Compartmentalization of innate immune responses in the central nervous system during cryptococcal meningitis/HIV coinfection

Baseline Serum C-Reactive Protein Level Predicts Mortality in Cryptococcal Meningitis

BACKGROUND

C-reactive protein (CRP) is an acute phase protein produced by the liver in response to systemic inflammation. CRP is a helpful surrogate biomarker used for following the progression and resolution of infection. We aimed to determine the association of baseline CRP level and the temporal change in CRP over time with cryptococcal meningitis outcome.

METHODS

We reviewed 168 prospectively enrolled HIV-infected Ugandans with confirmed first-episode cryptococcal meningitis. Baseline plasma CRP collected within 5 days of meningitis diagnosis was categorized into quartiles. We compared baseline CRP with 18-week survival using time-to-event analysis.

RESULTS

Of 168 participants, the baseline first quartile of serum CRP was <29.0 mg/L, second quartile 29.0-49.5 mg/L, third quartile 49.6-83.6 mg/L, and fourth quartile >83.6 mg/L. Baseline CD4 count, HIV viral load, and cerebrospinal fluid results did not differ by CRP quartile. Participants with CRP >49.5 mg/L more likely presented with Glasgow Coma Scale (GCS) <15 (P = .03). The 18-week mortality rate was 55% (46/84) in the highest 2 quartile CRP groups (>49.5 mg/L), 41% (17/42) in the mid-range CRP group (29.0-49.5 mg/L), and 14% (6/42) in the low-CRP group (<29.0 mg/L; P < .001). After adjustment for possible confounding factors including GCS <15, CRP remained significantly associated with mortality (adjusted hazard ratio, 1.084 per 10 mg/L; 95% CI, 1.031-1.139; P = .0016).

CONCLUSIONS

Higher baseline CRP is associated with increased mortality in HIV-infected individuals with first-episode cryptococcal meningitis. CRP could be a surrogate marker for undiagnosed coinfections or may reflect immune dysregulation, leading to worse outcomes in persons with advanced AIDS and concomitant cryptococcal meningitis.

Chemokine receptor CXCR3 is required for lethal brain pathology but not pathogen clearance during cryptococcal meningoencephalitis

Cryptococcal meningoencephalitis (CM) is the major cause of infection-related neurological death, typically seen in immunocompromised patients. However, T cell-driven inflammatory response has been increasingly implicated in lethal central nervous system (CNS) immunopathology in human patients and murine models. Here, we report marked up-regulation of the chemokine receptor CXCR3 axis in human patients and mice with CM. CXCR3 deletion in mice improves survival, diminishes neurological deficits, and limits neuronal damage without suppressing fungal clearance. CD4+ T cell accumulation and TH1 skewing are reduced in the CNS but not spleens of infected CXCR3-/- mice. Adoptive transfer of WT, but not CXCR3-/- CD4+ T cells, into CXCR3-/- mice phenocopies the pathology of infected WT mice. Collectively, we found that CXCR3+CD4+ T cells drive lethal CNS pathology but are not required for fungal clearance during CM. The CXCR3 pathway shows potential as a therapeutic target or for biomarker discovery to limit CNS inflammatory damages.

Immune cell characteristics and cytokine responses in adult HIV-negative tuberculous meningitis: an observational cohort study

Immunopathology contributes to high mortality in tuberculous meningitis (TBM) but little is known about the blood and cerebrospinal fluid (CSF) immune response. We prospectively characterised the immune response of 160 TBM suspects in an Indonesian cohort, including 67 HIV-negative probable or definite TBM cases. TBM patients presented with severe disease and 38% died in 6 months. Blood from TBM patients analysed by flow cytometry showed lower αβT and γδT cells, NK cells and MAIT cells compared to 26 pulmonary tuberculosis patients (2.4-4-fold, all p < 0.05) and 27 healthy controls (2.7-7.6-fold, p < 0.001), but higher neutrophils and classical monocytes (2.3-3.0-fold, p < 0.001). CSF leukocyte activation was higher than in blood (1.8-9-fold). CSF of TBM patients showed a predominance of αβT and NK cells, associated with better survival. Cytokine production after ex-vivo stimulation of whole blood showed a much broader range in TBM compared to both control groups (p < 0.001). Among TBM patients, high ex-vivo production of TNF-α, IL-6 and IL-10 correlated with fever, lymphocyte count and monocyte HLA-DR expression (all p < 0.05). TBM patients show a strong myeloid blood response, with a broad variation in immune function. This may influence the response to adjuvant treatment and should be considered in future trials of host-directed therapy.

