Measurement of candidacidal activity of specific leukocyte types in mixed cell populations I. Normal, myeloperoxidase-deficient, and chronic granulomatous disease neutrophils

Phagocytosis and the antigen-processing abilities of macrophages derived from monocytes in spinal tuberculosis patients

This study examined the hypothesis that there is an impairment of macrophageal function in spinal TB. We examined macrophageal functions in spinal TB patients. Monocytes were isolated from peripheral blood mononuclear cells (PBMCs) of five spinal TB patients and five healthy persons as control. The isolated monocytes were cultured with stimulation of macrophage colony-stimulating factor (M-CSF) for seven days for maturation. The phagocytic ability of the macrophages derived from monocytes was measured. Also, nitric oxide (NO), myeloperoxidase (MPO), beta-glucuronide, and acid phosphatase activity was investigated. We found that the monocytes collected from patient PBMCs were significantly fewer than those of the control group (2992.10³ vs. 6474.10³ (cells/mL)). There were also fewer macrophages that had adhered to sheep red blood cells (SRBC) (598.10³ vs. 264.10³ (cells/mL)). However, NO production (2346 vs. 325.17 (µmol/gram of protein)), and the MPO (570.7 vs. 17.4 (unit/mg), beta-glucuronide (0.149 vs. 0.123 (μmol/hour/100 mg of protein)), and acid phosphatase activities (1776.9 vs. 287.9 (μmol/hour/100 mg of protein)) of the macrophages in the spinal TB group were markedly higher than in the healthy group. Despite the low adhesion to foreign bodies, the intracellular processing of TB macrophages, including oxidative activity and lysosome function, was significantly high. These results suggested the impairment of macrophageal function in spinal TB. Possibly, there is a dominance of innate non-specific immunity in spinal TB infection.

The role of neutrophils in host defense against invasive fungal infections

Purpose of Review

Invasive fungal infections caused by the commensal yeast Candida and the ubiquitous, inhaled mold Aspergillus have emerged as major causes of morbidity and mortality in critically ill and immunosuppressed patient populations. Here, we review how neutrophils contribute to effective immunity against these infections.

Recent Findings

Studies in mouse models of invasive candidiasis and aspergillosis, and observations in hematological patients with chemotherapy-induced neutropenia and in patients with primary immunodeficiency disorders that manifest with these infections have highlighted the critical role of neutrophils and have identified key immune factors that promote neutrophil-mediated effective host defense against invasive fungal disease.

Summary

Neutrophils are crucial in host protection against invasive candidiasis and aspergillosis. Recent advances in our understanding of the molecular cues that mediate protective neutrophil recruitment and effector function against these infections hold promise for developing immune-based strategies to improve the outcomes of affected patients.

Invasive candidiasis

Invasive candidiasis is an important health-care-associated fungal infection that can be caused by several Candida spp.; the most common species is Candida albicans, but the prevalence of these organisms varies considerably depending on geographical location. The spectrum of disease of invasive candidiasis ranges from minimally symptomatic candidaemia to fulminant sepsis with an associated mortality exceeding 70%. Candida spp. are common commensal organisms in the skin and gut microbiota, and disruptions in the cutaneous and gastrointestinal barriers (for example, owing to gastrointestinal perforation) promote invasive disease. A deeper understanding of specific Candida spp. virulence factors, host immune response and host susceptibility at the genetic level has led to key insights into the development of early intervention strategies and vaccine candidates. The early diagnosis of invasive candidiasis is challenging but key to the effective management, and the development of rapid molecular diagnostics could improve the ability to intervene rapidly and potentially reduce mortality. First-line drugs, including echinocandins and azoles, are effective, but the emergence of antifungal resistance, especially among Candida glabrata, is a matter of concern and underscores the need to administer antifungal medications in a judicious manner, avoiding overuse when possible. A newly described pathogen, Candida auris, is an emerging multidrug-resistant organism that poses a global threat.

Oxidative responses and fungal infection biology

The balance between reactive oxygen species and reactive nitrogen species production by the host and stress response by fungi is a key axis of the host-pathogen interaction. This review will describe emerging themes in fungal pathogenesis underpinning this axis.

Anti-Immune Strategies of Pathogenic Fungi

Pathogenic fungi have developed many strategies to evade the host immune system. Multiple escape mechanisms appear to function together to inhibit attack by the various stages of both the adaptive and the innate immune response. Thus, after entering the host, such pathogens fight to overcome the immune system to allow their survival, colonization and spread to different sites of infection. Consequently, the establishment of a successful infectious process is closely related to the ability of the pathogen to modulate attack by the immune system. Most strategies employed to subvert or exploit the immune system are shared among different species of fungi. In this review, we summarize the main strategies employed for immune evasion by some of the major pathogenic fungi.

New insights into innate immune control of systemic candidiasis

Systemic infection caused by Candida species is the fourth leading cause of nosocomial bloodstream infection in modern hospitals and carries high morbidity and mortality despite antifungal therapy. A recent surge of immunological studies in the mouse models of systemic candidiasis and the parallel discovery and phenotypic characterization of inherited genetic disorders in antifungal immune factors that are associated with enhanced susceptibility or resistance to the infection have provided new insights into the cellular and molecular basis of protective innate immune responses against Candida. In this review, the new developments in our understanding of how the mammalian immune system responds to systemic Candida challenge are synthesized and important future research directions are highlighted.

