Differential susceptibility of yeast and hyphal forms of Candida albicans to macrophage-derived nitrogen-containing compounds

Morphological and physiological changes induced by contact-dependent interaction between Candida albicans and Fusobacterium nucleatum

Candida albicans and Fusobacterium nucleatum are well-studied oral commensal microbes with pathogenic potential that are involved in various oral polymicrobial infectious diseases. Recently, we demonstrated that F. nucleatum ATCC 23726 coaggregates with C. albicans SN152, a process mainly mediated by fusobacterial membrane protein RadD and Candida cell wall protein Flo9. The aim of this study was to investigate the potential biological impact of this inter-kingdom interaction. We found that F. nucleatum ATCC 23726 inhibits growth and hyphal morphogenesis of C. albicans SN152 in a contact-dependent manner. Further analysis revealed that the inhibition of Candida hyphal morphogenesis is mediated via RadD and Flo9 protein pair. Using a murine macrophage cell line, we showed that the F. nucleatum-induced inhibition of Candida hyphal morphogenesis promotes C. albicans survival and negatively impacts the macrophage-killing capability of C. albicans. Furthermore, the yeast form of C. albicans repressed F. nucleatum-induced MCP-1 and TNFα production in macrophages. Our study suggests that the interaction between C. albicans and F. nucleatum leads to a mutual attenuation of virulence, which may function to promote a long-term commensal lifestyle within the oral cavity. This finding has significant implications for our understanding of inter-kingdom interaction and may impact clinical treatment strategies.

R432 is a key residue for the multiple functions of Ndt80p in Candida albicans

Ndt80p is an important transcription modulator to various stress-response genes in Candida albicans, the most common human fungal pathogen in systemic infections. We found that Ndt80p directly regulated its target genes, such as YHB1, via the mid-sporulation element (MSE). Furthermore, the ndt80(R432A) allele, with a reduced capability to bind MSE, failed to complement the defects caused by null mutations of NDT80. Thus, the R432 residue in the Ndt80p DNA-binding domain is involved in all tested functions, including cell separation, drug resistance, nitric oxide inactivation, germ tube formation, hyphal growth, and virulence. Hence, the importance of the R432 residue suggests a novel approach for designing new antifungal drugs by blocking the interaction between Ndt80p and its targets.

Candida albicans actively modulates intracellular membrane trafficking in mouse macrophage phagosomes

The intracellular trafficking/survival strategies of the opportunistic human pathogen Candida albicans are poorly understood. Here we investigated the infection of RAW264.7 macrophages with a virulent wild-type (WT) filamentous C. albicans strain and a hyphal signalling-defective mutant (efg1Delta/cph1Delta). A comparative analysis of the acquisition by phagosomes of actin, and of early/late endocytic organelles markers of the different fungal strains was performed and related to Candida's survival inside macrophages. Our results show that both fungal strains have evolved a similar mechanism to subvert the 'lysosomal' system, as seen by the inhibition of the phagosome fusion with compartments enriched in the lysobisphosphatidic acid and the vATPase, and thereby the acquisition of a low pH from the outset of infection. Besides, the virulent WT strain displayed additional specific survival strategies to prevent its targeting to compartmentsdisplaying late endosomal/lysosomal features, such as induction of active recycling out of phagosomes of the lysosomal membrane protein LAMP-1, the lysosomal protease cathepsin D and preinternalized colloidal gold. Finally, both virulent and efg1Delta/cph1Delta mutant fungal strains actively suppressed the production of macrophage nitric oxide (NO), although their cell wall extracts were potent inducers of NO.

