CD4+ T-helper-cell responses in mice with low-level Candida albicans infection

Effects of Boric Acid Gel on Vaginal Candida albicans Infections and the Local Immune System in Mice

The objective was to determine the effect of 5% boric acid gel on vaginal Candida albicans (CA) infections in mice and its effect on the local immune system (i.e., Th1, Th2, and Th17). Female mice were divided into four groups, with 10 mice in each group. Mycelial suspensions were administered into the vaginal lumen close to the cervix in groups B, F, and M. Mice in group B were given boric acid gel, and group F was treated with fluconazole gel for 30 min every 12 h. Group M was treated with sterile water, and group N was not given treatment. After the seventh day of treatment, each group was observed with the naked eye, and vaginal lavage fluid and vaginal tissue were collected. Expression levels of cytokines were measured using enzyme-linked immunosorbent assays (ELISA) and immunohistochemistry. Periodic acid Schiff (PAS) staining was used to measure the fungi in vaginal tissues. There were no significant changes in group M. In groups B and F, there was less vaginal injury and less exudate, with group B doing better than group F. The numbers of CA colonies were higher in groups B, F, and M than in group N (P < 0.01). There was less vaginal colonization of CA in group B than in group F (P < 0.01). After the seventh day of treatment, levels of IFN-γ, IL-17, IL-6, TGF-β, IL-4, and IL-10 were significantly greater in groups B, F, and M than in group N (P < 0.001); levels of IFN-γ, IL-17, IL-6, and TGF-β in groups B and F were higher than those of group M (P < 0.01), while IL-4 and IL-10 levels were significantly lower (P < 0.001). The trends of cytokine increases and decreases were more significant in group B than in group F (P < 0.05). Immunohistochemical results were similar to ELISA results. PAS staining revealed that boric acid inhibited hyphal reproduction. The boric acid significantly reduced the symptoms associated with CA vaginal infection. It inhibited the CA growth, prevented vaginal lesions, promoted the secretion of Th1 and Th17 cytokines, and reduced Th2 cytokines.

Repositioning Lopinavir, an HIV Protease Inhibitor, as a Promising Antifungal Drug: Lessons Learned from Candida albicans-In Silico, In Vitro and In Vivo Approaches

The repurposing strategy was applied herein to evaluate the effects of lopinavir, an aspartic protease inhibitor currently used in the treatment of HIV-infected individuals, on the globally widespread opportunistic human fungal pathogen Candida albicans by using in silico, in vitro and in vivo approaches in order to decipher its targets on fungal cells and its antifungal mechanisms of action. Secreted aspartic proteases (Saps) are the obviously main target of lopinavir. To confirm this hypothesis, molecular docking assays revealed that lopinavir bound to the Sap2 catalytic site of C. albicans as well as inhibited the Sap hydrolytic activity in a typically dose-dependent manner. The inhibition of Saps culminated in the inability of C. albicans yeasts to assimilate the unique nitrogen source (albumin) available in the culture medium, culminating with fungal growth inhibition (IC₅₀ = 39.8 µM). The antifungal action of lopinavir was corroborated by distinct microscopy analyses, which evidenced drastic and irreversible changes in the morphology that justified the fungal death. Furthermore, our results revealed that lopinavir was able to (i) arrest the yeasts-into-hyphae transformation, (ii) disturb the synthesis of neutral lipids, including ergosterol, (iii) modulate the surface-located molecules, such as Saps and mannose-, sialic acid- and N-acetylglucosamine-containing glycoconjugates, (iv) diminish the secretion of hydrolytic enzymes, such as Saps and esterase, (v) negatively influence the biofilm formation on polystyrene surface, (vi) block the in vitro adhesion to epithelial cells, (vii) contain the in vivo infection in both immunocompetent and immunosuppressed mice and (viii) reduce the Sap production by yeasts recovered from kidneys of infected animals. Conclusively, the exposed results highlight that lopinavir may be used as a promising repurposing drug against C. albicans infection as well as may be used as a lead compound for the development of novel antifungal drugs.

Pathogen Dose in Animal Models of Hemorrhagic Fever Virus Infections and the Potential Impact on Studies of the Immune Response

Viral hemorrhagic fever viruses come from a wide range of virus families and are a significant cause of morbidity and mortality worldwide each year. Animal models of infection with a number of these viruses have contributed to our knowledge of their pathogenesis and have been crucial for the development of therapeutics and vaccines that have been approved for human use. Most of these models use artificially high doses of virus, ensuring lethality in pre-clinical drug development studies. However, this can have a significant effect on the immune response generated. Here I discuss how the dose of antigen or pathogen is a critical determinant of immune responses and suggest that the current study of viruses in animal models should take this into account when developing and studying animal models of disease. This can have implications for determination of immune correlates of protection against disease as well as informing relevant vaccination and therapeutic strategies.

