Neurological complications of human immunodeficiency virus infection

Determinants of neurological syndromes caused by varicella zoster virus (VZV)

Varicella zoster virus (VZV) is a pathogenic human herpes virus which causes varicella as a primary infection, following which it becomes latent in peripheral autonomic, sensory, and cranial nerve ganglionic neurons from where it may reactivate after decades to cause herpes zoster. VZV reactivation may also cause a wide spectrum of neurological syndromes, in particular, acute encephalitis and vasculopathy. While there is potentially a large number of coding viral mutations that might predispose certain individuals to VZV infections, in practice, a variety of host factors are the main determinants of VZV infection, both disseminated and specifically affecting the nervous system. Host factors include increasing age with diminished cell-mediated immunity to VZV, several primary immunodeficiency syndromes, secondary immunodeficiency syndromes, and drug-induced immunosuppression. In some cases, the molecular immunological basis underlying the increased risk of VZV infections has been defined, in particular, the role of POL III mutations, but in other cases, the mechanisms have yet to be determined. The role of immunization in immunosuppressed individuals as well as its possible efficacy in preventing both generalized and CNS-specific infections will require further investigation to clarify in such patients.

Brain macrophages harbor latent, infectious simian immunodeficiency virus

: The current review examines the role of brain macrophages, that is perivascular macrophages and microglia, as a potential viral reservoir in antiretroviral therapy (ART) treated, simian immunodeficiency virus (SIV)-infected macaques. The role, if any, of latent viral reservoirs of HIV and SIV in the central nervous system during ART suppression is an unresolved issue. HIV and SIV infect both CD4 lymphocytes and myeloid cells in blood and tissues during acute and chronic infection. HIV spread to the brain occurs during acute infection by the infiltration of activated CD4 lymphocytes and monocytes from blood and is established in both embryonically derived resident microglia and monocyte-derived perivascular macrophages. ART controls viral replication in peripheral blood and cerebrospinal fluid in HIV-infected individuals but does not directly eliminate infected cells in blood, tissues or brain. Latently infected resting CD4 lymphocytes in blood and lymphoid tissues are a well recognized viral reservoir that can rebound once ART is withdrawn. In contrast, central nervous system resident microglia and perivascular macrophages in brain have not been examined as potential reservoirs for HIV during suppressive ART. Macrophages in tissues are long-lived cells that are HIV and SIV infected in tissues such as gut, lung, spleen, lymph node and brain and contribute to ongoing inflammation in tissues. However, their potential role in viral persistence and latency or their potential to rebound in the absence ART has not been examined. It has been shown that measurement of HIV latency by HIV DNA PCR in CD4 lymphocytes overestimates the size of the latent reservoirs of HIV that contribute to rebound that is cells containing the genomes of replicative viruses. Thus, the quantitative viral outgrowth assay has been used as a reliable measure of the number of latent cells that harbor infectious viral DNA and, may constitute a functional latent reservoir. Using quantitative viral outgrowth assays specifically designed to quantitate latently infected CD4 lymphocytes and myeloid cells in an SIV macaque model, we demonstrated that macrophages in brain harbor SIV genomes that reactivate and produce infectious virus in this assay, demonstrating that these cells have the potential to be a reservoir.

