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

Nanoparticle-Based Mycosis Vaccine

Many diseases that were considered major affliction of mankind in the past have been successfully eradicated with introduction of appropriate vaccine strategies. In order to expedite new challenges coming up to deal with various infectious diseases, nano-particulate-based subunit vaccines seem to be the demand of ordeal. The nano-vaccines can find better scope for the diseases that were not rampant in the semi-advanced world few years back. For example in present-day circumstances that corroborate with advancement in the field of medical sciences in terms of cancer chemotherapy, organ transplantation, therapy of autoimmune diseases, etc.; along with prevalence of altogether unheard diseases such as HIV infection, people are at risk of infliction with many more pathogens. In this regard, development of an effective prophylactic strategy against many opportunistic infections primarily caused by fungal pathogens needs better understanding of host pathogen relation and role of active immunity against pathogenic fungi. In the present study, we have tried to decipher effectiveness of a nano-sized vaccine delivery system in imparting protection against fungal pathogens.

Specific Human and Candida Cellular Interactions Lead to Controlled or Persistent Infection Outcomes during Granuloma-Like Formation

A delayed type of multicellular process could be crucial during chronic candidiasis in determining the course of infection. This reaction, consisting of organized immune cells surrounding the pathogen, initiates an inflammatory response to avoid fungal dissemination. The goal of the present study was to examine, at an in vitro cellular scale, Candida and human immune cell interaction dynamics during a long-term period. By challenging human peripheral blood immune cells from 10 healthy donors with 32 Candida albicans and non-albicans (C. glabrata, C. tropicalis, C. parapsilosis, C. dubliniensis, C. lusitaniae, C. krusei, and C. kefyr) clinical isolates, we showed that Candida spp. induced the formation of granuloma-like structures within 6 days after challenge, but their sizes and the respective fungal burdens differed according to the Candida species. These two parameters are positively correlated. Phenotypic characteristics, such as hypha formation and higher axenic growth rate, seem to contribute to yeast persistence within granuloma-like structures. We showed an interindividual variability of the human response against Candida spp. Higher proportions of neutrophils and elevated CD4⁺/CD8⁺ T cell ratios during the first days after challenge were correlated with early production of gamma interferon (IFN-γ) and associated with controlled infection. In contrast, the persistence of Candida could result from upregulation of proinflammatory cytokines such as interleukin-6 (IL-6), IFN-γ, and tumor necrosis factor alpha (TNF-α) and a poor anti-inflammatory negative feedback (IL-10). Importantly, regulatory subsets of NK cells and CD4^lo CD8^hi doubly positive (DP) lymphocytes at late stage infiltrate granuloma-like structures and could correlate with the IL-10 and TNF-α production. These data offer a base frame to explain cellular events that guide infection control or fungal persistence.

Is a vaccine needed against Candida albicans?

The development of a useful Candida vaccine is a distinct possibility despite the fact that individuals with a lifetime of commensal sensitization do not develop sterile immunity to the organism. An effective Candida vaccine would be invaluable in preventing hematogenously disseminated candidiasis, as well as mucocutaneous disease. This review is a discussion of our current understanding of the interplay between commensal and pathogenic forms of Candida albicans and approaches toward active and passive immunoprevention against candidiasis.

Vaginal yeast colonisation, prevalence of vaginitis, and associated local immunity in adolescents

OBJECTIVES

To evaluate point prevalence vaginal yeast colonisation and symptomatic vaginitis in middle adolescents and to identify relation of these yeast conditions with reproductive hormones, sexual activity, sexual behaviours, and associated local immunity.

METHODS

Middle adolescent females (n = 153) were evaluated for sexually transmitted infections (STIs), asymptomatic yeast colonisation, and symptomatic vulvovaginal candidiasis (VVC) by standard criteria. Also evaluated were local parameters, including vaginal associated cytokines, chemokines, and antibodies, vaginal epithelial cell antifungal activity, and Candida specific peripheral blood lymphocyte responses. Correlations between yeast colonisation/vaginitis and local immunomodulators, reproductive hormones, douching, sexual activity, condom use, and STIs were identified.