Current research on the immune response to experimental sporotrichosis

Sporotrichosis is often manifested as a chronic granulomatous infection and the monocytes/macrophages play a central role in the host defense system. Surface components of Sporothrix schenckii have been characterized and suggestions have been made as to their possible role in pathogenicity. Ergosterol peroxide, cell-wall compounds (alkali-insoluble fraction-F1 and lipid extract-LEY), and exoantigen from the yeast form of the fungus have been characterized as virulence factors, activating both innate, by cytotoxins linked to the activation of reactive oxygen and nitrogen species (H2O2 and NO), and adaptive immune response to produce cytokines Th1 and Th2 profile. In this study, preliminary results have demonstrated that, in systemic sporotrichosis, TLR-4 triggers the innate immune response, activating an oxidative burst. These data represent the first report of the participation of TLR-4 in murine sporotrichosis, in the presence of lipids from the cell wall of S. schenckii. These results taken together may open new perspectives of study leading to an antifungal agent that could be used to benefit the entire population.

Long-term effect of early protein malnutrition on growth curve, hematological parameters and macrophage function of rats

To evaluate the long-term effect of mild-early maternal protein malnutrition on weight gain, hematological parameters and macrophage function in rats at adult age, we compared rats whose dams were fed diets containing either 9.5% (low protein-LPD) or 23% protein (normal-NPD) for the first 12 d of lactation. At 80 d of age, the functions of spreading, phagocytosis and killing Candida albicans were determined in resident peritoneal macrophages, whereas leukocytes and red blood cells were counted in peripheral blood. The number of resident peritoneal macrophages from LPD was the same as from NPD, but the ability of spreading and phagocytosing opsonised yeast was impaired. Besides, they were not able to block the germ tube formation or kill C. albicans to the same extent as in the control group. The low protein diet produced a significant reduction in the pups' growth and in hematological parameters although no difference was found in leukocyte counts. Taken together the data suggest that protein malnutrition during early lactation induces permanent alterations in macrophage function, body composition and hematological status, which are not restored completely even after a normal protein diet is supplied.

Inducible defense mechanism against nitric oxide in Candida albicans

The yeast Candida albicans is an opportunistic pathogen that threatens patients with compromised immune systems. Immune cell defenses against C. albicans are complex but typically involve the production of reactive oxygen species and nitrogen radicals such as nitric oxide (NO) that damage the yeast or inhibit its growth. Whether Candida defends itself against NO and the molecules responsible for this defense have yet to be determined. The defense against NO in various bacteria and the yeast Saccharomyces cerevisiae involves an NO-scavenging flavohemoglobin. The C. albicans genome contains three genes encoding flavohemoglobin-related proteins, CaYHB1, CaYHB4, and CaYHB5. To assess their roles in NO metabolism, we constructed strains lacking each of these genes and demonstrated that just one, CaYHB1, is responsible for NO consumption and detoxification. In C. albicans, NO metabolic activity and CaYHB1 mRNA levels are rapidly induced by NO and NO-generating agents. Loss of CaYHB1 increases the sensitivity of C. albicans to NO-mediated growth inhibition. In mice, infections with Candida strains lacking CaYHB1 still resulted in lethality, but virulence was decreased compared to that in wild-type strains. Thus, C. albicans possesses a rapid, specific, and highly inducible NO defense mechanism involving one of three putative flavohemoglobin genes.

Effect of Candida albicans septicemia on the cardiovascular function of rabbits

Candida albicans is an opportunistic pathogen that causes life-threatening systemic infection in immunocompromised host. However, little is known about the effects of yeast on the cardiovascular functions. This study examined the effects of C. albicans septicemia on the heart and vessel functions and nitric oxide (NO) production in infected rabbits. Anaesthetized animals were challenged with intravenous C. albicans (6 x 10(8)/kg) or saline and the blood pressure of rabbits were measured over 5 h. After that response of the isolated thoracic aorta, right atrium and left papillary muscle were recorded. Blood pressure significantly decreased in the infected rabbits during the septicemia but in the control animals it was stable. The blood nitrite levels and NO-synthases (eNOS, iNOS) expression and tissue nitrite levels in the heart and aorta were similar in the both groups. In the aorta isolated from C. albicans-infected rabbits, acetylcholine-induced endothelium-dependent relaxation was decreased, but contractions induced by phenylephrine were potentiated. The NOS inhibitor, L-N(G)-nitro-arginine methyl ester (L-NAME)-induced contraction increase in the right atrium was depressed by the yeast-infection. In the heart and aorta, microscopic examination revealed no tissue invasion of C. albicans. These results indicate the ability of C. albicans-induced septicemia to destroy NO-related responses of the heart and aorta and may have important implications for functional damage to endothelium and the regulation of cardiovascular functions. In addition, NOS induction and NO over-production are not stimulated by systemic C. albicans infection, which would alter the host immune reaction and homeostasis.