Humoral and cell-mediated immunity following vaccination with synthetic Candida cell wall mannan derived heptamannoside-protein conjugate: immunomodulatory properties of heptamannoside-BSA conjugate

Chemically defined glycoprotein conjugate composed of synthetically prepared mannan-derived heptamannoside with terminal β-1,2-linked mannose residue attached to the α-1,3-linked mannose residues and BSA as carrier protein (M7-BSA conjugate) was analysed for the capacity to induce protective humoral immunity and appropriate alteration cellular immunity. To identify protective antigenic structure of Candida cell wall mannan M7-BSA conjugate was used for BALB/c mice immunization. The obtained results were compared with placebo group and with heat-inactivated C. albicans whole cells immunization. The administration route of M7-BSA conjugate secondary booster injection significantly affected the intensity of humoral immune response and the specificity of produced antibodies. All prepared sera were able to elevate candidacidal activity of polymorphonuclear leukocytes (PMN) in cooperation with complement. Moreover, polyclonal sera obtained after secondary subcutaneous (s.c.) booster injection of M7-BSA conjugate were able to induce candidacidal activity of PMN also in complement independent manner. M7-BSA conjugate immunization induced increases of phagocytic activity and respiratory burst of granulocytes, caused a raise of the proportion of CD3(+) T lymphocytes and increased the CD4(+)/CD8(+) T lymphocyte ratio. We observed also an increasing proportion of CD4(+)CD25(+) T cells compared to immunization with heat inactivated whole C. albicans cells, which in turn promoted an increase of the CD8(+)CD25(+) cell proportion. Immunization with M7-BSA conjugate induced Th1, Th2 and Th17 immune responses as indicated by the elevation of relevant cytokines levels. These data provide some insights on the immunomodulatory properties of oligomannosides and contribute to the development of synthetic oligosaccharide vaccines against fungal diseases.

Some Opportunistic Parasitic Infections in AIDS: Candidiasis, Pneumocystosis, Cryptosporidiosis, Toxoplasmosis

Almost 80% of patients with AIDS die from infections other than human immunodeficiency virus (HIV). These infections usually occur late in the course of disease when CD4(+) T-cell count has fallen below 200 permm(3) cells per milliliter. Most of these infections are caused by organisms that do not normally afflict healthy individuals and are thus considered to be opportunistic. In this article, Lloyd Kasper and Dominique Buzoni-Gatel review the host-parasite interaction for four important pathogens: Candida albicans and Pneumocystis carinii (usually non-invasive pathogens), Cryptosporidium parvum (invades the cells but remains localized in the gut) and Toxoplasma gondii (penetrates through the gut to cause systemic infection). These organisms, which generally cause limited or even insignificant clinical evidence of infection in the normal host, were chosen because of their high prevalence in AIDS patients and because they exhibit different invasive abilities. The reason why individuals with AIDS are susceptible to this particular group of pathogens is uncertain.

Mixed bacterial-fungal infections in the CF respiratory tract

Cystic fibrosis (CF) is a common genetic disease whose major clinical manifestations include repeated episodes of airway infection and inflammation that ultimately result in premature death from respiratory failure. The consequences of infection by individual bacteria have been well studied and the evidence is building that fungal pathogens may be playing an important role in lung disease progression. In contrast, though many CF patients have airway infections characterized by the presence of both bacteria and fungi, our understanding of the impact of such polymicrobial infections on the host is limited. In this review, we discuss what is currently known about incidence of mixed bacterial-fungal infections, and the potential consequences of these mixed infections on the progression of CF lung disease.

Genetic susceptibility to aspergillosis in allogeneic stem-cell transplantation

Invasive aspergillosis (IA) is a major threat to positive outcomes for allogeneic stem-cell transplantation (allo-SCT) patients. Despite presenting similar degrees of immunosuppression, not all individuals at-risk ultimately develop infection. Therefore, the traditional view of neutropenia as a key risk factor for aspergillosis needs to be accommodated within new conceptual advances on host immunity and its relationship to infection. Polymorphisms in innate immune genes, such as those encoding TLRs, cytokines and cytokine receptors, have recently been associated with susceptibility to IA in allo-SCT recipients. This suggests that understanding host-pathogen interactions at the level of host genetic susceptibility will allow the formulation of new targeted and patient-tailored antifungal therapeutics, including improved donor screening.

IL-22 defines a novel immune pathway of antifungal resistance

The role of IL-17 and Th17 cells in immunity vs. pathology associated with the human commensal Candida albicans remains controversial. Both positive and negative effects on immune resistance have been attributed to IL-17/Th17 in experimental candidiasis. In this study, we provide evidence that IL-22, which is also produced by Th17 cells, has a critical, first-line defense in candidiasis by controlling the growth of infecting yeasts as well as by contributing to the host's epithelial integrity in the absence of acquired Th1-type immunity. The two pathways are reciprocally regulated, and IL-22 is upregulated under Th1 deficiency conditions and vice versa. Whereas both IL-17A and F are dispensable for antifungal resistance, IL-22 mediates protection in IL-17RA-deficient mice, in which IL-17A contributes to disease susceptibility. Thus, our findings suggest that protective immunity to candidiasis is made up of a staged response involving an early, IL-22-dominated response followed by Th1/Treg reactivity that will prevent fungal dissemination and supply memory.

p85beta phosphoinositide 3-kinase regulates CD28 coreceptor function

CD28 is a receptor expressed on T cells that regulates their differentiation after antigen stimulation to long-term-survival memory T cells. CD28 enhances T-cell receptor signals and reduces expression of CBL ubiquitin ligases, which negatively control T-cell activation. In the absence of CD28 ligation during the primary stimulation, CBL levels remain high and T cells fail to mount an efficient secondary response. CD28 associates with p85alpha, one of the regulatory subunits of phosphoinositide-3-kinase (PI3K), but the relevance of this interaction is debated. We examined here the contribution of the other ubiquitous PI3K regulatory subunit, p85beta, in CD28 function. We describe that p85beta bound to CD28 and to CBL with greater affinity than p85alpha. Moreover, deletion of p85beta impaired CD28-induced intracellular events, including c-CBL and CBL-b down-regulation as well as PI3K pathway activation. This resulted in defective differentiation of activated T cells, which failed to exhibit an efficient secondary immune response. Considering that p85beta-deficient T cells fail in recall responses and that p85beta binds to and regulates CD28 signals, the presented observations suggest the involvement of p85beta in CD28-mediated activation and differentiation of antigen-stimulated T cells.

