The fungicidal mechanisms of human monocytes. I. Evidence for myeloperoxidase-linked and myeloperoxidase-independent candidacidal mechanisms

Are reactive oxygen species always detrimental to pathogens?

Reactive oxygen species (ROS) are deadly weapons used by phagocytes and other cell types, such as lung epithelial cells, against pathogens. ROS can kill pathogens directly by causing oxidative damage to biocompounds or indirectly by stimulating pathogen elimination by various nonoxidative mechanisms, including pattern recognition receptors signaling, autophagy, neutrophil extracellular trap formation, and T-lymphocyte responses. Thus, one should expect that the inhibition of ROS production promote infection. Increasing evidences support that in certain particular infections, antioxidants decrease and prooxidants increase pathogen burden. In this study, we review the classic infections that are controlled by ROS and the cases in which ROS appear as promoters of infection, challenging the paradigm. We discuss the possible mechanisms by which ROS could promote particular infections. These mechanisms are still not completely clear but include the metabolic effects of ROS on pathogen physiology, ROS-induced damage to the immune system, and ROS-induced activation of immune defense mechanisms that are subsequently hijacked by particular pathogens to act against more effective microbicidal mechanisms of the immune system. The effective use of antioxidants as therapeutic agents against certain infections is a realistic possibility that is beginning to be applied against viruses.

α-Defensins in human innate immunity

Defensins are small, multifunctional cationic peptides. They typically contain six conserved cysteines whose three intramolecular disulfides stabilize a largely β-sheet structure. This review of human α-defensins begins by describing their evolution, including their likely relationship to the Big Defensins of invertebrates, and their kinship to the β-defensin peptides of many if not all vertebrates, and the θ-defensins found in certain non-human primates. We provide a short history of the search for leukocyte-derived microbicidal molecules, emphasizing the roles played by luck (good), preconceived notions (mostly bad), and proper timing (essential). The antimicrobial, antiviral, antitoxic, and binding properties of human α-defensins are summarized. The structural features of α-defensins are described extensively and their functional contributions are assessed. The properties of HD6, an enigmatic Paneth cell α-defensin, are contrasted with those of the four myeloid α-defensins (HNP1-4) and of HD5, the other α-defensin of human Paneth cells. The review ends with a decalogue that may assist researchers or students interested in α-defensins and related aspects of neutrophil function.

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.

Impaired host defence against Mycobacterium avium in mice with chronic granulomatous disease

Patients with chronic granulomatous disease (CGD), an inherited disorder of phagocytic cells, often contract recurrent life-threatening bacterial and fungal infections. CGD is considered to arise from a functional defect of the O(2)-generating nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in phagocytes. To determine whether or not NADPH oxidase is crucial to the host defence against Mycobacterium avium, we investigated the response against M. avium using CGD model mice (gp91-phox(-)) of C57BL/6 strain. A tracheal injection of 1 x 10(7) colony-forming units (CFU)/head of M. avium strain FN into the CGD mice resulted in a pulmonary infection, while also increasing the mortality rate. In contrast, normal C57BL/6 mice injected with same dose of the organisms did not develop severe pulmonary infection and were able to survive through 2 months of observation. The macrophages obtained from the CGD mice were observed to have a higher burden of the bacterial growth than macrophages from normal C57BL/6 mice. These results suggest that the defect of the NADPH oxidase function impairs the host defence against M. avium infection.

Enhanced killing of Candida albicans by human macrophages adherent to type 1 collagen matrices via induction of phagolysosomal fusion

Candida albicans, a component of the normal flora of the alimentary tract and mucocutaneous membranes, is the leading cause of invasive fungal disease in premature infants, diabetics, and surgical patients and of oropharyngeal disease in AIDS patients. As little is known about the regulation of monocyte/macrophage anti-Candida activity, we sought to determine if fungicidal activity might be regulated by extracellular matrix proteins to which monocytes/macrophages are adherent in vivo. Compared to monocyte/macrophages that adhered to plastic, human monocytes and monocyte-derived macrophages that adhered to type 1 collagen matrices, but not to fibronectin, vitronectin, or laminin, demonstrated a significant increase in candidacidal activity. The enhancement of monocyte fungicidal activity was maintained over a 4-h period, whereas macrophage fungicidal activity was maximum at 1 h. Although adherence of monocytes and macrophages to collagen matrices concomitantly enhanced the production of superoxide anion, only the fungicidal activity of collagen-adherent monocytes was partially blocked by superoxide dismutase and catalase. Remarkably, we found that only 10% of the phagosomes in C. albicans-infected macrophages that adhered to plastic fused with lysosomes. In contrast, 80% of yeast-containing phagosomes of collagen-adherent macrophages fused with lysosomes. These data suggest that nonoxidative mechanisms are critical for human macrophage anti-Candida activity and that C. albicans pathogenicity is mediated, in part, by its ability to inhibit phagolysosomal fusion in macrophages.

Impaired host defense against Sporothrix schenckii in mice with chronic granulomatous disease

We compared the immune defense of mice with chronic granulomatous disease (CGD mice) with that of wild-type C57BL/6 mice for their response to Sporothrix schenckii. A subcutaneous injection of 5 x 10(4) CFU S. schenckii strain IFM41598 into CGD mice resulted in systemic infection and death within 84 days. In contrast, injected C57BL/6 mice did not develop systemic infection and were able to survive through 100 days of observation. Differences in host resistance were analyzed in vitro. Neutrophils and macrophages obtained from CGD mice were found to allow greater growth of this organism than did those obtained from C57BL/6 mice. Moreover, macrophages obtained from immunized CGD mice were able to simply inhibit the growth of this fungus whereas macrophages obtained from immunized C57BL/6 mice killed the fungus within 48 h after phagocytosis. These results suggest that (i) the lack of NADPH oxidase function is a risk factor for lethal S. schenckii infection and (ii) superoxide anion and its reactive oxidative metabolites produced by neutrophils and macrophages are involved in fungistatic and fungicidal activities.

