Interactions between brain endothelial cells and human T-cell leukemia virus type 1-infected lymphocytes: mechanisms of viral entry into the central nervous system

HAM/TSP Pathogenesis: The Transmigration Activity of HTLV-1-Infected T Cells into Tissues

Slowly progressive spastic paraparesis with bladder dysfunction, the main clinical feature of human T-cell leukemia virus-1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP), is induced by chronic inflammation in the spinal cord, mainly the lower thoracic cord. A long-standing bystander mechanism, such as the destruction of surrounding tissues by inflammatory cytokines, etc., induced under the interaction between infiltrated HTLV-1-infected CD4⁺ T cells and HTLV-1-specific CD8⁺ cytotoxic T cells, has been considered implicated for the induction of chronic inflammation. As this bystander mechanism is triggered conceivably by the transmigration of HTLV-1-infected CD4⁺ T cells to the spinal cord, heightened transmigrating activity of HTLV-1-infected CD4⁺ T cells to the spinal cord might play a crucial role as the first responder in the development of HAM/TSP. This review evaluated the functions of HTLV-1-infected CD4⁺ T cells in HAM/TSP patients as the prerequisite for the acquisition of the activity such as adhesion molecule expression changes, small GTPases activation, and expression of mediators involved in basement membrane disruption. The findings suggest that HTLV-1-infected CD4⁺ T cells in HAM/TSP patients have enough potential to facilitate transmigration into the tissues. Future HAM/TSP research should clarify the molecular mechanisms leading to the establishment of HTLV-1-infected CD4⁺ T cells as the first responder in HAM/TSP patients. In addition, a regimen with an inhibitory activity against the transmigration of HTLV-1-infected CD4⁺ T cells into the spinal cord might be recommended as one of the therapeutic strategies against HAM/TSP patients.

Gene Expression Study of Host and Mycobacterium tuberculosis Interactions in the Manifestation of Acute Tuberculosis

Mycobacterium tuberculosis (M.tb) could induce type IV hypersensitivity. The chemotaxis of the leukocytes toward the site of infection and producing matrix metalloproteinases (MMPs) are key factors in the immune pathogenesis of tuberculosis (TB). Mononuclear cells were isolated from bronchoalveolar lavage (BAL) specimens, and the target from genomic DNA was used for qPCR TB diagnosis and cDNA for specific RT-qPCR gene expression. The subjects were then classified into TB⁺ and TB^- groups, and the expression levels of CFP-10, ESAT-6, CCR1, CCR12 and MMP3,9 were evaluated. The mean level of CCR1 expression in TB⁺ and TB^- patients' BAL was 1.71 ± 0.78 and 0.5 ± 0.22, respectively, which was statistically different (p = 0.01). The CCR2 level, in TB⁺ (2.07 ± 1.4), was higher than in TB^- patients (1.42 ± 0.89, p = 0.01). The MMP9 expression in TB⁺ was 2.56 ± 0.68, also higher than in TB^- patients (1.13 ± 0.35), while MMP3 was lower in TB⁺ (0.22 ± 0.09) than in TB^- (0.64 ± 0.230, p = 0.05). The CCR2/CCR1 and MMP3/MMP9 balance in TB⁺ were reduced, compared to the TB^-. The CFP-10 and ESAT-6 were highly expressed in TB⁺ patients. The CFP-10 expression had a strong negative correlation with albumin (r =  - 0.93, p = 0.001), and a negative correlation with neutrophil (r =  - 0.444, p = 0.1 with 90% CI). The MMP-9 expression showed a positive correlation with WBC count (r = 0.61, p = 0.02), in TB⁺, and had a negative correlation with BMI (r = 0.59, p = 0.02) in TB^-. The M.tb CFP-10 might be implicated in lowering CCR2 and MMP3 expression in favour of M.tb dissemination. Moreover, the balance of CCR2/CCR1 and MMP3/MMP9 can be used as prognostic factors in the severity of TB.