A Quantitative Approach to SIV Functional Latency in Brain Macrophages

Lentiviruses are retroviruses that primarily infect myeloid cells, leading to acute inflammatory infections in many tissues particularly, lung, joints and the central nervous system (CNS). Acute infection by lentiviruses is followed by persistent/latent infections that are not cleared by the host immune system. HIV and SIV are lentiviruses that also infect CD4+ lymphocytes as well as myeloid cells in blood and multiple tissues. HIV infection of myeloid cells in brain, lung and heart cause tissue specific diseases as well as infect cells in gut, lymph nodes and spleen. AIDS dementia and other tissue specific disease are observed when infected individuals are immunosuppressed and the number of circulating CD4+ T cells declines to low levels. Antiretroviral therapy (ART) controls viral spread and dramatically changes the course of immunodeficiency and AIDS dementia. However, ART does not eliminate virus-infected cells. Brain macrophages contain HIV DNA and may represent a latent reservoir that persists. HIV latency in CD4+ lymphocytes is the main focus of current research and concern in efforts to eradicate HIV. However, a number of studies have demonstrated that myeloid cells in blood and tissues of ART suppressed individuals harbor HIV DNA. The resident macrophages in tissues such as brain (microglia), spleen (red pulp macrophages) and alveolar macrophages in lung are derived from the yolk sac and can self renew. The question of the latent myeloid reservoir in HIV has not been rigorously examined and its potential as a barrier to eradication been considered. Using a well characterized SIV ART suppressed, non-human primate (NHP) model, our laboratory developed the first quantitative viral outgrowth assay (QVOA) designed to evaluate latently infected CD4+ lymphocytes and more recently developed a similar protocol for the assessment of latently infected myeloid cells in blood and brain. Using an SIV ART model, it was demonstrated that myeloid cells in blood and brain harbor latent SIV that can be reactivated and produce infectious virus in vitro. These studies demonstrate for the first time that myeloid cells have the potential to be a latent reservoir of HIV that produces infectious virus that can be reactivated in the absence of ART and during HIV eradication strategies. Graphical Abstract.

SIV Latency in Macrophages in the CNS

Lentiviruses infect myeloid cells, leading to acute infection followed by persistent/latent infections not cleared by the host immune system. HIV and SIV are lentiviruses that infect CD4+ lymphocytes in addition to myeloid cells in blood and tissues. HIV infection of myeloid cells in brain, lung, and heart causes tissue-specific diseases that are mostly observed during severe immunosuppression, when the number of circulating CD4+ T cells declines to exceeding low levels. Antiretroviral therapy (ART) controls viral replication but does not successfully eliminate latent virus, which leads to viral rebound once ART is interrupted. HIV latency in CD4+ lymphocytes is the main focus of research and concern when HIV eradication efforts are considered. However, myeloid cells in tissues are long-lived and have not been routinely examined as a potential reservoir. Based on a quantitative viral outgrowth assay (QVOA) designed to evaluate latently infected CD4+ lymphocytes, a similar protocol was developed for the assessment of latently infected myeloid cells in blood and tissues. Using an SIV ART model, it was demonstrated that myeloid cells in blood and brain harbor latent SIV that can be reactivated and produce infectious virus in vitro, demonstrating that myeloid cells have the potential to be an additional latent reservoir of HIV that should be considered during HIV eradication strategies.

Brain Targeting of anti-HIV Nucleosides: in vitro and in vivo Evaluation of 6-chloro-2′,3′-dideoxypurine, a Lipophilic Prodrug of 2′,3′-dideoxyinosine

Lipophilic 6-halo-2′,3′-dideoxypurine nucleosides may be useful prodrugs for the targeting of 2′,3′-dideoxyinosine (ddl) to the central nervous system. The purpose of this study was to evaluate the potential effectiveness of 6-chloro-2′,3′-dideoxypurine (6-CI-ddP) for the targeting of ddl to the brain. In vitro studies indicated that the adenosine deaminase-mediated biotransformation of 6-CI-ddP to ddl was more rapid in mouse brain homogenate than in mouse serum. The brain distribution of 6-CI-ddP and ddl was assessed in vivo in mice following intravenous and oral administration of the prodrug or parent drug. Brain concentrations of ddl were similar after intravenous administration of 6-CI-ddP or ddl. However, after oral administration of the 6-CI-ddP prodrug, significantly greater concentrations of ddl were seen in the brain compared to those found after oral administration of ddl. The brain:serum AUG ratio (expressed as a percentage) of ddl after intravenous administration of 50 mg kg−1 of the active nucleoside was 3%. Following oral administration of 250 mg kg−1 ddl, low concentrations of ddl were detected in the brain. Brain:serum AUC ratios following intravenous and oral administration of the prodrug 6-CI-ddP were 19–25%. Thus, brain:serum AUC ratios were 6- to 8-fold higher after prodrug administration than those obtained after administration of the parent nucleoside. Oral administration of 6-CI-ddP yielded concentrations of ddl in the brain similar to those obtained following intravenous administration. The results of this study provide further evidence that 6-CI-ddP may be a useful prodrug for delivering ddl to the central nervous system, particularly after oral administration.

