Human immunodeficiency virus type 1 in spinal cords of acquired immunodeficiency syndrome patients with myelopathy: expression and replication in macrophages

Understanding HIV-associated neurocognitive and neurodegenerative disorders (neuroAIDS): enroute to achieve the 95-95-95 target and sustainable development goal for HIV/AIDS response

The world's sustained commitment to the HIV/AIDS response and to reaching the 2030 Sustainable Development Goal (SDG) of "ending AIDS" as a public health issue is indicated by the ambitious 95-95-95 targets for all relevant populations. Neurological conditions of AIDS (neuroAIDS) are the most significant and severe central nervous system complication associated with HIV infection in which viral antigens can enter in the brain by breaching the blood brain barrier and cause dementia, neuroinflammation and encephalopathy. The prevalence of neuroAIDS is 10-50% in people with advanced HIV disease, whereas 5-25% in people on ART. Currently, MRI, CT and other tools are used to diagnose the neuroAIDS/ HIV-associated dementia and antiretroviral therapy is widely used to treat the neuroAIDS. In spite of many advanced tools and pathogenesis of neuroAIDS, developing therapeutics remains a formidable challenge. Long acting cabotegravir type of therapeutics is an advanced stage of research which shows good results for the treatment of neuroAIDS. Therefore, here we are discussing the recent insights of the pathogenesis, possible therapeutics and current strategies and treatment to overcome the neuroAIDS.

Astrocytes as an HIV CNS reservoir: highlights and reflections of an NIMH-sponsored symposium

This a summary of a National Institute of Mental Health (NIMH) sponsored symposium that was focused on the role of astrocytes as a reservoir of the human immunodeficiency virus in the brain. The talks were grouped into four themes. The first theme reviewed the evidence for HIV infection of astrocytes and discussed the challenges in the use of traditional methods of immunostaining and in situ hybridization for detection of infected astrocytes. The second theme focused on mechanisms of HIV entry into astrocytes and discussed CD4 independent mechanisms, such as receptor-mediated endocytosis and transmission of HIV by cell-to-cell contact with infected lymphocytes. The third theme focused on epigenetic regulation of HIV latency in astrocytes and other factors, such as cytokines and transcriptional factors regulating HIV replication in astrocytes. The fourth theme focused on therapeutic approaches, such as gene editing to block persistently infected astrocytes. A discussion that followed was focused on major unanswered questions in the field and future directions for research.

Monocyte-lymphocyte fusion induced by the HIV-1 envelope generates functional heterokaryons with an activated monocyte-like phenotype

Enveloped viruses induce cell-cell fusion when infected cells expressing viral envelope proteins interact with target cells, or through the contact of cell-free viral particles with adjoining target cells. CD4⁺ T lymphocytes and cells from the monocyte-macrophage lineage express receptors for HIV envelope protein. We have previously reported that lymphoid Jurkat T cells expressing the HIV-1 envelope protein (Env) can fuse with THP-1 monocytic cells, forming heterokaryons with a predominantly myeloid phenotype. This study shows that the expression of monocytic markers in heterokaryons is stable, whereas the expression of lymphoid markers is mostly lost. Like THP-1 cells, heterokaryons exhibited FcγR-dependent phagocytic activity and showed an enhanced expression of the activation marker ICAM-1 upon stimulation with PMA. In addition, heterokaryons showed morphological changes compatible with maturation, and high expression of the differentiation marker CD11b in the absence of differentiation-inducing agents. No morphological change nor increase in CD11b expression were observed when an HIV-fusion inhibitor blocked fusion, or when THP-1 cells were cocultured with Jurkat cells expressing a non-fusogenic Env protein, showing that differentiation was not induced merely by cell-cell interaction but required cell-cell fusion. Inhibition of TLR2/TLR4 signaling by a TIRAP inhibitor greatly reduced the expression of CD11b in heterokaryons. Thus, lymphocyte-monocyte heterokaryons induced by HIV-1 Env are stable and functional, and fusion prompts a phenotype characteristic of activated monocytes via intracellular TLR2/TLR4 signaling.

Therapeutic doses of irradiation activate viral transcription and induce apoptosis in HIV-1 infected cells

The highly active antiretroviral therapy reduces HIV-1 RNA in plasma to undetectable levels. However, the virus continues to persist in the long-lived resting CD4(+) T cells, macrophages and astrocytes which form a viral reservoir in infected individuals. Reactivation of viral transcription is critical since the host immune response in combination with antiretroviral therapy may eradicate the virus. Using the chronically HIV-1 infected T lymphoblastoid and monocytic cell lines, primary quiescent CD4(+) T cells and humanized mice infected with dual-tropic HIV-1 89.6, we examined the effect of various X-ray irradiation (IR) doses (used for HIV-related lymphoma treatment and lower doses) on HIV-1 transcription and viability of infected cells. Treatment of both T cells and monocytes with IR, a well-defined stress signal, led to increase of HIV-1 transcription, as evidenced by the presence of RNA polymerase II and reduction of HDAC1 and methyl transferase SUV39H1 on the HIV-1 promoter. This correlated with the increased GFP signal and elevated level of intracellular HIV-1 RNA in the IR-treated quiescent CD4(+) T cells infected with GFP-encoding HIV-1. Exposition of latently HIV-1infected monocytes treated with PKC agonist bryostatin 1 to IR enhanced transcription activation effect of this latency-reversing agent. Increased HIV-1 replication after IR correlated with higher cell death: the level of phosphorylated Ser46 in p53, responsible for apoptosis induction, was markedly higher in the HIV-1 infected cells following IR treatment. Exposure of HIV-1 infected humanized mice with undetectable viral RNA level to IR resulted in a significant increase of HIV-1 RNA in plasma, lung and brain tissues. Collectively, these data point to the use of low to moderate dose of IR alone or in combination with HIV-1 transcription activators as a potential application for the "Shock and Kill" strategy for latently HIV-1 infected cells.

Implications of gliotransmission for the pharmacotherapy of CNS disorders

The seminal discovery that glial cells, particularly astrocytes, can release a number of gliotransmitters that serve as signalling molecules for the cross-talk with neighbouring cellular populations has recently changed our perception of brain functioning, as well as our view of the pathogenesis of several disorders of the CNS. Since glutamate was one of the first gliotransmitters to be identified and characterized, we tackle the mechanisms that underlie its release from astrocytes, including the Ca2+ signals underlying its efflux from astroglia, and we discuss the involvement of these events in a number of relevant physiological processes, from the modulatory control of neighbouring synapses to the regulation of blood supply to cerebral tissues. The relevance of these mechanisms strongly indicates that the contribution of glial cells and gliotransmission to the activities of the brain cannot be overlooked, and any study of CNS physiopathology needs to consider glial biology to have a comprehensive overview of brain function and dysfunction. Abnormalites in the signalling that controls the astrocytic release of glutamate are described in several experimental models of neurological disorders, for example, AIDS dementia complex, Alzheimer's disease and cerebral ischaemia. While the modalities of glutamate release from astrocytes remain poorly understood, and this represents a major impediment to the definition of novel therapeutic strategies targeting this process at the molecular level, some key mediators deputed to the control of the glial release of this excitatory amino acid have been identified. Among these, we can mention, for instance, proinflammatory cytokines, such as tumour necrosis factor-α, and prostaglandins. Agents that are able to block the major steps of tumour necrosis factor-α and prostaglandin production and/or signalling can be proposed as novel therapeutic targets for the treatment of these disorders.

