Direct interactions of human natural killer cells with Cryptococcus neoformans inhibit granulocyte-macrophage colony-stimulating factor and tumor necrosis factor alpha production

Disseminated cryptococcosis and anti-granulocyte-macrophage colony-stimulating factor autoantibodies: An underappreciated association

The development of disseminated cryptococcosis has historically occurred in patients living with advanced human immunodeficiency virus or other immunosuppressive conditions affecting T-cell function. Recently, patients with anti-cytokine neutralising autoantibodies have been recognised to be at risk for disseminated infections by opportunistic intracellular pathogens, including Cryptococcus species. Herein, we present a previously healthy 26-year-old man who was evaluated with disseminated cryptococcosis involving the bone, lung, mediastinum and brain. The patient's serum cryptococcal antigen titres were >1:1,100,000, and evaluation for an underlying immunodeficiency revealed high titres for anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) autoantibodies. We also review the literature of all published cases of disseminated cryptococcosis associated with the presence of anti-GM-CSF autoantibodies. Clinicians should have a heightened awareness of anti-cytokine autoantibodies in patients without a known immunodeficiency and development disseminated infections by opportunistic intracellular pathogens.

Dormancy in Cryptococcus neoformans: 60 years of accumulating evidence

Cryptococcus neoformans is an opportunistic yeast that is present worldwide and interacts with various organisms. In humans, it is responsible for cryptococcosis, a deadly invasive fungal infection that represents around 220,000 cases per year worldwide. Starting from the natural history of the disease in humans, there is accumulating evidence on the capacity of this organism to enter dormancy. In response to the harsh host environment, the yeast is able to adapt dramatically and escape the vigilance of the host's immune cells to survive. Indeed, the yeast exposed to the host takes on pleiotropic phenotypes, enabling the generation of populations in heterogeneous states, including dormancy, to eventually survive at low metabolic cost and revive in favorable conditions. The concept of dormancy has been validated in C. neoformans from both epidemiological and genotyping data, and more recently from the biological point of view with the characterization of dormancy through the description of viable but nonculturable cells.

TNF-α-Producing Cryptococcus neoformans Exerts Protective Effects on Host Defenses in Murine Pulmonary Cryptococcosis

Tumor necrosis factor alpha (TNF-α) plays a critical role in the control of cryptococcal infection, and its insufficiency promotes cryptococcal persistence. To explore the therapeutic potential of TNF-α supplementation as a booster of host anti-cryptococcal responses, we engineered a C. neoformans strain expressing murine TNF-α. Using a murine model of pulmonary cryptococcosis, we demonstrated that TNF-α-producing C. neoformans strain enhances protective elements of host response including preferential T-cell accumulation and improved Th1/Th2 cytokine balance, diminished pulmonary eosinophilia and alternative activation of lung macrophages at the adaptive phase of infection compared to wild type strain-infected mice. Furthermore, TNF-α expression by C. neoformans enhanced the fungicidal activity of macrophages in vitro. Finally, mice infected with the TNF-α-producing C. neoformans strain showed improved fungal control and considerably prolonged survival compared to wild type strain-infected mice, but could not induce sterilizing immunity. Taken together, our results support that TNF-α expression by an engineered C. neoformans strain while insufficient to drive complete immune protection, strongly enhanced protective responses during primary cryptococcal infection.

