Impaired neutrophil response and CD4+ T helper cell 1 development in interleukin 6-deficient mice infected with Candida albicans

CR3 and Dectin-1 Collaborate in Macrophage Cytokine Response through Association on Lipid Rafts and Activation of Syk-JNK-AP-1 Pathway

Collaboration between heterogeneous pattern recognition receptors (PRRs) leading to synergistic coordination of immune response is important for the host to fight against invading pathogens. Although complement receptor 3 (CR3) and Dectin-1 are major PRRs to detect fungi, crosstalk between these two receptors in antifungal immunity is largely undefined. Here we took advantage of Histoplasma capsulatum which is known to interact with both CR3 and Dectin-1 and specific particulate ligands to study the collaboration of CR3 and Dectin-1 in macrophage cytokine response. By employing Micro-Western Array (MWA), genetic approach, and pharmacological inhibitors, we demonstrated that CR3 and Dectin-1 act collaboratively to trigger macrophage TNF and IL-6 response through signaling integration at Syk kinase, allowing subsequent enhanced activation of Syk-JNK-AP-1 pathway. Upon engagement, CR3 and Dectin-1 colocalize and form clusters on lipid raft microdomains which serve as a platform facilitating their cooperation in signaling activation and cytokine production. Furthermore, in vivo studies showed that CR3 and Dectin-1 cooperatively participate in host defense against disseminated histoplasmosis and instruct adaptive immune response. Taken together, our findings define the mechanism of receptor crosstalk between CR3 and Dectin-1 and demonstrate the importance of their collaboration in host defense against fungal infection.

The incidence of life-threatening fungal infections is increasing during the last decades. A better understanding of the interactions between fungal pathogen and its host cell is important to the development of new therapeutic strategies against fungal infections. Dimorphic fungus Histoplasma capsulatum becomes disseminated and threatens life in immunocompromised individuals. This fungal pathogen utilizes complement receptor 3 (CR3) and Dectin-1, two pattern recognition receptors on the surface of innate immune cells, to induce macrophage cytokine response. In this study, we demonstrated that CR3 and Dectin-1 act collaboratively to induce macrophage TNF and IL-6 response through a mechanism dependent on activation of the Syk-JNK-AP-1 signaling axis. CR3 and Dectin-1 are recruited and form clusters on lipid raft microdomains upon stimulation by H. capsulatum, leading to activation of their signaling convergence at Syk kinase and induction of subsequent cytokine response. In addition, we showed that CR3 and Dectin-1 cooperatively instruct the adaptive antifungal immunity to defense against H. capsulatum infection. Our findings define the molecular mechanisms underlying receptor crosstalk between CR3 and Dectin-1 and provide a valuable model for receptor collaboration in the context of host-fungus interactions.

Vaginal innate immune mediators are modulated by a water extract of Houttuynia cordata Thunb

Background

Vaginal epithelial cells (VECs) produce antimicrobial peptides including human β-defensin 2 (hBD2) and secretory leukocyte protease inhibitor (SLPI), as well as cytokines and chemokines that play vital roles in mucosal innate immunity of the female reproductive tract. Houttuynia cordata Thunb (H. cordata), a herbal plant found in Asia, possesses various activities including antimicrobial activity and anti-inflammation. As inflammation and infection are commonly found in female reproductive tract, we aimed to investigate the effects of H. cordata water extract in modulating innate immune factors produced by VECs.

Methods

Primary human VECs were cultured and treated with H. cordata at a concentration ranging from 25–200 μg/ml for 6 or 18 h. After treatment, the cells and culture supernatants were harvested. The expression of hBD2 and SLPI mRNA was evaluated by quantitative real-time reverse transcription PCR. Levels of secreted hBD2 and SLPI as well as cytokines and chemokines in the supernatants were measured by ELISA and Luminex assay, respectively. Cytotoxicity of the extract on VECs was assessed by CellTiter-Blue Cell Viability Assay.

Results

H. cordata did not cause measurable toxicity on VECs after exposure for 18 h. The expression of hBD2 and SLPI mRNA as well as the secreted hBD2 protein were increased in response to H. cordata exposure for 18 h when compared to the untreated controls. However, treatment with the extract for 6 h had only slight effects on the mRNA expression of hBD2 and SLPI. The secretion of IL-2 and IL-6 proteins by VECs was also increased, while the secretion of CCL5 was decreased after treatment with the extract for 18 h. Treatment with H. cordata extract had some effects on the secretion of IL-4, IL-8, CCL2, and TNF-α, but not statistically significant.

Conclusions

H. cordata water extract modulates the expression of antimicrobial peptides and cytokines produced by VECs, which play an important role in the mucosal innate immunity in the female reproductive tract. Our findings suggest that H. cordata may have immunomodulatory effects on the vaginal mucosa. Further studies should be performed in vivo to determine if it can enhance mucosal immune defenses against microbial pathogens.

Houttuynia cordata modulates oral innate immune mediators: potential role of herbal plant on oral health

OBJECTIVE

Epithelial cells play an active role in oral innate immunity by producing various immune mediators. Houttuynia cordata Thunb (H. cordata), a herbal plant found in Asia, possesses many activities. However, its impacts on oral innate immunity have never been reported. The aim of this study was to determine the effects of H. cordata extract on the expression of innate immune mediators produced by oral epithelial cells.

MATERIALS AND METHODS

Primary gingival epithelial cells (GECs) were treated with various concentrations of the extract for 18 h. The gene expression of hBD2, SLPI, cytokines, and chemokines was measured using quantitative real-time RT-PCR. The secreted proteins in the culture supernatants were detected by ELISA or Luminex assay. Cytotoxicity of the extract was assessed using CellTiter-Blue Assay.

RESULTS

H. cordata significantly induced the expression of hBD2, SLPI, IL-8, and CCL20 in a dose-dependent manner without cytotoxicity. The secreted hBD2 and SLPI proteins were modulated, and the levels of IL-2, IL-6, IL-8, and IFN-γ were significantly induced by the extract.

CONCLUSIONS

Our data indicated that H. cordata can modulate oral innate immune mediators. These findings may lead to the development of new topical agents from H. cordata for the prevention and treatment of immune-mediated oral diseases.

CX3CR1 is dispensable for control of mucosal Candida albicans infections in mice and humans

Candida albicans is part of the normal commensal microbiota of mucosal surfaces in a large percentage of the human population. However, perturbations of the host's immune response or bacterial microbiota have been shown to predispose individuals to the development of opportunistic Candida infections. It was recently discovered that a defect in the chemokine receptor CX3CR1 increases susceptibility of mice and humans to systemic candidiasis. However, whether CX3CR1 confers protection against mucosal C. albicans infection has not been investigated. Using two different mouse models, we found that Cx3cr1 is dispensable for the induction of interleukin 17A (IL-17A), IL-22, and IL-23 in the tongue after infection, as well as for the clearance of mucosal candidiasis from the tongue or lower gastrointestinal (GI) tract colonization. Furthermore, the dysfunctional human CX3CR1 allele CX3CR1-M280 was not associated with development of recurrent vulvovaginal candidiasis (RVVC) in women. Taken together, these data indicate that CX3CR1 is not essential for protection of the host against mucosal candidiasis, underscoring the dependence on different mammalian immune factors for control of mucosal versus systemic Candida infections.

