrome (IRS) can be generally defined as a restoration of host immunity in a previously immunosuppressed patient that becomes dysregulated and overly robust, resulting in host damage and sometimes death. IRS associated with opportunistic mycoses presents as new or worsening clinical symptoms or radiographic signs consistent with an inflammatory process that occur during receipt of an appropriate antifungal, and that cannot be explained by a newly acquired infection. Because there are currently no established tests or biomarkers for IRS, it can be difficult to distinguish from progression of the original infection, although culture and biomarkers for the fungal pathogen or infection are typically negative during diagnostic workup. IRS was originally characterized in human immunodeficiency virus-infected patients receiving antiretroviral therapy, but has subsequently been described in solid-organ transplant recipients, neutropenic patients, women in the postpartum period, and recipients of tumor necrosis factor-α inhibitor therapy. In each of these cases, recovery of the host's immunity during treatment of an initial infection results in a powerful proinflammatory environment that overshoots and leads to host damage. Optimal management of IRS has not been established at present, but often involves treatment with a corticosteroid or other anti-inflammatory compounds. This article uses a number of patient cases to explore the intricacies of diagnosing and managing a patient with IRS, as well as the other extreme, namely patients who are so immunocompromised without immune recovery that they essentially become breeding grounds for a wide range of opportunistic pathogens, often simultaneously.

Ghrelin inhibits AGEs-induced apoptosis in human endothelial cells involving ERK1/2 and PI3K/Akt pathways

Endothelial dysfunction caused by cell apoptosis is thought to be a major cause of diabetic vascular complications. Advanced glycation end products (AGEs) play an important role in the pathogenesis of diabetic vascular complications by inducing apoptosis of endothelial cells. The aim of this study was to explore the effect of ghrelin on AGEs-induced apoptosis in cultured human umbilical vein endothelial cells (HUVECs) and the potential mechanisms involved in this process. Exposure to AGEs (200 mg l(-1) ) for 48 h caused a significant increase in cell apoptosis, while pretreatment with ghrelin eliminated AGEs-induced apoptosis in HUVECs, as evaluated by MTT assays, flow cytometry and Hoechst 33258 staining. The induction of caspase-3 activation was also prevented by ghrelin in cells incubated with AGEs. Exposure to ghrelin (10(-6)  M) resulted in a rapid activation of extracellular signal-regulated protein kinase (ERK)1/2 and Akt. The inhibitory effect of ghrelin on caspase-3 activity was attenuated by inhibitors of ERK1/2 (PD98059), PI3K/Akt (LY294002) and growth hormone secretagogue receptor (GHSR)-1a (D-Lys(3) -growth hormone releasing peptide-6). The results of this study indicated that ghrelin could inhibit AGEs-mediated cell apoptosis via the ERK1/2 and PI3K/Akt pathways and GHSR-1a was also involved in the protective action of ghrelin in HUVECs. As such, ghrelin demonstrates significant potential for preventing diabetic cardiovascular complications.

Effects of endomorphins on human umbilical vein endothelial cells under high glucose

The endomorphin-1 (EM1) and endomorphin-2 (EM2) are endogenous opioid peptides, which modulate extensive bioactivities such as pain, cardiovascular responses, immunological responses and so on. The present study was undertaken to investigate the effects of EM1/EM2 on the primary cultured human umbilical vein endothelial cells (HUVECs) damaged by high glucose. PI AnnexinV-FITC detection was performed to evaluate the apoptosis rate. Levels of nitric oxide (NO) and nitric oxide synthase (NOS) activity were measured by the Griess reaction and the conversion of 3H-arginine to 3H-citrulline, respectively. Endothelin-1 (ET-1) was evaluated by the enzyme-linked immunosorbent assay (ELISA). Cell proliferation was determined by the MTT viability assay. mRNA expression of endothelial nitric oxide synthase (eNOS) and ET-1 were measured by real-time PCR. Our data showed that EM1/EM2 inhibited cell apoptosis. The high glucose induced increase in expression of NO, NOS and ET-1 were significantly attenuated by pretreatment with EM1/EM2 in a dose dependent manner. In addition, EM1/EM2 suppressed the mRNA eNOS and mRNA ET-1 expression in HUVECs under high glucose conditions. Naloxone, the nonselective opioid receptor antagonist, did not influence the mRNA eNOS expression when it was administrated on its own; but it could significantly antagonize the effects induced by EM1/EM2. Furthermore, in all assay systems, EM1 was more potent than EM2. The results suggest that EM1/EM2 have a beneficial effect in protecting against the endothelial dysfunction by high glucose in vitro, and these effects were mediated by the opioid receptors in HUVECs.