Natural Killer Cells in Antifungal Immunity

Invasive fungal infections are still an important cause of morbidity and mortality in immunocompromised patients such as patients suffering from hematological malignancies or patients undergoing hematopoietic stem cell transplantion. In addition, other populations such as human immunodeficiency virus-patients are at higher risk for invasive fungal infection. Despite the availability of new antifungal compounds and better supportive care measures, the fatality rate of invasive fungal infection remained unacceptably high. It is therefore of major interest to improve our understanding of the host-pathogen interaction to develop new therapeutic approaches such as adoptive immunotherapy. As experimental methodologies have improved and we now better understand the complex network of the immune system, the insight in the interaction of the host with the fungus has significantly increased. It has become clear that host resistance to fungal infections is not only associated with strong innate immunity but that adaptive immunity (e.g., T cells) also plays an important role. The antifungal activity of natural killer (NK) cells has been underestimated for a long time. In vitro studies demonstrated that NK cells from murine and human origin are able to attack fungi of different genera and species. NK cells exhibit not only a direct antifungal activity via cytotoxic molecules but also an indirect antifungal activity via cytokines. However, it has been show that fungi exert immunosuppressive effects on NK cells. Whereas clinical data are scarce, animal models have clearly demonstrated that NK cells play an important role in the host response against invasive fungal infections. In this review, we summarize clinical data as well as results from in vitro and animal studies on the impact of NK cells on fungal pathogens.

NK Cells and Their Role in Invasive Mold Infection

There is growing evidence that Natural Killer (NK) cells exhibit in vitro activity against both Aspergillus and non-Aspergillus molds. Cytotoxic molecules such as NK cell-derived perforin seem to play an important role in the antifungal activity. In addition, NK cells release a number of cytokines upon stimulation by fungi, which modulate both innate and adaptive host immune responses. Whereas the in vitro data of the antifungal activity of NK cells are supported by animal studies, clinical data are scarce to date.

Cryptococcus neoformans meningoencephalitis in a patient with polyarteritis nodosa

Case of 59-year-old male with chronic obstructive pulmonary disease and a number of comorbidities, who has developed meningoencephalitis caused by Cryptococcus neoformans var. grubii with polyarteritis nodosa diagnosed during hospitalization, was presented. Before evidence of meningoencephalitis, the patient was being treated with ketoconazole and low doses of fluconazole (200 mg/day) for alleged candidiasis. The dosage was increased (800 mg/day) following laboratory diagnosis of C. neoformans based on positive latex agglutination test and biochemical identification of encapsulated yeast isolated from the blood and CSF. Later, the yeast identification was confirmed by sequencing analysis. Owing to inadequate clinical response, fluconazole therapy was switched to voriconazole (400 mg/day) and later to intravenous amphotericin B (1.0 mg/kg per day). Despite of a temporary stabilization and improvement, which correlated with decline of cryptococcal antigen titers (from 1:1024 to 1:8), after 6 weeks, the patient's underlying condition deteriorated due to severe pancolitis and serious nosocomial bacterial infections. The patient died of multiorgan failure several days later. Our case demonstrates a possible connection between the development of life-threatening cryptococcosis and an autoimmune vasculitis disease and emphasizes that the outcome of the management of cryptococcal meningoencephalitis is highly dependent on early diagnosis, adequate treatment, including dosage, and last but not least control of underlying disease and risk factors.

Compartmentalization of innate immune responses in the central nervous system during cryptococcal meningitis/HIV coinfection

OBJECTIVE

The role of innate immunity in the pathogenesis of cryptococcal meningitis is unclear. We hypothesized that natural killer (NK) cell and monocyte responses show central nervous system (CNS) compartment-specific profiles, and are altered by antifungal therapy and combination antiretroviral therapy (cART) during cryptococcal meningitis/HIV coinfection.

DESIGN

Substudy of a prospective cohort study of adults with cryptococcal meningitis/HIV coinfection in Durban, South Africa.

METHODS

We used multiparametric flow cytometry to study compartmentalization of subsets, CD69 (a marker of activation), CXCR3 and CX3CR1 expression, and cytokine secretion of NK cells and monocytes in freshly collected blood and cerebrospinal fluid (CSF) at diagnosis (n = 23), completion of antifungal therapy induction (n = 19), and after a further 4 weeks of cART (n = 9).