Defect internalization and tyrosine kinase activation in Aire deficient antigen presenting cells exposed to Candida albicans antigens

Patients with Autoimmune polyendocrine syndrome type I (APS I) present with multiple endocrine failures due to organ-specific autoimmune disease, thought to be T-cell-mediated. Paradoxically, APS I patients suffer from chronic mucocutaneous candidiasis. The mutated gene has been identified as the Autoimmune regulator (AIRE). Aire is expressed in medullary epithelial cells of the thymus and in antigen presenting cells in the periphery. T cells from Aire deficient mice and men displayed an enhanced proliferative response against Candida antigen in vitro, suggesting that Aire deficient T cells are competent in recognizing Candida albicans. In contrast, monocytes from APS I patients displayed a decreased and delayed internalization of zymosan. Furthermore, Candida antigen activated monocytes from APS I patients show decreased and altered phoshotyrosine kinase activation. In conclusion, Aire deficient APCs have a defect receptor mediated internalization of Candida which affects kinase activation, likely altering the innate Candida immune response.

Host defence against disseminated Candida albicans infection and implications for antifungal immunotherapy

The different manifestations of Candida albicans infection are dictated by an underlying defect in the immune response of the host. Protective immunity to disseminated candidiasis, the manifestation of C. albicans infection discussed in this review, has traditionally been ascribed to innate immunity with emphasis on the role of granulocytes. Lately, however, immunological studies have learned that host defence against disseminated candidiasis is based on a complex interplay between innate and cell-mediated immunity. Despite the availability of new antifungal agents, mortality associated with disseminated C. albicans infection remains high. Immunotherapy that augments host defence is an important strategic option in the battle against disseminated candidiasis. Here, the authors review the chronological events in the pathogenesis of disseminated candidiasis that aid in predicting the impact of existing immunotherapy and the development of future immunomodulating strategies.

Vaccination with recombinant N-terminal domain of Als1p improves survival during murine disseminated candidiasis by enhancing cell-mediated, not humoral, immunity

Candida spp. are opportunistic fungal pathogens that are among the most common causes of nosocomial bloodstream infections. The mortality attributable to disseminated candidiasis is 40 to 50% despite antifungal therapy. Clearly, new strategies are needed to prevent this life-threatening infection. Because risk factors for disseminated candidiasis are well defined and frequently of limited duration, vaccination is an appealing prophylactic strategy. We have identified a cell surface protein, Als1p, that mediates adherence of Candida albicans to a variety of human substrates and plastic. Here we report that immunizing BALB/c mice with the recombinant N-terminal domain of Als1p (rAls1p-N) improved survival during a subsequent challenge with a lethal inoculum of C. albicans. The protective 20-mug dose of rAls1p-N significantly increased Candida stimulation of Th1 splenocytes and increased in vivo delayed-type hypersensitivity. In contrast, antibody titers did not correlate with protection. Finally, the vaccine was not protective in T-cell-deficient mice but was protective in B-cell-deficient mice. These data indicate that the mechanism of action of the rAls1p-N vaccine is stimulation of cell-mediated, rather than humoral, immunity against C. albicans. The majority of efforts to date have focused on the development of passive immunization strategies to prevent or treat disseminated candidiasis. In contrast, our results provide proof of principle for vaccination with an adhesin of C. albicans and emphasize the potential for cell-mediated immune modulation as a prophylactic or therapeutic strategy against disseminated candidiasis.

Dual role of interleukin-4 (IL-4) in pulmonary paracoccidioidomycosis: endogenous IL-4 can induce protection or exacerbation of disease depending on the host genetic pattern

Resistance to paracoccidioidomycosis, the most important endemic mycosis in Latin America, is thought to be primarily mediated by cellular immunity and the production of gamma interferon. To assess the role of interleukin-4 (IL-4), a Th2 cytokine, pulmonary paracoccidioidomycosis in IL-4-depleted susceptible (B10.A) and intermediate (C57BL/6) mice was studied. Two different protocols were used to neutralize endogenous IL-4 in B10.A mice: 1 mg of anti-IL-4 monoclonal antibody (MAb)/week and 8 mg 1 day before intratracheal infection with 10(6) Paracoccidioides brasiliensis yeast cells. Unexpectedly, both protocols enhanced pulmonary infection but did not alter the levels of pulmonary cytokines and specific antibodies. Since in a previous work it was verified that C57BL/6 mice genetically deficient in IL-4 were more resistant to P. brasiliensis infection, we also investigated the effect of IL-4 depletion in this mouse strain. Treatment with the MAb at 1 mg/week led to less severe pulmonary disease associated with impaired synthesis of Th2 cytokines in the lungs and liver of control C57BL/6 mice. Conversely, in IL-4-depleted C57BL/6 mice, increased levels of tumor necrosis factor alpha and IL-12 were found in the lungs and liver, respectively. In addition, higher levels of immunoglobulin G2a (IgG2a) and lower levels of IgG1 antibodies were produced by IL-4-depleted mice than by control mice. Lung pathologic findings were equivalent in IL-4-depleted and untreated B10.A mice. In IL-4-depleted C57BL/6 mice, however, smaller and well-organized granulomas replaced the more extensive lesions that developed in untreated mice. These results clearly showed that IL-4 can have a protective or a disease-promoting effect in pulmonary paracoccidioidomycosis depending on the genetic background of the host.