Study of BBB Dysregulation in Neuropathogenicity Using Integrative Human Model of Blood-Brain Barrier

The blood-brain barrier (BBB) is a cellular and physical barrier with a crucial role in homeostasis of the brain extracellular environment. It controls the imports of nutrients to the brain and exports toxins and pathogens. Dysregulation of the blood-brain barrier increases permeability and contributes to pathologies, including Alzheimer's disease, epilepsy, and ischemia. It remains unclear how a dysregulated BBB contributes to these different syndromes. Initial studies on the role of the BBB in neurological disorders and also techniques to permit the entry of therapeutic molecules were made in animals. This review examines progress in the use of human models of the BBB, more relevant to human neurological disorders. In recent years, the functionality and complexity of in vitro BBB models have increased. Initial efforts consisted of static transwell cultures of brain endothelial cells. Human cell models based on microfluidics or organoids derived from human-derived induced pluripotent stem cells have become more realistic and perform better. We consider the architecture of different model generations as well as the cell types used in their fabrication. Finally, we discuss optimal models to study neurodegenerative diseases, brain glioma, epilepsies, transmigration of peripheral immune cells, and brain entry of neurotrophic viruses and metastatic cancer cells.

Immunopathogenesis and Cellular Interactions in Human T-Cell Leukemia Virus Type 1 Associated Myelopathy/Tropical Spastic Paraparesis

HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP) is a neuropathological disorder in 1–3% of individuals infected with Human T-lymphotropic virus 1 (HTLV-1). This condition is characterized by progressive spastic lower limb weakness and paralysis, lower back pain, bladder incontinence, and mild sensory disturbances resembling spinal forms of multiple sclerosis. This disease also causes chronic disability and is therefore associated with high health burden in areas where HTLV-1 infection is endemic. Despite various efforts in understanding the virus and discovery of novel diagnostic markers, and cellular and viral interactions, HAM/TSP management is still unsatisfactory and mainly focused on symptomatic alleviation, and it hasn’t been explained why only a minority of the virus carriers develop HAM/TSP. This comprehensive review focuses on host and viral factors in association with immunopathology of the disease in hope of providing new insights for drug therapies or other forms of intervention.

CD49d Is Upregulated in Circulating T Lymphocytes from HTLV-1-Infected Patients

INTRODUCTION

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic progressive myelopathy associated with an inflammation of the central nervous system (CNS), being characterized by perivascular infiltration of inflammatory cells. HTLV-1-infected cells have the capacity to migrate through endothelial layers by enhancing adhesion receptor expression and corresponding ligands. T cells interact with the extracellular matrix via integrin receptors and these interactions affect both cell migration and proliferation. The importance of these interactions in retrovirus-induced diseases, however, remains less clear.

METHODS

Herein we studied the expression of 3 integrin alpha chains (CD49d, CD49e, and CD49f) on the membrane of T-cell subsets in patients infected by HTLV-1, both HAM/TSP patients and oligo/asymptomatic subjects who were asymptomatic or presented slight manifestations related to the virus infection.

RESULTS

We observed higher peripheral blood frequency of CD49dhiCD4+ and CD49dhiCD8+ T cells in HTLV-1-infected patients.

CONCLUSION

Our findings suggest that the increased expression of adhesion molecules, such as CD49d on T lymphocytes from HTLV-1-infected patients may contribute to the pathogenesis of the disease, in both oligo/asymptomatic and HAM/TSP-infected subjects. Accordingly, it is conceivable that there is a potential use of CD49d as target for a therapeutic approach aiming at blocking migration of activated T cells from HTLV-1-infected patients into the CNS, thus avoiding the progression to HAM/TSP.

Pentosan Polysulfate Demonstrates Anti-human T-Cell Leukemia Virus Type 1 Activities In Vitro and In Vivo