A concise panel of biomarkers identifies neurocognitive functioning changes in HIV-infected individuals

Neurocognitive (NC) impairment (NCI) occurs commonly in people living with HIV. Despite substantial effort, no biomarkers have been sufficiently validated for diagnosis and prognosis of NCI in the clinic. The goal of this project was to identify diagnostic or prognostic biomarkers for NCI in a comprehensively characterized HIV cohort. Multidisciplinary case review selected 98 HIV-infected individuals and categorized them into four NC groups using normative data: stably normal (SN), stably impaired (SI), worsening (Wo), or improving (Im). All subjects underwent comprehensive NC testing, phlebotomy, and lumbar puncture at two timepoints separated by a median of 6.2 months. Eight biomarkers were measured in CSF and blood by immunoassay. Results were analyzed using mixed model linear regression and staged recursive partitioning. At the first visit, subjects were mostly middle-aged (median 45) white (58 %) men (84 %) who had AIDS (70 %). Of the 73 % who took antiretroviral therapy (ART), 54 % had HIV RNA levels below 50 c/mL in plasma. Mixed model linear regression identified that only MCP-1 in CSF was associated with neurocognitive change group. Recursive partitioning models aimed at diagnosis (i.e., correctly classifying neurocognitive status at the first visit) were complex and required most biomarkers to achieve misclassification limits. In contrast, prognostic models were more efficient. A combination of three biomarkers (sCD14, MCP-1, SDF-1α) correctly classified 82 % of Wo and SN subjects, including 88 % of SN subjects. A combination of two biomarkers (MCP-1, TNF-α) correctly classified 81 % of Im and SI subjects, including 100 % of SI subjects. This analysis of well-characterized individuals identified concise panels of biomarkers associated with NC change. Across all analyses, the two most frequently identified biomarkers were sCD14 and MCP-1, indicators of monocyte/macrophage activation. While the panels differed depending on the outcome and on the degree of misclassification, nearly all stable patients were correctly classified.

Tumour necrosis factor-alpha mediates blood-brain barrier damage in HIV-1 infection of the central nervous system

The pathogenesis of brain inflammation and damage by human immunodeficiency virus (HIV) infection is unclear. Because blood–brain barrier damage and impaired cerebral perfusion are common features of HIV-1 infection, we evaluated the role of tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in mediating disruption of the blood–brain barrier. Levels of TNF-α were more elevated in cerebrospinal fluid (CSF) than in serum of HIV-1 infected patients and were mainly detected in those patients who had neurologic involvement. Intrathecal TNF-α levels correlated with signs of blood–brain barrier damage, manifested by high CSF to serum albumin quotient, and with the degree of barrier impairment. In contrast, intrathecal IL-1β levels did not correlate with blood-brain barrier damage in HIV-1 infected patients. TNF-α seems to be related to active neural inflammation and to blood–brain barrier damage. The proinflammatory effects of TNF-α in the nervous system are dissociated from those of IL-1β.

AIDS and cerebrovascular disease

BACKGROUND

Although neurological complications of human immunodeficiency virus (HIV) infection are common, the presence of cerebrovascular disease (CVD) has been seldom reported. The purpose of this report is to review available data on the association between stroke and acquired immunodeficiency syndrome (AIDS).

