Role of CD4+ lymphocytes in resistance to mucosal candidiasis

Fungal morphogenetic pathways are required for the hallmark inflammatory response during Candida albicans vaginitis

Vulvovaginal candidiasis, caused primarily by Candida albicans, presents significant health issues for women of childbearing age. As a polymorphic fungus, the ability of C. albicans to switch between yeast and hyphal morphologies is considered its central virulence attribute. Armed with new criteria for defining vaginitis immunopathology, the purpose of this study was to determine whether the yeast-to-hypha transition is required for the hallmark inflammatory responses previously characterized during murine vaginitis. Kinetic analyses of vaginal infection with C. albicans in C57BL/6 mice demonstrated that fungal burdens remained constant throughout the observation period, while polymorphonuclear leukocyte (PMN), S100A8, and interleukin-1β levels obtained from vaginal lavage fluid increased by day 3 onward. Lactate dehydrogenase activity was also positively correlated with increased effectors of innate immunity. Additionally, immunodepletion of neutrophils in infected mice confirmed a nonprotective role for PMNs during vaginitis. Determination of the importance of fungal morphogenesis during vaginitis was addressed with a two-pronged approach. Intravaginal inoculation of mice with C. albicans strains deleted for key transcriptional regulators (bcr1Δ/Δ, efg1Δ/Δ, cph1Δ/Δ, and efg1Δ/Δ cph1Δ/Δ) controlling the yeast-to-hypha switch revealed a crucial role for morphogenetic signaling through the Efg1 and, to a lesser extent, the Bcr1 pathways in contributing to vaginitis immunopathology. Furthermore, overexpression of transcription factors NRG1 and UME6, to maintain yeast and hyphal morphologies, respectively, confirmed the importance of morphogenesis in generating innate immune responses in vivo. These results highlight the yeast-to-hypha switch and the associated morphogenetic response as important virulence components for the immunopathogenesis of Candida vaginitis, with implications for transition from benign colonization to symptomatic infection.

Cytokines and the regulation of fungus-specific CD4 T cell differentiation

CD4 T cells play important and non-redundant roles in protection against infection with diverse fungi. Distinct CD4 T cell subsets can mediate protection against fungal disease where Th1 and Th17 CD4 T cell subsets have been found to promote fungal clearance and protective immunity against diverse fungal pathogens. The differentiation of naïve CD4 T cells into Th1 or Th17 cells is crucially controlled by their interaction with dendritic cells and instructed by cytokines. IL-12 and IFN-γ promote Th1 differentiation while TGF-β, IL-6, IL-1, IL-21 and IL-23 promote Th17 differentiation and maintenance. The production of these cytokines by DCs is in turn regulated by innate receptors triggered in response to fungal infection. In this review we will discuss the contributions of cytokines found to influence fungus-specific CD4 T cell differentiation and their role in defense against fungal disease. We will also highlight the contributions of innate receptors involved in recognition of fungi and how they shape cytokine secretion and CD4 T cell differentiation.

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.

Macrophage-mediated responses to Candida albicans in mice expressing the human immunodeficiency virus type 1 transgene

The critical impairments of innate and adaptive immunity that cause susceptibility to mucosal candidiasis in human immunodeficiency virus (HIV) infection have not been fully determined. We therefore conducted an analysis of macrophage-mediated responses to Candida albicans in transgenic (Tg) mice expressing Nef, Env, and Rev of HIV type 1 (HIV-1) in CD4(+) T cells, dendritic cells, and macrophages and developing an AIDS-like disease (CD4C/HIV(MutA) Tg mice). Macrophages were successfully recruited to the oral and gastric mucosae of these Tg mice in response to chronic carriage of C. albicans and displayed polarization toward an alternatively activated phenotype. Functionally, peritoneal macrophages from uninfected Tg mice exhibited increased phagocytosis of C. albicans and enhanced production of interleukin 6 and monocyte chemoattractant protein 1, demonstrating that the HIV-1 transgene independently activates selected macrophage functions. Production of H(2)O(2) by macrophages from Tg mice primed with gamma interferon and treated with phorbol 12-myristate 13-acetate or C. albicans was moderately reduced, but expression of the HIV-1 transgene did not alter production of nitric oxide or reduce killing of C. albicans. A knockout of the inducible nitric oxide synthase (NOS2) gene in these Tg mice did not augment oral or gastrointestinal burdens during chronic carriage of C. albicans or cause systemic dissemination, likely due to a redundancy provided by partially preserved production of H(2)O(2) and oxygen-independent candidacidal mechanisms. Thus, the macrophage response to C. albicans is largely preserved in these Tg mice, and no functional macrophage defect appears to primarily determine the susceptibility to mucosal candidiasis.

Immune defence mechanisms and immunoenhancement strategies in oropharyngeal candidiasis

The prevalence of oropharyngeal candidiasis continues to be high, mainly because of an increasing population of immunocompromised patients. Traditional treatment of oropharyngeal candidiasis has relied on the use of antimicrobial drugs. However, unsatisfactory results with drug monotherapy and the emergence of resistant strains have prompted investigations into the potential use of adjunctive immunoenhancing therapies for the treatment of these infections. Here we review the host-recognition systems of Candida albicans, the immune and inflammatory response to infection, and antifungal effector mechanisms. The potential of immune modulation as a therapeutic strategy in oropharyngeal candidiasis is also discussed.

