Role of TNF-alpha in the induction of fungicidal activity of mouse peritoneal exudate cells against Cryptococcus neoformans by IL-12 and IL-18

Is the production of reactive oxygen and nitrogen species by macrophages associated with better infectious control in female mice with experimentally disseminated and pulmonary mucormycosis?

Different levels of resistance against Rhizopus oryzae infection have been observed between inbred (BALB/c) and outbred (Swiss) mice and are associated with the genetic background of each mouse strain. Considering that macrophages play an important role in host resistance to Rhizopus species, we used different infectious outcomes observed in experimental mucormycosis to identify the most efficient macrophage response pattern against R. oryzae in vitro and in vivo. For this, we compared BALB/c and Swiss macrophage activity before and after intravenous or intratracheal R. oryzae infections. The production of hydrogen peroxide (H2O2) and nitric oxide (NO) was determined in cultures of peritoneal (PMΦ) or alveolar macrophages (AMΦ) challenged with heat-killed spores of R. oryzae. The levels of tumor necrosis factor-alpha (TNF-α) and interleukin-10 (IL-10) were measured to confirm our findings. Naïve PMΦ from female BALB/c mice showed increased production of H2O2, TNF-α, and IL-10 in the presence of heat-killed spores of R. oryzae. Naïve PMΦ from female Swiss mice were less responsive. Naïve AMΦ from the two strains of female mice were less reactive to heat-killed spores of R. oryzae than PMΦ. After 30 days of R. oryzae intravenous infection, lower fungal load in spleen from BALB/c mice was accompanied by higher production of H2O2 by PMΦ compared with Swiss mice. In contrast, AMΦ from BALB/c mice showed higher production of NO, TNF-α, and IL-10 after 7 days of intratracheal infection. The collective findings reveal that, independent of the female mouse strain, PMΦ is more reactive against R. oryzae upon first contact than AMΦ. In addition, increased PMΦ production of H2O2 at the end of disseminated infection is accompanied by better fungal clearance in resistant (BALB/c) mice. Our findings further the understanding of the parasite-host relationship in mucormycosis.

Early production of proinflammatory cytokines in response to Scedosporium apiospermum during murine pulmonary infection

Scedosporium apiospermum is an opportunistic pathogen that can cause pulmonary infections in both immunosuppressive and immunocompetent patients. Cytokines are molecules that mediate the immune response to promote or eliminate fungal infections. In this work, we evaluated the cytokines profile in the lung and serum of mice infected with Scedosporium apiospermum. We found early production of IL-6, IL-1β and TNF-α cytokines in the lung of infected mice during the first 5 days of infection. We suggest that release of pro-inflammatory cytokines could play a role in the control of fungal invasion.

IL-9 plays a protective role on host defense against the infection of Cryptococcus Neoformans

Cryptococcus neoformans is an opportunistic fungal pathogen that causes neurological disease in immunocompromised patients. Preliminary experiments showed that cryptococcal strains could induce the expression of interleukin-9 (IL-9). The use of a neutralizing antibody against IL-9 decreased the survival rates of mice in a murine model. In this study, we found that in vitro, IL-9 could enhance the phagocytic function of M1 macrophages and promote the killing of extracellular pathogens by had no effect on the killing of invading pathogens. IL-9 could also promote the expression of IL-6 while suppressing the expression of TNF-α in M1 macrophages. In vivo, IL-9 reduced the colony-forming units (CFUs) in the brain and liver, but there were no differences in the lung. Furthermore, the weight of mice in the IL-9 group decreased slower than that of mice in the phosphate-buffered saline (PBS) group after infection. Moreover, IL-9 could enhance the survival rate at 21 days. The results also showed that IL-9 could promote the secretion of IL-17 while blocking the secretion of IL-4. Therefore, we concluded that IL-9 plays a protective role in C. neoformans infection.

Role of Dectin-2 in the phagocytosis of Cryptococcus neoformans by dendritic cells

The cell walls and capsules of Cryptococcus neoformans, a yeast-type fungal pathogen, are rich in polysaccharides. Dectin-2 is a C-type lectin receptor (CLR) that recognizes high-mannose polysaccharides. Previously, we demonstrated that Dectin-2 is involved in cytokine production by bone marrow-derived dendritic cells (BM-DCs) in response to stimulation with C. neoformans. In the present study, we analyzed the role of Dectin-2 in the phagocytosis of C. neoformans by BM-DCs. The engulfment of this fungus by BM-DCs was significantly decreased in mice lacking Dectin-2 (Dectin-2KO) or caspase recruitment domain-containing protein 9 (CARD9KO), a common adapter molecule that delivers signals triggered by CLRs, compared to wild-type (WT) mice. Phagocytosis was likewise inhibited, to a similar degree, by the inhibition of Syk, a signaling molecule involved in CLR-triggered activation. A PI3K inhibitor, in contrast, completely abrogated the phagocytosis of C. neoformans. Actin polymerization, i.e., conformational changes in cytoskeletons detected at sites of contact with C. neoformans, was also decreased in BM-DCs of Dectin-2KO and CARD9KO mice. Finally, the engulfment of C. neoformans by macrophages was significantly decreased in the lungs of Dectin-2KO mice compared to WT mice. These results suggest that Dectin-2 may play an important role in the actin polymerization and phagocytosis of C. neoformans by DCs, possibly through signaling via CARD9 and a signaling pathway mediated by Syk and PI3K.

