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S M Levitz

Publications and source records attributed to S M Levitz.

At least 73 records · Page 4Linked to original sources
PubMed1990

Growth inhibition of Cryptococcus neoformans by cultured human monocytes: role of the capsule, opsonins, the culture surface, and cytokines.

Despite a presumed critical role of macrophages in the host response to cryptococcal infections, previous studies have failed to show growth inhibition of encapsulated Cryptococcus neoformans by human peripheral blood cultured monocyte-derived macrophages (MO-M phi). Here, we examined whether MO-M phi could be induced to inhibit growth of an encapsulated strain and an isogenic acapsular mutant strain of C. neoformans. MO-M phi were cultured in microwells, and inhibition was measured by comparing CFU at 0 and 24 h after fungal challenge. MO-M phi cultured on plastic surfaces failed to inhibit growth of the encapsulated strain, even in the presence of pooled human serum and/or anticapsular antibody. Moreover, the presence of anticapsular antibody significantly enhanced fungal growth. However, if MO-M phi were cultured on surfaces coated with fibronectin or poly-L-lysine (but not laminin or collagen) and yeast cells were opsonized with pooled human serum, then complete growth inhibition occurred. Preincubation with various concentrations of tumor necrosis factor, granulocyte macrophage colony-stimulating factor, 1,25-dihydroxycholecalciferol, or supernatants from C. neoformans-stimulated lymphocytes failed to activate macrophages for enhanced antifungal activity. The addition of gamma interferon resulted in a significant loss of growth inhibition. For the acapsular strain, complete growth inhibition was observed regardless of the choice of culture surface, opsonins, or cytokines. Fungicidal activity, as measured by a significant decrement in CFU compared with the initial inoculum, was not observed under any conditions tested. These data demonstrate that macrophages are capable of inhibiting cryptococcal growth but that this capacity is markedly influenced by the culture surface, opsonins, cytokines, and the fungal capsule.

Antibodies, Fungal↗
PubMed1989

Paradoxical role of capsule in murine bronchoalveolar macrophage-mediated killing of Cryptococcus neoformans.

Infections with the encapsulated fungus Cryptococcus neoformans are usually acquired via inhalation, and the presence of a capsule has been identified as a virulence factor. Therefore, we studied murine bronchoalveolar macrophage (BAM)-mediated killing and phagocytosis of encapsulated and acapsular strains of C. neoformans. After 2 h, BAM killed encapsulated strains CN52 and MP415 more readily than acapsular strains CN602 and CAP67 (54.9 and 36.2% vs 26.1 and 6.7%, respectively, p less than 0.001). Pre-incubating CN602 with purified capsular polysaccharide increased killing to 42.7% (p = 0.04). Significantly greater killing of the encapsulated strains also occurred in vivo. BAM-mediated killing of CN52 appeared to proceed by non-oxidative mechanisms, as BAM released minimal amounts of H2O2 after stimulation with CN52, and killing was not reduced by inhibitors or scavengers of the respiratory burst. The association between encapsulation and susceptibility to BAM fungicidal effects was not attributable to differences in yeast ingestion. Using the same low ratio of organisms to BAM as in the killing assay, greater than 95% of both CN52 and CN602 were phagocytosed. However, BAM phagocytosed significantly greater numbers of acapsular CN602 when incubated with a higher inoculum. Phagocytosis and killing of CN52 and CN602 required fresh serum as a source of C. Phagocytosis of CN52, but not CN602, was profoundly inhibited if BAM were plated on surfaces coated with mAb against the C3bR (CR1). mAb against the iC3b receptor (CR3) did not affect phagocytosis of either strain. These data demonstrate the innate ability of BAM to preferentially kill, by apparently non-oxidative mechanisms, an encapsulated as opposed to acapsular organism. Inasmuch as different receptors appear involved in phagocytosis of encapsulated versus acapsular C. neoformans, the disparity in killing may result from the greater ability of receptors mediating uptake of encapsulated organisms to trigger the antimicrobial armamentarium of the BAM.

