Disparate effects of interferon-gamma and tumor necrosis factor-alpha on early neutrophil respiratory burst and fungicidal responses to Candida albicans hyphae in vitro

Non-canonical activation of IRE1α during Candida albicans infection enhances macrophage fungicidal activity

While the canonical function of IRE1α is to detect misfolded proteins and activate the unfolded protein response (UPR) to maintain cellular homeostasis, microbial pathogens can also activate IRE1α, which modulates innate immunity and infection outcomes. However, how infection activates IRE1α and its associated inflammatory functions have not been fully elucidated. Recognition of microbe-associated molecular patterns can activate IRE1α, but it is unclear whether this depends on protein misfolding. Here, we report that a common and deadly fungal pathogen, Candida albicans, activates macrophage IRE1α through C-type lectin receptor signaling, reinforcing a role for IRE1α as a central regulator of host responses to infection by a broad range of pathogens. This activation did not depend on protein misfolding in response to C. albicans infection. Moreover, lipopolysaccharide treatment was also able to activate IRE1α prior to protein misfolding, suggesting that pathogen-mediated activation of IRE1α occurs through non-canonical mechanisms. During C. albicans infection, we observed that IRE1α activity promotes phagolysosomal fusion that supports the fungicidal activity of macrophages. Consequently, macrophages lacking IRE1α activity displayed inefficient phagosome maturation, enabling C. albicans to lyse the phagosome, evade fungal killing, and drive aberrant inflammatory cytokine production. Mechanistically, we show that IRE1α activity supports phagosomal calcium flux after phagocytosis of C. albicans, which is crucial for phagosome maturation. Importantly, deletion of IRE1α activity decreased the fungicidal activity of phagocytes in vivo during systemic C. albicans infection. Together, these data provide mechanistic insight for the non-canonical activation of IRE1α during infection, and reveal central roles for IRE1α in macrophage antifungal responses.

Role of Exercise Intensity on Th1/Th2 Immune Modulations During the COVID-19 Pandemic

The COVID-19 pandemic has led to several pioneering scientific discoveries resulting in no effective solutions with the exception of vaccination. Moderate exercise is a significant non-pharmacological strategy, to reduce the infection-related burden of COVID-19, especially in patients who are obese, elderly, and with additional comorbidities. The imbalance of T helper type 1 (Th1) or T helper type 2 (Th2) cells has been well documented among populations who have suffered as a result of the COVID-19 pandemic, and who are at maximum risk of infection and mortality. Moderate and low intensity exercise can benefit persons at risk from the disease and survivors by favorable modulation in Th1/Th2 ratios. Moreover, in COVID-19 patients, mild to moderate intensity aerobic exercise also increases immune system function but high intensity aerobic exercise may have adverse effects on immune responses. In addition, sustained hypoxia in COVID-19 patients has been reported to cause organ failure and cell death. Hypoxic conditions have also been highlighted to be triggered in COVID-19-susceptible individuals and COVID-19 survivors. This suggests that hypoxia inducible factor (HIF 1α) might be an important focus for researchers investigating effective strategies to minimize the effects of the pandemic. Intermittent hypoxic preconditioning (IHP) is a method of exposing subjects to short bouts of moderate hypoxia interspersed with brief periods of normal oxygen concentrations (recovery). This methodology inhibits the production of pro-inflammatory factors, activates HIF-1α to activate target genes, and subsequently leads to a higher production of red blood cells and hemoglobin. This increases angiogenesis and increases oxygen transport capacity. These factors can help alleviate virus induced cardiopulmonary hemodynamic disorders and endothelial dysfunction. Therefore, during the COVID-19 pandemic we propose that populations should engage in low to moderate exercise individually designed, prescribed and specific, that utilizes IHP including pranayama (yoga), swimming and high-altitude hiking exercise. This would be beneficial in affecting HIF-1α to combat the disease and its severity. Therefore, the promotion of certain exercises should be considered by all sections of the population. However, exercise recommendations and prescription for COVID-19 patients should be structured to match individual levels of capability and adaptability.

Renal CD169++ resident macrophages are crucial for protection against acute systemic candidiasis

Disseminated candidiasis remains as the most common hospital-acquired bloodstream fungal infection with up to 40% mortality rate despite the advancement of medical and hygienic practices. While it is well established that this infection heavily relies on the innate immune response for host survival, much less is known for the protective role elicited by the tissue-resident macrophage (TRM) subsets in the kidney, the prime organ for Candida persistence. Here, we describe a unique CD169++ TRM subset that controls Candida growth and inflammation during acute systemic candidiasis. Their absence causes severe fungal-mediated renal pathology. CD169++ TRMs, without being actively involved in direct fungal clearance, increase host resistance by promoting IFN-γ release and neutrophil ROS activity.

Lessons Learned from Protective Immune Responses to Optimize Vaccines against Cryptosporidiosis

In developing countries, cryptosporidiosis causes moderate-to-severe diarrhea and kills thousands of infants and toddlers annually. Drinking and recreational water contaminated with Cryptosporidium spp. oocysts has led to waterborne outbreaks in developed countries. A competent immune system is necessary to clear this parasitic infection. A better understanding of the immune responses required to prevent or limit infection by this protozoan parasite is the cornerstone of development of an effective vaccine. In this light, lessons learned from previously developed vaccines against Cryptosporidium spp. are at the foundation for development of better next-generation vaccines. In this review, we summarize the immune responses elicited by naturally and experimentally-induced Cryptosporidium spp. infection and by several experimental vaccines in various animal models. Our aim is to increase awareness about the immune responses that underlie protection against cryptosporidiosis and to encourage promotion of these immune responses as a key strategy for vaccine development. Innate and mucosal immunity will be addressed as well as adaptive immunity, with an emphasis on the balance between T_H1/T_H2 immune responses. Development of more effective vaccines against cryptosporidiosis is needed to prevent Cryptosporidium spp.-related deaths in infants and toddlers in developing countries.

Commensal enteric bacteria lipopolysaccharide impairs host defense against disseminated Candida albicans fungal infection

Commensal enteric bacteria maintain systemic immune responsiveness that protects against disseminated or localized infection in extra-intestinal tissues caused by pathogenic microbes. However, as shifts in infection susceptibility after commensal bacteria eradication have primarily been probed using viruses, the broader applicability to other pathogen types remains undefined. In sharp contrast to diminished antiviral immunity, we show commensal bacteria eradication bolsters protection against disseminated Candida albicans fungal infection. Enhanced antifungal immunity reflects more robust systemic expansion of Ly6G(hi)Ly6C(int) neutrophils, and their mobilization into infected tissues among antibiotic-treated compared with commensal bacteria-replete control mice. Reciprocally, depletion of neutrophils from expanded levels or intestinal lipopolysaccharide reconstitution overrides the antifungal protective benefits conferred by commensal bacteria eradication. This discordance in antifungal compared with antiviral immunity highlights intrinsic differences in how commensal bacteria control responsiveness for specific immune cell subsets, because pathogen-specific CD8(+) T cells that protect against viruses were suppressed similarly after C. albicans and influenza A virus infection. Thus, positive calibration of antiviral immunity by commensal bacteria is counterbalanced by restrained activation of other immune components that confer antifungal immunity.

