Immune dysfunction in HIV-seronegative, Cryptococcus gattii meningitis

Clinical characteristics and prognostic factors of 60 patients with acquired immune deficiency syndrome combined with Cryptococcus neoformans

OBJECTIVE

Cryptococcal meningitis (CM) threatens people's health and is the main cause of opportunistic fungus-related death in acquired immune deficiency syndrome (AIDS) patients. Herein, we investigate the clinical characteristics and prognostic factors of AIDS patients with Cryptococcus neoformans in Wenzhou, Zhejiang Province, China.

METHODS

Our study enrolled AIDS patients diagnosed with Cryptococcus neoformans infection who were hospitalised in our hospital. They were divided into Group A (32 patients with CM) and Group B (28 patients without CM) according to their diagnosis. The differences between the two groups of patients' clinical symptoms, imaging examinations and laboratory examinations were observed. Statistical methods were used to analyse the difference in prognosis between the two groups.

RESULTS

Headache and fever were the most common clinical characteristics for patients with CM, while respiratory symptoms and fever were the most common clinical characteristics for patients without CM. The positive rate of cryptococcal capsular antigen, India ink staining and culture in the cerebrospinal fluid examination was higher in the CM patients than in the non-CM patients. The overall morbidity and mortality rate after systemic antifungal therapy was higher in the CM patients than in the non-CM patients. A higher incidence of headache, impaired consciousness, nuchal rigidity, first intracranial pressure > 200 mmH₂O and mortality was observed in the CM patients than in the non-CM patients. Multifactorial logistic regression analysis showed that headache risk factors affecting the patient's prognosis at 12 weeks.

CONCLUSION

Patients with AIDS diagnosed with Cryptococcus neoformans infection have insidious clinical symptoms in the early stage, and their manifestation is often non-specific, resulting in poor prognosis and high mortality among CM patients compared to patients without CM. Therefore, early identification and timely antifungal therapy before the disease progresses to meningitis are of great value in improving the survival rate of patients.

Effects of combination of Cryptococcus gattii and IFN-γ, IL-4 or IL-27 on human bronchial epithelial cells

BACKGROUND

Airway epithelial cells are crucial for the establishment of cryptococcosis. In experimental cryptococcosis, the Th2 immune response is associated with host susceptibility, while Th1 cells are associated with protection. The absence of IL-27 receptor alpha in mice favor the increase Cryptococcus neoformans burden in the lung. Here, we evaluated the effects of the combination of IL-4, IFN-γ or IL-27 with C. gattii on human bronchial epithelial cells (BEAS-2B).

METHODS

BEAS-2B were stimulated with IL-4, IFN-γ or IL-27 (100 ng/mL) and/or live yeast forms of C. gattii (multiplicities of infection (MOI) of 1-100) and vice-versa, as well as with heat-killed cells of C. gattii for 24 h.

RESULTS

None of the C. gattii MOIs had cytotoxic effects on BEAS-2B when compared to control. The cells stimulated by cytokines (IL-4, IFN-γ or IL-27) followed by live yeast forms of C. gattii (MOI of 100) infection and vice-versa demonstrated a reduction in IL-6, IL-8 and/or CCL2 production and activation of STAT6 (induced by IL-4) and STAT1 (induced by IL-27 or IFN-γ) when compared to cells stimulated with C. gattii, IL-4, IFN-γ or IL-27. In the combination of cytokines and heat-killed cells of C. gattii, no inhibition of these inflammatory parameters was observed. The growth of C. gattii was increased while the phagocytosis of live yeast forms of C. gattii in the BEAS-2B were reduced in the presence of IL-4, IFN-γ or IL-27. Conclusion The association of live yeast forms, but not heat-killed yeast forms, of C. gattii with IL-4, IFN-γ or IL-27 induced an anti-inflammatory effect.

