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S M Levitz

Publications and source records attributed to S M Levitz.

At least 55 records · Page 3Linked to original sources
PubMed1994

Macrophage-Cryptococcus interactions.

Macrophages are a heterogeneous population that vary depending on their species of origin, anatomic location, state of activation, and conditions of culture. Moreover, macrophages normally interact with other cells both within and without the immune system. It is clear from the data reviewed in this chapter that all of these aforementioned variables greatly influence macrophage-C. neoformans interactions. While circumstantial evidence strongly supports a major role for the macrophage in host defenses against cryptococcosis, the nature and extent of the contribution macrophages make remain to be defined. One major challenge for researchers in this field will be to design experiments that closely mimic what occurs in human physiological and pathological states.

Animals↗
PubMed1993

Idiopathic CD4+ T-lymphocytopenia--four patients with opportunistic infections and no evidence of HIV infection.

BACKGROUND AND METHODS: We describe four patients without major risk factors for human immunodeficiency virus (HIV) infection, each of whom presented with severe opportunistic infections and was found to have idiopathic CD4+ T-lymphocytopenia. We performed assays to detect the presence of retroviruses and undertook immunophenotyping of subgroups of peripheral-blood lymphocytes. RESULTS: The opportunistic infections at presentation included Pneumocystis carinii pneumonia, cryptococcal meningitis (two patients, one with concurrent pulmonary tuberculosis), and histoplasma-induced brain abscess. During 10 to 68 months of observation, none of the four patients had evidence of infection with HIV type 1 or 2 or human T-cell lymphotropic virus type I or II on the basis of epidemiologic, serologic, or polymerase-chain-reaction studies or culture, nor was there any detectable reverse transcriptase activity. Although all the patients had severe, persistent CD4+ T-lymphocytopenia (range, 12 to 293 cells per cubic millimeter), the CD4+ cell count progressively declined in only one and was accompanied by multiple opportunistic infections. All four patients had significantly reduced numbers of circulating CD8+ T cells, natural killer cells, or B cells (or all three). CONCLUSIONS: These four patients had idiopathic CD4+ T-lymphocytopenia with opportunistic infections but no evidence of HIV infection. Instead of the progressive, selective depletion of CD4+ T cells characteristic of HIV infection, some patients with idiopathic immunodeficiency have stable CD4+ cell counts accompanied by reductions in the levels of several other lymphocyte subgroups.

Adult↗
PubMed1993

Effect of endothelial cells on phagocyte-mediated anticryptococcal activity.

The anticryptococcal activity of peripheral blood polymorphonuclear leukocytes (PMN) and monocytes was compared on plastic versus human umbilical vein endothelial cell surfaces. Various amounts of PMN and monocytes were incubated on plastic or endothelial surfaces and then challenged for 18 h with Cryptococcus neoformans. Both phagocyte populations exhibited significantly more anticryptococcal activity on an endothelial cell monolayer than on plastic. Prestimulating the endothelial cell monolayer with interleukin-1 augmented the antifungal activity of PMN but not that of monocytes. In the absence of phagocytes, endothelial cells lacked activity. Blocking antibodies directed against endothelial adhesion molecules ICAM-1 and ELAM-1 did not affect PMN-mediated inhibition of fungal growth. Recombinant interleukin-1 and interleukin-8 (two cytokines secreted by endothelial cells) activated neutrophils for modestly enhanced antifungal activity. However, supernatants derived from endothelial cells, as well as neutralizing antibodies directed against the endothelial cell-derived cytokines interleukin-8 and granulocyte-macrophage colony-stimulating factor failed to augment PMN antifungal activity. PMN viability after 18 h was diminished on plastic compared with endothelial surfaces. While the percentages of C. neoformans bound to neutrophils were similar on both surfaces, the patterns of binding were markedly different: on endothelial (but not plastic) surfaces, most cryptococci were surrounded by greater than five PMN. Thus, phagocyte-mediated inhibition of cryptococcal growth is enhanced on endothelial monolayers compared with plastic surfaces, possibly as a result of differences in phagocyte viability and patterns of binding. Bolstering the activity of circulating phagocytes by stimulating endothelial cells may be of relevance in the treatment of patients with or at risk for cryptococcemia.