Individuals with HIV-1 Subtype C Infection and Cryptococcal Meningitis Exhibit Viral Genetic Intermixing of HIV-1 Between Plasma and Cerebrospinal Fluid and a High Prevalence of CXCR4-Using Variants

The genotypic properties of human immunodeficiency virus type 1 (HIV-1) subtype C in individuals presenting with cryptococcal meningitis (CM) are not well established. Employing single-genome amplification as well as bulk PCR, cloning and sequencing strategies, we evaluated the genetic properties of HIV-1 subtype C env in 16 antiretroviral therapy-naive study participants with CM. Eleven of the 16 participants had matched blood plasma and cerebrospinal fluid (CSF) evaluated, with the rest having either a plasma or CSF sample evaluated. Before antiretroviral therapy initiation, matched plasma and CSF-derived env sequences of all 11 participants displayed genetic intermixing between the two compartments. Overall, 7 of the 16 (∼43.8%) participants harbored CXCR4-using variants in plasma and/or CSF, according to coreceptor usage prediction algorithms. This study suggests that HIV-1 subtype C genetic intermixing between peripheral blood and the central nervous system is common in individuals presenting with CM, and that CXCR4 usage is present in one or both compartments in approximately 44% of individuals.

Plasma But Not Cerebrospinal Fluid Interleukin 7 and Interleukin 5 Levels Pre-Antiretroviral Therapy Commencement Predict Cryptococcosis-Associated Immune Reconstitution Inflammatory Syndrome

Background

Patients with human immunodeficiency virus/AIDS-associated cryptococcal meningitis (CM) frequently experience clinical deterioration, known as cryptococcosis-associated immune reconstitution inflammatory syndrome (C-IRIS), upon initiation of antiretroviral therapy (ART). The immunological mechanisms underlying C-IRIS are incompletely defined and no reliable predictive biomarkers exist. We investigated whether plasma or cerebrospinal fluid (CSF) levels of cytokines and chemokines predicted C-IRIS and are potential predictive biomarkers.

Methods

Patients with CM who experienced C-IRIS (N = 27) upon ART initiation were compared to CD4+ T-cell count-matched patients without C-IRIS (N = 27). Plasma and CSF collected pre-ART were assayed for cytokines and chemokines using a 17-plex Luminex kit or enzyme-linked immunosorbent assay. Cox proportional hazards regression and principal component analyses were also performed.

Results

Plasma interleukin (IL) 2, IL-4, IL-5, IL-7, IL-17, interferon-γ, and tumor necrosis factor-α levels were higher in C-IRIS patients compared to controls (all P < .05), with IL-5 and IL-7 significant after Bonferroni-Holm correction. In multivariate Cox proportional hazards regression, high IL-5 (hazard ratio [HR], 5.76 [95% confidence interval {CI}, .77-43.0]; P = .088) and IL-7 (HR, 9.30 [95% CI, 1.96-44.0]; P = .005) were predictive of C-IRIS. Plasma IL-5 (P = .0008) and IL-10 (P = .0089) were lower in those who achieved CSF cryptococcal culture negativity compared to those with positive cultures pre-ART. There were no significant differences in CSF cytokine or chemokine levels between cases and controls.

Conclusions

High plasma IL-5 and IL-7 levels pre-ART were associated with increased risk of developing C-IRIS. High IL-5 levels may reflect a Th2 environment associated with impaired clearance of cryptococci while high IL-7 levels may reflect IL-7/IL-7R pathway dysfunction in T cells, both of which could be associated with C-IRIS immunopathogenesis.