Cryptococcosis in the Vocal Cords, Trachea, and Bronchi

Laryngeal and endobronchial cryptococcosis are rare conditions, and to our knowledge, there have been only 23 cases of laryngeal cryptococcosis, and 18 cases of endobronchial cryptococcosis previously reported in the English literature. We herein report an extremely rare case of cryptococcosis with simultaneous laryngeal and endobronchial involvement. This case highlights the importance of paying close attention to possible occurrence of cryptococcosis of the airway tract in patients with asthma treated with high-dose inhaled corticosteroids.

Cryptococcosis caused by cryptococcus gattii: 2 case reports and literature review

Cryptococcosis caused by Cryptococcus gattii, is a life threatening fungal infection with recently increasing prevalence. C. gattii is a species complex comprising multiple independent species. However, many biological characteristics and clinical features of cryptococcosis due to C. gattii are relatively less well defined. In this paper, we identify two cases of C. gattii infection, and laboratory findings of genotype VGI and VGII in two groups of apparently immunocompetent Chinese individuals respectively. Upon detailed review of all 35 cases of C. gattii infections, it was observed that C. gattii can cause debilitating illness in both immunocompetent and immunocompromised individuals. Cryptococcosis due to C. gattii is a serious systemic fungal infection, with pulmonary central nervous system tropism. Epidemiologically, C. gattii infection is not only restricted in tropical and subtropical regions, but also in other geographical settings.

Cryptococcal Meningitis in an Apparent Immunocompetent Patient

Cryptococcal meningitis is an uncommon and severe infection that tends to affect immunocompromised hosts worldwide and in the United States. Annually it is estimated that there are 200 000 cases of cryptococcal meningitis, with the most recent estimate of 3400 cases per year in the United States alone. However, despite the low incidence, 1-year mortality is estimated at 20% to 30% even with long-term consolidation antifungal therapy. A 37-year-old man presented to the emergency department with headaches, dysarthria, hallucinations, and acute worsening of altered mental status, and he was found to have increased intracranial pressure, cerebrospinal fluid leukocytosis, and few encapsulated yeasts consistent with Cryptococcus neoformans meningitis in addition to radiologic evidence consistent with a cryptococcoma of the lungs. This report highlights the occurrence of Cryptococcus neoformans meningitis in a presumed immunocompetent host. The clinician should be aware of sources of minor immunosuppression, as they may contribute to development of Cryptococcus neoformans meningitis. Mortality in this condition remains high due to subacute presentations and delayed diagnosis in non-immunocompromised patients.

Incidental Cryptococcal lung mass in an immunocompetent patient

Cryptococcus is an encapsulated fungal organism often implicated in central nervous system and pulmonary disease in patients with AIDS or other immunocompromising diseases. However, immunocompetent hosts can also be infected. In these cases, symptoms are generally mild and common radiographic findings include small, well-defined, smoothly marginated pulmonary nodules. We present a case of a 31-year-old man without any immunocompromising factors found to have pulmonary Cryptococcal infection presenting as a large lung mass.

Cryptococcus gattii Complex Infections in HIV-Infected Patients, Southeastern United States

Increased awareness of C. gattii infections in these patients is critical for improving diagnosis, treatment, and outcomes.

Cryptococcus gattii traditionally infects immunocompetent hosts and causes devastating pulmonary or central nervous system disease. However, this infection rarely occurs in patients infected with HIV. We report 3 cases of HIV-associated C. gattii complex infections in the southeastern United States. Detection of C. gattii in HIV-infected patients in this region warrants increased awareness of this threat to ensure appropriate diagnosis and treatment to optimize patient outcomes.