Immunostimulatory activity of potential probiotic yeast strains in the dorsal air pouch system and the gut mucosa

AIMS

To determine the immunostimulatory activity of 15 presumptive probiotic yeast strains in the dorsal air pouch system in comparison with their activity in the gut mucosa.

METHODS AND RESULTS

Presumptive probiotic yeast strains previously isolated from human gastrointestinal tract and Feta cheese were further characterized genotypically and biochemically. The Saccharomyces cerevisiae 982, Saccharomyces boulardii KK1 and Kluyveromyces lactis 630 strains exhibited in the air pouch increased polymorphonuclear cell influx and phagocytic activity as well as cytokine production with similar potency as the probiotics Ultra levure S. boulardii and Lactobacillus acidophilus NCFB 1748. Oral administration of these strains in mice results in differential activation of small intestine immune responses concerning IgA and cytokine production as well as Toll-like receptor expression.

CONCLUSION

Besides the Saccharomyces strains 982 and KK1, the K. lactis 630 strain could also be considered as a candidate probiotic.

SIGNIFICANCE AND IMPACT OF THE STUDY

The air pouch model may be used as an alternative and rapid method for the discrimination and selection of potential probiotic yeast strains.

Immune defence mechanisms and immunoenhancement strategies in oropharyngeal candidiasis

The prevalence of oropharyngeal candidiasis continues to be high, mainly because of an increasing population of immunocompromised patients. Traditional treatment of oropharyngeal candidiasis has relied on the use of antimicrobial drugs. However, unsatisfactory results with drug monotherapy and the emergence of resistant strains have prompted investigations into the potential use of adjunctive immunoenhancing therapies for the treatment of these infections. Here we review the host-recognition systems of Candida albicans, the immune and inflammatory response to infection, and antifungal effector mechanisms. The potential of immune modulation as a therapeutic strategy in oropharyngeal candidiasis is also discussed.

Effect of interleukin-10 on the Paracoccidioides brasiliensis killing by gamma-interferon activated human neutrophils

Paracoccidioidomycosis, a deep mycosis endemic in Latin America, is a chronic granulomatous disease caused by the fungus Paracoccidioides brasiliensis. Phagocytic cells play a critical role against this fungus, and several studies have shown the effects of activator and suppressive cytokines on macrophage and monocyte functions. However, studies on polymorphonuclear neutrophils (PMNs), that are the first cells recruited to the infection sites, are scarcer. Thus, the objective of this paper was to assess whether interleukin-10 (IL-10), a potent anti-inflammatory cytokine, is able to block the activity of IFN-gamma-activated human PMNs upon P. brasiliensis intracellular killing, in vitro. The results showed that IFN-gamma-activated PMNs have an effective fungicidal activity against the fungus. This activity was associated with the release of high levels of H(2)O(2), the metabolite involved in phagocytic cells antifungal activities. However, the concomitant incubation of these cells with IFN-gamma and IL-10 significantly blocked IFN-gamma activation. As a consequence, PMNs killing activity and H(2)O(2) release were inhibited. Together, our results show the importance of PMNs exposure to activator or suppressor cytokines in the early stages of paracoccidioidomycosis infection.

Protein synthesis inhibition as a potential strategy for metabolic down-regulation

OBJECTIVE

This pilot study tested the potential of puromycin (PUR) to inhibit protein synthesis and reduce oxygen utilization in a non-hibernating, whole animal preparation.

METHODS

After anesthesia and instrumentation, male rats received a single dose of PUR or 0.9% saline (control), followed 60 min later with [(35)S] methionine/cysteine radiolabeling. Thirty minutes after isotope injection, organ biopsies were taken for quantification of de novo protein synthesis. Arterial and central venous blood gases were obtained at baseline and 60 min after injection of PUR or 0.9% saline. Temperature, mean arterial pressure (MAP), and heart rate were recorded continuously.

RESULTS

Animals receiving PUR demonstrated significant reductions in protein synthesis in all organ systems sampled (p<0.05). The overall reduction averaged 67.8%. Central venous oxygen saturations (S(cv)O(2)) were higher in the PUR group than the controls at 60 min (90+/-2% versus 80+/-4%, p<0.05). The oxygen extraction ratio (O(2)ER) decreased from 16.1+/-1.7% to 6.8+/-1.2% in the PUR group (p<0.05) and increased from 12.5+/-3.2% to 16.0+/-4.2% in the controls (p=0.44). There was no difference in temperature, MAP, heart rate or blood gas variables, other than S(cv)O(2), at baseline or 60 min between groups.

CONCLUSIONS

These results demonstrate that PUR is capable of reducing whole body protein synthesis significantly within a relatively short duration of time. This appears to decrease whole body oxygen utilization as evidenced by an increase in S(cv)O(2) and a decrease in O(2)ER. Protein synthesis inhibition may reduce metabolic demands and should be tested for its potential to improve outcomes where oxygen demands exceed oxygen delivery.

Variable Number of Tandem Repeats of TNF Receptor Type 2 Promoter as Genetic Biomarker of Susceptibility to Develop Invasive Pulmonary Aspergillosis

Tumor necrosis factor alpha (TNF-alpha) and lymphotoxin alpha (LT-alpha) are pivotal mediators of inflammatory responses in fungal infection diseases. We hypothesized that polymorphisms in genes of these cytokines or their receptors might increase the susceptibility of hematologic patients to develop invasive pulmonary aspergillosis (IPA). One hundred two hematologic patients and 124 age-matched controls were enrolled in the study, and the following standard single nucleotide polymorphisms were investigated: TNF-alpha -308 and +489, LT-alpha +252 and Tumor Necrosis Factor Receptor 2 (TNFR2) +676. Variable number of tandem repeats (VNTRs) at position -322 of the TNFR2 gene were also studied. Genotypic and allelic frequencies were similar between patients and controls. IPA was diagnosed in 54 of the 102 patients according to consensus criteria published by the European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group. TNF-alpha and LT-alpha polymorphisms were not associated with presence of IPA. Susceptibility to IPA was strongly associated with VNTR at position -322 in the promoter region of the TNR2 gene (p = 0.029) but was not associated with the presence of TNFR2 +676 polymorphism. A genetic difference in TNFR2 promoter VNTR may play a major role in susceptibility to IPA infection.