Parenchymal organ, and not splenic, immunity correlates with host survival during disseminated candidiasis

We examined the relationship between host survival and renal and splenic immune responses in a murine model of hematogenously disseminated candidiasis. Male BALB/c mice were infected via tail vein injection with wild-type C. albicans or with an isogenic, Deltaefg1/Deltaefg1 hypha-deficient mutant. Host survival, organ fungal burden, intracellular cytokine content of splenic and kidney lymphocytes, and whole-organ cytokine profiles were determined. Wild-type C. albicans induced type 2 splenocyte responses with both nonfatal and fatal inocula. In the kidney, conversely, wild-type inocula causing no or low mortality induced type 1 responses and 100% fatal inocula induced type 2 or interleukin-10 (IL-10)-dominant responses. Hypha-deficient mutant C. albicans caused no or low mortality while inducing type 1 responses in both the spleen and kidney. To our knowledge, this is the first demonstration that host survival during systemic infection correlates with the type of immune response engendered in a nonlymphoid, parenchymal organ and not with the response in the spleen. Furthermore, the results provide in vivo confirmation that hyphal formation by C. albicans induces type 2 or IL-10-dominant host responses in tissues.

Role of complement C5 and T lymphocytes in pathogenesis of disseminated and mucosal candidiasis in susceptible DBA/2 mice

The aims of the study were to compare the pathogenesis of Candida albicans infection in various organs and anatomical regions of C5-deficient (DBA/2) and C5-sufficient (BALB/c) mice, and to evaluate the importance of complement C5 and T lymphocytes as factors that determine host susceptibility or resistance. The kidneys of DBA/2 mice showed higher colonisation and more severe tissue damage than those of BALB/c, but infection at other sites, including oral and vaginal mucosa, was generally similar in the two strains. Passive transfer of C5-sufficient serum into DBA/2 mice decreased the fungal burden in the kidney, and prolonged survival of the reconstituted animals. Depletion of CD4(+) and/or CD8(+) cells did not exacerbate either systemic or mucosal infection when compared to controls, and passive transfer of splenocytes from infected donors caused only a small and transient reduction in numbers of yeasts recovered from the kidney of sub-lethally infected recipients. It is concluded that the acute susceptibility of the kidneys in this mouse strain is due to C5 deficiency expressed on a susceptible genetic background. T lymphocytes, however, appear to have minimal influence on recovery from systemic infection with this isolate of C. albicans.

Mannoprotein from Cryptococcus neoformans promotes T-helper type 1 anticandidal responses in mice

We previously demonstrated that mannoprotein (MP) from Cryptococcus neoformans (CnMP) stimulates interleukin-12 production by human monocytes, thus fostering a T-helper type 1 (Th1) protective anticryptococcal response. In this paper we show that CnMP was also able to induce a Candida albicans-directed protective Th1 response. This was demonstrated for mice immunized with CnMP by induction of a delayed-type hypersensitivity (DTH) reaction to C. albicans MP (CaMP) as well as induction of gamma interferon production by CD4(+) and CD8(+) splenic T cells stimulated in vitro with CaMP. CnMP-immunized mice were also partially protected from lethal systemic challenge with C. albicans, as shown by prolonged median survival times and decreased fungal burden in the kidney. Much evidence supports the validity of these cross-reactive and functional Th1 responses: (i) a non-cross-reactive C. albicans antigen, such as enolase, did not produce a DTH response to CaMP; (ii) passive adoptive transfer of T cells primed with CnMP induced a DTH reaction; (iii) C. neoformans extract elicited a DTH response to CaMP; and (iv) a monoclonal antibody (7H6) directed against a major and immunodominant T-cell-stimulatory 65-kDa MP (MP65) of C. albicans also recognized discrete 100-kDa constituents of C. neoformans extracts, as well as secretory constituents of the fungus. These results suggest the presence of common Th1 antigenic determinants in the mannoproteic material of C. neoformans and C. albicans epitopes, which should be considered in devising common strategies for immunoprophylactic or immunotherapeutic control of the fungi.