Differential In Vitro Cytokine Induction by the Species of Cryptococcus gattii Complex

Cryptococcal species vary in capsule and cell size, thermotolerance, geographic distribution, and affected populations. Cryptococcus gattii sensu stricto and C. deuterogattii affect mainly immunocompetent hosts; however, C. bacillisporus, C. decagattii, and C. tetragattii cause infections mainly in immunocompromised hosts. This study aimed to compare the capacities of different species of the C. gattii species complex to induce cytokines and antimicrobial molecules in human peripheral blood mononuclear cells (PBMCs). Cryptococcus bacillisporus and C. deuterogattii induced the lowest levels of tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), and IL-6 among the five species of the C. gattii complex. Cryptococcus deuterogattii induced higher levels of IL-22 than those induced by C. tetragattii and the environmental species C. flavescens In addition, C. bacillisporus and C. gattii sensu stricto proliferated inside human monocyte-derived macrophages after 24 h of infection. All Cryptococcus species were able to generate reactive oxygen species (ROS) in human PBMCs, with C. bacillisporus and C. deuterogattii being more efficient than the other species. In conclusion, C. bacillisporus and C. deuterogattii induce lower levels of the proinflammatory cytokines TNF-α, IL-1β, and IL-6 and higher ROS levels than those induced by the other species. Species of the Cryptococcus gattii complex have different abilities to induce cytokine and ROS production by human PBMCs.

Cytokine patterns in a prospective cohort of HIV-infected patients with cryptococcal meningitis following initiation of antifungal and antiretroviral therapy

Cryptococcal meningitis (CM) is a life-threatening infection in HIV-infected patients, especially in resource-limited settings. Cytokine patterns in the cerebrospinal fluid (CSF) and sera may be related to clinical outcomes. This study aimed to evaluate cytokine patterns in the CSF and sera of HIV-infected patients with CM as well as the cytokines produced by peripheral blood mononuclear cells (PBMCs) when stimulated with LPS and cryptococcal GXM. CSF and serum levels of IL-2, IL-4, IL-8, IL-10, IL-12p40, IL-17A, INF-γ, TNF-α and CXCL-10 were measured in HIV-infected patients with CM (CM⁺ HIV⁺) at various time points. Cytokine levels were evaluated in the PBMC culture supernatants and the baseline values were compared to those of HIV-infected patients without CM (CM^- HIV⁺) and healthy controls (CM^- HIV^-). CSF cytokine levels at admission (n = 33) were higher than levels among the 23 survivors at week 2, but statistically significant differences were observed for IL-8 and IFN-γ (p<0.05). CSF and serum levels of IL-4 and IL-17A at week 10 (n = 16) were lower than the baseline values, whereas IL-2 levels increased compared to week 2 (p<0.05). At week 16 (n = 15), CSF and serum levels of IL-4, IL-10 and CXCL-10 were decreased compared to the baseline values (p<0.05). PBMCs from CM^- HIV^- individuals produced significantly higher levels of proinflammatory cytokines in response to LPS, with the exception of TNF-α, which showed higher levels among CM⁺ HIV⁺ patients. The PBMCs of CM patients produced higher levels of IL-4 than those of CM^- HIV^- patients in response to GXM stimulation, and levels progressively decreased during treatment (p<0.05). Then, a progressive shift in cytokine expression favoring a Th1 pattern was observed, which is crucial in controlling cryptococcal infection. A better understanding of the protective immune response against Cryptococcus neoformans will help to develop novel strategies to improve the outcomes of patients with cryptococcosis.

Immunization with Antigen-Pulsed Dendritic Cells Against Highly Virulent Cryptococcus gattii Infection: Analysis of Cytokine-Producing T Cells

Cryptococcosis caused by highly virulent Cryptococcus gattii (Hv-Cg) is an emerging infectious disease that affects immunocompetent individuals. The Hv-Cg outbreak began in 1999, but the mechanisms responsible for its hyper-virulence as well as protective immunity against Hv-Cg infection remain to be elucidated. To better understand the protective immunity against Hv-Cg infection, we developed a novel immunization method using antigen-pulsed dendritic cells (DCs). We constructed a capsule-deficient Cg strain (∆cap60) and used it as a vaccine antigen. Mouse bone marrow-derived DCs were pulsed with ∆cap60 and transferred into mice twice before pulmonary infection with Hv-Cg strain R265. This DC-based immunization strongly induced cell-mediated immunity, including Th1 cells, Th17 cells, and multinucleated giant cells enclosing fungal cells in lungs. This vaccination significantly ameliorated the fungal burden and the survival rate after pulmonary infection with R265. The efficacy of DC-based immunization was significantly but partially reduced in IFNγ-deficient mice, thereby suggesting that the Th1 and Th17 responses play roles in vaccine-induced protection against Hv-Cg infection. This approach might provide new insights into overcoming Hv-Cg infections in immunocompetent subjects. In this chapter, we describe the procedures for DC-vaccine preparation and the analysis of cytokine-producing CD4⁺ T cells.

