- Immunological phenomena associated with chronic mucocutaneous candidiasis have recently been intensively studied by many workers (reviewed by Kirkpatrick, Rich & Bennett, 1971). The results have shown that there is no common immunological denominator in this disease. The most common finding, however, is defective cellular immunity, which may or may not be accompanied by failure of in vitro lymphocyte transformation.
Immunological Feautures in a Case of Chronic Granulomatous Candidiasis and its Treatment with Transfer Factor
VALDIMARSSON, C. B. S. WOOD, J. R. HOBBS AND P. J. L. HOLT
- The ability of Candida albicans to establish an infection involves multiple components of this fungal pathogen, but its ability to persist in host tissue may involve primarily the immunosuppressive property of a major cell wall glycoprotein, mannan. Mannan and oligosaccharide fragments of mannan are potent inhibitors of cell-mediated immunity and appear to reproduce the immune deficit of patients with the mucocutaneous form of candidiasis. However, neither the exact structures of these inhibitory species nor their mechanisms of action have yet been clearly defined. Different investigators have proposed that mannan or mannan catabolites act upon monocytes or suppressor T lymphocytes, but research from unrelated areas has provided still other possibilities for consideration. These include interference with cytokine activities, lymphocyte-monocyte interactions, and leukocyte homing. To stimulate further research of the immunosuppressive property of C. albicans mannan, we have reviewed (i) the relationship of mannan to other antigens and virulence factors of the fungus; (ii) the chemistry of mannan, together with methods for preparation of mannan and mannan fragments; and (iii) the historical evidence for immunosuppression by Candida mannan and the mechanisms currently proposed for this property; and (iv) we have speculated upon still other mechanisms by which mannan might influence host defense functions. It is possible that understanding the immunosuppressive effects of mannan will provide clues to novel therapies for candidiasis that will enhance the efficacy of both available and future anti-Candida agents. Immunosuppressive properties observed for isolated Candida mannan and its catabolites in vivo and in vitro provide additional evidence that fungal mannan is responsible for patient immune dysfunction.
Candida mannan: chemistry, suppression of cell-mediated immunity, and possible mechanisms of action.
R D Nelson, N Shibata, R P Podzorski, and M J Herron
- Phagocytic cells of the innate immune system, such as macrophages and neutrophils, are a primary line of defense against microbial infections. Patients with defects in innate immunity, such as those with chronic granulomatous disease or neutropenia, are extremely sensitive to a variety of infections. When a phagocyte recognizes the presence of an invading cell, it engulfs the microbe with its membrane to form the phagosome, an intracellular compartment containing the microbe. This compartment matures by fusion with lysosomes to create the phagolysosome, an organelle replete with antimicrobial compounds and an acidic pH. Internalization creates a hostile environment for the microorganism, which, of course, is the intent. The phagolysosome is a precarious neighborhood even before the onslaught of antimicrobial compounds. Engulfment by the macrophage thrusts the microorganism into an alien milieu, one devoid of key nutrients necessary for metabolism and division. Surviving the antimicrobial assault in the phagolysosome depends on the microbe’s ability to synthesize the proteins and other cellular components necessary to counteract these stresses. Thus, a pathogen must find the requisite nutrients to provide the building blocks for these complex macromolecules and the energy with which to synthesize them.
In this article we consider the initial responses of several microbes to nutrient deprivation inside the macrophage. The first of these, Mycobacterium tuberculosis, the bacterium that causes tuberculosis, resides for prolonged periods within the macrophage, in which it can proliferate and subsequently spread throughout the body. The second, the yeast Saccharomyces cerevisiae, is killed efficiently by the macrophage. The third, the opportunistic fungal pathogen Candida albicans, survives ingestion by changing rapidly from a yeast to a filamentous morphology, lysing the macrophage from the inside out. Once free, C. albicans cells are able to disseminate through the body. The interaction of C. albicans with the macrophage is transient, as opposed to the long-term persistence of M. tuberculosis. Although the outcomes of this macrophage capture are quite different among the three microbes, the initial responses of all three to the internal environment are remarkably similar: induction of the glyoxylate cycle, a pathway that permits the utilization of compounds with two carbons (C2 compounds), such as acetate, to satisfy cellular carbon requirements.