The biocontrol fungus Trichoderma stromaticum downregulates respiratory burst and nitric oxide in phagocytes and IFN-gamma and IL-10

Trichoderma stromaticum, a biocontrol agent of the cacao witches' broom pathogen Moniliophthora perniciosa, has been used in Brazil as part of the integrated pest management of cacao. At the present time, little is known about the effects of T. stromaticum on the modulation of in vitro or in vivo immune responses. The present study examined the interaction of T. stromaticum spores with cellular and molecular components of the immune system following intranasal sensitization of mice. Our results showed that T. stromaticum spores prevented the expression and production of inflammatory mediators in macrophages stimulated with interferon (IFN)-γ plus lipopolysaccharide (LPS) and neutrophils stimulated with phorbol myristate 13-acetate (PMA). Quantitative polymerase chain reaction (qPCR) assays revealed that T. stromaticum spores inhibited the expression of dectin-1 and Toll-like-receptor (TLR)2/TLR4. Intranasal injection of BALB/c mice and subsequent challenge with spores of T. stromaticum induced a discrete inflammatory response in the lungs. Interestingly, the spores inhibited local and systemic production of the regulatory IL-10 and proinflammatory IFN-γ cytokines. In addition the spores presented an antiproliferative effect on spleen cells. These findings showed that the biopesticide T. stromaticum may exert immunosuppressive effects in vitro and in vivo.

Mechanisms of cryptococcal virulence and persistence

Cryptococcus neoformans is an environmental yeast that is a leading cause of fatal mycosis in AIDS patients and a major cause of meningoencephalitis and CNS-related mortality around the globe. Although C. neoformans infection is mostly a manifestation of immune deficiency, up to 25% of cases reported in the USA occur in patients without recognizable immune defects, indicating that C. neoformans can develop mechanisms that allow it to evade immune defenses and persist in noncompromised hosts. This article discusses mechanisms and routes of infection and the most important elements of host response as well as the mechanisms that promote cryptococcal survival within the host. Metabolic adaptation to physiological host conditions and the mechanisms limiting immune recognition, interfering with phagocytosis and extending intracellular survival of C. neoformans are highlighted. We describe the mechanisms by which C. neoformans can alter adaptive host responses, especially cell-mediated immunity, which is required for clearance of this microbe. We also review cryptococcal strategies of survival in the CNS and briefly discuss adaptations developing in response to medical treatment.

HMGB1 activates nuclear factor-κB signaling by RAGE and increases the production of TNF-α in human umbilical vein endothelial cells

OBJECTIVE

High mobility group box chromosomal protein 1 (HMGB1) is a lately discovered candidate molecule identified as an important extracellular mediator in systemic inflammation. Systemic inflammation results in endothelial cell activation and microvascular injury. In the present study, we investigated the effects of HMGB1 on the activation of human umbilical vein endothelial cells (HUVECs) and defined pathways activated by HMGB1.

METHODS

HUVECs obtained by collagenase treatment of umbilical cord veins were stimulated in vitro with HMGB1. The activation of HUVECs was studied regarding (i) the kinetics of tumor necrosis factor-α (TNF-α) production in HUVECs, (ii) HMGB1-induced up-regulation of receptor for advanced glycation end products (RAGE), (iii) HMGB1-induced nuclear translocation of nuclear factor kappa B (NF-κB) in HUVECs, (iv) the activation of signalling transduction pathways.

RESULTS

HUVECs activation was stimulated by HMGB1 partially in a RAGE-dependent manner. Additionally, the HMGB1-induced activation of HUVECs was significantly inhibited by anti-RAGE monoclonal antibody and Ethyl pyruvate (EP) that had been shown to be an effective anti-inflammatory agent. Short-term prestimulation of HUVECs with HMGB1 caused a time-dependent increase in the secretion of TNF-α and expression of RAGE. Furthermore, HMGB1 stimulation resulted in nuclear translocation of transcription factor NF-κB. Most importantly, pretreatment with anti-RAGE monoclonal antibody significantly decreased the amounts of TNF-α and inhibited the nuclear translocation of NF-κB. Additionally in HUVECs cultures, EP specifically inhibited activation of NF-κB signaling pathway that are critical for TNF-α release.