Immunoregulatory activity by daucosterol, a β-sitosterol glycoside, induces protective Th1 immune response against disseminated Candidiasis in mice

In the present study, we investigated immunomodulatory effect of daucosterol, a beta-sitosterol glycoside, against disseminated candidiasis caused by Candida albicans. Results showed that direct interaction of daucosterol with C. albicans yeast cells resulted in no growth-inhibition by in vitro susceptibility analysis. In contrast, mice given daucosterol (DS) intraperitoneally before intravenous challenge with live C. albicans yeast cells survived longer than DS-untreated control mice against disseminated candidiasis (P<0.05). By assessment of the fungal CFU in kidneys, DS-treated mice before the challenge developed about 81% fewer kidney CFU than untreated controls. This protection was removable by pretreatment of mice with anti-CD4+ antibody before the DS-treatment and challenge with the yeast. However, the protection was transferable by the CD4+ T cells from DS-treated mice not infected with the yeast. ELISA analysis revealed there were predominant production of IFNgamma and IL-2 cytokines as compared to IL-4, and IL-10 productions in DS-treated mice. By treatment of DS-given mice with anti-mouse IFNgamma, the protection was also abolished. Our studies show that DS protects mice against disseminated candidiasis by the CD4+ Th1 immune response.

Ginsenoside Rg1 helps mice resist to disseminated candidiasis by Th1 type differentiation of CD4+ T cell

Ginsenosides, the most important component isolated from Panax ginseng, exhibits a variety of biological activities. Particularly, ginsenoside Rg1 is known to have various immune-modulating activities such as increase of immune activity of T helper (Th) cells. In this present work, we investigated the effect of the Rg1 on Candida albicans growth. Results showed that direct interaction of the Rg1 to C. albicans yeast cells resulted in no growth inhibition as tested by agar diffusion susceptibility method. Reversely, mice given the Rg1 intraperitoneally (i.p.) before intravenous (i.v.) challenge with live C. albicans yeast cells protected the mice to experimental disseminated candidiasis. By kidney candidal CFU (colony forming unit) determination, the disease severity of the Rg1-treated mice was confirmed far less than Rg1-untreated control mice. The protection was transferable by CD4+ T cells (RGCD4T) isolated from Rg1-treated mice. ELISA analysis revealed that there were cytokine inductions of IFNgamma, IL-2, IL-4 and IL-10 from the RGCD4T, demonstrating the Th1-lineage development of predominant IFNgamma and IL-2 production. Anti-mouse IFNgamma antibody treatment of Rg1-treated mice abolished the protection to disseminated disease. Our studies show that ginsenoside Rg1 helps the host resists disseminated candidiasis by the CD4(+) T cell-mediated immune response led from a Th1-dominant cytokine response.

CD8+ T cells but not polymorphonuclear leukocytes are required to limit chronic oral carriage of Candida albicans in transgenic mice expressing human immunodeficiency virus type 1

Candida albicans causes oropharyngeal candidiasis (OPC) but rarely disseminates to deep organs in human immunodeficiency virus (HIV) infection. Here, we used a model of OPC in CD4C/HIV(Mut) transgenic (Tg) mice to investigate the role of polymorphonuclear leukocytes (PMNs) and CD8+ T cells in limiting candidiasis to the mucosa. Numbers of circulating PMNs and their oxidative burst were both augmented in CD4C/HIV(MutA) Tg mice expressing rev, env, and nef of HIV type 1 (HIV-1), while phagocytosis and killing of C. albicans were largely unimpaired compared to those in non-Tg mice. Depletion of PMNs in these Tg mice did not alter oral or gastrointestinal burdens of C. albicans or cause systemic dissemination. However, oral burdens of C. albicans were increased in CD4C/HIV(MutG) Tg mice expressing only the nef gene of HIV-1 and bred on a CD8 gene-deficient background (CD8-/-), compared to control or heterozygous CD8+/- CD4C/HIV(MutG) Tg mice. Thus, CD8+ T cells contribute to the host defense against oral candidiasis in vivo, specifically in the context of nef expression in a subset of immune cells.

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.

HIV-1 and its transmembrane protein gp41 bind to different Candida species modulating adhesion

Oral candidiasis in HIV-1-infected individuals is widely believed to be triggered by the acquired T-lymphocyte immunodeficiency. Recently, binding of the HIV-1 envelope protein gp160 and its subunit gp41, and also of the whole virus itself, to Candida albicans has been shown. The present study shows that, in addition to C. albicans, HIV-1 gp41 also binds to yeast and hyphal forms of Candida dubliniensis, a species which is closely related to C. albicans, and to Candida tropicalis but not to Candida krusei, Candida glabrata or Saccharomyces cerevisiae. The previous finding that gp41 binding to C. albicans augments fungal virulence in vitro is supported by the observation that the yeast showed an enhanced adhesion to HIV-infected H9 cells in comparison to uninfected cells. In line with these results soluble gp41 itself reduced binding of C. albicans to both endothelial and epithelial cell lines, confirming a dominant role of the gp41 binding moiety on the surface of Candida for adhesion. Surface-associated secreted aspartic proteinases (Saps) play an important role in candidial adhesion, but are not likely to be involved in the interaction as gp41 binding to the C. albicans parental wild-type strain was comparable to that of three different isogenic Sap deletion mutants. Furthermore, gp41 binding to the yeast killer toxin-susceptible C. albicans strain 10S was not inhibitable by an anti-YKT receptor antibody. In conclusion, HIV-1 interacts with different clinically important Candida spp., and may thereby affect the outcome of the respective fungal infection.

Anti-tumor mechanism of Z-100, an immunomodulatory Arabinomannan extracted from Mycobacterium tuberculosis strain Aoyama B, on pulmonary metastases of B16F10 melanoma: restoration of helper T cell responses via suppression of glucocorticoid-genesis