Paracoccidioides brasiliensiskilling by IFN-γ, TNF-α and GM-CSF activated human neutrophils: role for oxygen metabolites

Paracoccidioidomycosis, a deep mycosis endemic in Latin America, is a chronic granulomatous disease caused by the fungus Paracoccidioides brasiliensis. Phagocytic cells play a critical role against the fungus and several papers show the effects of activator and suppressive cytokines on macrophage and monocyte functions. However, the studies focusing on polymorphonuclear neutrophils (PMNs) antifungal functions are scarcer. Thus, the objective of the present paper was to assess the capacity of human PMNs to kill virulent P. brasiliensis strain in vitro, before and after priming with different cytokines. Moreover, the involvement of oxygen metabolites in this activity was evaluated. Nonactivated cells failed to exhibit antifungal activity. However, when these cells were IFN-gamma, TNF-alpha or GM-CSF activated, a significative fungicidal activity was detected. This process was significantly inhibited when P. brasiliensis challenge occurred in presence of catalase (CAT - a scavenger of H2O2) and superoxide dismutase (SOD - a scavenger of superoxide anion). From these results it is concluded that cytokines activation is required for P. brasiliensis killing by human PMNs, and that H2O2 and superoxide anion participate as effectors molecules in this process.

Host defence against disseminated Candida albicans infection and implications for antifungal immunotherapy

The different manifestations of Candida albicans infection are dictated by an underlying defect in the immune response of the host. Protective immunity to disseminated candidiasis, the manifestation of C. albicans infection discussed in this review, has traditionally been ascribed to innate immunity with emphasis on the role of granulocytes. Lately, however, immunological studies have learned that host defence against disseminated candidiasis is based on a complex interplay between innate and cell-mediated immunity. Despite the availability of new antifungal agents, mortality associated with disseminated C. albicans infection remains high. Immunotherapy that augments host defence is an important strategic option in the battle against disseminated candidiasis. Here, the authors review the chronological events in the pathogenesis of disseminated candidiasis that aid in predicting the impact of existing immunotherapy and the development of future immunomodulating strategies.

Signalling and oxidant adaptation in Candida albicans and Aspergillus fumigatus

Candida species and Aspergillus fumigatus were once thought to be relatively benign organisms. However, it is now known that this is not the case - Candida species rank among the top four causes of nosocomial infectious diseases in humans and A. fumigatus is the most deadly mould, often having a 90% mortality rate in immunocompromised transplant recipients. Adaptation to stress, including oxidative stress, is a necessary requisite for survival of these organisms during infection. Here, we describe the latest information on the signalling pathways and target proteins that contribute to oxidant adaptation in C. albicans and A. fumigatus, which has been obtained primarily through the analysis of mutants or inference from genome annotation.

Effective storage of granulocytes collected by centrifugation leukapheresis from donors stimulated with granulocyte-colony-stimulating factor

BACKGROUND

Donor stimulation with granulocyte-colony-stimulating factor (G-CSF) has increased the number of neutrophils (PMNs) that can be collected for granulocyte transfusion therapy. Clinical utility, however, has been limited by the inability to store functional PMNs ex vivo. This study was conducted to determine whether granulocyte products from G-CSF-stimulated donors could be effectively stored at reduced temperature (22 degrees C vs. 10 degrees C) with maintenance of functional properties in vitro and in vivo.

STUDY DESIGN AND METHODS

Nine normal subjects received G-CSF (600 microg subcutaneously) 12 hours before centrifugation leukapheresis. Granulocyte products were divided and stored for 24 and 48 hours under four conditions: 1) 22 degrees C; 2) 22 degrees C, with supplemental G-CSF (100 ng/mL); 3) 10 degrees C; and 4) 10 degrees C, with supplemental G-CSF. Functional PMN activity during ex vivo storage was assessed in vitro and in vivo by the skin-window technique for granulocytes stored at 10 degrees C for 24 hours.

RESULTS

Surface expression of CD11b/CD18, CD14, CD16, CD32, and CD64 was maintained during 48-hour storage at reduced temperature. Inducible respiratory burst activity, bactericidal activity, and fungicidal activity were preserved during storage for 48-hour storage at 10 degrees C. Proinflammatory cytokine production was decreased in product stored at 10 degrees C. Supplemental G-CSF ex vivo did not substantially improve functional activity during storage. After storage at 10 degrees C for 24 hours, in vitro chemotactic potential was maintained, and transfused granulocytes retained capacity to circulate and migrate appropriately in vivo.

CONCLUSIONS

Granulocyte product collected by centrifugation leukapheresis from G-CSF-stimulated donors can be effectively stored at subphysiologic temperature for 24 hours with preservation of functional activity. Storage at 10 degrees C appears to be slightly superior to storage at 22 degrees C.

Influence of endogenous pro-inflammatory cytokines on neutrophil-mediated damage ofCandida albicanspseudohyphae, quantified in a modified tetrazolium dye assay

For quantitative assessment of polymorphonuclear granulocyte (PMN)-mediated pseudohyphal damage, an improved tetrazolium (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide; XTT) dye assay was developed. The modified assay proved to be a reliable indicator of viable pseudohyphal inoculum sizes. In addition, the influence of various endogenous pro-inflammatory cytokines on the capacity of PMN to damage Candida albicans pseudohyphae was investigated. PMN obtained from mice in which the genes encoding for tumor necrosis factor-alpha/lymphotoxin-alpha (TNF/LT), interferon-gamma (IFNgamma), interleukin (IL)-1alpha, or IL-1beta were disrupted, showed a significantly reduced pseudohyphal damage capacity in comparison with control PMN. The reduction amounted 25% for TNF-/- LT-/-, 11% for IFNgamma-/-, 21% for IL-1alpha-/-, and 34% for IL-1alpha-/-beta-/- PMN. In contrast, deficiency of IL-12 or IL-18 did not result in a diminished capacity to damage pseudohyphae and the capacity of PMN to damage Candida pseudohyphae was even slightly increased by 10% in IL-18-/- mice. These data suggest that endogenous pro-inflammatory cytokines are able to modulate antihyphal activity of PMN, the main effector cells against disseminated candidiasis by virtue of their capacity to kill both Candida blastoconidia and pseudohyphae.

Induction of genes mediating interferon-dependent extracellular trap formation during neutrophil differentiation

Interferons (IFNs) are cytokines that possess potent anti-viral and immunoregulatory activities. In contrast, their potential role(s) in anti-bacterial defense and neutrophil activation mechanisms is less well explored. By comparing gene expression patterns between immature and mature human neutrophils, we obtained evidence that intracellular proteases and other anti-bacterial proteins are produced at earlier stages of maturation, whereas the genes for receptors and signaling molecules required for the release of these effector molecules are preferentially induced during terminal differentiation. For instance, mature neutrophils strongly expressed genes that increase their responses to type I and type II IFNs. Interestingly, granulocyte/macrophage colony-stimulating factor was identified as a repressor of IFN signaling components and consequently of IFN-responsive genes. Both IFN-alpha and IFN-gamma induced strong tyrosine phosphorylation of STAT1 in mature but not in immature neutrophils. Functional in vitro studies suggested that IFNs act as priming factors on mature neutrophils, allowing the formation of extracellular traps upon subsequent stimulation with complement factor 5a (C5a). In contrast, both IFN-alpha and IFN-gamma had only little capacity to prime immature cells in this system. Moreover, both IFNs did not have significant anti-proliferative effects on immature neutrophils. These data contribute to our understanding regarding changes of gene expression during neutrophil differentiation and IFN-mediated anti-bacterial defense mechanisms.

