Cryptococcus neoformans Infection in the Central Nervous System: The Battle between Host and Pathogen

Mechanisms and Virulence Factors of Cryptococcus neoformans Dissemination to the Central Nervous System

Cryptococcosis is a prevalent fungal infection of the central nervous system (CNS) caused by Cryptococcus neoformans, a yeast with a polysaccharide capsule in the basidiomycete group. Normally, C. neoformans infects the respiratory tract and then breaches the blood-brain barrier (BBB), leading to meningitis or meningoencephalitis, which leads to hundreds of thousands of deaths each year. Although the mechanism by which C. neoformans infiltrates the BBB to invade the brain has yet to be fully understood, research has revealed that C. neoformans can cross the BBB using transcellular penetration, paracellular traversal, and infected phagocytes (the "Trojan horse" mechanism). The secretion of multiple virulence factors by C. neoformans is crucial in facilitating the spread of infection after breaching the BBB and causing brain infections. Extensive research has shown that various virulence factors play a significant role in the dissemination of infection beyond the lungs. This review explores the mechanisms of C. neoformans entering the CNS and explains how it bypasses the BBB. Additionally, it aims to understand the interplay between the regulatory mechanisms and virulence factors of C. neoformans.

Clinical features and prognostic factors of cryptococcal infections in HIV-infected patients: a 10-year study from an infectious disease specialist hospital

Background

Cryptococcosis is an invasive infection that commonly affects immunosuppressed individuals, especially patients with HIV infection. Cryptococcal infection in HIV-infected patients should be considered a major health concern because it is associated with high morbidity and mortality rates. In this study, we aimed to evaluate the clinical characteristics and prognostic factors of cryptococcal infections in human immunodeficiency virus (HIV)-infected patients to facilitate effective clinical management and improve patient outcomes.

Methods

We reviewed and analyzed the clinical data and relevant laboratory test results of HIV-infected patients with positive cryptococcal cultures and reserved strains between 2013 and 2023 from Beijing Youan Hospital affiliated to Capital Medical University. The clinical characteristics and laboratory test results of the patients were compared, and the correlation between parameters and the prognoses of the patients at different observation timepoints (3, 6, 9, and 12 months) was analyzed.

Results

A total of 76 patients (70 males and six females; median age, 37 years) were included in this study. The results indicated that the later the initiation of antiretroviral therapy (ART) after the diagnosis of HIV infection (> 6 months), the higher the probability of death. Analysis of the correlation between the time of ART initiation and the timing of treatment for cryptococcal infections showed that the time of ART initiation was strongly related to survival at different timepoints. Initiation of ART time within 0-4 weeks, 4-6 weeks and more than 6weeks of starting treatment for Cryptococcus infection was associated with a lower mortality rate at 12-month, the 3-month, 6- and 9-month follow-up timepoint separately.

Conclusions

Although cryptococcal infection in HIV-infected patients continues to be a challenging and intricate issue, ART is a key factor that affects its prognosis. The later ART is started, the worse the prognosis of the infection. The time of ART initiation and the timing of treatment for cryptococcal infections should be further refined and balanced based on different clinical courses. Thus, clinicians should pay closer attention to cryptococcal infections in patients with HIV infection and initiate ART based on the patient's clinical condition.

Elucidation of furanone as ergosterol pathway inhibitor in Cryptococcus neoformans

In the era of antiretroviral therapy, the prevalence of Cryptococcal infection among HIV patients in developed countries has decreased considerably. However, C. neoformans ranks top among the critical priority pathogen that affects a wide range of immunocompromised individuals. The threat of C. neoformans is because of its incredibly multifaceted intracellular survival capabilities. Cell membrane sterols especially ergosterol and enzymes of its biosynthetic pathway are considered fascinating drug targets because of their structural stability. In this study, the ergosterol biosynthetic enzymes were modeled and docked with furanone derivatives. Among the tested ligands Compound 6 has shown a potential interaction with Lanosterol 14 α-demethylase. This best-docked protein-ligand complex was taken further to molecular dynamics simulation. In addition, Compound 6 was synthesized and an in vitro study was conducted to quantify the ergosterol in Compound 6 treated cells. Altogether the computational and in vitro study demonstrates that Compound 6 has anticryptococcal activity by targeting the biosynthetic pathway of ergosterol.Communicated by Ramaswamy H. Sarma.