The Host Immune Response to Scedosporium/Lomentospora

Infections caused by the opportunistic pathogens Scedosporium/Lomentospora are on the rise. This causes problems in the clinic due to the difficulty in diagnosing and treating them. This review collates information published on immune response against these fungi, since an understanding of the mechanisms involved is of great interest in developing more effective strategies against them. Scedosporium/Lomentospora cell wall components, including peptidorhamnomannans (PRMs), α-glucans and glucosylceramides, are important immune response activators following their recognition by TLR2, TLR4 and Dectin-1 and through receptors that are yet unknown. After recognition, cytokine synthesis and antifungal activity of different phagocytes and epithelial cells is species-specific, highlighting the poor response by microglial cells against L. prolificans. Moreover, a great number of Scedosporium/Lomentospora antigens have been identified, most notably catalase, PRM and Hsp70 for their potential medical applicability. Against host immune response, these fungi contain evasion mechanisms, inducing host non-protective response, masking fungal molecular patterns, destructing host defense proteins and decreasing oxidative killing. In conclusion, although many advances have been made, many aspects remain to be elucidated and more research is necessary to shed light on the immune response to Scedosporium/Lomentospora.

Production of IL-17A at Innate Immune Phase Leads to Decreased Th1 Immune Response and Attenuated Host Defense against Infection with Cryptococcus deneoformans

IL-17A is a proinflammatory cytokine produced by many types of innate immune cells and Th17 cells and is involved in the elimination of extracellularly growing microorganisms, yet the role of this cytokine in the host defense against intracellularly growing microorganisms is not well known. Cryptococcus deneoformans is an opportunistic intracellular growth fungal pathogen that frequently causes fatal meningoencephalitis in patients with impaired immune responses. In the current study, we analyzed the role of IL-17A in the host defense against C. deneoformans infection. IL-17A was quickly produced by γδT cells at an innate immune phase in infected lungs. In IL-17A gene-disrupted mice, clearance of this fungal pathogen and the host immune response mediated by Th1 cells were significantly accelerated in infected lungs compared with wild-type mice. Similarly, killing of this fungus and production of inducible NO synthase and TNF-α were significantly enhanced in IL-17A gene-disrupted mice. In addition, elimination of this fungal pathogen, Th1 response, and expression of IL-12Rβ2 and IFN-γ in NK and NKT cells were significantly suppressed by treatment with rIL-17A. The production of IL-12p40 and TNF-α from bone marrow-derived dendritic cells stimulated with C. deneoformans was significantly suppressed by rIL-17A. In addition, rIL-17A attenuated Th1 cell differentiation in splenocytes from transgenic mice highly expressing TCR for mannoprotein 98, a cryptococcal Ag, upon stimulation with recombinant mannoprotein 98. These data suggest that IL-17A may be involved in the negative regulation of the local host defense against C. deneoformans infection through suppression of the Th1 response.

Macrolides Inhibit Capsule Formation of Highly Virulent Cryptococcus gattii and Promote Innate Immune Susceptibility

Cryptococcus gattii is a fungal pathogen, endemic in tropical and subtropical regions, the west coast of Canada, and the United States, that causes a potentially fatal infection in otherwise healthy individuals. Because the cryptococcal polysaccharide capsule is a leading virulence factor due to its resistance against innate immunity, the inhibition of capsule formation may be a promising new therapeutic strategy for C. gattii Macrolides have numerous nonantibiotic effects, including immunomodulation of mammalian cells and suppression of bacterial (but not fungal) pathogenicity. Thus, we hypothesized that a macrolide would inhibit cryptococcal capsule formation and improve the host immune response. Coincubation with clarithromycin (CAM) and azithromycin significantly reduced the capsule thickness and the amount of capsular polysaccharide of both C. gattii and C. neoformans CAM-treated C. gattii cells were significantly more susceptible to H₂O₂ oxidative stress and opsonophagocytic killing by murine neutrophils. In addition, more C. gattii cells were phagocytosed by murine macrophages, resulting in increased production of tumor necrosis factor alpha (TNF-α) by CAM exposure. After CAM exposure, dephosphorylation of Hog1, one of the mitogen-activated protein kinase (MAPK) signaling pathways of Cryptococcus, was observed in Western blot analysis. In addition, CAM exposure significantly reduced the mRNA expression of LAC1 and LAC2 (such mRNA expression is associated with cell wall integrity and melanin production). These results suggest that CAM may aid in inhibiting capsular formation via the MAPK signaling pathway and by suppressing virulent genes; thus, it may be a useful adjunctive agent for treatment of refractory C. gattii infection.

Innate Immunity Acts as the Major Regulator in Talaromyces marneffei Coinfected AIDS Patients: Cytokine Profile Surveillance During Initial 6-Month Antifungal Therapy

Background

Talaromycosis caused by Talaromyces marneffei infection is a fatal systemic mycosis in immunosuppressed individuals, such as patients with AIDS. Cytokines and immunocytes play a central role against fungus infection. However, how the host immune system responds to infection and treatment has not been reported to date.