In the present study, the anti-tumor mechanism of Z-100 was investigated with the use of pulmonary metastasis of B16F10 melanoma. In B16F10 mice, Th1 cytokine production (IL-2, IFN-gamma) was suppressed in comparison with normal mice. On the other hand, Th2 cytokine production (IL-4, IL-10) was increased in the B16F10 mice. The administration of Z-100 to B16F10 mice restored the balance of Th1/Th2 cell responses from the Th2 dominant state to the normal state. Z-100 significantly suppressed the pulmonary metastasis of B16F10 melanoma in a dose-dependent manner. These results suggest that Z-100 restored the breakdown of Th1 cell responses, resulting in the suppression of pulmonary metastasis of B16F10 melanoma. Moreover, Z-100 decreased the corticosterone levels, which is known to suppress the Th1 cell responses, in both serum specimens and splenic tissue, and the steroidogenic CYP11A1 mRNA expression in CD4+ T cells. These results suggest that a suppression of pulmonary metastasis and restoration of Thl/Th2 cell responses by Z-100 may be due to the decrease in the corticosterone levels and the steroidogenic CYP11A1 mRNA expression of CD4+ T cells in B16F10 mice. Further, the role of Th1 cytokine, IFN-gamma, on these activities of Z-100 was examined. The suppressive effects of Z-100 on pulmonary metastasis and restoration of Th1/Th2 cell responses were eliminated by the administration of anti-IFN-gamma mAb. Moreover, the suppressive effects of Z-100 on glucocorticoid-genesis were eliminated by the administration of anti-IFN-gamma-mAb. These results suggest that Z-100 restores the balance of Th1/Th2 cell responses via the suppression of glucocorticoid-genesis by Z-100-induced IFN-gamma. IFN-gamma acts as a key cytokine in anti-tumor activities of Z-100.

Immune cell-mediated protection against vaginal candidiasis: evidence for a major role of vaginal CD4(+) T cells and possible participation of other local lymphocyte effectors

The protective roles of different lymphocyte subsets were investigated in a rat vaginal candidiasis model by adoptive transfer of vaginal lymphocytes (VL) or sorted, purified CD3(+) T cells, CD4(+) or CD8(+) T cells, or CD3(-) CD5(+) B cells from the vaginas of naïve or immune rats following three rounds of Candida albicans infection. The adoptive transfer of total VL from nonimmune animals did not alter the course of vaginal candidiasis of the recipient rats. In contrast, the animals receiving total VL or CD3(+) T cells from immune rats showed a highly significant acceleration of fungus clearance compared with animals which received nonimmune VL. The animals with vaginal CD3(-) CD5(+) B cells transferred from immune rats also had fewer Candida CFU than the controls, but fungal clearance was significantly retarded with respect to the animals administered immune T cells. Sorted, purified CD4(+) and CD8(+) vaginal T cells from immune rats were also adoptively transferred to naïve animals. Although both populations were seen to accelerate the clearance of the fungus from the vagina, CD4(+) T cells were much more effective than CD8(+) T cells. Overall, there was no difference between the antifungal effects of immune vaginal CD4(+) T cells and those achievable with the transfer of whole, immune VL. Histological observations of the vaginal tissues of rats with adoptively transferred immune T cells demonstrated a remarkable accumulation of lymphocytes in the subepithelial lamina propria and also infiltrating the mucosal epithelium. These results strongly suggest that distinct vaginal lymphocyte subsets participate in the adaptive anti-Candida immunity at the vaginal level, with the vaginal CD4(+) T cells probably playing a major role.

Deletion of the two-component histidine kinase gene (CHK1) of Candida albicans contributes to enhanced growth inhibition and killing by human neutrophils in vitro

We have observed that human neutrophils (polymorphonuclear leukocytes [PMNs]) have an increased growth-inhibitory and killing effect on a strain of Candida albicans with a deletion of CHK1, a gene encoding a putative histidine kinase. The PMN effect was not due to increased phagocytosis of the null strain. This observation may partially explain the reduced virulence in a hematogenously disseminated murine model of candidiasis.

Primary role for CD4(+) T lymphocytes in recovery from oropharyngeal candidiasis

Oropharyngeal candidiasis is associated with defects in cell-mediated immunity and is commonly seen in human immunodeficiency virus positive individuals and AIDS patients. A model for oral candidiasis in T-cell-deficient BALB/c and CBA/CaH nu/nu mice was established. After inoculation with 10(8) Candida albicans yeasts, these mice displayed increased levels of oral colonization compared to euthymic control mice and developed a chronic oropharyngeal infection. Histopathological examination of nu/nu oral tissues revealed extensive hyphae penetrating the epithelium, with polymorphonuclear leukocyte microabscess formation. Adoptive transfer of either naive or immune lymphocytes into immunodeficient mice resulted in the recovery of these animals from the oral infection. Reconstitution of immunodeficient mice with naive CD4(+) but not CD8(+) T cells significantly decreased oral colonization compared to controls. Interleukin-12 and gamma interferon were detected in the draining lymph nodes of immunodeficient mice following reconstitution with naive lymphocytes. This study demonstrates the direct requirement for T lymphocytes in recovery from oral candidiasis and suggests that this is associated with the production of cytokines by CD4(+) T helper cells.

Nitric oxide-enhanced resistance to oral candidiasis

A murine model of oral candidiasis was used to show that nitric oxide (NO) is involved in host resistance to infection with Candida albicans in infection-'resistant' BALB/c and infection-'prone' DBA/2 mice. Following infection, increased NO production was detected in saliva. Postinfection samples of saliva inhibited the growth of yeast in vitro. Treatment with NG-monomethyl-L-arginine (MMLA), an inhibitor of NO synthesis, led to reduced NO production, which correlated with an increase in C. albicans growth. Reduction in NO production following MMLA treatment correlated with an abrogation of interleukin-4 (IL-4), but not interferon-gamma (IFN-gamma), mRNA gene expression in regional lymph node cells. Down-regulation of IL-4 production was accompanied with an increase in IFN-gamma production in infection-'prone' DBA/2 mice. There was a functional relationship between IL-4 and NO production in that mice treated with anti-IL-4 monoclonal antibody showed a marked inhibition of NO production in saliva and in culture of cervical lymph node cells stimulated with C. albicans antigen. The results support previous conclusions that IL-4 is associated with resistance to oral candidiasis and suggest that NO is involved in controlling colonization of the oral mucosal surface with C. albicans.