Destructive Cryptococcal Osteomyelitis Mimicking Tuberculous Spondylitis

BACKGROUND Cryptococcosis is an opportunistic fungal infection that typically occurs in patients with compromised immune systems, primarily affecting the respiratory and central nervous systems. However, cryptococcal osteomyelitis is a rare manifestation of cryptococcal infection, characterized by nonspecific clinical features. Here, we present a case of vertebral cryptococcal osteomyelitis in a middle-aged woman and discuss diagnostic approaches. CASE REPORT A 56-year-old woman presented with lower back pain and limited mobility, without fever, and with a history of pulmonary tuberculosis. Physical examination revealed enlarged lymph nodes and tenderness in the thoracic vertebrae. A computed tomography-guided biopsy confirmed granulomatous inflammation caused by Cryptococcus, with abundant 10 μm spherical microbial spores. After 4 weeks of treatment with amphotericin B and fluconazole, symptoms and lesions improved. Upon discharge, the patient was prescribed oral fluconazole. Follow-up examinations showed a stable condition and a negative serum cryptococcal capsular polysaccharide antigen test. CONCLUSIONS Given the rarity and lack of specificity of clinical features of cryptococcal spondylitis, clinicians encountering similar presentations should consider tuberculous spondylitis and spinal tumors as differential diagnoses. Additionally, tissue biopsy of the affected vertebral bodies should be performed early to establish the type of vertebral infection, aiding in diagnosis, treatment, and prognosis.

Pleiotropic roles of LAMMER kinase, Lkh1 in stress responses and virulence of Cryptococcus neoformans

Dual-specificity LAMMER kinases are highly evolutionarily conserved in eukaryotes and play pivotal roles in diverse physiological processes, such as growth, differentiation, and stress responses. Although the functions of LAMMER kinase in fungal pathogens in pathogenicity and stress responses have been characterized, its role in Cryptococcus neoformans, a human fungal pathogen and a model yeast of basidiomycetes, remains elusive. In this study, we identified a LKH1 homologous gene and constructed a strain with a deleted LKH1 and a complemented strain. Similar to other fungi, the lkh1Δ mutant showed intrinsic growth defects. We observed that C. neoformans Lkh1 was involved in diverse stress responses, including oxidative stress and cell wall stress. Particularly, Lkh1 regulates DNA damage responses in Rad53-dependent and -independent manners. Furthermore, the absence of LKH1 reduced basidiospore formation. Our observations indicate that Lkh1 becomes hyperphosphorylated upon treatment with rapamycin, a TOR protein inhibitor. Notably, LKH1 deletion led to defects in melanin synthesis and capsule formation. Furthermore, we found that the deletion of LKH1 led to the avirulence of C. neoformans in a systemic cryptococcosis murine model. Taken together, Lkh1 is required for the stress response, sexual differentiation, and virulence of C. neoformans.

Global trends in Cryptococcus and its interactions with the host immune system: a bibliometric analysis

Objectives

This manuscript undertakes a systematic examination of the research landscape concerning global Cryptococcus species and their dynamism with the host immune system spanning the past decade. It furnishes a detailed survey of leading knowledge institutions and critical focal points in this area, utilizing bibliometric analysis.

Methods

VOSviewer and CiteSpace software platforms were employed to systematically analyze and graphically depict the relevant literature indexed in the WoSCC database over the preceding ten years.

Results

In the interval between October 1, 2013, and October 1, 2023, a corpus of 795 publications was amassed. The primary research institutions involved in this study include Duke University, the University of Minnesota, and the University of Sydney. The leading trio of nations, in terms of publication volume, comprises the United States, China, and Brazil. Among the most prolific authors are Casadevall, Arturo; Wormley, Floyd L., Jr.; and Olszewski, Michal A., with the most highly cited author being Perfect, Jr. The most esteemed journal is Mbio, while Infection and Immunity commands the highest citation frequency, and the Journal of Clinical Microbiology boasts the most significant impact factor. Present research foci encompass the intricate interactions between Cryptococcus pathogenesis and host immunity, alongside immune mechanisms, complications, and immunotherapies.