Candida survival strategies

Only few Candida species, e.g., Candida albicans, Candida glabrata, Candida dubliniensis, and Candida parapsilosis, are successful colonizers of a human host. Under certain circumstances these species can cause infections ranging from superficial to life-threatening disseminated candidiasis. The success of C. albicans, the most prevalent and best studied Candida species, as both commensal and human pathogen depends on its genetic, biochemical, and morphological flexibility which facilitates adaptation to a wide range of host niches. In addition, formation of biofilms provides additional protection from adverse environmental conditions. Furthermore, in many host niches Candida cells coexist with members of the human microbiome. The resulting fungal-bacterial interactions have a major influence on the success of C. albicans as commensal and also influence disease development and outcome. In this chapter, we review the current knowledge of important survival strategies of Candida spp., focusing on fundamental fitness and virulence traits of C. albicans.

Early expression of local cytokines during systemic Candida albicans infection in a murine intravenous challenge model

Local cytokine production is a significant indicator for disease pathogenesis or progression. Previous studies on cytokine production during systemic Candida albicans (C. albicans) infection were solely on kidney or single cell type interaction with C. albicans. Therefore, the present study aimed to assess the early cytokine expression of various target organs (kidney, spleen and brain) over a 72-h time course during systemic C. albicans infection. The local cytokine profiles of the target organs during systemic C. albicans infection were measured by cytometric bead array and ELISA analysis. The results demonstrated that interleukin-6 (IL-6) and IL-2 were statistically significant (P<0.05) in the spleen at 24 and 72 h post-infection, whereas in the kidney, IL-6 and tumor necrosis factor-α (TNF-α) were statistically significant (P<0.05) at 24 and 72 h post-infection and CXCL-1 and transforming growth factor-β (TGF-β) were statistically significant (P<0.05) at 72 h post-infection. In the brain, IL-6 and TNF-α were statistically significant (P<0.05) at 24 and 72 h post-infection, whereas TGF-β was statistically significant (P<0.05) at 72 h post-infection. These findings demonstrate that host immune responses were varied among target organs during systemic C. albicans infection. This could be important for designing targeted immunotherapy against this pathogen through immunomodulatory approaches in future exploratory research.

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

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

Inhibition of the JAK2/STAT3 pathway reduces gastric cancer growth in vitro and in vivo

Signal Transducer and Activator of Transcription-3 (STAT3) is constitutively activated in many cancers where it promotes growth, inflammation, angiogenesis and inhibits apoptosis. We have shown that STAT3 is constitutively activated in human gastric cancer, and that chronic IL-11-driven STAT3 transcriptional activity induces gastric tumourigenesis in the gp130^757FF mouse model of gastric cancer development. Here we show that treatment of human AGS gastric cancer cells with the Janus Kinase (JAK) inhibitor WP1066 dose-, and time-dependently inhibits STAT3 phosphorylation, in conjunction with reduced JAK2 phosphorylation, reduced proliferation and increased apoptosis. In addition, application of intraperitoneal WP1066 for 2 weeks, reduced gastric tumour volume by 50% in the gp130^757FF mouse coincident with reduced JAK2 and STAT3 activation compared with vehicle-treated, littermate controls. Gastric tumours from WP1066- treated mice had reduced polymorphonuclear inflammation, coincident with inhibition of numerous proinflammatory cytokines including IL-11, IL-6 and IL-1β, as well as the growth factors Reg1 and amphiregulin. These results show that WP1066 can block proliferation, reduce inflammation and induce apoptosis in gastric tumour cells by inhibiting STAT3 phosphorylation, and that many cytokines and growth factors that promote gastric tumour growth are regulated by STAT3-dependent mechanisms. WP1066 may form the basis for future therapeutics against gastric cancer.

Emergency granulopoiesis

Neutrophils are a key cell type of the innate immune system. They are short-lived and need to be continuously generated in steady-state conditions from haematopoietic stem and progenitor cells in the bone marrow to ensure their immediate availability for the containment of invading pathogens. However, if microbial infection cannot be controlled locally, and consequently develops into a life-threatening condition, neutrophils are used up in large quantities and the haematopoietic system has to rapidly adapt to the increased demand by switching from steady-state to emergency granulopoiesis. This involves the markedly increased de novo production of neutrophils, which results from enhanced myeloid precursor cell proliferation in the bone marrow. In this Review, we discuss the molecular and cellular events that regulate emergency granulopoiesis, a process that is crucial for host survival.

Serum interleukin-6 levels in murine models of Candida albicans infection

Two Balb/C mouse models of Candida infection were used to detect serum interleukin-6 (IL-6) responses. The first model used systemic infection by Candida albicans ATCC 10231 strain infected through the lateral tail vein of mice without any specific pretreatment. The median Candida burdens of the kidneys were 1.5 × 106 CFU/ml 24 h postinoculation (p.i.) and 1.2 × 107 CFU/ml 72 h p.i., while median serum IL-6 levels were 479.3 pg/ml and 934.5 pg/ml, respectively. The Candida burden showed significant correlation with serum IL-6 24 h p.i. (R2 = 0.6358; P = 0.0082) but not 72 h p.i.The second model was a mouse vaginitis model applying intravaginal inoculation of mice pretreated with subcutaneous estradiol-valerate (10 mg/ml) 3 days before infection. Candida cell count in vaginal lavage fluid was 2.8 × 106 CFU/ml 24 h p.i. and 1.4 × 108 CFU/ml 72 h p.i. Serum IL-6 response was detected in 4 of 15 mice 24 h p.i. and 9 of 15 mice 72 h p.i. Even the responders had low IL-6 serum levels (mean values 29.9 pg/ml and 60.1 pg/ml, respectively) not correlating with Candida cell count in vaginal lavage fluid.In conclusion, serum IL-6 had strong relationship with systemic C. albicans infection while the local C. albicans infection of the vagina led to partial, prolonged and limited serum IL-6 response.

Immune cell response to Candida cell wall mannan derived branched α-oligomannoside conjugates in mice

BACKGROUND

Constructs composed of cell wall mannan-derived moieties conjugated to immunogenic proteins could be promising agents for induction of protective anti-Candida immune responses.

METHODS

This report is focused on the cellular immune response differences induced by BSA-based conjugates bearing synthetic α-1,6-branched oligomannosides. For monitoring of the immune responses following active immunization we evaluated changes in the frequencies of T and B lymphocytes and their activation status in the blood and spleen. We compared the immunization-induced changes of co-stimulatory molecules CD80 and CD86 expression on blood neutrophils and Th1/Th2 polarization of the immune response based on IFN-γ, TNF-α (pro-Th1), IL-4, and IL-10 (pro-Th2) cytokines levels and induction of IL-17.

