[Show abstract][Hide abstract] ABSTRACT: Disseminated infections by the opportunistic yeast Cryptococcus neoformans are characterized by accumulation in tissues of glucuronoxylomannan (GXM), the major component of the capsular polysaccharide. We investigated binding, uptake, and disposal of GXM by peripheral blood neutrophils and monocytes, and the effect of GXM uptake on phagocytic cell function. GXM was efficiently bound and internalized by both types of phagocytic cells, with maximal loading at 50 microg/ml, a GXM concentration found in serum and cerebrospinal fluid of some cryptococcosis patients. However, substantial differences were noted in the kinetics for uptake by macrophages and neutrophils. Whereas neutrophils rapidly ingested limited amounts of GXM and then expelled or degraded it after 1 h of incubation, macrophages demonstrated continuous intracellular accumulation for up to 1 week of incubation. Accumulation of GXM by neutrophils was accompanied by reduced anticryptococcal activity, suggesting one more mechanism for virulence enhancement by the major capsular component of C. neoformans.
Full-text · Article · May 2003 · European Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: We previously demonstrated that the principal component of capsular material of Cryptococcus neoformans, glucuronoxylomannan (GXM), induces interleukin-10 (IL-10) secretion from human monocytes. Here we report that encapsulation
of the yeast with GXM is able to down-regulate interleukin-12 (IL-12) production by monocytes that would normally occur in
the absence of encapsulation. This phenomenon appeared to be the result of inhibition of the phagocytic process by encapsulation
with GXM as well as of negative signals such as IL-10 secretion produced by interaction of GXM with leukocytes. Decreased
secretion of IL-12 correlated with decreased release of gamma interferon (IFN-γ) from T cells, suggesting a role for encapsulation
with GXM in hindering a T helper type 1 (Th1) response. This is supported by the ability of encapsulation with GXM to limit
increased expression of B7-1 costimulatory molecules that otherwise might limit IL-10 secretion. Endogenous IL-10 played a
critical role in modulatory activity associated with encapsulation with GXM. Blocking IL-10 with monoclonal antibody to IL-10
resulted in increased (i) IL-12 secretion, (ii) IFN-γ release from T cells, and (iii) killing of C. neoformans by monocytes. These results suggest that encapsulation with GXM limits development of a protective Th1-type response, an
inhibitory process in which IL-10 plays a critical role. Scavengers of GXM and/or IL-10 could be useful in a protective Th1-type
response in patients with cryptococcosis.
Full-text · Article · Nov 2001 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: This study explored the role of CD40 / CD40 ligand (CD40L) in the induction of a lymphoproliferative response and killing of Cryptococcus neoformans in vitro. In our experimental system, monocytes exposed to C. neoformans were used as antigen-presenting cells (APC) and co-cultured with autologous T cells. The results showed that CD40 / CD40L strongly regulated the blastogenic response of T cells to C. neoformans. The fungus up-regulated CD40 expression on APC. An acapsular strain appeared to be a better inducer than an encapsulated strain. Time course experiments showed optimal regulation of CD40 expression at 48 h of incubation. Blocking the interaction of CD40 on APC with CD40L on T cells using mAb to CD40L resulted in a significant inhibition of IFN-gamma production. The anti-cryptococcal activity of monocytes was greatly influenced by the CD40 / CD40L interaction, and a positive correlation was found between nitric oxide secretion and enhanced killing of C. neoformans. Finally, the CD40 / CD40L interaction was critical for induction of optimal secretion of pro-inflammatory cytokines such as TNF-alpha and IL-1beta. These results indicate an important role for CD40 / CD40L interaction in inducing activation of T cells. Such cell-to-cell contact promotes anti-cryptococcal activity as well as secretion of pro-inflammatory cytokines by monocytes.
Full-text · Article · Jun 2000 · European Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: To analyse the contribution of HIV type 1 envelope glycoprotein gp120 to regulation of a T-cell response to Cryptococcus neoformans.
Monocytes treated with recombinant gp120 and exposed to C. neoformans were used as antigen presenting cells (APC) in coculture with autologous T lymphocytes.