Conclusion

This represents the first exhaustive scholarly review and bibliometric scrutiny of the evolving landscapes in Cryptococcus research and its interactions with the host immune system. The analyses delineated herein provide insights into prevailing research foci and trajectories, thus furnishing critical directions for subsequent inquiries in this domain.

Unveiling the menace: a thorough review of potential pandemic fungal disease

Fungal diseases have emerged as a significant global health threat, with the potential to cause widespread outbreaks and significant morbidity and mortality. Anticipating future pandemic fungal diseases is essential for effective preparedness and response strategies. This comprehensive literature review aims to provide a comprehensive analysis of the existing research on this topic. Through an extensive examination of scholarly articles, this review identifies potential fungal pathogens that have the potential to become pandemics in the future. It explores the factors contributing to the emergence and spread of these fungal diseases, including climate change, globalization, and antimicrobial resistance. The review also discusses the challenges in diagnosing and treating these diseases, including limited access to diagnostic tools and antifungal therapies. Furthermore, it examines the strategies and interventions that can be employed to mitigate the impact of future pandemic fungal diseases, such as improved surveillance systems, public health education, and research advancements. The findings of this literature review contribute to our understanding of the potential risks posed by fungal diseases and provide valuable insights for public health professionals and policymakers in effectively preparing for and responding to future pandemic outbreaks. Overall, this review emphasizes the importance of proactive measures and collaborative efforts to anticipate and mitigate the impact of future pandemic fungal diseases.

Host-Pathogen Interactions and Correlated Factors That Are Affected in Replicative-Aged Cryptococcus neoformans

Cryptococcus neoformans is a facultative intracellular fungal pathogen. Ten-generation-old (10GEN) C. neoformans cells are more resistant to phagocytosis and killing by macrophages than younger daughter cells. However, mechanisms that mediate this resistance and intracellular parasitism are poorly understood. Here, we identified important factors for the intracellular survival of 10GEN C. neoformans, such as urease activity, capsule synthesis, and DNA content using flow cytometry and fluorescent microscopy techniques. The real-time visualization of time-lapse imaging was applied to determine the phagosomal acidity, membrane permeability, and vomocytosis (non-lytic exocytosis) rate in J774 macrophages that phagocytosed C. neoformans of different generational ages. Our results showed that old C. neoformans exhibited higher urease activity and enhanced Golgi activity. In addition, old C. neoformans were more likely to be arrested in the G2 phase, resulting in the occasional formation of aberrant trimera-like cells. To finish, the advanced generational age of the yeast cells slightly reduced vomocytosis events within host cells, which might be associated with increased phagolysosome pH and membrane permeability. Altogether, our results suggest that old C. neoformans prevail within acidic phagolysosomes and can manipulate the phagosome pH. These strategies may be used by old C. neoformans to resist phagosomal killing and drive cryptococcosis pathogenesis. The comprehension of these essential host-pathogen interactions could further shed light on mechanisms that bring new insights for novel antifungal therapeutic design.

Preclinical Models for Cryptococcosis of the CNS and Their Characterization Using In Vivo Imaging Techniques

Infections caused by Cryptococcus neoformans and Cryptococcus gattii remain a challenge to our healthcare systems as they are still difficult to treat. In order to improve treatment success, in particular for infections that have disseminated to the central nervous system, a better understanding of the disease is needed, addressing questions like how it evolves from a pulmonary to a brain disease and how novel treatment approaches can be developed and validated. This requires not only clinical research and research on the microorganisms in a laboratory environment but also preclinical models in order to study cryptococci in the host. We provide an overview of available preclinical models, with particular emphasis on models of cryptococcosis in rodents. In order to further improve the characterization of rodent models, in particular the dynamic aspects of disease manifestation, development, and ultimate treatment, preclinical in vivo imaging methods are increasingly used, mainly in research for oncological, neurological, and cardiac diseases. In vivo imaging applications for fungal infections are rather sparse. A second aspect of this review is how research on models of cryptococcosis can benefit from in vivo imaging methods that not only provide information on morphology and tissue structure but also on function, metabolism, and cellular properties in a non-invasive way.