RESULTS

The results pointed out a comparable effect of the conjugates on the modulation of T and B lymphocytes frequencies in blood and spleen. Both conjugates induced upregulation of CD25 surface antigen on CD4(+) T lymphocytes, independently on the structural differences of oligosaccharides. The differences in structure of oligomannoside antigens or conjugate constructs were reflected in the increase of co-stimulatory molecules CD80 and CD86 expression on neutrophils, and in induced cytokine response. M5-BSA conjugate induced only a slight increase in CD80 expression but a significant increase in IFN-γ, TNF-α, and IL-10. M6-BSA conjugate induced a significant increase of CD80 expression and increase of TNF-α, IL-4, and IL-10.

CONCLUSION

Obtained data demonstrate the importance of cellular immune response analysis for investigation of immunomodulatory properties of oligomannoside-protein conjugates.

IL-6 controls susceptibility to helminth infection by impeding Th2 responsiveness and altering the Treg phenotype in vivo

IL-6 plays a pivotal role in favoring T-cell commitment toward a Th17 cell rather than Treg-cell phenotype, as established through in vitro model systems. We predicted that in the absence of IL-6, mice infected with the gastrointestinal helminth Heligmosomoides polygyrus would show reduced Th17-cell responses, but also enhanced Treg-cell activity and consequently greater susceptibility. Surprisingly, worm expulsion was markedly potentiated in IL-6-deficient mice, with significantly stronger adaptive Th2 responses in both IL-6^−/− mice and BALB/c recipients of neutralizing anti-IL-6 monoclonal Ab. Although IL-6-deficient mice showed lower steady-state Th17-cell levels, IL-6-independent Th17-cell responses occurred during in vivo infection. We excluded the Th17 response as a factor in protection, as Ab neutralization did not modify immunity to H. polygyrus infection in BALB/c mice. Resistance did correlate with significant changes to the associated Treg-cell phenotype however, as IL-6-deficient mice displayed reduced expression of Foxp3, Helios, and GATA-3, and enhanced production of cytokines within the Treg-cell population. Administration of an anti-IL-2:IL-2 complex boosted Treg-cell proportions in vivo, reduced adaptive Th2 responses to WT levels, and fully restored susceptibility to H. polygyrus in IL-6-deficient mice. Thus, in vivo, IL-6 limits the Th2 response, modifies the Treg-cell phenotype, and promotes host susceptibility following helminth infection.

FcγR-driven release of IL-6 by macrophages requires NOX2-dependent production of reactive oxygen species

Activation of the FcγR via antigen containing immune complexes can lead to the generation of reactive oxygen species, which are potent signal transducing molecules. However, whether ROS contribute to FcγR signaling has not been studied extensively. We set out to elucidate the role of NADPH oxidase-generated ROS in macrophage activation following FcγR engagement using antigen-containing immune complexes. We hypothesized that NOX2 generated ROS is necessary for propagation of downstream FcγR signaling and initiation of the innate immune response. Following exposure of murine bone marrow-derived macrophages (BMDMs) to inactivated Francisella tularensis (iFt)-containing immune complexes, we observed a significant increase in the innate inflammatory cytokine IL-6 at 24 h compared with macrophages treated with Ft LVS-containing immune complexes. Ligation of the FcγR by opsonized Ft also results in significant ROS production. Macrophages lacking the gp91(phox) subunit of NOX2 fail to produce ROS upon FcγR ligation, resulting in decreased Akt phosphorylation and a reduction in the levels of IL-6 compared with wild type macrophages. Similar results were seen following infection of BMDMs with catalase deficient Ft that fail to scavenge hydrogen peroxide. In conclusion, our findings demonstrate that ROS participate in elicitation of an effective innate immune in response to antigen-containing immune complexes through FcγR.

Alcohol impairs J774.16 macrophage-like cell antimicrobial functions in Acinetobacter baumannii infection

Acinetobacter baumannii (Ab) is a common cause of community-acquired pneumonia (CAP) in chronic alcoholics in tropical and sub-tropical climates and associated with a > 50% mortality rate. We demonstrated that exposure of J774.16 macrophage-like cells to physiological alcohol (EtOH) concentrations decreased phagocytosis and killing of Ab. EtOH-mediated macrophage phagocytosis dysfunction may be associated with reduced expression of GTPase-RhoA, a key regulator of the actin polymerization signaling cascade. EtOH inhibited nitric oxide (NO) generation via inducible NO-synthase inactivation, which enhanced Ab survival within macrophages. Additionally, EtOH alters cytokine production resulting in a dysregulated immune response. This study is a proof of principle which establishes that EtOH might exacerbate Ab infection and be an important factor enhancing CAP in individuals at risk.

Serial passaging of Candida albicans in systemic murine infection suggests that the wild type strain SC5314 is well adapted to the murine kidney

The opportunistic fungal pathogen Candida albicans has a remarkable ability to adapt to unfavorable environments by different mechanisms, including microevolution. For example, a previous study has shown that passaging through the murine spleen can cause new phenotypic characteristics. Since the murine kidney is the main target organ in murine Candida sepsis and infection of the spleen differs from the kidney in several aspects, we tested whether C. albicans SC5314 could evolve to further adapt to infection and persistence within the kidney. Therefore, we performed a long-term serial passage experiment through the murine kidney of using a low infectious dose. We found that the overall virulence of the commonly used wild type strain SC5314 did not change after eight passages and that the isolated pools showed only very moderate changes of phenotypic traits on the population level. Nevertheless, the last passage showed a higher phenotypic variability and a few individual strains exhibited phenotypic alterations suggesting that microevolution has occurred. However, the majority of the tested single strains were phenotypically indistinguishable from SC5314. Thus, our findings indicate that characteristics of SC5314 which are important to establish and maintain kidney infection over a prolonged time are already well developed.

LAB/NTAL facilitates fungal/PAMP-induced IL-12 and IFN-γ production by repressing β-catenin activation in dendritic cells

Fungal pathogens elicit cytokine responses downstream of immunoreceptor tyrosine-based activation motif (ITAM)-coupled or hemiITAM-containing receptors and TLRs. The Linker for Activation of B cells/Non-T cell Activating Linker (LAB/NTAL) encoded by Lat2, is a known regulator of ITAM-coupled receptors and TLR-associated cytokine responses. Here we demonstrate that LAB is involved in anti-fungal immunity. We show that Lat2-/- mice are more susceptible to C. albicans infection than wild type (WT) mice. Dendritic cells (DCs) express LAB and we show that it is basally phosphorylated by the growth factor M-CSF or following engagement of Dectin-2, but not Dectin-1. Our data revealed a unique mechanism whereby LAB controls basal and fungal/pathogen-associated molecular patterns (PAMP)-induced nuclear β-catenin levels. This in turn is important for controlling fungal/PAMP-induced cytokine production in DCs. C. albicans- and LPS-induced IL-12 and IL-23 production was blunted in Lat2-/- DCs. Accordingly, Lat2-/- DCs directed reduced Th1 polarization in vitro and Lat2-/- mice displayed reduced Natural Killer (NK) and T cell-mediated IFN-γ production in vivo/ex vivo. Thus our data define a novel link between LAB and β-catenin nuclear accumulation in DCs that facilitates IFN-γ responses during anti-fungal immunity. In addition, these findings are likely to be relevant to other infectious diseases that require IL-12 family cytokines and an IFN-γ response for pathogen clearance.