Antibodies, Monoclonal↗
PubMed1993

Phenotypic and functional characterization of human lymphocytes activated by interleukin-2 to directly inhibit growth of Cryptococcus neoformans in vitro.

Recently we demonstrated that the nonadherent (to plastic) fraction of human PBMC could be activated by IL-2 to inhibit Cryptococcus neoformans growth. Here we characterize the antifungal effector cells. Depletion by panning of natural killer (NK) (CD16+, CD56+) cells from nylon wool-treated, IL-2-activated PBMC markedly decreased lytic activity against a tumor cell target (K562) but did not affect antifungal activity. Panning out T (CD3+, CD5+) cells enhanced activity against tumor cells but partially abrogated activity against C. neoformans. IL-2-activated T cells of 95% purity, obtained by panning out NK cells from PBMC forming rosettes with sheep erythrocytes, had excellent antifungal activity but suboptimal antitumor activity. The nonrosetted cells (which were virtually free of T cells and enriched for NK cells) had both antitumor and antifungal activity, even if cultured without IL-2. CD4+, CD8+, and CD56+ cells, purified by positive selection by panning, directly inhibited cryptococcal growth. Conjugate formation between fungi and both CD56+ and CD5+ effector cells was demonstrated by videomicroscopy and immunoperoxidase staining. Thus, IL-2-activated T cells and NK cells form conjugates with and directly inhibit the growth of C. neoformans. To our knowledge, these data are the first demonstration of human T cells directly inhibiting growth of a microbial target.

Animals↗
PubMed1992

Invasive infections due to Candida krusei: report of ten cases of fungemia that include three cases of endophthalmitis.

Candida krusei has become an increasingly important invasive pathogen, particularly in immunocompromised patients. Previous experimental and clinical experience suggest that C. krusei has a low propensity for hematogenously infecting the eye. We report 10 cases of fungemia due to C. krusei at our institutions, including three cases of endophthalmitis due to C. krusei. Fungemia was associated with nodular skin lesions in all seven patients with neutropenia and occurred despite administration of antifungal prophylaxis or empirical therapy. None of the patients apparently died as a direct result of C. krusei fungemia. Treatment with amphotericin B resulted in resolution of endophthalmitis, although one patient required vitrectomy. Early institution of aggressive therapy with amphotericin B may alter the course and improve the prognosis of C. krusei infection, particularly in immunocompromised patients.

Aged↗
PubMed1992

Overview of host defenses in fungal infections.

Humans have a broad array of host defense mechanisms against fungal invasion. Most serious mycoses occur in patients who have defects in one or more of these defenses. Defense mechanisms not related to the immune system include barriers created by the skin and mucous membrane, competition from the normal indigenous bacterial flora, mucociliary clearance mechanisms, and fungistatic products in serum such as metal chelators. Among the immune mechanisms, activation of the complement system and generation of an antibody response facilitates recognition of fungi by specific receptors on immune cells. Quantitative and qualitative disorders of phagocytic function predispose patients to the development of invasive aspergillosis and candidiasis. Impairment of cell-mediated immunity predisposes patients to cryptococcosis, histoplasmosis, coccidioidomycosis, and mucocutaneous candidiasis. An overexuberant inflammatory response to fungal antigens can result in morbidity and mortality because of damage to host tissues. Knowledge of the type of immunocompromise that is afflicting a patient enables the clinician to predict which mycoses the patient is likely to have and to which the patient is predisposed.

Antibodies, Fungal↗
PubMed1992

Binding of unopsonized Cryptococcus neoformans by human bronchoalveolar macrophages: inhibition by a large-molecular-size serum component.