Systemic fungal infections have increased dramatically in prevalence and severity over the last few decades, in concert with the number of patients living for extended periods with significant immune dysfunction. AIDS, cancer chemotherapy, and organ transplantation have all contributed to this rise, as has the widespread use of antibiotics. The most common systemic fungal infection is candidiasis, which accounts for well over half of these invasive mycoses (3). A single species, C. albicans, causes the majority of these infections. C. albicans, which also causes oropharyngeal thrush and vaginitis, is normally a commensal of the mammalian gastrointestinal tract, in which it lives without adverse effects on the host. Both C. albicans and S. cerevisiae are readily phagocytosed by cultured macrophages in the presence of serum. While the macrophages efficiently kill S. cerevisiae, engulfment induces C. albicans cells to grow in a filamentous morphology. These hyphal filaments can penetrate through the membrane of the phagocytic cell, releasing the fungal cell back into the extracellular medium while killing the macrophage in the process. The different outcomes are not surprising; C. albicans is a common pathogen while S. cerevisiae is rarely found in human hosts.
The primary function of the glyoxylate cycle is to permit growth when C2 compounds, such as ethanol and acetate, are the only sources of carbon. The glyoxylate pathway (also dubbed the glyoxylate shunt, for clear reasons) bypasses these decarboxylations, allowing C2 compounds to serve as carbon sources in gluconeogenesis and to be incorporated into glucose and, from there, into amino acids, DNA, and RNA. Glucose, as the preferred carbon source in most organisms, can be both converted into five-carbon sugars (such as ribose and deoxyribose) via the pentose phosphate pathway and catabolized to acetyl-CoA via glycolysis. In microorganisms, however, glucose is frequently not available, and simple carbon compounds provide the only accessible carbon.
With the population of immunocompromised people on the rise, the frequency of invasive fungal infections continues to increase, making the need for effective treatments more imperative.
Life and Death in a Macrophage: Role of the Glyoxylate Cycle in Virulence
Michael C. Lorenz and Gerald R. Fink
- Fungal pathogens can be recognized by the immune system via their beta-glucan, a potent proinflammatory molecule that is present at high levels but is predominantly buried beneath a mannoprotein coat and invisible to the host. To investigate the nature and significance of “masking” this molecule, we characterized the mechanism of masking and consequences of unmasking for immune recognition. We found that the underlying beta-glucan in the cell wall of Candida albicans is unmasked by subinhibitory doses of the antifungal drug caspofungin, causing the exposed fungi to elicit a stronger immune response. Using a library of bakers’ yeast (Saccharomyces cerevisiae) mutants, we uncovered a conserved genetic network that is required for concealing beta-glucan from the immune system and limiting the host response. Perturbation of parts of this network in the pathogen C. albicans caused unmasking of its beta-glucan, leading to increased beta-glucan receptor-dependent elicitation of key proinflammatory cytokines from primary mouse macrophages. By creating an anti-inflammatory barrier to mask beta-glucan, opportunistic fungi may promote commensal colonization and have an increased propensity for causing disease.
A drug-sensitive genetic network masks fungi from the immune system.
- The interaction of Candida albicans with macrophages is considered a crucial step in the development of an adequate immune response in systemic candidiasis. An in vitro model of phagocytosis that includes a differential staining procedure to discriminate between internalized and non-internalized yeast was developed. Upon optimization of a protocol to obtain an enriched population of ingested yeasts, a thorough genomics and proteomics analysis was carried out on these cells. Both proteins and mRNA were obtained from the same sample and analyzed in parallel. The combination of two-dimensional PAGE with MS revealed a total of 132 differentially expressed yeast protein species upon macrophage interaction. Among these species, 67 unique proteins were identified. This is the first time that a proteomics approach has been used to study C. albicans-macrophage interaction. We provide evidence of a rapid protein response of the fungus to adapt to the new environment inside the phagosome by changing the expression of proteins belonging to different pathways. The clear down-regulation of the carbon-compound metabolism, plus the up-regulation of lipid, fatty acid, glyoxylate, and tricarboxylic acid cycles, indicates that yeast shifts to a starvation mode. There is an important activation of the degradation and detoxification protein machinery. The complementary genomics approach led to the detection of specific pathways related to the virulence of Candida. Network analyses allowed us to generate a hypothetical model of Candida cell death after macrophage interaction, highlighting the interconnection between actin cytoskeleton, mitochondria, and autophagy in the regulation of apoptosis. In conclusion, the combination of genomics, proteomics, and network analyses is a powerful strategy to better understand the complex host-pathogen interactions.