Interleukin-6 is essential for primary resistance to Francisella tularensis live vaccine strain infection

We employed Francisella tularensis live vaccine strain (LVS) to study mechanisms of protective immunity against intracellular pathogens and, specifically, to understand protective correlates. One potential molecular correlate identified previously was interleukin-6 (IL-6), a cytokine with pleotropic roles in immunity, including influences on T and B cell functions. Given its role as an immune modulator and the correlation with successful anti-LVS vaccination, we examined the role IL-6 plays in the host response to LVS. IL-6-deficient (IL-6 knockout [KO]) mice infected with LVS intradermally or intranasally or anti-IL-6-treated mice, showed greatly reduced 50% lethal doses compared to wild-type (WT) mice. Increased susceptibility was not due to altered splenic immune cell populations during infection or decreased serum antibody production, as IL-6 KO mice had similar compositions of each compared to WT mice. Although LVS-infected IL-6 KO mice produced much less serum amyloid A and haptoglobin (two acute-phase proteins) than WT mice, there were no other obvious pathophysiological differences between LVS-infected WT and IL-6 KO mice. IL-6 KO or WT mice that survived primary LVS infection also survived a high-dose LVS secondary challenge. Using an in vitro overlay assay that measured T cell activation, cytokine production, and abilities of primed splenocytes to control intracellular LVS growth, we found that IL-6 KO total splenocytes or purified T cells were slightly defective in controlling intracellular LVS growth but were equivalent in cytokine production. Taken together, IL-6 is an integral part of a successful immune response to primary LVS infection, but its exact role in precipitating adaptive immunity remains elusive.

An alternative pathway of imiquimod-induced psoriasis-like skin inflammation in the absence of interleukin-17 receptor a signaling

Topical application of imiquimod (IMQ) on the skin of mice induces inflammation with common features found in psoriatic skin. Recently, it was postulated that IL-17 has an important role both in psoriasis and in the IMQ model. To further investigate the impact of IL-17RA signaling in psoriasis, we generated IL-17 receptor A (IL-17RA)-deficient mice (IL-17RA(del)) and challenged these mice with IMQ. Interestingly, the disease was only partially reduced and delayed but not abolished when compared with controls. In the absence of IL-17RA, we found persisting signs of inflammation such as neutrophil and macrophage infiltration within the skin. Surprisingly, already in the naive state, the skin of IL-17RA(del) mice contained significantly elevated numbers of Th17- and IL-17-producing γδ T cells, assuming that IL-17RA signaling regulates the population size of Th17 and γδ T cells. Upon IMQ treatment of IL-17RA(del) mice, these cells secreted elevated amounts of tumor necrosis factor-α, IL-6, and IL-22, accompanied by increased levels of the chemokine CXCL2, suggesting an alternative pathway of neutrophil and macrophage skin infiltration. Hence, our findings have major implications in the potential long-term treatment of psoriasis by IL-17-targeting drugs.

Trophoblast cells are able to regulate monocyte activity to control Toxoplasma gondii infection

INTRODUCTION

Toxoplasma gondii is an intracellular parasite that causes severe disease when the infection occurs during pregnancy. Trophoblast cells constitute an important maternal-fetal barrier, with monocytes concentrating around them. Thus, interactions between trophoblasts and monocytes are important for maintaining a successful pregnancy, especially in cases of infection. This study aimed to evaluate the role of trophoblast cells (BeWo line) on monocyte (THP-1 line) activity in the presence or absence of T. gondii infection.

METHODS

THP-1 cells were stimulated with supernatants of BeWo cells, previously infected or not with T. gondii, and then infected with parasites. The supernatant of both cells were collected and analyzed for cytokine production and T. gondii proliferation in THP-1 cells was determined.

RESULTS

The results showed that after infection, the pattern of cytokines secreted by THP-1 and BeWo cells was characterized as a pro-inflammatory profile. Furthermore, supernatant of BeWo cells infected or not, was able to change the cytokine profile secreted by infected THP-1 cells, and this supernatant became THP-1 cells more able to control T. gondii proliferation than those that had not been stimulated.

DISCUSSION

This effect was associated with secretion of interleukin (IL)-6 by the THP-1 cells and soluble factors secreted by BeWo cells, such as IL-6 and MIF.

CONCLUSION

Together, these results suggest that trophoblast cells are able to modulate monocyte activity, resulting in the control of T. gondii infection and subsequent maintenance of pregnancy.

Immune responses and Lassa virus infection

Lassa fever is a hemorrhagic fever endemic to West Africa and caused by Lassa virus, an Old World arenavirus. It may be fatal, but most patients recover from acute disease and some experience asymptomatic infection. The immune mechanisms associated with these different outcomes have not yet been fully elucidated, but considerable progress has recently been made, through the use of in vitro human models and nonhuman primates, the only relevant animal model that mimics the pathophysiology and immune responses induced in patients. We discuss here the roles of the various components of the innate and adaptive immune systems in Lassa virus infection and in the control of viral replication and pathogenesis.

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.

Cutting edge: IL-6 is a marker of inflammation with no direct role in inflammasome-mediated mouse models

IL-6 is a known downstream target of IL-1β and is consistently increased in serum from patients with NLRP3 inflammasome-mediated conditions. Therefore, IL-6 could be a therapeutic target in the treatment of IL-1β-provoked inflammation. IL-6 was increased in serum with accompanying neutrophilia in tissues of an inducible mouse model of Muckle-Wells syndrome. However, an IL-6-null background failed to provide phenotypic rescue and did not significantly impact inflammatory cytokine levels. In a second model of IL-1β-driven inflammation, NLRP3 activation by monosodium urate crystals similarly increased IL-6. Consistent with our Muckle-Wells syndrome model, ablation of IL-6 did not impact an acute neutrophilic response in this in vivo evaluation of gouty arthritis. Taken together, our results indicate that IL-6 is a reliable marker of inflammation, with no direct role in inflammasome-mediated disease.