Infection with Cryptococcus neoformans usually begins after inhalation of airborne organisms. Since levels of opsonins in the alveolar space may be low, the ability of human bronchoalveolar macrophages to bind C. neoformans in the presence and absence of opsonins was studied. Bronchoalveolar macrophages bound unopsonized C. neoformans. Surprisingly, component(s) in pooled human serum (PHS) inhibited binding, as evidenced by 26% and 71% inhibition of binding when 20% PHS and heat-inactivated PHS (HI-PHS), respectively, were added to the system. Separation of PHS by molecular size revealed that the inhibitory component had an apparent molecular weight greater than 10(6) and was inhibitory at nanomolar concentrations. PHS stimulated and HI-PHS had no effect on binding of acapsular C. neoformans and zymosan particles to bronchoalveolar macrophages. These data demonstrate that bronchoalveolar macrophages can bind unopsonized, encapsulated C. neoformans, but that serum component(s) inhibits binding.

Bacterial Adhesion↗
PubMed1992

Biological activity of interleukin-2 bound to Candida albicans.

The lymphokine interleukin-2 (IL-2), which is necessary for the generation of an optimal cell-mediated immune response, has recently been shown to have lectinlike properties, with specificity for high-mannose groups. Therefore, the ability of IL-2 to bind to the mannose-rich fungus Candida albicans was examined. Heat-killed fungi preincubated with IL-2 stimulated, in a dose-dependent manner, proliferation of the IL-2-dependent cell line CTLL20. Soluble mannan, which is rich in exposed mannose groups, inhibited binding of IL-2 to C. albicans by approximately 60%, suggesting that the lectinlike properties of IL-2 are partially responsible for its fungal binding capacity. Binding of IL-2 to fungi appeared to be reversible, as C. albicans preincubated with IL-2 stimulated CTLL20 proliferation even when the fungi and cells were separated by an 0.4-microns-pore-size membrane. The lymphoproliferative response of normal human peripheral blood mononuclear cells to C. albicans was augmented when the fungus was preincubated with IL-2. Binding of 125I-IL-2 could not be inhibited by unlabeled IL-2, suggesting the absence of high-affinity receptors on C. albicans for IL-2. While the in vivo relevance remains to be determined, these data demonstrate that IL-2 can bind to C. albicans in vitro and thereby influence the host response to this medically important fungus.

Candida albicans↗
PubMed1992

HIV-1 envelope protein (gp120) inhibits the activity of human bronchoalveolar macrophages against Cryptococcus neoformans.

Cryptococcus neoformans infections are a major cause of morbidity and mortality for HIV-infected persons. Containment of the initial respiratory inoculation to the lung appears defective in patients with AIDS despite the low burden of HIV in bronchoalveolar macrophages. We have studied the fungistatic activity of human bronchoalveolar macrophages (BAM) cultured with an encapsulated strain of C. neoformans in the presence of pooled human serum. We observed 51.6% fungistasis after 24 h of culture. Fungistasis was diminished if the pooled human serum was heat-inactivated but was not affected by anticryptococcal capsular IgG. HIV envelope protein (gp120) has been shown to interfere with lymphocyte activation in vitro. We studied the effects of gp120 on BAM function and found that fungistatic activity was inhibited 25% (p < 0.001). Although binding of yeasts was not affected, gp120 inhibited the internalization of bound yeasts by 46% (p = 0.025). These experiments indicate that gp120 decreases the internalization and fungistasis of C. neoformans by human BAM, and they suggest a mechanism to explain how a small number of HIV-1-infected cells in the lung could impair the containment of C. neoformans.

Bronchoalveolar Lavage Fluid↗
PubMed1991

Killing of Cryptococcus neoformans by human peripheral blood mononuclear cells stimulated in culture.