RESULTS

Relative to blood, CSF was enriched with CD56(bright) (immunoregulatory) NK cells (P = 0.0004). At enrolment, CXCR3 expression was more frequent among blood CD56(bright) than either blood CD56(dim) (P < 0.0001) or CSF CD56(bright) (P = 0.0002) NK cells. Antifungal therapy diminished blood (P < 0.05), but not CSF CXCR3(pos) NK-cell proportions nor CX3CR1(pos) NK-cell proportions. CD56(bright) and CD56(dim) NK cells were more activated in CSF than blood (P < 0.0001). Antifungal therapy induction reduced CD56(dim) NK-cell activation in CSF (P = 0.02). Activation of blood CD56(bright) and CD56(dim) NK cells was diminished following cART commencement (P < 0.0001, P = 0.03). Immunoregulatory NK cells in CSF tended to secrete higher levels of CXCL10 (P = 0.06) and lower levels of tumor necrosis factor α (P = 0.06) than blood immunoregulatory NK cells. CSF was enriched with nonclassical monocytes (P = 0.001), but antifungal therapy restored proportions of classical monocytes (P = 0.007).

CONCLUSION

These results highlight CNS activation, trafficking, and function of NK cells and monocytes in cryptococcal meningitis/HIV and implicate immunoregulatory NK cells and proinflammatory monocytes as potential modulators of cryptococcal meningitis pathogenesis during HIV coinfection.

Anti-GM-CSF autoantibodies in patients with cryptococcal meningitis

Cryptococcal meningitis has been described in immunocompromised patients, as well as in those for whom no immune defect has been identified. GM-CSF regulates the function of phagocytes and pulmonary alveolar macrophages, critical elements in cryptococcal control. We performed clinical histories, immunological evaluation, and anticytokine autoantibody screening in four current patients with cryptococcal meningitis and identified and tested 103 archived plasma/cerebrospinal fluid samples from patients with cryptococcal meningitis. We assessed the ability of anti-GM-CSF autoantibody-containing plasmas to inhibit GM-CSF signaling. We recognized anti-GM-CSF autoantibodies in an otherwise healthy female with cryptococcal meningitis who later developed pulmonary alveolar proteinosis (PAP). Her diagnosis prompted screening of patients with cryptococcal meningitis for anticytokine autoantibodies. We identified seven HIV-negative patients with cryptococcal meningitis who tested positive for high-titer anti-GM-CSF autoantibodies. Two of the seven later developed evidence of PAP. Plasma from all patients prevented GM-CSF-induced STAT5 phosphorylation and MIP-1α production in normal PBMCs. This effect was limited to their IgG fraction. Anti-GM-CSF autoantibodies are associated with some cases of cryptococcal meningitis in otherwise immunocompetent patients. These cases need not have associated PAP.

Natural killer cells and antifungal host response

As a result of improved experimental methodologies and a better understanding of the immune system, there is increasing insight into the antifungal activity of natural killer (NK) cells. Murine and human NK cells are able to damage fungi of different genera and species in vitro, and they exert both direct and indirect antifungal activity through cytotoxic molecules such as perforin and through cytokines and interferons, respectively. On the other hand, recent data suggest that fungi exhibit immunosuppressive effects on NK cells. Whereas clear in vivo data are lacking in humans, the importance of NK cells in the host response against fungi has been demonstrated in animal models. Further knowledge of the interaction of NK cells with fungi might help to better understand the pathogenesis of invasive fungal infections and to improve treatment strategies.

Memory CD4+ T cells are required for optimal NK cell effector functions against the opportunistic fungal pathogen Pneumocystis murina

Little is known about the role of NK cells or their interplay with other immune cells during opportunistic infections. Using our murine model of Pneumocystis pneumonia, we found that loss of NK cells during immunosuppression results in substantial Pneumocystis lung burden. During early infection of C57B/6 CD4(+) T cell-depleted mice, there were significantly fewer NK cells in the lung tissue compared with CD4(+) T cell-intact animals, and the NK cells present demonstrated decreased upregulation of the activation marker NKp46 and production of the effector cytokine, IFN-γ. Furthermore, coincubation studies revealed a significant increase in fungal killing when NK cells were combined with CD4(+) T cells compared with either cell alone, which was coincident with a significant increase in perforin production by NK cells. Finally, however, we found through adoptive transfer that memory CD4(+) T cells are required for significant NK cell upregulation of the activation marker NK group 2D and production of IFN-γ, granzyme B, and perforin during Pneumocystis infection. To the best of our knowledge, this study is the first to demonstrate a role for NK cells in immunity to Pneumocystis pneumonia, as well as to establish a functional relationship between CD4(+) T cells and NK cells in the host response to an opportunistic fungal pathogen.