Human immunodeficiency virus type 1 endocytic trafficking through macrophage bridging conduits facilitates spread of infection

Bridging conduits (BC) sustain communication and homeostasis between distant tethered cells. These are also exploited commonly for direct cell-to-cell transfer of microbial agents. Conduits efficiently spread infection, effectively, at speeds faster than fluid phase exchange while shielding the microbe against otherwise effective humoral immunity. Our laboratory has sought to uncover the mechanism(s) for these events for human immunodeficiency virus type one (HIV-1) infection. Indeed, in our prior works HIV-1 Env and Gag antigen and fluorescent virus tracking were shown sequestered into endoplasmic reticulum-Golgi organelles but the outcomes for spreading viral infection remained poorly defined. Herein, we show that HIV-1 specifically traffics through endocytic compartments contained within BC and directing such macrophage-to-macrophage viral transfers. Following clathrin-dependent viral entry, HIV-1 constituents bypass degradation by differential sorting from early to Rab11⁺ recycling endosomes and multivesicular bodies. Virus-containing endocytic viral cargoes propelled by myosin II through BC spread to neighboring uninfected cells. Disruption of endosomal motility with cytochalasin D, nocodasole and blebbistatin diminish intercellular viral spread. These data lead us to propose that HIV-1 hijacks macrophage endocytic and cytoskeletal machineries for high-speed cell-to-cell spread.

Ultrastructural, immunofluorescence, and RNA evidence support the hypothesis of a "new" virus associated with Kawasaki disease

BACKGROUND

Intracytoplasmic inclusion bodies (ICI) have been identified in ciliated bronchial epithelium of Kawasaki disease (KD) patients using a synthetic antibody derived from acute KD arterial IgA plasma cells; ICI may derive from the KD etiologic agent.

METHODS

Acute KD bronchial epithelium was subjected to immunofluorescence for ICI and cytokeratin, high-throughput sequencing, and transmission electron microscopy (TEM). Interferon pathway gene expression profiling was performed on KD lung.

RESULTS

An intermediate filament cytokeratin "cage" was not observed around KD ICI, making it unlikely that ICI are overproduced or misfolded human protein aggregates. Many interferon-stimulated genes were detected in the bronchial epithelium, and significant modulation of the interferon response pathway was observed in the lung tissue of KD patients. No known virus was identified by sequencing. Aggregates of virus-like particles (VLP) were detected by TEM in all 3 acute KD patients from whom nonembedded formalin-fixed lung tissue was available.

CONCLUSIONS

KD ICI are most likely virus induced; bronchial cells with ICI contain VLP that share morphologic features among several different RNA viral families. Expedited autopsies and tissue fixation from acute KD fatalities are urgently needed to more clearly ascertain the VLP. These findings are compatible with the hypothesis that the infectious etiologic agent of KD may be a "new" RNA virus.

Neurologic presentations of AIDS

The human immunodeficiency virus (HIV), the cause of AIDS, has infected an estimated 33 million individuals worldwide. HIV is associated with immunodeficiency, neoplasia, and neurologic disease. The continuing evolution of the HIV epidemic has spurred an intense interest in a hitherto neglected area of medicine, neuroinfectious diseases and their consequences. This work has broad applications for the study of central nervous system (CNS) tumors, dementias, neuropathies, and CNS disease in other immunosuppressed individuals. HIV is neuroinvasive (can enter the CNS), neurotrophic (can live in neural tissues), and neurovirulent (causes disease of the nervous system). This article reviews the HIV-associated neurologic syndromes, which can be classified as primary HIV neurologic disease (in which HIV is both necessary and sufficient to cause the illness), secondary or opportunistic neurologic disease (in which HIV interacts with other pathogens, resulting in opportunistic infections and tumors), and treatment-related neurologic disease (such as immune reconstitution inflammatory syndrome).

Replication of HIV-1 in Vivo and in Vitro

A complex relationship exists between HIV and its cellular targets. The lethal effect of HIV on circulating CD4(+) helper T lymphocytes parallels the degree of the infected individual's immunodeficiency and ultimately the transition to AIDS and death. However, as with other members of the Lentivirus family of retroviruses, the ubiquitous, mobile macrophage is also a prime target for HIV infection, and apparently, in most instances, is the initial infected cell, since most people are infected with a CCR5 chemokine-tropic virus. Unlike the lymphocyte, the macrophage is apparently a more stable viral host, capable of a long infected life as an HIV reservoir and a chronic source of infectious virus. Published in vitro studies have indicated that whereas lymphocytes replicate HIV solely on their plasma membrane, macrophages have been envisaged to predominantly replicate HIV within cytoplasmic vacuoles, and thus have been likened to a "Trojan horse," when it comes to the immune system. Recent studies have revealed an ingenious way by which the cultured monocyte-derived macrophage (MDM) replicates HIV and releases it into the medium. The key macrophage organelle appears to be what is alternatively referred to as the "late endosome" (LE) or the "multivesicular body" (MVB), which have a short and a long history, respectively. Proof of the association is that chemically, LE/MVB and their vesicles possess several pathopneumonic membrane markers (e.g., CD63) that are found on released HIV particles. The hypothesis is that HIV usurps this vesicle-forming mechanism and employs it for its own replication. Release of the intravacuolar virus from the cell is hypothesized to occur by a process referred to as exocytosis, resulting from the fusion of virus-laden LE/MVB with the plasma membrane of the macrophage. Interestingly, LE/MVB are also involved in the infection stage of MDM by HIV. Close review of the literature reveals that along with the Golgi, which contributes to the formation of LE/MVB, the MVB was first identified as a site of HIV replication by macrophages many years ago, but the full implication of this observation was not appreciated at the time. As in many other areas of HIV research, what has been totally lacking is an in vivo confirmation of the in vitro phenomenon. Herein, the ultrastructure of HIV interaction with cells in vitro and in vivo is explored. It is shown that while HIV is regularly found in LE/MVB in vitro, it is infrequently the case in vivo. Therefore, the results challenge the "Trojan horse" concept.

Retrograde and anterograde transport of HIV protein gp120 in the nervous system

Neurodegeneration and gliosis are prominent pathological features of subjects with human immunodeficiency virus (HIV) dementia complex (HAD). In these patients, neurodegeneration occurs in uninfected neurons. In addition, these patients develop sensory neuropathy despite the antiretroviral therapy. The HIV protein gp120, which mimics some of the pathological alterations seen in HAD, is retrogradely transported in rodent neurons. However, it is still unclear whether gp120 can also be transported anterogradely and whether axonal transport can occur in the peripheral nervous system (PNS). To determine whether gp120 is transported retrogradely and/or anterogradely, we injected gp120IIIB together with the retrograde tracer fluoro-ruby (FR) or the anterograde tracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyamine perchlorate (DiI) into the rat superior colliculi. We discovered that gp120 is retrogradely transported with FR along a direct pathway from the superior colliculus to the retina and anterogradely transported with DiI to several areas of the occipital cortex. To determine whether gp120 is also axonally transported in the peripheral nerves, gp120 and FR were injected into the sciatic nerve. No gp120 immunoreactivity was found in the sciatic nerve or dorsal root ganglia, suggesting that gp120 axonal transport does not occur in the PNS. Gp120 axonal transport may play a role in neuronal injury. Therefore, we examined apoptosis at various time points after gp120 injection. Activated caspase-3 was evident within neurons transporting gp120. These results indicate that axonal transport of gp120 might exacerbate the pathogenesis of HIV-1.