Monitoring the allergic inflammation

Individual symptoms of allergy such as asthma, dermatitis, rhinitis have many different underlying mechanisms. The detailed characterization of the inflammatory mechanisms underlying symptom development in the individual patient is important in order to optimally control treatment. Measurement of eosinophil cationic protein (ECP) in sputum or blood and eosinophil protein X/eosinophil derived neurotoxin (EPX/EDN) in urine may be used to read the involvement of the eosinophil granulocyte in the process. An important information as eosinophil dominated processes seem to be particularly sensitive to corticosteroid treatment. The possibilities to measure the involvement of other inflammatory cells exist today, but are only used to a small extent. The dream would be that every patient with an inflammatory disease is characterized with respect to the profile of involving cells and mediators. Such information would provide us with a unique understanding of the underlying mechanisms of the development of disease symptoms and the possibilities of treating these.

Degradation of vincristine by myeloperoxidase and hypochlorous acid in children with acute lymphoblastic leukemia

Vincristine (VCR) is an effective drug against acute lymphoblastic leukemia (ALL), many solid tumors, but not acute myeloid leukemia. It has been hypothesized that resistance of myeloblasts to VCR is related to myeloperoxidase (MPO) and production of hypochlorous acid (HOCl). We investigated the relationship between VCR degradation and MPO expression and serum HOCl concentrations in pediatric patients with ALL, lymphoma and solid tumors. We studied the sera from 43 children, of which 23 were newly diagnosed and as yet untreated cancer patients, 10 on chemotherapy and 10 healthy control subjects. Patients' sera were incubated with VCR alone or in the presence of taurine (T) or acetaminophen (APAP) and post-incubation VCR and HOCL concentrations were measured. Significant correlations between serum MPO expression, HOCl concentrations and VCR degradation were seen. In the chemotherapy group, MPO-positive patients produced high levels of HOCl and reciprocally low post-incubation VCR levels. HOCl and VCR concentrations in this group were significantly different than other groups studied. Both APAP and T inhibited VCR degradation in the sera of the chemotherapy group but not to the same degree. The effects seen here were consistent for both ALL and the lymphoma/solid tumor cases. Our results indicate that HOCl can increase VCR degradation in vitro in the serum and this effect is significantly more pronounced in pediatric patients undergoing chemotherapy.

Stage-specific gene expression of Candida albicans in human blood

The pathogenic fungus Candida albicans commonly causes mucosal surface infections. In immunocompromised patients, C. albicans may penetrate into deeper tissue, enter the bloodstream and disseminate within the host causing life-threatening systemic infections. In order to elucidate how C. albicans responds to the challenge of a blood environment, we analysed the transcription profile of C. albicans cells exposed to human blood using genomic arrays and a cDNA subtraction protocol. By combining data obtained with these two methods, we were able to identify unique sets of different fungal genes specifically expressed at different stages of this model that mimics bloodstream infections. By removing host cells and incubation in plasma, we were also able to identify several genes in which the expression level was significantly influenced by the presence of these cells. Differentially expressed genes included those that are involved in the general stress response, antioxidative response, glyoxylate cycle as well as putative virulence attributes. These data point to possible mechanisms by which C. albicans ensures survival in the hostile environment of the blood and how the fungus may escape the bloodstream as an essential step in its systemic dissemination.

Immunohistochemical detection of myeloperoxidase and its oxidation products in Kupffer cells of human liver

Oxidative damage to tissue proteins has been implicated in the pathogenesis of liver disease, but the mechanisms that promote oxidation in vivo are unclear. Hydrogen peroxide is transformed into an array of potentially damaging reactants by the heme protein myeloperoxidase. This proinflammatory enzyme is expressed by circulating neutrophils and monocytes but is generally thought to be absent from tissue macrophages. To determine whether myeloperoxidase is present in Kupffer cells, the fixed-tissue macrophages of liver, Western blot analysis, and immunohistochemistry were performed. Two different antibodies monospecific for myeloperoxidase identified a 60-kd protein, the predicted molecular mass of myeloperoxidase, in human liver extracts. Immunostaining detected the enzyme in sinusoidal lining cells of normal and diseased human livers. Immunofluorescence confocal microscopy demonstrated co-localization of myeloperoxidase and CD68, a monocyte/macrophage marker, in sinusoidal lining cells. Numerous myeloperoxidase-expressing cells were also evident in the fibrous septa of cirrhotic livers. Immunostaining with an antibody to proteins modified by hypochlorous acid, a characteristic product of the enzyme, indicated that myeloperoxidase is enzymatically active in cases of acute liver injury and cirrhosis. These findings identify myeloperoxidase as a component of human Kupffer cells. Oxidative damage resulting from the action of myeloperoxidase may contribute to acute liver injury and hepatic fibrogenesis.