Administration, Intranasal↗
PubMed1989

Effect of cilofungin (LY121019), a fungal cell wall synthesis inhibitor, on interactions of Candida albicans with human neutrophils.

The effects of cilofungin, a lipopeptide antifungal agent active against several species of Candida, on human neutrophil candidacidal activity were investigated. While no increase or decrease in neutrophil killing of blastospores was observed when cilofungin was simultaneously incubated with neutrophils and yeasts, preincubation of yeasts with serum containing cilofungin resulted in approximately 90% decrease in killing of five of six strains. Attachment/phagocytosis of these strains was unchanged from controls. We conclude that cilofungin interferes with opsonization of most strains of C. albicans, resulting in a marked decrease in neutrophil candidacidal activity, a phenomenon which may be of significance in vivo in certain tissues where access to antibodies and/or complement is limited.

Antifungal Agents↗
PubMed1989

Activation of C3 and binding to Aspergillus fumigatus conidia and hyphae.

Complement activation by Aspergillus fumigatus may play a crucial role in stimulating binding and killing of this organism by phagocytes. We examined the amount and type of C3 deposited on resting conidia, swollen conidia, and hyphae of A. fumigatus after incubation in pooled human serum. All three life forms of A. fumigatus were potent activators of the complement cascade, with deposition on the organisms of similar amounts of C3 per unit of surface area. The rate of deposition was slowest for resting conidia, although maximal deposition was still achieved within 40 min. The roles of the alternative and classical pathways were assessed by use of serum chelated with magnesium EGTA [magnesium ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid] and with an alternative pathway reconstituted from the six purified alternative-pathway proteins. Complement activation by resting conidia was mediated by the alternative pathway. In contrast, there was a progressive dependence on the classical pathway as the fungal particles matured into swollen conidia and then hyphae. Treatment with hydroxylamine, which disrupts ester linkages, removed 89 to 95% of the C3 bound to all three forms of A. fumigatus. This released C3 contained a mixture of C3b and iC3b, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. These data demonstrate that although all three forms of A. fumigatus are potent activators of the complement system, the transition from resting conidia to swollen conidia to hyphae results in progressive changes in the manner in which the fungal particles interact with the complement system. The lack of participation of the classical pathway in complement activation by resting conidia may have important implications regarding their ability to effectively stimulate phagocytes.

Aspergillus fumigatus↗
PubMed1989

Aspergillosis.

The wide spectrum of disease states caused by fungi of the genus Aspergillus is dependent in large measure on environmental conditions leading to exposure, and to local and systemic host defenses. Allergic aspergillosis occurs in individuals hypersensitive to the fungus and is treated by immunosuppression, whereas invasive aspergillosis predominates in the severely immunocompromised and is treated with antifungal therapy. Aspergillomas generally arise from saprophytic colonization of a pre-existing pulmonary cavity with Aspergillus, and may be complicated by life-threatening hemoptosis.

Antifungal Agents↗
PubMed1988

Histatins, a novel family of histidine-rich proteins in human parotid secretion. Isolation, characterization, primary structure, and fungistatic effects on Candida albicans.

Histatins 1, 3, and 5 from human parotid secretion were isolated by gel filtration on Bio-Gel P-2 and reverse phase high performance liquid chromatography. The complete amino acid sequences of histatins determined by automated Edman degradation of the proteins, Staphylococcus aureus V8 protease, and tryptic peptides, are as follows: (Sequence: see text). Histatins 1, 3, and 5 contain 38, 32, and 24 amino acid residues, have molecular weights of 4929, 4063, and 3037, respectively, and contain 7 residues of histidine. Histatin 1 contains 1 mol of phosphate/mol of protein; histatins 3 and 5 lack phosphate. With the exception of Glu (residue 4) and Arg (residue 11) in histatin 1, the first 22 amino acid residues of all three histatins are identical, and the carboxyl-terminal 7 residues of histatins 1 and 3 are also identical. The sequence, -Glu-Phe-Pro-Phe-Tyr-Gly-Asp-Tyr-Gly- (residues 23-29), in histatin 1 is absent in histatin 3; and the sequence, -Gly-Tyr-Arg- (residues 23-25), in histatin 3 is absent in histatin 1. The complete sequence of histatin 5 is contained within the amino terminal 24 residues of histatin 3. The structural data suggest that histatins 1 and 3 are derived from different structural genes, whereas histatin 5 is a proteolytic product of histatin 3. All three histatins exhibit the ability to kill the pathogenic yeast, Candida albicans.