Dendritic Cell-Based Vaccine Against Fungal Infection

Several pathogenic fungi, including Cryptococcus gattii, Histoplasma capsulatum, Coccidioides immitis, and Penicillium marneffei, cause serious infectious diseases in immunocompetent humans. However, currently, prophylactic and therapeutic vaccines are not clinically used. In particular, C. gattii is an emerging pathogen and thus far protective immunity against this pathogen has not been well characterized. Experimental vaccines such as component and attenuated live vaccines have been used as tools to study protective immunity against fungal infection. Recently, we developed a dendritic cell (DC)-based vaccine to study protective immunity against pulmonary infection by highly virulent C. gattii strain R265 that was clinically isolated from bronchial washings of infected patients during the Vancouver Island outbreak. In this approach, bone marrow-derived DCs (BMDCs) are pulsed with heat-killed C. gattii and then transferred into mice prior to intratracheal infection. This DC vaccine significantly increases interleukin 17A (IL-17A)-, interferon gamma (IFN-γ)-, and tumor necrosis factor alpha (TNF-α)-producing T cells in the lungs and spleen and ameliorates the pathology, fungal burden, and mortality following C. gattii infection. This approach may result in the development of a new means of controlling lethal fungal infections. In this chapter, we describe the procedures of DC vaccine preparation and murine pulmonary infection model for analysis of immune response against C. gattii.

Deubiquitinase Ubp5 Is Required for the Growth and Pathogenicity of Cryptococcus gattii

Cryptococcus gattii is a resurgent fungal pathogen that primarily infects immunocompetent hosts. Thus, it poses an increasingly significant impact on global public health; however, the mechanisms underlying its pathogenesis remain largely unknown. We conducted a detailed characterization of the deubiquitinase Ubp5 in the biology and virulence of C. gattii using the hypervirulent strain R265, and defined its properties as either distinctive or shared with C. neoformans. Deletion of the C. gattii Ubp5 protein by site-directed disruption resulted in a severe growth defect under both normal and stressful conditions (such as high temperature, high salt, cell wall damaging agents, and antifungal agents), similar to the effects observed in C. neoformans. However, unlike C. neoformans, the C. gattii ubp5Δ mutant displayed a slight enhancement of capsule and melanin production, indicating the evolutionary convergence and divergence of Ubp5 between these two sibling species. Attenuated virulence of the Cg-ubp5Δ mutant was not solely due to its reduced thermotolerance at 37°C, as shown in both worm and mouse survival assays. In addition, the assessment of fungal burden in mammalian organs further indicated that Ubp5 was required for C. gattii pulmonary survival and, consequently, extrapulmonary dissemination. Taken together, our work highlights the importance of deubiquitinase Ubp5 in the virulence composite of both pathogenic cryptococcal species, and it facilitates a better understanding of C. gattii virulence mechanisms.

The absence of microbiota delays the inflammatory response to Cryptococcus gattii

The inflammatory response plays a crucial role in infectious diseases, and the intestinal microbiota is linked to maturation of the immune system. However, the association between microbiota and the response against fungal infections has not been elucidated. Our aim was to evaluate the influence of microbiota on Cryptococcus gattii infection. Germ-free (GF), conventional (CV), conventionalized (CVN-mice that received feces from conventional animals), and LPS-stimulated mice were infected with C. gattii. GF mice were more susceptible to infection, showing lower survival, higher fungal burden in the lungs and brain, increased behavioral changes, reduced levels of IFN-γ, IL-1β and IL-17, and lower NFκBp65 phosphorylation compared to CV mice. Low expression of inflammatory cytokines was associated with smaller yeast cells and polysaccharide capsules (the main virulence factor of C. gattii) in the lungs, and less tissue damage. Furthermore, macrophages from GF mice showed reduced ability to engulf, produce ROS, and kill C. gattii. Restoration of microbiota (CVN mice) or LPS administration made GF mice more responsive to infection, which was associated with increased survival and higher levels of inflammatory mediators. This study is the first to demonstrate the influence of microbiota in the host response against C. gattii.