Interferon-gamma activation of polymorphonuclear neutrophil function

As current research illuminates the dynamic interplay between the innate and acquired immune responses, the interaction and communication between these two arms has yet to be fully investigated. Polymorphonuclear neutrophils (PMNs) and interferon-gamma (IFN-gamma) are known critical components of innate and acquired immunity, respectively. However, recent studies have demonstrated that these two components are not entirely isolated. Treatment of PMNs with IFN-gamma elicits a variety of responses depending on stimuli and environmental conditions. These responses include increased oxidative burst, differential gene expression, and induction of antigen presentation. Many of these functions have been overlooked in PMNs, which have long been classified as terminal phagocytic cells incapable of protein synthesis. As this review reports, the old definition of the PMN is in need of an update, as these cells have demonstrated their ability to mediate the transition between the innate and acquired immune responses.

The Contribution of the Toll-Like/IL-1 Receptor Superfamily to Innate and Adaptive Immunity to Fungal Pathogens In Vivo

In vitro studies have indicated the importance of Toll-like receptor (TLR) signaling in response to the fungal pathogens Candida albicans and Aspergillus fumigatus. However, the functional consequences of the complex interplay between fungal morphogenesis and TLR signaling in vivo remain largely undefined. In this study we evaluate the impact of the IL-1R/TLR/myeloid differentiation primary response gene 88 (MyD88)-dependent signaling pathway on the innate and adaptive Th immunities to C. albicans and A. fumigatus in vivo. It was found that 1) the MyD88-dependent pathway is required for resistance to both fungi; 2) the involvement of the MyD88 adapter may occur through signaling by distinct members of the IL-1R/TLR superfamily, including IL-1R, TLR2, TLR4, and TLR9, with the proportional role of the individual receptors varying depending on fungal species, fungal morphotypes, and route of infection; 3) individual TLRs and IL-1R activate specialized antifungal effector functions on neutrophils, which correlates with susceptibility to infection; and 4) MyD88-dependent signaling on dendritic cells is crucial for priming antifungal Th1 responses. Thus, the finding that the innate and adaptive immunities to C. albicans and A. fumigatus require the coordinated action of distinct members of the IL-1R/TLR superfamily acting through MyD88 makes TLR manipulation amenable to the induction of host resistance to fungi.

Catalases of Aspergillus fumigatus

Upon infection of a host, the pathogenic fungus Aspergillus fumigatus is attacked by the reactive oxygen species produced by phagocytic cells. Detoxification of hydrogen peroxide by catalases was proposed as a way to overcome this host response. A. fumigatus produces three active catalases; one is produced by conidia, and two are produced by mycelia. The mycelial catalase Cat1p was studied previously. Here we characterized the two other catalases, their genes, and the phenotypes of gene-disrupted mutants. CatAp, a spore-specific monofunctional catalase, is resistant to heat, metal ions, and detergent. This enzyme is a dimeric protein with 84.5-kDa subunits. The 749-amino-acid polypeptide exhibits high levels of similarity to the Aspergillus nidulans CatA catalase and to bacterial catalase HPII of Escherichia coli. In spite of increased sensitivity to H(2)O(2), killing of DeltacatA conidia by alveolar macrophages and virulence in animals were similar to the killing of conidia by alveolar macrophages and virulence in animals observed for the wild type. In contrast to the Cat1p and CatAp catalases, the mycelial Cat2p enzyme is a bifunctional catalase-peroxidase and is sensitive to heat, metal ions, and detergent. This enzyme, an 82-kDa monomer, is homologous to catalase-peroxidases of several fungi and bacteria. Surprisingly, mycelium of the double Deltacat1Deltacat2 mutant with no catalase activity exhibited only slightly increased sensitivity to H(2)O(2) and was as sensitive to killing by polymorphonuclear neutrophils as mycelium of the wild-type strain. However, this mutant exhibited delayed infection in the rat model of aspergillosis compared to infection by the wild-type strain. These results indicate that conidial catalase is not a virulence factor and that mycelial catalases transiently protect the fungus from the host.

Cytokines in immunodeficient patients with invasive fungal infections: an emerging therapy

Immune response is the major contributor to host defense against opportunistic fungal infections such as candidiasis, aspergillosis and other rare infections. A number of cytokines have been developed and studied in vitro for activity against fungal pathogens. The most studied among them in relation to fungal infections are granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF) and interferon-gamma (IFN-gamma). The fields where these cytokines have been predominantly studied or where they may need more study are primary immunodeficiencies of the phagocytic cells, neonatal age, human immunodeficiency virus infection and cancer-related conditions such as neutropenia and hemopoietic cell transplantation. In this review, the in vitro, experimental animal and clinical data of cytokines are summarized in relation to invasive candidiasis, aspergillosis and emerging fungal infections. Cytokine administration to patients together with antifungal agents, as well as transfusion of cytokine-upgraded phagocytes, are promising immunotherapeutic modalities for further research.

Lethality of yeasts with low pathogenicity in mice immunocompromised by cyclophosphamide treatment

One strain each of Arxiozyma telluris, Saccharomyces cerevisiae, and S. kluyveri showed lethal activity in cyclophosphamide (CY)-treated mice. Accumulation of these yeast cells in the kidneys and elevation of the levels of cytokines, tumor necrosis factor-alpha, and interleukin-1alpha in the sera were recognized in the CY-treated infected-debilitated mice.

Human alveolar macrophage phagocytic function is impaired by aggregates of ultrafine carbon particles

Alveolar macrophages (AM) were collected by bronchoalveolar lavage from healthy volunteers. The AM were loaded with small masses (0.03-3 microg/10(6) AM) of ultrafine carbon particle aggregates. The phagocytic activity of the cells was studied 20 h after the loading. Fluorescein-labeled silica particles (3 microm) were used as test particles and the attachment and ingestion processes were studied separately. In some experiments, AM were incubated with interferon-gamma (IFN-gamma) for 20 h before and during the test of phagocytic activity and during measurement of oxidative metabolism. The ingested carbon particles induced a dose-related impairment of both the attachment and the ingestion processes with a marked impairment down to a carbon particle dose around 0.2 microg/10(6) AM. Such levels should reasonably occur after inhalation of existing concentrations of urban air particles, which to a considerable extent consist of aggregates of ultrafine particles with a carbon skeleton. Incubation with IFN-gamma (12.5 U/ml) also induced significant impairments in both the attachment and the ingestion processes. Loading with carbon further aggravated the effect of IFN-gamma. In contrast to earlier studies in rat AM, IFN-gamma did not impair the oxidative metabolism at rest in these human AM; instead the oxidative metabolism was increased. This difference was due to a difference between rat and human AM and not between rat and human IFN-gamma. Our results suggest that ingested environmental particles in AM, e.g., after an episode of high particle concentration, may impair phagocytic capacity of the cells, especially after infections that induce an increased production of IFN-gamma. Consequently, there might be a risk for additional infections. Moreover, inhaled particles not phagocytized by AM might damage the lung tissue.