Human T-cell leukemia virus type 1 (HTLV-1) infection causes T-cell leukemia and inflammatory diseases, most notably including HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The underlying mechanism for the pathogenesis of HAM/TSP remains unclear. According to a recent clinical trial, a humanized antibody that targets CCR4⁺ cells ameliorates inflammation by reducing the number of infected cells in the central nervous system; this result suggests that the transmigration of HTLV-1-infected cells plays a crucial role in HAM/TSP. Partly due to the blood-brain barrier, current treatments for HAM/TSP are mostly palliative. Pentosan polysulfate (PPS), a semisynthetic glycosaminoglycan, has recently been used to treat HAM/TSP and was found to alleviate the symptoms. In this study, we investigated the effect of PPS on HTLV-1-infected cells and provide evidence for its efficacy in HAM/TSP. PPS was cytotoxic to certain HTLV-1-infected cells and significantly suppressed HTLV-1 virion production. PPS also efficiently inhibited HTLV-1 cell-cell transmission in T cells. In addition, PPS blocked HTLV-1 infection of primary endothelial cells (human umbilical vascular endothelial cells) and suppressed the subsequent induction of proinflammatory cytokine expression. Furthermore, PPS was found to inhibit the adhesion and transmigration of HTLV-1-infected cells. We also confirmed the anti-HTLV-1 effect of PPS in vivo using two mouse models. PPS blocked HTLV-1 infection in a mouse model with peripheral blood mononuclear cell (PBMC)-humanized NOD-scid IL2Rgamma^null (huPBMC NSG) mice. PPS was also found to suppress the development of dermatitis and lung damage in HTLV-1 bZIP factor (HBZ)-transgenic (HBZ-Tg) mice, an HTLV-1 transgenic mouse model in which the mice develop systemic inflammation.IMPORTANCE HTLV-1 is the first human retrovirus to have been identified and is endemic in certain areas worldwide. HTLV-1 infection leads to the development of an inflammatory disease called HAM/TSP, a myelopathy characterized by slowly progressive spastic paraparesis. There have been no effective therapeutics available for HAM/TSP, but recently, a semisynthetic glycosaminoglycan, named pentosan polysulfate (PPS), has been found to alleviate the symptoms of HAM/TSP. Here we conducted a comprehensive study on the effect of PPS both in vitro and in vivo PPS demonstrated anti-HTLV-1 potential in infected cell lines, as shown by its suppressive effects on HTLV-1 replication and transmission and on the transmigration of infected T cells. Moreover, results obtained from two HTLV-1 mouse models demonstrate that PPS inhibits HTLV-1 infection and inflammation development in vivo Our work offers insights into the treatment of HAM/TSP by PPS and also suggests its possible use for treating other HTLV-1-induced inflammatory diseases.

HTLV-1-host interactions facilitate the manifestations of cardiovascular disease

Atherosclerosis is a multifactorial life-threatening disease which an epidemiologic study in Northeastern Iran showed its association with HTLV-1 infection. Therefore, a cross-sectional study of 39 newly diagnosed subjects with angiography test in three groups including 14 coronary artery disease⁺HTLV-1⁺ (CAD⁺HTLV-1⁺), 8 CAD^-HTLV-1⁺, and 17 CAD⁺HTLV-1^- patients and 11 healthy subjects (CAD^-HTLV-1^-) were conducted. In the present study, Tax and proviral load (PVL) as HTLV-1 virulence factors, along with host chemokine receptor 1 (CCR1), and CCR2 were investigated. Real-time PCR TaqMan method was carried out for PVL measurement and HTLV-1-Tax, CCR1, and CCR2 expressions in peripheral blood mononuclear cells (PBMCs). Furthermore, the main risk factors, lipid profile, and complete blood count (CBC) were assessed. Expression of CCR1 in CAD⁺HTLV-1⁺ group was higher than CAD^-HTLV-1⁺ (P = 0.01) and healthy subjects (P = 0.02). Expression of CCR1 in CAD⁺HTLV-1⁺ was higher in comparison with CAD⁺HTLV-1^-group but did not meet 95% CI (P = 0.02), but meaningful at 91% CI. In addition, expression of CCR2 in CAD⁺HTLV-1⁺ subjects was higher than CAD^-HTLV-1⁺ and CAD⁺HTLV-1^- (P = 0.001, P = 0.005, respectively). In CAD⁺HTLV-1^- subjects, CCR2 was higher than CAD^-HTLV-1⁺ (P = 0.03). The mean PVL in CAD⁺HTLV-1⁺ group is more than CAD^-HTLV-1⁺ (P = 0.041). In HTLV-1⁺ patients Tax had a positive correlation with cholesterol (R = 0.59, P = 0.01), LDL (R = 0.79, P = 0.004) and a negative correlation with HDL (R = -0.47, P = 0.04). These correlations were stronger in CAD⁺HTLV-1⁺. Findings showed that HTLV-1 could alter the expression of CCR2 and, less effect, on CCR1. Moreover, the strong correlation between CCR2 and HTLV-1-Tax with cholesterol, LDL and HDL showed that Tax as the main HTLV-1 virulence factor in cytokine deregulation might be had indirect effects on cholesterol, LDL, and HDL levels.