CONCLUSIONS

In conclusion, Our data present a link between HMGB1and RAGE function of endothelial cells and demonstrate the pathway activated by HMGB1. These findings may provide a novel therapeutic strategy to improve the endothelial cells function.

Formosanin C-induced apoptosis requires activation of caspase-2 and change of mitochondrial membrane potential

Formosanin C is a pure compound isolated from Paris formosana Hayata (Liliaceae). The antitumor efficacy of formosanin C has been observed in cultured cells and animal systems. However, the molecular mechanisms of formosanin C remain unknown. The results of the present study indicate that formosanin C induced apoptosis of HT-29 cells characterized by exposure of phosphatidylserine, accumulation of cells at the sub-G(1) phase, fragmentation of DNA, and change of nuclear morphology in a time- and dose-related manner. The apoptotic signaling cascades may proceed via proteolytic activation of caspase-2, change of mitochondrial membrane potential (Deltapsi(m)), release of cytochrome c and second mitochondria-derived activator of caspase/direct IAP binding protein with low pI (Smac/DIABLO), activation of caspase-9 and -3, and cleavage of poly(ADP-ribose) polymerase (PARP). Increase in apoptosis-inducing factor and endonuclease G expressions in nuclei, and increase in Bax and Bak expressions and decrease in Bcl-X(L) expression on mitochondria were also observed in formosanin C-treated HT-29 cells. Attenuation of formosanin C-induced change of Deltapsi(m) by caspase-2 inhibitor (Z-VDVAC) implies that caspase-2 acts upstream of the mitochondria. Blockage of formosanin C-induced apoptotic process by using either permeability transition pore inhibitor (cyclosporine A) or caspase-9 inhibitor (Z-LEHD) demonstrates the necessity of mitochondria and caspase-9 in formosanin C-induced apoptosis of HT-29 cells. Taken together, the apoptotic mechanism of formosanin C in human colorectal cancer HT-29 cells involves activation of caspase-2 and the dysfunction of mitochondria.

Evidence of a role for monocytes in dissemination and brain invasion by Cryptococcus neoformans

The pathogenesis of cryptococcosis, including the events leading to the production of meningoencephalitis, is still largely unknown. Evidence of a transcellular passage of Cryptococcus neoformans across the blood-brain barrier (BBB) and subsequent BBB disruption exists, but the paracellular passage of free yeasts and the role of monocytes in yeast dissemination and brain invasion (Trojan horse method) remain uncertain. We used our model of disseminated cryptococcosis, in which crossing of the BBB starts 6 h after intravenous inoculation, to study paracellular passage of the BBB. We prepared bone marrow-derived monocytes (BMDM) infected in vitro with C. neoformans (BMDM yeasts) and free yeasts and measured fungal loads in tissues. (i) Spleen and lung CFU were >2-fold higher in mice treated with BMDM yeasts than in those treated with free yeasts for 1 and 24 h (P < 0.05), while brain CFU were increased (3.9 times) only at 24 h (P < 0.05). (ii) By comparing the kinetics of brain invasion in naïve mice and in mice with preestablished cryptococcosis, we found that CFU were lower in the latter case, except at 6 h, when CFU from mice inoculated with BMDM yeasts were comparable to those measured in naïve mice and 2.5-fold higher than those in mice with preestablished cryptococcosis who were inoculated with free yeasts. (iii) Late phagocyte depletion obtained by clodronate injection reduced disease severity and lowered the fungal burden by 40% in all organs studied. These results provide evidence for Trojan horse crossing of the BBB by C. neoformans, together with mechanisms involving free yeasts, and overall for a role of phagocytes in fungal dissemination.

