Gastrointestinal candidiasis in a murine model of severe combined immunodeficiency syndrome

Antibodies to Combat Fungal Infections: Development Strategies and Progress

The finding that some mAbs are antifungal suggests that antibody immunity may play a key role in the defense of the host against mycotic infections. The discovery of antibodies that guard against fungi is a significant advancement because it gives rise to the possibility of developing vaccinations that trigger protective antibody immunity. These vaccines might work by inducing antibody opsonins that improve the function of non-specific (such as neutrophils, macrophages, and NK cells) and specific (such as lymphocyte) cell-mediated immunity and stop or aid in eradicating fungus infections. The ability of antibodies to defend against fungi has been demonstrated by using monoclonal antibody technology to reconsider the function of antibody immunity. The next step is to develop vaccines that induce protective antibody immunity and to comprehend the mechanisms through which antibodies mediate protective effects against fungus.

Comparative Analysis of the Fitness of Candida albicans Strains During Colonization of the Mice Gastrointestinal Tract

Candida albicans populations present in the mammalian gastrointestinal tract are a major source of candidemia and subsequent severe invasive candidiasis in those individuals with acquired or congenital immune defects. Understanding the mechanisms used by this fungus to colonize this niche is, therefore, of primary importance to develop new therapeutic options that could lead to control its proliferation in the host. The recent popularization of models of commensalism in mice combined with the already powerful tools in C. albicans genetics allows to analyze the role of specific genes during colonization. Fitness can be analyzed for a specific C. albicans strain (test strain) by comparing its growth in vivo with an otherwise isogenic control strain via the analysis of the luminal content of the mouse gastrointestinal tract using flow cytometry, qPCR, or viable fungal cell counting. While all these procedures have limitations, they can be used to estimate the degree of adaptation of the test strain to the mammalian tract by determining its relative abundance with an internal control strain. By using specific genetically engineered C. albicans and mouse strains, antibiotic regimes, or even germ-free mice, this methodology allows to determine the role of the host immunological status, the bacterial microbiota, or individual fungal features (e.g., dimorphism) in the process of colonization of C. albicans of the mammalian gut.

Adaptation of Candida albicans to commensalism in the gut

Candida albicans is a common resident of the oral cavity, GI tract and vagina in healthy humans where it establishes a commensal relationship with the host. Colonization of the gut, which is an important niche for the microbe, may lead to systemic dissemination and disease upon alteration of host defences. Understanding the mechanisms responsible for the adaptation of C. albicans to the gut is therefore important for the design of new ways of combating fungal diseases. In this review we discuss the available models to study commensalism of this yeast, the main mechanisms controlling the establishment of the fungus, such as microbiota, mucus layer and antimicrobial peptides, and the gene regulatory circuits that ensure its survival in this niche.

The protective role of immunoglobulins in fungal infections and inflammation

Increased incidence of fungal infections in the immunocompromised individuals and fungi-mediated allergy and inflammatory conditions in immunocompetent individuals is a cause of concern. Consequently, there is a need for efficient therapeutic alternatives to treat fungal infections and inflammation. Several studies have demonstrated that antibodies or immunoglobulins have a role in restricting the fungal burden and their clearance. However, based on the data from monoclonal antibodies, it is now evident that the efficacy of antibodies in fungal infections is dependent on epitope specificity, abundance of protective antibodies, and their isotype. Antibodies confer protection against fungal infections by multiple mechanisms that include direct neutralization of fungi and their antigens, inhibition of growth of fungi, modification of gene expression, signaling and lipid metabolism, causing iron starvation, inhibition of polysaccharide release, and biofilm formation. Antibodies promote opsonization of fungi and their phagocytosis, complement activation, and antibody-dependent cell toxicity. Passive administration of specific protective monoclonal antibodies could also prove to be beneficial in drug resistance cases, to reduce the dosage and associated toxic symptoms of anti-fungal drugs. The longer half-life of the antibodies and flexibilities to modify their structure/forms are additional advantages. The clinical data obtained with two monoclonal antibodies should incite interests in translating pre-clinical success into the clinics. The anti-inflammatory and immunoregulatory role of antibodies in fungal inflammation could be exploited by intravenous immunoglobulin or IVIg.