CCR9+ T cells contribute to the resolution of the inflammatory response in a mouse model of intestinal amoebiasis

Analysis of the mechanisms underlying the inflammatory response in amoebiasis is important to understand the immunopathology of the disease. Mucosal associated effector and regulatory T cells may play a role in regulating the inflammatory immune response associated to Entamoeba histolytica infection in the colon. A subpopulation of regulatory T cells has recently been identified and is characterized by the expression of the chemokine receptor CCR9. In this report, we used CCR9 deficient (CCR9(-/-)) mice to investigate the role of the CCR9(+) T cells in a murine model of E. histolytica intestinal infection. Intracecal infection of CCR9(+/+), CCR9(+/-) and CCR9(-/-) mice with E. histolytica trophozoites, revealed striking differences in the development and nature of the intestinal inflammatory response observed between these strains. While CCR9(+/+) and CCR9(+/-) mice were resistant to the infection and resolved the pathogen-induced inflammatory response, CCR9(-/-) mice developed a chronic inflammatory response, which was associated with over-expression of the cytokines IFN-γ, TNF-α, IL-4, IL-6 and IL-17, while IL-10 was not present. In addition, increased levels of CCL11, CCL20 and CCL28 chemokines were detected by qRT-PCR in CCR9(-/-) mice. E. histolytica trophozoites were identified in the lumen of the cecum of CCR9(-/-) mice at seven days post infection (pi), whereas in CCR9(+/+) mice trophozoites disappeared by day 1 pi. Interestingly, the inflammation observed in CCR9(-/-) mice, was associated with a delayed recruitment of CD4(+)CD25(+)FoxP3(+) T cells to the cecal epithelium and lamina propria, suggesting that this population may play a role in the early regulation of the inflammatory response against E. histolytica, likely through IL-10 production. In support of these data, CCR9(+) T cells were also identified in colon tissue sections obtained from patients with amoebic colitis. Our data suggest that a population of CCR9(+)CD4(+)CD25(+)FoxP3(+) T cells may participate in the control and resolution of the inflammatory immune response to E. histolytica infection.

Interplay between Candida albicans and the mammalian innate host defense

Candida albicans is both the most common fungal commensal microorganism in healthy individuals and the major fungal pathogen causing high mortality in at-risk populations, especially immunocompromised patients. In this review, we summarize the interplay between the host innate system and C. albicans, ranging from how the host recognizes, responds, and clears C. albicans infection to how C. albicans evades, dampens, and escapes from host innate immunity.

Demand-adapted regulation of early hematopoiesis in infection and inflammation

During systemic infection and inflammation, immune effector cells are in high demand and are rapidly consumed at sites of need. Although adaptive immune cells have high proliferative potential, innate immune cells are mostly postmitotic and need to be replenished from bone marrow (BM) hematopoietic stem and progenitor cells. We here review how early hematopoiesis has been shaped to deliver efficient responses to increased need. On the basis of most recent findings, we develop an integrated view of how cytokines, chemokines, as well as conserved pathogen structures, are sensed, leading to divisional activation, proliferation, differentiation, and migration of hematopoietic stem and progenitor cells, all aimed at efficient contribution to immune responses and rapid reestablishment of hematopoietic homeostasis. We also outline how chronic inflammatory processes might impinge on hematopoiesis, potentially fostering hematopoietic stem cell diseases, and, how clinical benefit is and could be achieved by learning from nature.

Adjunctive immunotherapy with recombinant cytokines for the treatment of disseminated candidiasis

Despite the discovery in the last decade of azoles and echinocandins as novel and potent antimycotic drugs, systemic Candida infections are still accompanied by an unacceptably high burden of morbidity and mortality. A rational novel therapeutic approach would be the use of adjuvant immunotherapy, with the aim of improving host defence against Candida. Increases in our understanding of the mechanisms that underlie the pathogenesis of Candida infections, such as the role played by pattern recognition receptors and the induction of proinflammatory cytokines during the early phases of infection, have led to the hypothesis of a potential therapeutic role of recombinant cytokines in systemic candidiasis. In the present review, we give an update of both experimental data and proof-of-principle studies in humans that argue for the use of adjunctive immunotherapy with recombinant cytokines in invasive Candida infections. Sufficiently powered studies on the role of cytokine-based treatment regimens for invasive candidiasis are needed to fully demonstrate the feasibility of this immunotherapeutic approach to improve the prognosis of severe invasive Candida infections.

Decreased leukocyte accumulation and delayed Bordetella pertussis clearance in IL-6-/- mice

IL-6, a pleiotropic cytokine primarily produced by the innate immune system, has been implicated in the development of acquired immune responses, though its roles are largely undefined and may vary in the context of different diseases. Using a murine model of infection, we established that IL-6 influences the adaptive immune responses against the endemic human respiratory pathogen Bordetella pertussis. IL-6 was induced in the lungs of C57BL/6 mice by B. pertussis. IL-6(-/-) mice showed a protracted infectious course and were less efficiently protected by B. pertussis vaccination than wild-type mice. Abs from IL-6(-/-) mice, though lower in titer, efficiently reduced B. pertussis numbers in IL-6-sufficient mice. Pulmonary leukocyte recruitment and splenic or pulmonary T cell cytokine responses to B. pertussis, including Th1 and Th17 cytokine production, were lower in IL-6(-/-) mice than in wild-type mice. Adoptive transfer of immune wild-type CD4(+) cells ameliorated the defect of IL-6(-/-) mice in the control of B. pertussis numbers. Together, these results reveal the dysregulation of multiple aspects of adaptive immune responses in B. pertussis-infected IL-6(-/-) mice and suggest that IL-6 is involved in regulating Ab generation, pulmonary leukocyte accumulation, and T cell cytokine production in response to B. pertussis as well as the generation of effective vaccine-induced immunity against this pathogen.

Intratumoral neutrophils: a poor prognostic factor for hepatocellular carcinoma following resection

BACKGROUND & AIMS

Neutrophil infiltration has been linked to clinical outcome of various cancer types. However, its role in hepatocellular carcinoma (HCC) is unclear. In this study, we investigated prognostic values for intratumoral and peritumoral neutrophils in HCC patients undergoing curative resection.

METHODS

The expression of CD66b, CD8, TGF-beta, and CD34 was assessed by immunohistochemistry in tissue microarrays containing paired intratumoral and peritumoral tissues from 197 patients receiving curative resection for HCC. Prognostic values for these and other clinicopathologic factors were evaluated.

RESULTS

Intratumoral CD66b(+) neutrophils significantly correlated with CD8(+) T cells (r=0.240, p=0.004), TGF-beta expression (p=0.012), BCLC stage (p=0.016), and early recurrence (p=0.041). Increased intratumoral neutrophils were significantly associated with decreased RFS/OS (p=0.001 and p<0.001, respectively) in univariate analysis and were identified as an independent prognostic factor (HR=1.845, 95% CI=1.169-2.911, p=0.008 for RFS; HR=2.578, 95% CI=1.618-4.106, p<0.001 for OS) in multivariate analysis. Intratumoral neutrophil-to-CD8(+) T cell ratio (iNTR) better predicted the outcome in terms of minimum p values. Intratumoral neutrophils were also demonstrated to be statistically predictive for RFS/OS in the normal AFP subgroup, small HCC subgroup, and validation cohort. However, peritumoral neutrophils were not associated with the outcome of HCC.

CONCLUSIONS

The presence of intratumoral neutrophils was a poor prognostic factor for HCC after resection. Intratumoral neutrophil-to-CD8(+) T cell ratio was a better predictor of outcome.