Humanized theta-defensins (retrocyclins) enhance macrophage performance and protect mice from experimental anthrax infections

Retrocyclins are humanized versions of the -defensin peptides expressed by the leukocytes of several nonhuman primates. Previous studies, performed in serum-free media, determined that retrocyclins 1 (RC1) and RC2 could prevent successful germination of Bacillus anthracis spores, kill vegetative B. anthracis cells, and inactivate anthrax lethal factor. We now report that retrocyclins are extensively bound by components of native mouse, human, and fetal calf sera, that heat-inactivated sera show greatly enhanced retrocyclin binding, and that native and (especially) heat-inactivated sera greatly reduce the direct activities of retrocyclins against spores and vegetative cells of B. anthracis. Nevertheless, we also found that retrocyclins protected mice challenged in vivo by subcutaneous, intraperitoneal, or intranasal instillation of B. anthracis spores. Retrocyclin 1 bound extensively to B. anthracis spores and enhanced their phagocytosis and killing by murine RAW264.7 cells. Based on the assumption that spore-bound RC1 enters phagosomes by "piggyback phagocytosis," model calculations showed that the intraphagosomal concentration of RC1 would greatly exceed its extracellular concentration. Murine alveolar macrophages took up fluorescently labeled retrocyclin, suggesting that macrophages may also acquire extracellular RC1 directly. Overall, these data demonstrate that retrocyclins are effective in vivo against experimental murine anthrax infections and suggest that enhanced macrophage function contributes to this property.

Live imaging of disseminated candidiasis in zebrafish reveals role of phagocyte oxidase in limiting filamentous growth

Candida albicans is a human commensal and a clinically important fungal pathogen that grows in both yeast and hyphal forms during human infection. Although Candida can cause cutaneous and mucosal disease, systemic infections cause the greatest mortality in hospitals. Candidemia occurs primarily in immunocompromised patients, for whom the innate immune system plays a paramount role in immunity. We have developed a novel transparent vertebrate model of candidemia to probe the molecular nature of Candida-innate immune system interactions in an intact host. Our zebrafish infection model results in a lethal disseminated disease that shares important traits with disseminated candidiasis in mammals, including dimorphic fungal growth, dependence on hyphal growth for virulence, and dependence on the phagocyte NADPH oxidase for immunity. Dual imaging of fluorescently marked immune cells and fungi revealed that phagocytosed yeast cells can remain viable and even divide within macrophages without germinating. Similarly, although we observed apparently killed yeast cells within neutrophils, most yeast cells within these innate immune cells were viable. Exploiting this model, we combined intravital imaging with gene knockdown to show for the first time that NADPH oxidase is required for regulation of C. albicans filamentation in vivo. The transparent and easily manipulated larval zebrafish model promises to provide a unique tool for dissecting the molecular basis of phagocyte NADPH oxidase-mediated limitation of filamentous growth in vivo.

Measurement of Candidacidal Activity of Specific Leukocyte Types in Mixed Cell Populations II. Normal and Chronic Granulomatous Disease Eosinophils

Normal human eosinophils possess appreciable intrinsic candidacidal activity. The leukocyte microbicidal deficiency of chronic granulomatous disease is manifested by eosinophils as well as by neutrophils and monocytes.

Assessment of phagocytic and antimicrobial activity of human granulocytes

A microassay for assessing two functions of polymorphonuclear leukocytes in the presence or absence of complement is presented. Requiring only minute amounts of blood (0.1 ml) and a minimum of laboratory equipment (microscope, incubator, and centrifuge), it allows the quantitation of phagocytosis and intracellular killing of microorganisms by leukocytes. To demonstrate the value of this assay, the phagocytic and microbicidal activity of leukocytes from healthy subjects and patients against Candida albicans was investigated. Apart from individual cases, no differences in the phagocytic activity between groups of healthy subjects and patients with candida vaginitis or different types of cancer could be found. However, the killing capacity of the leukocytes from women with recurrent candida vaginitis was reduced. The leukocytes of one patient showing a very low killing capacity lacked myeloperoxidase. Also, low values of killing were seen with leukocytes from three patients suffering from osteosarcoma, chronic lymphatic leukemia, or Hodgkins disease.

CD80+Gr-1+ myeloid cells inhibit development of antifungal Th1 immunity in mice with candidiasis

To find out whether polymorphonuclear neutrophils (PMN), abundantly recruited in disseminated Candida albicans infection, could directly affect the activation of Th cells we addressed the issues as to whether murine PMN, like their human counterparts, express costimulatory molecules and the functional consequence of this expression in terms of antifungal immune resistance. To this purpose, we assessed 1) the expression of CD80 (B7-1) and CD86 (B7-2) molecules on peripheral, splenic, and inflammatory murine Gr-1+ PMN; 2) its modulation upon interaction with C. albicans in vitro, in vivo, and in human PMN; 3) the effect of Candida exposure on the ability of murine PMN to affect CD4+ Th1 cell proliferation and cytokine production; and 4) the mechanism responsible for this effect. Murine PMN constitutively expressed CD80 molecules on both the surface and intracellularly; however, in both murine and human PMN, CD80 expression was differentially modulated upon interaction with Candida yeasts or hyphae in vitro as well as in infected mice. The expression of the CD86 molecule was neither constitutive nor inducible upon exposure to the fungus. In vitro, Gr-1+ PMN were found to inhibit the activation of IFN-gamma-producing CD4+ T cells and to induce apoptosis through a CD80/CD28-dependent mechanism. A population of CD80+Gr-1+ myeloid cells was found to be expanded in conventional as well as in bone marrow-transplanted mice with disseminated candidiasis, but its depletion increased the IFN-gamma-mediated antifungal resistance. These data indicate that alternatively activated PMN expressing CD80 may adversely affect Th1-dependent resistance in fungal infections.