HAM/TSP-derived HTLV-1-infected T cell lines promote morphological and functional changes in human astrocytes cell lines: possible role in the enhanced T cells recruitment into Central Nervous System

BACKGROUND

The mechanisms through which HTLV-1 leads to and maintains damage in the central nervous system of patients undergoing HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) are still poorly understood. In recent years, increasing evidence indicates that, not only lymphocytes but also glial cells, in particular astrocytes, play a role in the pathophysiology of HAM/TSP. In this study we used a model of co-culture between human HTLV-1-infected (CIB and C91PL) and non-infected (CEM) T lymphocyte cell lines and astrocyte (U251 and U87) cell lines to mimic the in vivo T cell-astrocyte interactions.

RESULTS

We first observed that CIB and C91PL adhere strongly to cultured astrocytes cell lines, and that co-cultures of HTLV-1 infected and astrocyte cell lines cells resulted in rapid syncytium formation, accompanied by severe morphological alterations and increased apoptotic cell death of astrocyte cells. Additionally, cultures of astrocyte cell lines in presence of supernatants harvested from HTLV-1-infected T cell cultures resulted in significant increase in the mRNA of CCL2, CXCL1, CXCL2, CXCL3, CXCL10, IL-13, IL-8, NFKB1, TLR4, TNF, MMP8 and VCAM1, as compared with the values obtained when we applied supernatants of non-infected T- cell lines. Lastly, soluble factors secreted by cultured astrocytic cell lines primed through 1-h interaction with infected T cell lines, further enhanced migratory responses, as compared to the effect seen when supernatants from astrocytic cell lines were primed with non-infected T cell lines.

CONCLUSION

Collectively, our results show that HTLV-1 infected T lymphocyte cell lines interact strongly with astrocyte cell lines, leading to astrocyte damage and increased secretion of attracting cytokines, which in turn may participate in the further attraction of HTLV-1-infected T cells into central nervous system (CNS), thus amplifying and prolonging the immune damage of CNS.

Neuroinvasion of the highly pathogenic influenza virus H7N1 is caused by disruption of the blood brain barrier in an avian model

Influenza A virus (IAV) causes central nervous system (CNS) lesions in avian and mammalian species, including humans. However, the mechanism used by IAV to invade the brain has not been determined. In the current work, we used chickens infected with a highly pathogenic avian influenza (HPAI) virus as a model to elucidate the mechanism of entry of IAV into the brain. The permeability of the BBB was evaluated in fifteen-day-old H7N1-infected and non-infected chickens using three different methods: (i) detecting Evans blue (EB) extravasation into the brain, (ii) determining the leakage of the serum protein immunoglobulin Y (IgY) into the brain and (iii) assessing the stability of the tight-junction (TJ) proteins zonula occludens-1 and claudin-1 in the chicken brain at 6, 12, 18, 24, 36 and 48 hours post-inoculation (hpi). The onset of the induced viremia was evaluated by quantitative real time RT-PCR (RT-qPCR) at the same time points. Viral RNA was detected from 18 hpi onward in blood samples, whereas IAV antigen was detected at 24 hpi in brain tissue samples. EB and IgY extravasation and loss of integrity of the TJs associated with the presence of viral antigen was first observed at 36 and 48 hpi in the telencephalic pallium and cerebellum. Our data suggest that the mechanism of entry of the H7N1 HPAI into the brain includes infection of the endothelial cells at early stages (24 hpi) with subsequent disruption of the TJs of the BBB and leakage of virus and serum proteins into the adjacent neuroparenchyma.