Candida albicans is phagocytosed, killed, and processed for antigen presentation by human dendritic cells

Candida albicans is a component of the normal flora of the alimentary tract and also is found on the mucocutaneous membranes of the healthy host. Candida is the leading cause of invasive fungal disease in premature infants, diabetics, and surgical patients, and of oropharyngeal disease in AIDS patients. As the induction of cell-mediated immunity to Candida is of critical importance in host defense, we sought to determine whether human dendritic cells (DC) could phagocytose and degrade Candida and subsequently present Candida antigens to T cells. Immature DC obtained by culture of human monocytes in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4 phagocytosed unopsonized Candida in a time-dependent manner, and phagocytosis was not enhanced by opsonization of Candida in serum. Like macrophages (Mphi), DC recognized Candida by the mannose-fucose receptor. Upon ingestion, DC killed Candida as efficiently as human Mphi, and fungicidal activity was not enhanced by the presence of fresh serum. Although phagocytosis of Candida by DC stimulated the production of superoxide anion, inhibitors of the respiratory burst (or NO production) did not inhibit killing of Candida, even when phagocytosis was blocked by preincubation of DC with cytochalasin D. Further, although apparently only modest phagolysosomal fusion occurred upon DC phagocytosis of Candida, killing of Candida under anaerobic conditions was almost equivalent to killing under aerobic conditions. Finally, DC stimulated Candida-specific lymphocyte proliferation in a concentration-dependent manner after phagocytosis of both viable and heat-killed Candida cells. These data suggest that, in vivo, such interactions between DC and C. albicans may facilitate the induction of cell-mediated immunity.

Neutrophil function in workers exposed to organophosphate and carbamate insecticides

Neutrophil function in 40 workers occupationally exposed to carbamate and organophophate insecticides were examined and compared to those of non-exposed individuals. Phagocytosis and intracellular killing of Candida albicans and Candida pseudotropicalis by neutrophils were studied. Two species of Candida were used since in individuals with myeloperoxidase deficiency neutrophils are unable to kill Candida albicans, while Candida pseudotropicalis can be effectively lysed. Phagocytosis of both antigens was normal in all the workers studied. On the other hand, there was a considerable reduction in the ability of neutrophils from exposed workers to kill Candida albicans whereas Candida pseudotropicalis was effectively lysed. This finding indicates some interference with the myeloperoxidase activity in the exposed population. The levels of cholinesterase activity in all workers were normal. These results demonstrate that exposure to carbamates and organophophates insecticides may lead to changes in neutrophil function even in workers presenting no impairment in the cholinesterase activity.

Comparison of fungal viability assays using Candida albicans yeast cells undergoing prolonged incubation in the absence of nutrients

Staining methods for determining fungal viability are usually assessed by comparisons with enumeration of colony-forming units (CFU) on solid media. The purpose of the present study was to compare viability as assessed by the acridine orange (AO) and MTT methods with the numbers of CFUs obtained for Candida albicans yeast cells undergoing prolonged incubation in distilled water. In initial assessments of the assays using various proportions of control and heat-killed C. albicans, the AO and MTT methods consistently indicated significantly higher values for viability than did CFU determinations. Experiments using organisms cultured overnight revealed that approximately 95% of the cells were capable of dividing at least once in a microscopic proliferation assay, whereas only 69% were capable of forming colonies. Parallel assays comparing AO uptake and MTT reduction gave excellent agreement with the microscopic proliferation assay, but not with CFU determinations. Using organisms undergoing prolonged incubations in distilled water, much lower viabilities were obtained with the CFU method at 7 and 10 days than with the microscopic proliferation assay or the two staining methods. These results indicate that the AO and MTT assays correlate well with the ability of C. albicans to divide at least once, but may not accurately indicate the percentage of organisms actually able to form colonies.

Role of arachidonic acid metabolites in the action of a beta adrenergic agonist on human monocyte phagocytosis

The mechanisms by which beta adrenergic stimulation regulates phagocytosis of Candida albicans by human peripheral monocytes (HPM) are characterized. Isoproterenol (ISO) inhibits phagocytosis in a concentration-dependent manner. This effect was blunted by propranolol, inhibitors of phospholipase A2 (PLA2), cyclooxygenase and verapamil, pointing to a participation of arachidonic acid (AA) metabolites and calcium in the phenomenon. Prostaglandin E2 (PGE2) and dibutyryl cyclic AMP (db-cAMP) also exerted the same inhibitory effect on phagocytosis. ISO interacts with beta adrenergic receptors of HPM increasing PGE2 and cAMP. We conclude that the mechanisms by which beta adrenergic stimulation regulates phagocytosis of Candida albicans by HPM appear to be secondary to beta adrenoceptor-mediated hydrolysis of AA accompanied by an increase in PGE2 generation and cAMP production. Both PGE2 and cAMP could act as mediators of the inhibitory action of beta agonists on the HPM-phagocytosis process.

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.

Immunomodulatory activity of amphiphilic antimicrobials on mouse macrophages

A quaternary ammonium salt (1-methyldodecyl)-trimethylammonium iodide, a structurally analogous amine oxide (1-methyldodecyl)-dimethylamine-N-oxide and the amine oxide lacking long alkyl chain trimethylamine-N-oxide were tested for their immunomodulatory activity. Inbred mice strain C57/BL6 were pretreated for 7 days by the compounds under study. The activity of elicited peritoneal macrophages was also tested. Both compounds have a long alkyl chain. In concentrations of 10(-6) M there was a significant increase of the phagocytic, candidacidal and lysozyme activities of the cells. We also observed a suppressed peroxidase activity. The colicidal activity of both the peritoneal and spleen cells were not affected. The amine oxide lacking the long alkyl chain has the same effect at high concentration. A similarity between the effects of the amphiphilic compounds on the macrophages and their antimicrobial efficacy elicits the conclusion that both activities are caused by their ability to interact with the cell membranes.