Methods

Forty-one Talaromyces marneffei coinfected AIDS patients were followed up, their immunocytes and cytokine profiles were obtained at different antifungal treatment stages, and data on clinical features and laboratory examinations were collected. Correlation analysis was used to identify factors associated with host immunity against Talaromyces marneffei infection in AIDS patients.

Results

Common diseases and conditions of these 41 patients were lymphadenopathy, hepatomegaly, and splenomegaly. CD4⁺ T cells were extremely low in all of them. Moreover, significant increases of proinflammatory cytokines (IL-12, IL-17A, TNF-α, IFN-γ, IL-18, and IL-1β), anti-inflammatory cytokines (IL-10), and chemokines (IP-10) were observed in talaromycosis before treatment (P < .05), comparing to both AIDS patients and healthy controls. The cytokines IL-6, IL-8, TNF-α, IL-18, IL-17A, IL-7, IP-10, and IL-1β reached peak levels 3 days after initial antifungal therapy, and then gradually decreased. The symptoms of the patients gradually decreased. Furthermore, patients who died showed the highest levels of IL-6, TNF-α, IL-8, IL-1β, and IP-10, which were 1.4- to 164-fold higher than in surviving patients.

Conclusions

Our findings indicate that innate immune-cell-derived cytokines are critical for host defense against AIDS-associated Talaromyces marneffei infection; furthermore, excessive inflammatory cytokines are associated with poor outcomes.

The war on cryptococcosis: A Review of the antifungal arsenal

Cryptococcal meningitis is the most common central nervous system infection in the world today. It occurs primarily, but not exclusively, in immunocompromised individuals and despite substantial improvement in management of clinical events like AIDS, the numbers of cases of cryptococcosis remain very high. Unfortunately, despite several antifungal agents available for treatment, morbidity and mortality rates remain high with this fungal infection. In this Review, we will describe the treatments and strategies for success, identify the failures, and provide insights into the future developments / improvements for management. This sugar-coated yeast can play havoc within the human brain. Our goals must be to either prevent or diagnose disease early and treat aggressively with all our clinical tools when disease is detected.

Role of dendritic cell-pathogen interactions in the immune response to pulmonary cryptococcal infection

This review discusses the unique contributions of dendritic cells (DCs) to T-cell priming and the generation of effective host defenses against Cryptococcus neoformans (C.neo) infection. We highlight DC subsets involved in the early and later stages of anticryptococcal immune responses, interactions between C.neo pathogen-associated molecular patterns and pattern recognition receptors expressed by DC, and the influence of DC on adaptive immunity. We emphasize recent studies in mouse models of cryptococcosis that illustrate the importance of DC-derived cytokines and costimulatory molecules and the potential role of DC epigenetic modifications that support maintenance of these signals throughout the immune response to C.neo. Lastly, we stipulate where these advances can be developed into new, immune-based therapeutics for treatment of this global pathogen.

Proinflammatory cytokine response and viral replication in mouse bone marrow derived macrophages infected with influenza H1N1 and H5N1 viruses

The pathogenesis of human influenza H5N1 virus infection remains poorly understood and controversial. Cytokine dysregulation in human infection has been hypothesized to contribute to disease severity. We developed in vitro cultures of mouse bone marrow derived macrophages (BMDMΦ) from C57BL/6N mouse to compare influenza A (H5N1 and H1N1) virus replication and pro-inflammatory cytokine and chemokine responses. While both H1N1 and H5N1 viruses infected the mouse bone marrow derived macrophages, only the H1N1 virus had showed evidence of productive viral replication from the infected cells. In comparison with human seasonal influenza H1N1 (A/HK/54/98) and mouse adapted influenza H1N1 (A/WSN/33) viruses, the highly pathogenic influenza H5N1 virus (A/HK/483/97) was a more potent inducer of the chemokine, CXCL 10 (IP-10), while there was not a clear differential TNF-α protein expression pattern. Although human influenza viruses rarely cause infection in mice without prior adaption, the use of in vitro cell cultures of primary mouse cells is of interest, especially given the availability of gene-defective (knock-out) mice for specific genes.

Cytokine milieu in renal cavities of immunocompetent mice in response to intravenous challenge of Aspergillus flavus leading to aspergillosis

Investigations in mice have demonstrated that Aspergillus flavus is more virulent than all other Aspergillus species except A. tamari. However, there is a complete lack of information on the immune responses elicited by A. flavus in systemic model. This communication reports the progression of infection and cytokine profile in BALB/c mice in response to intravenous challenge of A. flavus. The pathogenesis of infection was evaluated morphologically and by the analysis of Colony Forming Units (CFUs) in kidney homogenates. The kinetics of regulated cytokines was determined in kidneys by cytokine-specific murine ELISA. During the initial phase of infection the rate of clearance of A. flavus was high, most likely through recruited neutrophils and the resident renal macrophages with concurrent significant release of pro-inflammatory cytokines (IFN-γ, TNF-α, IL-12/IL-23p40, IL-6) indicating antifungal innate immune response to be active at the site. However, at 24h PI there was a significant rise of IL-17 and IL-23 suggesting the activation of IL-17/IL-23 axis of inflammation resulting in rise of CFU. The lack of significant induction in the anti-inflammatory cytokines like IL-4 and IL-10 confirmed the absence of Th2 type of response. In the late phase, after 3days post-infection, there was a rise in the number of pathogen in the kidneys as determined by histopathology and CFU counts. The A. flavus hyphae were evident in the renal pelvis and ureter and we propose the production of blastoconidia by metamorphosed hyphae.