In vitro and in vivo effect of PD-1/PD-L1 blockade on microglia/macrophage activation and T cell subset balance in cryptococcal meningitis

This study aimed to investigate the PD-1/ PD-L1 signaling pathway and its effects the activation of microglia/macrophage and balancing T cell subsets in cryptococcal meningitis (CM). A total of 126 CM patients and 126 healthy individuals were recruited for the study. The CM patients were treated with amphotericin B (AmB). Seventy five C57BL/6 mice were grouped into the normal control, CM model, CM + AmB, sham, and CM + PD-1 antibodies (Ab) groups. CD4⁺ and CD8⁺ T cells as well as microglia/macrophages were analyzed by means of flow cytometry. Ionized calcium-binding adaptor molecule 1 (Ibal) expression was detected using western blotting and immunohistochemistry techniques. And the expression of Rab5 and Rab11 were detected using an immunofluorescence assay. Both PD-1 and PD-L1 mRNA and protein expression among the mice in the study were evaluated by qRT-PCR and western blotting methods. Compared to the CM model group, the CM + AmB and CM + PD-1 Ab groups exhibited increased levels of Th1 cytokines and chemokines expression, and reduced levels of Th2 cytokines expressions. Elevated cell purity and viability of CD4⁺ T cell were recorded as well as increases in microglia, however, there were reductions in the number of CD8⁺ T cells. Depleted expressions of Ibal, Rab5, and Rab11 as well as reduced mRNA expressions of PD-1 and PD-L1 in CD4⁺ , microglia, and macrophage cells. The findings suggested that suppression of the PD-1/PD-L1 signaling pathway restricts the proliferation of CM by down-regulating the expressions of Th2 cells and suppressing microglia and macrophage activation.

Monocyte Phenotype and IFN-γ-Inducible Cytokine Responses Are Associated with Cryptococcal Immune Reconstitution Inflammatory Syndrome

A third of adults with AIDS and cryptococcal meningitis (CM) develop immune reconstitution inflammatory syndrome (IRIS) after initiating antiretroviral therapy (ART), which is thought to result from exaggerated inflammatory antigen-specific T cell responses. The contribution of monocytes to the immunopathogenesis of cryptococcal IRIS remains unclear. We compared monocyte subset frequencies and immune responses in HIV-infected Ugandans at time of CM diagnosis (IRIS-Baseline) for those who later developed CM-IRIS, controls who did not develop CM-IRIS (Control-Baseline) at CM-IRIS (IRIS-Event), and for controls at a time point matched for ART duration (Control-Event) to understand the association of monocyte distribution and immune responses with cryptococcal IRIS. At baseline, stimulation with IFN-γ ex vivo induced a higher frequency of TNF-α- and IL-6-producing monocytes among those who later developed IRIS. Among participants who developed IRIS, ex vivo IFN-γ stimulation induced higher frequencies of activated monocytes, IL-6⁺, TNF-α⁺ classical, and IL-6⁺ intermediate monocytes compared with controls. In conclusion, we have demonstrated that monocyte subset phenotype and cytokine responses prior to ART are associated with and may be predictive of CM-IRIS. Larger studies to further delineate innate immunological responses and the efficacy of immunomodulatory therapies during cryptococcal IRIS are warranted.

Relationship of Human Immunodeficiency Virus Viral Load in Cerebrospinal Fluid and Plasma in Patients Co-infected With Cryptococcal Meningitis

We measured human immunodeficiency virus (HIV) ribonucleic acid (RNA) in paired cerebrospinal fluid (CSF) and plasma samples in a prospective study of 91 HIV-infected, antiretroviral therapy-naive patients with cryptococcal meningitis. Cerebrospinal fluid HIV RNA was lower than in plasma (median 4.7 vs 5.2 log₁₀ copies/mL, P < .0001) and positively correlated with plasma HIV RNA, peripheral CD4⁺ T-cell percentage, and CSF CXCL10. Plasma/CSF ratio of HIV RNA ranged widely from 0.2 to 265.5 with a median of 2.6. Cerebrospinal fluid quantitative cryptococcal culture positively correlated with CSF CCL2 and CCL3. CSF-plasma viral discordance was not associated with cryptococcal-associated immune reconstitution inflammatory syndrome.

The immunopathogenesis of cryptococcal immune reconstitution inflammatory syndrome: understanding a conundrum

PURPOSE OF REVIEW

Cryptococcal meningitis causes significant mortality among HIV-infected patients, despite antifungal therapy and use of antiretroviral therapy (ART). In patients with cryptococcal meningitis, ART is often complicated by immune reconstitution inflammatory syndrome (IRIS), manifesting as unmasking of previously unrecognized subclinical infection (unmasking CM-IRIS) or paradoxical worsening of symptoms in the central nervous system after prior improvement with antifungal therapy (paradoxical CM-IRIS). We review our current understanding of the pathogenesis of this phenomenon, focusing on unifying innate and adaptive immune mechanisms leading to the development of this often fatal syndrome.