Infectomic analysis of gene expression profiles of human brain microvascular endothelial cells infected with Cryptococcus neoformans

In order to dissect the pathogenesis of Cryptococcus neoformans meningoencephalitis, a genomic survey of the changes in gene expression of human brain microvascular endothelial cells infected by C. neoformans was carried out in a time-course study. Principal component analysis (PCA) revealed significant fluctuations in the expression levels of different groups of genes during the pathogen-host interaction. Self-organizing map (SOM) analysis revealed that most genes were up- or downregulated 2 folds or more at least at one time point during the pathogen-host engagement. The microarray data were validated by Western blot analysis of a group of genes, including β-actin, Bcl-x, CD47, Bax, Bad, and Bcl-2. Hierarchical cluster profile showed that 61 out of 66 listed interferon genes were changed at least at one time point. Similarly, the active responses in expression of MHC genes were detected at all stages of the interaction. Taken together, our infectomic approaches suggest that the host cells significantly change the gene profiles and also actively participate in immunoregulations of the central nervous system (CNS) during C. neoformans infection.

Inhibition of interleukin-8 production in human endothelial cells by Staphylococcus aureus supernatant

Recent reports have shown that Staphylococcus aureus infection increases the expression of cytokines and cell adhesion molecules in endothelial cells and enhances leucocyte migration, thereby resulting in bacterial elimination. In this study, we analysed the production of the chemokine interleukin (IL)-8 in human umbilical vein endothelial cells (HUVEC) infected with several S. aureus strains by using reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. We found that the avirulent strains (00-51 and 00-62) increased IL-8 production but the virulent strains (A17 and A151) decreased it at both the mRNA and protein levels. We considered that the inhibition of IL-8 production depended on certain inhibitory factor(s) secreted by bacteria. This was because S. aureus also abolished IL-8 expression in HUVEC treated with cytochalasin D, and the addition of culture supernatants of strains A17 and A151 decreased IL-8 production in HUVEC. This factor(s) in the bacterial culture supernatant inhibited both basal and tumour necrosis factor (TNF)-alpha-induced IL-8 production. In contrast, no inhibitory effect was observed on monocyte chemotactic protein-1 (MCP-1) production. These results indicate that S. aureus can down-regulate IL-8 release in endothelial cells through the secretion of inhibitory factor(s), and this may result in decreased neutrophil recruitment, thus interfering with the host immune response to bacterial infection.

Hepatocyte growth factor protects human endothelial cells against advanced glycation end products-induced apoptosis

Advanced glycation end products (AGEs) form by a non-enzymatic reaction between reducing sugars and biological proteins, which play an important role in the pathogenesis of atherosclerosis. In this study, we assessed AGEs effects on human umbilical vein endothelial cells (HUVECs) growth, proliferation and apoptosis. Additionally, we investigated whether hepatocyte growth factor (HGF), an anti-apoptotic factor for endothelial cells, prevents AGEs-induced apoptosis of HUVECs. HUVECs were treated with AGEs in the presence or absence of HGF. Treatment of HUVECs with AGEs changed cell morphology, decreased cell viability, and induced DNA fragmentation, leading to apoptosis. Apoptosis was induced by AGEs in a dose- and time-dependent fashion. AGEs markedly elevated Bax and decreased NF-kappaB, but not Bcl-2 expression. Additionally, AGEs significantly inhibited cell growth through a pro-apoptotic action involving caspase-3 and -9 activations in HUVECs. Most importantly, pretreatment with HGF protected against AGEs-induced cytotoxicity in the endothelial cells. HGF significantly promoted the expression of Bcl-2 and NF-kappaB, while decreasing the activities of caspase-3 and -9 without affecting Bax level. Our data suggest that AGEs induce apoptosis in endothelial cells. HGF effectively attenuate AGEs-induced endothelial cell apoptosis. These findings provide new perspectives in the role of HGF in cardiovascular disease.