Type 1/Type 2 immunity in infectious diseases

T helper type 1 (Th1) lymphocytes secrete secrete interleukin (IL)-2, interferon-gamma, and lymphotoxin-alpha and stimulate type 1 immunity, which is characterized by intense phagocytic activity. Conversely, Th2 cells secrete IL-4, IL-5, IL-9, IL-10, and IL-13 and stimulate type 2 immunity, which is characterized by high antibody titers. Type 1 and type 2 immunity are not strictly synonymous with cell-mediated and humoral immunity, because Th1 cells also stimulate moderate levels of antibody production, whereas Th2 cells actively suppress phagocytosis. For most infections, save those caused by large eukaryotic pathogens, type 1 immunity is protective, whereas type 2 responses assist with the resolution of cell-mediated inflammation. Severe systemic stress, immunosuppression, or overwhelming microbial inoculation causes the immune system to mount a type 2 response to an infection normally controlled by type 1 immunity. In such cases, administration of antimicrobial chemotherapy and exogenous cytokines restores systemic balance, which allows successful immune responses to clear the infection.

Modulation of neutrophil function in host defense against disseminated Candida albicans infection in mice

Neutrophils (PMNs) constitute the main mechanism of host defense against acute invasive and disseminated candidiasis. Recent studies have demonstrated that tumor necrosis factor-alpha (TNFalpha), interleukin-6 (IL-6) and granulocyte colony-stimulating factor (G-CSF) play an important role in the recruitment of PMNs at the site of invasive Candida infection. In the absence of either TNFalpha or IL-6, the course of experimental disseminated candidiasis is more severe, due to defective PMN recruitment. Treatment of mice with recombinant G-CSF (rG-CSF) leads to a significantly reduced mortality during disseminated candidiasis. The outgrowth of Candida albicans from the organs of rG-CSF-treated mice is significantly decreased. Treatment with the combination of rG-CSF and fluconazole has an additive effect on the reduction of fungal load in the organs. In subacute or chronic disseminated Candida infection, rG-CSF is less effective, indicating that neutrophil recruitment and activation are crucial in acute, life-threatening candidiasis, whereas other host defense mechanisms control the outcome of less overwhelming invasive Candida infection.

Increased severity of Candida vaginitis in BALB/c nu/nu mice versus the parent strain is not abrogated by adoptive transfer of T cell enriched lymphocytes

The role of the host immune system in combating candidal infections in the vagina is poorly understood. A murine model of Candida vaginitis was used to elucidate the role of T cells in a candidal infection. Athymic BALB/c nu/nu mice or normal BALB/c mice were induced into estrus and then infected with 1 x 10(6) Candida albicans intravaginally. The infection was monitored over 1 week. Samples from blood, small intestine, tongue, kidney, spleen, liver, uterus and vagina were tested for recoverable C. albicans. Histology of the vagina was assessed for both inflammation and extent of infection. Results indicated that the BALB/c nu/nu mice had similar levels of vaginal yeast load to the normal BALB/c mice. In 25-30% of nude mice Candida was also recovered from extra vaginal sites (kidney, liver, small intestine), however, extra vaginal dissemination was not observed in any normal BALB/c animals. Histologically, both the nu/nu and control BALB/c had similar levels of vaginal inflammation; however, the nu/nu mice had more florid fungal growth in the vaginal epithelium. Adoptive transfer of either immune or non-immune BALB/c T cells into nude mice had no affect on either infection or vaginal inflammation. Immunohistochemical staining of vaginal tissues from normal BALB/c mice or nude mice adoptively transferred with either immune or non-immune T cells with anti-CD3 monoclonal antibody revealed no significant difference between groups in the numbers of CD3+ vaginal T cells. However, in mice receiving either immune or non-immune T cells no yeast was recovered from any tissues except the vagina. These data show that T cells have a limited role in protecting the vagina from C. albicans infection.

Ingested aggregates of ultrafine carbon particles and interferon-gamma impair rat alveolar macrophage function

Alveolar macrophages (AM), obtained by lavage from the rat lung, were allowed to ingest aggregated ultrafine carbon particles, about 1 microgram/10(6) AM, which is a realistic result of long-term exposure to ambient air. The effects of the ingested carbon on the phagocytosis of test particles and oxidative metabolism of the AM were studied. In addition, the effects of short-term (40 min or 2 h) and long-term (28 or 44 h) incubation with interferon gamma (IFN-gamma) on AM loaded and unloaded with carbon were investigated. Phagocytic activity was studied using fluorescein-labeled 3.2-microgram silica particles. The attachment and ingestion processes were evaluated separately. The ingested carbon markedly impaired the phagocytosis of silica particles; the accumulated attachment (sum of attached and ingested particles per AM) decreased from 5.0 to 4.2 particles/AM and the ingested fraction (number of ingested particles per AM divided with accumulated attachment) from 0.42 to 0.27. The short-term incubation with IFN-gamma tended to increase the accumulated attachment (from 5.0 to 5.7 particles/AM) and decreased the ingested fraction (from 0.42 to 0.34) in unloaded AM. Long-term incubation with IFN-gamma markedly impaired both the accumulated attachment (to 3.8 particles/AM) and the ingested fraction (to 0.24) in unloaded AM and the carbon load further decreased the accumulated attachment to 2.8 particles/AM, and the ingested fraction to 0.21. The oxidative metabolism was not effected by the ingested carbon or the short-term incubation with IFN-gamma, but the long-term incubation with IFN-gamma increased it with a factor of almost 3. Our results suggest that ingested environmental particles in AM may markedly impair their phagocytic capacity, especially during long-term exposure to IFN-gamma as after infections, and there might be an increased risk for additional infections. Moreover, during an episode of high ambient particle concentration the inhaled particles will not be efficiently phagocytized and may thereby damage the Lung tissue.

The bZip transcription factor Cap1p is involved in multidrug resistance and oxidative stress response in Candida albicans

Candida albicans is an opportunistic pathogenic yeast which frequently develops resistance to the antifungal agent fluconazole (FCZ) in patients undergoing long-term therapy. FCZ-resistant strains often display a reduced intracellular FCZ accumulation which correlates with the overexpression of the ATP-binding cassette transporters CDR1 and CDR2 or the major facilitator (MF) MDR1. We have recently cloned a C. albicans gene, named CAP1, which codes for a bZip transcription factor of the AP-1 family homologous to the Yap1 protein involved in multidrug resistance and response to oxidative stress in Saccharomyces cerevisiae. CAP1 was found to confer FCZ resistance in S. cerevisiae by transcriptionally activating FLR1, a gene coding for an MF homologous to the C. albicans MDR1 gene product (A.-M. Alarco, I. Balan, D. Talibi, N. Mainville, and M. Raymond, J. Biol. Chem. 272:19304-19313, 1997). To study the role of CAP1 in C. albicans, we constructed a CAI4-derived mutant strain carrying a homozygous deletion of the CAP1 gene (CJD21). We found that deletion of CAP1 did not affect the susceptibility of CJD21 cells to FCZ, cerulenin, brefeldin A, and diamide but caused hypersensitivity to cadmium, 4-nitroquinoline N-oxide, 1,10-phenanthroline, and hydrogen peroxide, an effect which was reverted by reintroduction of the CAP1 gene in these cells. Introduction of a hyperactive truncated allele of CAP1 (CAP1-TR) in CJD21 resulted in resistance of the cells to all of the above compounds except hydrogen peroxide. The hyperresistant phenotype displayed by the CJD21 CAP1-TR transformants was found to correlate with the overexpression of a number of potential CAP1 transcriptional targets such as MDR1, CaYCF1, CaGLR1, and CaTRR1. Taken together, our results demonstrate that CAP1 is involved in multidrug resistance and oxidative stress response in C. albicans. Finally, disruption of CAP1 in strain FR2, selected in vitro for FCZ resistance and constitutively overexpressing MDR1, did not suppress but rather increased the levels of MDR1 expression, demonstrating that CAP1 acts as a negative transcriptional regulator of the MDR1 gene in FR2 and is not responsible for MDR1 overexpression in this strain.