T cells augment monocyte and neutrophil function in host resistance against oropharyngeal candidiasis

The purpose of this study was to identify the cell populations involved in recovery from oral infections with Candida albicans. Monoclonal antibodies specific for CD4+ cells, CD8+ cells, and polymorphonuclear leukocytes were used to deplete BALB/c and CBA/CaH mice of the relevant cell populations in systemic circulation. Monocytes were inactivated with the cytotoxic chemical carrageenan. Mice were infected with 10(8) C. albicans yeast cells and monitored for 21 days. Systemic depletion of CD4+ and CD8+ T lymphocytes alone did not increase the severity of oral infection compared to that of controls. Oral colonization persisted in animals treated with head and neck irradiation and depleted of CD4+ T cells, whereas infections in animals that received head and neck irradiation alone or irradiation and anti-CD8 antibody cleared the infection in a comparable fashion. The depletion of polymorphonuclear cells and the cytotoxic inactivation of mononuclear phagocytes significantly increased the severity of oral infection in both BALB/c and CBA/CaH mice. High levels of interleukin 12 (IL-12) and gamma interferon (IFN-gamma) were produced by lymphocytes from the draining lymph nodes of recovering animals, whereas IL-6, tumor necrosis factor alpha, and IFN-gamma were detected in the oral mucosae of both naïve and infected mice. The results indicate that recovery from oropharyngeal candidiasis in this model is dependent on CD4+-T-cell augmentation of monocyte and neutrophil functions exerted by Th1-type cytokines such as IL-12 and IFN-gamma.

Cellular and cytokine correlates of mucosal protection in murine model of oral candidiasis

Host protection against Candida albicans infection in a model of oral candidiasis involving infection-prone [DBA/2 (H-2(d))] and less infection-prone [BALB/c (H-2(d))] mouse strains was analyzed in terms of antibody and cellular responses, and in terms of cytokine patterns from regional lymph node cells. There was a selective expansion of gamma/delta(+) T-cell receptor cells, which correlated with the patterns of colonization in both mouse strains, with higher numbers of gamma/delta T cells detected in BALB/c mice. Antigen-induced T-cell proliferation was significantly higher in BALB/c mice than in DBA/2 mice. Higher levels of serum immunoglobulin G (IgG) and salivary IgA antibodies were detected in BALB/c mice than in DBA/2 mice, but only after the infection was cleared. The cervical lymph node cells from infected mice were assessed for interleukin-4 (IL-4), IL-12, and gamma interferon (IFN-gamma) mRNA gene expression by reverse transcription-PCR and protein production in the culture supernatants following restimulation in vitro. In BALB/c mice, an early increase in levels of IL-4, IFN-gamma, and IL-12 correlated with rapid elimination of C. albicans. In DBA/2 mice, where resolution of infection was delayed, IL-4 message expression was delayed and the IL-4 secretion level was lower. Neutralization of IL-4 by multiple injections of an anti-IL-4 monoclonal antibody in BALB/c mice resulted in increased carriage rate and delayed clearance of the yeasts. Collectively, the data suggest that the T-cell response to C. albicans in the regional lymph nodes which correlates best with rapid oral clearance of C. albicans is a balanced Th0 cytokine response involving early secretion of both IFN-gamma and IL-4.

Esophageal candidiasis in pediatric acquired immunodeficiency syndrome: clinical manifestations and risk factors

BACKGROUND

Little is known about the epidemiology and clinical features of esophageal candidiasis (EC) in pediatric AIDS. We therefore investigated the clinical presentation and risk factors of EC in a large prospectively monitored population of HIV-infected children at the National Cancer Institute.

PATIENTS AND METHODS

We reviewed the records of all HIV-infected children (N = 448) followed between 1987 and 1995 for a history of esophageal candidiasis to characterize the epidemiology, clinical features, therapeutic interventions and outcome of esophageal candidiasis. To understand further the risk factors for EC in pediatric AIDS, we then performed a matched case-control analysis of 25 patients for whom control cases were available.

RESULTS

There were 51 episodes of EC documented in 36 patients with 23 male and 13 female patients (0.2 to 17 years; median CD4, count 11/microl), representing a frequency of EC of 8.0%. Concurrent oropharyngeal candidiasis (OPC) was the most common clinical presentation of EC (94%); other signs and symptoms included odynophagia (80%), retrosternal pain (57%), fever (29%), nausea/vomiting (24%), drooling (12%), dehydration (12%), hoarseness (6%) and upper gastrointestinal bleeding (6%). The causative organism documented in 36 episodes (18 from OPC, 17 from endoscopic biopsy and 1 from autopsy) was Candida albicans in all cases. Patients received treatment for EC with amphotericin B (63%), fluconazole (29%), ketoconazole (4%) or itraconazole (1%). A clinical response was documented in all 45 evaluable episodes. In 6 other cases, EC was a final event without contributing to the cause of death. By a conditional logistic regression model for matched data, the best predictor of EC was the presence of prior OPC (P<0.0001), followed by CD4 count and CD4 percentage (P = 0.0002) and use of antibacterial antibiotics (P = 0.0013). The risks associated with low CD4 count were independent of that of prior OPC.

CONCLUSION

EC in pediatric AIDS is a debilitating infection, which develops in the setting of prior OPC, low CD4 counts and previous antibiotics.