Immunotherapy of Cryptococcus infections

Despite appropriate antifungal treatment, the management of cryptococcal disease remains challenging, especially in immunocompromised patients, such as human immunodeficiency virus-infected individuals and solid organ transplant recipients. During the past two decades, our knowledge of host immune responses against Cryptococcus spp. has been greatly advanced, and the role of immunomodulation in augmenting the response to infection has been investigated. In particular, the role of 'protective' Th1 (tumour necrosis factor-α, interferon (IFN)-γ, interleukin (IL)-12, and IL-18) and Th17 (IL-23 and IL-17) and 'non-protective' Th2 (IL-4, IL-10, and IL-13) cytokines has been extensively studied in vitro and in animal models of cryptococcal infection. Immunomodulation with monoclonal antibodies against the capsular polysaccharide glucuronoxylomannan, glucosylceramides, melanin and β-glucan and, lately, with radioimmunotherapy has also yielded promising results in animal models. As a balance between sufficiently protective Th1 responses and excessive inflammation is important for optimal outcome, the effect of immunotherapy may range from beneficial to deleterious, depending on factors related to the host, the infecting organism, and the immunomodulatory regimen. Clinical evidence supporting immunomodulation in patients with cryptococcal infection remains too limited to allow firm recommendations. Limited human data suggest a role for IFN-γ. Identification of surrogate markers characterizing patients' immunological status could possibly suggest candidate patients for immunotherapy and the type of immunomodulation to be administered.

Th1 and Th2 cytokines in a self-healing primary pulmonary Aspergillus flavus infection in BALB/c mice

Studies with non-immunocompromised mice have demonstrated that Aspergillus flavus is more virulent than almost all other Aspergillus species. However, the type of immune response this fungus induces in mammals has not been investigated thoroughly. The study was carried out to analyze the sequential pathogenesis of pulmonary A. flavus infection and the role of cytokines in host response in BALB/c mice. Two distinct phases were observed in mice: First, an intense rate of clearance of A. flavus occurred, most likely through recruited neutrophils and the resident alveolar macrophages with concurrent release of pro-inflammatory cytokines and second, fungal and cellular debris were cleaned by recruited monocytes, pro-inflammatory cytokine production rapidly decreased and infection self-healed. The pro-inflammatory cytokine IFN-γ demonstrated an upward trend up to 24h PI followed by a steady decline. The titers of TNF-α (a pro-inflammatory Th1 cytokine) were, however, inversely related to the titers of IL-10 an anti-inflammatory Th2 cytokine. The anti-inflammatory cytokine IL-4 showed slightly decreasing trend between 12 and 48 h PI, beyond that it again reached to the titers observed at 6h PI. The infected mice produced signs of Th1 type response with self healing capabilities.

Extracellular vesicles from Cryptococcus neoformans modulate macrophage functions

Cryptococcus neoformans and distantly related fungal species release extracellular vesicles that traverse the cell wall and contain a varied assortment of components, some of which have been associated with virulence. Previous studies have suggested that these extracellular vesicles are produced in vitro and during animal infection, but the role of vesicular secretion during the interaction of fungi with host cells remains unknown. In this report, we demonstrate by fluorescence microscopy that mammalian macrophages can incorporate extracellular vesicles produced by C. neoformans. Incubation of cryptococcal vesicles with murine macrophages resulted in increased levels of extracellular tumor necrosis factor alpha (TNF-alpha), interleukin-10 (IL-10), and transforming growth factor beta (TGF-beta). Vesicle preparations also resulted in a dose-dependent stimulation of nitric oxide production by phagocytes, suggesting that vesicle components stimulate macrophages to produce antimicrobial compounds. Treated macrophages were more effective at killing C. neoformans yeast. Our results indicate that the extracellular vesicles of C. neoformans can stimulate macrophage function, apparently activating these phagocytic cells to enhance their antimicrobial activity. These results establish that cryptococcal vesicles are biologically active.

Differential activation of peritoneal cells by subcutaneous treatment of rats with cryptococcal antigens

Previous studies in our laboratory have shown that the subcutaneous pretreatment of rats with heat-killed cells (HKC) of Cryptococcus neoformans emulsified in complete Freund adjuvant (CFA) promotes protective immunity against an intraperitoneal challenge with C. neoformans. In contrast, subcutaneous treatment with the capsular polysaccharide (PSC) emulsified in CFA exacerbates the cryptococcal infection. The purpose of this study was to analyze the mechanisms involved in these phenomena. Adherent peritoneal cells from rats treated with HKC-CFA showed upregulated ED2, CD80, and CD86 expression; an increase in the level of production of anticryptococcal metabolites; and the enhanced production of interleukin-12 (IL-12) in comparison with the findings for cells from rats treated with CFA-phosphate-buffered saline (PBS). Adherent peritoneal cells from rats treated with PSC-CFA, however, also presented upregulated ED2, CD80, and CD86 expression compared to the level of expression for peritoneal cells from controls, but these cells showed an increase in arginase activity and decreased levels of production of IL-12 and tumor necrosis factor (TNF) compared with the activity and levels of production by peritoneal cells from CFA-PBS-treated rats. In addition, treatment with HKC-CFA resulted in a rise in the phagocytic and anticryptococcal activities of adherent peritoneal cells compared to those for control rats. However, adherent peritoneal cells from rats treated with PSC-CFA presented a reduction in anticryptococcal activity in comparison with that for cells from animals treated with CFA-PBS. These results show the differential activation between adherent peritoneal cells from HKC-CFA- and PSC-CFA-treated rats, with this differential activation at the primary site of infection possibly being responsible, at least in part, for the phenomena of protection and exacerbation observed in our model.