Lactoferrin feeding augments peritoneal macrophage activities in mice intraperitoneally injected with inactivated Candida albicans

Oral administration of lactoferrin (LF), an innate-defense protein present in exocrine secretions such as milk and in neutrophils, is reported to improve host-protection against infections with microorganisms including pathogenic fungi, possibly due to an immunomodulatory effect. This study aimed to evaluate the effect of bovine LF feeding on peritoneal macrophage activities in mice intraperitoneally injected with inactivated Candida albicans. Time course analysis during the 14 days following Candida-priming revealed that LF administration slightly increased the number of peritoneal exudate cells, and significantly enhanced the production of superoxide anion (O2(-)) and nitric oxide (NO) by peritoneal macrophages at day 7. LF administration facilitated NO production and Candida hyphal-growth inhibition by macrophages derived from Candida-primed mice but not non-primed mice, suggesting that the action of LF is dependent on the immune status of the host. LF administration altered the kinetics of cytokines in the peritoneal lavage fluid of Candida-primed mice. Enhancement of cytokine levels by LF was observed for IL-12 at day 5 and IFN-gamma at day 9, but not for TNF-alpha or IL-10. In conclusion, LF feeding augmented the activities of macrophages in a manner dependent on Candida-priming and these effects may be related to enhanced cytokine levels.

Immunocompetence of macrophages in rats exposed to Candida albicans infection and stress

The integration of innate and adaptive immune responses is required for efficient control of Candida albicans. The present work aimed to assess, at the local site of the infection, the immunocompetence of macrophages in rats infected intraperitoneally with C. albicans and exposed simultaneously to stress during 3 days (CaS group). We studied the 1) ability to remove and kill C. albicans, 2) tumor necrosis factor-alpha (TNF-alpha) release, 3) balance of the inducible enzymes NO synthase (iNOS) and arginase, and 4) expression of interleukin (IL)-1beta and IL-1 receptor antagonist (ra) mRNA. Compared with only infected animals (Ca group), the number of colony-forming units was significantly higher in CaS rats (P < 0.01), and the macrophage candidicidal activity was approximately 2.5-fold lower (P < 0.01). Release of TNF-alpha was diminished in both unstimulated and heat-killed C. albicans restimulated macrophages of the CaS group (Ca vs. CaS, P < 0.03 and P < 0.05, respectively). In Ca- and CaS-group rats, the rates for both the arginase activity and the NO synthesis were significantly enhanced. However, the stress exposure downregulated the activity of both enzymes (CaS vs. Ca, P < 0.05). After in vitro restimulation, the IL-1ra/IL-1beta ratio was significantly diminished in CaS-group rats (P < 0.05). Our results indicate that a correlation exists between early impairment of macrophage function and stress exposure.

Suppression of type 2 NO-synthase activity in macrophages by Candida albicans

Macrophages (Mphi) are important for the defence against experimental disseminated candidiasis. Nitric oxide (NO) generated by the inducible isoform of NO-synthase (iNOS or NOS2) is thought to contribute to candidacidal effector functions by activated Mphi. In vitro, however, Mphi cannot control the growth and hyphal formation of Candida (C.) albicans. Using mouse peritoneal exudate Mphi stimulated with IFN-gamma and LPS, we examined the effect of C. albicans on NO synthesis, NOS2 enzyme activity and macrophage survival. C. albicans effectively inhibited the production of NO via suppression of total NOS2 protein and enzyme activity. Hyphal formation of C. albicans and direct interaction with host cells was required for maximum inhibition of NO production, whereas non-filamentous C. albicans mutants released soluble products that effected only partial inhibition. Ultimately, Mphi underwent apoptotic cell death after infection with C. albicans wild-type strains capable of hyphal formation, indicated by loss of the mitochondrial membrane potential and onset of chromatin degradation. NO suppression and Mphi killing are potent activities of C. albicans that may augment virulence of C. albicans.