IL-12 and related cytokines: function and regulatory implications in Candida albicans infection

IL-12 is a cytokine with links to both innate and adaptive immunity systems. In mice, its deletion leads to acute susceptibility to oral infection with the yeast Candida albicans, whereas such mice are resistant to systemic disease. However, it is an essential component of the adaptive response that leads to the generation of Th1-type cytokine responses and protection against disseminated disease. This paper presents an overview of the role of IL-12 in models of systemic and mucosal infection and the possible relationships between them.

Animal models: an important tool in mycology

Animal models of fungal infections are, and will remain, a key tool in the advancement of the medical mycology. Many different types of animal models of fungal infection have been developed, with murine models the most frequently used, for studies of pathogenesis, virulence, immunology, diagnosis, and therapy. The ability to control numerous variables in performing the model allows us to mimic human disease states and quantitatively monitor the course of the disease. However, no single model can answer all questions and different animal species or different routes of infection can show somewhat different results. Thus, the choice of which animal model to use must be made carefully, addressing issues of the type of human disease to mimic, the parameters to follow and collection of the appropriate data to answer those questions being asked. This review addresses a variety of uses for animal models in medical mycology. It focuses on the most clinically important diseases affecting humans and cites various examples of the different types of studies that have been performed. Overall, animal models of fungal infection will continue to be valuable tools in addressing questions concerning fungal infections and contribute to our deeper understanding of how these infections occur, progress and can be controlled and eliminated.

Innate versus adaptive immunity in Candida albicans infection

Candida albicans is a common opportunistic pathogen, causing both superficial and systemic infection. Clinical observations indicate that mucocutaneous infections are commonly associated with defective cell-mediated immune responses, whereas systemic infection is more frequently seen in patients with deficiencies in neutrophil number or function. Analysis of mechanisms of host resistance against gastrointestinal and oral infection in mouse models has demonstrated an absolute dependence on CD4(+) T cells, although clearance also involves phagocytic cells. Both IL-12 and TNF-alpha appear to be important mediators, but mouse strain-dependent variations in susceptibility to infection may be related to T-cell enhancement of production of phagocytic cells by the bone marrow. In murine systemic infection, the role of innate and adaptive responses is less well defined. Studies in immunodeficient and T-cell-depleted mice suggest that clearance of the yeast may be predominantly a function of the innate response, whereas the adaptive response may either limit tissue damage or have the potential to cause immunopathology, depending on the host genetic context in which the infection takes place.

Immunopathogenesis of oropharyngeal candidiasis in human immunodeficiency virus infection

Oropharyngeal and esophageal candidiases remain significant causes of morbidity in human immunodeficiency virus (HIV)-infected patients, despite the dramatic ability of antiretroviral therapy to reconstitute immunity. Notable advances have been achieved in understanding, at the molecular level, the relationships between the progression of HIV infection, the acquisition, maintenance, and clonality of oral candidal populations, and the emergence of antifungal resistance. However, the critical immunological defects which are responsible for the onset and maintenance of mucosal candidiasis in patients with HIV infection have not been elucidated. The devastating impact of HIV infection on mucosal Langerhans' cell and CD4(+) cell populations is most probably central to the pathogenesis of mucosal candidiasis in HIV-infected patients. However, these defects may be partly compensated by preserved host defense mechanisms (calprotectin, keratinocytes, CD8(+) T cells, and phagocytes) which, individually or together, may limit Candida albicans proliferation to the superficial mucosa. The availability of CD4C/HIV transgenic mice expressing HIV-1 in immune cells has provided the opportunity to devise a novel model of mucosal candidiasis that closely mimics the clinical and pathological features of candidal infection in human HIV infection. These transgenic mice allow, for the first time, a precise cause-and-effect analysis of the immunopathogenesis of mucosal candidiasis in HIV infection under controlled conditions in a small laboratory animal.