Local anticandidal immune responses in a rat model of vaginal infection by and protection against Candida albicans

Humoral (antibody [Ab]) and cellular Candida-specific immune responses in the vaginas of pseudoestrus rats were investigated during three successive infections by Candida albicans. After the first, protective infection, Abs against mannan and aspartyl proteinase antigens were present in the vaginal fluid, and their titers clearly increased during the two subsequent, rapidly healing infections. In all animals, about 65 and 10% of vaginal lymphocytes (VL) were CD3(+) (T cells) and CD3(-) CD5(+) (B cells), respectively. Two-thirds of the CD3(+) T cells expressed the alpha/beta and one-third expressed the gamma/delta T-cell receptor (TCR). This proportion slightly fluctuated during the three rounds of C. albicans infection, but no significant differences between infected and noninfected rats were found. More relevant were the changes in the CD4(+)/CD8(+) T-cell ratio, particularly for cells bearing the CD25 (interleukin-2 receptor alpha) marker. In fact, a progressively increased number of both CD4(+) alpha/beta TCR and CD4(+) CD25(+) VL was observed after the second and third Candida challenges, reversing the high initial CD8(+) cell number of controls (estrogenized but uninfected rats). The CD3(-) CD5(+) cells also almost doubled from the first to the third infection. Analysis of the cytokines secreted in the vaginal fluid of Candida-infected rats showed high levels of interleukin 12 (IL-12) during the first infection, followed by progressively increasing amounts of IL-2 and gamma interferon during the subsequent infections. No IL-4 or IL-5 was ever detected. During the third infection, VL with in vitro proliferative activity in response to an immunodominant mannoprotein antigen of C. albicans were present in the vaginal tissue. No response to this antigen by mitogen-responsive blood, lymph node, and spleen cells was found. In summary, the presence of protective Ab and T helper type 1 cytokines in the vaginal fluids, the in vitro proliferation of vaginal lymphocytes in response to Candida antigenic stimulation, and the increased number of activated CD4(+) cells and some special B lymphocytes after C. albicans challenge constitute good evidence for induction of locally expressed Candida-specific Ab and cellular responses which are potentially involved in anticandidal protection at the vaginal level.

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.

High aspartyl proteinase production and vaginitis in human immunodeficiency virus-infected women

Vaginal isolates of Candida albicans from human immunodeficiency virus-positive (HIV+) and HIV- women with or without candidal vaginitis were examined for secretory aspartyl proteinase (Sap) production in vitro and in vivo and for the possible correlation of Sap production with pathology and antimycotic susceptibility in vitro. HIV+ women with candidal vaginitis were infected by strains of C. albicans showing significantly higher levels of Sap, a virulence enzyme, than strains isolated from HIV+, C. albicans carrier subjects and HIV- subjects with vaginitis. The greater production of Sap in vitro was paralleled by greater amounts of Sap in the vaginal fluids of infected subjects. In an estrogen-dependent, rat vaginitis model, a strain of C. albicans producing a high level of Sap that was isolated from an HIV+ woman with vaginitis was more pathogenic than a strain of C. albicans that was isolated primarily from an HIV-, Candida carrier. In the same model, pepstatin A, a strong Sap inhibitor, exerted a strong curative effect on experimental vaginitis. No correlation was found between Sap production and antimycotic susceptibility, as most of the isolates were fully susceptible to fluconazole, itraconazole, and other antimycotics, regardless of their source (subjects infected with strains producing high or low levels of Sap, subjects with vaginitis or carrier subjects, or subjects with or without HIV). Thus, high Sap production is associated with virulence of C. albicans but not with fungal resistance to fluconazole in HIV-infected subjects, and Sap is a potentially new therapeutic target in candidal vaginitis.

Candida albicans suppresses nitric oxide (NO) production by interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS)-stimulated murine peritoneal macrophages

We examined the in vitro effect of Candida albicans on NO production by macrophages. Candida albicans suppressed not only NO production but also expression of inducible NO synthase (iNOS) mRNA by murine IFN-gamma and bacterial LPS-stimulated peritoneal macrophages. The suppression was not associated with inhibition but rather stimulation of IL-1 beta production. This effect was observed when more than 1 x 10(3)/ml of Candida albicans were added to macrophage cultures (1 x 10(6) cells/ml) and reached a maximal level at 1 x 10(6)/ml. The NO inhibitory effect of Candida albicans was mediated predominantly by as yet unidentified soluble factor(s) and to a lesser extent by direct contact. In addition, heat- or paraformaldehyde-killed Candida albicans did not show this inhibitory activity. Culture supernatant of Candida albicans also inhibited NO production by activated macrophages in a dose-dependent manner, and increased IL-1 beta production. Finally, the inhibitory effect was not mediated by IL-10 and transforming growth factor-beta (TGF-beta), since neutralizing antibodies to these cytokines did not influence Candida albicans-induced reduction in macrophage NO production. Our results suggest that Candida albicans may evade host defence mechanism(s) through a soluble factor-mediated suppression of NO production by stimulated macrophages, and that the effect is independent of production of immunosuppressive cytokines such as IL-10 and TGF-beta.

Effectiveness of a vaccine composed of heat-killed Candida albicans and a novel mucosal adjuvant, LT(R192G), against systemic candidiasis

The incidence of fungal infections caused by the opportunistic yeast Candida albicans has increased significantly in recent years. The ability to vaccinate selected patients against the organism would be advantageous. In this paper we describe a potential anti-C. albicans vaccine consisting of heat-killed C. albicans (HK-CA) in combination with the novel mucosal adjuvant LT(R192G), a genetically detoxified form of the heat-labile toxin of enterotoxigenic Escherichia coli. Groups of male CBA/J mice were immunized intranasally on three occasions at weekly intervals with 2 x 10(7) HK-CA per dose, alone or in conjunction with 10 micrograms of LT(R192G) per dose. Two weeks following the last application of antigen, some animals were challenged intravenously (i.v.) with 10(4), 10(5), or 10(6) viable C. albicans to assess protection as measured by survival and/or culture. Some groups of animals were footpad tested with C. albicans mannan to assess delayed-type hypersensitivity (DTH), and all the animals were bled for antibody assays. In two independent studies, all the animals immunized with HK-CA plus LT(R192G) were able to eradicate 10(4) C. albicans completely, as determined by kidney culture 4 weeks after challenge. Animals immunized with HK-CA only had reduced levels of C. albicans compared to the adjuvant or saline-only control. Greatly enhanced survival was observed when mice immunized with HK-CA plus LT(R192G) were challenged with 10(5) live C. albicans as well. Animals immunized with HK-CA plus LT(R192G) developed a significant DH response, while those given HK-CA alone developed only marginal DH responses. High immunoglobulin G (IgG) levels to cytoplasmic antigens developed in mice immunized with HK-CA plus LT(R192G), but they were found only after i.v. challenge. Addition of adjuvant shifted the antibody isotype production in i.v.-challenged animals to a response dominated by IgG2a. Clearly, intranasal immunization with killed C. albicans in conjunction with LT(R192G) afforded significant levels of protection. This novel approach offers new possibilities for the development of an effective vaccine against candidiasis for use in humans.