Cryptococcus neoformans activates bone marrow-derived conventional dendritic cells rather than plasmacytoid dendritic cells and down-regulates macrophages

Induction of IL-12 and IL-23 is essential for protective immunity against Cryptococcusneoformans. The contribution of dendritic cells vs. macrophages to IL-12/23 production in response to C. neoformans infection is unclear. Activation of conventional bone marrow-derived dendritic cells (BMDC), plasmacytoid BMDC, and bone marrow-derived macrophages (BMMPhi) was assessed by analyzing cytokine responses and the expression of MHC-II, CD86, and CD80 in each cell type. Cryptococcus neoformans induced the release of IL-12/23p40 by BMDC, but not by BMMPhi, in a TLR2- and TLR4-independent but MyD88-dependent manner. Conventional BMDC rather than plasmacytoid BMDC up-regulated MHC-II and CD86, while BMMPhi down-regulated MHC-II and CD86 in response to C. neoformans. The up-regulation of MHC-II and CD86 on BMDC required MyD88. Our data point to conventional DC as critical IL-12/23-producing antigen-presenting cells during cryptococcosis.

Phenotypic switching in Cryptococcus neoformans contributes to virulence by changing the immunological host response

Cryptococcus neoformans is an encapsulated opportunistic organism that can undergo phenotypic switching. In this process, the parent smooth colony (SM) switches to a more virulent mucoid colony (MC) variant. The host responses mounted against the SM and MC variants differ, and lower tissue interleukin 10 (IL-10) levels are consistently observed in lungs of MC-infected C57BL/6 and BALB/c mice. This suggested different roles of this cytokine in SM and MC infections. The objective of this study was to compare survival rates and characterize the host responses of SM- and MC-infected IL-10-depleted (IL-10(-/-)) mice, which exhibit a Th1-polarized immune response and are considered resistant hosts. As expected, SM-infected IL-10(-/-) mice survived longer than wild-type mice, whereas MC-infected IL-10(-/-) mice did not exhibit a survival benefit. Consistent with this observation, we demonstrated marked differences in the inflammatory responses of SM- and MC-infected IL-10(-/-) and wild-type mice. This included a more Th1-polarized inflammatory response with enhanced recruitment of macrophages and natural killer and CD8 cells in MC- than in SM-infected IL-10(-/-) and wild-type mice. In contrast, both SM-infected IL-10(-/-) and wild-type mice exhibited higher recruitment of CD4 cells, consistent with enhanced survival and differences in recruitment and Th1/Th2 polarization. Lung tissue levels of IL-21, IL-6, IL-4, transforming growth factor beta, IL-12, and gamma interferon were higher in MC-infected IL-10(-/-) and wild-type mice than in SM-infected mice, whereas tumor necrosis factor alpha levels were higher in SM-infected IL-10(-/-) mice. In conclusion, the MC variant elicits an excessive inflammatory response in a Th1-polarized host environment, and therefore, the outcome is negatively affected by the absence of IL-10.

Killing of Paracoccidioides brasiliensis yeast cells by IFN-gamma and TNF-alpha activated murine peritoneal macrophages: evidence of H(2)O (2) and NO effector mechanisms

Paracoccidioidomycosis is a deep mycosis, endemic in Latin America, caused by Paracoccidioides brasiliensis. Macrophage activation by cytokines is the major effector mechanism against this fungus. This work aimed at a better understanding of the interaction between yeast cells-murine peritoneal macrophages and the cytokine signals required for the effective killing of high virulence yeast-form of P. brasiliensis. In addition, the killing effector mechanisms dependent on the generation of reactive oxygen or nitrogen intermediates were investigated. Cell preincubation with IFN-gamma or TNF-alpha, at adequate doses, resulted in effective yeast killing as demonstrated in short-term (4-h) assays. Both, IFN-gamma and TNF-alpha activation were associated with higher levels of H(2)O(2) and NO when compared to nonactivation. Treatment with catalase (CAT), a H(2)O(2 )scavenger, and N(G)-monomethyl-L: -arginine (L: -NMMA), a nitric oxide synthase inhibitor, reverted the killing effect of activated cells. Taken together, these results suggest that both oxygen and L: -arginine-nitric oxide pathways play a role in the killing of highly virulent P. brasiliensis.