Anti-IL-6 receptor antibody causes less promotion of tuberculosis infection than anti-TNF-α antibody in mice

Objective. Our aim was to investigate the effects of IL-6 blockade on the progression of Mycobacterium tuberculosis (TB) and compare them with those of TNF-α blockade in mice. Methods. Mice were intravenously infected with TB and injected with antibodies. Survival was monitored and histological and immunological studies were carried out. Results. All anti-IL-6R Ab-treated mice and 8 of 10 control mice survived until sacrificed 224 days after TB challenge, whereas anti-TNF-α Ab-treated mice all died between 120 and 181 days. Anti-IL-6R Ab-treated mice exhibited no significant differences in TB CFU in organs, including the lungs, and no deterioration in histopathology compared to control mice at 4 weeks. In contrast, anti-TNF-α Ab-treated mice exhibited increased TB CFU and greater progression of histopathological findings in organs than control mice. Spleen cells from anti-TNF-α Ab-treated mice had decreased antigen-specific response in IFN-γ release and proliferation assays. The results in anti-IL-6R Ab-treated mice suggest that spleen cell responses were decreased to a lesser degree. Similar results were obtained in IL-6 knockout (KO) mice, compared with TNF receptor 1 (TNFR1) KO and TNFR1/IL-6 double KO (DKO) mice. Conclusion. IL-6R blockade promotes the progression of TB infection in mice far less than TNF-α blockade.

Pathogenesis of invasive candidiasis

PURPOSE OF REVIEW

Disseminated candidiasis remains a life-threatening disease in the ICU. The development of invasive disease with Candida albicans is dependent on multiple factors, such as colonization and efficient host defense at the mucosa. In the present review, we describe the host defense mechanisms against Candida that are responsible for counteracting mucosal invasion, and eliminating the pathogen once invasion has taken place.

RECENT FINDINGS

The newly described T-helper subset Th17 is critical for mucosal anti-Candida host defense and plays a major role in controlling C. albicans colonization, whereas the Th1 response and monocyte-dependent cytokines such as IL-1 and TNF are predominantly responsible for activation of neutrophils and macrophages during disseminated candidiasis.

SUMMARY

This knowledge provides the basis of exploring new treatment options in the fight against invasive candidiasis. Reports of beneficial effects of recombinant cytokine therapy in fungal infections, renders them prime candidates for adjuvant immunotherapy in Candida sepsis.

gp130 at the nexus of inflammation, autoimmunity, and cancer

Glycoprotein 130 (gp130) is a shared receptor utilized by several related cytokines, including IL-6, IL-11, IL-27, Leukemia Inhibitory Factor (LIF), Oncostatin M (OSM), Ciliary Neurotrophic Factor (CNTF), Cardiotrophin 1 (CT-1) and Cardiotrophin-like Cytokine (CLC). Gp130 plays critical roles during development and gp130-deficient mice are embryonically lethal. However, the best characterized facet of this receptor and its associated cytokines is the ability to promote or suppress inflammation. The aim of this review is to discuss the role of gp130 in promoting or preventing the development of autoimmunity and cancer, two processes that are associated with aberrant inflammatory responses.

Early-expressed chemokines predict kidney immunopathology in experimental disseminated Candida albicans infections

BACKGROUND

The mouse intravenous challenge model of Candida albicans infection is widely used to determine aspects of host-fungus interaction. We investigated the production of cytokines in the kidneys and spleen of animals up to 48 h after challenge with virulent and attenuated isolates and related these responses to semi-quantitative estimations of histopathological changes in the kidney.

METHODOLOGY/PRINCIPAL FINDINGS

Progression of Candida albicans infection of the kidney in response to highly virulent fungal strains was characterized by higher levels of host cellular infiltrate, higher lesion densities and greater quantities of fungal elements at 24 and 48 h, and by higher kidney concentrations of IL-1beta, MCP-1, KC, IL-6, G-CSF, TNF, MIP-2 and MIP-1beta, among the immune effectors measured. Levels of the chemokine KC as early as 12 h after challenge correlated significantly with all later measurements of lesion severity. Early renal IL-6 and MIP-1beta concentrations also correlated with subsequent damage levels, but less significantly than for KC. All chemokines tested appeared in kidney homogenates, while most of the cytokines were undetectable in kidney and spleen homogenates. GM-CSF and IL-10 showed inverse correlations with measures of lesion severity, suggesting these alone may have exerted a defensive role. Spleen levels of KC at all times showed significant associations with kidney lesion measurements.

CONCLUSIONS/SIGNIFICANCE

Elevated chemokine levels, including KC, represent the earliest responses to C. albicans infection in the mouse kidney. Fungal strains of low mouse virulence stimulate a lower innate response and less host infiltrate than more virulent strains. These findings are consistent with immunopathological damage to kidneys in the mouse C. albicans infection model and with growing evidence implicating some TLR pathways as the main point of interaction between fungal surface polysaccharides and leukocytes.

Markers of early disease and prognosis in COPD

COPD is a complex disease with multiple pathological components, which we unfortunately tend to ignore when spirometry is used as the only method to evaluate the disorder. Additional measures are needed to allow a more complete and clinically relevant assessment of COPD. The earliest potential risk factors of disease in COPD are variations in the genetic background. Genetic variations are present from conception and can determine lifelong changes in enzyme activities and protein concentrations. In contrast, measurements in blood, sputum, exhaled breath, broncho-alveolar lavage, and lung biopsies may vary substantially over time. This review explores potential markers of early disease and prognosis in COPD by examining genetic markers in the α₁-antitrypsin, cystic fibrosis transmembrane conductance regulator (CFTR), and MBL-2 genes, and by examining the biochemical markers fibrinogen and C-reactive protein (CRP), which correlate with degree of pulmonary inflammation during stable conditions of COPD. Chronic lung inflammation appears to contribute to the pathogenesis of COPD, and markers of this process have promising predictive value in COPD. To implement markers for COPD in clinical practice, besides those already established for the α₁-antitrypsin gene, further research and validation studies are needed.

Early and strong immune responses are associated with control of viral replication and recovery in lassa virus-infected cynomolgus monkeys

Lassa virus causes a hemorrhagic fever endemic in West Africa. The pathogenesis and the immune responses associated with the disease are poorly understood, and no vaccine is available. We followed virological, pathological, and immunological markers associated with fatal and nonfatal Lassa virus infection of cynomolgus monkeys. The clinical picture was characterized by fever, weight loss, depression, and acute respiratory syndrome. Transient thrombocytopenia and lymphopenia, lymphadenopathy, splenomegaly, infiltration of mononuclear cells, and alterations of the liver, lungs, and endothelia were observed. Survivors exhibited fewer lesions and a lower viral load than nonsurvivors. Although all animals developed strong humoral responses, antibodies appeared more rapidly in survivors and were directed against GP(1), GP(2), and NP. Type I interferons were detected early after infection in survivors but only during the terminal stages in fatalities. The mRNAs for CXCL10 (IP-10) and CXCL11 (I-TAC) were abundant in peripheral blood mononuclear cells and lymph nodes from infected animals, but plasma interleukin-6 was detected only in fatalities. In survivors, high activated-monocyte counts were followed by a rise in the total number of circulating monocytes. Activated T lymphocytes circulated in survivors, whereas T-cell activation was low and delayed in fatalities. In vitro stimulation with inactivated Lassa virus induced activation of T lymphocytes from all infected monkeys, but only lymphocytes from survivors proliferated. Thus, early and strong immune responses and control of viral replication were associated with recovery, whereas fatal infection was characterized by major alterations of the blood formula and, in organs, weak immune responses and uncontrolled viral replication.