New insights for FOXO and cell-fate decision in HIV infection and HIV associated neurocognitive disorder

Human immunodeficiency virus Type 1 (HIV-1) infection and associated diseases continue to represent major health problem worldwide. FOXO transcriptional factors play an important role in the regulation of cell apoptosis, cell cycle arrest, stress resistance, metabolism and differentiation. This chapter will discuss the diverse functions of FOXO in different cell types including T-cells, macrophages, neurons and astrocytes within the context of HIV-1 infection. Given the overwhelming evidence that FOXO proteins influence the cell fate of immune cells and involve in the homeostasis of the central nervous system (CNS), we will also discuss the potential role of FOXO factors in HIV-1-associated neurological disorders.

Regulated exocytosis from astrocytes physiological and pathological related aspects

Astrocytes have traditionally been considered ancillary, satellite cells of the nervous system. However, it is a very recent acquisition that glial cells generate signaling loops which are integral to the brain circuitry and participate, interactively with neuronal networks, in the processing of information. Such a conceptual breakthrough makes this field of investigation one of the hottest in neuroscience, as it calls for a revision of past theories of brain function as well as for new strategies of experimental exploration of brain function. Glial cells are electrically not excitable, and it was only the use of optical recording techniques together with calcium sensitive dyes, that allowed the chemical excitability of glial cells to become apparent. Studies using these new techniques have shown for the first time that glial cells are activated by surrounding synaptic activity and translate neuronal signals into their own calcium code. Intracellular calcium concentration([Ca2+]i) elevations in glial cells have then shown to underlie spatial transfer of information in the glial network, accompanied by release of chemical transmitters (gliotransmitters) such as glutamate and back-signaling to neurons. As a consequence, optical imaging techniques applied to cell cultures or intact tissue have become a state-of-the-art technology for studying glial cell signaling. The molecular mechanisms leading to release of "gliotransmitters," especially glutamate, from glia are under debate. Accumulating evidence clearly indicates that astrocytes secrete numerous transmitters by Ca(2+)-dependent exocytosis. This review will discuss the mechanisms underlying the release of chemical transmitters from astrocytes with a particular emphasis to the regulated exocytosis processes.

CB2 receptors in the brain: role in central immune function

Recently, it has been recognized that the cannabinoid receptor CB2 may play a functionally relevant role in the central nervous system (CNS). This role is mediated primarily through microglia, a resident population of cells in the CNS that is morphologically, phenotypically, and functionally related to macrophages. These cells also express the cannabinoid receptor CB1. The CB1 receptor (CB1R) is constitutively expressed at low levels while the CB2 receptor (CB2R) is expressed at higher levels and is modulated in relation to cell activation state. The relatively high levels of the CB2R correspond with microglia being in 'responsive' and 'primed' states, suggesting the existence of a 'window' of functional relevance during which activation of the CB2R modulates microglial activities. Signature activities of 'responsive' and 'primed' microglia are chemotaxis and antigen processing, respectively. The endocannabinoid 2-arachidonylglycerol has been reported to stimulate a chemotactic response from these cells through the CB2R. In contrast, we have shown in vivo and in vitro that the exogenous cannabinoids delta-9-tetrahydrocannabinol and CP55940 inhibit the chemotactic response of microglia to Acanthamoeba culbertsoni, an opportunistic pathogen that is the causative agent of Granulomatous Amoebic Encephalitis, through activation of the CB2R. It is postulated that these exogenous cannabinoids superimpose an inhibitory effect on pro-chemotactic endocannabinoids that are elicited in response to Acanthamoeba. Furthermore, the collective results suggest that the CB2R plays a critical immune functional role in the CNS.

Epidemics to eradication: the modern history of poliomyelitis

Poliomyelitis has afflicted humankind since antiquity, and for nearly a century now, we have known the causative agent, poliovirus. This pathogen is an enterovirus that in recent history has been the source of a great deal of human suffering. Although comparatively small, its genome is packed with sufficient information to make it a formidable pathogen. In the last 20 years the Global Polio Eradication Initiative has proven successful in greatly diminishing the number of cases worldwide but has encountered obstacles in its path which have made halting the transmission of wild polioviruses a practical impossibility. As we begin to realize that a change in strategy may be crucial in achieving success in this venture, it is imperative that we critically evaluate what is known about the molecular biology of this pathogen and the intricacies of its interaction with its host so that in future attempts we may better equipped to more effectively combat this important human pathogen.

HIV-1 infection and AIDS: consequences for the central nervous system

Infection with the human immunodeficiency virus-1 (HIV-1) can induce severe and debilitating neurological problems that include behavioral abnormalities, motor dysfunction and frank dementia. After infiltrating peripheral immune competent cells, in particular macrophages, HIV-1 provokes a neuropathological response involving all cell types in the brain. HIV-1 also incites activation of chemokine receptors, inflammatory mediators, extracellular matrix-degrading enzymes and glutamate receptor-mediated excitotoxicity, all of which can trigger numerous downstream signaling pathways and disrupt neuronal and glial function. This review will discuss recently uncovered pathologic neuroimmune and degenerative mechanisms contributing to neuronal damage induced by HIV-1 and potential approaches for development of future therapeutic intervention.

Oligodendrocyte-specific expression of human immunodeficiency virus type 1 Nef in transgenic mice leads to vacuolar myelopathy and alters oligodendrocyte phenotype in vitro

Vacuolar myelopathy (VM) is a frequent central nervous system complication of human immunodeficiency virus type 1 (HIV-1) infection. We report here that transgenic (Tg) mice expressing even low levels of Nef in oligodendrocytes under the regulation of the myelin basic protein (MBP) promoter (MBP/HIV(Nef)) developed VM similar to the human disease in its appearance and topography. The spinal cords of these Tg mice showed lower levels of the myelin proteins MAG and CNPase and of the 21-kDa isoform of MBP prior to the development of vacuoles. In addition, Tg oligodendrocytes in primary in vitro cultures appeared morphologically more mature but, paradoxically, exhibited a less mature phenotype based on O4, O1, CNPase, and MBP staining. In particular, mature CNPase(+) MBP(+) Tg oligodendrocytes were less numerous than non-Tg oligodendrocytes. Therefore, Nef appears to affect the proper differentiation of oligodendrocytes. These data suggest that even low levels of Nef expression in human oligodendrocytes may be responsible for the development of VM in HIV-1-infected individuals.