Integrated proteomics and genomics strategies bring new insight into Candida albicans response upon macrophage interaction.
- Intestinal homeostasis is critical for efficient energy extraction from food and protection from pathogens. Its disruption can lead to an array of severe illnesses with major impacts on public health, such as inflammatory bowel disease characterized by self-destructive intestinal immunity. However, the mechanisms regulating the equilibrium between the large bacterial flora and the immune system remain unclear. Intestinal lymphoid tissues generate flora-reactive IgA-producing B cells, and include Peyer’s patches and mesenteric lymph nodes, as well as numerous isolated lymphoid follicles (ILFs). Here we show that peptidoglycan from Gram-negative bacteria is necessary and sufficient to induce the genesis of ILFs in mice through recognition by the NOD1 (nucleotide-binding oligomerization domain containing 1) innate receptor in epithelial cells, and -defensin 3- and CCL20-mediated signalling through the chemokine receptor CCR6. Maturation of ILFs into large B-cell clusters requires subsequent detection of bacteria by toll-like receptors. In the absence of ILFs, the composition of the intestinal bacterial community is profoundly altered. Our results demonstrate that intestinal bacterial commensals and the immune system communicate through an innate detection system to generate adaptive lymphoid tissues and maintain intestinal homeostasis.
Lymphoid tissue genesis induced by commensals through NOD1 regulates intestinal homeostasis
Djahida Bouskra, Christophe Brézillon, Marion Bérard, Catherine Werts, Rosa Varona, Ivo Gomperts Boneca & Gérard Eberl
http://www.nature.com/nature/journal/v456/n7221/full/nature07450.html – a1#a1
- 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. However, when immune defenses are compromised or the normal microflora balance is disrupted, Candida transforms itself into an opportunistic pathogenic killer. 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 (M), DC recognized Candida by the mannose-fucose receptor. Upon ingestion, DC killed Candida as efficiently as human M, 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. Despite appropriate therapy, mortality from systemic Candida infections in immunocompromised individuals is nearly 30%. In human immunodeficiency virus-infected individuals who have not yet developed advanced immunodeficiency, the prevalence of oropharyngeal Candida is from 7 to 48% of patients. As the immunodeficiency in AIDS patients progresses, the prevalence of oral candidiasis increases to 43 to 93%. Furthermore, the development of oral candidiasis in the early stages of human immunodeficiency virus infection is highly predictive of worsening immunodeficiency.
Candida albicans Is Phagocytosed, Killed, and Processed for Antigen Presentation by Human Dendritic Cells
Simon L. Newman and Angela Holly
- Systemic candidiasis remains a major cause of disease and death, particularly among patients suffering from hematological malignancies. In an attempt to contribute to the discovery of useful biomarkers for its diagnosis and therapeutic monitoring, we embarked on a mapping of Candida albicans immunogenic proteins specifically recognized by antibodies produced during the natural course of systemic Candida infection in this high-risk population. About 85 immunoreactive protein species were detected with systemic candidiasis patients’ serum specimens by using immunoproteomics (i.e., two-dimensional electrophoresis followed by Western blotting), and identified through a combination of peptide mass fingerprinting by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS), de novo peptide sequencing using nano-electrospray ionization-ion trap (ESI-IT) MS, and genomic database searches. This proteomic approach has led to the characterization of 42 different housekeeping enzymes as C. albicans antigens. Their biological significance is also discussed. Furthermore, this study is the first to report that 26 of them exhibit antigenic properties in C. albicans, and 35 of them become targets of the human antibody response to systemic candidiasis. Our findings suggest that the production of antibodies to C. albicans phosphoglycerate kinase and alcohol dehydrogenase during systemic candidiasis could be associated with a differentiation of the human immune response. We also highlight the relationship between changes in maintenance of circulating levels of specific anti-Candida antibodies and patients’ outcome. Some of these variations, especially the rise of high anti-enolase antibody concentrations, appear to be related to recovery from systemic candidiasis in these patients, which might serve as markers for predicting their outcome.