RESULTS

Rates of point prevalence asymptomatic yeast colonisation (22%) were similar to adults and similarly dominated by Candida albicans, but with uncharacteristically high vaginal yeast burden. In contrast with the high rate of STIs (18%), incidence of symptomatic VVC was low (<2%). Immunological properties included high rates of Candida specific systemic immune sensitisation, a Th2 type vaginal cytokine profile, total and Candida specific vaginal antibodies dominated by IgA, and moderate vaginal epithelial cell anti-Candida activity. Endogenous reproductive hormones were in low concentration. Sexual activity positively correlated with vaginal yeast colonisation, whereas vaginal cytokines (Th1, Th2, proinflammatory), chemokines, antibodies, contraception, douching, or condom use did not.

CONCLUSION

Asymptomatic vaginal yeast colonisation in adolescents is distinct in some ways with adults, and positively correlates with sexual activity, but not with local immunomodulators or sexual behaviours. Despite several factors predictive for VVC, symptomatic VVC was low compared to STIs.

Phagocytosis and intracellular killing of Candida albicans blastoconidia by neutrophils and macrophages: a comparison of different microbiological test systems

Polymorphonuclear neutrophils (PMN) and mononuclear phagocytes represent an important first line and effector function in the control of Candida infections. Their relative contribution to host defence is frequently assessed by means of microbiological assays. However, reported results are divergent and might well be associated with study design-related issues. In the present study, we compared frequently used microbiological candidacidal assays, with the purpose of determining the most adequate method for assessment of phagocytosis and intracellular killing. We concluded that microbiological assays using yeast-phagocyte suspensions are inappropriate for the assessment of intracellular killing of Candida blastoconidia by murine macrophages, due to adherence or clumping of cells. In contrast, an adherent monolayer of phagocytes can be applied as a single microbiological assay to independently study the process of phagocytosis and intracellular killing, by exudate peritoneal macrophages as well as exudate peritoneal PMN.

Invasive candidiasis stimulates hepatocyte and monocyte production of active transforming growth factor beta

Candida albicans is an opportunistic fungal pathogen and a major cause of morbidity and mortality in patients with compromised immune function. The cytokine response to tissue invasion by C. albicans can influence the differentiation and function of lymphocytes and other mononuclear cells that are critical components of the host response. While the production of transforming growth factor beta (TGF-beta) has been documented in mice infected with C. albicans and is known to suppress phagocyte function, the cellular source and role of this cytokine in the pathogenesis of systemic candidiasis are not well understood. We have investigated the source of production of TGF-beta by immunohistochemical studies in tissue samples from patients with an uncommon complication of lymphoreticular malignancy, chronic disseminated candidiasis (CDC), and from a neutropenic-rabbit model of CDC. Liver biopsy specimens from patients with documented CDC demonstrated intense staining for extracellular matrix-associated TGF-beta1 within inflammatory granulomas, as well as staining for TGF-beta1 and TGF-beta3 within adjacent hepatocytes. These results correlate with the immunolocalization of TGF-beta observed in livers of infected neutropenic rabbits, using a neutralizing antibody that recognizes the mature TGF-beta protein. Human peripheral blood monocytes incubated with C. albicans in vitro release large amounts of biologically active TGF-beta1. The data demonstrate that local production of active TGF-betas by hepatocytes and by infected mononuclear cells is a component of the response to C. albicans infection that most probably contributes to disease progression in the immunocompromised host.

Characterisation of Candida albicans infections of haematogenous and mucosal origin in mice lacking the interferon gamma receptor protein