Fungal infections in patients after recovering from COVID-19: a systematic review

Background and aims

The presence of fungal infections has been described in patients after recovering from COVID-19. This study aims to conduct a systematic review of studies that reported fungal infections (Mucor spp., Pneumocystis jirovecii, or Aspergillus spp.) in adults after recovering from COVID-19.

Methods

We performed a systematic review through PubMed, Web of Science, OVID-Medline, Embase, and Scopus. The study selection process was performed independently and by at least two authors. We performed a risk of bias assessment using the Newcastle-Ottawa Scale for cohort and case-control studies, and the Joanna Briggs Institute's Checklists for Case Series and Case Reports.

Results

The systematic search found 33 studies meeting all inclusion criteria. There was a total population of 774 participants, ranging from 21 to 87 years. From them, 746 developed a fungal infection. In 19 studies, Mucor spp. was reported as the main mycosis. In 10 studies, P. jirovecii was reported as the main mycosis. In seven studies, Aspergillus spp. was reported as the main mycosis. Regarding the quality assessment, 12 studies were classified as low risk of bias and the remaining studies as high risk of bias.

Conclusion

Patients' clinical presentation and prognosis after recovering from COVID-19 with fungal infection differ from those reported patients with acute COVID-19 infection and those without COVID-19 infection.

Macropinocytosis as a potential mechanism driving neurotropism of Cryptococcus neoformans

Cryptococcus neoformans can invade the central nervous system by crossing the blood-brain barrier via a transcellular mechanism that relies on multiple host factors. In this narrative, we review the evidence that a direct interplay between C. neoformans and brain endothelial cells forms the basis for invasion and transmigration across the brain endothelium. Adherence and internalization of C. neoformans is dependent on transmembrane proteins, including a hyaluronic acid receptor and an ephrin receptor tyrosine kinase. We consider the role of EphA2 in facilitating the invasion of the central nervous system by C. neoformans and highlight experimental evidence supporting macropinocytosis as a potential mechanism of internalization and transcytosis. How macropinocytosis might be conclusively demonstrated in the context of C. neoformans is also discussed.

BIOMOLECULAR ACTIVITY OF CRYPTOCOCCUS DURING CRYPTOCOCCOSIS: A REVIEW OF MOLECULAR INTERACTIONS OF CRYPTOCOCCUS WITH HUMAN IMMUNE SYSTEM AND BLOOD-BRAIN-BARRIER

Global mycosis is still a problem. One of these is the cryptococcal disease. A systemic mycosis brought on by Cryptococcus is called cryptococcosis. Host immunological conditions influence infection with Cryptococcosis. When environmental spores are inhaled by the host, the spores get to the lungs, an infection is created. Alveolar macrophages and other immune cells recognize Cryptococcus in the lung. The initial line of defense against pathogens in the phagolysosome is provided by alveolar macrophages found in the lungs. When the immune system is weak, Cryptococcus uses the evasion system as a molecular interaction with the immune system and persists in the lungs without causing any symptoms such as Factor Transcription, Cell masking, N-glycan structure, Extracellular molecule, and Antioxidant system. The evasion mechanism protects and makes Cryptococcus disseminate throughout the other organs, especially CNS. If Cryptococcus escapes against the host immune system, it will disseminate to other organs, especially Cerebrospinal System by Three mechanisms. There are Trojan Horse, Paracellular, and Transcellular interactions with Blood-Brain Barrier. Disease severity is determined by the Interaction between the host's immune system and the fungus.