Proteomics-based identification of novel Candida albicans antigens for diagnosis of systemic candidiasis in patients with underlying hematological malignancies.
- Humans rely on their native microbiota for nutrition and resistance to colonization by pathogens; furthermore, recent discoveries have shown that symbiotic microbes make essential contributions to the development, metabolism, and immune response of the host. Co-evolved, beneficial, human–microbe interactions can be altered by many aspects of a modern lifestyle, including urbanization, global travel, and dietary changes, but in particular by antibiotics. The acute effects of antibiotic treatment on the native gut microbiota range from self-limiting “functional” diarrhea to life-threatening pseudomembranous colitis. The long-term consequences of such perturbations for the human–microbial symbiosis are more difficult to discern, but chronic conditions such as asthma and atopic disease have been associated with childhood antibiotic use and an altered intestinal microbiota. Because many chemical transformations in the gut are mediated by specific microbial populations, with implications for cancer and obesity, among other conditions, changes in the composition of the gut microbiota could have important but undiscovered health effects.
The Pervasive Effects of an Antibiotic on the Human Gut Microbiota, as Revealed by Deep 16S rRNA Sequencing
Les Dethlefsen , Sue Huse, Mitchell L. Sogin, David A. Relman
- A new study has uncovered the genetic wiring diagram underlying the infectiousness of Candida albicans, a fungus that causes thrush in babies, vaginal infections in women, and life-threatening infections in chemotherapy and AIDS patients. The study, led by Dr. Gerald R. Fink, Director of the Whitehead Institute for Biomedical Research, reveals that one key to Candida’s infectiousness lies in its ability to switch from a rounded form to filamentous forms. Fungal infections in hospitalized patients have almost doubled throughout the 1980s, often with life-threatening results in individuals with weakened immune systems. Candida, in particular, poses a serious threat and is associated with high mortality rates in patients undergoing chemotherapy. Candida is also a major cause of infection in hospitalized patients, especially those in Intensive Care Units, patients after major injuries or surgery, patients with burns, and premature babies.
In this study, Dr. Fink and his colleagues used molecular biology techniques to identify the components of the filamentation circuit in yeast. With the recently completed yeast genome to guide them, the scientists began to knock out suspicious genes and, by a process of elimination, discovered the culprits that are responsible for filamentation. Once scientists identified the key yeast filamentation genes, they simply plucked out the analogous genes in Candida. “Candida albicans is three hundred million years apart evolutionarily from yeast-as far away in evolution as humans are from turtles-and yet, the basic logic circuit was conserved,” says Dr. Fink.
Discovery Of Genetic Pathways May Provide New Ways To Combat Candida Infections
Gerald R. Fink, et al.
- The mechanisms by which corticosteroids (CCs) improve the outcome of AIDS patients with severe Pneumocystis carinii pneumonia (PCP) are unclear. We studied IL-1b and TNFα release from alveolar macrophages (AMs) of patients receiving CCs for the treatment of PCP and also the effect of in vitro hydrocortisone on this release. Cytokine release from AMs of AIDS patients with pulmonary complications not receiving CCs (group 1) was compared with that from AM of those receiving CCs for PCP (group 2). The AMs of HIV-negative normal subjects (group 3) served as controls. AU participants were nonsmokers or exsmokers. We found that lipopolysaccharide-stimulated AM from group 2 released significantly less interleukin-1 beta (IL-1b) and tumor necrosis factor alpha (TNFα) than AM from group 1 and was similar to that from group 3
Effect of corticosteroids on IL 1β and TNFα releae by alveolar macrophages from patients with AIDS and Pneumocystis carinii pneumonia
ZHENG BO HUANG ; EDEN E.