RECENT FINDINGS

We propose that HIV-associated CD4 T-cell depletion, chemokine-driven trafficking of monocytes into cerebrospinal fluid in response to cryptococcal meningitis, and poor localized innate cytokine responses lead to inadequate cryptococcal killing and clearance of the fungus. Subsequent ART-associated recovery of T-cell signaling and restored cytokine responses, characterized by IFN-γ production, triggers an inflammatory response. The inflammatory response triggered by ART is dysregulated because of impaired homeostatic and regulatory mechanisms, culminating in the development of CM-IRIS.

SUMMARY

Despite our incomplete understanding of the immunopathogenesis of CM-IRIS, emerging data exploring innate and adaptive immune responses could be exploited to predict, prevent and manage CM-IRIS and associated morbid consequences.

Paradoxical Immune Responses in Non-HIV Cryptococcal Meningitis

The fungus Cryptococcus is a major cause of meningoencephalitis in HIV-infected as well as HIV-uninfected individuals with mortalities in developed countries of 20% and 30%, respectively. In HIV-related disease, defects in T-cell immunity are paramount, whereas there is little understanding of mechanisms of susceptibility in non-HIV related disease, especially that occurring in previously healthy adults. The present description is the first detailed immunological study of non-HIV-infected patients including those with severe central nervous system (s-CNS) disease to 1) identify mechanisms of susceptibility as well as 2) understand mechanisms underlying severe disease. Despite the expectation that, as in HIV, T-cell immunity would be deficient in such patients, cerebrospinal fluid (CSF) immunophenotyping, T-cell activation studies, soluble cytokine mapping and tissue cellular phenotyping demonstrated that patients with s-CNS disease had effective microbiological control, but displayed strong intrathecal expansion and activation of cells of both the innate and adaptive immunity including HLA-DR+ CD4+ and CD8+ cells and NK cells. These expanded CSF T cells were enriched for cryptococcal-antigen specific CD4+ cells and expressed high levels of IFN-γ as well as a lack of elevated CSF levels of typical T-cell specific Th2 cytokines -- IL-4 and IL-13. This inflammatory response was accompanied by elevated levels of CSF NFL, a marker of axonal damage, consistent with ongoing neurological damage. However, while tissue macrophage recruitment to the site of infection was intact, polarization studies of brain biopsy and autopsy specimens demonstrated an M2 macrophage polarization and poor phagocytosis of fungal cells. These studies thus expand the paradigm for cryptococcal disease susceptibility to include a prominent role for macrophage activation defects and suggest a spectrum of disease whereby severe neurological disease is characterized by immune-mediated host cell damage.

Cryptococcus is an important cause of fungal meningitis with significant mortality globally. Susceptibility to the fungus in humans has been related to T-lymphocyte defects in HIV-infected individuals, but little is known about possible immune defects in non HIV-infected patients including previously healthy individuals. This latter group also has some of the worst response rates to therapy with almost a third dying in the United States, despite available therapy. Here we conducted the first detailed immunological analysis of non-HIV apparently immunocompetent individuals with active cryptococcal disease. In contrast to HIV-infected individuals, these studies identified a highly activated antigen-presenting dendritic cell population within CSF, accompanied by a highly active T-lymphocyte population with potentially damaging inflammatory cytokine responses. Furthermore, elevated levels of CSF neurofilament light chains (NFL), a marker of axonal damage in severe central nervous system infections suggest a dysfunctional role to this acute inflammatory state. Paradoxically, CSF macrophage proportions were reduced in patients with severe disease and biopsy and autopsy samples identified alternatively activated tissue macrophage populations that failed to appropriately phagocytose fungal cells. Our study thus provides new insights into the susceptibility to human cryptococcal disease and identifies a paradoxically active T-lymphocyte response that may be amenable to adjunctive immunomodulation to improve treatment outcomes in this high-mortality disease.

Neuro OIs: developed and developing countries

PURPOSE OF REVIEW

To review recent studies that address the pathogenesis, diagnosis and treatment of HIV positive patients with cryptococcal and tuberculous meningitis and progressive multifocal leukoencephalopathy in resource-different settings.