Efficacy of ravuconazole in treatment of mucosal candidosis in SCID mice

A model of orogastric candidosis in SCID mice, which mimics disease seen in AIDS patients, was used to evaluate ravuconazole in comparison with fluconazole for treatment. Mice were infected orally with Candida albicans and received either no treatment or oral treatment once daily for 12 days with 1, 5, or 25 mg of ravuconazole per kg of body weight per day, 5 or 25 mg of fluconazole per kg per day, or diluent (10% dimethyl sulfoxide in 0.5% carboxymethyl cellulose). The numbers of C. albicans CFU in the esophagus, stomach, small intestine, and cecum on day 25 in mice given no treatment and diluent were equivalent. Both doses of fluconazole significantly reduced numbers of CFU in all four tissues but were equivalent to each other. Ravuconazole showed dose-responsive improvement of clearance of CFU. Ravuconazole at 25 mg/kg was superior in reduction of numbers of CFU in all tissues to controls or 25 mg of fluconazole per kg and to other regimens in at least three tissues. Fluconazole at 25 mg/kg cured no infection in any tissue, whereas 25 mg of ravuconazole/kg cleared infection in all tissues from 50% of mice. Ravuconazole has good efficacy and the potential to cure mucosal candidosis in the absence of a functional immune response.

Sustained gastrointestinal colonization and systemic dissemination by Candida albicans, Candida tropicalis and Candida parapsilosis in adult mice

The ability of nine clinical isolates of Candida species (three C. albicans, three C. tropicalis and three C. parapsilosis) to colonize and invade the gastrointestinal (GI) tract of adult male CD-1 (ICR) mice was determined. The effect of dietary tetracycline plus glucose supplementation on colonization was evaluated. Strains were intragastrically inoculated. Tetracycline and glucose altered substantially aerobic flora, especially streptococci (average fall 1.1 +/-0.3 log(10) CFU/g, p<0.01 by the Student's t test). At two weeks after oral challenge, sustained and high colonization of GI tract by Candida (mean 5,28 +/- 0.18 log(10) CFU/g, p<0.01) was achieved in all mice receiving glucose-tetracycline supplementation, excepting in animals inoculated with one of C. tropicalis isolates. Histologic sections of the stomachs revealed multiple intraepithelial micro-abscesses associated with hyphae in the region of the cardial-atrium fold. Under immunosuppression, systemic spread of C. albicans and C. tropicalis was observed in 62% and 24% of animals receiving dietary supplementation respectively. Dissemination was not noted for C. parapsilosis isolates. We have developed a simple and inexpensive murine model of sustained colonization of GI tract. This model could be useful for analyzing prophylaxis, treatment and diagnosis of systemic Candida infections and for evaluating virulence of strains.

Treatment of orogastrointestinal candidosis in SCID mice with fluconazole alone or in combination with recombinant granulocyte colony-stimulating factor or interferon-gamma

Mucosal candidosis is common in acquired immune deficiency syndrome (AIDS) patients, where there is extensive mucosal involvement, but rarely dissemination. To mimic this disease, SCID mice were inoculated orally with Candida albicans, which could be recovered from standardized tissue samples of the esophagus, stomach, small intestine and caecum of all mice. Treatment with fluconazole at 5 or 10 mg kg(-1) per day were equivalent to each other and efficacious in reducing the fungal burden from all four tissues compared with no treatment or lower doses of fluconazole (P < 0.01-0.001). Fluconazole at 5 or 10 mg kg(-1) reduced fungal burden in the stomach by about 200 or 580-fold, respectively, and by approximately 25-fold in the other tissues, with 80 or 100% of mice cleared of esophageal infection, and 40 or 80% cleared of infection in the small intestine, respectively; the same doses cleared < or =20% of stomach infection and none of caecal infection. Treatment with recombinant human granulocyte colony-stimulating factor (G-CSF) up to 500 microg kg(-1) per day or 10(5) U of murine interferon-gamma (IFN-gamma) alone was ineffective, nor were combinations with a suboptimal dose fluconazole synergistic. Overall, fluconazole had dose-responsive efficacy, whereas neither G-CSF nor IFN-gamma alone or in combination with fluconazole improved efficacy. These studies demonstrate the utility of this model for examining antifungal efficacy in a situation that mimics clinical disease in AIDS patients.