Role of endogenous IFN-gamma in macrophage programming induced by IL-12 and IL-18

Besides the established role of interleukin-12 (IL-12) and IL-18 on interferon-gamma (IFN-gamma) production by natural killer (NK), T, and B cells, the effects of these cytokines on macrophages are largely unknown. Here, we investigated the role of IL-12/IL-18 on nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) production by CD11b(+) adherent peritoneal cells, focusing on the involvement of endogenously produced IFN-gamma. C57BL/6 cells released substantial amounts of NO when stimulated with IFN-gamma or lipopolysaccharide (LPS), but failed to respond to IL-12 or IL-18 or both. However, IL-12/IL-18 pretreatment was able to program these cells to release 6-8-fold more NO and TNF-alpha in response to LPS or Trypanosoma cruzi stimulation, with NO levels directly correlating with macrophage resistance to intracellular parasite growth. Analysis of IL-12/IL-18-primed cells from mice deficient in IFN-gamma, IFNGR, and IFN regulatory factor-1 (IRF-1) revealed that these molecules were essential for LPS-induced NO release, but TNF-alpha production was IFN-gamma independent. Conversely, the myeloid differentiation factor 88 (MyD88)-dependent pathway was indispensable for IL-12/IL-18-programmed LPS-induced TNF-alpha production, but not for NO release. Contaminant T and NK cells largely modulated the IL-12/IL-18 programming of LPS-induced NO response through IFN-gamma secretion. Nevertheless, a small population of IFN-gamma(+) cells with a macrophage phenotype was also identified, particularly in the peritoneum of chronically T. cruzi-infected mice, reinforcing the notion that macrophages can be an alternative source of IFN-gamma. Taken together, our data contribute to elucidate the molecular basis of the IL-12/IL-18 autocrine pathway of macrophage activation, showing that endogenous IFN-gamma plays an important role in programming the NO response, whereas the TNF-alpha response occurs through an IFN-gamma-independent pathway.

Role of granulocyte macrophage colony-stimulating factor in host defense against pulmonary Cryptococcus neoformans infection during murine allergic bronchopulmonary mycosis

We investigated the role of granulocyte macrophage colony-stimulating factor (GM-CSF) in host defense in a murine model of pulmonary cryptococcosis induced by intratracheal inoculation of Cryptococcus neoformans. Pulmonary C. neoformans infection of C57BL/6 mice is an established model of an allergic bronchopulmonary mycosis. Our objective was to determine whether GM-CSF regulates the pulmonary Th2 immune response in C. neoformans-infected C57BL/6 mice. Long-term pulmonary fungistasis was lost in GM-CSF knockout (GM(-/-)) mice, resulting in increased pulmonary burden of fungi between weeks 3 and 5. GM-CSF was required for the early influx of macrophages and CD4 and CD8 T cells into the lungs but was not required later in the infection. Lack of GM-CSF also resulted in reduced eosinophil recruitment and delayed recruitment of mononuclear cells into the airspace. Macrophages from GM(+/+) mice showed numerous hallmarks of alternatively activated macrophages: higher numbers of intracellular cryptococci, YM1 crystals, and induction of CCL17. These hallmarks are absent in macrophages from GM(-/-) mice. Mucus-producing goblet cells were abundantly present within the bronchial epithelial layer in GM(+/+) mice but not in GM(-/-) mice at week 5 after infection. Production of both Th1 and Th2 cytokines was impaired in the absence of GM-CSF, consistent with both reduced C. neoformans clearance and absence of allergic lung pathology.

Pulmonary adverse events of anti-tumor necrosis factor-alpha antibody therapy

It is well established that anti-tumor necrosis factor-alpha (TNFalpha) antibody is an efficacious disease-modifying drug for rheumatoid arthritis and Crohn's disease. Unfortunately, its long-term use can be associated with ominous pulmonary adverse events, most notably mycobacterial and fungal lung infections. To this end, reactivation of latent tuberculosis infection represents a serious concern of anti-TNFalpha antibody therapy. Given the anticipated increase in the approved indications for these drugs, community-based physicians should be made aware of these events for implementation of better patient selection for anti-TNFalpha antibody therapy and initiation of appropriate measures once these adverse events are observed. This review will address this issue by outlining: 1) the role of TNFalpha in host inflammatory response to injury, particularly during mycobacterial and fungal infections; 2) the salutary effects of anti-TNFalpha antibody therapy in human diseases; and 3) the ominous pulmonary adverse events associated with these drugs.

Cytokines and fungal infections

The very poor outcome of invasive fungal infections (IFI) in patients with haematological malignancies or recipients of haematopoietic stem cell transplantation is largely attributed to their compromised host defence mechanisms. The restoration or augmentation of immune responses in these patients is now considered as one of the cornerstones of effective antifungal therapy. Major advances in the field of experimental immunology have provided insight on the important regulatory role of cytokines in both innate and adaptive immunity to fungal pathogens. Preclinical studies have convincingly demonstrated that immunomodulation with cytokines can enhance the antifungal activity of neutrophils and monocytes/macrophages as well as upregulate protective T-helper type 1 adaptive immune responses. Evidence on the clinical use of cytokines in immunocompromised hosts with IFI is, however, still scant and inconclusive. The present review summarizes experimental and clinical data on the role of cytokines in the immune response to fungal pathogens and on their potential use for prevention or treatment of fungal infections. Implications for future research are also briefly discussed.