RECENT FINDINGS

Central nervous system opportunistic infections remain globally prevalent in HIV+ populations. Several recent papers have highlighted the urgent need for rapid point of care tests in low-income settings for cryptococcal and tuberculous meningitis, better access to antifungal therapy for cryptococcal meningitis and better treatment strategies for tuberculous meningitis. In one recent study of 299 HIV+ patients with cryptococcal meningitis, amphotericin plus flucytosine was associated with less mortality and disability compared to amphotericin alone. In a study of patients with tuberculous meningitis in Indonesia, short-term, high dose rifampicin and moxifloxacin, designed to achieve higher levels of anti-TB drugs in the brain, saw significantly reduced patient mortality at 6 months. The timing of ART initiation in patients with central nervous system opportunistic infections remains challenging and a recent study reported that deferred vs early antiretroviral therapy was associated with better survival outcomes in patients diagnosed with cryptococcal meningitis. Recent studies have reported on predictors of immune reconstitution inflammatory syndrome for patients with central nervous system opportunistic infections, but require validation in resource-different settings.

SUMMARY

Recent studies related to the diagnosis and treatment of central nervous system opportunistic infections in HIV+ populations show promising findings. Increased funding and research commitment are required to maintain this positive momentum and to achieve improved global outcomes for people who develop central nervous system opportunistic infections.

Cytokine profiles at admission can be related to outcome in AIDS patients with cryptococcal meningitis

Cryptococcal meningitis (CM) remains as common life-threatening AIDS-defining illness mainly in resource-limited settings. Previous reports suggested that baseline cytokine profiles can be associated to fungal burden and clinical outcome. This study aimed to evaluate the baseline cytokine profiles in AIDS patients with CM and its relation with the outcome at weeks 2 and 10. Thirty AIDS patients with CM diagnosed by cerebrospinal fluid (CSF) Cryptococcus neoformans positive culture, India ink stain and cryptococcal antigen test were prospectively evaluated. As controls, 56 HIV-infected patients without CM and 48 non-HIV individuals were included. Baseline CSF and sera levels of IL-2, IL-4, IL-8, IL-10, IL-12p40, IL-17A, INF-γ and TNF-α were measured by ELISA. Of 30 CM patients, 24 (80%) were male, median age of 38.1. The baseline CSF high fungal burden and positive blood culture were associated with a positive CSF culture at week 2 (p = 0.043 and 0.029). Most CSF and sera cytokines presented higher levels in CM patients than control subjects (p < 0.05). CSF levels of IL-8, IL-12p40, IL-17A, TNF-α, INF-γ and sera TNF-α were significantly higher among survivors at weeks 2 and 10 (p < 0.05). Patients with increased intracranial pression exhibited CSF IL-10 high levels and poor outcome at week 10 (p = 0.032). Otherwise, baseline CSF log10 IFN-γ and IL-17A were negatively correlated with fungal burden (r = -0.47 and -0.50; p = 0.0175 and 0.0094, respectively). The mortality rate was 33% (10/30) at week 2 and 57% (17/30) at week 10. The severity of CM and the advanced immunodeficiency at admission were related to a poor outcome in these patients. Otherwise, the predominant Th1 cytokines profile among survivors confirms its pivotal role to infection control and would be a prognostic marker in cryptococcal meningitis.

Immune reconstitution disorders in patients with HIV infection: from pathogenesis to prevention and treatment

An immune reconstitution disorder occurs in up to 40 % of severely immunodeficient HIV patients who commence antiretroviral therapy (ART), with an immune reconstitution inflammatory syndrome (IRIS) being encountered most commonly. Differences in the immunopathogenesis of an IRIS associated with different types of pathogen have become apparent but common features have also been defined. These include severe immunodeficiency prior to commencing ART associated with a high pathogen load and 'compensatory' immune responses, particularly innate immune responses, which inadequately control the pathogen and increase the risk of immunopathology as the immune system recovers on ART. Prevention of an IRIS may be achieved by optimising therapy for opportunistic infections before ART is commenced, delaying ART or using immunomodulatory therapy to prevent or suppress the immune response that causes the immunopathology. However, further clinical studies are required to examine these options in a systematic manner for the various types of IRIS.