Potential role for CD63 in CCR5-mediated human immunodeficiency virus type 1 infection of macrophages

Macrophages and CD4(+) lymphocytes are the principal target cells for human immunodeficiency virus type 1 (HIV-1) infection, but the molecular details of infection may differ between these cell types. During studies to identify cellular molecules that could be involved in macrophage infection, we observed inhibition of HIV-1 infection of macrophages by monoclonal antibody (MAb) to the tetraspan transmembrane glycoprotein CD63. Pretreatment of primary macrophages with anti-CD63 MAb, but not MAbs to other macrophage cell surface tetraspanins (CD9, CD81, and CD82), was shown to inhibit infection by several R5 and dualtropic strains, but not by X4 isolates. The block to productive infection was postfusion, as assessed by macrophage cell-cell fusion assays, but was prior to reverse transcription, as determined by quantitative PCR assay for new viral DNA formation. The inhibitory effects of anti-CD63 in primary macrophages could not be explained by changes in the levels of CD4, CCR5, or beta-chemokines. Infections of peripheral blood lymphocytes and certain cell lines were unaffected by treatment with anti-CD63, suggesting that the role of CD63 in HIV-1 infection may be specific for macrophages.

Analysis of cellular factors influencing the replication of human immunodeficiency virus type I in human macrophages derived from blood of different healthy donors

We analyzed parameters influencing HIV-1 infectibility of cells of the monocyte/macrophage lineage (MO/MAC) isolated from different healthy donors. The proportion of in vitro-infected cells and replication kinetics in different donor MAC ranged from 0.03 to 99% p24 antigen-positive MAC and from undetectable RT activity up to 5 x 10(6) cpm/ml/90 min, respectively. As a quantitative measurement for HIV-1 susceptibility of donor MO/MAC, we determined TCID(50) values of defined virus stocks which varied up to 3000-fold depending on the donor MAC used for titration. As host factors which may influence the viral infection we determined the expression of virus receptors CD4, CCR5, CXCR4, and CCR3 as well as the secretion of the natural ligands of CCR5, which altogether showed no correlation with HIV-1 infectibility of the cells. Moreover, other MO-derived secretory factors which might affect viral infection of these cells could be excluded. Furthermore, expression of maturation-related antigens CD14, CD16, HLA-DR, and MAX.1/CPM was determined. Analysis of the reverse transcription process revealed that restricted HIV-1 infection was reflected by highly reduced or even undetectable full-length HIV-1 DNA formation, although early and intermediate transcripts appeared, suggesting that viral replication is blocked after entry at the level of early reverse transcription.

Biology of HIV-1 in women and men

The HIV epidemic continues to spread worldwide, particularly among women and nonwhites. Development of vaccines and improved treatments depend on understanding pathogenesis. In the past few years, studies have begun to focus on HIV-1 pathogenesis in women, in whom some differences have been found in comparison with men. Attention is now focused on HIV-1 infection in reservoirs other than blood, particularly the genital tract. In addition, study of the genetic determinants of susceptibility to HIV-1 infection, including the chemokine receptors, have provided knowledge useful for the design of new treatments.

Human immunodeficiency virus type 1 long terminal repeat quasispecies differ in basal transcription and nuclear factor recruitment in human glial cells and lymphocytes

The generation of genomic diversity during the course of infection has the potential to affect all aspects of HIV-1 replication, including expression of the proviral genome. To gain a better understanding of the impact of long terminal repeat (LTR) sequence diversity on LTR-directed gene expression in cells of the central nervous system (CNS) and immune system, we amplified and cloned LTRs from proviral DNA in HIV-1-infected peripheral blood. Sequence analysis of nineteen LTRs cloned from 2 adult and 3 pediatric patients revealed an average of 33 nucleotide changes (with respect to the sequence of the LAI LTR) within the 455-bp U3 region. Transient expression analyses in cells of neuroglial and lymphocytic origin demonstrated that some of these LTRs had activities which varied significantly from the LAI LTR in U-373 MG cells (an astrocytoma cell line) as well as in Jurkat cells (a CD4-positive lymphocyte cell line). While LTRs which demonstrated the highest activities in U-373 MG cells also yielded high activities in Jurkat cells, the LTRs were generally more active in Jurkat cells when compared to the LAI LTR. Differences in LTR sequence also resulted in differences in transcription factor recruitment to cis-acting sites within the U3 region of the LTR, as demonstrated by electrophoretic mobility shift assays. In particular, naturally occurring sequence variation impacted transcription factor binding to an activating transcription factor/cAMP response element binding (ATF/CREB) binding site (located between the LEF-1 and distal NF-kappaB transcription factor binding sites) that we identified in previous studies of the HIV-1 LTR. These findings suggest that LTR sequence changes can significantly affect basal LTR function and transcription factor recruitment, which may, in turn, alter the course of viral replication in cells of CNS and immune system origin.

Induction of the chemokines interleukin-8 and IP-10 by human immunodeficiency virus type 1 tat in astrocytes

A finding commonly observed in human immunodeficiency virus type 1 (HIV-1)-infected patients is invasion of the brain by activated T cells and infected macrophages, eventually leading to the development of neurological disorders and HIV-1-associated dementia. The recruitment of T cells and macrophages into the brain is likely the result of chemokine expression. Indeed, earlier studies revealed that levels of different chemokines were increased in the cerebrospinal fluid of HIV-1-infected patients whereas possible triggers and cellular sources for chemokine expression in the brain remain widely undefined. As previous studies indicated that HIV-1 Tat, the retroviral transactivator, is capable of inducing a variety of cellular genes, we investigated its capacity to induce production of chemokines in astrocytes. Herein, we demonstrate that HIV-1 Tat(72aa) is a potent inducer of MCP-1, interleukin-8 (IL-8), and IP-10 expression in astrocytes. Levels of induced IP-10 protein were sufficiently high to induce chemotaxis of peripheral blood lymphocytes. In addition, Tat(72aa) induced IL-8 expression in astrocytes. IL-8 mRNA induction was seen less then 1 h after Tat(72aa) stimulation, and levels remained elevated for up to 24 h, leading to IL-8 protein production. Tat(72aa)-mediated MCP-1 and IL-8 mRNA induction was susceptible to inhibition by the MEK1/2 inhibitor UO126 but was only modestly decreased by the inclusion of the p38 mitogen-activated protein kinase (MAPK) inhibitor SB202190. In contrast, Tat-mediated IP-10 mRNA induction was suppressed by SB202190 but not by the MEK1/2 inhibitor UO126. These findings indicate that MAPKs play a major role in Tat(72aa)-mediated chemokine induction in astrocytes.

Lentivirus infection in the brain induces matrix metalloproteinase expression: role of envelope diversity

Infection of the brain by lentiviruses, including human immunodeficiency virus (HIV) and feline immunodeficiency virus (FIV), causes inflammation and results in neurodegeneration. Molecular diversity within the lentivirus envelope gene has been implicated in the regulation of cell tropism and the host response to infection. Here, we examine the hypothesis that envelope sequence diversity modulates the expression of host molecules implicated in lentivirus-induced brain disease, including matrix metalloproteinases (MMP) and related transcription factors. Infection of primary macrophages by chimeric HIV clones containing brain-derived envelope fragments from patients with HIV-associated dementia (HAD) or nondemented AIDS patients (HIV-ND) showed that MMP-2 and -9 levels in conditioned media were significantly higher for the HAD clones. Similarly, STAT-1 and JAK-1 levels were higher in macrophages infected by HAD clones. Infections of primary feline macrophages by the neurovirulent FIV strain (V(1)CSF), the less neurovirulent strain (Petaluma), and a chimera containing the V(1)CSF envelope in a Petaluma background (FIV-Ch) revealed that MMP-2 and -9 levels were significantly higher in conditioned media from V(1)CSF- and FIV-Ch-infected macrophages, which was associated with increased intracellular STAT-1 and JAK-1 levels. The STAT-1 inhibitor fludarabine significantly reduced MMP-2 expression, but not MMP-9 expression, in FIV-infected macrophages. Analysis of MMP mRNA and protein levels in brain samples from HIV-infected persons or FIV-infected cats showed that MMP-2 and -9 levels were significantly increased in lentivirus-infected brains compared to those of uninfected controls. Elevated MMP expression was accompanied by significant increases in STAT-1 and JAK-1 mRNA and protein levels in the same brain samples. The present findings indicate that two lentiviruses, HIV and FIV, have common mechanisms of MMP-2 and -9 induction, which is modulated in part by envelope sequence diversity and the STAT-1/JAK-1 signaling pathway.