Fatal disseminated Candida lusitaniae infection in an infant with chronic granulomatous disease

A 3-month-old boy born to a mother carrying an X-linked form of chronic granulomatous disease presented with persistent fever and hepatosplenomegaly. The diagnosis was confirmed as a gp91phox defect by genetic analysis, and the patient was managed with broad spectrum antibacterial agents, gamma-interferon and later amphotericin B. A liver biopsy revealed granulomata with budding yeast forms, and cultures of blood and urine grew Candida lusitaniae. The patient died 26 days after admission.

T cells augment monocyte and neutrophil function in host resistance against oropharyngeal candidiasis

The purpose of this study was to identify the cell populations involved in recovery from oral infections with Candida albicans. Monoclonal antibodies specific for CD4+ cells, CD8+ cells, and polymorphonuclear leukocytes were used to deplete BALB/c and CBA/CaH mice of the relevant cell populations in systemic circulation. Monocytes were inactivated with the cytotoxic chemical carrageenan. Mice were infected with 10(8) C. albicans yeast cells and monitored for 21 days. Systemic depletion of CD4+ and CD8+ T lymphocytes alone did not increase the severity of oral infection compared to that of controls. Oral colonization persisted in animals treated with head and neck irradiation and depleted of CD4+ T cells, whereas infections in animals that received head and neck irradiation alone or irradiation and anti-CD8 antibody cleared the infection in a comparable fashion. The depletion of polymorphonuclear cells and the cytotoxic inactivation of mononuclear phagocytes significantly increased the severity of oral infection in both BALB/c and CBA/CaH mice. High levels of interleukin 12 (IL-12) and gamma interferon (IFN-gamma) were produced by lymphocytes from the draining lymph nodes of recovering animals, whereas IL-6, tumor necrosis factor alpha, and IFN-gamma were detected in the oral mucosae of both naïve and infected mice. The results indicate that recovery from oropharyngeal candidiasis in this model is dependent on CD4+-T-cell augmentation of monocyte and neutrophil functions exerted by Th1-type cytokines such as IL-12 and IFN-gamma.

Increased atherosclerosis in myeloperoxidase-deficient mice

Myeloperoxidase (MPO), a heme enzyme secreted by activated phagocytes, generates an array of oxidants proposed to play critical roles in host defense and local tissue damage. Both MPO and its reaction products are present in human atherosclerotic plaque, and it has been proposed that MPO oxidatively modifies targets in the artery wall. We have now generated MPO-deficient mice, and show here that neutrophils from homozygous mutants lack peroxidase and chlorination activity in vitro and fail to generate chlorotyrosine or to kill Candida albicans in vivo. To examine the potential role of MPO in atherosclerosis, we subjected LDL receptor-deficient mice to lethal irradiation, repopulated their marrow with MPO-deficient or wild-type cells, and provided them a high-fat, high-cholesterol diet for 14 weeks. White cell counts and plasma lipoprotein profiles were similar between the two groups at sacrifice. Cross-sectional analysis of the aorta indicated that lesions in MPO-deficient mice were about 50% larger than controls. Similar results were obtained in a genetic cross with LDL receptor-deficient mice. In contrast to advanced human atherosclerotic lesions, the chlorotyrosine content of aortic lesions from wild-type as well as MPO-deficient mice was essentially undetectable. These data suggest an unexpected, protective role for MPO-generated reactive intermediates in murine atherosclerosis. They also identify an important distinction between murine and human atherosclerosis with regard to the potential involvement of MPO in protein oxidation.

Disparate requirement for T cells in resistance to mucosal and acute systemic candidiasis

Although highly susceptible to orogastric candidiasis, T-cell receptor delta- and alpha-chain knockout mice, deficient in gammadelta and alphabeta T cells, respectively, were found to be resistant to disseminated candidiasis of endogenous origin and to acute systemic candidiasis (resulting from intravenous injection).

The involvement of nitric oxide in the anti-Candida albicans activity of rat neutrophils

Rat peritoneal neutrophils (PMN) spontaneously release nitric oxide (NO) when incubated in vitro. Addition of the NO synthase inhibitor L-monomethylarginine (L-NMMA) to the PMN reduces NO production and impairs the killing of the yeast Candida albicans, both effects being reversed by L-arginine. These data strongly suggest that oxidative metabolism of L-arginine by PMN is involved in the candidacidal activity of these cells. Rat blood PMN, which do not produce significant amounts of NO, exhibit a reduced killing capacity compared with peritoneal cells, except when they are obtained from lipopolysaccharide (LPS)-treated rats. In this case they produce measurable amounts of nitrite and express high fungicidal activity in vitro. Confirming the candidacidal activity of NO, the exposure of the C. albicans cultures to different concentrations of NO donors leads to a reduction in their survival. The candidacidal activity related to the NO pathway in rat PMN is phagocytosis dependent, since the activity can be inhibited by cytochalasin B. However, the oxidative products of oxygen released by rat PMN do not seem to be involved in their candidacidal activity, as incubation of the cells with phorbol myristate acetate (PMA) increases release of superoxide anion but does not affect the pattern of killing. Our results suggest that NO could be an important candidacidal pathway in rat neutrophils.