Virus infection, antiviral immunity, and autoimmunity

As a group of disorders, autoimmunity ranks as the third most prevalent cause of morbidity and mortality in the Western World. However, the etiology of most autoimmune diseases remains unknown. Although genetic linkage studies support a critical underlying role for genetics, the geographic distribution of these disorders as well as the low concordance rates in monozygotic twins suggest that a combination of other factors including environmental ones are involved. Virus infection is a primary factor that has been implicated in the initiation of autoimmune disease. Infection triggers a robust and usually well-coordinated immune response that is critical for viral clearance. However, in some instances, immune regulatory mechanisms may falter, culminating in the breakdown of self-tolerance, resulting in immune-mediated attack directed against both viral and self-antigens. Traditionally, cross-reactive T-cell recognition, known as molecular mimicry, as well as bystander T-cell activation, culminating in epitope spreading, have been the predominant mechanisms elucidated through which infection may culminate in an T-cell-mediated autoimmune response. However, other hypotheses including virus-induced decoy of the immune system also warrant discussion in regard to their potential for triggering autoimmunity. In this review, we discuss the mechanisms by which virus infection and antiviral immunity contribute to the development of autoimmunity.

Wild-type measles virus infection upregulates poliovirus receptor-related 4 and causes apoptosis in brain endothelial cells by induction of tumor necrosis factor-related apoptosis-inducing ligand

Small numbers of brain endothelial cells (BECs) are infected in children with neurologic complications of measles virus (MV) infection. This may provide a mechanism for virus entry into the central nervous system, but the mechanisms are unclear. Both in vitro culture systems and animal models are required to elucidate events in the endothelium. We compared the ability of wild-type (WT), vaccine, and rodent-adapted MV strains to infect, replicate, and induce apoptosis in human and murine brain endothelial cells (HBECs and MBECs, respectively). Mice also were infected intracerebrally. All MV stains productively infected HBECs and induced the MV receptor PVRL4. Efficient WT MV production also occurred in MBECs. Extensive monolayer destruction associated with activated caspase 3 staining was observed in HBECs and MBECs, most markedly with WT MV. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), but not Fas ligand, was induced by MV infection. Treatment of MBECs with supernatants from MV-infected MBEC cultures with an anti-TRAIL antibody blocked caspase 3 expression and monolayer destruction. TRAIL was also expressed in the endothelium and other cell types in infected murine brains. This is the first demonstration that infection of low numbers of BECs with WT MV allows efficient virus production, induction of TRAIL, and subsequent widespread apoptosis.

Methodologies to assess drug permeation through the blood-brain barrier for pharmaceutical research

The drug discovery process for drugs that target the central nervous system suffers from a very high rate of failure due to the presence of the blood-brain barrier, which limits the entry of xenobiotics into the brain. To minimise drug failure at different stages of the drug development process, new methodologies have been developed to understand the absorption, distribution, metabolism, excretion and toxicity (ADMET) profile of drug candidates at early stages of drug development. Additionally, understanding the permeation of drug candidates is also important, particularly for drugs that target the central nervous system. During the first stages of the drug discovery process, in vitro methods that allow for the determination of permeability using high-throughput screening methods are advantageous. For example, performing the parallel artificial membrane permeability assay followed by cell-based models with interesting hits is a useful technique for identifying potential drugs. In silico models also provide interesting information but must be confirmed by in vitro models. Finally, in vivo models, such as in situ brain perfusion, should be studied to reduce a large number of drug candidates to a few lead compounds. This article reviews the different methodologies used in the drug discovery and drug development processes to determine the permeation of drug candidates through the blood-brain barrier.

Mesenchymal stem cells transmigrate between and directly through tumor necrosis factor-α-activated endothelial cells via both leukocyte-like and novel mechanisms