CD86 (B7-2), but not CD80 (B7-1), expression in the epidermis of transgenic mice enhances the immunogenicity of primary cutaneous Candida albicans infections

Transgenic (Tg) mice whose epidermal keratinocytes constitutively overexpress either B7-1 (CD80) or B7-2 (CD86) exhibited exaggerated cutaneous delayed type hypersensitivity (DTH) to haptens compared to non-Tg mice. To determine whether enhanced DTH in these Tg mice is seen in response to cutaneous fungal infections, a primary infection with Candida albicans was established by inoculating this organism on the occluded skin of Tg and non-Tg mice. These infections resolved 7 days after removal of occlusive dressing in all three groups of mice, without evidence of exaggerated inflammation in either the Tg or non-Tg mice. Only B7-2 Tg mice developed enhanced Th1-lymphocyte-mediated immune responses to C. albicans antigens after resolving this infection: enhanced footpad swelling in response to intradermal C. albicans antigens, enhanced production of mRNA encoding Th1 lymphokines in draining lymph nodes, and increased gamma interferon secreted into culture supernatants by lymph node T lymphocytes stimulated with Candida antigens in vitro. Lastly, Western blotting of sera from mice that had resolved this fungal infection indicated that only B7-2 Tg mice recognized a wide range of Candida-associated antigens. These data suggest that these two costimulatory molecules, when expressed by keratinocytes, do not deliver identical signals to C. albicans antigen-reactive Th1 lymphocytes. The enhanced immune response in B7-2 Tg mice to a cutaneous C. albicans infection demonstrates the importance of antigen presentation and costimulation in immune reactivity to fungi. Furthermore, B7-2 Tg mice may be useful in identification of protective Candida antigens.

Biotherapeutic effects of probiotic bacteria on candidiasis in immunodeficient mice

Four species of probiotic bacteria were assessed for their capacities to protect athymic bg/bg-nu/nu and euthymic bg/bg-nu/+ mice from mucosal and systemic candidiasis. Each bacterial species and Candida albicans colonized the gastrointestinal tracts of both strains of mice. The presence of probiotic bacteria (Lactobacillus acidophilus, Lactobacillus reuteri, Lactobacillus casei GG, or Bifidobacterium animalis) in the gastrointestinal tracts prolonged the survival of adult and neonatal bg/bg-nu/nu mice compared to that of isogenic mice colonized with C. albicans alone. The incidence of systemic candidiasis in bg/bg-nu/nu mice was significantly reduced by each of the four probiotic bacterial species. The numbers of C. albicans present in the alimentary tracts of euthymic bg/bg-nu/+ mice were significantly reduced by L. casei GG and B. animalis. None of the probiotic bacteria species completely prevented mucosal candidiasis, but B. animalis reduced its incidence and severity. Probiotic bacteria also modulated antibody- and cell-mediated immune responses to C. albicans. The prolonged survival of mice, decreased severity of mucosal and systemic candidiasis, modulation of immune responses, decreased number of C. albicans in the alimentary tract, and reduced numbers of orogastric infections demonstrated not only that probiotic bacteria have biotherapeutic potential for prophylaxis against and therapy of this fungal disease but also that probiotic bacteria protect mice from candidiasis by a variety of immunologic (thymic and extrathymic) and nonimmunologic mechanisms in this model.

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.

Oral carriage of Candida albicans in murine AIDS

Oral candidiasis is a common fungal infection in patients infected with the human immunodeficiency virus (HIV). Although rare at the time of primary HIV infection, it is frequently found throughout the asymptomatic phase and is predictive of progressive immunodeficiency. However, the precise immune defect which results in outgrowth of commensal Candida albicans in HIV infection has not been identified. Mice infected with the Du5H(G6T2) mixture of mouse leukemia viruses develop a syndrome, designated murine AIDS (MAIDS), that has many of the immune abnormalities found in HIV infection. Retrovirus-infected C57BL/6 mice were examined for their ability to resist the development of oral candidiasis from the carrier state established after a self-limiting acute infection and to clear a subsequent secondary inoculum of oral C. albicans. Most of the mice orally colonized with C. albicans and then inoculated with the retrovirus mixture maintained a low-level oral carriage of C. albicans, while 30% of coinfected mice developed recurring 2- to 3-week episodes of acute Candida proliferation, separated by transient recoveries to the carrier state. The frequencies of CD4+ and CD8+ lymphocytes were, respectively, unchanged and significantly decreased (P < 0.05) in both cervical lymph nodes and spleens of coinfected mice compared to the corresponding frequencies in C. albicans-carrying, virus-free, age-matched control animals. Secretion of gamma interferon by concanavalin A (ConA)-stimulated spleen cells from Candida-carrying, retrovirus-infected mice was significantly decreased (P < 0.05) compared to that of C. albicans-carrying, retrovirus-free mice, in accordance with known abnormalities associated with MAIDS. However, production of this cytokine by ConA-stimulated or unstimulated cervical lymph node cells from coinfected mice was enhanced compared to that of virus-free animals colonized with C. albicans. Acquired resistance to reinfection with C. albicans was maintained in retrovirus-infected mice and was associated with a mucosal recruitment of CD8+ cells not observed in control mice. These results suggest that alterations in mucosal immunity which occur in MAIDS differ substantially from defects observed at other sites and that surrogate epithelial defense mechanisms may function locally to limit Candida proliferation.

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.

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.