Costimulatory and major histocompatibility complex class II molecules were evaluated on APC by flow cytometry analysis. T-cell proliferation was determined as 3H thymidine incorporation. Cytokine production was analysed by enzyme-linked immunosorbent assay.
gp120 had multiple effects on APC and the T-cell response including: (i) up-regulation of major histocompatibility complex class II antigens on the APC surface resulting from both redistribution of molecules from the intracellular pool and synthesis of new molecules; (ii) up-regulation of B7-2 molecules on the APC surface; (iii) altered T-cell proliferation; and (iv) promotion of interleukin-4 and inhibition of interferon-gamma synthesis and release.
These data indicate that gp120 alters the normal T-cell response to C. neoformans, promoting a T-helper type 2 response. The altered T-cell response produced by gp120 may play an important role in the pathogenesis of cryptococcosis in the patient with AIDS.
[Show abstract][Hide abstract] ABSTRACT: To determine the contribution of anti-glucuronoxylomannan monoclonal antibody (MAb18B7) to the fungicidal capacity of polymorphonuclear leukocytes (PMNL) from HIV-infected patients towards Cryptococcus neoformans.
Killing activity and superoxide anion generation were evaluated in the presence or absence of MAb18B7 in an in vitro system.
Killing activity was determined by colony forming unit inhibition assay. Superoxide generation was measured in the presence or absence of zymosan, C. neoformans, or Candida albicans. CD16, CD32, and CD64 molecules on PMNL were evaluated by cytofluorometric analysis.
MAb18B7 strongly influenced the phagocytic and killing activities against encapsulated C. neoformans and consistently enhanced superoxide anion generation. Expression of CD16, and to a lesser extent CD64, on PMNL was required for MAb18B7-induced superoxide generation. By blocking CD16 and CD64 molecules with anti-CD16 and anti-CD64 MAb, a significant down-regulation of MAb18B7-induced fungicidal activity was observed.
Our results demonstrate that MAb18B7 selectively enhances the killing mechanisms of PMNL from HIV-infected patients against encapsulated C. neoformans. The availability of CD16 and CD64 molecules on PMNL plays a critical role.
[Show abstract][Hide abstract] ABSTRACT: IL-12 production mediated by a T cell-independent and/or T cell-dependent pathway was investigated in human monocytes responding to Cryptococcus neoformans. The data of this study showed that: 1) appreciable levels of IL-12 were observed when freshly isolated monocytes were exposed to acapsular C. neoformans or Candida albicans and secretion occurred within 24-48 h of incubation; 2) monocytes alone were poor producers of IL-12 when stimulated with encapsulated C. neoformans; 3) the presence of specific anti-glucuronoxylomannan mAb favored IL-12 secretion and Fc cross-linking could play a role; 4) monocytes were able to secrete consistent levels of IL-12 when cultured with activated T cells responding to C. neoformans; 5) the maximum secretion of IL-12 was observed at 5-7 days of culture and was strongly regulated by the presence of endogenous IFN-gamma; and 6) the interaction between CD40 on monocytes and CD40 ligand on activated T lymphocytes responding to C. neoformans played a critical role in IL-12 secretion. These data highlight the mechanisms of IL-12 production by human monocytes exposed to C. neoformans, indicating a possible biphasic secretion of IL-12, dependent on the direct effect of fungal insult, and characterized by consistent secretion of IL-12 that is dependent on the interaction of CD40 with the CD40 ligand expressed on activated T cells responding to C. neoformans.
Full-text · Article · Mar 1999 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: This study examined the capability of Candida albicans and Cryptococcus neoformans to modulate CD4 expression on human monocytes. C. albicans and an acapsular strain of C. neoformans induced higher levels of CD4 expression than encapsulated strains. Purified glucuronoxylomannan did not regulate CD4 expression
on monocytes, but down-regulation of CD4 expression compared with stimulation by acapsular C. neoformans alone was observed when glucuronoxylomannan was used in combination with acapsular C. neoformans. The ability of opsonic
factors to facilitate fungal-mediated CD4 overexpression suggests that binding or internalization (or both) of the yeast cells
is a critical event. Protein synthesis was required, excluding redistribution of the intracellular pool of CD4 receptors to
the cellular surface as the sole possible mechanism. Results demonstrate a new effect of fungi on professional phagocytic
cells and raise the possibility that modulation of CD4 could influence gp120-mediated human immunodeficiency virus entry.