Cryptococcal meningitis and cerebral vasculitis in a patient with primary intestinal lymphangiectasia: a case report

Primary intestinal lymphangiectasia (Waldmann's disease) is a rare exudative enteropathy without precisely assessed infectious risk. We report the case of a 49-year-old male patient with meningitis and cerebral vasculitis due to Cryptococcus neoformans complicating Waldmann's disease diagnosed 12 years ago. The treatment combined liposomal amphotericin B, 3 mg/kg daily plus flucytosine 25 mg/kg/6 h, both intravenously during 15 days, then fluconazole 800 mg daily during 8 weeks, and finally 200 mg daily indefinitely. Dexamethasone 0.4 mg/kg daily during the first week was gradually decreased over 2 months. The outcome was good, and the patient is still followed 3 years later without any recurrence.

New silicate-substituted hydroxyapatite materials doped with silver ions as potential antifungal agents

BACKGROUND

Hydroxyapatites (HAp) are widely used as medical preparations for e.g., bone replacement or teeth implants. Incorporation of various substrates into HAp structures could enhance its biological properties, like biocompatibility or antimicrobial effects. Silver ions possess high antibacterial and antifungal activity and its application as HAp dopant might increase its clinical value.

RESULTS

New silicate-substituted hydroxyapatites (HAp) doped with silver ions were synthesized via hydrothermal methods. The crystal structure of HAp was investigated by using the X-ray powder diffraction. Antifungal activity of silver ion-doped HAp (with 0.7 mol%, 1 mol% and 2 mol% of dopants) was tested against the yeast-like reference and clinical strains of Candida albicans, C. glabrata, C. tropicalis, Rhodotorula rubra, R. mucilaginosa, Cryptococcus neoformans and C. gattii. Spectrophotometric method was used to evaluate antifungal effect of HAp in SD medium. It was shown that already the lowest dopant (0.7 mol% of Ag⁺ ions) significantly reduced fungal growth at the concentration of 100 µg/mL. Increase in the dopant content and the concentration of HAp did not cause further growth inhibition. Moreover, there were some differences at the tolerance level to Ag⁺ ion-doped HAp among tested strains, suggesting strain-specific activity.

CONCLUSIONS

Preformed studies confirm antimicrobial potential of hydroxyapatite doped with silver. New Ag⁺ ion-HAp material could be, after further studies, considered as medical agent with antifungal properties which lower the risk of a surgical-related infections.

Innate Pulmonary Phagocytes and Their Interactions with Pathogenic Cryptococcus Species

Cryptococcus neoformans is an opportunistic fungal pathogen that causes over 180,000 annual deaths in HIV/AIDS patients. Innate phagocytes in the lungs, such as dendritic cells (DCs) and macrophages, are the first cells to interact with the pathogen. Neutrophils, another innate phagocyte, are recruited to the lungs during cryptococcal infection. These innate cells are involved in early detection of C. neoformans, as well as the removal and clearance of cryptococcal infections. However, C. neoformans has developed ways to interfere with these processes, allowing for the evasion of the host's innate immune system. Additionally, the innate immune cells have the ability to aid in cryptococcal pathogenesis. This review discusses recent literature on the interactions of innate pulmonary phagocytes with C. neoformans.

Clinical and Epidemiological Characteristics of Neurocryptococcosis Associated with HIV in Northeastern Brazil