Disparate requirement for T cells in resistance to mucosal and acute systemic candidiasis

Although highly susceptible to orogastric candidiasis, T-cell receptor delta- and alpha-chain knockout mice, deficient in gammadelta and alphabeta T cells, respectively, were found to be resistant to disseminated candidiasis of endogenous origin and to acute systemic candidiasis (resulting from intravenous injection).

Increased severity of Candida vaginitis in BALB/c nu/nu mice versus the parent strain is not abrogated by adoptive transfer of T cell enriched lymphocytes

The role of the host immune system in combating candidal infections in the vagina is poorly understood. A murine model of Candida vaginitis was used to elucidate the role of T cells in a candidal infection. Athymic BALB/c nu/nu mice or normal BALB/c mice were induced into estrus and then infected with 1 x 10(6) Candida albicans intravaginally. The infection was monitored over 1 week. Samples from blood, small intestine, tongue, kidney, spleen, liver, uterus and vagina were tested for recoverable C. albicans. Histology of the vagina was assessed for both inflammation and extent of infection. Results indicated that the BALB/c nu/nu mice had similar levels of vaginal yeast load to the normal BALB/c mice. In 25-30% of nude mice Candida was also recovered from extra vaginal sites (kidney, liver, small intestine), however, extra vaginal dissemination was not observed in any normal BALB/c animals. Histologically, both the nu/nu and control BALB/c had similar levels of vaginal inflammation; however, the nu/nu mice had more florid fungal growth in the vaginal epithelium. Adoptive transfer of either immune or non-immune BALB/c T cells into nude mice had no affect on either infection or vaginal inflammation. Immunohistochemical staining of vaginal tissues from normal BALB/c mice or nude mice adoptively transferred with either immune or non-immune T cells with anti-CD3 monoclonal antibody revealed no significant difference between groups in the numbers of CD3+ vaginal T cells. However, in mice receiving either immune or non-immune T cells no yeast was recovered from any tissues except the vagina. These data show that T cells have a limited role in protecting the vagina from C. albicans infection.

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.

Timing of treatment for nonneutropenic patients colonized with Candida

There has been a continuing evolution of the clinical spectrum of Candida infection in nonneutropenic patients. With better understanding of the predisposing factors for fungemia in critically ill patients, interest now centers on indications for early therapy, prior to the progression of colonization to fungemia. Recent prospective trials have identified persistence of Candida species in repetitive cultures of various sites as an essential if not necessary precursor for fungemia. Treatment for patients requiring prolonged intensive-care-unit residence and demonstrating colonization with Candida is suggested, based on the frequency with which such patients progress to fungemia. The efficacy of such treatment is undocumented, and clinical trials of various regimens of polyene or azole antifungals is needed.

Importance of beta2-microglobulin in murine resistance to mucosal and systemic candidiasis

beta2-Microglobulin knockout (beta2m-/-) mice, which lack major histocompatibility complex class I expression and are deficient in CD8alpha/beta T-cell receptor alpha/beta (TcRalpha/beta) T cells, were as resistant to systemic (intravenous) challenge with Candida albicans as immunocompetent controls. Conversely, the beta2m-/- mutant mice were susceptible to systemic candidiasis of endogenous origin despite the induction of C. albicans-specific antibody and cell-mediated immune responses after colonization with a pure culture of C. albicans. Despite some superficial and transient infections of tongues and esophagi (detected by histology) at 1 to 2 weeks after oral colonization and gastric infections (cardia-antrum section) which were observed at 10 to 12 weeks after oral challenge, C. albicans-colonized beta2m-/- mice showed an overall resistance to candidiasis in other mucosal and cutaneous tissues. These data suggest that immune defects that accompany the loss of beta2-microglobulin play an important role in murine resistance to gastric and disseminated candidiasis of endogenous (intestinal tract) origin and that innate immunity and CD4 TcRalpha/beta as well as CD8alpha/alpha TcRalpha/beta (or -gamma/delta) T cells play an important role in resistance to systemic, cutaneous, and nongastric mucosal tissues.