Signaling through interleukin-1 type 1 receptor diminishes Haemophilus somnus lipooligosaccharide-mediated apoptosis of endothelial cells

During sepsis, endothelial cells are both a source and target of pro-inflammatory cytokines (e.g. IL-1alpha, IL-1beta, TNFalpha and others), which may be detrimental to vascular homeostasis. Our laboratory has demonstrated that Haemophilus somnus, a gram-negative pathogen of cattle that causes sepsis and vasculitis, and its lipooligosaccharide (LOS) induce caspases-3, -8 and -9 activation, and apoptosis of endothelial cells in vitro. In this study, we provide evidence that H. somnus LOS increases IL-1alpha and IL-1beta mRNA expression, and caspase-1 activation in endothelial cells. Addition of a caspase-1 inhibitor (YVAD), or incubation in a high extracellular potassium buffer (150 mM), reduced caspase-1 activation and significantly enhanced H. somnus LOS-mediated caspase-3 activation. Likewise, blocking the IL-1 type 1 receptor by addition of IL-receptor antagonist (IL-1ra) significantly enhanced LOS-mediated caspase-3 activation. Conversely, addition of exogenous recombinant bovine IL-1beta (100 ng/mL) to endothelial cells diminished LOS-mediated apoptosis. IL-1beta has been reported previously to protect numerous cell types from apoptosis by activating PI3 kinase/p-Akt signaling pathways. Addition of selective PI3 kinase inhibitors (e.g. wortmannin and LY294002) significantly enhanced LOS-mediated caspase-3 activation. Exposure of endothelial cells to IL-1beta or LOS increased pAkt protein as assessed by western blot. Overall, these results suggest that signaling through the IL-1 type 1 receptor diminishes H. somnus LOS-mediated apoptosis.

Surface localization of the Yps3p protein of Histoplasma capsulatum

The YPS3 gene of Histoplasma capsulatum encodes a protein that is both resident in the cell wall and also released into the culture medium. This protein is produced only during the pathogenic yeast phase of infection and is also expressed differently in H. capsulatum strains that differ in virulence. We investigated the cellular localization of Yps3p. We demonstrated that the cell wall fraction of Yps3p was surface localized in restriction fragment length polymorphism class 2 strains. We also established that Yps3p released into the G217B culture supernatant binds to the surface of strains that do not naturally express the protein. This binding was saturable and occurred within 5 min of exposure and occurred similarly with live and heat-killed H. capsulatum. Flow cytometric analysis of H. capsulatum after enzymatic treatments was consistent with Yps3p binding to chitin, a carbohydrate polymer that is a component of fungal cell walls. Polysaccharide binding assays demonstrated that chitin but not cellulose binds to and extracts Yps3p from culture supernatants.

Inhibition of PMA-induced endothelial cell activation and adhesion by over-expression of domain negative IκBα protein

AIM: NF-κB, regulate the expression of cytokine-inducible genes involving immune and inflammatory responses, will be potential therapy approach for allograft from rejection. In this study, we use pCMV-IκBαM vector to inhibit NF-κB activation and investigate the effect of pCMV-IκBαM in inhibition of T cells adhesion to endothelial cells.

METHODS: The NF-κB activity was detected with pNF-κB reporter gene and electrophoretic mobility shift assay. Expression of cell surface molecules was detected by RT-PCR and flow cytometer. The cell-cell adhesion assay was performed to determine the effect of pCMV-IκBαM in inhibition of T cells adhesion to endothelial cells.

RESULTS: We could find that NF-κB activity is inhibited by over-expression of non-degraded IκBα protein. Expression of adhesion molecules like ICAM-1, VCAM-1, and P-selectin as well as cell-cell adhesion were inhibited significantly by transfection of the pCMV-IκBαM vector.

CONCLUSION: Our results indicate that the pCMV-IκBαM, which inhibit the activity of NF-κB through over-expression of non-degraded IκBα protein, can be used for gene therapy in diseases involving NF-κB activation abnormally like organ transplantation via inhibiting cell adhesion.

Urease expression by Cryptococcus neoformans promotes microvascular sequestration, thereby enhancing central nervous system invasion

Our objective was to determine the role of the cryptococcal virulence factor urease in pulmonary-to-central nervous system, dissemination, invasion, and growth. C. neoformans H99, the urease knockout strain (ure1) derived from H99, and the urease restored strain ure1+URE1-1 were used for the studies. The absence of cryptococcal urease (ure1infection) resulted in significant protection from the high mortality observed in H99-infected mice. All H99-infected mice had extremely high cryptococcal loads in their brains at the time of death, whereas only two of six animals that died of ure1 infection had detectable C. neoformans in the brain. Histological analysis of the blood-to-brain invasion by C. neoformans H99 demonstrated wedging of the yeasts in small capillaries, altered structure of microvessel walls, formation of mucoid cysts initiated in the proximity of damaged microcapillaries, and the absence of an inflammatory response. Direct inoculation of H99, ure1, and ure1+URE1-1 into the brain demonstrated that urease was not required to grow in the brain. However, the dissemination patterns in the brain, spleen, and other organs after intravenous inoculation indicated that cryptococcal urease contributes to the central nervous system invasion by enhancing yeast sequestration within microcapillary beds (such as within the brain) during hematogenous spread, thereby facilitating blood-to-brain invasion by C. neoformans.