Full-text · Article · Dec 1998 · The Journal of Infectious Diseases
[Show abstract][Hide abstract] ABSTRACT: In a previous paper we demonstrated that human polymorphonuclear cells (PMN) in the presence of normal human serum (NHS) secrete proinflammatory cytokines in response to Cryptococcus neoformans or its major capsular component, glucuronoxylomannan (GXM). The hypothesis that activation of the complement system could be responsible for the observed phenomenon is supported by the fact that encapsulated and acapsular C. neoformans isolates are activators of the complement system and, in particular, large encapsulated isolates are powerful activators. In the present study we demonstrate that (i) interleukin-8 (IL-8) release in response to acapsular or encapsulated strains of C. neoformans is significantly reduced in the presence of heat-inactivated serum rather than NHS and is completely abrogated in the absence of human serum; (ii) GXM-induced IL-8 release is strictly dependent on the presence of NHS, is inhibited by specific antibodies to either C3a and C5 complement components, and is completely abrogated by the combined use of these antibodies; (iii) the addition of purified C3a and C5a directly stimulates IL-8 release by PMN; and (iv) monoclonal antibody to GXM in combination with GXM or encapsulated C. neoformans potentiates IL-8 release by PMN. These data shed light on the mechanism involved in GXM-induced IL-8 secretion by PMN, provide an additional potential role for complement in the control of C. neoformans infections, and suggest a complex interplay between the complement system, humoral immunity, and cytokine regulation.
Full-text · Article · Oct 1998 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: Addition of a monoclonal antibody which binds the Cryptococcus neoformans capsule to suspensions of human monocytes, T lymphocytes, and cryptococcal cells (i) enhances interleukin-1beta (IL-1beta), tumor necrosis factor alpha, and IL-2 production; (ii) reduces IL-10 secretion; and (iii) promotes T-cell proliferation. The ability of specific antibody to influence cytokine production and lymphoproliferation suggests a mechanism by which humoral immunity can influence cell-mediated immunity.
Full-text · Article · Apr 1998 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: The key to success of fungal opportunistic pathogens in the immunocompromised host is related to survival inside phagocytic
cells, which represent the first line of defense against microorganisms. The contribution of human immunodeficiency virus-1
recombinant envelope protein gp120 on effector functions of peripheral blood monocytes (PBM) against Candida albicans was investigated. gp120 binds CD4 receptors on PBM while not affecting the access of the fungus into the lysosome compartment.
However, gp120 reduces the antifungal capacity of PBM. This phenomenon correlates with impaired oxygen-dependent antimicrobial
machinery and reduced ability of phagolysosome acidification. The maintenance of phagolysosomal pH at ∼6.2 restricts antimicrobial
properties of the enzyme that work at a low pH, as evidenced by reduced antifungal capability of lysosomal protein extracted
from gp120-treated PBM. These findings highlight gp120 perturbation of intracellular antimicrobial mechanisms of phagocytic
cells and suggest a new aspect for gp120 in impairing immune functions.
Full-text · Article · Mar 1998 · The Journal of Infectious Diseases
[Show abstract][Hide abstract] ABSTRACT: This report examines the effect of the major capsular polysaccharide of Cryptococcus neoformans, glucuronoxylomannan (GXM), on the antigen-presenting capability of human monocytes treated with acapsular cells of C. neoformans. We found that pretreatment of acapsular cryptococci with GXM downregulates, in a dose-dependent manner, the antigen-presenting capacity of monocytes, leading to reduced proliferative T-lymphocyte responses. Similar levels of suppression occurred when monocytes were exposed to encapsulated cryptococci or acapsular cryptococci that were pretreated with GXM. The magnitude of the T-cell response correlated with the ability of monocytes to ingest the yeast. Supernatant fluids from cocultures of monocytes and T cells cultured with encapsulated cryptococci contained higher levels of interleukin-10 (IL-10) than supernatant fluids of cells with acapsular cryptococci. Addition of anti-IL-10 monoclonal antibodies to the incubation medium of monocytes and T cells cultured with encapsulated cryptococci restored proliferative T-cell responses to levels observed during culture with acapsular cryptococci. Finally, treatment of monocytes with encapsulated cryptococci or GXM-treated acapsular cryptococci suppressed expression of class II major histocompatibility complex (MHC) molecules in a manner consistent with previous reports of IL-10-mediated suppression of class II MHC molecules and suppression of proliferative T-cell responses. These results suggest a link between GXM encapsulation, increased IL-10 synthesis by monocytes, decreased expression of class II MHC molecules on monocytes, and reduced proliferative T-cell responses.