CXCR4 mediates entry and productive infection of syncytia-inducing (X4) HIV-1 strains in primary macrophages

CCR5 and CXCR4 are the main coreceptors for non-syncytia-inducing (NSI) and syncytia-inducing (SI) HIV-1 strains, respectively. NSI HIV-1 isolates do not infect either human lymphoid or monocytoid cell lines, and this inability correlates with the absence of CCR5 expression in these cell types. The ability of SI HIV-1 isolates to infect human primary macrophages has been disputed. Here, we report that CXCR4 is expressed in primary blood-derived human mononuclear phagocytes at all stages of differentiation, although the maturation process correlates with downregulation of CXCR4 mRNA. Infection experiments with the SI molecular clone NL4-3 tagged with a mutant of the green fluorescent protein established that both monocytes and attached macrophages are susceptible to infection with CXCR4-restricted HIV-1 strains. NL4-3 entry into primary macrophages could be blocked by SDF-1alpha in a dose-dependent manner, or by the anti-CXCR4 monoclonal antibody 12G5. HIV-1 entry led to productive infection. No evidence of postentry defects or nuclear import delay for CXCR4-restricted HIV-1 strains was detected using a quantitative real-time PCR assay measuring HIV-1 DNA entry into the nucleus. Macrophages infected by HIV-1 and expressing virus were maintained in culture for long periods of time (up to 5 months). These results demonstrate that CXCR4 is the main HIV-1 SI coreceptor in human primary macrophages and underline the importance of the macrophage as a long-living viral reservoir for HIV-1.

Inflammatory Cytokines and HIV-1-Associated Neurodegeneration: Oncostatin-M Produced by Mononuclear Cells from HIV-1-Infected Individuals Induces Apoptosis of Primary Neurons

Neurologic abnormalities are common in HIV-1-infected patients and often represent the dominant clinical manifestation of pediatric AIDS. The neurological dysfunction has been directly related to CNS invasion by HIV-1 that is principally, if not exclusively, supported by blood-derived monocytes/macrophages and lymphocytes. By using primary long term cultures of human fetal sensory neurons as well as sympathetic precursors-like neuronal cells, we determined that blood-derived mononuclear cells from HIV-1-infected individuals spontaneously release soluble mediators that can potently inhibit the growth and survival of developing neurons as well as the viability of postmitotic neuronal cells by inducing apoptotic cell death. Analysis of the cytokines produced by lymphomonocytic cells, HIV-1 infected or activated, indicated that oncostatin M (oncM) is a major mediator of these effects. Since low TGF-β1 concentrations were capable of enhancing oncM-mediated neuronal alterations, our data indicate that by acting in concert with other cytokines, oncM may induce neuronal demise in both the developing and the mature brain. Thus, this cytokine may contribute to the setting of the neuronal cell damage observed in HIV-1-infected individuals.

The macrophage origin of the HIV-expressing multinucleated giant cells in hyperplastic tonsils and adenoids

Replication and storage of virus are characteristic features of hyperplastic lymphoid tissues in HIV infection. In opportunistic infections, HIV is synthesized by phagocytic mononuclear and Langhans'-type multinucleated macrophages that coexpress the dendritic cell-associated S-100 and p55 antigens. However, similar cells in hyperplastic tonsils and adenoids from HIV+ individuals were alternatively identified as macrophages or, on the basis of the same S-100 and p55 staining, as dendritic cells. To consider establishing the role of these HIV-rich cells in HIV disease, it is important to reconcile this apparent discrepancy in identity. Hyperplastic tonsils and adenoid specimens were analyzed by HIV RNA in situ hybridization (ISH), light and transmission electron microscopy (TEM), and immunohistochemistry (IHC) (HIV Gag p24 protein, S-100, p55, CD68, HAM56, lysozyme, alpha-1-anti-trypsin, and alpha-1-anti-chymotrypsin). In HIV+ pediatric and adult surgical specimens (n = 11), the giant cells and their mononuclear counterpart were positive for both macrophage and p55 and S-100 IHC markers. In addition, TEM, p24 IHC, and ISH showed HIV expression by cells with typical features of macrophages. Furthermore, these cells were not unique to HIV+ specimens, being seen in 20% of hyperplastic T&A surgical specimens (n = 57) lacking HIV as well as in several types of granulomatous processes, such as sarcoidosis. These cells appear to represent an activated phenotype that can develop independent of HIV, but that may represent a viral host in HIV-infected individuals. Thus, the giant and mononuclear cells that produce striking amounts of HIV in tonsils and adenoids are of macrophage origin, yet, as in opportunistic infections, share dendritic cell-associated antigens, reflecting a common CD34+ bone marrow progenitor.

HIV-1 DNA and mRNA concentrations are similar in peripheral blood monocytes and alveolar macrophages in HIV-1-infected individuals

OBJECTIVE

To determine the relative contribution of alveolar macrophages, peripheral blood monocytes (PBM) and peripheral blood lymphocytes (PBL) from HIV-infected individuals to HIV-1 viral load.

METHODS

Alveolar macrophages were obtained by flexible bronchoscopy, and PBM and PBL by venipuncture from HIV-1-infected individuals. Alveolar macrophages and PBM were purified using immunomagnetic bead selection to deplete CD3+ and CD19+ cells from bronchoalveolar lavage and peripheral blood mononuclear cells, respectively. DNA and mRNA were extracted and gag copy number quantified using polymerase chain reaction (PCR) and reverse transcriptase PCR. The titres of infectious cell-associated HIV-1 in cells were determined by the endpoint dilution coculture technique for alveolar macrophages and PBM.

RESULTS

Alveolar macrophages and PBM from HIV-1-infected subjects (n=11) contained equivalent concentrations of HIV-1 DNA and HIV-1 mRNA as determined by PCR and reverse transcriptase PCR, respectively. Antiretroviral therapy was associated with reduced viral DNA concentrations in alveolar macrophages but not in PBM. PBL had a significantly higher level of proviral DNA and mRNA than alveolar macrophages or PBM.

CONCLUSIONS

Although alveolar macrophages infected in vitro are more permissive for HIV-1 replication than PBM, this difference could not be demonstrated in vivo.

Biology of HIV-1 in women and men

The 1990s have been marked by tremendous progress in understanding HIV-1 infection and disease progression in infected individuals. The new discoveries have direct applications in predicting clinical outcomes and monitoring antiviral therapies. With the identification of secondary receptors for HIV-1 cell entry, the CCR-5 receptor was found to be a single genetically determined factor influencing both HIV-1 transmission and disease progression. Quantitation of HIV-1 RNA led to the discoveries that detectable or even high levels of HIV-1 replication occur during all phases of infection, and that plasma HIV-1 RNA levels are powerful predictors of clinical outcome. These findings have increased the ability to predict disease progression and to monitor-antiviral therapy in infected individuals.