Virulence of Sporothrix schenckii conidia and yeast cells, and their susceptibility to nitric oxide

The involvement of nitric oxide (NO) in macrophage (M phi) fungicidal activity against Sporothrix schenckii, and the relationship between NO susceptibility and the differential virulence of conidia and yeast cells, were investigated. Confirming a previously reported correlation between the length of time in culture and virulence of S. schenckii, conidia isolated from 12-day mycelial cultures (Ss-12) were less virulent to mice than conidia from 7-day cultures (Ss-7) or yeast cells. Indicative of NO production, infected animals showed a significant increase in serum levels of nitrite that was lower in mice infected with Ss-12 than in mice infected with Ss-7 or yeast. Stimulation of murine M phi with interferon-gamma (IFN-gamma) induced NO production and inhibition of fungal growth. The cytotoxic activity of M phi against Ss-12 was significantly greater than against Ss-7 or yeast cells, the highly virulent fungal forms. The addition of NO synthase inhibitors abrogated M phi cytotoxic activity against all fungal forms. The phagocytic activity of M phi against Ss-7 was significantly lower than against Ss-12 or yeast cells. Although the ingestion of fungal cells triggered the oxidative burst in M phi, the fungicidal activity was not altered in the presence of superoxide dismutase (SOD) and catalase. In addition, Ss-12 and yeast cells were more susceptible than Ss-7 to the direct fungicidal activity of the NO donors S-nitroso-N-acetyl-DL-penicillamine (SNAP), S-nitrosoglutathione (GSNO) and 3-morpholinosydnonimine (SIN-1). The results of this study indicate that NO is a key cytotoxic mediator involved in the murine M phi defence against S. schenckii, and that the virulence of Ss-7, Ss-12 and yeast cells may be related to a differential susceptibility to NO.

Nitric oxide participation in the fungicidal mechanism of gamma interferon-activated murine macrophages against Paracoccidioides brasiliensis conidia

Paracoccidioidomycosis, a systemic mycosis restricted to Latin America and produced by the dimorphic fungus Paracoccidioides brasiliensis, is probably acquired by inhalation of conidia produced by the mycelial form. The macrophage (Mphi) represents the major cell defense against this pathogen; when activated with gamma interferon (IFN-gamma), murine Mphis kill the fungus by an oxygen-independent mechanism. Our goal was to determine the role of nitric oxide in the fungicidal effect of Mphis on P. brasiliensis conidia. The results revealed that IFN-gamma-activated murine Mphis inhibited the conidium-to-yeast transformation process in a dose-dependent manner; maximal inhibition was observed in Mphis activated with 50 U/ml and incubated for 96 h at 37 degrees C. When Mphis were activated with 150 to 200 U of cytokine per ml, the number of CFU was 70% lower than in nonactivated controls, indicating that there was a fungicidal effect. The inhibitory effect was reversed by the addition of anti-IFN-gamma monoclonal antibodies. Activation by IFN-gamma also enhanced Mphi nitric oxide production, as revealed by increasing NO(2) values (8 +/- 3 microM in nonactivated Mphis versus 43 +/- 13 microM in activated Mphis). The neutralization of IFN-gamma also reversed nitric oxide production at basal levels (8 +/- 5 microM). Additionally, we found that there was a significant inverse correlation (r = -0.8975) between NO(2)(-) concentration and transformation of P. brasiliensis conidia. Additionally, treatment with any of the three different nitric oxide inhibitors used (arginase, N(G)-monomethyl-L-arginine, and aminoguanidine), reverted the inhibition of the transformation process with 40 to 70% of intracellular yeast and significantly reduced nitric oxide production. These results show that IFN-gamma-activated murine Mphis kill P. brasiliensis conidia through the L-arginine-nitric oxide pathway.