Synergy of human neutrophils with fluconazole in killing Candida species

The killing of Candida species by human neutrophils in a long-term 24-h assay and possible synergy with fluconazole (FCZ) for killing was investigated. The test medium (TM) consisted of RPMI-1640, penicillin and streptomycin (P/S), and 10% fresh autologous serum. TM alone was highly fungistatic for Candida species compared to TM without serum. When neutrophils were cocultured in TM with Candida species for 24 h the inoculum colony-forming units (CFU) were always significantly reduced (killing) by 58 to 99%. FCZ was tested over a range of 1-500 micrograms/ml, and though almost always fungistatic itself, it synergized with neutrophils for significantly increased killing of C. albicans (isolate Sh27) (P < 0.01) and C. albicans (isolate 94-20) (P < 0.05). Killing of non-albicans Candida species was so efficient in the absence of FCZ that demonstration of synergy with FCZ was difficult.

Quantitative analysis of phagocytosis and killing of Cryptococcus neoformans by human peripheral blood mononuclear cells by flow cytometry

Monocytes may represent an important defense mechanism in disseminated cryptococcosis. We have developed a flow cytometric method to study the interaction of Cryptococcus neoformans with monocytes. For phagocytosis, C. neoformans was labelled with fluorescein isothiocynate (FITC). Monocytes were identified on the flow cytometer by labelling with anti-CD14-R-phycoerythrin. Discrimination between attached cells (association) and internalized cells (uptake) was made by quenching FITC-labelled C. neoformans with trypan blue. Only internalized cells kept their FITC fluorescence after quenching. For comparison under the microscope, specific staining of the cell wall of C. neoformans with Uvitex was used. Internalized C. neoformans cells were not stained, as Uvitex was occluded from phagocytes. To assay killing, C. neoformans was labelled with 0.2 mM 2'-7(1)-bis(2-carboxyethyl)-5-carboxyfluorescein acetoxymethylester. After phagocytosis of labelled cells by monocytes, blood cells were lysed with 25 mM deoxycholate. Viable yeast cells retained the fluorescence, but nonviable cells lost it. Quantitative counts of viable cells on Sabouraud dextrose agar were performed for comparison. The change in the relative fluorescence of green within the monocyte region was used to quantitate association, uptake, and killing of C. neoformans by monocytes on the flow cytometer. The flow cytometry methods showed that 18% +/- 2%, 35% +/- 14%, 50% +/- 11%, 51% +/- 6% of monocytes had become associated with C. neoformans after 0, 30, 60, and 120 min, respectively. After 2 h of phagocytosis time, 30% of C. neoformans-associated monocytes had taken up the cells, and killing rates of 23% +/- 17%, 22% +/- 9%, and 40% +/- 13% were obtained with effector-to-target cell ratios of 1:1, 10:1, and 50:1, respectively. Results with the flow cytometry methods compared favorably with those by the conventional methods used, but the flow cytometry methods are simpler, rapid, more reproducible, and objective.

Zinc supplementation impairs monocyte function

Zinc has been shown to be involved in many functions of the immune system. This study was conducted to examine the effect of zinc supplementation on phagocytic, fungicidal and metabolic activity of blood monocytes of marasmic infants during nutritional rehabilitation. A controlled, double-blind design was used in which 19 infants fed a zinc-fortified formula were compared with 20 infants fed the same, unfortified formula. Evaluation of phagocytic-fungicidal capacity, growth, zinc, copper and iron status was performed in both groups on admission and after 60 and 105 days of nutritional rehabilitation. Although energy, copper and iron intakes were similar in the two groups, a decrease in the number of infants able to phagocytose one or more Candida buds was observed after 60 days of zinc supplementation compared to admission (p < 0.03). No change in phagocytic ability was detected between admission and 60 days in the control group. The number of infants with depressed fungicidal activity increased significantly after 105 days of nutritional rehabilitation in the zinc-fortified group as compared to controls (p < 0.04). The number and duration of impetigo episodes was significantly greater in the group fed the zinc-fortified formula. These results suggest that zinc supplements at the RDA level may impair monocyte function.

Flow cytometric assay for quantifying opsonophagocytosis and killing of Staphylococcus aureus by peripheral blood leukocytes

We describe a novel flow cytometric method for quantifying opsonophagocytosis and killing of Staphylococcus aureus in cell-rich plasma obtained after dextran sedimentation of erythrocytes. To analyze opsonophagocytosis, phagocytes were labeled with a phycoerythrin-conjugated monoclonal antibody and were incubated with viable staphylococci containing carboxyfluorescein as a vital fluorescent dye. Phagocytosing cells assumed a dual, orange-green fluorescence. The relative numbers of bacteria associating with phagocytes could be determined by quantifying the decrease of free green fluorescent particles. A parallel incubation of fluorescent bacteria with unlabeled cell-rich plasma was performed to assess phagocytic killing. Blood cells were lysed with 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propanesulfonate. This detergent spared viable bacteria, and residual green fluorescent particles were counted. The decrease in the number of these particles relative to the controls yielded the degree of killing. At bacteria-to-phagocyte ratios of 1:1 and 10:1, approximately 36 and 75% of the phagocytes participated in opsonophagocytosis, respectively. Over 90% of the staphylococci were phagocyte associated after 30 to 60 min. Killing rates were on the order of 66% +/- 12% and 80% +/- 7% after 1 and 2 h of incubation, respectively. These numbers, which were confirmed by colony countings, were significantly lower than those reported in the majority of past reports.