Exposure of BALB/c mice to low doses of Mycobacterium avium increases resistance to a subsequent high-dose infection

BALB/c mice exposed intranasally (i.n.), intradermally (i.d.) or intraperitoneally (i.p.) to low doses of Mycobacterium avium (20 c.f.u. at three different times two weeks apart) showed an increased resistance to a subsequent high-dose (10(5) c.f.u.) infection. I.n.-exposed mice had few mycobacteria in the tissues (>100 c.f.u.) and showed an expansion of CD4(+) T cells associated with overproduction of IL-12 and IFN-gamma, but not IL-4 and IgG antibodies. Parenterally (i.p. and i.d.) exposed animals showed c.f.u. numbers higher than i.n.-exposed mice, together with overproduction of IL-12, IFN-gamma and IL-4 in the case of i.p.-exposed mice, and of IL-12, IFN-gamma and IgG2a and IgG1 antibodies in the case of i.d.-exposed mice. Low-dose exposures were not contained by athymic BALB/c nude mice; however, naive nude mice reconstituted with i.n.-primed CD4(+) T cells of BALB/c mice were protected against high-dose infection, indicating that CD4(+) T cells are essential to control even low-dose infections by M. avium. Overall, these data suggest that continuous i.n. exposure to M. avium doses commonly found in the environment may play a role in determining the natural resistance of normal hosts against this organism.

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.

Comparison of pathogenesis and host immune responses to Candida glabrata and Candida albicans in systemically infected immunocompetent mice

Cytokine-mediated host defense against Candida glabrata infection was compared to that against C. albicans, using immunocompetent murine models of systemic candidiasis. The pathogenesis of infection was evaluated morphologically and by culture of target organs, while the kinetics of induction of cytokine mRNAs and corresponding proteins were determined in kidneys by real-time reverse transcription-PCR and cytokine-specific murine enzyme-linked immunosorbent assays, respectively. Systemic infection with C. glabrata resulted in a chronic, nonfatal infection with recovery of organisms from kidneys, while intravenous inoculation with C. albicans resulted in rapid mortality with logarithmic growth of organisms in kidneys and recovery of C. albicans from the spleen, liver, and lungs. Survival of C. glabrata-infected mice was associated with rapid induction of mRNAs and corresponding immunoreactive proteins for the proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha), interleukin-12 (IL-12), and gamma interferon (IFN-gamma) and the lack of induction of protein for the anti-inflammatory cytokine IL-10. In contrast, mortality in C. albicans-infected mice was associated with induction of mRNA and corresponding protein for IL-10 but delayed (i.e., TNF-alpha) or absent (i.e., IL-12 and IFN-gamma) induction of immunoreactive proinflammatory cytokines. Mice were subsequently treated with cytokine-specific neutralizing monoclonal antibodies (MAbs) to TNF-alpha, IL-12, or IFN-gamma, and the effect on growth of C. glabrata in kidneys was assessed. Neutralization of endogenous TNF-alpha resulted in a significant increase in C. glabrata organisms compared to similarly infected mice administered an isotype-matched control MAb, while neutralization of endogenous IL-12 or IFN-gamma had no significant effect on C. glabrata replication. These results demonstrate that in response to intravenous inoculation of C. glabrata, immunocompetent mice develop chronic nonfatal renal infections which are associated with rapid induction of the proinflammatory cytokines TNF-alpha, IL-12, and IFN-gamma. Furthermore, TNF-alpha plays a key role in host defense against systemic candidiasis caused by either C. glabrata or C. albicans, as the absence of endogenous TNF-alpha activity was associated with enhanced tissue burden in both infection models.

Effect of genetic modificationsby selection for immunological toleranceon fungus infection in mice

Two strains of mice genetically selected for extreme phenotypes of immunological tolerance to ovalbumin, susceptible (TS) and resistant (TR), were experimentally infected with Sporothrix schenckii. The objective was to observe whether the genetic modifications produced by the selection might be associated with interstrain differences in adaptive immune and innate responses to infection. Therefore, we evaluated the LD(50), CFU, phagocytic index, fungicidal activity, pro-inflammatory cytokines, specific antibody titres, and the delayed-type hypersensitivity reactivity. TR mice were tenfold more susceptible to infection than TS mice, as shown by LD(50) (5 x 10(6) conidia i.v.). In TS mice, the resistance was a consequence of the tissue fungal load reduction, consistent specific T-cell-mediated immunity, and tumour necrosis factor (TNF)-alpha activity at onset of infection. In TR mice, these responses were not precociously detected. Therefore, the absence of CD4(+) T-cell response in the first week of infection might explain the non-clearance of pathogen in TR mice. However, TR mice did show an increase in TNF level and delayed-type hypersensitivity response after the first week post-infection; there was also expansion and increase in granulomatous foci and CFU in the spleen. The expansion of granulomatous foci and the increase in TNF-alpha and tissue fungal load to damaging levels induced severe tissue destruction, general failure of the organs, cachexy and death in TR mice. The results show that genetic selection for extreme phenotypes of immunological tolerance also modified the responses to S. schenckii infection.

Type 1/Type 2 immunity in infectious diseases

T helper type 1 (Th1) lymphocytes secrete secrete interleukin (IL)-2, interferon-gamma, and lymphotoxin-alpha and stimulate type 1 immunity, which is characterized by intense phagocytic activity. Conversely, Th2 cells secrete IL-4, IL-5, IL-9, IL-10, and IL-13 and stimulate type 2 immunity, which is characterized by high antibody titers. Type 1 and type 2 immunity are not strictly synonymous with cell-mediated and humoral immunity, because Th1 cells also stimulate moderate levels of antibody production, whereas Th2 cells actively suppress phagocytosis. For most infections, save those caused by large eukaryotic pathogens, type 1 immunity is protective, whereas type 2 responses assist with the resolution of cell-mediated inflammation. Severe systemic stress, immunosuppression, or overwhelming microbial inoculation causes the immune system to mount a type 2 response to an infection normally controlled by type 1 immunity. In such cases, administration of antimicrobial chemotherapy and exogenous cytokines restores systemic balance, which allows successful immune responses to clear the infection.