Dendritic cell-based immunization ameliorates pulmonary infection with highly virulent Cryptococcus gattii

Cryptococcosis due to a highly virulent fungus, Cryptococcus gattii, emerged as an infectious disease on Vancouver Island in Canada and surrounding areas in 1999, causing deaths among immunocompetent individuals. Previous studies indicated that C. gattii strain R265 isolated from the Canadian outbreak had immune avoidance or immune suppression capabilities. However, protective immunity against C. gattii has not been identified. In this study, we used a gain-of-function approach to investigate the protective immunity against C. gattii infection using a dendritic cell (DC)-based vaccine. Bone marrow-derived dendritic cells (BMDCs) efficiently engulfed acapsular C. gattii (Δcap60 strain), which resulted in their expression of costimulatory molecules and inflammatory cytokines. This was not observed for BMDCs that were cultured with encapsulated strains. When Δcap60 strain-pulsed BMDCs were transferred to mice prior to intratracheal R265 infection, significant amelioration of pathology, fungal burden, and the survival rate resulted compared with those in controls. Multinucleated giant cells (MGCs) that engulfed fungal cells were significantly increased in the lungs of immunized mice. Interleukin 17A (IL-17A)-, gamma interferon (IFN-γ)-, and tumor necrosis factor alpha (TNF-α)-producing lymphocytes were significantly increased in the spleens and lungs of immunized mice. The protective effect of this DC vaccine was significantly reduced in IFN-γ knockout mice. These results demonstrated that an increase in cytokine-producing lymphocytes and the development of MGCs that engulfed fungal cells were associated with the protection against pulmonary infection with highly virulent C. gattii and suggested that IFN-γ may have been an important mediator for this vaccine-induced protection.

Cryptococcus gattii infection dampens Th1 and Th17 responses by attenuating dendritic cell function and pulmonary chemokine expression in the immunocompetent hosts

Cryptococcal infections are primarily caused by two related fungal species: Cryptococcus neoformans and Cryptococcus gattii. It is well known that C. neoformans generally affects immunocompromised hosts; however, C. gattii infection can cause diseases in not only immunocompromised hosts but also immunocompetent individuals. While recent studies suggest that C. gattii infection could dampen pulmonary neutrophil recruitment and inflammatory cytokine production in immunocompetent hosts, the impact of C. gattii infection on the development of their adaptive T helper cell immune response has not been addressed. Here, we report that C. neoformans infection with highly virulent and less virulent strains preferentially induced pulmonary Th1 and Th17 immune responses in the host, respectively. However, fewer pulmonary Th1 and Th17 cells could be detected in mice infected with C. gattii strains. Notably, dendritic cells (DC) in mice infected with C. gattii expressed much lower levels of surface MHC-II and Il12 or Il23 transcripts and failed to induce effective Th1 and Th17 differentiation in vitro. Furthermore, the expression levels of Ip10 and Cxcl9 transcripts, encoding Th1-attracting chemokines, were significantly reduced in the lungs of mice infected with the highly virulent C. gattii strain. Thus, our data suggest that C. gattii infection dampens the DC-mediated effective Th1/Th17 immune responses and downregulates the pulmonary chemokine expression, thus resulting in the inability to mount protective immunity in immunocompetent hosts.