Purification and partial characterization of the Cu,Zn superoxide dismutase from the dermatophyte Trichophyton mentagrophytes var. interdigitale

Cell homogenization, isoelectric focusing and gel filtration FPLC have been used to purify a superoxide dismutase (SOD) from the dermatophyte Trichophyton mentagrophytes var. interdigitale (T. interdigitale). N-terminal amino acid sequencing identified this enzyme as a Cu,ZnSOD, with a pH of 5.1, a reduced molecular mass of 18 kDa, and a non-reduced molecular mass of 59 kDa. SOD activity was detectable in culture filtrates, as early as the mid-log phase of growth. The known Cu,Zn inhibitor potassium cyanide caused some inhibition of the purified enzyme, whereas the inhibitors sodium azide, guanidinium hydrochloride, EDTA and chloroform/ethanol had no discernible effect. The T. interdigitale SOD was pH insensitive in the range 7.0-10.5 and remained active after prolonged incubation at 50 degrees C. The purification and characterization of this enzyme represents the first step in determining whether SOD plays any part in protecting T. interdigitale from free radicals generated by the oxidative burst of immune effector cells.

Candida albicans induces the release of inflammatory mediators from human peripheral blood monocytes

Candida albicans (C. albicans) is a major nosocomial pathogen. We examined arachidonic acid (AA) and cytokine production by monocytes stimulated with C. albicans. [14C]-AA labeled monocytes released 8.9 +/- 2.3% of the incorporated AA following stimulation with live C. albicans (C. albicans: monocyte of 16:1) (P = 0.0002). Prior studies indicate that soluble alpha-mannans and beta-glucans antagonize mannose and beta-glucan receptors, respectively. Preincubation of monocytes with alpha-mannan (100 micrograms/ml) caused 45.8 +/- 5.7% inhibition of [14C]-AA release, whereas beta-glucan (100 micrograms/ml) yielded 43.7 +/- 6.0% inhibition (P < 0.05 for each compared to control). Additionally, monocytes stimulated with C. albicans also released interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF alpha), interleukin-6 (IL-6) and interleukin-8 (IL-8). However, alpha-mannan or beta-glucan failed to inhibit IL-1 beta release. These data indicate that C. albicans induces monocytes to release AA and inflammatory cytokines. Furthermore, AA, but not cytokine liberation, is partially mediated by alpha-mannan and beta-glucan components of the fungus.

Vincristine degradation by serum from leukemic patients: role of myeloperoxidase

Myeloperoxidase (MPO) has been shown to catalyze the in vitro degradation of vincristine (VCR). Given that MPO is a lysosomal enzyme that can be released into the circulation by both normal activated and leukemic myeloid cells, we investigated the possibility that sera from patients with acute myeloblastic leukemia (AML) might exhibit an increased capacity to degrade VCR. 31 serum samples (23 from patients with acute myeloblastic leukemia and 8 from patients with other conditions) were analyzed after incubation with ((3)H)VCR by using HPLC. Sera from patients with AML demonstrated an increased ability to breakdown VCR when compared to either normal sera or to sera from patients with lymphoid leukemias. VCR degradation was significantly increased by adding hydrogen peroxide, an electron donor for MPO, to the sera and was almost completely inhibited by adding 1 mM acetaminophen, an inhibitor of MPO. VCR peroxidation in the presence of hydrogen peroxide correlated both with the number of leukemic blasts in the circulation at the time the sera were obtained and with serum MPO concentrations determined by an immunoassay. These data suggest that the inactivity of VCR in AML may be due in part to its rapid peroxidation to inactive species by the MPO of leukemic myeloblasts.

Purification, N-terminal amino acid sequence and partial characterization of a Cu,Zn superoxide dismutase from the pathogenic fungus Aspergillus fumigatus

A superoxide dismutase (SOD) has been purified to homogeneity from the fungal pathogen Aspergillus fumigatus using a combination of cell homogenization, isoelectric focusing and gel filtration FPLC. The N-terminal amino acid sequence of the purified enzyme demonstrated substantial homology to known Cu,Zn superoxide dismutases for a range of organisms, including Neurospora crassa and Saccharomyces cerevisiae. The enzyme subunit has a pI of 5.9, a relative molecular mass of 19 kDa and a spectral absorbance maximum of 550nm. The non reduced enzyme has a relative molecular mass of 95 kDa. The enzyme remained active after prolonged incubation at 70 degrees C and was pH insensitive in the range 7-11. Potassium cyanide and diethyldithiocarbamate, known Cu,Zn SOD inhibitors, caused inhibition of the purified enzyme at working concentrations of 0.25 mM, whilst sodium azide and o-phenanthroline demonstrated inhibition at higher concentrations (10-30 mM). SOD activity was also detectable in culture filtrate of A. fumigatus. This enzyme may have a potential role as a virulence factor in the avoidance of neutrophil and phagocyte oxidative burst killing mechanisms.