Rhizopus oryzae hyphae are damaged by human natural killer (NK) cells, but suppress NK cell mediated immunity

Mucormycosis has a high mortality and is increasingly diagnosed in hematopoietic stem cell transplant (HSCT) recipients. In this setting, there is a growing interest to restore host defense to combat infections by adoptively transferring donor-derived immunocompetent cells. Natural killer (NK) cells exhibit antitumor and antiinfective activity, but the interaction with Mucormycetes is unknown. Our data demonstrate that both unstimulated and IL-2 prestimulated human NK cells damage Rhizopus oryzae hyphae, but do not affect resting conidia. The damage of the fungus is mediated, at least in part, by perforin. R. oryzae hyphae decrease the secretion of immunoregulatory molecules by NK cells, such as IFN-γ and RANTES, indicating an immunosuppressive effect of the fungus. Our data indicate that NK cells exhibit activity against Mucormycetes and future research should evaluate NK cells as a potential tool for adoptive immunotherapy in HSCT.

Cryptococcus neoformans directly stimulates perforin production and rearms NK cells for enhanced anticryptococcal microbicidal activity

NK cells, in addition to possessing antitumor and antiviral activity, exhibit perforin-dependent microbicidal activity against the opportunistic pathogen Cryptococcus neoformans. However, the factors controlling this response, particularly whether the pathogen itself provides an activation or rearming signal, are largely unknown. The current studies were performed to determine whether exposure to this fungus alters subsequent NK cell anticryptococcal activity. NK cells lost perforin and mobilized lysosome-associated membrane protein 1 to the cell surface following incubation with the fungus, indicating that degranulation had occurred. Despite a reduced perforin content during killing, NK cells acquired an enhanced ability to kill C. neoformans, as demonstrated using auxotrophs that allowed independent assessment of the killing of two strains. De novo protein synthesis was required for optimal killing; however, there was no evidence that a soluble factor contributed to the enhanced anticryptococcal activity. Exposure of NK cells to C. neoformans caused the cells to rearm, as demonstrated by increased perforin mRNA levels and enhanced loss of perforin when transcription was blocked. Degranulation alone was insufficient to provide the activation signal as NK cells lost anticryptococcal activity following treatment with strontium chloride. However, NK cells regained the activity upon prolonged exposure to C. neoformans, which is consistent with activation by the microbe. The enhanced cytotoxicity did not extend to tumor killing since NK cells exposed to C. neoformans failed to kill NK-sensitive tumor targets (K562 cells). These studies demonstrate that there is contact-mediated microbe-specific rearming and activation of microbicidal activity that are necessary for optimal killing of C. neoformans.

Prostaglandin E(2) production by high and low virulent strains of Paracoccidioides brasiliensis

The production of prostaglandins (PGs) during fungal infections could be an important suppressor factor of host immune response. Host cells are one source of prostaglandin E(2) (PGE(2)); however another potential source of PGE(2) is the fungal pathogen itself. Thus, both host and fungal PGE2 production is theorized to play a role in pathogenesis, being critical for growth of the fungus and to modulate the host immune response. The purpose of this work was to investigate if high and low virulent strains of Paracoccidioides brasiliensis have the capacity to produce PGE(2) in vitro, and if this production was related to the fungal growth. The results demonstrated that both strains of P. brasiliensis produce high levels of PGE(2) and the treatment with indomethacin, a cyclooxygenase inhibitor, significantly reduced the production of this mediator, as well as the viability of the fungus. Thus, our data indicate that PGE(2) is produced by P. brasiliensis by a cyclooxygenase-dependent metabolic pathway, and its production is required for fungal survival. This discovery reveals an important factor that has potentially great implications for understanding the mechanisms of immune deviation during infection.