Elimination of Candida albicans from kidneys of mice during short-term systemic infections

The candidacidal activity of kidneys, liver, and spleen's phagocytic systems was studied in mouse. Different strains of mice were inoculated intravenously (i.v.) with 1 to 2.6 x 10(4) viable Candida albicans. Elimination of the microorganisms from the kidneys, liver, and spleen were evaluated by enumeration of colony forming units (C.F.U.) recovered from homogenates of organs dissected within a short period of time (0 to 5 hr). The results indicated that the kidneys possess a capable phagocytic system which was able to eliminate the microorganisms as efficiently as those of liver and spleen. Furthermore, the ability of the liver and spleen phagocytic system as well as that of kidneys were significantly enhanced when animals were treated with Bacillus Calmette-Guerin (BCG) of mycobacterium bovis four weeks prior to induction of systemic infection with C. albicans.

Quantitative analysis of opsonophagocytosis and of killing of Candida albicans by human peripheral blood leukocytes by using flow cytometry

We describe a simple, rapid, automated procedure for measuring opsonophagocytosis and killing of Candida albicans by human peripheral blood leukocytes. Yeast cells are labelled by allowing uptake and cleavage of membrane-permeable bis-carboxyethyl-carboxyfluorescein pentaacetoxymethylester to its membrane-impermeable fluorescent derivative bis-carboxyethyl-carboxyfluorescein. The yeast cells are added to cell-rich plasma obtained after dextran sedimentation of erythrocytes. Opsonophagocytosis and killing are quantified by using automated fluorescent cell analysis, and the following parameters can be obtained: (i) relative percentage of phagocytes that participate in opsonophagocytosis, (ii) relative percentage of yeast cells that become associated with phagocytes, and (iii) percentage of killing of C. albicans. The first two parameters are obtained through the additional use of a phycoerythrin-conjugated monoclonal antibody that selectively labels monocytes and polymorphonuclear granulocytes in peripheral blood. Killing is assessed by solubilizing blood cells with deoxycholate to liberate yeast cells from the phagocytes. Viable yeast cells retain carboxyfluorescein, but nonviable cells lose the fluorescent marker; thus, the reduction in number of fluorescent particles directly reflects phagocytic killing. Results obtained by the present method correlated excellently with parallel enumerations by colony counting. Test results with seven healthy individuals revealed a marked dissociation between the process of opsonophagocytosis, which was essentially complete after 20 min at 37 degrees C, and killing rates, which were 48% +/- 11% and 63% +/- 9% (standard deviation) after 1 and 2 h, respectively, when yeast cell-to-phagocyte ratios were in the range of 0.5:1 to 2:1. The described assay is unrivaled in simplicity, rapidity, and reproducibility and generates results for a large number of samples within hours.

Candidacidal activity of Crohn's disease neutrophils

The ability of normal and Crohn's disease neutrophils to kill Candida albicans has been studied using neutrophils isolated from peripheral blood and suspended in phosphate buffered saline at 5 x 10(6) cells per ml. C albicans was grown to a stationary phase in broth culture and suspended in phosphate buffered saline at 10(7) organisms/ml. Neutrophils and Candida were then incubated together at 37 degrees C in a shaking water bath in the presence of fresh serum. At 30 and 60 minutes samples were withdrawn, neutrophils lysed, and Candida survival assessed by colony counting. Results were compared with control suspensions of Candida incubated with serum alone. After 30 and 60 minutes in the presence of autologous serum normal neutrophils had killed significantly more Candida than Crohn's disease neutrophils (mean (SD) 61.0 (16.7)% v 40.5 (16.2)% at 30 minutes, p less than 0.0001; 83.2 (7)% v 70.8) 16)% at 60 minutes, p less than 0.005). The results did not alter significantly when normal neutrophils were incubated with Candida in the presence of Crohn's disease serum instead of normal serum. When Crohn's disease neutrophils were incubated with Candida in the presence of normal serum instead of autologous serum there was some improvement in candidacidal ability at 30 minutes (48.9 (20.6)% v 40.5 (16.2)%, p less than 0.03) but not at 60 minutes. Phagocytosis, measured using a radiometric assay, was normal. Neutrophils from patients with Crohn's disease have an impaired ability to kill this granuloma provoking organism. It is not due to serum inhibitors or defective phagocytosis.

Effect of Friend leukemia virus infection on susceptibility to Candida albicans

Previous studies have demonstrated that Friend leukemia virus (FLV) induces a profound immunosuppression in susceptible mice. The studies described in this report indicate that mice infected with FLV have an increased susceptibility to subsequent infection with the opportunistic pathogen Candida albicans, as measured by increased numbers of C. albicans CFU in the kidneys of FLV-infected mice relative to uninfected controls. Experiments in which the NB-tropic and N-tropic strains of FLV were used suggest that virus replication or the resulting virus burden may be important in the observed increased susceptibility to C. albicans. Since neutrophils are believed to be important in the response of mice to systemic Candida infections, the effect of FLV infection on neutrophil candidacidal activity was investigated. The percentage of neutrophils present in unfractionated Proteose Peptone-elicited peritoneal exudates of mice infected with FLV for 14 days was significantly lower than in uninfected control mice or mice infected with FLV for 6 or 10 days. When neutrophils from FLV-infected and control mice were purified, adjusted to equal concentrations, and tested for in vitro candidacidal activity, neutrophils from mice infected with FLV for 14 days were deficient in their ability to kill C. albicans relative to normal controls and mice infected with FLV for 6 or 10 days. Addition of normal mouse serum increased killing in all groups but did not restore candidacidal activity of neutrophils from mice infected with FLV for 14 days to levels of control neutrophils or neutrophils from mice infected for 6 or 10 days with the virus. These results suggest a defect in neutrophil function, at the later stages of FLV infection, involving in vitro candidacidal activity. In addition, neutrophils from FLV-infected mice may be deficient in in vivo chemotactic activity. These defects in neutrophil function could account, at least in part, for the observed increased susceptibility of FLV-infected mice to C. albicans.