Purification and biochemical characterization of a 65-kilodalton mannoprotein (MP65), a main target of anti-Candida cell-mediated immune responses in humans

A 65 kDa-constituent (MP65) of a whole-cell mannoprotein (MP) fraction of Candida albicans was purified by immunoaffinity chromatography with monoclonal antibodies directed against periodate-insensitive, protease-sensitive MP epitopes, putatively polypeptide in nature. These antibodies were obtained by immunization of mice with concanavalin A bead-coupled, low-glycosylated MP from hyphal cells of C. albicans grown in the presence of a subinhibitory dose of tunicamycin. The immunoaffinity-purified MP65 molecule had a pI of 4.1 and a protein/polysaccharide ratio of 1.8:1. It was resistant to hydrolysis by endoglycosidase H, endoglycosidase F, or N-glycoffanases but still reactive with concanavalin A. The polysaccharide moiety of MP65 was composed exclusively of mannose and glucose at a ratio of 12.7 to 1. The protein moiety showed numerous potential O-glycosidic linkage sites as suggested by the high proportion of serine and threonine (together accounting for more than 20% of the total amino acid composition) and susceptibility to diluted alkali. This treatment and digestion with alpha-mannosidase caused a reduction in the MP65 molecular mass to around 54 kDa. The N-terminal sequence of MP65 protein moiety was rich in alanine and valine (7 of 13 amino acids) and did not show any significant homology with deposited sequences in data banks. Purified MP65, at doses of a few nanograms, induced extensive T-cell proliferation of human peripheral blood mononuclear cells. This proliferation was specifically inhibited, in a dose-response fashion, by the antigen-binding fragment of the monoclonal antibody used for immunoaffinity purification. Overall, these results highlight biochemical and molecular details of MP65, a main target of human T-cell response to C.albicans.

Esophageal Candida infection and adherence mechanisms in the nonimmunocompromised rabbit

Candida infection of the esophagus has been reported not only in immunocompromised hosts but also in healthy individuals. However, its mechanisms of action in healthy individuals have not been clarified. Our previous study suggested that physical contact was an important factor for the adherence of Candida albicans. The aim of the present study was to test our hypothesis and clarify the adherence mechanisms. Suspensions of Candida albicans cells were given to rabbits in drinking water without the use of immunosuppressive drugs and/or antibiotics, and the esophagus was examined. Candidial lesions were observed in 14 of 15 rabbits given the suspensions held in water with and without 30% sucrose for 13 days. The number of Candida albicans cells adhering to the esophagus per square millimeter by subepithelial cell insertion was significantly larger than that adhering by attachment. These results indicate that adherence of Candida albicans to the esophagus occurs by sustained physical contact alone under a nonimmunosuppressive state, and that subepithelial cell insertion results in greater attachment on adherence. Our findings provide a clue that may help clarify the mechanism of Candida infection in healthy individuals.

Denture stomatitis: quantification of interleukin-2 production by mononuclear blood cells cultured with Candida albicans

Denture stomatitis is usually associated with the presence of yeast, particularly Candida albicans, and several bacteria. In this study mononuclear blood cells were grown in the presence of Candida albicans from a single colony, and interleukin-2 production induced in T lymphocytes was measured. Blood cells were from a population of patients with denture stomatitis and a control group of denture wearers without stomatitis. Induction of interleukin-2 production was correlated with factors that condition denture stomatitis, namely, isolation of Candida albicans in selective medium, age of the denture, and diabetes. Concentrations of interleukin-2 in supernatant and serum were also compared. Significant differences in interleukin-2 production were found between patients with denture stomatitis and controls. Statistical analysis demonstrated a significant association between isolation of Candida albicans and elevated interleukin-2 production in cultures from patients with and without denture stomatitis.

Elevated aspartic proteinase secretion and experimental pathogenicity of Candida albicans isolates from oral cavities of subjects infected with human immunodeficiency virus

Isolates of Candida albicans from the oral cavities of subjects at different stages of human immunodeficiency virus (HIV) infection or uninfected controls were examined for (i) production of aspartic proteinase(s), a putative virulence-associated factor(s); (ii) the presence in the fungal genome of two major genes (SAP1 and SAP2) of the aspartic proteinase family; and (iii) experimental pathogenicity in a murine model of systemic infection. It was found that the fungal isolates from symptomatic patients secreted, on average, up to eightfold more proteinase than the isolates from uninfected or HIV-infected but asymptomatic subjects. This differential property was stably expressed by the strains even after years of maintenance in stock cultures. Moreover, representative high-proteinase isolates were significantly more pathogenic for mice than low-proteinase isolates of C. albicans. The characters high proteinase and increased virulence were not associated with a single molecular type or category identifiable through DNA fingerprinting or pulsed-field electrophoretic karyotype, and both SAP1 and SAP2 genes were present in both categories of isolates, on the same respective chromosomes. In conclusion, our data suggest that during HIV infection more-virulent strains or biotypes of C. albicans which are identifiable by direct analysis of virulence determinants are selected. It also appears that the biotype switch to increased aspartic proteinase and virulence properties occurs before the HIV-infected subject enters the symptomatic stage and overt AIDS.

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.

T helper cell dichotomy to Candida albicans: implications for pathology, therapy, and vaccine design

Acquired immunity to Candida albicans is believed to prevent mucosal colonization of adult immunocompetent individuals from progressing to symptomatic infection. Resistance to disease appears to correlate with the detection of delayed-type hypersensitivity responses in vivo and a T helper type 1 (Th1) cytokine secretion profile in vitro. Cellular immunodeficiency, particularly HIV infection, greatly increases the risk of mucosal infection, confirming that CD(4+)-cell-directed immunity is effective locally in controlling infectivity of the yeast. While Th1-type CD4+ cell activation resulting in phagocyte-dependent immunity clearly represents an important mechanism of anticandidal resistance, clinical observations suggest that Th2-type CD4+ cell reactivity may be triggered by Candida antigens in several disease states, including symptomatic infections and immunopathology. This may imply that a Th1-type pattern of reactivity characterizes the saprophytic yeast carriage and resistance to disease by healthy humans, whereas Th2-type responses would be mostly associated with pathology. Moreover, Candida-specific T helper responses, namely humoral and cell-mediated immunity, appear to be reciprocally regulated, as typically occurs in experimental models of parasitic and retroviral infection, where the Th1/Th2 paradigm of acquired immunity has been best characterized. Recent studies, besides providing direct evidence for the occurrence of cross-regulatory Th1 and Th2 responses in mice with candidiasis, emphasize the potential of cytokine/anticytokine therapy for recruiting Candida-specific responses toward protective, Th1-type CD4+ cell reactivity. At the same time, these studies call attention to the possible consequences of C. albicans infection for immunopathology, allergy, and coinfection.