Since cell-mediated immunity (CMI) is critical for host defenses against the encapsulated fungus Cryptococcus neoformans, the production of human antifungal effector cells as a consequence of the CMI response was investigated. Peripheral blood mononuclear cells (PBMC) were stimulated in culture with killed C. neoformans. Stimulated (but not unstimulated) PBMC killed a subsequent inoculum of live encapsulated organisms, with maximal killing seen after 3-7 days. Killing required the presence of both adherent and nonadherent stimulated PBMC and was enhanced by anticapsular antibody. In contrast, unstimulated PBMC and the adherent fraction of stimulated PBMC killed an isogenic acapsular strain of C. neoformans. These data suggest that the CMI response controls cryptococcosis by eliciting two populations of fungicidal cells acting synergistically. Moreover, capsule, by thwarting the ability of unstimulated PBMC to kill C. neoformans, seems to obligate the host to mount an immune response to generate fungicidal cells.

Cell Division↗
PubMed1991

Activation of human peripheral blood mononuclear cells by interleukin-2 and granulocyte-macrophage colony-stimulating factor to inhibit Cryptococcus neoformans.

The abilities of selected cytokines to activate human peripheral blood mononuclear cells (PBMC) to inhibit and kill the opportunistic fungus Cryptococcus neoformans were studied. PBMC were cultured for 7 days in cell wells containing no cytokines, tumor necrosis factor (TNF), gamma interferon (IFN-gamma), 1,25-dihydroxycholecalciferol (vitamin D3), granulocyte-macrophage colony-stimulating factor (GM-CSF), or interleukin-2 (IL-2) and were then challenged for 24 h with a fixed number of CFU of C. neoformans. The number of CFU increased in wells containing no cytokines, TNF, IFN-gamma, or vitamin D3 and remained about the same in wells containing GM-CSF. In contrast, the number of CFU in wells containing IL-2-stimulated PBMC decreased, suggesting fungicidal activity. Optimal conditions for IL-2 stimulation included a minimum of 5 days of incubation of PBMC with IL-2, a concentration of 100 U of IL-2 per ml, and a high ratio of effectors to fungi. Separation of IL-2-stimulated PBMC based upon their adherence to plastic revealed that antifungal activity resided in the nonadherent fraction. These data demonstrate that IL-2 and GM-CSF are capable of stimulating PBMC-mediated antifungal activity and suggest that these cytokines may play physiological or pharmacological roles in host defenses against cryptococcosis.

Cells, Cultured↗
PubMed1991

Anticandidal activity of major human salivary histatins.

We have previously shown that histatins 1, 3, and 5 are homologous, histidine-rich proteins present in human parotid and submandibular secretions which contain 38, 32, and 24 amino acids, respectively. Interest in these proteins stems from the fact that histatins exhibit candidacidal and candidastatic activities. The goal of the present investigation was a detailed functional characterization of these anticandidal activities of histatins at the levels of killing of blastoconidia, killing of germinated cells, and inhibition of germination by using three bioassays. Candidacidal activities were evaluated at several ionic strengths, in the presence of different mono- and divalent ions, and at multiple pH values. In addition, the susceptibility of Candida albicans in different growth phases to histatins was investigated. While all three major human histatins demonstrated candidacidal activities, they differed in their abilities to kill blastoconidia and germinated cells, with histatin 5 being the most active, histatin 3 showing moderate activity, and histatin 1 exhibiting the lowest level of activity. For the inhibition of germination, however, histatin 3 exhibited more activity than either histatin 1 or histatin 5. The candidacidal activity of histatins was inversely proportional to both the ionic strength and the divalent cation concentration in the medium. Stepwise reduction of the pH of the assay medium enhanced the candidacidal activities of histatins 1 and 3, while the activity of histatin 5 was pH independent over the range of pHs 4 to 8. C. albicans in log-phase growth was more susceptible to histatins 1 and 3 than cells in stationary phase. Cells in either growth phase were still more vulnerable to histatin 5 than to histatins 1 and 3. The results obtained establish the functional relationship of the major histatins with respect to both their fungicidal and fungistatic activities and provide insights into their activities under ionic and pH conditions likely to be encountered in vivo in the oral cavity. Moreover, the data point towards possible mechanisms responsible for the anticandidal activities of histatins.