Effects of low molecular constituents from Aloe vera gel on oxidative metabolism and cytotoxic and bactericidal activities of human neutrophils

In traditional South-East Asian medicine the therapeutic value of the parenchymous leaf-gel of Aloe vera for inflammatory-based diseases is well-reputed. The aim of this study is to investigate at which level gel-constituents exert their activity. We show here that low -Mr constituents of an aqueous gel-extract inhibit the release of reactive oxygen species (ROS) by PMA-stimulated human PMN. The compounds inhibit the ROS-dependent extracellular effects of PMN such as lysis of red blood cells. The capacity of the PMN to phagocytose and kill micro-organisms at the intracellular level is not affected. The inhibitory activity of the low-Mr compounds is most pronounced in the PMA-induced ROS production, but is significantly antagonized by the Ca-ionophore A23187. It is shown that the inhibitory effect of the low-Mr compounds is the indirect result of the diminished availability of intracellular free Ca-ions.

Functions of polymorphonuclear leukocytes and individuality of Jorge Lobo's disease: absence of the specific leukocyte digestive defect against Paracoccidioides brasiliensis

Peripheral blood neutrophils (PMNs) from a patient with Jorge Lobo's disease (JLD) digested well phagocytosed Paracoccidioides brasiliensis. We found no circulating antibodies against P. brasiliensis in the patient's serum. Such neutrophils showed myeloperoxidase activity and also digested normally phagocytosed Candida albicans. We had previously reported the presence of a specific digestive deficiency of PMNs from patients with paracoccidioidomycosis (PARA) vis à vis P. brasiliensis. Current findings provide new information about leukocyte functions in JLD and bolster the view that JLD, PARA and their respective causative microorganisms are distinct.

Involvement of reactive oxygen metabolites in the candidacidal activity of human neutrophils stimulated by muramyl dipeptide or tumor necrosis factor

In the presence of the adjuvant glycopeptide muramyl dipeptide (MDP), purified human PMN exhibited an enhanced capacity to kill Candida albicans cells at various cell ratios. A significant effect was obtained at 100 ng/ml MDP, and the maximum was reached at 1 micrograms/ml MDP. Recombinant human tumor necrosis factor (rHuTNF), a monokine that enhances host resistance to bacterial and fungal infections, also stimulated the candidacidal potency of PMN with a maximal effect at 10(-2) ng/ml rHuTNF. When MDP- or rHuTNF-stimulated PMN were cultured with yeast cells, the intracellular production of oxygen metabolites was enhanced. Pretreatment with inhibitors of oxidative burst demonstrated that the yeast cell killing by MDP-stimulated PMN was not affected by SOD but was inhibited by sodium azide, indicating the involvement of myeloperoxidase (MPO)-halide system in fungicidal mechanisms induced by MDP. When PMN were stimulated with rHuTNF, the killing of yeast cells was neutralized by iodoacetamide, showing that the candidacidal potency of stimulated-PMN was due to oxygen derivatives. Inhibition by sodium azide and sodium benzoate indicated that these oxygen metabolites could be derived from the MPO-halide system but also from hydroxyl radical production. Moreover, SOD partially inhibited the fungicidal potency of rHuTNF-stimulated PMN, thus indicating a possible reutilization of the released O2- anion for intracellular killing. Cytochalasin B abrogated the PMN fungicidal potency in all cases.

Experimental basis for the clinical epidemiology of fungal infections. A review

Based on the concept that the agents of deep fungal infections can be divided into primary pathogens and opportunists the experimental basis for the clinical epidemiology of mycoses is outlined. Kinetics of experimental infections with opportunists and primary pathogens discriminate between the two fungal categories. Natural resistance eliminates opportunists and prevents the establishment of progressive infection in the normal host. Primary pathogens call upon mechanisms of adoptive cell mediated immunity for their control. Therefore athymic mice which are not more susceptible to opportunists than control mice, cannot control infection with primary pathogens. In order to induce comparable overwhelming opportunistic mycoses with reasonable challenge doses, non-specific phagocytic resistance has to be eliminated. In agreement with in vivo studies, in vitro studies of the susceptibility of fungi to killing by phagocytes point out, that the susceptibility of the tissue phase of fungi to killing by "immunologically unarmed" phagocytes discriminates between opportunists and primary pathogens. In order to restrain primary pathogenic fungi, phagocytes have also in vitro to call upon adoptive, T cell-dependent immune mechanisms, which appear superfluous for control of opportunists. This difference explains the discrepant opportunistic proclivities of the two fungal categories. Patients with defective phagocytic defenses are prone to opportunistic mycoses, while deficient cell mediated immunity results in a greater vulnerability to primary pathogens.