Systemically administered adult mesenchymal stem cells (MSCs), which are being explored in clinical trials to treat inflammatory disease, exhibit the critical ability to extravasate at sites of inflammation. We aimed to characterize the basic cellular processes mediating this extravasation and compare them to those involved in leukocyte transmigration. Using high-resolution confocal and dynamic microscopy, we show that, like leukocytes, human bone marrow-derived MSC preferentially adhere to and migrate across tumor necrosis factor-α-activated endothelium in a vascular cell adhesion molecule-1 (VCAM-1) and G-protein-coupled receptor signaling-dependent manner. As several studies have suggested, we observed that a fraction of MSC was integrated into endothelium. In addition, we observed two modes of transmigration not previously observed for MSC: Paracellular (between endothelial cells) and transcellular (directly through individual endothelial cells) diapedesis through discrete gaps and pores in the endothelial monolayer, in association with VCAM-1-enriched "transmigratory cups". Contrasting leukocytes, MSC transmigration was not preceded by significant lateral migration and occurred on the time scale of hours rather than minutes. Interestingly, rather than lamellipodia and invadosomes, MSC exhibited nonapoptotic membrane blebbing activity that was similar to activities previously described for metastatic tumor and embryonic germ cells. Our studies suggest that low avidity binding between endothelium and MSC may grant a permissive environment for MSC blebbing. MSC blebbing was associated with early stages of transmigration, in which blebs could exert forces on underlying endothelial cells indicating potential functioning in breaching the endothelium. Collectively, our data suggest that MSC transmigrate actively into inflamed tissues via both leukocyte-like and novel mechanisms.

Blood-brain barrier and retroviral infections

Homeostasis in the central nervous system (CNS) is maintained by active interfaces between the bloodstream and the brain parenchyma. The blood-brain barrier (BBB) constitutes a selective filter for exchange of water, solutes, nutrients, and controls toxic compounds or pathogens entry. Some parasites, bacteria, and viruses have however developed various CNS invasion strategies, and can bypass the brain barriers. Concerning viruses, these strategies include transport along neural pathways, transcytosis, infection of the brain endothelial cells, breaching of the BBB, and passage of infected-leukocytes. Moreover, neurotropic viruses can alter BBB functions, thus compromising CNS homeostasis. Retroviruses have been associated to human neurological diseases: HIV (human immunodeficiency virus 1) can induce HIV-associated dementia, and HTLV-1 (human T lymphotropic virus 1) is the etiological factor of tropical spastic paraparesis/HTLV-1 associated myelopathy (TSP/HAM). The present review focuses on how the different retroviruses interact with this structure, bypass it and alter its functions.

Neuroimmunity of HTLV-I Infection

Human T-lymphotrophic virus type I (HTLV-I) is an oncogenic retrovirus and its infection is associated with a variety of human diseases including HTLV-I-associated myelopathy/tropic spastic paraparesis (HAM/TSP). Large numbers of epidemiological, virological, immunological, and clinical studies on HTLV-I- and HTLV-I-associated diseases have been published, although the pathogenesis of HAM/TSP remains to be fully understood. In the last several years, researchers have shown that several key factors are important in HTLV-I-associated neurologic disease including high HTLV-I proviral load and a strong immune response to HTLV-I. Here, we review pathophysiological findings on HAM/TSP and focus on viral-host immune responses to the virus in HTLV-I infected individuals. In particular, the role of HTLV-I-specific CD8+ T cell response is highlighted.

Cytokine and growth factor expression by HTLV-1 Lck-tax transgenic cells in SCID mice

The Tax protein encoded by HTLV-1 plays a key role in the development of ATL in infected individuals. Our previous studies showed that tax transgenic mice develop disease that is almost identical to human ATL, with widespread organ invasion by lymphomatous cells and the development of leukemia. The same pathology develops rapidly in SCID mice engrafted with cells from the transgenic animals. In the present study, we used this SCID model to analyze the expression levels of several cytokines, growth factors, and adhesion molecules to determine their possible involvement in the development of disease. We showed that Tax expression was undetectable at the protein level in the tax-transformed cells used to inoculate the SCID mice and that these cells displayed constitutive NF-kappaB and Akt activity. We demonstrated significant differences in the levels of circulating PDGF-BB, TNF-alpha, sICAM-1, and sVCAM-1 in inoculated animals. Cell-surface staining of the tax transgenic cells showed that they do not express receptors for any of the upregulated growth factors. Significant differences were not found in the secreted levels of bFGF, MMP9, VEGF, or E-selectin, whereas IL-2, IL-15, IL-6, IL-1beta, and IFN-gamma expression was undetectable. Even though the number of factors analyzed is limited, our study identified TNF-alpha, PDGF-BB, and the adhesion molecules sICAM-1 and sVCAM-1 as factors that may contribute to the high levels of organ infiltration by leukemic cells in this tax transgenic SCID model.