Amino Acid Sequence↗
PubMed1991

Binding of Cryptococcus neoformans by human cultured macrophages. Requirements for multiple complement receptors and actin.

We studied the receptors on human cultured macrophages (MO-M phi) responsible for binding encapsulated and isogenic mutant acapsular strains of Cryptococcus neoformans, and whether such binding leads to a phagocytic event. Both strains required opsonization with complement components in normal human serum in order for binding to occur. Binding of the acapsular, but not the encapsulated, strain led to phagocytosis. MAb directed against any of the three defined complement receptors (CR) on MO-M phi (CR1, CR3, and CR4) profoundly inhibited binding of serum-opsonized encapsulated (and to a lesser extent acapsular) organisms to MO-M phi. Immunofluorescence studies demonstrated migration of CR to the area of the cryptococcal binding site. Trypsin and elastase inhibited binding of encapsulated and, to a lesser extent, acapsular yeasts to MO-M phi. Binding of encapsulated C. neoformans was profoundly inhibited by incubation in the cold or by inhibitors of receptor capping and actin microfilaments. Thus, multiple CR appear to contribute to binding of serum-opsonized encapsulated C. neoformans by MO-M phi. Binding is an energy-dependent process that requires conformational changes in actin yet does not lead to phagocytosis of the organism. In contrast, energy is not required for binding of acapsular yeasts by MO-M phi and binding triggers phagocytosis.

Actins↗
PubMed1990

Human neutrophil degranulation stimulated by Aspergillus fumigatus.

Previous studies have established that human neutrophils (PMN) are unable to kill resting conidia (RC) of Aspergillus fumigatus but can kill conidia that have been preincubated in culture medium until swollen but not yet germinated. Compared with swollen conidia (SC), RC stimulate a relatively weak PMN respiratory burst. In the present study, we further examined the mechanisms of resistance of RC to neutrophil killing by comparing neutrophil degranulation and phagocytosis following stimulation by RC and SC opsonized in pooled human serum. RC, compared with SC, stimulated significantly less release of both the primary granule marker beta-glucuronidase and the secondary granule marker lactoferrin. PMN also phagocytosed significantly greater numbers of SC, although the differences in phagocytosis were not great enough to account for the differences in degranulation. Suboptimal stimulation of degranulation and phagocytosis may thus contribute to the inability of neutrophils to kill RC. Moreover, reagent lactoferrin bound avidly to both RC and SC, raising the possibility that PMN-released lactoferrin may contribute to antifungal activity at the conidial surface by competing for iron or catalyzing the formation of oxygen radicals.

Aspergillus fumigatus↗
PubMed1990

Inhibition and killing of fungi by the polyamine oxidase-polyamine system. Antifungal activity of the PAO-polyamine system.

Both components of the polyamine oxidase (PAO)-polyamine system are known to be present in phagocytes and have thus been postulated to contribute to the antimicrobial activity of these cells. Therefore, the effects of the PAO-polyamine system on three medically important opportunistic fungi were examined. Yeasts of Cryptococcus neoformans, but not Candida albicans blastoconidia or Aspergillus fumigatus conidia, were efficiently killed by the system. Two putative end products of the system, hydrogen peroxide and acrolein, both killed C. neoformans at concentrations attainable with the whole system. However, catalase failed to inhibit activity of the whole system, making hydrogen peroxide an unlikely mediator of killing. Although C. albicans blastoconidia and A. fumigatus conidia were not killed by the PAO-polyamine system, germ tube formation by the former, and hyphal growth by the latter, were markedly inhibited. These data establish that the PAO-polyamine system possesses antifungal activity.

Acrolein↗