- A transporter in the colon called SLC5A8 plays an important role in enabling the colon to get the last bit of good out of food before the unusable is flushed away, according to research currently published online as an accelerated communication in the Journal of Biological Chemistry. The finding that SLC5A8 is the transporter helps clarify why fruits and vegetables are good for you and why antibiotics, which wipe out good bacteria along with bad, should only be taken when absolutely necessary, upset the model and colonic cells get sick and may even become cancerous. “We do not make the enzyme to digest cellulose; bacteria make the enzyme in the colon,” says Dr. Ganapathy. “Therefore, you need to eat dietary fiber to provide the food for bacteria. Otherwise, they are not going to su'”/>rvive there. Antibiotics can wipe out good bacteria as well, leaving a void where disease-causing bacteria can grow.” “The gut is a huge immune organ; there are more immune cells in our gut than there are in the rest of the body put together,” says Dr. Robert G. Martindale, MCG gastrointestinal surgeon and nutritionist with a special interest in probiotics giving patients good bacteria to restore a healthy flora. “The work that Dr. Ganapathy is doing is showing very nicely that if, in fact, we keep this short-chain fatty acid transporter healthy, we then can keep the whole immune system healthy.” Immune cells also have a specific receptor for short-chain fatty acids on the cell surface, and Drs. Ganapathy and Martindale are pursuing the idea that the SLC5A8 transporter is delivering these fatty acids to immune cells to interact with the receptors and keep the immune cells vigilant as well.
Transporter’s function provides support for eating vegetables, limiting antibiotics
Dr. Vadivel Ganapathy
- Although Candida albicans is present in many mammals including humans, normal bacterial flora and various immune factors usually restrict the growth of C. albicans in the alimentary tracts of immune competent hosts. Infection of the alimentary tract mucosae, including the mucosae of the oropharynx, esophagus, and gastrointestinal tract, with C. albicans is occurring with greater frequency, presumably because of the increased population of immune compromised individuals. Recent evidence suggests that cell-mediated immunity, and more specifically, CD41 T lymphocytes, play an important role in resistance to mucosal candidiasis. Patient populations with AIDS or other defects in cellular immune function show an increased incidence of mucocutaneous, but not necessarily disseminated, candidiasis, whereas patients with phagocytic cell defects, such as those that occur in patients with neutropenic or chronic granulomatous disease states, show a higher incidence of disseminated candidiasis. A combination of defective cell-mediated immunity and phagocytic cell defects in athymic beige (bg/bg nu/nu) mice was found to predispose them to severe mucosal candidiasis with subsequent Candida dissemination. Existing mouse models of mucosal candidiasis use combinations of chemically induced immune suppression, elimination or alteration of the host microflora by administration of antibiotics, high inocula, trauma, infant animals, or animals with congenital, functional, physiological, immunological, or metabolic defects to facilitate colonization of the gastrointestinal tract by C. albicans.
New Model Of Oropharyngeal and Gastrointestinal Colonization by Candida albicans in CD41 T-Cell-Deficient Mice for Evaluation of Antifungal Agents
AMY M. FLATTERY, GEORGE K. ABRUZZO, CHARLES J. GILL, JEFFREY G. SMITH, AND KEN BARTIZAL
- Underlying acquired immunity to the fungus Candida albicans is usually present in adult immunocompetent individuals and is presumed to prevent mucosal colonization progressing to symptomatic infection. Exploration of immunological events leading to Candida resistance or susceptibility has indicated the central role of the innate and adaptive immune systems, the relative contribution of which may vary depending on the site of the primary infection. Nevertheless, acquired resistance to infection results from the development of Th1 responses. Cytokines produced by Th1 cells activate phagocytic cells to a Candidacidal state. In contrast, cytokines produced by Th2 cells inhibit Th1 development and deactivate phagocytic effector cells. Because reciprocal influences have been recognized between innate and adaptive Th immunity, it appears that an integrated immune response determines the life-long commensalism of the fungus at the mucosal level, as well as the transition from mucosal saprophyte to pathogen. However, if the ability of C. albicans to establish a disseminated infection involves neutropenia as a major predisposing factor, its ability to persist in infected tissues or to behave as a commensal may involve primarily downregulation of host cell-mediated adaptive immunity. As a commensal, C. albicans may be endowed with the ability to elude the host’s immunological surveillance, thus allowing its persistence on mucosal surfaces. Th1 and Th2 CD41 T-cells develop from a common, naïve CD41 T-cell precursor, and several parameters have been shown to influence the pathway of differentiation of CD41 T-cell precursors. Among these, cytokines appear to play a major role, acting not only as modulators of antifungal effector functions but also as key regulators in the development of the different Th subsets from precursor Th cells. Studies in mice have shown that development of protective AntiCandidal Th1 responses requires the concerted actions of several cytokines, such as interferon (IFN)-g, transforming growth factor (TGF)-b, interleukin (IL)-6