David L. Goldman

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.

Persistent Cryptococcus neoformans pulmonary infection in the rat is associated with intracellular parasitism, decreased inducible nitric oxide synthase expression, and altered antibody responsiveness to cryptococcal polysaccharide

ABSTRACT Fungal pathogens are notorious for causing chronic and latent infections, but the mechanism by which they evade the immune response is poorly understood. A major limitation in the study of chronic fungal infection has been the lack of suitable animal models where the infection is controlled and yet persists. Pulmonary Cryptococcus neoformans infection in rats results in a diffuse pneumonitis that resolves without dissemination or scarring except for the persistence of interstitial and subpleural granulomas that harbor viable cryptococci inside macrophages and epithelioid cells. Infected rats are asymptomatic but remain infected for as long as 18 months after inoculation with C. neoformans. Containment of infection is associated with granuloma formation that can be partially abrogated by glucocorticoid administration. Using this model, we identified several features associated with persistent infection in the rat lung, including (i) localization of C. neoformans to discrete, well-organized granulomas; (ii) intracellular persistence ofC. neoformans within macrophages and epithelioid cells; (iii) reduced inducible nitric oxide synthase expression by granulomas harboring C. neoformans; and (iv) reduced antibody responses to cryptococcal polysaccharide. The results show that maintenance of persistent infection is associated with downregulation of both cellular and humoral immune responses.

An Innate Immune System Cell Is a Major Determinant of Species-Related Susceptibility Differences to Fungal Pneumonia

Rats and mice are considered resistant and susceptible hosts, respectively, for experimental cryptococcosis. For both species, alveolar macrophages (AM) are central components of the host response to pulmonary Cryptococcus neoformans infection. We explored the role of AM in three strains of mice and three strains of rats during cryptococcal infection by comparing the outcome of infection after macrophage depletion using liposomal clodronate. AM depletion was associated with enhancement and amelioration of disease in rats and mice, respectively, as measured by lung fungal burden. The apparent protective role for AM in rats correlated with enhanced anticryptococcal activity as measured by phagocytic activity, oxidative burst, lysozyme secretion, and ability to limit intracellular growth of C. neoformans. Furthermore, rat AM were more resistant to lysis in association with intracellular infection. In summary, differences in AM function in rats and mice suggest an explanation for the species differences in susceptibility to C. neoformans based on the inherent efficacy of a central effector cell of the innate immune system.

Neurologic Manifestations Associated with Parvovirus B19 Infection

Eighty-one cases of neurologic disease, including encephalitis, meningitis, stroke, and peripheral neuropathy, that were associated with parvovirus B19 infection were reviewed. Most patients were children, and two-thirds had central nervous system manifestations. One-third had altered immunity. Viral symptoms (odds ratio [OR], 5.7; P= .002), rash (OR, 11.5; P< .001), and peripheral nervous system involvement (OR, 12.1; P= .004) were more frequent in immunocompetent patients. Brain magnetic resonance imaging abnormalities were more frequent in patients with altered immunity (OR, 10; P= .04). In central nervous system disease, parvovirus B19 DNA was commonly detected in cerebrospinal fluid (81% of samples) and serum (85%), whereas specific antibodies were found in 33% of cerebrospinal fluid samples. Neurologic sequelae occurred in 22% of 77 patients with a known outcome, and some improvement occurred in 16%. No differences in the prevalence of sequealae were noted between immunocompetent patients (21% of whom experienced sequealae) and patients with altered immunity (25%) or between patients with central nervous system manifestations who received intravenous immunoglobulin with or without steroids and those patients with central nervous system manifestations who did not. Five patients died.

Serologic Evidence for Reactivation of Cryptococcosis in Solid-Organ Transplant Recipients

ABSTRACT Cryptococcosis is a significant infection with a high mortality in solid-organ transplant recipients. Nonetheless, the pathogenesis of this disease is poorly understood. It has been hypothesized that cryptococcosis may result from either primary infection or reactivation of a latent infection. Sera were obtained from transplant recipients prior to transplantation and at the time they developed cryptococcosis. Control sera were obtained before and after transplant from patients who did not develop cryptococcosis. Sera were tested for antibodies against Cryptococcus neoformans by using an immunoblot assay. Antibody responses were also compared with those observed in sera from rats with experimental pulmonary cryptococcosis. In all, 52% of the transplant recipients who developed cryptococcosis exhibited serologic evidence of cryptococcal infection before transplantation. These patients developed cryptococcosis significantly earlier after transplant than patients without preexisting reactivity did (5.6 ± 3.4 months compared to 40.6 ± 63.8 months, respectively [P = 0.0011]). The results from our study suggest that a substantial proportion of transplant-associated cryptococcosis cases result from the reactivation of a latent infection. These findings also highlight the potential utility of serologic studies in identifying patients at risk for the development of cryptococcosis after transplantation.

A Monoclonal Antibody to Bacillus anthracis Protective Antigen Defines a Neutralizing Epitope in Domain 1

ABSTRACT Antibody (Ab) responses to Bacillus anthracis toxins are protective, but relatively few protective monoclonal antibodies (MAbs) have been reported. Protective antigen (PA) is essential for the action of B. anthracis lethal toxin (LeTx) and edema toxin. In this study, we generated two MAbs to PA, MAbs 7.5G and 10F4. These MAbs did not compete for binding to PA, consistent with specificities for different epitopes. The MAbs were tested for their ability to protect a monolayer of cultured macrophages against toxin-mediated cytotoxicity. MAb 7.5G, the most-neutralizing MAb, bound to domain 1 of PA and reduced LeTx toxicity in BALB/c mice. Remarkably, MAb 7.5G provided protection without blocking the binding of PA or lethal factor or the formation of the PA heptamer complex. However, MAb 7.5G slowed the proteolytic digestion of PA by furin in vitro, suggesting a potential mechanism for Ab-mediated protection. These observations indicate that some Abs to domain 1 can contribute to host protection.