Distinct roles for IL-4 and IL-10 in regulating T2 immunity during allergic bronchopulmonary mycosis

Pulmonary Cryptococcus neoformans infection of C57BL/6 mice is an established model of an allergic bronchopulmonary mycosis that has also been used to test a number of immunomodulatory agents. Our objective was to determine the role of IL-4 and IL-10 in the development/manifestation of the T2 response to C. neoformans in the lungs and lung-associated lymph nodes. In contrast to wild-type (WT) mice, which develop a chronic infection, pulmonary clearance was significantly greater in IL-4 knockout (KO) and IL-10 KO mice but was not due to an up-regulation of a non-T cell effector mechanism. Pulmonary eosinophilia was absent in both IL-4 KO and IL-10 KO mice compared with WT mice. The production of IL-4, IL-5, and IL-13 by lung leukocytes from IL-4 KO and IL-10 KO mice was lower but IFN-gamma levels remained the same. TNF-alpha and IL-12 production by lung leukocytes was up-regulated in IL-10 KO but not IL-4 KO mice. Overall, IL-4 KO mice did not develop the systemic (lung-associated lymph nodes and serum) or local (lungs) T2 responses characteristic of the allergic bronchopulmonary C. neoformans infection. In contrast, the systemic T2 elements of the response remained unaltered in IL-10 KO mice whereas the T2 response in the lungs failed to develop indicating that the action of IL-10 in T cell regulation was distinct from that of IL-4. Thus, although IL-10 has been reported to down-regulate pulmonary T2 responses to isolated fungal Ags, IL-10 can augment pulmonary T2 responses if they occur in the context of fungal infection.

Proinflammatory Cytokines in the Treatment of Bacterial and Fungal Infections

Mortality due to severe bacterial infections has not been markedly effected by the introduction of new antimicrobial drugs over the last 30-40 years. This has emphasized the need for development of new therapeutic strategies to combat sepsis. The outcome of an infection depends on two factors: the growth of the microorganisms (including the effect of antibacterial drugs), and the host's defensive response to the invading organism. It is known that injection of bacterial products into experimental animals leads to enhanced nonspecific resistance to a variety of microorganisms. The discovery of the specific mediators responsible for modulation of host defense has created new possibilities for the development of alternative treatment strategies. Molecules such as interleukins, interferons, tumor necrosis factors and hematopoietic growth factors have become available in recombinant form, and their therapeutic potential in various infectious diseases has been tested in various experimental models of infections. Initial data in various patient groups indicate that adjunctive therapy with recombinant proinflammatory cytokines may have beneficial effects in the treatment of bacterial and fungal infections.

Pulmonary cryptococcosis after initiation of anti-tumor necrosis factor-alpha therapy

Many patients with rheumatoid arthritis are being treated with immunosuppressive regimens that include an agent directed at blocking tumor necrosis factor (TNF)-alpha. Although reportedly safe, tuberculous and fungal infections have emerged as significant complications of therapy. We report a case of pulmonary cryptococcosis soon after the initiation of therapy with the anti-TNF-alpha antibody, infliximab. A diagnosis was made early in the disease course, and the patient responded quickly to antifungal therapy. This case should alert clinicians to the increased incidence of pulmonary mycoses in patients receiving anti-TNF-alpha therapy.

Is there a common mechanism of gastrointestinal nematode expulsion?

Parasitic gastrointestinal (GI) nematodes are one of the most commonly acquired infections in the world. Although they cause relatively little mortality, infections result in high levels of morbidity that can result in developmental consequences in infected children and cause significant economic loss in infected animals. Over the last 30 years there has been extensive research into the mechanisms controlling the expulsion of gastrointestinal nematodes. Although many of the effector mechanisms that contribute to the loss of the parasite have been defined, we still appear to be some way from understanding the actual cause of parasite loss. Part of this stems from the different responses induced by different gastrointestinal parasites. It is clear that a Th2 response is essential for the expulsion of GI helminths; however, each of the characteristic immunological effector mechanisms induced following infection with these parasites may not be required or may be insufficient in isolation, but together they operate to expel GI helminths. These responses then succeed more efficiently in some cases than in others to induce parasite expulsion. The contribution made by various effector mechanisms to the expulsion of these parasites may therefore be a reflection of both the niche which the parasite inhabits as well as possible evasive/suppressive mechanisms employed by the parasites. In this review the various aspects of parasite expulsion will be described and the controversial issues in the field will be discussed.

Imiquimod, a topical immune response modifier, in the treatment of cutaneous metastases of malignant melanoma

BACKGROUND

Imiquimod 5% cream (Aldara, a novel topical immune response modifier, has been approved for the topical treatment of anogenital HPV-induced warts. In addition, several studies have demonstrated antitumoral activity in solar keratoses, superficial basal cell carcinomas and Bowen's disease.

AIM

Given the convincing therapeutic results of imiquimod when used for treating selected types of epithelial skin cancer, we became interested to study imiquimod as an adjuvant for treating cutaneous metastases of malignant melanoma.

METHODS

Three patients with multiple, i.e. more than 15, cutaneous in-transit metastases of malignant melanoma in unilateral localization on the leg were treated topically with imiquimod 5% cream.