Immunosuppression in experimental cryptococcosis in rats: modification of macrophage functions by T suppressor cells. Macrophages functions in cryptococcosis

The influence of lymphocytes on the modulation of macrophage functions in altered immune states induced by Cryptococcus neoformans infection in rats has been investigated. In this report we observed a decrease of 'in vitro' phagocytic activity by peritoneal cells (PC) from rats that received T suppressor cells induced by cryptococcal infection, against both the same microorganism that stimulated this suppressor population (p less than 0.05) and another non-pathogenic primary yeast (Candida tropicalis), (p less than 0.02). The microbicide function of the PC from these animals present a significant decrease in challenge by C. tropicalis (p less than 0.002) when compared with PC from animals transferred with T normal cells. The transference of T suppressor cells induced by cryptococcal infection in animals immunized with human serum albumin-complete Freund's adjuvant (HSA-CFA) produces a significant alteration of the phagocytosis to HSA-human red cells (HSA-HRC) when compared with the phagocytosis observed in animals that received T normal cells or the phagocytosis of normal animals (p less than 0.001). We could also observe that the DTH to HSA studied during 30 days was negative in rats transferred with PC sensitizated with HSA and treated with suppressor T cells, when compared with the DTH response of animals transferred with PC-HSA cocultured with normal cells (p less than 0.05 21st day). The data presented in this paper illustrated that following infection of rats with C. neoformans there is a change in some population of accessory cells behavior reflected by the modification of several functions, such as phagocytosis, lytic activity and antigen presentation.

Immune response in mice infected with Candida albicans in the mycelial form

The effect of the infection with the mycelial form of a Candida albicans strain (Mycology Dept.) upon the immune system in mice was studied. BALB/c mice were infected intraperitoneally in a single dose of a 3 x 10(6), 6 x 10(6) and 12 x 10(6) cell suspension of the strain. Macrophages's activity was studied the days 7, 14, 21, 28, 35, and 42 after inoculation, by the following assays: phagocytosis in vitro, mononucleated phagocytic system by the colloidal carbon clearance technique, the lymphocyte's activity by the direct plaque forming cells technique (PFC) and delayed hypersensitivity (DTH). Infection with the mycelial form did not affect the peritoneal macrophage's phagocytic ability, neither modified the delayed hypersensitivity to sheep red blood cells (SRBC). However, a slight and transient depression of the lymphocyte stimulation was found. Suppression of PFC to SRBC was high when a 12 x 10(6) cell suspension was used in contrast to the infection with blastospores. These results suggest that systemic infection by Candida albicans in its mycelial form do not induce a non specific immunosuppression.

Digestion of killed Paracoccidioides brasiliensis by neutrophils

We previously described an in vitro assay showing that neutrophils (PMNs) from patients with paracoccidioidomycosis (PARA) have a specific digestive deficiency against suspensions of live Paracoccidioides brasiliensis. We now report that this defect is equally detectable against autoclaved, but not Amphotericin B-killed P. brasiliensis. The use of autoclaved suspensions facilitates the use of our in vitro assay. It might allow the development of an in vitro intradermal test for digestion of fungi. Differential digestive ability of phagocytes against live (or autoclaved) and Amphotericin-B killed fungi is of conceptual interest. It may be relevant in understanding therapeutic effect of Amphotericin B.

Polymorphonuclear leukocyte functions in psoriasis

Circulating polymorphonuclear leukocyte (CPMN) functions were studied in patients with widespread psoriasis as well as in persons with chronic alcoholic liver disease (CALD), paracoccidioidomycosis, diverse granulomatous diseases, and normal individuals. We were unable to find stimulation or increase in CPMN functions in patients with psoriasis compared to normal individuals. Leukocytes from individuals with CALD had a lowering of their metabolic activation, chemotaxis, random movement, and adherence. CPMNs from patients with paracoccidioidomycosis showed a significant deficiency in their ability to digest Paracoccidioides brasiliensis. Our results are against the concept that functions of circulating PMNs are stimulated in psoriatics.

Genetic control of blood neutrophil concentration in the rat

Two phenotypes that characterize low and high neutrophil concentrations in blood were found in the rat. It is possible that either two regulating alleles control the high (Nr-1a) and the low (Nr-1b) neutrophil concentration or that a polygenic system affects the neutrophil concentration in blood. The F1 hybrids of four intercrosses had low neutrophil levels in blood that suggested a dominant effect of the Nr-1b allele. The backcross progeny showed abnormal segregation of the neutrophil phenotypes. The high phenotype was expressed in only 5% of the offspring. The presence of the two phenotypes and their distribution in the backcross progeny was confirmed by the computer program SKUMIX that resolved the quantitative traits into two discrete distributions with 95% and 5% representation. Because the logistic of SKUMIX can not rule out the polygenic effect, only further breeding studies using linked markers can resolve the mechanism of the genetic control of neutrophil concentration in the rat.

The relationship of oral Candida tropicalis infection to systemic candidiasis in a patient with leukemia

Oropharyngeal candidiasis is an extremely common complication in patients receiving chemotherapy for leukemia. Candida tropicalis appears to be the major infectious agent when these patients develop candidemia. In this article, a case of C tropicalis fungemia with oropharyngeal manifestations is presented. The relationship of oropharyngeal candidiasis to oral candidal infection is discussed.