Cryptococcal meningitis is a serious infection of the central nervous system that is predominant in developing countries, caused by fungi of the genus Cryptococcus, and which affects immunosuppressed patients, especially those with HIV. Here, we aim to diagnose and characterize the clinical-epidemiological profile of cryptococcosis in patients admitted to two tertiary public hospitals in northeastern Brazil. The study is divided into three moments: (1) the isolation of fungus and diagnosis from biological samples collected between 2017 and 2019, (2) a description of the clinical and epidemiological characteristics of the patients, and (3) the experimental tests related to an in vitro susceptibility antifungal profile. The species were identified by MALDI-TOF/MS. Among the 100 patients evaluated, 24 (24.5%) were diagnosed with cryptococcosis based on positive culture. Clinical-epidemiological analysis showed a slightly higher prevalence in men between 30 and 39 years. When comparing the date of HIV diagnosis and the development of cryptococcosis, it was observed that 50% received the diagnosis of infection by cryptococcosis after or equal to a period of 12 months from being diagnosed with HIV; the other 50% received it within the first 30 days of the HIV diagnosis. Neurocryptococcosis was the most prevalent clinical form, and, at the time of hospital admission, the most common clinical signs were high fever (75%), intense headache (62.50%), and neck stiffness (33.33%). The cerebrospinal fluid showed 100% sensitivity and positivity for direct examination by India ink, and fungal culture. The mortality rate in this study was 46% (11/24), a lower rate than in the other literature. An antifungigram showed that 20 (83.33%) isolates were susceptible to amphotericin B and 15 (62.5%) to fluconazole. Mass spectrometry identified 100% of the isolates as Cryptococcus neoformans. In Brazil, this infection is not mandatory notifiable. Therefore, although there is little information on the subject, it is obsolete and does not express the reality of the facts, mainly in the northeast region, where this information is insufficient. The data obtained in this research contribute to the epidemiological knowledge of this mycosis in Brazil and will serve as a basis for future globally comparative epidemiological studies.

Alternatively activated lung alveolar and interstitial macrophages promote fungal growth

How lung macrophages, especially interstitial macrophages (IMs), respond to invading pathogens remains elusive. Here, we show that mice exhibited a rapid and substantial expansion of macrophages, especially CX3CR1+ IMs, in the lung following infection with Cryptococcus neoformans, a pathogenic fungus leading to high mortality among patients with HIV/AIDS. The IM expansion correlated with enhanced CSF1 and IL-4 production and was affected by the deficiency of CCR2 or Nr4a1. Both alveolar macrophages (AMs) and IMs were observed to harbor C. neoformans and became alternatively activated following infection, with IMs being more polarized. The absence of AMs by genetically disrupting CSF2 signaling reduced fungal loads in the lung and prolonged the survival of infected mice. Likewise, infected mice depleted of IMs by the CSF1 receptor inhibitor PLX5622 displayed significantly lower pulmonary fungal burdens. Thus, C. neoformans infection induces alternative activation of both AMs and IMs, which facilitates fungal growth in the lung.

Entrapment Syndrome in a Kidney Transplant Recipient with Cryptococcal Meningitis

Cryptococcus neoformans primarily affects immunocompromised individuals and the central nervous system (CNS) is the most common site of dissemination. Entrapped temporal horn syndrome (ETH) remains a rare CNS manifestation and has not previously been described in solid organ transplant recipients. Here, we present a case of ETH in a 55-year-old woman with history of renal transplant and prior treated Cryptococcal meningitis.

Cerebral Cryptococcosis Associated with CD4+ T-lymphocytopenia in Non-HIV Patients after SARS-CoV-2 Infection: Case Series in a Specialized Institute in Lima, Peru

Cases of cryptococcosis have been reported in patients with COVID-19. The majority are in patients with severe symptoms or who received immunosuppressants. However, there is still no clear association between COVID-19 and cryptococcosis. We report eight cases of cerebral cryptococcosis associated with CD4+ T lymphocytopenia in non-HIV patients after SARS-CoV-2 infection. The median age was 57 years and 5/8 were male. In addition, 2/8 of patients had diabetes, and 8/8 had a history of mild COVID-19, with a median of 75 days before diagnosis of cerebral cryptococcosis. All patients denied having received prior immunosuppressive therapy. The most frequent symptoms were confusion (8/8), headache (7/8), vomiting (6/8), and nausea (6/8) All patients were diagnosed by isolating Cryptococcus in cerebrospinal fluid. The median CD4+ and CD8+ T lymphocytes were 247 and 173.5, respectively. Other causes of immunosuppression, such as HIV or HTLV infection, were excluded in all patients. Finally, three patients died, and one presented long-term visual and auditory sequelae. The CD4+/CD8+ T lymphocyte count normalized during follow-up in those patients who survived. We hypothesize that CD4+ T lymphocytopenia in the patients in this case series could increase the risk of cryptococcosis after SARS-CoV-2 infection.