Immunotherapy of Cryptococcus infections

Despite appropriate antifungal treatment, the management of cryptococcal disease remains challenging, especially in immunocompromised patients, such as human immunodeficiency virus-infected individuals and solid organ transplant recipients. During the past two decades, our knowledge of host immune responses against Cryptococcus spp. has been greatly advanced, and the role of immunomodulation in augmenting the response to infection has been investigated. In particular, the role of 'protective' Th1 (tumour necrosis factor-α, interferon (IFN)-γ, interleukin (IL)-12, and IL-18) and Th17 (IL-23 and IL-17) and 'non-protective' Th2 (IL-4, IL-10, and IL-13) cytokines has been extensively studied in vitro and in animal models of cryptococcal infection. Immunomodulation with monoclonal antibodies against the capsular polysaccharide glucuronoxylomannan, glucosylceramides, melanin and β-glucan and, lately, with radioimmunotherapy has also yielded promising results in animal models. As a balance between sufficiently protective Th1 responses and excessive inflammation is important for optimal outcome, the effect of immunotherapy may range from beneficial to deleterious, depending on factors related to the host, the infecting organism, and the immunomodulatory regimen. Clinical evidence supporting immunomodulation in patients with cryptococcal infection remains too limited to allow firm recommendations. Limited human data suggest a role for IFN-γ. Identification of surrogate markers characterizing patients' immunological status could possibly suggest candidate patients for immunotherapy and the type of immunomodulation to be administered.

Fatal disseminated Cryptococcus gattii infection in New Mexico

We report a case of fatal disseminated infection with Cryptococcus gattii in a patient from New Mexico. The patient had no history of recent travel to known C. gattii-endemic areas. Multilocus sequence typing revealed that the isolate belonged to the major molecular type VGIII. Virulence studies in a mouse pulmonary model of infection demonstrated that the strain was less virulent than other C. gattii strains. This represents the first documented case of C. gattii likely acquired in New Mexico.

Cryptococcus gattii genotype VGI infection in New England

Cryptococcus gattii is a known, emerging infectious disease pathogen predominantly in the Pacific Northwest, the United States, and British Columbia, Canada. We report a case of an immunocompetent adolescent from New England who had severe pulmonary and central nervous system infection caused by the VGI genotype of C. gattii.

Cryptococcus gattii: a resurgent fungal pathogen

Cryptococcus gattii and Cryptococcus neoformans are causal agents of cryptococcosis, which manifests as pneumonia and meningitis. C. gattii has recently received widespread attention owing to outbreaks in British Columbia, Canada and the US Pacific Northwest. The biology of this tree-dwelling yeast is relatively unexplored, and there are few clues about how it causes infections in humans and animals. In this review, we summarize recent discoveries about C. gattii genetics and its ecological niche and highlight areas ripe for future exploration. Increased focus on epidemiology, ecological modeling and host-pathogen interactions is expected to yield a better understanding of this enigmatic yeast, and ultimately lead to better measures for its control.

Exogenous interferon-gamma immunotherapy for invasive fungal infections in kidney transplant patients

The incidence of invasive fungal infections (IFIs) in nonneutropenic solid organ transplant patients is increasing. We report our clinical experience with the use of interferon-gamma (IFN-gamma) immunotherapy in seven renal transplant patients who developed life threatening, disseminated IFIs refractory to conventional antifungal drug therapy. The infections were all microbiologically and histologically proven. The rapid cure of these disseminated infections with exogenous IFN-gamma injections was not associated with impaired kidney allograft function despite the use of liposomal amphotericin B in all cases. No clinical toxicity from the IFN-gamma immunotherapy was seen and no IFI relapsed during long-term follow-up. Our experience is both uncontrolled and in patients with unpredictable fungal infection-related outcomes. However, compared to standard approaches, the accelerated cure of life threatening, disseminated IFIs with 6 weeks of combination antifungal drug therapy and IFN-gamma immunotherapy saved lives, retained allograft function and led to substantial cost savings in this small patient group.