Cytokines in the treatment of fungal infections

The incidence of invasive fungal infections in the immunocompromized host has increased during the past decade. Even the recently developed antifungal drugs are unable to cure these infections in patients with severely impaired host defense mechanisms. Cytokines have great potential to augment host resistance and as adjunctive therapy of invasive mycoses. We discuss the mechanisms of host defense against invasive candidiasis, aspergillosis, and cryptococcosis, and review the use of cytokines and growth factors in this setting. Interleukin-1 has been shown effective in an animal model of disseminated candidiasis, even during severe granulocytopenia. Interferon-gamma has been very effective as a modulator of resistance against a variety of fungal infections in vitro. The effect of interferon-gamma against disseminated candidiasis has been demonstrated in a mouse model. Activation of neutrophils is the main mechanism by which interferon-gamma enhances the elimination of Candida, and consequently the agent is not effective in severely granulocytopenic animals. Data on the role of colony-stimulating factors against fungal pathogens are accumulating, and trials with these agents for hematologic patients with invasive fungal infections are now being performed.

Novel aspect of amphotericin B action: accumulation in human monocytes potentiates killing of phagocytosed Candida albicans

The influence of low doses of amphotericin B on the capacity of human monocytes to kill Candida albicans was investigated. Killing rates were quantified by a novel flow cytometric assay and were found to be 37% +/- 3% (standard error of the mean) after 3 h. Preincubation of monocytes for 6 to 20 h with low concentrations of amphotericin B (0.2 microgram/ml) resulted in a markedly augmented fungicidal capacity. Enhancement of killing was 80% +/- 11% (standard error of the mean) over that by the controls. This effect did not appear to be due to amphotericin B-dependent monocyte activation; the respiratory burst and expression of human leukocyte antigen-DR were unaltered, and no stimulation of interleukin-1 beta release occurred. Cell-associated amphotericin B was extracted with acetonitrile and was quantified by scanning spectrophotometry. Amphotericin B appeared to accumulate in the cells, and intracellular concentrations attained after overnight incubation in 1 microgram of the drug per ml were estimated to be in the range of 50 fg per cell. The fact that intracellular accumulation was responsible for the enhanced fungicidal capacity of monocytes was supported by the findings that killing of Staphylococcus aureus remained normal and enhancement of killing of an amphotericin B-resistant C. albicans strain was minimal. Dramatic enhancement of monocyte fungicidal capacity probably extends to other amphotericin B-susceptible fungi and could represent a hitherto unrecognized determinant underlying the curative properties and prophylactic efficacy of this drug.

Antimicrobial proteins of murine macrophages

Three murine microbicidal proteins (MUMPs) were purified from cells of the murine macrophage cell line RAW264.7 that had been activated by gamma interferon. Similar proteins were also present in nonactivated RAW264.7 cells, in cells of the murine macrophage cell line J774A.1, and in resident and activated murine peritoneal macrophages. MUMP-1, MUMP-2, and MUMP-3 killed Salmonella typhimurium, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, Mycobacterium fortuitum, and Cryptococcus neoformans in vitro. MUMP-1 resembled an H1 histone but was unusual because its N-terminal residue (serine) was not N acetylated. Although MUMP-2 was N terminally blocked, its high lysine/arginine ratio and its reactivity with an antibody to H1 histones suggested that it also belonged to the H1 histone family. MUMP-3 was identical to histone H2B in 30 of 30 amino-terminal residues. Although the antimicrobial properties of histones have been recognized for decades, this is the first evidence that such proteins may endow the lysosomal apparatus of macrophages with nonoxidative antimicrobial potential. Other MUMPs, including some with a more restricted antimicrobial spectrum and one that appeared to be induced in RAW264.7 cells after gamma interferon stimulation, were noted but remain to be characterized.

Enhancement of macrophage candidacidal activity by interferon-gamma. Increased phagocytosis, killing, and calcium signal mediated by a decreased number of mannose receptors

In contrast to its macrophage-activating capacity, IFN-gamma downregulates expression of the macrophage mannose receptor (MMR), which mediates uptake of Candida and other microorganisms. We found that IFN-gamma induced a concentration-dependent increase in the capacity of human monocyte-derived macrophages to ingest and kill both opsonized and unopsonized Candida albicans and to release superoxide anion upon stimulation with Candida. Mannan or mannosylated albumin inhibited this activated uptake of unopsonized Candida, but glucan did not. Addition of mAb to complement receptor (CR) 3 did not inhibit ingestion; macrophages that lacked CR3 (leukocyte adhesion defect) showed normal upregulation of ingestion by IFN-gamma. The increased candidacidal activity of IFN-gamma-activated macrophages was associated with reduced expression of MMR by a mean of 79% and decreased pinocytic uptake of 125I-mannosylated BSA by 73%; K(uptake) of pinocytosis was not changed. Exposure of resident macrophages to unopsonized Candida did not elicit a transient increase in intracellular free Ca2+ ([Ca2+]i); macrophages activated by IFN-gamma expressed a brisk increase in [Ca2+]i on exposure to Candida. These data suggest that macrophage activation by IFN-gamma can enhance resistance to C. albicans infection in spite of downregulation of the MMR, perhaps through enhanced coupling of the MMR to microbicidal functions.

Candidicidal activity of the human recombinant myeloperoxidase system

The effect of the human recombinant myeloperoxidase (recMPO) system on the viability of Candida albicans blastospores was determined. Cells were incubated in the presence of the enzyme, H2O2, and various substrates. In optimal conditions, 100% mortality was reached with only 41 mU of recMPO per ml, confirming its powerful candidicidal activity.