Experimental systemic cryptococcosis in SCID mice

The susceptibility of severe combined immune deficiency (SCID) mice to experimental systemic cryptococcosis was studied. SCID mice were at least 16-fold more susceptible to lethal infection than were immunocompetent control mice (P < 0.001). Histological assessment showed that control mice responded with a granulomatous inflammatory response, whereas SCID mice showed no evidence of a cellular host response. In a therapeutic study, 5 mg kg-1 day-1 of fluconazole caused a significant reduction in the infectious burden in the spleen, liver, kidney and lungs of treated mice compared with no treatment. These results indicate that a model of systemic cryptococcosis with meningitis in SCID mice may have utility in the study of immunology and therapy of this disease in the severely immunocompromised host.

New model of oropharyngeal and gastrointestinal colonization by Candida albicans in CD4+ T-cell-deficient mice for evaluation of antifungal agents

A new model for the evaluation of antifungal compounds against oropharyngeal and gastrointestinal mucosal colonization by Candida albicans was developed. To simulate the immune deficiency observed in AIDS patients, mice were depleted of CD4+ T lymphocytes by the injection of either GK1.5 hybridoma cells or purified anti-CD4+ T lymphocytes by the injection of either GK1.5 hybridoma cells or purified anti-CD4+ monoclonal antibody derived from GK1.5 hybridoma cells in tissue culture. Fluorescence-activated cell sorter analysis of splenic lymphocytes confirmed the elimination of the CD4+ T-cell population. Gentamicin, a broad-spectrum, nonabsorbable aminoglycoside antibiotic, was given via the drinking water to reduce the normal gastrointestinal microflora, allowing less competition for colonization of the gastrointestinal tract by the C. albicans isolates. Mice were challenged by gavage and swabbing their oral mucosae with a pure culture of C. albicans. Gentamicin was withdrawn 3 days postchallenge, and antifungal compounds were administered via the drinking water ad libitum at concentrations ranging from 25 to 400 micrograms/ml. L-693989, a water-soluble phosphorylated cyclic lipopeptide prodrug of pneumocandin Bo, and L-733560, a semisynthetic derivative of pneumocandin Bo, are inhibitors of 1,3-beta-D-glucan synthesis that exhibit potent in vivo anti-Candida spp. and anti-Pneumocystis carinii activities. The efficacies of L-693989, L-733560, fluconazole, ketoconazole, and nystatin were evaluated in this new oropharyngeal and gastrointestinal model of mucosal colonization. L-693989, L-733560, fluconazole, and ketoconazole showed superior efficacies in reducing the numbers of C. albicans CFU per gram of feces and the numbers of oral CFU relative to those in sham-treated controls in this model, while nystatin was moderately effective in reducing oral and fecal colonization by C. albicans in this model.

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.

Gamma delta T cell-induced nitric oxide production enhances resistance to mucosal candidiasis

Despite the prevalence of gamma delta T cells in mucosae that are typically colonized by Candida albicans, little is known of the possible role of these cells in resistance to candidiasis. A sharp increase in the number of gamma delta T cells and macrophages following intraperitoneal inoculation of mice with C. albicans led us to examine the role of these cells in the immune response to C. albicans. We show that the gamma delta T cells enhance macrophage nitric oxide (NO) production and anti-candida activity, in vitro. We also propose that the gamma delta T cells regulate macrophage function during candidiasis in vivo as well, because depletion of these cells abrogated inducible NO synthase expression in mucosae and enhanced murine susceptibility to candidiasis.

Pulmonary alveolar proteinosis. A spontaneous and inducible disease in immunodeficient germ-free mice

Spontaneous pulmonary alveolar proteinosis (PAP), which resembles human PAP, was found in aging (35 to 40 weeks) germ-free SCID-beige (scid/scid-bg/bg) mice. Spontaneous PAP was not observed in germ-free SCID mice. We describe the induction of PAP in SCID mice monoassociated with a pure culture of Candida albicans for 15 to 40 weeks. The gastrointestinal tracts only are colonized, and disseminated or pulmonary candidiasis does not occur. Another spontaneous form of PAP, designated type II, was discovered in germ-free beige (bg/bg and bg/+) mice and in beige-nude (bg/bg-nu/nu) mice. In this form of PAP, macrophages appear to be unable to digest the ingested phospholipoprotein complex and then accumulate in the alveolar spaces. These murine models should prove useful in elucidating the relationships between immune deficiencies, infections, and cytokine regulation of granulocyte and macrophage production and function in pulmonary alveolar proteinosis.