Contemplating the murine test tube: lessons from natural killer cells andCryptococcus neoformans

Murine experimentation has provided many useful tools, including the ability to knockout or over-express genes and to perform experiments that are limited by ethical considerations. Over the past century, mice have imparted valuable insights into the biology of many systems, including human immunity. However, although there are many similarities between the immune response of humans and mice, there are also many differences; none is more prominent than when examining natural killer cell biology. These differences include tissue distribution, effector molecules, receptor repertoire, and cytokine responses, all of which have important implications when extrapolating the studies to the human immune responses to Cryptococcus neoformans.

The immune response to fungal infections

During the past two decades, invasive fungal infections have emerged as a major threat to immunocompromised hosts. Patients with neoplastic diseases are at significant risk for such infections as a result of their underlying illness and its therapy. Aspergillus, Candida, Cryptococcus and emerging pathogens, such as the zygomycetes, dark walled fungi, Trichosporon and Fusarium, are largely opportunists, causing infection when host defences are breached. The immune response varies with respect to the fungal species and morphotype encountered. The risk for particular infections differs, depending upon which aspect of immunity is impaired. This article reviews the current understanding of the role and relative importance of innate and adaptive immunity to common and emerging fungal pathogens. An understanding of the host response to these organisms is important in decisions regarding use of currently available antifungal therapies and in the design of new therapeutic modalities.

Transient neutralization of tumor necrosis factor alpha can produce a chronic fungal infection in an immunocompetent host: potential role of immature dendritic cells

The mechanisms underlying induction of immune dysregulation and chronic fungal infection by a transient tumor necrosis factor alpha (TNF-alpha) deficiency remain to be defined. The objective of our studies was to determine the potential contribution of neutropenia and immature dendritic cells to the immune deviation. Administration of an anti-TNF-alpha monoclonal antibody at day 0 neutralized TNF-alpha only during the first week of a pulmonary Cryptococcus neoformans infection. Transient neutralization of TNF-alpha resulted in transient depression of interleukin-12 (IL-12), monocyte chemotactic protein 1 (MCP-1), and gamma interferon (IFN-gamma) production but permanently impaired long-term clearance of the infection from the lungs even after the levels of these cytokines increased and a vigorous inflammatory response developed. Early neutrophil recruitment was defective in the absence of TNF-alpha. However, as demonstrated by neutrophil depletion studies, this did not account for the decrease in IL-12 and IFN-gamma levels and did not play a role in establishing chronic pulmonary cryptococcal infection. Transient TNF-alpha neutralization also produced a deficiency in CD11c(+) MHC II(+) cells and IL-12 in the lymph nodes, potentially implicating a defect in mature dendritic cell trafficking. Transfer of cryptococcal antigen-pulsed immature dendritic cells into naive mice prior to intratracheal challenge resulted in the development of a nonprotective immune response to C. neoformans that was similar to that observed in anti-TNF-alpha-treated mice (increased IL-4, IL-5, and IL-10 levels, pulmonary eosinophilia, and decreased clearance). Thus, stimulation of an antifungal response by immature dendritic cells can result in an immune deviation similar to that produced by transient TNF-alpha deficiency, identifying a new mechanism by which a chronic fungal infection can occur in an immunocompetent host.

Tolerability and anti-inflammatory effects of glucuronoxylomannan in collagen-induced arthritis