Anti-Candida activity of calprotectin in combination with neutrophils or lactoferrin

The effect of an anti-microbial protein, calprotectin, in combination with neutrophils on the growth of Candida albicans was investigated. The growth inhibition of C. albicans by murine neutrophils was augmented by the addition of a low concentration of calprotectin prepared from rat peritoneal exudate cells. The concentrations of calprotectin causing 50% inhibition of growth of C. albicans in the absence or presence of neutrophils at an effector-to-target (E/T) ratio of 30 and 60 were estimated to be 0.45, 0.34 and 0.28 U/ml, respectively. The anti-Candida activity of calprotectin was completely inhibited by 2 microM of zinc ion, while it only partially lowered the activity of the combination of calprotectin and neutrophils. Lactoferrin, which is an anti-microbial protein released from neutrophils, strongly inhibited the growth of C. albicans in combination with calprotectin. These results suggest that calprotectin and lactoferrin released from neutrophils may cooperate to inhibit the growth of C. albicans at a local lesion of the infection where there is an accumulation of neutrophils.

Tumor necrosis factor alpha enhances antifungal activities of polymorphonuclear and mononuclear phagocytes against Aspergillus fumigatus

Invasive aspergillosis is a serious complication in immunocompromised patients. The effects of recombinant human tumor necrosis factor alpha (TNF-alpha) on antifungal activities of human neutrophils (polymorphonuclear leukocytes [PMNs]), human monocytes (MNCs), and rabbit pulmonary alveolar macrophages (PAMs) against Aspergillus fumigatus were studied. The percentage of PMN-induced hyphal damage was increased after 30 min of incubation of PMNs with 0.1 ng of TNF-alpha per ml at 37 degreesC (P = 0.043). At 0.1 to 10 ng/ml, TNF-alpha also increased superoxide anion (O2-) produced by PMNs in response to phorbol myristate acetate, N-formylmethionyl leucyl phenylalanine, and unopsonized hyphae (P < 0.01) but did not exert any effect on PMN phagocytosis of conidia in the presence of serum. By comparison, TNF-alpha induced only a slight increase in O2- production by MNCs in response to phorbol myristate acetate (P = 0.05) and no concomitant increase in the percentage of MNC-induced hyphal damage. Incubation of MNCs with TNF-alpha at 0.001 to 10 ng/ml for 2 days had no effect on phagocytosis or conidiocidal activity. By contrast, incubation of PAMs with TNF-alpha at 0.1 to 10 ng/ml for 2 days increased phagocytosis of conidia (P = 0.03). Thus, TNF-alpha augments the capacity of PMNs to damage Aspergillus hyphae, possibly through enhanced oxidative mechanisms, and increases PAM phagocytic activity against conidia. As such, TNF-alpha may have an important role in host defense against aspergillosis, and neutralization of its activity may be complicated by increased susceptibility to aspergillosis.

Interaction between human interleukin-2-activated natural killer cells and heat-killed germ tube forms of Candida albicans

Human interleukin-2-activated natural killer (LAK) cells are able to recognize and to bind to both live and heat-killed germ tube forms of Candida albicans, establishing a wide and intimate contact as revealed by electron microscopic observations. Following the interaction, LAK cells are activated: an increased expression of some cytokine mRNA (in particular, TNF-alpha, GM-CSF, and IFN-gamma) has been revealed by RT-PCR and perforin secretion has been suggested by immunofluorescence microscopy. Nonetheless, neither morphological damage or growth inhibition of fungal target cells have been detected. Instead, evident signs of cell damage could be noticed in interacting LAK cells. Moreover, the observation by transmission electron microscopy of LAK cell-germ tube conjugates revealed the presence of apoptotic cells. The analysis of LAK cell cytotoxic activity against DAUDI cells showed that the lymphocytic effector underwent a significant reduction in its lytic capability after the interaction with C. albicans. The results obtained in this in vitro study seem to indicate that in such an interaction LAK cells cannot directly inhibit or kill the fungal pathogen by using their lytic machinery but they secrete those cytokines which have stimulatory effects on phagocytic cells. The ultimate results are the programmed death of LAK cells and the enhancement of the fungicidal activity exerted by competent cells.

Cloning and sequencing of a Candida albicans catalase gene and effects of disruption of this gene

Catalase plays a key role as an antioxidant, protecting aerobic organisms from the toxic effects of hydrogen peroxide, and in some cases has been postulated to be a virulence factor. To help elucidate the function of catalase in Candida albicans, a single C. albicans-derived catalase gene, designated CAT1, was isolated and cloned. Degenerate PCR primers based on highly conserved areas of other fungal catalase genes were used to amplify a 411-bp product from genomic DNA of C. albicans ATCC 10261. By using this product as a probe, catalase clones were isolated from genomic libraries of C. albicans. Nucleotide sequence analysis revealed an open reading frame encoding a protein of 487 amino acid residues. Construction of a CAT1-deficient mutant was achieved by using the Ura-blaster technique for sequential disruption of multiple alleles by integrative transformation using URA3 as a selectable marker. Resulting mutants exhibited normal morphology and comparable growth rates of both yeast and mycelial forms. Enzymatic analysis revealed an abundance of catalase in the wild-type strain but decreasing catalase activity in heterozygous mutants and no detectable catalase in a homozygous null mutant. In vitro assays showed the mutant strains to be more sensitive to damage by both neutrophils and concentrations of exogenous peroxide that were sublethal for the parental strain. Compared to the parental strain, the homozygous null mutant strain was far less virulent for mice in an intravenous infection model of disseminated candidiasis. Definitive linkage of CAT1 with virulence would require restoration of activity by reintroduction of the gene into mutants. However, initial results in mice, taken together with the enhanced susceptibility of catalase-deficient hyphae to damage by human neutrophils, suggest that catalase may enhance the pathogenicity of C. albicans.