Mice immunized by primary vaginal Candida albicans infection develop acquired vaginal mucosal immunity

It has been postulated that systemic cell-mediated immunity (CMI) is an important host defense mechanism against Candida infections of the vagina. However, in an estrogen-dependent murine model of experimental vaginal candidiasis, we recently showed that systemic Candida-specific Th1-type CMI induced by immunization with Candida culture filtrate antigen had no effect on vaginal Candida population levels during the course of a vaginal infection. In the present study, mice given a second vaginal inoculation in the presence of peripheral Candida-specific Th1-type CMI induced by prior vaginal infection had anamnestic-type increased delayed-type hypersensitivity (DTH) responses, concomitant with significantly fewer Candida organisms in the vagina than in primary-infected mice. In addition, organisms in secondary-infected mice were fragmented and superficial penetration into the epithelium was reduced. The systemic presence of Candida-specific T suppressor (Ts) cells that significantly suppressed the infection-derived anamnestic DTH reactivity did not abrogate the protective effect in the vagina. Additional experiments showed that vaginally immunized mice were not protected from gastrointestinal or systemic candidiasis and, in contrast to mice with a second vaginal infection, did not demonstrate anamnestic DTH reactivity. These results suggest that a moderate level of local protection against a Candida vaginal infection can be achieved by vaginal immunization but that the protective role of acquired peripheral Candida-specific Th1-type reactivity at the vaginal mucosa appears to be limited.

The role of cell-mediated immunity in candidiasis

Clinical observations and animal models show that cell-mediated immunity (CMI) is an important host defense mechanism against Candida albicans infections. In HIV-infected patients, a switch from TH1- to TH2-type CMI responses correlates with the progression to AIDS, and may also increase susceptibility to mucosal candidiasis.

Effect of abrogation of natural killer cell activity on the course of candidiasis induced by intraperitoneal administration and gastrointestinal candidiasis in mice with severe combined immunodeficiency

Candida albicans CFU per gram of tissue recovered from livers, spleens, and kidneys of 12 severe combined immunodeficiency (scid) and 12 BALB/c mice 5 days after intraperitoneal (i.p.) administration of 10(7) C. albicans cells were not significantly different. Nine scid mice given normal rabbit serum (NRS) as a control and eight scid mice given anti-asialo-GM1 (alpha-ASGM1) had C. albicans CFU per gram recovered from livers and spleens 1 week after i.p. administration of C. albicans that were not significantly different, despite virtual elimination of natural killer (NK) cell activity in mice treated with alpha-ASGM1. At 2 weeks after i.p. administration, despite significantly increased NK cell activity in eight infected NRS-treated scid mice and virtual elimination of NK cell activity by alpha-ASGM1 treatment of eight scid mice, C. albicans CFU per gram recovered from livers and kidneys were not significantly different. At 2 weeks after intragastric administration of 2 x 10(6) C. albicans cells, eight NRS- and eight alpha-ASGM1-treated scid mice had identical proportions colonized with C. albicans and similar C. albicans CFU per gram recovered from feces. There was no evidence of hematogenous dissemination in either group. Similar results were seen 1 week after intragastric administration of 10(7) C. albicans cells. We conclude that NK cell activity is increased by i.p. administration of C. albicans in scid mice, but nontheless, abrogation of NK cell activity is not associated with enhanced susceptibility to candidiasis induced by i.p. administration and also is not associated with enhanced susceptibility to gastrointestinal colonization or hematogenous dissemination after intragastric administration of C. albicans.