Effect of lectins on hepatic clearance and killing of Candida albicans by the isolated perfused mouse liver

The isolated perfused mouse liver model was used to study the effects of various lectins on hepatic trapping and killing of Candida albicans. After mouse livers were washed with 20 to 30 ml of perfusion buffer, 10(6) C. albicans CFU were infused into the livers. At the time of recovery, 63% +/- 2% (mean +/- standard error of the mean) of the infused C. albicans CFU were recovered from the liver and 14% +/- 1% were recovered from the effluent for a total recovery of 77% +/- 2%. This indicated that 86% +/- 9% of the original inoculum was trapped by the liver and that 23% +/- 2% was killed within the liver. When included in both preperfusion and postperfusion buffers (0.2 mg of lectin per ml), Ulex europeaus lectin (binding specificity for fucose) decreased hepatic trapping of C. albicans by 37% and eluted trapped C. albicans from the liver only when included in postperfusion buffer. By comparison, treatment of C. albicans with U. europeaus lectin before infusion had no effect on the trapping or killing of yeast cells. When Lens culinaris lectin (binding specificity for mannose) was included in the perfusion buffers, hepatic killing of C. albicans increased by 16% with no significant effect on hepatic killing when yeast cells were treated with L. culinaris lectin before infusion. Forty to 55% of the infused C. albicans were killed when concanavalin A (binding specificities for mannose and glucose), Glycine max (binding specificity for N-acetylgalactosamine), or Arachis hypogea (binding specificity for galactose) lectin was included in the perfusion buffer or when yeast cells were treated with these lectins before their infusion. When C. albicans was treated with concanavalin A at a concentration of less than 0.02 mg/ml, hepatic killing of yeast cells was not significantly increased. The data suggest that a fucose-containing receptor on the surface of either sinusoidal endothelial cells or Kupffer cells is involved in the trapping of C. albicans by the perfused mouse liver. Moreover, lectins with binding specificities for mannose, N-acetylgalactosamine, and galactose increased hepatic killing of C. albicans.

Interaction and intracellular killing of Candida albicans blastospores by human polymorphonuclear leucocytes, monocytes and monocyte-derived macrophages in aerobic and anaerobic conditions

Polymorphonuclear leucocytes (PMN), monocytes and monocyte-derived macrophages were capable of interacting with opsonized C. albicans in both aerobic and anaerobic conditions. Superoxide anion release by these cells was inhibited in anaerobic conditions while lysozyme release and phagocytosis were equally efficient in both aerobic and anaerobic conditions. All cell types tested were capable of intracellular killing of C. albicans and this appeared to be maximum at 6 h for monocytes and macrophages and 24 h for PMN. Monocytes killed the lowest number of organisms, 1 x 10(6), and the killing was similar for aerobic and anaerobic conditions. In contrast, PMN and macrophages demonstrated greater killing of C. albicans in aerobic conditions compared with anaerobic conditions; PMN killed 1.9 x 10(6) organisms and macrophages 3 x 10(6) when incubated anaerobically. Inhibitors of oxygen metabolism decreased intracellular killing of C. albicans by macrophages and PMN in aerobic but not anaerobic conditions. The oxygen reaction products involved in the killing of C. albicans appeared to be different however: macrophage killing was decreased by superoxide anion and hydrogen peroxide inhibitors. PMN killing was decreased by superoxide anion, hydrogen peroxide, hypochlorous acid and hydroxyl radical inhibitors. The present study shows that although monocytes, macrophages and PMN function similarly in their interaction with C. albicans, they appear to use different oxygen reactive products for the intracellular killing of C. albicans.

Lactoferrin inhibits or promotes Legionella pneumophila intracellular multiplication in nonactivated and interferon gamma-activated human monocytes depending upon its degree of iron saturation. Iron-lactoferrin and nonphysiologic iron chelates reverse monocyte activation against Legionella pneumophila

We have been exploring the role of iron in the pathogenesis of the intracellular bacterial pathogen Legionella pneumophila. In previous studies, we have demonstrated that L. pneumophila intracellular multiplication in human monocytes is iron dependent and that IFN gamma-activated monocytes inhibit L. pneumophila intracellular multiplication by limiting the availability of iron. In this study, we have investigated the effect on L. pneumophila intracellular multiplication of lactoferrin, an iron-binding protein which is internalized via specific receptors on monocytes, and of nonphysiologic iron chelates which enter monocytes by a receptor-independent route. Apolactoferrin completely inhibited L. pneumophila multiplication in nonactivated monocytes, and enhanced the capacity of IFN gamma-activated monocytes to inhibit L. pneumophila intracellular multiplication. In contrast, iron-saturated lactoferrin had no effect on the already rapid rate of L. pneumophila multiplication in nonactivated monocytes. Moreover, it reversed the capacity of activated monocytes to inhibit L. pneumophila intracellular multiplication, demonstrating that L. pneumophila can utilize iron from the lactoferrin-lactoferrin receptor pathway. The capacity of iron-lactoferrin to reverse monocyte activation was dependent upon its percent iron saturation and not just its total iron content. Similarly, the nonphysiologic iron chelates ferric nitrilotriacetate and ferric ammonium citrate completely reverse and ferric pyrophosphate partially reversed the capacity of IFN gamma-activated monocytes to inhibit L. pneumophila intracellular multiplication, demonstrating that L. pneumophila can utilize iron derived from nonphysiologic iron chelates internalized by monocytes independently of the transferrin and lactoferrin endocytic pathways. This study suggests that at sites of inflammation, lactoferrin may inhibit or promote L. pneumophila intracellular multiplication in mononuclear phagocytes depending upon its degree of iron saturation. In addition, this study suggests a potential role for PMN in host defense against L. pneumophila--providing apolactoferrin to infected monocytes--and it supports the concept that PMN and monocytes may cooperate in host defense against intracellular parasites and other pathogens.