Neutrophil granulocytes--Trojan horses for Leishmania major and other intracellular microbes?

Polymorphonuclear neutrophil granulocytes (PMNs) possess numerous effector mechanisms to kill ingested pathogens as the first line of defence. However, several microorganisms evade intracellular killing in neutrophils, survive and retain infectivity. There is increasing evidence that several pathogens even multiply within neutrophils. Taking Leishmania major as a prototypic intracellular pathogen, we suggest an evasion strategy that includes the manipulation of PMNs in such a way that the pathogens are able to use the granulocytes as host cells. The ability to survive and maintain infectivity in PMNs subsequently enables these organisms to establish productive infection. These organisms can use granulocytes as Trojan horses before they enter their definitive host cells, the macrophages.

Cryptococcal glucuronoxylomannan inhibits adhesion of neutrophils to stimulated endothelium in vitro by affecting both neutrophils and endothelial cells

Cryptococcal infections are often characterized by a paucity of leukocytes in the infected tissues. Previous research has shown that the capsular polysaccharide glucuronoxylomannan (GXM) inhibits leukocyte migration. In this study we investigated whether the capsular polysaccharide GXM affects the migration of neutrophils (polymorphonuclear leukocytes [PMN]) through the endothelium by interfering with adhesion in a static adhesion model. Pretreatment of PMN with GXM inhibited PMN adhesion to tumor necrosis factor alpha (TNF-alpha)-stimulated endothelium up to 44%. Treatment of TNF-alpha-stimulated endothelium with GXM led to a 27% decrease in PMN adhesion. GXM treatment of both PMN and endothelium did not have an additive inhibitory effect. We demonstrated that GXM-induced L-selectin shedding does not play an important role in the detected inhibition of adhesion. L-selectin was still present on PMN in sufficient amounts after GXM treatment, since it could be further inhibited by blocking antibodies. Furthermore, blocking of GXM-related L-selectin shedding did not abolish the GXM-related inhibition of adhesion. GXM most likely exerts its effect on PMN by interfering with E-selectin-mediated binding. The use of blocking monoclonal antibodies against E-selectin, which was shown to decrease adhesion in the absence of GXM, did not cause additive inhibition of PMN adhesion after GXM pretreatment. The use of blocking antibodies also demonstrated that the inhibiting effect found after GXM treatment of endothelium probably involves interference with both intercellular adhesion molecule-1 and E-selectin binding.

Hepatocyte growth factor is a survival factor for endothelial cells and is expressed in human atherosclerotic plaques

Hepatocyte growth factor (HGF) has multiple effects on target cells upon activation of its receptor, c-Met. In endothelial cells, HGF induces migration, proliferation, and angiogenesis. HGF can also act as an anti-apoptotic factor for several cell types. The signal transduction pathways involved in mediating its anti-apoptotic effects have not been fully clarified. We demonstrated that HGF is anti-apoptotic for human endothelial cells, and identified the signaling pathways by which it mediates its effects. Human umbilical vein endothelial cells (HUVEC) exhibited significant levels of apoptosis after serum deprivation. HGF inhibited apoptosis in a dose dependent manner in serum-deprived cultures. HGF induced the phosphorylation of Akt and Erk1/2, cell survival factors, in a time dependent manner in serum deprived HUVEC. Inhibition of Akt and Erk1/2 activation abolished the anti-apoptotic effects of HGF. The transcription factor, NF-kappaB, can also play a role in promoting cell survival. However, NF-kappaB does not appear to contribute to the anti-apoptotic properties of HGF, as nuclear translocation of NF-kappaB was not detected in HGF-treated cultures. Endothelial cell migration, proliferation, and apoptosis contribute to the pathogenesis of atherosclerosis, and HGF may play a role in the development and progression of vascular lesions. Immunohistochemical analysis of human carotid artery sections demonstrated HGF protein localization within atherosclerotic lesions but not in normal vessels, suggesting that HGF may participate in atherogenesis.