Interleukin-4 suppresses antifungal activity of human mononuclear phagocytes against Candida albicans in association with decreased uptake of blastoconidia

Pathogenesis of invasive candidiasis may involve regulatory activities of Th2 immunity on phagocytic host defenses. The effects of interleukin (IL)-4 on antifungal capacity of human mononuclear phagocytes against Candida albicans were studied. Incubation of adherent mononuclear leukocytes from healthy donors with IL-4 (1-5 ng ml(-1)) at 37 degrees C for 2-4 days suppressed uptake of C. albicans blastoconidia in the presence of human serum (P < or = 0.01), and anti-IL-4 inhibited its suppressive effect. The effect of IL-4 was protein synthesis-dependent. Interferon-gamma (0.25-25 ng ml(-1)), granulocyte-macrophage colony-stimulating factor (CSF, 20 ng ml(-1)), macrophage-CSF (15 ng ml(-1)) but not IL-10 (100 ng ml(-1)) somewhat counteracted the suppressive effect of IL-4. In contrast, mannose receptor-mediated uptake of blastoconidia in the absence of serum was increased by IL-4. Killing of conidia was decreased after incubation of morphonuclear leukocytes with IL-4 for 2 days (P < 0.05). While superoxide anion production in response to phorbol myristate acetate was decreased by IL-4 (P < 0.05), it was not altered in response to blastoconidia and pseudohyphae. Morphonuclear leukocyte-induced pseudohyphal damage also remained unaltered. These findings suggest that IL-4 plays its detrimental role in invasive candidiasis by predominantly suppressing uptake and killing of blastoconidia by morphonuclear leukocytes. Anti-IL-4, IFN-gamma, GM-CSF and M-CSF appear to counteract suppression of morphonuclear leukocyte phagocytic activity suggesting new approaches to the management of disseminated candidiasis.

Studies on polymorphonuclear leukocyte bactericidal function III: the role of extracellular matrix proteins

We investigated the effect of the extracellular matrix proteins fibronectin (Fn) and laminin (Ln) on polymorphonuclear leukocytes (PMN) bactericidal activity. Adherence of PMN to increasing concentrations of Ln significantly increased the killing of Escherichia coli after 240 min of adherence, while fibronectin significantly increased PMN staphlacidal activity after 240 min of adherence. The addition of IL-1beta and IL-8 but not TNF-alpha increased PMN bactericidal activity against E. coli when PMN were adhered to Ln, while TNF-alpha and IL-8 increased PMN bactericidal activity against Staphylococcus aureus when PMN were adhered to Ln. TNF-alpha increased PMN killing of E. coli when PMN were adhered to Fn, while only IL-1beta increased the killing of S. aureus when PMN were adhered to FN. Anti-VLA-3 (alpha3/beta1) monoclonal antibodies (mAbs) inhibited the effect of Ln on PMN bactericidal activity, while anti-VLA-5 (alpha5/beta1) mAbs inhibited the effect of Fn on PMN bactericidal activity. Progressive cross-linkage of these two receptors led to a dose-dependent reduction in PMN bactericidal activity for both pathogens when PMN were adhered to Ln or Fn, respectively. These results demonstrate that extracellular matrix proteins +/- exogenously added cytokines have the capacity to regulate PMN bactericidal activity. The signals sent by these matrix proteins to increase PMN bactericidal activity are transduced primarily via separate alpha subunits of the beta1 integrin complex. Stimulation of these receptors might lead to potential upregulation of PMN bactericidal activity which would be potentially advantageous in vivo at sites of infection.

Macrophages in resistance to candidiasis

Candida albicans, an increasingly common opportunistic pathogenic fungus, frequently causes disease in immunodeficient but not immunocompetent hosts. Clarifying the role of the phagocytic cells that participate in resistance to candidiasis not only is basic to understanding how the host copes with this dimorphic pathogen but also will expedite the development of innovative prophylactic and therapeutic approaches for treating the multiple clinical presentations that candidiasis encompasses. In this review, we present evidence that a diverse population of mononuclear phagocytes, in different states of activation and differentiation and from a variety of host species, can phagocytize C. albicans blastoconidia via an array of opsonic and nonopsonic mechanisms and can kill C. albicans blastoconidia and hyphae by means of oxygen-dependent and -independent mechanisms. Reactive nitrogen intermediates should now be added to the well-established candidacidal reactive oxygen intermediates of macrophages. Furthermore, what were thought to be two independent pathways, i.e., nitric oxide and superoxide anion, have now been shown to combine to form a potent macrophage candidacidal molecule, peroxynitrite. In contrast to monocytes and neutrophils, which are important in resistance to early stages of C. albicans infections, more differentiated macrophages activated by cytokines such as gamma interferon participate in the acquired resistance of hosts with C. albicans-specific, cell-mediated immunity. Evidence presented in this review demonstrates that mononuclear phagocytes, in some instances in the absence of other professional phagocytes such as neutrophils, play an import role in resistance to systemic and mucosal candidiasis.

Gamma interferon is not essential in host defense against disseminated candidiasis in mice

In vitro studies have suggested a role for interferon gamma (IFN-gamma) in host defense against disseminated candidiasis, but in vivo studies are inconclusive. We utilized homozygous IFN-gamma knockout (GKO) mice to determine if the cytokine is essential in host defense against this disease. Genotypes of mice were determined by PCR with specific primers for the normal or disrupted IFN-gamma gene. The GKO status of the mice was confirmed by an enzyme-linked immunosorbent assay, which showed no detectable IFN-gamma produced by their splenocytes stimulated by concanavalin A. To test the susceptibility of GKO mice to candidiasis, the animals were infected either intravenously (i.v.) or intragastrically (i.g.) with Candida albicans. GKO mice infected i.v. survived as long as wild-type (WT) mice and showed no difference in Candida CFU counts in liver, spleen, or kidneys compared to those for WT mice. When animals were given Candida i.g., at 3 h or at 10 or 21 days after infection, there was no dissemination of Candida to the lung, liver, spleen, or kidneys for either GKO or WT mice. There was no difference in Candida CFU counts recovered from the stomach or intestines between GKO and WT mice. Histological examination of the stomach cardial-atrium fold, where the fungus was located, showed that GKO mice did not have evidence of more tissue damage or fungal invasion than WT mice. Finally, the jejunum for both types of mice showed no evidence of tissue damage or fungal invasion. These studies indicate that IFN-gamma is not essential in host defense against C. albicans that originates from a mucosal site or that is given directly into the bloodstream in a mouse model.

Gamma interferon protects endothelial cells from damage by Candida albicans by inhibiting endothelial cell phagocytosis

Once Candida albicans comes in contact with endothelial cells, it induces cellular injury. This endothelial cell injury may be a mechanism by which blood-borne organisms escape from the intravascular compartment and invade the tissue parenchyma during hematogenous infection. We have been investigating the ability of cytokines to modulate endothelial cell injury caused by C. albicans. Previously we reported that pretreatment of endothelial cells with gamma interferon (IFN-gamma) protects these cells from candidal injury in vitro. In the current study, we examined potential mechanisms of the cytoprotective effects of IFN-gamma. Time course experiments demonstrated that maximal reduction in candidal injury of endothelial cells occurred after the endothelial cells had been exposed to IFN-gamma for at least 72 h. In other studies, we determined that IFN-gamma reduced endothelial cell phagocytosis of C. albicans by 41.3% compared with that of untreated endothelial cells (P < 0.01). Since endothelial cell phagocytosis of C. albicans is required for damage to occur, inhibition of phagocytosis is likely a mechanism by which IFN-gamma protects endothelial cells from candidal injury. We also found that the cytoprotective effect of IFN-gamma is not mediated by reducing access of the organisms to intracellular endothelial cell iron or by upregulating the synthesis of reactive oxygen intermediates (which could potentially reduce the ability of C. albicans to injure endothelial cells). Thus, inhibiting endothelial cell phagocytosis of C. albicans may be a mechanism by which IFN-gamma augments the host defense against hematogenously disseminated candidal infections.