Amino Acid Sequence↗
PubMed1988

Factitious dermatosis masquerading as recurrent herpes zoster.

A 35-year-old nurse's aide presented with monthly episodes, during her menses, of self-induced cutaneous lesions intended to simulate recurrent herpes zoster. Features of the clinical presentation that prompted the correct diagnosis are discussed.

Adult↗
PubMed1988

Differential stimulation of murine resident peritoneal cells by selectively opsonized encapsulated and acapsular Cryptococcus neoformans.

Stimulation of murine resident peritoneal cells (RPCs) by encapsulated strain 52 and acapsular strain 602 of Cryptococcus neoformans was compared. Fresh serum was required for fungistasis of both strains. Encapsulated organisms were killed only if the RPCs were activated with gamma interferon (IFN-gamma) or if the organisms were opsonized with anticapsular immunoglobulin G (IgG). In contrast, acapsular organisms were killed by unactivated RPCs, with enhanced killing seen if the cells were activated with IFN-gamma. Except for unopsonized strain 52, all organisms of both strains were phagocytosed. The respiratory burst was stimulated in unactivated and IFN-gamma-activated RPCs by encapsulated strain 52 only if organisms were opsonized with both IgG and serum. In contrast, the burst was stimulated by acapsular strain 602, with or without opsonization. Only unopsonized strain 602 stimulated significant lysosomal enzyme release. Nitrite synthesis by unactivated RPCs was seen only if strain 52 was opsonized with anticapsular IgG or if strain 602 was opsonized with serum. If RPCs were activated with IFN-gamma, then serum-opsonized strain 52 was also able to stimulate nitrite synthesis. Thus, RPC killing, phagocytosis, respiratory burst, lysosomal enzyme release, and nitrite synthesis following challenge by both unopsonized and opsonized with serum or anticapsular IgG strains 52 and 602 varied according to the surface properties of the organisms, the state of activation of the RPCs, and the particular RPC event studied. However, stimulation of nitrite synthesis was the only RPC event which correlated with killing of both strains.

Animals↗
PubMed1987

A rapid fluorescent assay to distinguish attached from phagocytized yeast particles.

In studies of phagocytosis and its consequences for cell activation, it is important to distinguish those particulate stimuli which are completely ingested and internalized from those which are only attached to phagocytic surfaces. Ingestion can be profoundly influenced by both the type of opsonins on the surface of the stimulus and the expression and activation of receptors on the phagocytes for these opsonins. We report a new fluorescent assay which facilitates rapid and reproducible quantitation of attached versus fully internalized live or dead yeast particles by phagocytes. The assay employs the fluorescent dye diaethanol (Uvitex 2B) which stains chitin on the cell wall of fungi and is excluded from live phagocytes. The diaethanol assay and a standard, previously published methylene blue dye exclusion assay yielded comparable results using human neutrophils or monocytes incubated with heat-killed, serum-opsonized Candida albicans. The diaethanol assay proved useful in distinguishing differences in effects of various opsonins, as human neutrophils selectively opsonized with either pooled human serum (PHS), IgG (heat-inactivated PHS) or complement (IgG-depleted PHS) completely internalized 69.5%, 91.3% and 52.5% of cell-associated zymosan particles respectively. Finally, the new assay permitted comparisons of differing macrophage populations, as resident murine peritoneal macrophages internalized only 10.6% of complement-opsonized, cell-associated zymosan particles compared with 41.7% when the macrophages were elicited with thioglycolate. The assay should prove useful to investigators studying both fungal phagocytosis and killing, as well as to those performing general studies of receptor expression, regulation and function.

Candida albicans↗
PubMed1987

Cytosolic calcium changes in individual neutrophils stimulated by opsonized and unopsonized Candida albicans hyphae.