A new azole derivative of 1,4-benzothiazine increases the antifungal mechanisms of natural effector cells

The most widely used drug for treatment of candidiasis is fluconazole (FCZ). Recently, a new derivative of 1,4-benzothiazine, compound FS5, was developed. FS5 had an appreciable protective effect against murine candidiasis. The present study was designed to dissect the antifungal mechanisms triggered by FS5 and to establish whether this compound could enhance the antimicrobial abilities of natural effector cells. The results show that intraperitoneal injection of FS5 in mice (i) induced an increase in circulating neutrophil levels comparable to that observed in FCZ-treated mice; (ii) enhanced phagocytosis and the killing activities of macrophages (Mphis) isolated from the spleen or peritoneal cavity, with the latter effect correlating with induction of nitric oxide synthesis and production by Mphis; and (iii) increased the levels of expression and synthesis of tumor necrosis factor alpha. These results suggest that the compound-induced synthesis of antimicrobial and proinflammatory molecules by heterogeneous Mphi populations is part of the beneficial effect of FS5 exerted against murine candidiasis.

The role of iron in protozoan and fungal infectious diseases

To survive and replicate in vertebrate hosts, protozoan and fungal invaders must be capable of securing host iron. Successful pathogens obtain the metal from either extraction of heme, binding of siderophilins, binding of siderophores, and/or iron pools within host cells. The actual strategy can vary with the availability of iron in the particular host milieu. As a corollary, hosts have developed an elaborate iron withholding defense system. Conditions that can compromise the system as well as procedures that can strengthen it are reviewed.

Tetanus toxin impairs accessory and secretory functions in interferon-gamma-treated murine macrophages

Tetanus neurotoxin (TT), a product of microbial origin, acts as a zinc endopeptidase on vesicle-associated membrane proteins (VAMP). We have demonstrated that TT displays inhibitory effects on secretory and accessory functions in the murine macrophage (Mphi) cell line GG2EE. Nitric oxide (NO) secretion was decreased when interferon (IFN)-gamma-pretreated GG2EE Mphis were coincubated with a fungal costimulus (SMP200) and TT. When heat-inactivated TT was used this effect was not evident. The TT-mediated phenomenon was dose-dependent and specific since, under the same experimental conditions, it did not affect interleukin-6 or tumor necrosis factor-alpha secretion. Furthermore, IFN-gamma-induced major histocompatibility complex class II molecule expression and GG2EE accessory function, assessed by SMP200-stimulated lymphoproliferation, were also inhibited by TT. Such inhibition was incomplete, in line with our previous results showing that TT partially cleaves VAMP proteins in murine M&phi;.

Different susceptibilities of yeasts and conidia of Penicillium marneffei to nitric oxide (NO)-mediated fungicidal activity of murine macrophages

Penicillium marneffei is an important opportunistic fungal pathogen. Host defence mechanisms against P. marneffei are not fully understood. We investigated the fungicidal activity of murine peritoneal macrophages against two forms of P. marneffei, conidia and yeast cells, and the involvement of the NO-mediated killing system. Peritoneal macrophages suppressed the intracellular growth of P. marneffei yeast cells and conidia. The number of live yeast cells within macrophages was significantly reduced by activation of macrophages by interferon-gamma (IFN-gamma), while a similar response was not observed with conidia. IFN-gamma-induced macrophage fungicidal activity against yeast cells was mediated by NO and was almost completely inhibited by N(G)-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of NO synthesis, while N(G)-monomethyl-D-arginine (D-NMMA), an optical isomer of L-NMMA, did not show any influence. NO production by macrophages stimulated with IFN-gamma was significantly enhanced when these macrophages were cultured with P. marneffei yeast cells, while conidia did not enhance macrophage NO production. Furthermore, yeast cells were more susceptible to the killing effect of chemically generated NO than conidia. Our results indicate that the yeast form of P. marneffei is more sensitive to the fungicidal activity of IFN-gamma-stimulated macrophages than conidia, and suggest that the different effects of two forms of P. marneffei on macrophage NO production and their different susceptibilities to NO may be reasons for the present findings.