[Implication of the blood-brain barrier in neurological diseases: part II]

The main characteristic of the blood-brain-barrier (BBB) is its extremely low permeability, due to tight intercellular endothelial junctions and a variety of transporters, which provides the brain with a unique protection against the potential toxicity of several xenobiotics, but also constitutes a major limitation to drug delivery to the central nervous system. Several dysfunctions of the BBB have been recently implicated in the pathophysiology of neurological diseases: inflammatory, vascular, tumoral, infectious and neurodegenerative diseases. Based on a better knowledge of the BBB biology, new therapeutic strategies are emerging, which by-pass the BBB or take advantage of the selective expression of membrane proteins by brain endothelial cells or circulating leucocytes to target new drugs, such as the anti-VLA4 antibody recently approved for multiple sclerosis treatment. This review will focus on the recently described BBB dysfunctions presumably involved in various neurological diseases.

Role of resident CNS cell populations in HTLV-1-associated neuroinflammatory disease

Human T cell leukemia virus type 1 (HTLV-1), the first human retrovirus discovered, is the etiologic agent for a number of disorders; the two most common pathologies include adult T cell leukemia (ATL) and a progressive demyelinating neuroinflammatory disease, HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The neurologic dysfunction associated with HAM/TSP is a result of viral intrusion into the central nervous system (CNS) and the generation of a hyperstimulated host response within the peripheral and central nervous system that includes expanded populations of CD4+ and CD8+ T cells and proinflammatory cytokines/chemokines in the cerebrospinal fluid (CSF). This robust, yet detrimental immune response likely contributes to the death of myelin producing oligodendrocytes and degeneration of neuronal axons. The mechanisms of neurological degeneration in HAM/TSP have yet to be fully delineated in vivo and may involve the immunogenic properties of the HTLV-1 transactivator protein Tax. This comprehensive review characterizes the available knowledge to date concerning the effects of HTLV-1 on CNS resident cell populations with emphasis on both viral and host factors contributing to the genesis of HAM/TSP.

Alteration of blood-brain barrier integrity by retroviral infection

The blood–brain barrier (BBB), which forms the interface between the blood and the cerebral parenchyma, has been shown to be disrupted during retroviral-associated neuromyelopathies. Human T Lymphotropic Virus (HTLV-1) Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP) is a slowly progressive neurodegenerative disease associated with BBB breakdown. The BBB is composed of three cell types: endothelial cells, pericytes and astrocytes. Although astrocytes have been shown to be infected by HTLV-1, until now, little was known about the susceptibility of BBB endothelial cells to HTLV-1 infection and the impact of such an infection on BBB function. We first demonstrated that human cerebral endothelial cells express the receptors for HTLV-1 (GLUT-1, Neuropilin-1 and heparan sulfate proteoglycans), both in vitro, in a human cerebral endothelial cell line, and ex vivo, on spinal cord autopsy sections from HAM/TSP and non-infected control cases. In situ hybridization revealed HTLV-1 transcripts associated with the vasculature in HAM/TSP. We were able to confirm that the endothelial cells could be productively infected in vitro by HTLV-1 and that blocking of either HSPGs, Neuropilin 1 or Glut1 inhibits this process. The expression of the tight-junction proteins within the HTLV-1 infected endothelial cells was altered. These cells were no longer able to form a functional barrier, since BBB permeability and lymphocyte passage through the monolayer of endothelial cells were increased. This work constitutes the first report of susceptibility of human cerebral endothelial cells to HTLV-1 infection, with implications for HTLV-1 passage through the BBB and subsequent deregulation of the central nervous system homeostasis. We propose that the susceptibility of cerebral endothelial cells to retroviral infection and subsequent BBB dysfunction is an important aspect of HAM/TSP pathogenesis and should be considered in the design of future therapeutics strategies.