Previous experiments suggest the critical central role of the neutrophil (PMN) respiratory burst in the prevention and containment of disseminated candidiasis. A rise in cytosolic free calcium concentrations ([Ca2+]i) has been documented as an early event after PMN stimulation which is involved in the subsequent genesis of microbicidal and inflammatory respiratory burst products. [Ca2+]i were therefore determined in individual PMN, loaded with the fluorescent calcium probe fura-2 as they attached to and spread over serum-opsonized or unopsonized Candida albicans hyphae, particles that are too big to be completely ingested. After contact between hyphae and PMN, the PMN rapidly spread over hyphal surfaces. Although both opsonized and unopsonized hyphae stimulated similar magnitudes of peak median increases in PMN [Ca2+]i, the kinetics of responses differed; median [Ca2+]i peaked within 1 min after contact with opsonized hyphae versus 4 min after contact with unopsonized hyphae. Moreover, a detectable calcium transient did not invariably follow contact and spreading of each individual PMN over a hyphal surface. In contrast to patterns seen after stimulation of PMN with opsonized zymosan, in which [Ca2+]i is greatest in the periphagosomal region, there was a more uniform distribution throughout the cytoplasm in PMN stimulated with the noningestable hyphae. These alterations in the early patterns and timing of PMN stimulation may reflect analogous differences in subsequent events which control the efficiency and specificity of microbicidal responses to uningestible hyphae and which also determine whether host tissues are damaged by the generation of toxic PMN activation products.

Benzofurans↗
PubMed1986

In vitro killing of spores and hyphae of Aspergillus fumigatus and Rhizopus oryzae by rabbit neutrophil cationic peptides and bronchoalveolar macrophages.

The fungicidal activity of six rabbit neutrophil cationic peptides (NP) against resting (dormant) spores, preincubated (swollen) spores, and hyphae of Aspergillus fumigatus and Rhizopus oryzae was examined. Whereas resting spores of both fungi were totally resistant to killing by up to 500 micrograms of NP/ml, preincubated spores and hyphae were sensitive, under optimal conditions, to less than 1 microgram /ml. NP-1 and NP-2, also found in rabbit bronchoalveolar macrophages, were the most active of the peptides. Activity was inhibited with increasing ionic strength, calcium but not magnesium, incubation at 4 C, and the chitin fragments chitobiose and chitotriose. 125I-labeled NP-1 bound to all three forms of A. fumigatus. Finally, killing of A. fumigatus conidia by rabbit bronchoalveolar macrophages was faster and greater if the conidia were first preincubated in RPMI 1640 medium. Thus, although NP did not kill the resting A. fumigatus conidia, a role for cationic peptides in macrophage-mediated killing is not precluded, as fungicidal activity of both isolated cationic peptides and intact bronchoalveolar macrophages appeared to occur only after the conidia became activated.

Animals↗
PubMed1985

Mechanisms of resistance of Aspergillus fumigatus Conidia to killing by neutrophils in vitro.

Despite the critical role for neutrophils in host defenses against invasive aspergillosis, previous studies have established that neutrophils are unable to kill resting conidia of Aspergillus fumigatus. The mechanisms of resistance of the conidia were therefore investigated. Electron microscopy studies showed the fusion of phagosomes containing A. fumigatus conidia with lysosomes of the neutrophil. Resting conidia of A. fumigatus were then compared with those that had been preincubated in broth until swollen, but not germinated, as well as with blastospores of Candida albicans (two fungal forms that are killed by neutrophils) and zymosan particles. Despite comparable susceptibility to phagocytosis, resting conidia of A. fumigatus stimulated production of significantly less superoxide anion, hydrogen peroxide, and hypochlorous acid and induced less myeloperoxidase-dependent iodination by neutrophils than did the preincubated conidia of A. fumigatus, blastospores of C. albicans, or zymosan particles. In addition, resting conidia of A. fumigatus were relatively resistant to cell-free killing by oxidants presumed to be generated by neutrophils. Thus, resistance of resting conidia of A. fumigatus to neutrophil fungicidal mechanisms appears to be secondary to both failure of the conidia to stimulate an optimal respiratory burst as well as resistance of the conidia to neutrophil oxidants. However, the reversal of this resistance by preincubation of the conidia suggests that neutrophils still may form an important host defense against the conidia of A. fumigatus.