This investigation was planned to assess the therapeutic efficacy of glucuronoxylomannan (GXM) in collagen-induced arthritis (CIA). GXM was isolated from culture filtrate of Cryptococcus neoformans var. gattii, serotype C. CIA was induced by the immunization of Dark Agouti rats with bovine type II collagen in incomplete Freund's adjuvant. GXM solution at two doses, 25 and 50 mg/kg, was administered intraperitoneally. Onset of i.p. injections of GXM to prevention and treatment groups was days 0 and 10 postimmunization, respectively. The WEHI-164 cell line was used for assaying tolerability, matrix metalloproteinase type 2 (MMP-2) activity and apoptosis. MMP-2 activity was assessed using zymography. For assessment of apoptosis, the terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labelling method was used. The results of this experiment showed that the treatment of CIA with GXM at a dose of 50 mg/kg could suppress disease development both prophylactically and therapeutically. This beneficial effect of GXM was associated with a significant decrease in the anti-CII antibody response compared with untreated rats. Moreover, GXM therapy could diminish MMP-2 activity, but it had no notable effect on apoptosis. GXM also showed a high tolerability compared with certain steroidal and non-steroidal anti-inflammatory drugs. We conclude that GXM suppresses the development of disease in CIA and it could be recommended as a new immunosuppressive and anti-inflammatory agent for further investigations.

Identification of App1 as a regulator of phagocytosis and virulence of Cryptococcus neoformans

Cryptococcus neoformans is a fungal pathogen that, after inhalation, can disseminate to the brain. Host alveolar macrophages (AMs) represent the first defense against the fungus. Once phagocytosed by AMs, fungal cells are killed by a concerted mechanism, involving the host-cellular response. If the cellular response is impaired, phagocytosis of the fungus may be detrimental for the host, since C. neoformans can grow within macrophages. Here, we identified a novel cryptococcal gene encoding antiphagocytic protein 1 (App1). App1 is a cryptococcal cytoplasmic protein that is secreted extracellularly and found in the serum of infected patients. App1 does not affect melanin production, capsule formation, or growth of C. neoformans. Treatment with recombinant App1 inhibited phagocytosis of fungal cells through a complement-mediated mechanism, and Deltaapp1 mutant is readily phagocytosed by AMs. Interestingly, the Deltaapp1 mutant strain showed a decreased virulence in mice deficient for complement C5 (A/Jcr), but it was hypervirulent in mice deficient for T and NK cells (Tgepsilon26). This study identifies App1 as a novel regulator of virulence for C. neoformans, and it highlights that internalization of fungal cells by AMs increases the dissemination of C. neoformans when the host cellular response is impaired.

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.

Induction of interleukin-12 and gamma interferon requires tumor necrosis factor alpha for protective T1-cell-mediated immunity to pulmonary Cryptococcus neoformans infection

The development of T1-cell-mediated immunity is required to clear a pulmonary Cryptococcus neoformans infection. The objective of these studies was to determine the mechanism by which tumor necrosis factor alpha (TNF-alpha) augments the development of pulmonary T1 immunity to C. neoformans infection. TNF-alpha expression was detected in lavage sample cells at days 2, 3, and 7 following C. neoformans infection. The numbers of CFU in the lung were not different between control and anti-TNF-alpha-treated mice at any time point examined during the afferent phase of the response (days 0 to 7). However, neutralization of TNF-alpha prevented the initiation of pulmonary clearance during the efferent phase of the response (day 14). Administration of anti-TNF-alpha monoclonal antibody (day 0) diminished the lung levels of TNF-alpha, interleukin-12 (IL-12), and gamma interferon (IFN-gamma) induced by C. neoformans at day 7 postinfection. Neutralization of TNF-alpha (day 0) also altered the IFN-gamma/IL-4 ratio in the lung-associated lymph nodes at day 7 following C. neoformans infection. Anti-TNF-alpha-treated mice developed a pulmonary eosinophilia at day 14 postinfection. Consistent with the pulmonary eosinophilia, anti-TNF-alpha-treated mice exhibited elevated serum immunoglobulin E and inhibition of the anticryptococcal delayed-type hypersensitivity response, indicating a shift toward a T2 response. Neutralization of IL-12 also prevented lung leukocyte production of IFN-gamma in response to the infection. These findings demonstrate that afferent-phase TNF-alpha production is essential for the induction of IL-12 and IFN-gamma and neutralization of early TNF-alpha results in a T2 shift of the T1/T2 balance of antifungal immunity.

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.