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.

Modulation of anti-Candida activity of human alveolar macrophages by interferon-gamma or interleukin-1-alpha

The fungicidal and bactericidal activities of human alveolar macrophages (AM) and peripheral blood monocytes (PBM) from 18 healthy volunteers were evaluated. The results showed that AM were able to phagocytize and kill Candida albicans, Pseudomonas aeruginosa, and Staphylococcus aureus. However, killing of the bacteria was already complete in 2 h, whereas killing of Candida required 4 to 6 h despite an early phagocytosis of yeast cells. The fungicidal activity of freshly collected AM and PBM was also tested after effector cell exposure to interferon-gamma (IFN-gamma), interleukin-1-alpha (IL-1 alpha), endotoxin lipopolysaccharide (LPS), or interleukin 2 (IL-2). It was found that treatment with IFN-gamma, IL-1 alpha, or LPS significantly augmented macrophage and PBM candidacidal activity, whereas the addition of IL-2 was ineffective. We also evaluated killing of C. albicans by AM cultured in vitro for different times. While phagocytosis was apparently unaffected, the candidacidal activity progressively decreased over the in vitro culture period, an effect that was largely reversed by cell exposure to IFN-gamma, IL-1 alpha, or LPS. In an experimental model in which mice infected with an agerminative C. albicans strain (PCA-2) resisted lethal microbial challenge, freshly harvested AM showed increased cytotoxic activity to Aspergillus fumigatus in vitro as well as enhanced IL-1 production. In conclusion, present data confirm the crucial role of AM in the surveillance of bacterial and fungal infections and indicate that treatment of these cells with IFN-gamma or IL-1 alpha is able to enhance their antimicrobial capability.

Chronic mucocutaneous candidiasis

Chronic mucocutaneous candidiasis can be defined as a group of syndromes that have as a common feature infections of the skin, nails and mucous membranes with Candida albicans. A variety of disorders including endocrine dysfunctions, alopecia, vitiligo, malabsorption syndromes, neoplasms and other infections may also occur in patients with chronic mucocutaneous candidiasis, but these vary considerably from patient to patient. In most patients with chronic mucocutaneous candidiasis, there are abnormalities of cell-mediated immunity. These may be limited to antigens of Candida albicans, but in some patients they are more extensive and involve the T-lymphocyte-mediated responses to all antigens. These immunologic defects are the factors that predispose patients to infections with opportunistic organisms such as Candida spp. Fungal infections in patients with chronic mucocutaneous candidiasis usually respond to treatment with conventional antifungal agents, but often relapse shortly after treatment is stopped unless the defects in the cell-mediated immune system have been corrected.

Biological properties in vitro of a combination of recombinant murine interleukin-3 and granulocyte-macrophage colony-stimulating factor

The effect of recombinant murine interleukin-3 (rIL-3) and recombinant murine granulocyte-macrophage colony-stimulating factor (rGM-CSF) on in vitro murine myeloid progenitor cell (CFU-C) growth and on the function of murine resident peritoneal macrophages was investigated. Both rIL-3 and rGM-CSF are known to support the growth of CFU-C and, when combined, were found to act synergistically to induce the development of an increased number of CFU-C. The distribution pattern of myeloid colonies in the presence of these two growth factors was in general similar to that in the presence of rGM-CSF alone. Both rGM-CSF and rIL-3 enhanced the phagocytosis of Candida albicans (CA) by mature macrophages producing an increase in the percentage of phagocytosing cells as well as an increase in the number of yeast particles ingested per cell. No additive effect on the phagocytosis was observed when the two growth factors were added concurrently. rGM-CSF, but not rIL-3, enhanced the killing of CA by macrophages. This killing was inhibited by scavengers of oxygen radicals.

Contribution of granulocytes and monocytes to resistance against experimental disseminated Candida albicans infection

The aim of the present study was to investigate the contribution of granulocytes and monocytes to resistance against an acute systemic candidal infection in mice. To this end granulocytopenia and monocytopenia were induced by irradiation or treatment with cyclophosphamide, and monocytopenia was obtained by treatment with VP-16. After intravenous injection of 1 X 10(4) Candida albicans into mice irradiated with 8 GY, the number of Candida albicans cultured from the kidneys, expressed as the geometric mean of the number of CFU/g tissue, was 5.4 X 10(4), 7.1 X 10(6) and 5.8 X 10(7) on days 1, 3 and 5 of infection respectively (p less than 0.001 compared to normal mice). The number of Candida albicans cultured from the liver and spleen was also significantly higher for irradiated animals than for normal mice (p less than 0.001). For cyclophosphamide-treated mice the number of organisms in the kidney (1.7 X 10(4) CFU/g on day 1, 1.9 X 10(6) on day 3 and 3.8 X 10(6) on day 5 of infection) and spleen was significantly higher (p at least less than 0.02) than for normal mice after injection of 1 X 10(3) Candida albicans. Monocytopenia induced by VP-16 did not result in an increase in the number of Candida albicans cultured from the kidney or spleen after infection. From these studies it is concluded that granulocytes and not monocytes or exudate macrophages play an important role in resistance against Candida albicans during the first five days of a systemic infection.