Aspergillus fumigatus↗
PubMed1985

A rapid colorimetric assay of fungal viability with the tetrazolium salt MTT.

A rapid colorimetric assay for viability of fungi that uses the tetrazolium salt MTT is described. All live species of a wide range of medically important fungi that were tested reduced MTT, with resultant intracellular formation within several hours of clearly visible purple crystals of MTT-formazan. The assay proved particularly useful in measuring viability of individual hyphae; greater than 99% of live Aspergillus fumigatus and Rhizopus oryzae hyphae stained purple when incubated with MTT compared with 0% of hyphae killed by any of a variety of methods. The MTT method for measuring fungal viability closely correlated with a slide-culture technique when killing of A. fumigatus hyphae by graded concentrations of hydrogen peroxide was compared. MTT-formazan was easily extracted from the fungi by alcohol, a procedure allowing spectrophotometric quantification of fungal killing in both cell-free and cellular systems. A linear relation between inocula and MTT reduction of several fungi, including Candida albicans blastospores and A. fumigatus hyphae, was demonstrated. Human leukocytes killed 80.3% of C. albicans blastospores as measured by the MTT assay, compared with 70.5% as measured by dilutions and pour plates. Killing of A. fumigatus hyphae by human leukocytes was also quantitated by using the MTT assay.

Fungi↗
PubMed1984

In vivo bronchoalveolar macrophage defense against Rhizopus oryzae and Aspergillus fumigatus.

The ability of bronchoalveolar macrophages from normal, diabetic, and cortisone-treated mice to inhibit spore germination and kill fungal spores in vivo was investigated. The data indicated that the normal host controls different fungal infections in the lungs by different mechanisms. Prevention of mucormycosis required inhibition of fungal spore germination by alveolar macrophages. In contrast, pulmonary defense against aspergillosis depended on early killing of conidia by alveolar macrophages and not on inhibition of germination by bronchoalveolar macrophages. Bronchoalveolar macrophages in diabetic and cortisone-treated animals allowed fungal spore germination, thereby permitting infection by Rhizopus oryzae. In the cortisone-treated mouse, bronchoalveolar macrophages did not kill fungal conidia and progressive infection by Aspergillus fumigatus occurred. Fungicidal activity of bronchoalveolar macrophages was measured with a new in vivo killing assay.

Animals↗
PubMed1984

Killing of Aspergillus fumigatus spores and Candida albicans yeast phase by the iron-hydrogen peroxide-iodide cytotoxic system: comparison with the myeloperoxidase-hydrogen peroxide-halide system.

A new fungicidal system composed of ferrous ion, H2O2, and iodide is described and compared with the myeloperoxidase-hydrogen peroxide-halide system. Both systems had similar activity against Aspergillus fumigatus spores and the Candida albicans yeast phase, but only the ferrous ion-hydrogen peroxide-iodide system was inhibited by hydroxyl radical scavengers.

Animals↗
PubMed1984

Changing patterns of aspergillosis infections.

Aspergillus may cause a wide range of clinical illnesses. In large part, manifestations depend on the status of underlying local and systemic host immunologic responses. Therefore, it is critical to specifically define the different types of aspergillosis. With such distinctions between allergic bronchopulmonary aspergillosis, aspergilloma, and invasive aspergillosis with vasculitis, specific host factors that predispose to the development of each of these entities are becoming recognized. Understanding of such immunologic factors better explains the occurrence of clinical forms which overlap to include more than one type of aspergillosis. In general, the different types of aspergillosis have been increasingly recognized as significant health problems, though in different subpopulations of patients. Advances in knowledge of the immunopathogenesis of aspergillosis raise prospects for more rapid diagnosis as well as for successful prevention or therapy (directed toward both the host and pathogen) of diseases caused by these fungi.

Alveolitis, Extrinsic Allergic↗