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

Cryptococcus neoformans is an encapsulated fungal pathogen commonly acquired by inhalation. Extrapulmonary dissemination can lead to infection of the bloodstream and various organs, most commonly resulting in meningoencephalitis. However, infection with C. neoformans is often characterized by a scant inflammatory response. The leukocyte response to infection depends in part upon a gradient of chemotactic factors and adhesion molecules expressed by the host vascular endothelium, yet the inflammatory response of human endothelial cells (EC) to C. neoformans has not been previously investigated. We found that incubation of primary human EC with C. neoformans did not induce chemokine synthesis, and resulted in differential inhibition of cytokine-induced IL-8, IFN-gamma-inducible protein-10, and monocyte chemoattractant protein-1. In contrast, C. neoformans had little effect on EC surface expression of the leukocyte ligand, ICAM-1, as determined by flow cytometry. Modulation of chemokine production was dependent on the chemokine under study, the inoculum of C. neoformans used, fungal viability, and cell-cell contact, but independent of cryptococcal strain or encapsulation. These observations suggest a novel mechanism whereby C. neoformans can affect EC function and interfere with the host inflammatory response.

Effect of Salmonella typhi wild type and O-antigen mutants on human natural killer cell activity

We investigated the effect of glutaraldehyde-fixed Salmonella typhi Ty2 (Vi(-)) wild-type (World Health Organization's vaccine strain) and mutant strains MEI028 (rough, O-antigen(-)) and MEI012 [smooth (O-antigen(+)95%), immunomagnetically isolated NK cell preparations. Incubation of PBMC with each and every one of the S. typhi strains studied consistently and significantly, increased this cellular immune function, as well as the supernatant level of the various cytokines tested e.g. IFN-gamma, TNF-alpha, IL-10 and IL-12 (ELISA). In similar experiments, a significant increase in the cytolytic activity of HPNK cells was elicited by S. typhi Ty2 but not by mutant strain MEI028; neither of the cytokines assayed (IFN-gamma and TNF-alpha) was detected in the supernatant. Our results suggest that S. typhi O-antigen plays an essential role in a mechanism resulting in the direct activation of NK cell activity in HPNK cell preparations. However, the relative quantitative significance of this antigen in the direct stimulation of NK cell cytotoxicity expression in PBMC samples is less clear, as it appears that in this case bacterial-induced monocyte-released cytokines plays a most important role. Incubation with S. typhi Ty2 or MEI028 elicited significant expression of CD69, an early marker of NK cell activation, in PBMC but not in HPNK cell samples (flow cytometry); in similar experiments, the expression of CD16/56 and activation marker CD25 remained essentially unchanged.

Novel therapeutic approach by culture filtrate of Cryptococcus neoformans var. gattii (CneF) in experimental immune complex glomerulonephritis

The present study was undertaken to determine the therapeutic effect of the culture filtrate of Cryptococcus neoformans var. gattii (CneF) in experimental immune complex glomerulonephritis. Bovine serum albumin (BSA) nephritis was induced in rats by a subcutaneous immunization and daily intravenous administration of BSA. CneF solution at three different doses (36, 54, and 90 mg/kg based on carbohydrate concentration) was administered intraperitoneally at regular 72-h intervals for 4 weeks. Onset of treatment was day 65, and urinary protein was measured at different intervals. Animals were euthanized on day 107. Serum and urine determinants were measured at the time of sacrifice and kidney specimens were examined. Results of this experiment showed that CneF therapy could significantly reduce the urinary protein excretion, blood urea nitrogen (BUN), plasma concentration of triglyceride, and increase the serum HDL cholesterol in treated rats vs. nontreated controls. Moreover, there was significant difference in glomerular changes between treated and nontreated groups. These observations show that the beneficial effect of CneF may be related to decreased number of glomerular leukocytes. Our findings suggest that treatment with CneF as a new antiinflammatory compound can reduce proteinuria, suppress the development of glomerular lesions, and exert lipid-lowering property in a rat model of immune complex glomerulonephritis.