Acquisition of peroxidase activity by rat alveolar macrophages during pulmonary inflammation

The authors investigated the ability of rat alveolar macrophages to acquire peroxidase activity in the course of pulmonary inflammation. Granulomatous pulmonary inflammation was induced in bacille Calmette-Guérin (BCG)-immunized rats by intravenous injection of BCG in mineral oil. In contrast to normal alveolar macrophages, which are peroxidase-negative, alveolar macrophages lavaged from the BCG-treated rats showed significant peroxidase activity in large cytoplasmic inclusions compatible with internalized exogenous material. Alveolar macrophage uptake of intact peroxidase-positive neutrophils was also observed. Maximal numbers of peroxidase-positive alveolar macrophages were observed after the initial influx of neutrophils into the lungs, and peroxidase activity could be demonstrated in cell-free lavage fluid during the acute phase of lung injury. Normal alveolar macrophages acquired peroxidase activity after incubation with peritoneal exudate neutrophils, with purified soluble human myeloperoxidase, and with opsonized erythrocytes. It is concluded that alveolar macrophages acquire peroxidase activity from multiple sources during pulmonary inflammation. Internalization of peroxidase by the alveolar macrophage may serve to clear a potentially toxic enzyme(s) from the alveolar space and contribute to the resolution of pulmonary inflammation.

In vitro susceptibility of fungi to killing by neutrophil granulocytes discriminates between primary pathogenicity and opportunism

Pathogenic fungi, according to their propensity to cause infection of apparently normal individuals, can be grouped into either primary pathogens (e.g., Coccidioides, Histoplasma, Paracoccidioides, Blastomyces, and Sporothrix) or opportunists (e.g., Candida, Mucoraceae, Aspergillus spp., Petriellidium, and Trichosporon). There is, however, no unifying concept explaining the difference between the virulence of the two fungal categories. Previously we have speculated that neutrophils are the common denominator of the high natural resistance to opportunistic fungi. Accordingly, we then compared the susceptibility to killing by neutrophil granulocytes of Histoplasma, Blastomyces, Paracoccidioides, and Sporothrix with that of 14 opportunistic fungi. We found the four virulent dimorphic yeasts, in contrast to opportunistic fungi, to be resistant to killing by neutrophils. Virulent dimorphic yeasts were ingested by neutrophils, and triggered a respiratory burst comparably to opportunists but were less susceptible to hydrogen peroxide, suggesting that differences in the susceptibility to microbicidal products of leukocytes may explain the difference in virulence.

Primary Candida meningitis and chronic granulomatous disease

The occurrence of two rare entities in a single patient can be fortuitous or may signify some deeper relationship. A young boy was recently treated for primary Candida meningitis. Autopsy findings suggested to an experienced pathologist the presence of chronic granulomatous disease (CGD), unrecognized during his life. The patient's identical twin brother was tested and found to have the typical laboratory features of CGD. The literature on Candida meningitis was reviewed and 15 cases were discovered that apparently arose in the absence of recognized predisposing causes. All but one of these cases occurred in males, and most occurred during the first three decades of life. The case reports and literature review presented herein suggest that CGD should be suspected when a case of "primary" Candida meningitis is encountered.

Host-parasite relationship in opportunistic mycoses

Aspergillosis and mucormycosis are opportunistic fungal infections that share several unique features. The etiologic agents of aspergillosis and mucormycosis are ubiquitous in the environment, but are opportunistic organisms and usually infect only patients predisposed by some underlying disease or treatment. These infections are typically characterized by hyphal tissue invasion and a predilection of the organism for blood vessel invasion with hemorrhage, necrosis, and infarction. Also, these organisms are not dimorphic, like the true pathogenic dimorphic fungi, as they grow both in the environment and within the host in hyphal forms. However, the host must contend with several forms to successfully eliminate them. Each form displays different antigenic and surface features and elicits different host responses. Finally, if germination and hyphal growth occur, the host must compete with a rapidly growing organism that is too large to be ingested by a single cell and so must be handled by extracellular defense mechanisms.

Rapid killing of monocytes in vitro by Candida albicans yeast cells

To study the interaction between Candida albicans blastoconidia and human phagocytes, we incubated peripheral leukocytes with fungi for 1 h at 37 degrees C and stained the cells with fluorescent vital stains ethidium bromide (EB) and fluorescein diacetate. Fungi that had been phagocytosed showed little staining; however, some leukocytes containing blastoconidia exhibited nuclear staining with EB, even though their cell membranes showed no signs of penetration by fungi. The number of EB-positive leukocytes was related to viability of the yeast cells and the temperature at which they were maintained before use. Because efforts to quantitate EB-positive leukocytes microscopically were frustrated by cell aggregation, we labeled the leukocytes with 51Cr and measured isotope release. We determined that leukocytes incubated with viable fungi released significantly more isotope than cells incubated alone or with killed blastoconidia. Furthermore, 51Cr release correlated directly with concentration of fungi in the assay, time of incubation, and temperature at which fungi were maintained before use. Using a number of isolates of C. albicans and several other species of Candida, we found that all exhibited cytotoxic activity against leukocytes, but the level of activity varied among organisms. Finally, we depleted or enriched peripheral leukocytes for specific cell populations and determined that only monocytes released more 51Cr after incubation with viable blastoconidia. Blastoconidia can lyse phagocytic cells through germination and penetration of cell membranes within 1 to 2 h, but the cytotoxic phenomenon we describe occurs within 15 to 30 min after yeast cells have been phagocytosed. Therefore, this capacity may represent a more immediate response by blastoconidia against phagocytosis and killing by monocytes.

Intracellular killing of Candida albicans by human polymorphonuclear leucocytes: comparison of three methods of assessment

Three different methods, [3H]uridine uptake, viable count and 51Cr-release were used to assess the intracellular survival of a strain of Candida albicans, 19321, which was lethal for mice injected intravenously. Intracellular survival 1 h after ingestion ranged from 50 to 80% depending on the method employed and the detergent used to lyse the phagocytes. Inhibition of uridine uptake by detergents used to lyse the phagocytes led to difficulty in assessment of intracellular killing by this method.