Mice harbouring a null deletion mutation in the IFNgamma receptor gene were used to study the role of IFNgamma responsiveness during experimental systemic candidiasis of mucosal or haematogenous origin. After intravenous (i.v.) or intranasal (i.n.) challenge with Candida albicans the progression of infection and concomitant cellular and antibody anti-C. albicans immune responses were analysed. During the week following i.v. challenge, the rate of C. albicans multiplication in kidneys, liver and spleen was faster in IFNgammaR (-/-) than IFNgammaR (+/+) mice. As a result, IFNgammaR (-/-) mice perished earlier than IFNgammaR (+/+) mice when challenged with equal numbers of live yeast cells. However, the overall susceptibility of the two mouse strains, in terms of survival against different C. albicans challenge doses over a 60-day period, was similar. No differences were found in the cellular anti-C. albicans response generated by i.v. challenge in both mouse strains. In contrast the kinetics and strength of the serum anti-C. albicans antibody responses were markedly different. Significantly stronger, predominantly IgG2a antibody responses accompanied the eventual control of C. albicans infection in IFNgammaR (-/-) mice. Following intranasal challenge, there was no difference in the rate of C. albicans clearance from the lungs of IFNgammaR (-/-) and IFNgammaR (+/+) mice. However, 48 h after challenge, large, conspicuous abscesses appeared in the lungs, liver, kidneys and spleen of IFNgammaR (-/-) mice. These abscesses were characterised by the presence of C. albicans and abundant neutrophilic infiltrates, but very few macrophages. No such abscesses developed in i.n. challenged IFNgammaR (+/+) mice. In both mouse strains, i.n. challenge induced strong systemic anti-C. albicans cellular responses, but relatively low titre systemic antibody responses. Mucosal anti-C. albicans antibody responses were detected in IFNgammaR (+/+), but not IFNgammaR (-/-) mice. Splenic adherent macrophages obtained from IFNgammaR (-/-) mice exhibited a significantly lower candidacidal activity than those of IFNgammaR (+/+) mice, and as expected, were not responsive to IFNgamma. In summary, these data suggest that IFNgamma has a role in limiting C. albicans multiplication during the early stages of infection, as well as in preventing the development of C. albicans-associated abscesses. Activation of macrophages by IFNgamma might be pivotal in mediating this role.

The Interleukin-12–Mediated Pathway of Immune Events Is Dysfunctional in Human Immunodeficiency Virus–Infected Individuals

Interleukin-12 (IL-12) is a potentially critical factor in the immune response against human immunodeficiency virus (HIV) because it is important for regulating proliferation and interferon-γ (IFN-γ) production by T cells and natural killer (NK) cells, antigen presentation and accessory cell function by macrophages and dendritic cells, and cytolytic activities of cytotoxic T-lymphocyte cells and NK cells, which are all functions known to be dysfunctional in patients with acquired immune deficiency syndrome. Peripheral blood mononuclear cells (PBMC) from HIV-infected patients have been previously shown to be deficient in the ability to produce IL-12 in response to the bacterial pathogen Staphylococcus aureus Cowan. In this study, impaired IL-12 production in cells from PBMC of HIV-infected patients compared with healthy donors was observed across a broad panel of stimuli derived from infectious pathogens with or without priming with cytokines such as IFN-γ and IL-4, which amplify the IL-12 induction signal. Analysis of p40 and p35 mRNA accumulation showed that reductions in both subunits contribute to the lower IL-12 secretion of cells from HIV-infected individuals. PBMC from HIV-infected donors also failed to upregulate the IL-12 receptor β2 chain (IL-12Rβ2) in response to mitogenic stimuli. The expression of the IL-12Rβ2 gene could, however, be restored by in vitro exposure to rIL-12. Thus, it is possible that a primary IL-12 defect may lead to secondary deficiencies in expression of the genes for IL-12Rβ2 and IFN-γ, thus amplifying immune deficiency during HIV infection.

Evaluation of the intranasal challenge route in mice as a mucosal model for Candida albicans infection

The intranasal route was used to study Candida albicans infections in mice. Mice from two different inbred strains were challenged intranasally with C. albicans and the level of local and systemic colonization was monitored. DBA/2 mice were highly susceptible to challenge and viable C. albicans disseminated from the lungs to deeper tissues, including kidneys, liver and spleen within 48 h. In contrast, in BALB/c mice challenged in the same manner, C. albicans were retained within the lungs and cleared. Local and systemic anti-C. albicans immune responses were investigated. BALB/c mice exhibited higher titres of serum and mucosal anti-C. albicans IgA than DBA/2 mice. Splenocytes from BALB/c mice, but not from DBA/2 mice, produced detectable levels of interleukin-4 and -5 following stimulation with C. albicans antigens. Both DBA/2- and BALB/c-derived splenocytes produced interferon-gamma and interleukin-10 in response to similar stimulation. In conclusion, the intranasal route provided a simple, non-invasive murine model for investigating C. albicans infection through mucosal surfaces.