Characteristics of invasive candidiasis in gamma interferon- and interleukin-4-deficient mice: role of macrophages in host defense against Candida albicans

Murine models of invasive candidiasis were used to study the in vivo importance of gamma interferon (IFN-gamma) and interleukin-4 (IL-4) in host defense against Candida albicans and to characterize the tissue inflammatory reactions, with special reference to macrophages (Mphi). Knockout (KO) IFN-gamma-deficient (GKO) and IL-4-deficient (IL-4 KO) and C57BL/6 parental mouse strains were challenged intraperitoneally with 10(8) C. albicans blastoconidia. Survival of GKO mice was significantly lower (16.7%) than that of C57BL/6 control (55.5%) and IL-4 KO (61.1%) animals, but was not correlated with the extent of organ colonization. Immunohistological analysis with a panel of myeloid and lymphoid markers revealed multiple renal abscesses, myocarditis, hepatitis, meningoencephalitis, and pneumonia in each strain, with a dominant presence of Mphi. In the absence of IFN-gamma, C. albicans induced striking changes in the phenotype of alveolar Mphi and extensive perivascular lymphoid infiltrates in the lung. Impairment in nitric oxide production by peritoneal Mphi was shown only in GKO mice, and they produced Candida-specific immunoglobulin G (IgG), IgM, IgA, and IgG subclasses in lower titers. Our in vivo studies with KO mice elucidate a critical role for IFN-gamma, but not IL-4, in host defense against C. albicans.

Macrophages in resistance to candidiasis

Candida albicans, an increasingly common opportunistic pathogenic fungus, frequently causes disease in immunodeficient but not immunocompetent hosts. Clarifying the role of the phagocytic cells that participate in resistance to candidiasis not only is basic to understanding how the host copes with this dimorphic pathogen but also will expedite the development of innovative prophylactic and therapeutic approaches for treating the multiple clinical presentations that candidiasis encompasses. In this review, we present evidence that a diverse population of mononuclear phagocytes, in different states of activation and differentiation and from a variety of host species, can phagocytize C. albicans blastoconidia via an array of opsonic and nonopsonic mechanisms and can kill C. albicans blastoconidia and hyphae by means of oxygen-dependent and -independent mechanisms. Reactive nitrogen intermediates should now be added to the well-established candidacidal reactive oxygen intermediates of macrophages. Furthermore, what were thought to be two independent pathways, i.e., nitric oxide and superoxide anion, have now been shown to combine to form a potent macrophage candidacidal molecule, peroxynitrite. In contrast to monocytes and neutrophils, which are important in resistance to early stages of C. albicans infections, more differentiated macrophages activated by cytokines such as gamma interferon participate in the acquired resistance of hosts with C. albicans-specific, cell-mediated immunity. Evidence presented in this review demonstrates that mononuclear phagocytes, in some instances in the absence of other professional phagocytes such as neutrophils, play an import role in resistance to systemic and mucosal candidiasis.

Development of an in vitro macrophage system to assess Penicillium marneffei growth and susceptibility to nitric oxide