Fcγ Receptor I- and III-Mediated Macrophage Inflammatory Protein 1α Induction in Primary Human and Murine Microglia

ABSTRACT Microglial cell phagocytic receptors may play important roles in the pathogenesis and treatment of several neurological diseases. We studied microglial Fc receptor (FcR) activation with respect to the specific FcγR types involved and the downstream signaling events by using monoclonal antibody (MAb)-coated Cryptococcus neoformans immune complexes as the stimuli and macrophage inflammatory protein 1α (MIP-1α) production as the final outcome. C. neoformans complexed with murine immunoglobulin G (IgG) of γ1, γ2a, and γ3, but not γ2b isotype, was effective in inducing MIP-1α in human microglia. Since murine γ2b binds to human FcγRII (but not FcγRI or FcγRIII), these results indicate that FcγRI and/or FcγRIII is involved in MIP-1α production. Consistent with this, an antibody that blocks FcγRII (IV.3) failed to inhibit MIP-1α production, while an antibody that blocks FcγRIII (3G8) did. An anti-C. neoformans MAb, 18B7 (IgG1), but not its F(ab′)2, induced extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase kinase phosphorylation, and MIP-1α release was suppressed by the ERK inhibitor U0126. C. neoformans plus 18B7 also induced degradation of I-κBα, and MIP-1α release was suppressed by the antioxidant NF-κB inhibitor pyrrolidine dithiocarbamate. To confirm the role of FcR more directly, we isolated microglia from wild-type and various FcR-deficient mice and then challenged them with C. neoformans plus 18B7. While FcγRII-deficient microglia showed little difference from the wild-type microglia, both FcγRI α-chain- and FcγRIII α-chain-deficient microglia produced less MIP-1α, and the common Fc γ-chain-deficient microglia showed no MIP-1α release. Taken together, our results demonstrate a definitive role for FcγRI and FcγRIII in microglial chemokine induction and implicate ERK and NF-κB as the signaling components leading to MIP-1α expression. Our results delineate a new mechanism for microglial activation and may have implications for central nervous system inflammatory diseases.

Effect of Immune Mechanisms on the Pharmacokinetics and Organ Distribution of Cryptococcal Polysaccharide

Cryptococcus neoformans is an encapsulated opportunistic fungus that can cause chronic infections accompanied by high tissue levels of capsular polysaccharide (CPS). CPS or its major component, glucuronoxylomannan (GXM), was administered to mice, and whole-body and tissue levels were measured. The role of monoclonal antibody (MAb), complement, and CD4 T cells in GXM clearance was also examined. These studies demonstrate that CPS is cleared from the blood within days but is retained in the body for weeks; that MAbs of all isotypes examined promote GXM clearance; that MAb-mediated GXM deposition in liver, but not in spleen, is Fc-dependent; that complement enhances IgM-mediated GXM sequestration in liver but not spleen; and that CD4 T cells are not necessary for serum GXM clearance. The results have important implications for the eventual use of MAbs in treatment of cryptococcosis.

Enhanced Allergic Inflammation and Airway Responsiveness in Rats with Chronic Cryptococcus neoformans Infection: Potential Role for Fungal Pulmonary Infection in the Pathogenesis of Asthma

Although Cryptococcus neoformans is recognized for its ability to cause meningoencephalitis and pneumonia among immunocompromised persons, subclinical pulmonary infection is also common among immunocompetent persons. The significance of this infection is unknown. Using a rat model, we explored the potential for pulmonary cryptococcosis to modify allergic responses and airway reactivity. Our findings indicate that localized pulmonary cryptococcal infection (but not disseminated infection) can exacerbate allergic responses to respiratory challenge with ovalbumin, as measured by total immunoglobulin E levels, ovalbumin-specific immunoglobulin E titers, and eosinophil content of bronchoalveolar lavage fluid. Infection-associated enhancement of allergic responses was not dependent on cryptococcal encapsulation and was partially ameliorated by the administration of fluconazole. Increases in both the number of goblet cells and airway responsiveness, which are also features of reactive airway disease, were also present with pulmonary infection. An examination of lung cytokine levels in the context of active pulmonary infection revealed increased expression of interleukin (IL)-10, tumor necrosis factor- alpha , and IL-13, but not IL-12 or interferon- gamma . In contrast, systemic infection was associated with higher levels of interferon- gamma but lower levels of IL-13. Our studies highlight the potential for localized pulmonary C. neoformans infection to potentiate allergic responses and airway reactivity and suggest a potential role for subclinical pulmonary cryptococcosis in the pathogenesis of asthma.

Phenotypic switching in Cryptococcus neoformans

Phenotypic switching has been described in serotype A and D strains of Cryptococcus neoformans. It occurs in vivo during chronic infection and is associated with differential gene expression and changes in virulence. The switch involves changes in the polysaccharide capsule and cell wall that affect the yeasts ability to resist phagocytosis. In addition, the phenotypic switch variants elicit qualitatively different inflammatory responses in the host. In animal models of chronic cryptococosis, the immune response of the host ultimately determines which of the switch variants are selected and maintained. The importance of phenotypic switching is further underscored by several findings that are relevant in the setting of human disease. These include the ability of the mucoid colony variant of RC-2 (RC-2 MC) but not the smooth variant (RC-2 SM) to promote increased intracerebral pressure in a rat model of cryptococcal meningitis. Furthermore, chemotherapeutic and immunological antifungal interventions can promote the selection of the RC-2 MC variant during chronic murine infection.