Serologic response to cell wall mannoproteins and proteins of Candida albicans

The cell wall of Candida albicans not only is the structure in which many biological functions essential for the fungal cells reside but also is a significant source of candidal antigens. The major cell wall components that elicit a response from the host immune system are proteins and glycoproteins, the latter being predominantly mannoproteins. Both the carbohydrate and protein moieties are able to trigger immune responses. Although cell-mediated immunity is often considered to be the most important line of defense against candidiasis, cell wall protein and glycoprotein components also elicit a potent humoral response from the host that may include some protective antibodies. Proteins and glycoproteins exposed at the most external layers of the wall structure are involved in several types of interactions of fungal cells with the exocellular environment. Thus, coating of fungal cells with host antibodies has the potential to influence profoundly the host-parasite interaction by affecting antibody-mediated functions such as opsonin-enhanced phagocytosis and blocking the binding activity of fungal adhesins for host ligands. In this review, the various members of the protein and glycoprotein fraction of the C. albicans cell wall that elicit an antibody response in vivo are examined. Although a number of proteins have been shown to stimulate an antibody response, for some of these species the response is not universal. On the other hand, some of the studies demonstrate that certain cell wall antigens and anti-cell wall antibodies may be the basis for developing specific and sensitive serologic tests for the diagnosis of candidasis, particularly the disseminated form. In addition, recent studies have focused on the potential for antibodies to cell wall protein determinants to protect the host against infection. Hence, a better understanding of the humoral response to cell wall antigens of C. albicans may provide the basis for the development of (i) effective procedures for the serodiagnosis of disseminated candidiasis and (ii) novel prophylactic (vaccination) and therapeutic strategies for the management of this type of infection.

DNA vaccination with cytokine fusion constructs biases the immune response to ovalbumin

DNA vaccination may work through direct transfection of antigen presenting cells (APC), or by secretion of the encoded protein by muscle or skin cells for uptake by APC. If cytokines are attached to the antigen, they may influence APC or responding T cells to drive the response toward a Th1 or Th2 direction, and/or potentiate it in an antigen-specific manner. To test this concept, expression vectors were constructed containing the ovalbumin (OVA) gene either alone, or linked to cytokine genes including GM-CSF, IFN-gamma, IL-2, IL-4, IL-12, or a sequence encoding nine amino acids of IL-1 beta. These constructs expressed OVA-cytokine fusion proteins in vitro which retained cytokine bioactivity. C57BL/6 mice were injected intramuscularly with the DNA constructs. Little if any OVA-specific antibody was produced in response to any of the DNA constructs, except for OVA-IL-4. However, lymphocytes from BALB/c mice vaccinated with OVA-IL-12 and OVA-IL-1 beta constructs produced more IFN-gamma and less IL-4 during in vitro restimulation assays than did other groups. All constructs elicited OVA-specific cytotoxic responses which were maintained or even increased over 16 weeks. The OVA-IL-12 and OVA-IL-1 beta peptide constructs elicited the strongest cytotoxic responses at 2 weeks postinjection. Cytotoxic responses were seen in all animals, even those lacking OVA-specific Ab, and were not related to Ab level. These studies indicate that the humoral, cytokine, and cytotoxic responses to DNA vaccination can be effectively altered by certain cytokine fusion constructs.

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.

Lymphoproliferation and cytokine profiles in human peripheral blood mononuclear cells stimulated by Cryptococcus neoformans

Cell-mediated immunity is critical to host defenses against the fungal infection cryptococcosis. Here, two functions critical to effective cell-mediated immunity (CMI), lymphoproliferation and cytokine release, were studied in Cryptococcus neoformans-stimulated peripheral blood mononuclear cells (PBMC) from seven healthy donors (controls) and two patients with cryptococcosis. PBMC responses to C. neoformans were compared with responses to Candida albicans. Control and patient PBMC had significant lymphoproliferation in response to whole C. neoformans, with peak proliferation seen following 8 days of culture, but only patient PBMC proliferated when stimulated with C. neoformans mannoprotein. C. neoformans-stimulated control PBMC released IL-2, IFN-gamma, and IL-10 into the supernatant with peak or near peak concentrations of these three cytokines generally seen by day 1. Release of IL-4 was low or undetectable. In contrast, C. neoformans-stimulated patient PBMC released IFN-gamma, which peaked on day 7, as well as IL-4, IL-10, and in one of two patients, IL-2. Cytokine release occurred later in patient (compared with control) PBMC. Lymphoproliferation and cytokine release were similar comparing control PBMC stimulated with C. neoformans versus Candida albicans. Thus, the magnitude and kinetics of the lymphoproliferative response to whole C. neoformans is similar comparing PBMC from controls and patients, but the cytokine profiles differ. Moreover, the capacity of patient PBMC to respond to soluble mannoprotein lends support to studies of mannoprotein components as vaccine candidates.