Generation of a recombinant 65-kilodalton mannoprotein, a major antigen target of cell-mediated immune response to Candida albicans

A 65-kDa mannoprotein (CaMp65) has long been studied as a major, immunodominant antigen of the human opportunistic pathogen Candida albicans. An expression library of C. albicans was screened with serum from mice immunized with ScMp65 (ScW10), a Saccharomyces cerevisiae recombinant protein of about 48 kDa. This serum recognized the CaMp65 from a cell wall extract of C. albicans. After cloning and sequencing of the relevant C. albicans cDNA, an open reading frame encoding a protein of 379 amino acids was identified. Its deduced amino acid sequence showed regions of identity with all previously characterized tryptic fragments of CaMp65, as well as with the corresponding regions of ScMp65. A prepeptide of 32 amino acids with signal peptidase and Kex2 cleavage sites as well as a high number of potential O-glycosylation sites but no N-glycosylation sites or GPI anchor were observed in sequence studies of CaMp65. A putative adhesin RGD sequence was also present in the C-terminal region of the molecule. This triplet was absent in the ScMp65. The relevant gene (designated CaMP65) was localized to chromosome R of C. albicans as determined by pulse-field gel electrophoresis. Northern blot analysis demonstrated that gene transcription was heat inducible and associated with germ-tube formation by the fungus. A recombinant, His(6)-tagged protein (rCaMp65) was expressed in Escherichia coli under an inducible promoter. After purification by nickel-chelate affinity chromatography, the recombinant product was detected as a 47-kDa protein band in immunoblots with the anti-ScMp65 serum, as well as with CaMp65-specific monoclonal antibodies. Both ScMp65 and CaMp65 were assayed for antigenic stimulation in cultures of peripheral blood mononuclear cells (PBMC) from 10 unselected human donors. While ScMp65 was substantially nonstimulatory, both rCaMp65 and the native CaMp65 were equally able to induce lymphoproliferation of the PBMC from all the donors. In addition, a number of CD4(+) T-cell clones were generated using a C. albicans mannoprotein fraction as an antigenic stimulant. Several of these clones specifically responded to both the native and the recombinant C. albicans Mp65 but not to ScMp65. Thus, the recombinant Mp65 of C. albicans retains antigenicity and, as such, could be a valid, standardized reagent for serodiagnostic and immunological studies.

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.

Dendritic cells discriminate between yeasts and hyphae of the fungus Candida albicans. Implications for initiation of T helper cell immunity in vitro and in vivo

The fungus Candida albicans behaves as a commensal as well as a true pathogen of areas highly enriched in dendritic cells, such as skin and mucosal surfaces. The ability of the fungus to reversibly switch between unicellular yeast to filamentous forms is thought to be important for virulence. However, whether it is the yeast or the hyphal form that is responsible for pathogenicity is still a matter of debate. Here we show the interaction, and consequences, of different forms of C. albicans with dendritic cells. Immature myeloid dendritic cells rapidly and efficiently phagocytosed both yeasts and hyphae of the fungus. Phagocytosis occurred through different phagocytic morphologies and receptors, resulting in phagosome formation. However, hyphae escaped the phagosome and were found lying free in the cytoplasm of the cells. In vitro, ingestion of yeasts activated dendritic cells for interleukin (IL)-12 production and priming of T helper type 1 (Th1) cells, whereas ingestion of hyphae inhibited IL-12 and Th1 priming, and induced IL-4 production. In vivo, generation of antifungal protective immunity was induced upon injection of dendritic cells ex vivo pulsed with Candida yeasts but not hyphae. The immunization capacity of yeast-pulsed dendritic cells was lost in the absence of IL-12, whereas that of hypha-pulsed dendritic cells was gained in the absence of IL-4. These results indicate that dendritic cells fulfill the requirement of a cell uniquely capable of sensing the two forms of C. albicans in terms of type of immune responses elicited. By the discriminative production of IL-12 and IL-4 in response to the nonvirulent and virulent forms of the fungus, dendritic cells appear to meet the challenge of Th priming and education in C. albicans saprophytism and infections.

Biochemical and immunological characterization of MP65, a major mannoprotein antigen of the opportunistic human pathogen Candida albicans

In the search of the antigenic determinants of a 65-kDa mannoprotein (MP65) of Candida albicans, tryptic fragments of immunoaffinity-purified MP65 preparations were tested for their ability to induce lymphoproliferation of human peripheral blood mononuclear cells (PBMC). Five major peptides (T1 to T5) were shown to induce a vigorous proliferation of PBMC from the majority of the eight healthy human subjects tested. With the use of synthetic peptides, critical amino acid sequences of the two most immunoactive (T1 and T2) peptides were determined. Similar to what was found for the MP65 molecule, no PBMC multiplication was induced by the antigenic peptides in cultures of naive cord blood cells. The amino acid sequence analysis of tryptic and chymotryptic peptides of MP65 demonstrated a substantial homology with the deduced sequences of two cell wall proteins of Saccharomyces cerevisiae, encoded by the genes YRM305C and YGR279C. However, the antigenic peptides were those showing the least similarity with the corresponding regions of the above proteins. In particular, the lymphoproliferation-inducing sequence of the T1 peptide scored only 20% identity with the homologous regions of S. cerevisiae proteins. Besides disclosing the amino acid sequence of MP65, this study provides an initial characterization of some of its antigenic determinants, as well as of synthetic peptides of potential use to detect specific immune responses against MP65, a major target of anticandidal cell-mediated immunity in humans.