Cerebrospinal fluid: a target of some fungi and an overview

Meningitis is a potentially life-threatening infection characterised by the inflammation of the leptomeningeal membranes. The estimated annual prevalence of 8.7 million cases globally and the disease is caused by many different viral, bacterial, and fungal pathogens. Although several genera of fungi are capable of causing infections in the central nervous system (CNS), the most significant number of registered cases have, as causal agents, yeasts of the genus Cryptococcus. The relevance of cryptococcal meningitis has changed in the last decades, mainly due to the increase in the number of people living with human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) and medications that impair the immune responses. In this context, coronavirus disease 19 (COVID-19) has also emerged as a risk factor for invasive fungal infections (IFI), including fungal meningitis (FM), due to severe COVID-19 disease is associated with increased pro-inflammatory cytokines, interleukin (IL)-1, IL-6, and tumour necrosis factor-alpha, reduced CD4-interferon-gamma expression, CD4 and CD8 T cells. The gold standard technique for fungal identification is isolating fungi in the culture of the biological material, including cerebrospinal fluid (CSF). However, this methodology has as its main disadvantage the slow or null growth of some fungal species in culture, which makes it difficult to finalise the diagnosis. In conclusions, this article, in the first place, point that it is necessary to accurately identify the etiological agent in order to assist in the choice of the therapeutic regimen for the patients, including the implementation of actions that promote the reduction of the incidence, lethality, and fungal morbidity, which includes what is healthy in the CNS.

Cryptococcal Immune Reconstitution Inflammatory Syndrome: From Clinical Studies to Animal Experiments

Cryptococcus neoformans is an encapsulated pathogenic fungus that initially infects the lung but can migrate to the central nervous system (CNS), resulting in meningoencephalitis. The organism causes the CNS infection primarily in immunocompromised individuals including HIV/AIDS patients, but also, rarely, in immunocompetent individuals. In HIV/AIDS patients, limited inflammation in the CNS, due to impaired cellular immunity, cannot efficiently clear a C. neoformans infection. Antiretroviral therapy (ART) can rapidly restore cellular immunity in HIV/AIDS patients. Paradoxically, ART induces an exaggerated inflammatory response, termed immune reconstitution inflammatory syndrome (IRIS), in some HIV/AIDS patients co-infected with C. neoformans. A similar excessive inflammation, referred to as post-infectious inflammatory response syndrome (PIIRS), is also frequently seen in previously healthy individuals suffering from cryptococcal meningoencephalitis. Cryptococcal IRIS and PIIRS are life-threatening complications that kill up to one-third of affected people. In this review, we summarize the inflammatory responses in the CNS during HIV-associated cryptococcal meningoencephalitis. We overview the current understanding of cryptococcal IRIS developed in HIV/AIDS patients and cryptococcal PIIRS occurring in HIV-uninfected individuals. We also describe currently available animal models that closely mimic aspects of cryptococcal IRIS observed in HIV/AIDS patients.

Exploring Cryptococcus neoformans CYP51 and Its Cognate Reductase as a Drug Target

Cryptococcus remains a leading cause of invasive fungal infections in immunocompromised people. Resistance to azole drugs has imposed a further challenge to the effective treatment of such infections. In this study, the functional expression of full-length hexahistidine-tagged Cryptococcus neoformans CYP51 (CnCYP51-6×His), with or without its cognate hexahistidine-tagged NADPH-cytochrome P450 reductase (CnCPR-6×His), in a Saccharomyces cerevisiae host system has been used to characterise these enzymes. The heterologous expression of CnCYP51-6×His complemented deletion of the host CYP51 and conferred increased susceptibility to both short-tailed and long-tailed azole drugs. In addition, co-expression of CnCPR-6×His decreased susceptibility 2- to 4-fold for short-tailed but not long-tailed azoles. Type 2 binding of azoles to CnCYP51-6×His and assay of NADPH cytochrome P450 reductase activity confirmed that the heterologously expressed CnCYP51 and CnCPR are functional. The constructs have potential as screening tools and use in structure-directed antifungal discovery.