Leishmania promastigotes release a granulocyte chemotactic factor and induce interleukin-8 release but inhibit gamma interferon-inducible protein 10 production by neutrophil granulocytes

Recent data from our laboratory suggest that neutrophil granulocytes (polymorphonuclear leukocytes [PMN]) can serve as host cells for Leishmania major in the early phase of infection. In line with these findings, an early influx of PMN to the infected tissues was shown by others to be associated with susceptibility to infection with L. major. The mechanisms underlying the initial PMN recruitment to the site of infection is poorly understood. In the present study we investigated whether Leishmania can influence PMN migration. Supernatants of Leishmania promastigotes were tested for their chemotactic activity using an in vitro chemotaxis assay. All Leishmania species tested (L. major, L. aethiopica, and L. donovani) displayed a marked chemotactic effect on human PMN. However, no effect on the migration of macrophages and NK cells was observed. Checkerboard analysis revealed that the observed PMN migration was due to chemotaxis rather than chemokinesis. Most of the chemotactic activity was found in fractions containing molecules with sizes between 10 and 50 kDa. Pretreatment of PMN with N-formyl-methionyl-leucyl-phenylalanine blocked the chemotactic activity of Leishmania supernatants up to 75%. In addition, we found that leishmanial contact induced the release of interleukin-8 (IL-8) and inhibited the production of gamma interferon-inducible protein 10 (IP-10) by PMN. These data suggest that infection with Leishmania promastigotes leads to PMN accumulation via the production of a chemotactic factor by the parasites, and this effect is amplified by the induction of IL-8 production in PMN. On the other hand, the inhibition of IP-10 production can lead to prevention of NK cell activation.

Treatment of experimental nephrosis by culture filtrate of Cryptococcus neoformans var. gattii (CneF)

The therapeutic effect of the culture filtrate of cryptococcus neoformans var. gattii (CneF) was tested in Adriamycin-induced nephropathy. The CneF was administered at different doses (36, 54 and 90 mg/kg based on carbohydrate concentration), one i.p. injection every 72 hours for a total of 10 injections. The treated patient rats showed a significant reduction in proteinuria, plasma cholesterol concentration, BUN and significant increase in urine creatinine levels. Moreover, treatment with CneF significantly reduced number of glomerular leukocytes and decreased the tubular casts. These data suggest that CneF therapy can ameliorate proteinuria, hypercholesterolemia and suppress the progression of glomerular lesions in experimental model of nephrosis.

Cryptococcal infection and Th1-Th2 cytokine balance

Cytokines have been recognized as key factors in determining host resistance to infectious pathogens. In particular, Th1-Th2 cytokine balance in hosts is profoundly associated with the outcome of infection caused by intracellular microbes. In a murine model of pulmonary and disseminated infection with Cryptococcus neoformans, an opportunistic fungal pathogen that frequently leads to fatal meningoencephalitis in severely immunocompromised hosts, expression of cytokine mRNA in the lungs from infected animals revealed Th2-dominant profiles, while administration of IL-12, which rescued mice from fatal infection, converted such balance toward Th1-dominant states in a drastic fashion. Thus, commitment of Th phenotypes critically determines host sensitivity to cryptococcal infection. In this review, we described how Th1-Th2 cytokine balance influences host protective responses to C. neoformans, and we identify the host and pathogen factors that regulate such balance.

Phenotypic switching of Cryptococcus neoformans occurs in vivo and influences the outcome of infection

Phenotypic switching has been linked to the virulence of many pathogens, including fungi. However, it has not been conclusively shown to occur in vivo or to influence the outcome of infection. Cryptococcus neoformans undergoes phenotypic switching in vitro to colony types that differ in their virulence in mice. In this study, we asked whether C. neoformans undergoes phenotypic switching in vivo and whether this phenomenon contributes to virulence. By using a small inoculum to preclude the introduction of variants that had already switched during in vitro propagation, we demonstrated that in vivo switching to a mucoid phenotype occurred in two mice strains and was associated with a lethal outcome. Phenotypic switching resulted in changes of the capsular polysaccharide that inhibited phagocytosis by alveolar macrophages. This promoted a more vigorous inflammatory response and rapid demise. These data document in vivo switching in a fungus and associate this phenomenon with enhanced virulence and a lethal outcome. The importance of this finding is underscored by the increased likelihood of phenotypic switching in chronic cryptococcosis; thus this mechanism may account for the inability to eradicate the organism in immunocompromised hosts.