We investigated the effect of nitric oxide (NO) and reactive nitrogen intermediates on the in vitro growth of Penicillium marneffei both in a cell-free system and in a novel macrophage culture system. In the cell-free system, NO that was chemically generated from NaNO2 in acid media (pH 4 and 5) markedly inhibited the growth of P. marneffei. On the contrary, inhibition of growth did not occur in neutral medium (pH 7.4) in which NO was not produced. P. marneffei conidia were phagocytized by nonstimulated murine J774 macrophages after 2 h of incubation. During the following 24 h, P. marneffei grew as yeast-like cells replicating by fission in the J774 macrophages. The intracellular growth of P. marneffei damaged nonstimulated J774 macrophages, as confirmed by electron microscopy. When J774 cells were stimulated by gamma interferon and lipopolysaccharide, which led to enhanced production of reactive nitrogen intermediates, the percentage of yeast-like cells was significantly reduced and P. marneffei conidia were damaged in the J774 macrophages. The inhibition of NO synthesis by N-monomethyl-L-arginine restored the intracellular growth of P. marneffei. The inverse correlation between intramacrophage growth and the amount of nitrite detected in culture supernatants supports the hypothesis that the L-arginine-dependent NO pathway plays an important role in the murine macrophage immune response against P. marneffei.

Indications for the occurrence of nitric oxide synthases in fungi and plants and the involvement in photoconidiation of Neurospora crassa

Indications for the occurrence of nitric oxide synthases in Dictyostelium, Neurospora, Phycomyces and the leguminous plant Mucuna hassjoo as well as a physiological role of nitric oxide in Neurospora crassa are demonstrated. An exogenous nitic oxide donor, sodium nitroprusside, inhibited light-stimulated conidiation in N. crassa. Specific inhibitors of nitric oxide synthase, like the arginine derivatives NG -nitro-L-arginine (L-NA) and NG-nitro-L-arginine-methyl ester (L-NAME), enhanced conidiation in darkness nad in the light, whereas the stereoisomer D-NAME was inactive. This communication reports to our knowledge the first time the presence of enzymatic activity of nitric oxide synthase in fungi and a higher plant and an effect of nitric oxide in fungal photo-physiology.

Developmental expression of a tandemly repeated, proline-and glutamine-rich amino acid motif on hyphal surfaces on Candida albicans

cDNA sequences encoding a cell wall protein have been isolated from the opportunistic pathogen, Candida albicans, an organism that can cause serious disease in immunocompromised patients such as those with AIDS. The cDNA encodes a peptide that is largely composed of an acidic, repeated motif 10 amino acids in length that is rich in proline and glutamine residues. The cDNA gene product was found to be present on hyphal surfaces by immunofluorescence assays using monospecific antisera raised to the recombinant protein produced in Pichia pastoris. The hyphae-specific surface location was also seen on organisms colonizing the gastrointestinal mucosa of mice, indicating that the antigen is produced and developmentally regulated during growth in host tissues. The cDNA clone hybridized to an abundant messenger RNA 2.3 kilobases in size that was present in hyphal but not yeast forms. These studies demonstrate that the bud-hypha transition is accompanied by the de novo synthesis of proteins that are targeted to hyphal surfaces. The primary sequence of the unique amino acid motif shares features with surface proteins of other lower eukaryotic microorganisms and with host acidic salivary proline-rich proteins.

Production and function of cytokines in natural and acquired immunity to Candida albicans infection

Host resistance against infections caused by the yeast Candida albicans is mediated predominantly by polymorphonuclear leukocytes and macrophages. Antigens of Candida stimulate lymphocyte proliferation and cytokine synthesis, and in both humans and mice, these cytokines enhance the candidacidal functions of the phagocytic cells. In systemic candidiasis in mice, cytokine production has been found to be a function of the CD4+ T helper (Th) cells. The Th1 subset of these cells, characterized by the production of gamma interferon and interleukin-2, is associated with macrophage activation and enhanced resistance against reinfection, whereas the Th2 subset, which produces interleukins-4, -6, and -10, is linked to the development of chronic disease. However, other models have generated divergent data. Mucosal infection generally elicits Th1-type cytokine responses and protection from systemic challenge, and identification of cytokine mRNA present in infected tissues of mice that develop mild or severe lesions does not show pure Th1- or Th2-type responses. Furthermore, antigens of C. albicans, mannan in particular, can induce suppressor cells that modulate both specific and nonspecific cellular and humoral immune responses, and there is an emerging body of evidence that molecular mimicry may affect the efficiency of anti-Candida responses within defined genetic contexts.