Clinical practice guidelines for the management of cryptococcal disease: 2010 update by the infectious diseases society of america

Cryptococcosis is a global invasive mycosis associated with significant morbidity and mortality. These guidelines for its management have been built on the previous Infectious Diseases Society of America guidelines from 2000 and include new sections. There is a discussion of the management of cryptococcal meningoencephalitis in 3 risk groups: (1) human immunodeficiency virus (HIV)-infected individuals, (2) organ transplant recipients, and (3) non-HIV-infected and nontransplant hosts. There are specific recommendations for other unique risk populations, such as children, pregnant women, persons in resource-limited environments, and those with Cryptococcus gattii infection. Recommendations for management also include other sites of infection, including strategies for pulmonary cryptococcosis. Emphasis has been placed on potential complications in management of cryptococcal infection, including increased intracranial pressure, immune reconstitution inflammatory syndrome (IRIS), drug resistance, and cryptococcomas. Three key management principles have been articulated: (1) induction therapy for meningoencephalitis using fungicidal regimens, such as a polyene and flucytosine, followed by suppressive regimens using fluconazole; (2) importance of early recognition and treatment of increased intracranial pressure and/or IRIS; and (3) the use of lipid formulations of amphotericin B regimens in patients with renal impairment. Cryptococcosis remains a challenging management issue, with little new drug development or recent definitive studies. However, if the diagnosis is made early, if clinicians adhere to the basic principles of these guidelines, and if the underlying disease is controlled, then cryptococcosis can be managed successfully in the vast majority of patients.

Cryptococcus gattii isolates from the British Columbia cryptococcosis outbreak induce less protective inflammation in a murine model of infection than Cryptococcus neoformans

The fungal pathogen Cryptococcus neoformans causes approximately one million cases of cryptococcosis per year in people with AIDS. In contrast, the related species C. gattii is responsible for a much smaller number of cases, but these often occur in immunocompetent people. In fact, C. gattii has emerged in the last decade as the frequent cause of cryptococcosis in otherwise healthy people in British Columbia. We analyzed the immune responses elicited by three C. gattii strains and one C. neoformans strain in mice as a first step toward understanding why C. gattii is able to cause disease in immunocompetent hosts. The C. gattii strains all induced a less protective inflammatory response in C57BL/6 mice by inhibiting or failing to provoke the migration of neutrophils to sites of infection. The C. gattii strains also failed to elicit the production of protective cytokines, such as tumor necrosis factor alpha, compared to the ability of the C. neoformans strain. Despite these differences, the strain representing the major outbreak genotype from British Columbia showed a virulence equivalent to that of the C. neoformans strain, while two other C. gattii strains had reduced virulence. Taken together, our results indicate that C. gattii strains thrive in immunocompetent hosts by evading or suppressing the protective immune responses that normally limit the progression of disease caused by C. neoformans.

Central nervous system involvement in cryptococcal infection in individuals after solid organ transplantation or with AIDS

BACKGROUND

Cryptococcus neoformans is an important pathogen of immunocompromised hosts. Manifestations of cryptococcal infection have not been compared between populations based on the nature of the underlying immune deficiencies.

METHODS

The Prospective Antifungal Therapy Alliance (PATH) is a registry that collects clinical data from patients with invasive fungal infections from medical centers in North America. Univariate analyses and group comparisons were conducted from the PATH registry for cases of infection due to Cryptococcus species occurring between March 2004 and April 2008.

RESULTS

A total 235 cases of proven infection due to Cryptococcus species were documented, all of which were due to C. neoformans (52 in solid organ transplant [SOT] recipients, 107 in patients infected with the human immunodeficiency virus [HIV], and 76 with neither HIV nor organ transplantation). A total of 140 cases manifested as meningitis (25 in SOT recipients, 88 in HIV-positive patients, and 27 in those with neither risk factor). Of individuals with cryptococcal infection, 44.2% of SOT recipients had central nervous system (CNS) disease, while 84.1% of those with HIV infection presented with CNS involvement (P=0.0265). SOT recipients receiving calcineurin inhibitors (CNIs) were less likely to have CNS involvement in cryptococcal infection (40.1% versus 66.7%). Overall, 12-week mortality for patients with cryptococcal infection in the PATH Alliance registry was 22.6% (21.2% for SOT, 15.9% for HIV-infected patients, and 32.9% for patients with risk factors other than HIV infection or organ transplantation).