Cellular immune activation in cerebrospinal fluid from ugandans with cryptococcal meningitis and immune reconstitution inflammatory syndrome

Background. Human immunodeficiency virus (HIV)-associated cryptococcal meningitis (CM) is characterized by high fungal burden and limited leukocyte trafficking to cerebrospinal fluid (CSF). The immunopathogenesis of CM immune reconstitution inflammatory syndrome (IRIS) after initiation of antiretroviral therapy at the site of infection is poorly understood.

Methods. We characterized the lineage and activation status of mononuclear cells in blood and CSF of HIV-infected patients with noncryptococcal meningitis (NCM) (n = 10), those with CM at day 0 (n = 40) or day 14 (n = 21) of antifungal therapy, and those with CM-IRIS (n = 10).

Results. At diagnosis, highly activated CD8⁺ T cells predominated in CSF in both CM and NCM. CM-IRIS was associated with an increasing frequency of CSF CD4⁺ T cells (increased from 2.2% to 23%; P = .06), a shift in monocyte phenotype from classic to an intermediate/proinflammatory, and increased programmed death ligand 1 expression on natural killer cells (increased from 11.9% to 61.6%, P = .03). CSF cellular responses were distinct from responses in peripheral blood.

Conclusions. After CM, T cells in CSF tend to evolve with the development of IRIS, with increasing proportions of activated CD4⁺ T cells, migration of intermediate monocytes to the CSF, and declining fungal burden. These changes provide insight into IRIS pathogenesis and could be exploited to more effectively treat CM and prevent CM-IRIS.

Neutrophil-associated central nervous system inflammation in tuberculous meningitis immune reconstitution inflammatory syndrome

BACKGROUND

The immunopathogenesis of tuberculosis-associated immune reconstitution inflammatory syndrome (IRIS) remains incompletely understood, and we know of only 1 disease site-specific study of the underlying immunology; we recently showed that Mycobacterium tuberculosis culture positivity and increased neutrophils in the cerebrospinal fluid (CSF) of patients with tuberculous meningitis (TBM) are associated with TBM-IRIS. In this study we investigated inflammatory mediators at the disease site in patients with TBM-IRIS.

METHODS

We performed lumbar puncture at 3-5 time points in human immunodeficiency virus (HIV)-infected patients with TBM (n = 34), including at TBM diagnosis, at initiation of antiretroviral therapy (ART) (day 14), 14 days after ART initiation, at presentation of TBM-IRIS, and 14 days thereafter. We determined the concentrations of 40 mediators in CSF (33 paired with blood) with Luminex or enzyme-linked immunosorbent assays. Findings were compared between patients who developed TBM-IRIS (n = 16) and those who did not (TBM-non-IRIS; n = 18).

RESULTS

At TBM diagnosis and 2 weeks after ART initiation, TBM-IRIS was associated with severe, compartmentalized inflammation in the CSF, with elevated concentrations of cytokines, chemokines, neutrophil-associated mediators, and matrix metalloproteinases, compared with TBM-non-IRIS. Patients with TBM-non-IRIS whose CSF cultures were positive for M. tuberculosis at TBM diagnosis (n = 6) showed inflammatory responses similar to those seen in patients with TBM-IRIS at both time points. However, at 2 weeks after ART initiation, S100A8/A9 was significantly increased in patients with TBM-IRIS, compared with patients with TBM-non-IRIS whose cultures were positive at baseline.

CONCLUSIONS

A high baseline M. tuberculosis antigen load drives an inflammatory response that manifests clinically as TBM-IRIS in most, but not all, patients with TBM. Neutrophils and their mediators, especially S100A8/A9, are closely associated with the central nervous system inflammation that characterizes TBM-IRIS.

Unmasking cryptococcal meningitis immune reconstitution inflammatory syndrome in pregnancy induced by HIV antiretroviral therapy with postpartum paradoxical exacerbation

Cryptococcosis is the most common cause of meningitis in Africa due to the high burden of HIV. Immune reconstitution inflammatory syndrome (IRIS) is a frequent and deadly complication of cryptococcal meningitis. We report a fatal case of cryptococcal-IRIS in a pregnant woman that began after starting antiretroviral therapy (unmasking IRIS) and markedly worsened postpartum after delivery (paradoxical IRIS).