Circular forms of unintegrated human immunodeficiency virus type 1 DNA and high levels of viral protein expression: association with dementia and multinucleated giant cells in the brains of patients with AIDS

Thirty-one histologically abnormal brains from patients with AIDS were studied in order to establish the relationship between multinucleated giant cells, viral protein expression, the various forms of human immunodeficiency virus type 1 (HIV-1) DNA, and clinical evidence of dementia. Unintegrated HIV-1 DNA of 2 to 8 kb was found in 22 of the 31 brains. Multinucleated giant cells without any other pathology were found in 14 cases; unintegrated 1-long terminal repeat (1-LTR) circular forms of HIV-1 DNA and strongly positive immunohistochemistry for gp41 and p24 were found in most of these brains. Most of these patients had a clinical diagnosis of HIV-1-associated dementia and cerebral atrophy. In all the other brains studied, 1-LTR circles were absent and immunohistochemistry for gp41 and p24 was usually negative. Very few of these patients had a clinical diagnosis of dementia. Sequence comparison of the LTR region from integrated HIV-1 DNA with that from unintegrated 1-LTR circular forms of HIV-1 DNA in 12 cases showed no significant differences. A further comparison of these brain-derived LTR sequences with LTR sequences derived directly from lymphoid tissue also showed strong sequence conservation. The V3 loop of the virus from the brain was sequenced in 6 cases and had a non-syncytium inducing-macrophage-tropic genotype. Our results show that (i) although unintegrated HIV-1 DNA was present in most brains from patients with AIDS, molecular evidence of high levels of viral replication was associated with the presence of multinucleated giant cells and dementia, and that (ii) the HIV-1 LTR is not a determinant of neurotropism. These observations suggest that replication of HIV-1 and not just the presence of HIV-1 DNA within giant cells makes the important contribution to central nervous system damage.

Viruses and rickettsiae

In this review I shall try to provide a brief, up-to-date, account of the neuropathology of those viral and rickettsial diseases that are particularly prevalent in tropical regions. These diseases are not, however, exclusive to the tropics. Some, such as AIDS, are common in temperate regions as well, though others are closer to being exclusively tropical, such as some of the arthropod-borne (ARBO) virus encephalides. The latter are dependent for their dissemination on an existence during part of their infectious cycle in insects which are, in turn, climatically and seasonally sensitive. This necessarily limits their geographical distribution. Factors that influence some of the other diseases are less closely dependent on climate and geography and reflect more the social or cultural conditions under which people live. Thus, diseases that depend for their spread on forms of human behavior such as promiscuity or drug abuse (AIDS), or poor hygiene and living conditions (polio, rickettsial diseases) or on contact with domestic and other animals (rabies) may occur in a more widespread distribution, for the tropics are not the only places that afford opportunities for these diseases to flourish. I shall select for discussion aspects of the pathology of these diseases that are currently undergoing investigation but will aim to present these against the backdrop of more established aspects of their pathology. Recent reviews of the pathology of viral encephalitis can be found in Hamilton and Wiley (33) and Esiri and Kennedy (20) and of HIV-1 infection in Price & Sidtis (78) and Scaravilli (85).

HIV type 1 RNA expression in bone marrows of patients with a spectrum of disease

HIV-1-infected individuals at various stages of disease harbor virus in their lymphoid organs, which serve as reservoirs of viral replication throughout the course of infection. Hematologic abnormalities are extremely common in HIV-1-infected individuals and occur at all stages of disease. To determine if the bone marrow is a reservoir of HIV-1 in vivo and if active HIV-1 RNA expression in that site is related to hematologic disease in infected individuals, we examined HIV-1 RNA expression in bone marrow biopsies from 37 patients with a broad spectrum of hematologic and HIV-1-related disease. To detect HIV-1 RNA expression, we performed in situ hybridization. Double-label in situ hybridization-immunohistochemistry was used for precise identification of the type of cell expressing viral RNA. Six of 37 (16%) patients demonstrated HIV-1 RNA expression in the bone marrow. Double-label analysis performed on two marrows localized HIV-1 RNA to cells of the macrophage lineage. Active HIV-1 expression correlated with advanced HIV-1-related disease and CD4 cell depletion rather than a specific hematologic or clinical diagnosis. These data suggest that although the bone marrow does not serve as a reservoir of viral expression throughout the course of infection as do the lymphoid organs, HIV-1-expressing cells are present in the bone marrow during late stages of disease. These data also suggest that hematologic abnormalities in the majority of infected individuals may result from indirect effects of HIV-1 such as cytokine dysregulation rather than HIV-1 expression in the bone marrow itself.

Vacuolar myelopathy in transgenic mice expressing human immunodeficiency virus type 1 proteins under the regulation of the myelin basic protein gene promoter

Vacuolar myelopathy is a common neurological complication in AIDS patients. The pathogenesis of this spinal cord white matter disease remains unclear and it is still debated whether infection of spinal cord with the human immunodeficiency virus type 1 (HIV-1) is causing the disease. We have generated transgenic mice expressing the entire HIV-1 genome under the regulation of an oligodendrocyte-specific promoter. These mice develop spinal cord vacuolar lesions similar to those found in AIDS patients. This animal model provides in vivo evidence linking the expression of HIV-1 proteins in oligodendrocytes to the spinal cord damage found in vacuolar myelopathy.

Augmentation of virus secretion by the human immunodeficiency virus type 1 Vpu protein is cell type independent and occurs in cultured human primary macrophages and lymphocytes

The human immunodeficiency virus type 1-specific Vpu protein is a small integral membrane phosphoprotein that induces degradation of the virus receptor CD4 in the endoplasmic reticulum and, independently, increases the release of progeny virions from infected cells. To address the importance of Vpu for virus replication in primary human cells such as peripheral blood mononuclear cells (PBMC) and monocyte-derived macrophages (MDM), we used three different sets of monocyte-tropic molecular clones of human immunodeficiency virus type 1: a primary isolate, AD8+, and two chimeric variants of the T-cell-tropic isolate NL4-3 carrying the env determinants of either AD8+ or SF162 monocyte-tropic primary isolates. Isogenic variants of these chimeric viruses were constructed to express either wild-type Vpu or various mutants of Vpu. The effects of these mutations in the vpu gene on virus particle secretion from infected MDM or PBMC were assessed by determination of the release of virion-associated reverse transcriptase into culture supernatants, Western blot (immunoblot) analysis of pelleted virions, and steady-state or pulse-chase metabolic labeling. Wild-type Vpu increased virus release four- to sixfold in MDM and two- to threefold in PBMC, while nonphosphorylated Vpu and a C-terminal truncation mutant of Vpu were partially active on virus release in primary cells. These results demonstrate that Vpu regulates virus release in primary lymphocyte and macrophage cultures in a similar manner and to a similar extent to those previously observed in HeLa cells or CD4+ T-cell lines. Thus, our findings provide evidence that Vpu functions in a variety of human cells, both primary cells and continuous cell lines, and mutations in Vpu affect its biological activity independent of the cell type and virus isolate used.