Molecular machinations: chemokine signals in host-pathogen interactions

Chemokines and their G-protein-coupled receptors represent an ancient and complex system of cellular communication participating in growth, development, homeostasis and immunity. Chemokine production has been detected in virtually every microbial infection examined; however, the precise role of chemokines is still far from clear. In most cases they appear to promote host resistance by mobilizing leukocytes and activating immune functions that kill, expel, or sequester pathogens. In other cases, the chemokine system has been pirated by pathogens, especially protozoa and viruses, which have exploited host chemokine receptors as modes of cellular invasion or developed chemokine mimics and binding proteins that act as antagonists or inappropriate agonists. Understanding microbial mechanisms of chemokine evasion will potentially lead to novel antimicrobial and anti-inflammatory therapeutic agents.

Mechanisms for induction of immunosuppression during experimental cryptococcosis: role of glucuronoxylomannan

In previous work we have demonstrated that spleen mononuclear (Spm) cells from rats obtained 14 days after infection with Cryptococcus neoformans showed a diminution in proliferative response to Concanavalin A (Con A). In this study we further investigate some characteristics of the Spm cell population involved in the immunosuppressor phenomenon induced by C. neoformans. We observed that unstimulated Spm cells expressing T-cell receptor (TCR+) from infected rats were reduced in number after 96 h of culture. When the Spm cells from infected rats were stimulated with Con A, increased production of IL-10, reduced levels of IL-2, and decreased CD11a surface expression were shown. These immunosuppressor phenomena were also observed when the capsular polysaccharide, glucuronoxylomannan (GXM), was added to cultures of Spm cells from normal rats. However, GXM had a more pronounced effect in reducing the number of cells surviving in culture than that observed during infection and produced an increase in IL-4 production by Con-A-stimulated Spm cells. Addition of anti-IL-10 monoclonal antibody to cultures restored the lymphoproliferation of Spm cells from infected animals, indicating that IL-10 production is a suppressor mechanism of cell-mediated immunity during experimental infection. The results presented here indicate that at least two mechanisms mediate the nonspecific suppression in this model of cryptococcosis: IL-10 production and diminution of the number of T cells. GXM could be involved, since it has a pronounced effect in the reduction of Spm cells in vitro.

Pathogenic yeasts Cryptococcus neoformans and Candida albicans produce immunomodulatory prostaglandins

Enhanced prostaglandin production during fungal infection could be an important factor in promoting fungal colonization and chronic infection. Host cells are one source of prostaglandins; however, another potential source of prostaglandins is the fungal pathogen itself. Our objective was to determine if the pathogenic yeasts Cryptococcus neoformans and Candida albicans produce prostaglandins and, if so, to begin to define the role of these bioactive lipids in yeast biology and disease pathogenesis. C. neoformans and C. albicans both secreted prostaglandins de novo or via conversion of exogenous arachidonic acid. Treatment with cyclooxygenase inhibitors dramatically reduced the viability of the yeast and the production of prostaglandins, suggesting that an essential cyclooxygenase like enzyme may be responsible for fungal prostaglandin production. A PGE series lipid was purified from both C. albicans and C. neoformans and was biologically active on both fungal and mammalian cells. Fungal PGE(x) and synthetic PGE(2) enhanced the yeast-to-hypha transition in C. albicans. Furthermore, in mammalian cells, fungal PGE(x) down-modulated chemokine production, tumor necrosis factor alpha production, and splenocyte proliferation while up-regulating interleukin 10 production. These are all activities previously documented for mammalian PGE(2). Thus, eicosanoids are produced by pathogenic fungi, are critical for growth of the fungi, and can modulate host immune functions. The discovery that pathogenic fungi produce and respond to immunomodulatory eicosanoids reveals a virulence mechanism that has potentially great implications for understanding the mechanisms of chronic fungal infection, immune deviation, and fungi as disease cofactors.