Immunity to Candida albicans: Th1, Th2 cells and beyond

Resistance to Candida albicans infection in mice results from the development of T helper (Th) type 1 cell responses. Cytokines produced by Th1 cells activate macrophages and neutrophils to a candidacidal state. The development of Th2 responses underlines susceptibility to infection, because cytokines produced by Th2 cells inhibit Th1 development and deactivate phagocytic effector cells. With the recognition of the reciprocal influences between innate and adaptive Th immunity, it appears that the coordinated action of these two lines of immune defense is required to efficiently oppose the infectivity of the fungus and to determine its lifelong commensalism at the mucosal level.

IL-10 Is Required for Development of Protective Th1 Responses in IL-12-Deficient Mice upon Candida albicans Infection

IL-12 is both required and prognostic for Th1 development in mice with Candida albicans infection. To delineate further the physiologic role of IL-12 in antifungal immunity, mice deficient for this cytokine were assessed for susceptibility to C. albicans infections, and for parameters of innate and adaptive immunity. IL-12-deficient mice were highly susceptible to gastrointestinal infection or to reinfection and showed elevated production of Candida-specific IgE and IL-4 and defective production of IFN-γ. The failure to mount protective Th1 responses occurred despite the presence of an unimpaired innate antifungal immune response, which correlated with unaltered IFN-γ production, but defective production of, and responsiveness to, inhibitory IL-10. IL-10 or IL-12 neutralization increased the innate antifungal resistance in wild-type mice. However, in IL-12-deficient mice, treatment with exogenous IL-12 or IL-10 impaired IL-4 production and increased resistance to infection, through a negative effect on the CTLA-4/B7-2 costimulatory pathway. These results confirm the obligatory role of IL-12 in the induction of anticandidal Th1 responses, and indicate the existence of a positive regulatory loop between IL-12 and IL-10 that may adversely affect the innate antifungal response, but is required for optimal costimulation of IL-12-dependent CD4+Th1 cells.

Mycobacterial dose defines the Th1/Th2 nature of the immune response independently of whether immunization is administered by the intravenous, subcutaneous, or intradermal route

It is believed that cell-mediated immunity alone can contain Mycobacterium tuberculosis, the pathogen responsible for tuberculosis. The induction of antibody, or of a mixed cell-mediated/humoral response, is associated with tuberculous disease. It is therefore important to determine the conditions of immunization with bacille Calmette Guérin (BCG), the attenuated strain of Mycobacterium bovis used to vaccinate humans against tuberculosis, that optimally induces an exclusive cell-mediated, Th1 response. Such a determination will then allow an assessment of whether the generation of such an exclusive Th1 response results in the generation of a Th1 imprint against mycobacteria. This Th1 imprint would ensure that the Th1 response is predominant following any challenge. We therefore tested the proposition that the dose of mycobacteria used for immunization generally determines the Th1/Th2 nature of the ensuing response. Our results demonstrate that relatively low doses lead to an almost exclusive cell-mediated, Th1 response, while higher doses induce a mixed Th1/Th2 response. Furthermore, the dependence on dose is independent of whether BCG is administered intravenously, subcutaneously, or intradermally. The implications of our findings to understanding how different classes of immunity are induced, to the epidemiology of tuberculosis, and to the design of effective vaccination strategies are discussed.

Endogenous interleukin 4 is required for development of protective CD4+ T helper type 1 cell responses to Candida albicans

Interleukin (IL)-4-deficient mice were used to assess susceptibility to systemic or gastrointestinal Candida albicans infections, as well as parameters of innate and elicited T helper immunity. In the early stage of systemic infection with virulent C. albicans, an unopposed interferon (IFN)-gamma response renders IL-4-deficient mice more resistant than wild-type mice to infection. Yet, IL-4-deficient mice failed to efficiently control infection in the late stage and succumbed to it. Defective IFN-gamma and IL-12 production, but not IL-12 responsiveness, was observed in IL-4-deficient mice that failed to mount protective T helper type 1 cell (Th1)-mediated acquired immunity in response to a live vaccine strain of the yeast or upon mucosal immunization in vivo. In vitro, IL-4 primed neutrophils for cytokine release, including IL-12. However, late treatment with exogenous IL-4, while improving the outcome of infection, potentiated CD4(+) Th1 responses even in the absence of neutrophils. These findings indicate that endogenous IL-4 is required for the induction of CD4(+) Th1 protective antifungal responses, possibly through the combined activity on cells of the innate and adaptive immune systems.