The tetraspanin protein CD37 regulates IgA responses and anti-fungal immunity

Immunoglobulin A (IgA) secretion by plasma cells in the immune system is critical for protecting the host from environmental and microbial infections. However, the molecular mechanisms underlying the generation of IgA⁺ plasma cells remain poorly understood. Here, we report that the B cell–expressed tetraspanin CD37 inhibits IgA immune responses in vivo. CD37-deficient (CD37−/−) mice exhibit a 15-fold increased level of IgA in serum and significantly elevated numbers of IgA⁺ plasma cells in spleen, mucosal-associated lymphoid tissue, as well as bone marrow. Analyses of bone marrow chimeric mice revealed that CD37–deficiency on B cells was directly responsible for the increased IgA production. We identified high local interleukin-6 (IL-6) production in germinal centers of CD37−/− mice after immunization. Notably, neutralizing IL-6 in vivo reversed the increased IgA response in CD37−/− mice. To demonstrate the importance of CD37—which can associate with the pattern-recognition receptor dectin-1—in immunity to infection, CD37−/− mice were exposed to Candida albicans. We report that CD37−/− mice are evidently better protected from infection than wild-type (WT) mice, which was accompanied by increased IL-6 levels and C. albicans–specific IgA antibodies. Importantly, adoptive transfer of CD37−/− serum mediated protection in WT mice and the underlying mechanism involved direct neutralization of fungal cells by IgA. Taken together, tetraspanin protein CD37 inhibits IgA responses and regulates the anti-fungal immune response.

Antibody, or immunoglobulin (Ig), production by plasma cells in the immune system is important for protecting the host from microbial infections. IgA is the most abundant antibody isotype produced in the body. However, the molecular mechanisms underlying the generation of IgA–producing plasma cells remain poorly understood. We now report that the B cell–expressed protein CD37 regulates IgA immune responses, both in steady-state conditions and during infection. We found highly increased levels of IgA in serum and elevated numbers of IgA⁺ plasma cells in lymphoid tissue of mice that are deficient for CD37 (CD37−/− mice). To demonstrate the importance of CD37 in immunity to infection, CD37−/− mice were exposed to the fungus Candida albicans. C. albicans can cause systemic infection with high mortality in immunocompromised patients. We demonstrate that CD37−/− mice are evidently better protected from infection than wild-type mice, which was dependent on C. albicans–specific IgA antibodies. The underlying mechanism involved direct neutralization of fungal cells by IgA. In summary, the B cell protein CD37 inhibits IgA responses and anti-fungal immunity. This study may contribute to the development of novel immunotherapeutic approaches for invasive fungal disease.

Plasma interleukin-1beta, -6, -8 and tumor necrosis factor-alpha as highly informative markers of pelvic inflammatory disease

BACKGROUND

The role of proinflammatory cytokines in pelvic inflammatory disease (PID) is unclear. We therefore determined whether plasma proinflammatory cytokines, interleukin-1beta (IL-1beta), IL-6, IL-8 and tumor necrosis factor-alpha (TNF-alpha) were useful plasma markers in PID patients.

METHODS

Multiplex bead array analysis was used to measure the plasma levels of proinflammatory cytokines in 50 healthy controls as well as in 41 PID patients before and after routine protocol treatments.

RESULTS

IL-1beta, IL-6, IL-8 and TNF-alpha were significantly elevated in PID patients before antibiotic treatment than after treatment. However, IL-8 was not significantly different between healthy controls and PID patients. The relative increase in ratio of IL-6 was significantly correlated with white blood cell count (r=0.448, p=0.003), neutrophil count (r=0.472, p=0.002) and C-reactive protein level (r=0.412, p=0.008).

CONCLUSIONS

IL-1beta, IL-6, IL-8 and TNF-alpha may play an important role in the pathogenesis of PID. These biomarkers, particularly IL-6, could be useful adjuncts for the clinical diagnosis of PID.

A role for tumour necrosis factor-alpha, complement C5 and interleukin-6 in the initiation and development of the mycobacterial cord factor trehalose 6,6'-dimycolate induced granulomatous response

Trehalose 6,6'-dimycolate (TDM) is a glycolipid component of the mycobacterial cell wall that causes immune responses in mice similar to Mycobacterium tuberculosis (MTB) infection, including granuloma formation with production of proinflammatory cytokines. The precise roles of tumour necrosis factor (TNF)-alpha, complement C5 and interleukin (IL)-6 in the molecular events that lead to the initiation and maintenance of the granulomatous response to TDM have not been fully elucidated. Macrophage proinflammatory responses from wild-type and complement-deficient mice after infection with MTB were assessed, and compared to responses from organisms in which surface TDM had been removed. Removal of TDM abolished proinflammatory responses, markedly so in the complement-deficient macrophages. Mice deficient in TNF-alpha, C5a and IL-6, along with wild-type C57BL/6 controls, were intravenously injected with TDM in a water-in-oil emulsion, and analysed for histological response and cytokine production in lungs. Wild-type C57BL/6 mice formed granulomas with increased production of IL-1beta, IL-6, TNF-alpha, macrophage inflammatory protein-1alpha (MIP-1alpha), IL-12p40, interferon-gamma (IFN-gamma), and IL-10 protein and mRNA. TNF-alpha-deficient mice failed to produce a histological response to TDM, with no increases in cytokine production following TDM administration. While C5a-deficient mice exhibited inflammation, they did not form structured granulomas and initially had decreased production of proinflammatory mediators. IL-6-deficient mice initiated granuloma formation, but failed to maintain the granulomas through day 7 and demonstrated decreased early production of proinflammatory mediators in comparison to wild-type mice. These data suggest that TNF-alpha is critical for initiation of the granulomatous response, C5a is necessary for formation of cohesive granulomas, and IL-6 plays a key role in the granuloma maintenance response to mycobacterial TDM.

IL-17 and therapeutic kynurenines in pathogenic inflammation to fungi

Largely viewed as proinflammatory, innate responses combine with adaptive immunity to generate the most effective form of antifungal resistance, and T cells exercise feedback control over diverse effects of inflammation on infection. Some degree of inflammation is required for protection, particularly in mucosal tissues, during the transitional response occurring between the rapid innate and slower adaptive response. However, progressive inflammation worsens disease and ultimately prevents pathogen eradication. IDO, tryptophan catabolites ("kynurenines"), and regulatory T cells help to tame overzealous and exaggerated inflammatory responses. In this context, IL-23 and the Th17 pathway, which down-regulate tryptophan catabolism, may instead favor pathology and serve to accommodate the seemingly paradoxical association of chronic inflammation with fungal persistence. Recent data support a view in which IL-23/IL-17 antagonistic strategies, including the administration of synthetic kynurenines, could represent a new means of harnessing progressive or potentially harmful inflammation.