Dysfunction of monocytes in Hodgkin's disease by excessive production of PGE-2 in long-term remission patients

The candidacidal activity and the production of oxygen radicals by monocytes were investigated in untreated and long-term remission patients with Hodgkin's disease (HD). Both groups showed a decreased candidacidal function of monocytes with a chemiluminescence (CL) response significantly lower and delayed with respect to normal controls. Indomethacin at 1 microgram/ml corrected the monocyte deficiency increasing the CL response to normal values and normalizing the kinetics in the untreated patients. However, in patients in remission, the peak was delayed and followed by a significant increase in the production of oxygen radicals compared with untreated patients. A direct linear correlation was found between the percentages of lysed Candida and maximum CL peak of stimulated monocytes. When prostaglandin E2 (PGE-2) levels, measured in supernatants of cultured mononuclear cells, were plotted against the percentages of killed Candida, an inverse linear correlation was found. Therefore, monocytes from HD patients have a dysfunction in the generation of oxygen radicals and a decreased candidacidal activity associated with excessive production of PGE-2. Indomethacin can correct the oxidative metabolism in the untreated patients while in apparently "cured" patients the disorder persists.

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.

Cerebrospinal fluid macrophage response to experimental cryptococcal meningitis: relationship between in vivo and in vitro measurements of cytotoxicity

The functional abilities of macrophages from cerebrospinal fluid (CSF) have so far been little studied. We examined the acquisition of activation characteristics by CSF macrophages during the course of experimental cryptococcal meningitis. CSF macrophages developed the ability for increased reactive oxidative intermediate (H2O2) production and tumor and fungal cytotoxicity. Despite having been activated, CSF macrophages could not inhibit the growth of Cryptococcus neoformans in vitro. Immunosuppression with cyclosporine, which eliminates the natural resistance of rabbits to cryptococcal meningitis, did not prevent or diminish H2O2 production by CSF macrophages but did reduce their tumoricidal activity. Activation of CSF macrophages appears to be an integral part of the central nervous system immune response to C. neoformans in this model, but alone is insufficient to eliminate C. neoformans from the central nervous system.

Comparative oxidative microbicidal activity of human blood monocytes and alveolar macrophages and activation by recombinant gamma interferon

The relative oxidative and microbicidal activities of human blood monocytes compared with those of alveolar macrophages (AM) are poorly defined. Furthermore, the comparative efficiency of recombinant gamma interferon (rIFN gamma) to enhance microbicidal function of these 2 cell populations is uncertain. In this study, blood monocytes and AM were obtained concomitantly from 10 healthy, nonsmoking human subjects. Cells were adjusted to equivalent cell concentrations and assayed for respiratory burst activity (superoxide anion production) during soluble (Concanavalin A) or particulate (bacteria) stimulation. Microbicidal activity against Pseudomonas aeruginosa, Listeria monocytogenes, and Candida albicans was also determined for each cell type. Finally, the capacity of rIFN gamma treatment (200 U/ml for 24 h) to enhance these cellular activities was determined. Oxidative activity of AM was greater than that of blood monocytes (p less than 0.01, bacteria; p less than 0.02, Con A). Likewise, AM exhibited greater killing of P. aeruginosa (p less than 0.01) and L. monocytogenes (p less than 0.01) than did monocytes. Neither cell killed C. albicans. Treatment with rIFN gamma greatly enhanced both respiratory burst and microbicidal activity of blood monocytes, but had no effect on AM respiratory burst. Despite this, rIFN gamma-treated AM did exhibit some enhanced killing of L. monocytogenes (p less than 0.05). We conclude that oxidative microbicidal activity of resident AM greatly exceeds that of blood monocytes, but that blood monocytes are relatively more susceptible to activation by rIFN gamma.

Fungicidal activity of human neutrophils and monocytes on dermatophyte fungi, Trichophyton quinckeanum and Trichophyton rubrum

Human peripheral polymorphonuclear neutrophils exhibited potent cytotoxic activity against the dermatophyte fungi Tricophyton quinckeanum and T. rubrum as assessed by inhibition of fungal replication in Sabouraud's agar. Monocytes also showed cytotoxic activity, but this was less pronounced than that of neutrophils, while lymphocytes had no toxic effect. Cytotoxicity showed a linear relationship to the target cell:effector cell ratio, with significant killing detected at a ratio of one neutrophil to one fungal cell. Fungal killing was optimal at incubation times of 2-24 hr for T. rubrum and 2-48 hr for T. quinckeanum. Thereafter, neutrophils were unable to prevent fungal replication while remaining viable. cytotoxicity was markedly reduced by sodium azide, an agent that inhibits haem enzymes, and by catalase, but not by heat-inactivated catalase or superoxide dismutase. The fungicidal activity of neutrophils and monocytes was greatly increased by stimulation with phorbol myristate acetate (PMA) or with concanavalin A (Con A) compounds known to stimulate the secretion of lysosomal enzymes and the production of highly reactive oxygen intermediates. The cytotoxic activity of monocytes to T. quinckeanum, but not to T. rubrum, was also increased by Con A treatment. Neutrophil and monocyte phagocytosis of dermatophytes was demonstrated by electron microscopy studies. Disrupted T. quinckeanum and T. rubrum germlings were identified in the cytoplasm of the phagocytic cells, and similarly disruption of hyphae surrounded, but not engulfed, by neutrophils was also observed. These studies suggest that phagocytosis and/or oxidative products of the respiratory burst of neutrophils and monocytes may be implicated in the killing of dermatophytes in vivo.