Tumor necrosis factor primes neutrophils to kill Staphylococcus aureus by an oxygen-dependent mechanism and Plasmodium falciparum by an oxygen-independent mechanism

The cytokine tumor necrosis factor (TNF) plays the important role of priming neutrophils for increased antimicrobial activity. We now demonstrate that human neutrophils which lack the ability to generate oxygen radicals, from patients with chronic granulomatous disease, show TNF-induced enhancement of killing of intraerythrocytic stages of Plasmodium falciparum but not of Staphylococcus aureus.

Tumor necrosis factor priming of peripheral blood neutrophils from rheumatoid arthritis patients

Recently it was shown that tumor necrosis factor-alpha (TNF) receptors on neutrophils may be down-regulated after stimulation with proinflammatory mediators. Since in rheumatoid arthritis neutrophils are likely to encounter these mediators in the circulation, we tested the hypothesis that rheumatoid arthritis neutrophil TNF receptors are down-regulated. Peripheral blood neutrophils from patients with rheumatoid arthritis and healthy subjects were compared with respect to their TNF binding activity and ability to be primed by TNF. There were no differences between rheumatoid arthritis and control neutrophils in receptor-mediated TNF binding, superoxide release in response to agonist, and TNF priming of this respiratory burst or in the ability to degrade cartilage in vitro and TNF priming for increased cartilage damage. It is evident that rheumatoid arthritis blood neutrophils retain the ability to bind TNF and can be primed by TNF for increased oxygen radical production and augmented cartilage damage. These findings further implicate the role of neutrophils in the pathogenesis of arthritis.

Inhibition of neutrophil respiratory burst and cytokine priming by gamma-linolenic acid

The effect of n-6 fatty acids, particularly gamma-linolenic acid (GLA), on the oxidase response and neutrophil priming by tumour necrosis factor alpha and interleukin 8 was studied in both normal volunteers and patients with obstructive jaundice. GLA inhibited the neutrophil respiratory burst at concentrations higher than 50 mummol/l, but abolished cytokine priming at concentrations as low as 1 mummol/l. Inhibition was not the result of either cytotoxicity to the neutrophils or alteration in cytosolic free calcium homoeostasis. It is concluded that GLA is a potential inhibitor of neutrophil priming by cytokines and of the oxidative response.

gamma Interferon gene expression and release in human lymphocytes directly activated by Cryptococcus neoformans and Candida albicans

Previous studies in our laboratory and others have demonstrated that T and/or NK cells can directly bind to and inhibit the growth of the medically important fungal pathogens Cryptococcus neoformans and Candida albicans by apparently non-major histocompatibility complex-restricted mechanisms. Here, we examined whether this direct interaction between lymphocytes and fungi also results in cytokine gene expression and release. Nonadherent lymphocytes (NAL), isolated from human peripheral blood mononuclear cells by depletion of cells adherent to plastic and nylon wool, released gamma interferon (IFN-gamma), but not interleukin-4 (IL-4) and IL-10, following stimulation with C. neoformans yeast cells and C. albicans yeast cells, hyphae, and supernatants. The fungal stimuli also induced IFN-gamma mRNA, with peak gene expression seen at or after 18 h. IFN-gamma release was still seen even when either NK cells or T lymphocytes were depleted by negative selection, suggesting that both cell types can be stimulated by fungi to produce IFN-gamma. Release of IFN-gamma from fungus-stimulated NAL occurred in the absence of an intact complement system and was not especially enhanced by culture with IL-2 or IL-12. These data expand the mechanisms by which the direct interaction of NAL with fungal targets can lead to immune activation. Moreover, to our knowledge, this is the first demonstration of direct stimulation of T-cell cytokine release by microbial pathogens.

Production and function of cytokines in natural and acquired immunity to Candida albicans infection

Host resistance against infections caused by the yeast Candida albicans is mediated predominantly by polymorphonuclear leukocytes and macrophages. Antigens of Candida stimulate lymphocyte proliferation and cytokine synthesis, and in both humans and mice, these cytokines enhance the candidacidal functions of the phagocytic cells. In systemic candidiasis in mice, cytokine production has been found to be a function of the CD4+ T helper (Th) cells. The Th1 subset of these cells, characterized by the production of gamma interferon and interleukin-2, is associated with macrophage activation and enhanced resistance against reinfection, whereas the Th2 subset, which produces interleukins-4, -6, and -10, is linked to the development of chronic disease. However, other models have generated divergent data. Mucosal infection generally elicits Th1-type cytokine responses and protection from systemic challenge, and identification of cytokine mRNA present in infected tissues of mice that develop mild or severe lesions does not show pure Th1- or Th2-type responses. Furthermore, antigens of C. albicans, mannan in particular, can induce suppressor cells that modulate both specific and nonspecific cellular and humoral immune responses, and there is an emerging body of evidence that molecular mimicry may affect the efficiency of anti-Candida responses within defined genetic contexts.

Administration of rHuGM-CSF activates monocyte reactive oxygen species secretion and adhesion molecule expression in vivo in patients following high-dose chemotherapy

Microbicidal and cytocidal products of the respiratory burst and integrin adhesion molecule expression have been studied in monocytes from patients who received rHuGM-CSF during regeneration after high-dose chemotherapy. In this study, administration of rHuGM-CSF after high-dose chemotherapy significantly augmented the secretion of inducible products of the monocyte respiratory burst. Monocyte activation persisted for several weeks after the cessation of GM-CSF therapy. Under in vitro conditions that mimicked gram-negative (LPS) and gram-positive (opsonized Staphylococcus aureus) sepsis, the monocyte responded to such stimulation by exhibiting an enhanced release of hydrogen peroxide at both regeneration and several weeks later (P < 0.001). Similarly, GM-CSF administration significantly augmented the phenotypic expression of the beta 2-integrin adhesion molecules and allowed the leucocyte-specific selectin, LAM-1, and the beta 2-integrins to respond normally to inflammatory stimulation by LPS. We further present evidence that GM-CSF therapy restored the otherwise refractory status of monocytes to inflammatory stimulation that existed in those patients given chemotherapy alone. The restoration of monocyte responsiveness by GM-CSF following high-dose chemotherapy could be a potentially valuable and hitherto not described action of rHuGM-CSF on monocyte function. We conclude that administration of GM-CSF may have the potential for restoring as well as augmenting the anti-microbial and anti-tumour function of the monocyte after high-dose chemotherapy.