Syncytium formation in cultured human lymphoid tissue: fusion of implanted HIV glycoprotein 120/41-expressing cells with native CD4+ cells

While glycoprotein gp120/41 clearly causes HIV-infected cells to form syncytia in monolayers and in suspension, there is unfortunately scant knowledge on syncytium formation in tissues. We implanted gp120/41-expressing cells labeled with fluorescent particles inside blocks of human lymphoid tissue kept in long-term histoculture. Observed by confocal microscopy, together with immunohistochemical and morphological analysis of implanted cells, more than one-third of these gp120/41-expressing cells fused with native CD4+ cells of the host tissue, yielding small (three to five nuclei) syncytia. Such widespread fusion of gp120/41-expressing cells in tissue in vitro, together with the finding of increased virulence of syncytium-inducing isolates of HIV, support the hypothesis that syncytium formation within lymph tissue of HIV-infected individuals contributes to AIDS pathogenesis. This system and the methods developed may provide a way to study HIV-infected cells inside the very tissue whose destruction may prevent immune system repopulation.

Neurovirulent simian immunodeficiency virus replicates productively in endothelial cells of the central nervous system in vivo and in vitro

The perivascular location of human immunodeficiency virus-infected cells suggests that the virus enters the central nervous system (CNS) by traversing the blood-brain barrier (BBB). In this study, the simian immunodeficiency virus (SIV) macaque model was used to determine whether SIV infects CNS endothelial cells. SIV RNA was detected in capillary endothelial cells in brain sections from animals parenterally inoculated with a neurovirulent strain of SIV by double immunohistochemistry and in situ hybridization and by reverse transcriptase-in situ PCR. These in vivo observations were extended by examining whether SIV replicated productively in cultured macaque brain endothelial cells (MBEC). A neurovirulent strain, SIVmac239/17E-Br, replicated productively in MBEC as determined by the presence of viral cytopathic effect (syncytia), viral DNA by PCR, viral RNA by in situ hybridization, and viral antigen by immunohistochemistry and by the production of high titers of cell-free virus. Virus replication was confirmed by electron microscopy. In contrast, a nonneurovirulent strain, SIVmac239, did not infect MBEC. Infection of the endothelial cells was not blocked by soluble CD4. Thus, endothelial cells may provide a CD4-independent pathway of virus entry to the CNS. In addition, damage to the BBB as a result of endothelial cell infection may provide a mechanism for amplification of viral load in the CNS and may contribute to the CNS dysfunction that characterizes AIDS dementia and SIV encephalitis. These data suggest that MBEC may serve a selective role in determining virus entry to the CNS.

Dual tropism for macrophages and lymphocytes is a common feature of primary human immunodeficiency virus type 1 and 2 isolates

We have investigated the ability of human immunodeficiency virus type 1 (HIV-1) and HIV-2 isolates to infect and replicate in primary human macrophages. Monocytes from blood donors were allowed to differentiate into macrophages by culture in the presence of autologous lymphocytes and human serum for 5 days before infection. A panel of 70 HIV-1 and 12 HIV-2 isolates were recovered from seropositive individuals with different severities of HIV infection. A majority of isolates (55 HIV-1 and all HIV-2) were obtained from peripheral blood mononuclear cells, but isolates from cerebrospinal fluid, monocytes, brain tissue, plasma, and purified CD4+ lymphocytes were also included. All isolates were able to infect monocyte-derived macrophages, even though the replicative capacity of the isolates varied. Interestingly, isolates with a rapid/high, syncytium-inducing phenotype did not differ from slow/low, non-syncytium-inducing isolates in their ability to replicate in monocyte-derived macrophages. Others have reported that rapid/high, syncytium-inducing isolates have a reduced ability to infect and replicate in monocytes. However, different methods to isolate and culture the monocytes/macrophages were used in these studies and our study. Thus, the ability of HIV isolates to replicate in monocytes/macrophages appears to be strongly influenced by the isolation and culture procedures. It remains to be determined which culture procedure is more relevant for the in vivo situation.

Co-infection and synergy of human immunodeficiency virus-1 and herpes simplex virus-1

The human immunodeficiency virus (HIV-1) uses the CD4 molecule, expressed by T helper cells and activated macrophages, as a receptor for entry into host cells. In tissues co-infected with herpes simplex type 1 (HSV-1), HIV-1 virions were observed to infect keratinocytes, which, because they lack the CD4 molecule, are normally incapable of being infected by HIV-1. Although a number of other viruses have been reported to enhance HIV-1 viral transcription in vitro, this is the first in-vivo report to our knowledge of reciprocal enhancement of viral replication associated with co-infection of keratinocytes and macrophages by HIV-1 and HSV-1 in patients with AIDS and non-genital herpes simplex lesions. The virions in the co-infected cells were larger, morphologically atypical, and appear to be hybrids; most contain the HIV-1 envelope necessary for infectivity. The increased viral load and the proximity of the virions to the cutaneous surface may lead to increased risk of transcutaneous transmission of both viruses. These findings point to the need for incorporation of suppressive treatment for herpes simplex in the treatment of AIDS.

Infection of human monocyte-derived macrophages by human immunodeficiency virus mediated by cell-to-cell transmission

We have infected ten-day-old primary cultures of human monocyte-derived macrophages (MDM) with HIV-1 by cocultivation with chronically infected monocytic cell lines. This work has involved the U-937 monocytoid cell line, chronically infected with the HIV-IIIB strain of HIV-1 (U-937HIV IIIB) as well as a number of cell clones, termed UHC, which were derived from U-937HIV IIIB by limiting dilution. Cell-free virus, derived from each of U-937HIV IIIB cells and the UHC1 clone were noninfectious for MDM, as determined by failure to express viral p24 antigen (Ag). In contrast, viral p24 Ag production was detected in MDM that had been cocultivated with U-937HIV IIB, and with each of three UHC clones that produced infectious virus. Infection, in each case, was confirmed by polymerase chain reaction detection via the amplification of proviral DNA. In contrast, cocultivation with the UHC15.7 clone, which fails to cleave viral gp160 to its gp120 and gp41 products or the UHC8 clone, which lacks functional reverse transcriptase, did not lead to infection of MDM. Pretreatment of MDM for 2 hr with 1 microM AZT completely prevented infection by culture fluids containing HIVada, a macrophage-tropic virus, but did not affect infection mediated by cocultivation. These results suggest that cell-to-cell transmission of HIV-1, among monocyte-derived macrophages, can be mediated by proviral DNA. Moreover, gp120 at the surface of infected cells may play an important role in this process, since cell-to-cell HIV transmission could not be demonstrated with the UHC clone that is defective in cleavage of the viral envelope glycoprotein gp160.