RESULTS

Twice daily application under occlusive conditions for a period of 21-28 weeks resulted in >90% regression of cutaneous metastases in 2 patients. The third patient showed marked response only when topical imiquimod was intermittently supplemented by intralesional interleukin (IL)-2 for 2 weeks. Unwanted side effects were mild in all patients.

CONCLUSION

Overall, imiquimod as a single agent or in combination with intralesional IL-2 may be a promising immunomodulatory compound for the adjuvant topical treatment of patients with multiple cutaneous metastases of malignant melanoma.

Interleukin-18 induces acute biphasic reduction in the levels of circulating leukocytes in mice

We investigated the acute hematological changes caused by interleukin-18 (IL-18) in mice. Intraperitoneal administration of IL-18 (2 microg/mouse) resulted in biphasic decreases in the number of leukocytes in the blood. The first phase of decrease occurred within 2 h of IL-18 administration and was followed by a transient increase at 5 h. The second phase of decrease occurred at around 6 h, reaching a nadir which lasted for more than 24 h. In mice deficient in inducible nitric oxide (NO) synthase, the first phase of reduction of leukocytes did not occur although the second phase of decrease was observed. In mice deficient in gamma interferon (IFN-gamma) or in mice depleted of natural killer cells and incapable of producing IFN-gamma, IL-18 had no effect on the number of circulating leukocytes. Levels of nitrite and/or nitrate in the serum were elevated within 2 h after administration of IL-18, reaching a peak at 4 h and then decreasing gradually to the basal level over a 24-h period of time. On the other hand, serum IFN-gamma levels changed in a biphasic manner, reaching a peak at 2 h after IL-18 administration, followed by a decrease in the basal level and a second increase at 6 h. Levels of IL-18 receptor mRNAs also showed biphasic changes in correlation with the changes in serum IFN-gamma levels. These results suggest that the changes in the leukocyte number following IL-18 administration are mediated by NO and IFN-gamma, with NO being involved in the first phase of reduction and IFN-gamma being involved in both phases.

Interleukin-18 regulates both Th1 and Th2 responses

Although interleukin-18 is structurally homologous to IL-1 and its receptor belongs to the IL-1R/Toll-like receptor (TLR) superfamily, its function is quite different from that of IL-1. IL-18 is produced not only by types of immune cells but also by non-immune cells. In collaboration with IL-12, IL-18 stimulates Th1-mediated immune responses, which play a critical role in the host defense against infection with intracellular microbes through the induction of IFN-gamma. However, the overproduction of IL-12 and IL-18 induces severe inflammatory disorders, suggesting that IL-18 is a potent proinflammatory cytokine that has pathophysiological roles in several inflammatory conditions. IL-18 mRNA is expressed in a wide range of cells including Kupffer cells, macrophages, T cells, B cells, dendritic cells, osteoblasts, keratinocytes, astrocytes, and microglia. Thus, the pathophysiological role of IL-18 has been extensively tested in the organs that contain these cells. Somewhat surprisingly, IL-18 alone can stimulate Th2 cytokine production as well as allergic inflammation. Therefore, the functions of IL-18 in vivo are very heterogeneous and complicated. In principle, IL-18 enhances the IL-12-driven Th1 immune responses, but it can also stimulate Th2 immune responses in the absence of IL-12.

NK cells eliminate Cryptococcus neoformans by potentiating the fungicidal activity of macrophages rather than by directly killing them upon stimulation with IL-12 and IL-18

In the present study, we examined whether natural killer (NK) cells have direct fungicidal activity against Cryptococcus neoformans. Splenic NK cells were obtained from SCID mice and stimulated with a combination of interleukin (IL)-12 and IL-18 in flat culture plates or round tubes. They were then or at the same time cultured with the yeast cells and the number of viable yeast cells was examined. We could not detect direct fungicidal activity by NK cells under any culture condition, although they produced a large amount of IFN-gamma and exerted marked cytotoxic activity against YAC-1 cells. On the other hand, NK cells significantly potentiated the nitric oxide-mediated cryptococcocidal activity of thioglycolate-elicited peritoneal macrophages obtained from SCID mice upon stimulation with IL-12 and IL-18. The culture supernatants of NK cells stimulated with IL-12 and IL-18 provided similar results when used in place of NK cells. The induction of macrophage anticryptococcal activity by NK cells and NK cell culture supernatants were both mediated by IFN-gamma because the specific mAb almost completely abrogated such effect. Considered collectively, our results suggested that NK cells may play a regulatory role in potentiating macrophage-mediated fungicidal mechanisms in host resistance to infection with C. neoformans rather than exerting a direct killing activity against the fungal pathogen.

Interleukin-18 (IL-18) and infectious diseases, with special emphasis on diseases induced by intracellular pathogens

Interleukin-18 (IL-18) is a novel cytokine mainly produced by activated macrophages. IL-18 was originally called interferon-gamma inducing factor, due to its action in inducing IFN-gamma secretion from Th1 cells, NK cells and NKT cells. It has been reported that IL-18 may play important roles in various diseases including cancer and infectious diseases. This review deals with the roles of IL-18 in infectious diseases, with special emphasis on IL-18 in infectious diseases caused by intracellular pathogens including Mycobacterium tuberculosis, Mycobacterium leprae, Listeria monocytogenes and Salmonella typhimurium.