SUMMARY OF REVIEW

A review of all literature published between mid-1976 and December 1994 was performed through a MEDLINE search with the following key words: AIDS, CVD, human T-cell lymphotropic virus type III, and HIV-1. Only reports of clinical stroke in patients with AIDS or HIV infection and autopsy series with stroke findings were selected. The type of study, population, number of stroke patients, subtype and etiology of stroke, and associated AIDS conditions were described. Six clinical series and 11 autopsy series were found, with a total of 1885 cases with AIDS, AIDS-related complex, and HIV carriers. Forty percent had a neurological complication, but only 1.3% had a stroke syndrome. Ischemic infarcts were more common than intracerebral hemorrhages. Cerebral infarcts were generally due to nonbacterial thrombotic endocarditis or concomitant opportunistic central nervous system infection, and intracerebral hemorrhages were usually associated with thrombocytopenia, primary central nervous system lymphoma, and metastatic Kaposi's sarcoma. Autopsy findings of CVD were generally not related with clinical stroke before death. Data are not available to determine the role of risk factors for AIDS in CVD.

CONCLUSIONS

Because of limitations of the available data, it is still not clear whether there is an association between AIDS and stroke. Further studies are needed to better define the epidemiology of CVD in association with AIDS.

Molecular studies of viral pathogenesis in the central nervous system. The Linacre Lecture 1991

What is the molecular biological basis of viral pathogenesis in the central nervous system (CNS), ie by what molecular mechanisms do different viruses produce particular patterns of neurological disease in man and animal models, and can one use molecular techniques to ascertain the viral aetiology of certain neurological conditions? This complex subject can be approached in three different but interrelated ways. First, one may relate molecular techniques to specific biological properties such as viral spread to the CNS, to neurotropism, ie the affinity of the virus for particular neural regions and cells, and to neurovirulence, which refers to the actual ability to cause neurological disease. Second, the reverse approach can be adopted by considering these different aspects of virus-host relationships and then how the techniques have contributed to their understanding. Third, one can select specific neurotropic viruses, such as polio or herpes viruses, and then relate these to both particular techniques and pathogenetic mechanisms [1]. The second component of this paper will deal with the immunopathological mechanisms seen in three specific CNS viral infections, all of which have been the focus of study in the author's laboratory over the past six years.

Autonomic dysfunction in patients with human immunodeficiency virus infection

Autonomic function tests have been recorded in 40 male homosexual patients with serum antibodies to human immunodeficiency virus (HIV) and 12 male homosexuals without such antibodies. Abnormalities of autonomic function were found in 15 of 31 patients without other recognized reasons for autonomic dysfunction. Four patients had two or more test abnormalities. The profile of these abnormalities was found to be different from that of autonomic neuropathy associated with diabetes and other disorders and was consistent with the presence of sympathetic overactivity. Abnormalities in autonomic function were particularly associated with clinically identifiable neurological complications of HIV infection.

The use of molecular techniques in studying viral pathogenesis in the nervous system

Molecular biological techniques have been used extensively to gain insights into the pathogenesis of a variety of diseases caused by neurotropic viruses. Increasingly sensitive methods for detecting viral nucleic acids and proteins in pathological nervous tissues have clarified the viral aetiology of certain neurological disorders and are now being used to investigate possible viral involvement in others. In addition, a diverse range of molecular techniques has greatly enhanced our understanding of the molecular basis of viral neurotropism and neurovirulence in both humans and experimental animals. This article provides an overview of these various approaches with examples drawn from both clinical neurological disease and animal models.

Idiopathic granulomatous meningitis

A 69 year old female presented with eight discrete episodes of paraparesis over a period of six weeks. Each episode lasted between 10 and 30 minutes and resolved spontaneously. The cause of her symptoms was not established during life and at necropsy she was found to have granulomatous meningitis of the cerebral convexites. The clinical and pathological aspects of this rare condition are discussed.

Neurological features of HIV-related disease in Glasgow

The neurological features of 10 patients with HIV-related disease seen in Glasgow between July 1984 and May 1988 are described. Two of these patients presented with ARC and eight with AIDS. Six patients showed features consistent with a diagnosis of AIDS-dementia complex, one had cerebral toxoplasmosis, one had CNS lymphoma, one had a probable drug-induced encephalopathy and one patient had a meningoencephalitis of undetermined cause. Seven of these patients have now died. The implications of these findings are discussed.