Comparative pharmacokinetics of two prodrugs of zidovudine in rabbits: enhanced levels of zidovudine in brain tissue

The pharmacokinetics of two prodrugs of zidovudine (AZT), 1,4-dihydro-1-methyl-3-[(pyridylcarbonyl)oxy] ester and isoleucinyl ester (DPAZT and IAZT, respectively), were investigated in a rabbit model to determine their potential utility as drugs against human immunodeficiency virus. Drugs were administered by intravenous infusion over 5 min at doses equal to 10 mg of AZT per kg of body weight. The levels of the prodrugs and of released AZT in plasma, cerebrospinal fluid (CSF), and brain were determined by high-performance liquid chromatography analysis. DPAZT disappeared rapidly from plasma, whereas IAZT maintained a sustained level in plasma for up to 4 h. The levels in plasma of AZT released from DPAZT were consistently lower than the levels of AZT released from IAZT or AZT itself. At 75 min after infusion of AZT, DPAZT, and IAZT, the CSF plasma AZT ratios were 0.23, 0.30, and 0.25, while the brain/CSF AZT ratios were 0.32, 0.63, and 0.64, respectively. These results indicate that the administration of each of the prodrugs produced a higher concentration of AZT in the brain than did the direct administration of AZT. Both prodrugs therefore may be superior to AZT itself with respect to achieving anti-human immunodeficiency virus concentrations within the central nervous system.

The neurologic complications of human immunodeficiency virus infection

The physician caring for HIV-1-infected patients must have a good working knowledge of the broad spectrum of neurologic diseases that occur in association with this infection. As with any other neurologic disorder, the site of the neuraxis that is affected must be properly identified. In HIV-1-infected persons, more than one site may be involved simultaneously, such as the coexistence of myelopathy and peripheral neuropathy, often resulting in a confusing array of neurologic signs and symptoms. The frequent occurrence of two or more diseases affecting the neuraxis, such as progressive multifocal leukoencephalopathy and toxoplasmosis, further complicates the picture. With the AIDS patient, the physician cannot rely on the clinical adage that all attempts should be made to ascribe the patient's problems to one disease. Often, it is not the case. As with other illnesses, the approach to the HIV-1-infected person with neurologic disease needs to be thorough and fluid. After rendering a diagnosis and embarking on therapy, the physician needs to be open minded about the possibility of an incorrect or additional diagnosis not previously considered. Lastly, despite all the knowledge that has been accumulated in the first decade of the AIDS epidemic, new illnesses occurring with HIV-1 infection are recognized with regularity. The physician must always bear in mind that the illness with which he or she is confronted may be one that has not been previously described.

Expression directed from HIV long terminal repeats in the central nervous system of transgenic mice

Infection with the human immunodeficiency virus (HIV) is frequently accompanied by the AIDS (acquired immunodeficiency syndrome) dementia complex. The role of specific HIV genetic elements in the pathogenesis of central nervous system (CNS) disease is not clear. Transgenic mice were constructed that contained the long terminal repeats (LTRs) of two CNS-derived strains and a T cell tropic strain of HIV-1. Only mice generated with CNS-derived LTRs directed expression in the CNS, particularly in neurons. Thus, some strains of HIV-1 have a selective advantage for gene expression in the brain, and neurons can supply the cellular factors necessary for their transcription.

Wild-type equine infectious anemia virus replicates in vivo predominantly in tissue macrophages, not in peripheral blood monocytes

In situ hybridization of tissues from two horses infected with the wild-type Wyoming strain of equine infectious anemia virus (EIAV) identified the liver, spleen, lymph nodes, kidney, lung, and adrenal gland as the primary host tissue sites for viral transcription during acute infection. Combined immunohistochemistry, with a monoclonal antibody recognizing a cytoplasmic antigen of equine mononuclear phagocytes, and in situ hybridization for viral RNA identified most infected cells as mature tissue macrophages. In contrast, in situ hybridization of adherent peripheral blood mononuclear cells collected from horses on various days during the first 2 weeks postinfection with the Wyoming strain of EIAV failed to detect any viral RNA in these cells. For the two horses described here, serum reverse transcriptase activity correlated directly with the degree of replication detected in tissue macrophages on the day of sacrifice. These results suggest that unlike other lentivirus infections in which mature tissue macrophages accumulate cytoplasmic viral RNA to a high level but fail to produce infectious virions, mature tissue macrophages are the likely primary source of the high titer of viremia present during acute infection with EIAV. No significant posttranscriptional block of viral replication in tissue macrophages appears to occur with EIAV.

Simultaneous detection of ferritin and HIV-1 in reactive microglia

Using ferritin as a marker of reactive microglia, we demonstrated a close association between proliferation of reactive microglia and expression of human immunodeficiency virus type 1 (HIV-1) in brain tissue from autopsied cases of acquired immunodeficiency syndrome (AIDS). An increased number of ferritin-positive reactive microglia was observed in formalin-fixed paraffin-embedded brain sections from all 13 AIDS cases examined. Similar findings were observed in brain tissue from other neurological diseases (subacute sclerosing panencephalitis, herpes simplex encephalitis and multiple sclerosis). Multinucleated giant cells were found in 7 of the AIDS cases which were also intensely labeled for ferritin. Dual-label immunohistochemistry using anti-ferritin and cell-specific markers showed that ferritin-positive cells were distinct from astrocytes, neurons and endothelia using anti-glial fibrillary acidic protein (anti-GFAP), anti-neurofilament protein and Ulex europaeus agglutinin 1, respectively. In 5 AIDS brains, only ferritin-positive cells were shown to contain HIV-1 gp41 antigen using dual-label immunohistochemistry. In addition, HIV-1 RNA was localized in ferritin-positive reactive microglia but not in GFAP-positive astrocytes using immunohistochemistry combined with in situ hybridization. Ferritin-positive reactive microglia and multinucleated giant cells were co-labeled with the microglial marker, Ricinus communis agglutinin 1 (RCA-1). However, RCA-1 also extensively stained resting microglia only a few of which were co-labeled for ferritin. The density of ferritin-positive cells was correlated with the presence of HIV-1 RNA-positive cells in AIDS brain. Thus, ferritin immunoreactivity can be used as an activation marker of microglia in archival paraffin sections and reflects the extent of inflammation in HIV-1-infected brain.

Morphometry, histopathology, and tomography of cerebral atrophy in the acquired immunodeficiency syndrome

Patients with the acquired immunodeficiency syndrome (AIDS) commonly display evidence of gross cerebral atrophy, but its true incidence and pathophysiology in the general AIDS population are unknown. In this study, we measured cerebrospinal fluid (CSF) spaces in 64 consecutively autopsied patients with AIDS, compared them with age-matched non-AIDS subjects, and correlated them with the microscopic neuropathology at autopsy. Thirty-seven of the patients with AIDS (58%) had a CSF space index greater than two standard deviations above the mean of the age-matched control subjects. CSF spaces were expanded the most in frontal and temporal lobes; ventricular spaces were expanded more than sulcal spaces. Regression analysis between age and the measured CSF indexes showed that practically none of the deviation in patients with AIDS could be explained by age-related atrophy. Patients with atrophy were much more likely to have human immunodeficiency virus type 1-associated histopathological changes in their brains, but the relationships were too weak to establish the microscopic cause of the atrophy. Measurement of CSF spaces in antemortem computed tomographic (CT) scans from 47 of the patients with AIDS revealed the same regional pattern of brain wasting. CT diagnosis of cerebral atrophy was strongly concordant with the postmortem diagnosis, but its severity was diagnosed slightly more conservatively at autopsy. Thus, quantitative analysis of CSF spaces in a robust sampling of patients with AIDS confirms that cerebral atrophy is a sensitive, common, and frequently subtle indication of central nervous system human immunodeficiency virus type 1 infection that may occur independently from any single specific microscopic abnormality. Its presence, severity, and regional pattern are detected with reasonable consistency using CT scanning.