Full-text · Article · Mar 1998 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: To induce a specific response in primary resting T cells, two signals must be provided by antigen-presenting cells (APC). The first antigen-specific signal is mediated by formation of the T cell receptor major histocompatibility complex molecule ternary complexes. The second signal is delivered by interaction of either B7-1 or B7-2 expressed by APC with CD28 or CTLA-4 on T cells. In this study, we examined the modulation of B7-1 and B7-2 molecules on human monocytes exposed to encapsulated or acapsular Cryptococcus neoformans or Candida albicans. In our experimental system, C. albicans or acapsular C. neoformans are able to induce B7-1 expression while the encapsulated yeast is a poor stimulator. A modest increase of B7-2 expression was also observed after monocyte treatment with acapsular C. neoformans or C. albicans, while the encapsulated yeast was ineffective in inducing B7-2 molecules. Kinetic analysis showed the maximum expression of B7-1 after 24 to 48 h. Addition of the opsonic IgG1 mAb 2H1 to monocytes and C. neoformans significantly increased B7-1, but not B7-2, expression. The contribution of B7-1 and B7-2 co-stimulatory (CS) molecules to cryptococcal-specific T cell activation was analyzed and a substantial inhibition of T cell proliferation was observed. In this study we provide the first demonstration of fungal interference in the regulation of CS molecules. Our results suggest a potential mechanism for poor inflammatory responses observed in C. neoformans infections.
Full-text · Article · Jan 1998 · European Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: In the present study we investigated the response of monocytes from AIDS patients, susceptible to cryptococcosis (<200 CD4 cells/microl), against Cryptococcus neoformans. Different patterns of response were observed in these cells compared to cells from healthy donors. In particular, fungicidal activity versus this fungus was impaired; this phenomenon could be due to the difficulty of monocytes to internalize C. neoformans in the presence of an intact complement system. Impairment of complement receptor type 3 and direct involvement of this receptor in phagocytosis of C. neoformans were found in monocytes from AIDS patients, which may account for the difficulty in phagocytosis of the fungus. Also, superoxide anion production was dramatically reduced in monocytes from AIDS patients. An increase of spontaneous tumor necrosis factor (TNF) production was evidenced after in vitro addition of C. neoformans. However, this did not activate the antifungal capacity of monocytes from AIDS patients. Moreover, cryptococcus-laden monocytes from AIDS patients were able to induce only a weak response of autologous T-lymphocytes. Hence, monocyte dysfunction could play a part in the progression of cryptococcosis in AIDS.
Full-text · Article · Dec 1997 · Journal of Infection
[Show abstract][Hide abstract] ABSTRACT: The most important event involved in host defence against Cryptococcus neoformans is the development of an adequate cell-mediated immune response. IL-10, abundantly produced during AIDS progression, could be a negative factor that affects the T cell response through its own immunosuppressive action on antigen-presenting cells. To determine whether this cytokine affects the course of immune response against C. neoformans, we added exogenous IL-10 to cultured Cryptococcus-laden monocytes plus T lymphocytes. The data from this study confirmed the down-regulatory effect of exogenous IL-10 on monocytes and expanded the known inhibitory role to include an increase of the deleterious effect due to capsular material of C. neoformans on (i) lymphoproliferation, (ii) down-regulation of MHC class II molecules, (iii) inhibition of IL-2 mRNA expression and protein secretion by T lymphocytes. These results indicate that the presence of IL-10 in AIDS patients, due to the progression of disease, could represent a pivotal problem contributing to augment the pathogenic effect of C. neoformans.
[Show abstract][Hide abstract] ABSTRACT: Human polymorphonuclear leukocytes from normal subjects produced proinflammatory cytokines in response to stimulation with Cryptococcus neoformans yeast cells. The cytokines released after stimulation of neutrophils included interleukin-1beta (IL-1beta), IL-6, IL-8 and tumor necrosis factor alpha. The magnitude of the cytokine response was related to the yeast capsule size. Cells of a large-capsule isolate stimulated release of greater amounts of cytokine than did a thinly encapsulated isolate, which, in turn, stimulated release of greater amounts of cytokine than an acapsular isolate. Cytokine release was also stimulated by supernatant fluids from cryptococcal cells that were preincubated with 10% human serum, suggesting the generation of a soluble mediator. The major capsular polysaccharide, glucuronoxylomannan, stimulated release of tumor necrosis factor alpha, IL-1beta, and IL-8 in a dose-dependent fashion. These results differ from previous studies of cytokine secretion by human monocytes in several important respects, including the importance of encapsulation in stimulation of cytokine secretion and the ability of purified glucuronoxylomannan to induce cytokine secretion.