Candida-specific cell-mediated immunity is demonstrable in mice with experimental vaginal candidiasis

Women with recurrent vulvovaginal candidiasis often demonstrate a down-regulation of cell-mediated immunity (CMI) to Candida albicans detected by a lack of cutaneous delayed-type hypersensitivity (DTH) to Candida antigens. However, the role of systemic CMI as a host defense mechanism against recurrent vulvovaginal candidiasis is not well understood, in part because of the lack of a well-defined murine model of vaginal candidiasis. The present study was undertaken to determine: (i) whether soluble Candida culture filtrate antigens (CaCF) could be used to induce and detect Candida-specific CMI in mice and (ii) whether these antigens would be useful in detecting systemic CMI in mice given an experimental Candida vaginal infection. To this end, mice were immunized subcutaneously with CaCF in complete Freund's adjuvant, and within 7 days they developed Candida-specific DTH reactivity detected by footpad swelling (increase in footpad thickness, 0.36 mm) 24 h after footpad challenge with CaCF. Adoptive transfer studies showed that the DTH responsiveness was elicited by CD4+ DTH T cells. In mice given a vaginal inoculum of C. albicans blastoconidia (5 x 10(5)), footpad challenge with CaCF resulted in positive DTH responses (0.24 mm) as early as 1 week, responses similar to immunization in 2 to 3 weeks (0.33 mm), and sustained low levels of DTH reactivity (0.15 mm) through 10 weeks of vaginal infection. Vaginal lavage cultures revealed that peak vaginal Candida burden occurred 1 week post-vaginal inoculation (10(5) CFU) and declined 16-fold by week 10. These results provide evidence that Candida-specific systemic CMI is generated and can be detected longitudinally in mice with Candida vaginitis by a multiantigen preparation of Candida organisms which both initiates and detects Candida-specific CMI.

Mucosal and disseminated candidiasis in gnotobiotic SCID mice

The alimentary tracts of germ-free SCID (severe combined immunodeficient) mice were susceptible to colonization with Candida albicans. Large viable populations (10(6)-10(8) colony forming units g-1) of C. albicans, in pure culture, were present in all sections of the intestinal tract. Candida-colonized SCID mice, sacrificed at various time intervals over a 16 week study, manifested chronic superficial mucosal candidiasis of keratinized epithelial surfaces (tongue and stomach). Despite the continuous presence of large viable populations of C. albicans in their intestinal tract, only superficial mucosal candidiasis and no progressive disseminated candidiasis of endogenous origin was evident in these mice. Treatment with cyclophosphamide (100 mg kg-1, intraperitoneally) enhanced the susceptibility of SCID mice to mucosal (tongue and stomach) candidiasis. Gnotobiotic (C. albicans-colonized) SCID mice were also found to be as resistant as immunocompetent BALB/c mice to acute (intravenous challenge) renal candidiasis. Colonization of the alimentary tract with a bacterial flora appeared to enhance the resistance of SCID mice to disseminated candidiasis. This study demonstrates that innate immune mechanisms (phagocytic and/or NK cells), in the absence of functional T- and B-cells, play an important role in the resistance of SCID mice to mucosal and disseminated candidiasis of endogenous (intestinal tract) or acute (intravenous challenge) origin.

Poly(I.C)-induced interferons enhance susceptibility of SCID mice to systemic candidiasis

In the absence of any demonstrable T- or B-cell responses, gnotobiotic CB-17 SCID (severe combined immunodeficient) mice not only show innate resistance to acute systemic (intravenous challenge) candidiasis but also manifest innate resistance to systemic candidiasis of endogenous (gastrointestinal tract) origin. Poly(I. C), a potent inducer of interferons (IFNs) in vivo, enhanced the susceptibility of CB-17 SCID mice to acute systemic candidiasis and to systemic candidiasis of endogenous origin, as demonstrated by increased numbers of viable Candida albicans in internal organs after poly(I. C) treatment. The poly(I. C)-enhanced susceptibility of mice to candidiasis was abrogated by in vivo treatment with antibodies to IFN-alpha, -beta, and -gamma. In vivo depletion of natural killer cells from SCID mice did not significantly enhance their susceptibility to systemic candidiasis or abrogate poly(I. C)-enhanced susceptibility. In vivo and in vitro, treatment with poly(I. C) impaired the candidacidal and phagocytic activity of thioglycollate-elicited macrophages from SCID mice. Antibody to IFN-alpha/beta or IFN-beta alone interfered with the ability of poly(I. C) to impair the candidacidal activity of macrophages from SCID mice in vitro. These data suggest that poly(I. C)-induced interferons can impair the candidacidal activity of macrophages in SCID mice and decrease their innate resistance to acute systemic candidiasis and to systemic candidiasis of endogenous origin.