CONCLUSIONS

In a prospectively assembled cohort of individuals with proven infection due to C. neoformans, CNS involvement was more common in individuals with HIV infection than in SOT recipients. The role of CNIs in the reduction of risk for CNS cryptococcosis remains to be defined. Overall survival of patients with cryptococcal infection in immunocompromised hosts has improved over time. Observed differences in the context of various host immune deficits provide a basis for further investigation of cryptococcosis and other opportunistic infections.

Managing cryptococcosis in the immunocompromised host

PURPOSE OF REVIEW

Expanding access to antiretroviral treatment has dramatically improved the long-term prognosis of patients with HIV-associated cryptococcal disease who survive the acute infection. However, the incidence and acute mortality of HIV-associated cryptococcal meningitis remain high. In this context, this review summarizes urgently needed recent work aimed at improving the acute management of cryptococcal infection in immunocompromised hosts.

RECENT FINDINGS

Studies have started to optimize antifungal regimens and address the complications of raised cerebrospinal fluid pressure and cryptococcal immune reconstitution syndrome. Amphotericin B at 1 mg/kg per day has been shown to be more rapidly fungicidal than the standard dose of 0.7 mg/kg per day, and new data support the importance of combination therapy with flucytosine. Amphotericin B and fluconazole at 800 mg is an alternative combination that appears superior to amphotericin B alone. At a dosage of 400 mg per day, fluconazole alone is much less rapidly fungicidal than amphotericin B and is associated with the development of secondary resistance.

SUMMARY

Recent findings support the use of rapidly fungicidal initial antifungal therapy with amphotericin B-based combination treatment. Where amphotericin B treatment is not yet feasible, studies are needed to optimize oral regimens. Based on accumulating data on rate of clearance of infection, the most promising new regimens in terms of fungicidal activity and safety could be selected for clinical endpoint trials.

Phenotypic switching in Cryptococcus neoformans contributes to virulence by changing the immunological host response

Cryptococcus neoformans is an encapsulated opportunistic organism that can undergo phenotypic switching. In this process, the parent smooth colony (SM) switches to a more virulent mucoid colony (MC) variant. The host responses mounted against the SM and MC variants differ, and lower tissue interleukin 10 (IL-10) levels are consistently observed in lungs of MC-infected C57BL/6 and BALB/c mice. This suggested different roles of this cytokine in SM and MC infections. The objective of this study was to compare survival rates and characterize the host responses of SM- and MC-infected IL-10-depleted (IL-10(-/-)) mice, which exhibit a Th1-polarized immune response and are considered resistant hosts. As expected, SM-infected IL-10(-/-) mice survived longer than wild-type mice, whereas MC-infected IL-10(-/-) mice did not exhibit a survival benefit. Consistent with this observation, we demonstrated marked differences in the inflammatory responses of SM- and MC-infected IL-10(-/-) and wild-type mice. This included a more Th1-polarized inflammatory response with enhanced recruitment of macrophages and natural killer and CD8 cells in MC- than in SM-infected IL-10(-/-) and wild-type mice. In contrast, both SM-infected IL-10(-/-) and wild-type mice exhibited higher recruitment of CD4 cells, consistent with enhanced survival and differences in recruitment and Th1/Th2 polarization. Lung tissue levels of IL-21, IL-6, IL-4, transforming growth factor beta, IL-12, and gamma interferon were higher in MC-infected IL-10(-/-) and wild-type mice than in SM-infected mice, whereas tumor necrosis factor alpha levels were higher in SM-infected IL-10(-/-) mice. In conclusion, the MC variant elicits an excessive inflammatory response in a Th1-polarized host environment, and therefore, the outcome is negatively affected by the absence of IL-10.