IL-6-dependent mucosal protection prevents establishment of a microbial niche for attaching/effacing lesion-forming enteric bacterial pathogens

Enteric infections with attaching/effacing lesion-inducing bacterial pathogens are a worldwide health problem. A murine infection model with one such pathogen, Citrobacter rodentium, was used to elucidate the importance of the pleiotropic immune regulator, IL-6, in the pathogenesis of infection. IL-6 was strongly induced in colonic epithelial cells and macrophages upon C. rodentium infection and was required for effective host defense, because mice lacking IL-6 failed to control bacterial numbers 2-3 wk after infection and exhibited increased mortality. IL-6 was not needed for mounting effective T and B cell responses to the pathogens, nor was it important for induction of IFN-gamma or TNF-alpha, cytokines involved in host defense against the bacteria, or the antibacterial effector, NO. Instead, IL-6 played a key role in mucosal protection, since its absence was associated with marked infection-induced apoptosis in the colonic epithelium and subsequent ulcerations. Cell culture studies confirmed that IL-6 protected colon epithelial cells directly against inducible apoptosis, which was accompanied by increased expression of an array of genes encoding antiapoptotic proteins, including Bcl-x(L), Mcl-1, cIAP-2, and Bcl-3. Ulcerations appeared to be pathogenetically important, because bacteria localized preferentially to those regions, and chemically induced colonic ulcerations promoted bacterial colonization. Furthermore, blood components likely present in ulcer exudates, particularly alanine, asparagine, and glycine, promoted bacterial growth. Thus, IL-6 is an important regulator of host defense against C. rodentium by protecting the mucosa against ulcerations which can act as a microbial niche for the bacteria.

Lack of Toll IL-1R8 exacerbates Th17 cell responses in fungal infection

TLRs contribute to the inflammatory response in fungal infections. Although inflammation is an essential component of the protective response to fungi, its dysregulation may significantly worsen fungal diseases. In this study, we tested the hypothesis that Toll IL-1R8 (TIR8)/single Ig IL-1-related receptor, a member of the IL-1R family acting as a negative regulator of TLR/IL-1R signaling, affects TLR responses in fungal infections. Genetically engineered Tir8(-/-) mice were assessed for inflammatory and adaptive Th cell responses to Candida albicans and Aspergillus fumigatus. Inflammatory pathology and susceptibility to infection were higher in Tir8(-/-) mice and were causally linked to the activation of the Th17 pathway. IL-1R signaling was involved in Th17 cell activation by IL-6 and TGF-beta in that limited inflammatory pathology and relative absence of Th17 cell activation were observed in IL-1RI(-/-) mice. These data demonstrate that TIR8 is required for host resistance to fungal infections and that it functions to negatively regulate IL-1-dependent activation of inflammatory Th17 responses. TIR8 may contribute toward fine-tuning the balance between protective immunity and immunopathology in infection.

Systemic and mucosal immunization with Candida albicans hsp90 elicits hsp90-specific humoral response in vaginal mucosa which is further enhanced during experimental vaginal candidiasis

The Candida albicans heat shock protein 90 kDa (hsp90-CA) is an important target for protective antibodies in disseminated candidiasis of experimental mice and humans. Hsp90-CA is present in the cell wall of Candida pseudohyphae or hyphae--typical pathogenic morphotypes in both mucosal and systemic Candida infections. However, the potential protective effects of hsp90-CA-specific antibodies in vaginal candidiasis has not yet been reported. In the present study we used various vaccine formulations (recombinant hsp90-CA protein and hsp90-CA-encoding DNA vaccine) and routes of administration (intradermal, intranasal, and intravenous) to induce both hsp90-CA-specific systemic and vaginal mucosa immune responses in experimental BALB/c mice. The results showed that intradermal recombinant hsp90-CA protein priming, followed by intranasal or intradermal recombinant hsp90-CA protein boosting induced significant increases in both serum and vaginal hsp90-CA-specific IgG and IgA antibodies compared to the control group, as well as enhanced hsp90-CA-specific splenocyte responses in vitro. In the intradermally boosted group, subsequent experimental vaginal Candida infection induced additional increases in the hsp90-CA specific IgG isotype, suggesting that Candida has the ability to induce a local hsp90-specific antibody (IgG) response during vulvovaginal candidiasis. Further work is required to elucidate the importance of immunity to highly conserved antigens during infection of the human female reproductive tract where a balance between immunity to and tolerance for commonly antigens such as hsp90 is necessary for the maintenance of fertility.

Mice lacking both G-CSF and IL-6 are more susceptible to Candida albicans infection: critical role of neutrophils in defense against Candida albicans

Neutrophils play an important role in the host's defense against infection with various pathogenic organisms. Granulocyte colony stimulating factor (G-CSF) is regarded as a major regulator of neutrophil production and function. Mice lacking G-CSF or its receptor are neutropenic. IL-6 is another cytokine that has been shown to promote neutrophil production and modulate the function of many types of immune cells. We have analyzed G-CSF/IL-6 double deficient (G-CSF(- / - )/IL-6(- / - )) mice to gain an insight into the possible contribution of IL-6 to the residual granulopoiesis in G-CSF-deficient (G-CSF(- / - )) mice. Furthermore, we have evaluated the ability of G-CSF(- / - )/IL-6(- / - ) mice to combat an experimental infection with Candida albicans. Our data shows that IL-6 plays a role in granulopoiesis during early post natal period but it is dispensable for steady-state granulopoiesis in adult mice. However, adult G-CSF(- / - )/IL-6(- / - ) mice are more susceptible to Candida infection than similarly infected G-CSF(- / - ) mice. Although, the candidacidal function of neutrophils of G-CSF(- / - )/IL-6(- / - ) mice is deficient, the ability to produce IFN-gamma and TNF-alpha in response to Candida infection is not compromised. Similarly, nitric oxide production by peritoneal macrophages from G-CSF(- / - )/IL-6(- / - ) mice in response to Candida is comparable to G-CSF(- / - ) mice.

IL6/sIL6R complex contributes to emergency granulopoietic responses in G-CSF- and GM-CSF-deficient mice

Mice defective in both granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) have severely impaired neutrophil production and function, yet these mice respond to acute pathogen challenge with a significant neutrophil response. We have recently reported the development of an in vitro system to detect granulopoietic cytokines secreted from cells isolated from G-CSF, GM-CSF double knockout mice. The conditioned media produced by these cells after stimulation with lipopolysaccharide or Candida albicans supports the production and differentiation of granulocytes (ie, the conditioned media contains neutrophil promoting activity [NPA]). We now show that the NPA in the G-CSF(-/-)/GM-CSF(-/-) conditioned media requires interleukin-6 (IL6), is abolished by soluble gp130, and can be specifically immunodepleted by an anti-IL6R antibody. NPA effects on bone marrow cells are also mimicked by Hyper-IL6, and the soluble IL6R is present in NPA. These results show that the IL6/sIL6R complex is the major effector of NPA. NPA production by mice defective for both G-CSF and GM-CSF uncovers an alternative pathway to granulocyte production, which is activated after exposure to pathogens.