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.

Noninhibitory binding of human interleukin-2-activated natural killer cells to the germ tube forms of Candida albicans

During incubation in vitro with yeast or germ tube forms of Candida albicans, only 2 to 6% of freshly isolated human natural killer (NK) cells (> 85% CD16+, CD56+, CD3-; < 15% CD3+; cytolytic for the NK-susceptible target K562 but not for the NK-resistant target DAUDI), were seen to interact with the fungal cells. As seen under the electron microscope, the contact area had a limited extent and was narrow, and neither the surface nor the intracytoplasmic organization of the NK cell was altered. In contrast, more than 30% of interleukin-2-activated NK (LAK) cells (> 96% CD16+, CD56+, CD3-; 1.5% CD3+; cytolytic for both K562 and DAUDI targets) interacted closely with the fungus. This interaction was particularly extensive with the surface of the fungal germ tube that was intimately enveloped by villous protrusions from the lymphocyte surface. The fungus-interacting LAK cell also showed a remarkable redistribution of surface microvilli and polarization of cytoplasmic organelles, such as the Golgi apparatus, centrioles, and granules, toward the area of fungal contact. Together with the elevated cytolytic potential against the K562 and DAUDI targets, all the morphological data suggested the presence of a potentially active lytic machinery in the fungus-interacting LAK cell. Nonetheless, two independent assays for anticandidal activity did not show consistent killing or fungal growth inhibition by either fresh NK or LAK cells. While offering direct evidence of the strong interaction between human LAK cells and the germ tubes, precursors of tissue-invasive hyphal forms of C. albicans, our observations also suggest that this interaction may not be sufficient to kill the fungus or arrest its growth.

Use of anti-CD4+ hybridoma cells to induce Pneumocystis carinii in mice

A reduction of peripheral CD4+ cell levels has been correlated with the onset of Pneumocystis carinii pneumonia in AIDS patients. Most in vivo drug discovery and development for P. carinii have been conducted in corticosteroid-treated rats. There is need for the development of new small animal models with more selective methods of immunosuppression. This study outlines a new mouse model in which specific depletion of the CD4+ T-lymphocyte population was achieved by subcutaneous injection of G.K1.5 hybridoma cells into C3HeB/FeJ mice. A significant reduction in splenic CD4+ cells was maintained over a 10-week period following a single injection of cells. Circulating anti-CD4+ antibody was detected throughout the 10-week period in hybridoma-injected mice, while circulating antibody was undetectable 4 weeks after repeated injection of purified monoclonal antibody. There was no significant increase in the CD8+ cell populations of the hybridoma-injected mice. P. carinii cysts increased in the lungs of CD4+ T-cell-depleted mice, with the number of cysts detected comparable to levels in dexamethasone-treated mice. High levels of cysts were detected when CD4+ cell populations in the spleen remained below 5% and decreased when CD4+ populations increased above the 5% level. In mice whose CD4+ population was not reduced below 5%, there was no significant increase in P. carinii cysts detected. This study presents a new mouse model with specific immunosuppression requiring a minimum of animal manipulation for use in discovery and development of potential new therapeutics for P. carinii pneumonia.

Animal models of oral candidiasis. A review

Candida albicans is the most common fungal infection of the human oral mucosa, yet much remains to be understood with respect to the pathogenesis of the disease. Numerous difficulties are inherent in designing studies that use human beings as subjects. The use of various animal species in experimental contexts has helped to provide insight with respect to this condition. A variety of manipulations of the system can be performed, including altering the host immune response, the mucosal environment, or the systemic environment. In addition, organism-related factors can be examined in a more controlled setting. The information obtained from such studies could not be obtained in an in vitro situation.

Immunologic aspects of oral candidiasis

Immunity to Candida infections in human beings is complex because of the different types of candidiasis, the different forms of Candida itself, and the interrelationships between the mucosal and systemic immune systems. Mucosal infection is by far the most common type of candidiasis, but systemic infection can also occur and the mechanisms for each may be quite different. In the oral cavity there are four main types of candidiasis, and hyphal and yeast forms of Candida may be present with both common and unique antigens. Humoral immunity is represented by salivary antibodies of the mucosal immune system and serum antibodies in the mucosa. Cell-mediated immunity may play a role particularly in chronic hyperplastic candidiasis. Salivary antibodies have been shown to inhibit adherence of Candida to buccal epithelial cells and to be protective in animal models. Serum antibodies against a 47kD antigen have been shown to correlate with protection and recovery from systemic candidiasis, but there is little evidence for a role of serum antibody in protection against infection of the oral cavity. In in vitro studies, both macrophages and polymorphonuclear leukocytes can kill yeast forms and inhibit hyphal forms of Candida and because chronic hyperplastic candidiasis is associated with intraepithelial polymorphonuclear leukocytes, these cells could be operative in vivo. Saliva contains a number of antifungal proteins including histatins and calprotectin that could act synergistically with specific factors. It is possible that cellular factors provide the main form of defense against mucocutaneous infection, whereas humoral factors play a larger role in the prevention of dissemination of Candida infections.(ABSTRACT TRUNCATED AT 250 WORDS)