Full-text · Article · Sep 1996 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: In this study, we demonstrated that purified capsular polysaccharide of Cryptococcus neoformans is a potent inducer of interleukin-10 (IL-10) secretion by human monocytes. Endogenous IL-10 was involved in regulating tumor necrosis factor alpha and IL-1beta secretion by human monocytes in response to encapsulated C. neoformans strains. Our results suggest a new immunosuppressive effect exerted by glucuronoxylomannan through the induction of IL-10, a potent downregulator of proinflammatory cytokines.
Full-text · Article · Aug 1996 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: To investigate the effect of human recombinant interleukin (hrIL)-4 or hrIL-10 on the functional status of polymorphonuclear leukocytes (PMNL) from normal subjects and HIV-infected patients.
In an in vitro system we studied the effect of hrIL-4 or hrIL-10 on phagocytosis, fungicidal activity and superoxide anion production by PMNL.
PMNL were treated in vitro with hrIL-4 or hrIL-10 or their combination for 6 h and then candidacidal activity was evaluated in a colony-forming unit inhibition assay. Superoxide anion generation by PMNL was measured in the presence or absence of preopsonized zymosan or Candida albicans.
Treatment in vitro with hrIL-4 or hrIL-10 of PMNL for 6 h was able to impair candidacidal activity of neutrophils in both normal or HIV-infected patients. The inhibitory effect was time- and dose-dependent and was more evident in PMNL from HIV-infected subjects, and reflected in these latter cells a decrease of superoxide anion generation. The impairment of candidacidal activity in PMNL from HIV-infected patients was accompanied by survival of the yeasts shown by budding formation into phagosomic organelles of cytokine-treated PMNL.
Our data highlight new biological effects of IL-4 and IL-10 evidenced by suppressed effector function of neutrophils; this phenomenon is emphasized in HIV-infected patients suggesting a role for these cytokines in mediating increased susceptibility to microbial infection during AIDS progression.
[Show abstract][Hide abstract] ABSTRACT: The regulation by Cryptococcus neoformans encapsulation of interleukin 1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF-alpha) production by human monocytes was investigated. By using encapsulated and acapsular C. neoformans, we demonstrated that both strains induce cytokine production, although the acapsular strain was a better stimulator than the thinly encapsulated strain. The cytokine levels produced by cells stimulated by the two strains were lower and followed a different kinetic than those stimulated by lipopolysaccharide (LPS). Purified capsular polysaccharide inhibits TNF-alpha secretion induced by LPS or acapsular C. neoformans. In contrast, no regulator effect on IL-1 beta was observed when LPS was used. The secretory response of these cytokines follows different pathways of macrophage activation; in fact, complete inhibition of TNF-alpha does not affect IL-1 beta production and vice versa. These data indicate that purified capsular polysaccharide of C. neoformans could contribute to the in vivo progress of cryptococcosis by suppressing cytokine production of macrophages and suggest that a therapeutic approach to address the suppressive effect of cryptococal polysaccharide could be devised.
Full-text · Article · Sep 1995 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: The effect of recombinant human granulocyte colony-stimulating factor (rhG-CSF) administration on the functional status of
polymorphonuclear leukocytes (PMNL) in neutropenic AIDS patients was investigated. PMNL destructive activity against Candida albicans or encapsulated or acapsular Cryptococcus neoformanswas significantly impaired with respect to control subjects before rhG-CSF treatment. After subcutaneous administration of
rhG-CSF (5 µg/kg), neutrophil counts increased 3- to 11-fold in 24 h and returned to baseline within 96 h. PMNL fungicidal
activity showed significant enhancement 48–72 h after rhG-CSF administration that decreased to baseline within 96 h. Enhanced
rhG-CSF-mediated destructive activity strictly correlated with augmented superoxide anion production by PMNL. These findings
suggest that therapeutic use of rhG-CSF at appropriate schedules in neutropenic AIDS patients could decrease the risk of infection
or, in association with antibiotic therapy, more rapidly resolve the occurring infections.
No preview · Article · Jul 1995 · The Journal of Infectious Diseases