Gastrointestinal colonization and systemic dissemination by Candida albicans and Candida tropicalis in intact and immunocompromised mice

Gastrointestinal colonization and systemic dissemination by Candida albicans and Candida tropicalis were compared in intact and immunocompromised mice. Five-day-old CFW mice were inoculated by the oral-intragastric route with 1.0 x 10(7) CFU of two C. albicans and two C. tropicalis strains isolated from the blood of patients with acute leukemia and with C. albicans 4918 and its cerulenin-resistant mutant 4918-10. C. albicans and C. tropicalis spread to the lungs, liver, and kidneys within 30 min postinoculation, and organ CFU of the two species were comparable over the following 10 days. Close association of blastoconidia with the villous surface of the small intestine resulted in lysis of microvilli and then progressive invasion of villi. Blastoconidia within villi were surrounded by a conspicuous zone of clearing. Persistent colonization of the small and large intestines by C. albicans blood isolates and strains 4918 and 4918-10 was similar for 31 days after inoculation, but consistently exceeded that of C. tropicalis. In mice colonized with C. albicans, immunosuppression with cortisone acetate and cyclophosphamide on days 30 and 33 after inoculation increased stomach CFU 40- to 370-fold and intestinal CFU 30- to 80-fold. In contrast, persistent colonization by C. tropicalis was undetectable before immunosuppression and only became apparent after treatment. C. albicans disseminated more frequently and with higher organ CFU than C. tropicalis. Despite this fact, 20% of mice infected with C. tropicalis died, compared with 4% infected with C. albicans blood isolates. Indirect immunofluorescence revealed penetrative growth by Candida hyphae exclusively in the mucosa and submucosa of the stomach from immunosuppressed, persistently colonized mice. Taken together, the data indicate that C. tropicalis appears to be more virulent than C. albicans and that factors responsible for gastrointestinal colonization, systemic dissemination, and mortality in immunocompromised mice may not be identical.

Retrovirus-induced immunodeficiency in mice exacerbates gastrointestinal candidiasis

Dysfunction of neutrophils in patients infected with human immunodeficiency virus is at least partly responsible for secondary microbial diseases in these individuals, including invasive gastrointestinal (GI) candidiasis. Immunoregulatory disturbances associated with the development of AIDS in human immunodeficiency virus-infected patients exacerbates Candida albicans infection of the upper GI tract and frequently leads to oropharyngeal and esophageal candidiasis. In this article, we present the first report of a murine model of invasive GI candidiasis associated with an AIDS-related murine immunodeficiency syndrome that results from infection of C57BL/6 mice with a previously described retrovirus complex (LP-BM5). Mice of the inbred strain were infected with C. albicans by oral-intragastric inoculation as infants and with the retrovirus by the intraperitoneal route 30 days later. Control mice of the same strain were infected with C. albicans as above and subsequently infected with the avirulent, ecotropic helper virus (MBI-5). Animals were killed 90 days after retroviral challenge. Total and differential blood cell counts, CD4+ T-cell counts in the spleen, and the histopathology of the gastric mucosa of experimental and control animals were determined. The virulent LP-BM5-infected animals developed murine AIDS and showed eruptive and suppurative lesions, with associated C. albicans mainly in regions of the cardial-atrium fold of the stomach. Well-defined abscesses with entrapped C. albicans hyphae were observed in the region of the cardial-atrium fold of control mice. A significant increase in the number of C. albicans CFU in homogenized and plated segments of the GI tract was recognized in mice with murine AIDS versus the control animals. The murine model of GI candidiasis reported here permits examination of the nature of C. albicans interaction with the gastric mucosa both in the immunocompetent host under conditions in which the yeast exists predominantly as a commensal organism and in the immunosuppressed host during progressive stages of AIDS induced by a retroviral infection.