Prospects for the development of fungal vaccines

In an era that emphasizes the term "cost-effective," vaccines are the ideal solution to preventing disease at a relatively low cost to society. Much of the previous emphasis has been on childhood scourges such as measles, mumps, rubella, poliomyelitis, and Haemophilus influenzae type b. The concept of vaccines for fungal diseases has had less impact because of the perceived limited problem. However, fungal diseases have become increasingly appreciated as serious medical problems that require recognition and aggressive management. The escalation in the incidence and prevalence of infection has prompted a renewed interest in vaccine development. Herein, I discuss the most recent developments in the search for vaccines to combat fungal infections. Investigators have discovered several inert substances from various fungi that can mediate protection in animal models. The next challenge will be to find the suitable mode of delivery for these immunogens.

Interleukin-12 in infectious diseases

Interleukin-12 (IL-12) is a potent immunoregulatory cytokine that is crucially involved in a wide range of infectious diseases. In several experimental models of bacterial, parasitic, viral, and fungal infection, endogenous IL-12 is required for early control of infection and for generation and perhaps maintenance of acquired protective immunity, directed by T helper type 1 (Th1) cells and mediated by phagocytes. Although the relative roles of IL-12 and gamma interferon in Th1-cell priming may be to a significant extent pathogen dependent, common to most infections is that IL-12 regulates the magnitude of the gamma interferon response at the initiation of infection, thus potentiating natural resistance, favoring Th1-cell development; and inhibiting Th2 responses. Treatment of animals with IL-12, either alone or as a vaccine adjuvant, has been shown to prevent disease by many of the same infectious agents, by stimulating innate resistance or promoting specific reactivity. Although IL-12 may enhance protective memory responses in vaccination or in combination with antimicrobial chemotherapy, it is yet unclear whether exogenous IL-12 can alter established responses in humans. Continued investigation into the possible application of IL-12 therapy to human infections is warranted by the role of the cytokine in inflammation, immunopathology, and autoimmunity.

The T cell response against fungal infections

A variety of pathological conditions, including impaired immune function, is believed to underlie host susceptibility to fungal infections and to determine both the severity and the characteristic of the associated pathology. Although the redundancy and the interdependence of antifungal responses may not favor the proper dissection and appreciation of individual effector mechanisms, the T helper type 1/type 2 paradigm of acquired immunity to fungi is proving essential for a better understanding of the host response from a regulatory perspective. The recent understanding of the importance of the different T helper cell subsets in fungal infections and the increasing appreciation of the reciprocal regulation between the innate, humoral, and adaptive immune systems in the development of optimal antimicrobial immunity have offered us new clues which may lead to an understanding of T cell dependent immunity to fungi.

Vaccine- and antigen-dependent type 1 and type 2 cytokine induction after primary vaccination of infants with whole-cell or acellular pertussis vaccines

Cytokine profiles were examined 1 month after primary vaccination of infants with a whole-cell pertussis vaccine (wP) (Connaught) or either of two acellular pertussis vaccines, aP-Chiron Biocine (aP-CB) or aP-SmithKline Beecham (aP-SB), each combined with diphtheria-tetanus toxoids (DT), in Bordetella pertussis antigen-stimulated or unstimulated peripheral blood mononuclear cells (PBMC). Pertussis toxin (PT), filamentous hemagglutinin (FHA), and pertactin (PRN) were used as antigens, and the children were defined as responsive when their PBMC proliferated in response to these antigens. The controls were either children who received only DT or children who received pertussis vaccine but whose PBMC did not proliferate upon stimulation with B. pertussis antigens (unresponsive children). Antigen-stimulated PBMC of responsive wP recipients were characterized by an elevated production of T-helper-cell type 1 cytokines gamma interferon (IFN-gamma) and interleukin 2 (IL-2), low to minimal production of IL-5, and no production of IL-4. The PBMC of aP vaccine-responsive recipients showed, in addition to the elevated IFN-gamma production, a consistent, antigen-dependent production of type 2 cytokines (IL-4 and IL-5), with PRN being the most and PT being the least effective antigen. Type 2 cytokine induction was more pronounced in aP-SB than in aP-CB recipients, as shown by the presence of IL-4 mRNA transcripts and higher IL-5 production in the former (161.6 +/- 36 and 47.9 +/- 44 pg/ml [mean +/- standard error for five subjects each], respectively, after PRN stimulation). Appreciable, antigen-unstimulated (constitutive) IFN-gamma production was also detected in PBMC cultures of all vaccinees. However, this spontaneous IFN-gamma production was, in most vaccinees, significantly lower than the antigen-driven cytokine production. In contrast, no constitutive type 2 cytokine production was ever observed in any vaccine group. PBMC from the two control groups (either DT or pertussis vaccine recipients) did not show any type 2 cytokine production, while IFN-gamma production was comparable in both antigen-stimulated and unstimulated conditions. Absence of type 2 cytokines and low levels of constitutive IFN-gamma production were also seen in prevaccination children. Thus, pertussis vaccines induce in infants a basically type 1 cytokine profile, which is, however, accompanied by some production of type 2 cytokines. The latter are more expressed by aP-SB than by aP-CB recipients, and with PRN than with other antigens, and they are minimally expressed in wP recipients and with PT as antigen. Our data also highlight a constitutive IFN-gamma production in infancy, which might reflect natural immunization and/or the burden of concomitant vaccinations and which may have an impact on T-helper-cell cytokine pattern polarization consequent to pertussis vaccination.