The blood–brain barrier (BBB) forms the interface between the blood and the central nervous system (CNS). BBB disruption is considered to be a key event in the pathogenesis of retroviral-associated neurological diseases. The present paper deals with the susceptibility of the endothelial cells (i.e., one of the main cellular components of BBB) to retroviral infection, and with the impact of infection in BBB function. This study focuses on the Human T-Lymphotropic Virus (HTLV-1), which infects 20 million people worldwide, and is the etiological agent of a neurodegenerative disease called HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP). We first demonstrated that the cerebral endothelial cells express the receptors for the retrovirus in vitro, and on spinal cord autopsy sections from non-infected and HAM/TSP patients. We found on these latter that vascular-like structures were infected and confirmed in vitro that the endothelial cells could be productively infected by HTLV-1. We demonstrated that such an infection impairs BBB properties in vitro, as well as tight junctions, that are cell adhesion structures. This study is the first to demonstrate the impact of HTLV-1 infection on human BBB integrity; such a susceptibility has to be considered in the design of future therapeutics strategies.

The blood-brain barrier in brain homeostasis and neurological diseases

Brain endothelial cells are unique among endothelial cells in that they express apical junctional complexes, including tight junctions, which quite resemble epithelial tight junctions both structurally and functionally. They form the blood-brain-barrier (BBB) which strictly controls the exchanges between the blood and the brain compartments by limiting passive diffusion of blood-borne solutes while actively transporting nutrients to the brain. Accumulating experimental and clinical evidence indicate that BBB dysfunctions are associated with a number of serious CNS diseases with important social impacts, such as multiple sclerosis, stroke, brain tumors, epilepsy or Alzheimer's disease. This review will focus on the implication of brain endothelial tight junctions in BBB architecture and physiology, will discuss the consequences of BBB dysfunction in these CNS diseases and will present some therapeutic strategies for drug delivery to the brain across the BBB.

Human Blood-Brain Barrier Disruption by Retroviral-Infected Lymphocytes: Role of Myosin Light Chain Kinase in Endothelial Tight-Junction Disorganization

The blood-brain barrier (BBB), which constitutes the interface between blood and cerebral parenchyma, has been shown to be disrupted during retroviral associated neuromyelopathies. Human T cell leukemia virus (HTLV-1)-associated myelopathy/tropical spastic paraparesis is a slowly progressive neurodegenerative disease, in which evidence of BBB breakdown has been demonstrated by the presence of lymphocytic infiltrates in the CNS and plasma protein leakage through cerebral endothelium. Using an in vitro human BBB model, we investigated the cellular and molecular mechanisms involved in endothelial changes induced by HTLV-1-infected lymphocytes. We demonstrate that coculture with infected lymphocytes induces an increase in paracellular endothelial permeability and transcellular migration, via IL-1alpha and TNF-alpha secretion. This disruption is associated with tight junction disorganization between endothelial cells, and alterations in the expression pattern of tight junction proteins such as zonula occludens 1. These changes could be prevented by inhibition of the NF-kappaB pathway or of myosin light chain kinase activity. Such disorganization was confirmed in histological sections of spinal cord from an HTLV-1-associated myelopathy/tropical spastic paraparesis patient. Based on this BBB model, the present data indicate that HTLV-1-infected lymphocytes can induce BBB breakdown and may be responsible for the CNS infiltration that occurs in the early steps of retroviral-associated neuromyelopathies.

Proinflammatory cytokine gene induction by human T-cell leukemia virus type 1 (HTLV-1) and HTLV-2 Tax in primary human glial cells

Infection with human T-cell leukemia virus type 1 (HTLV-1) can result in the development of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic inflammatory disease of the central nervous system (CNS). HTLV-2 is highly related to HTLV-1 at the genetic level and shares a high degree of sequence homology, but infection with HTLV-2 is relatively nonpathogenic compared to HTLV-1. Although the pathogenesis of HAM/TSP remains to be fully elucidated, previous evidence suggests that elevated levels of the proinflammatory cytokines in the CNS are associated with neuropathogenesis. We demonstrate that HTLV-1 infection in astrogliomas results in a robust induction of interleukin-1beta (IL-1beta), IL-1alpha, tumor necrosis factor alpha (TNF-alpha), TNF-beta, and IL-6 expression. HTLV encodes for a viral transcriptional transactivator protein named Tax that also induces the transcription of cellular genes. To investigate and compare the effects of Tax1 and Tax2 expression on the dysregulation of proinflammatory cytokines, lentivirus vectors were used to transduce primary human astrocytomas and oligodendrogliomas. The expression of Tax1 in primary human astrocytomas and oligodendrogliomas resulted in significantly higher levels of proinflammatory cytokine gene expression compared to Tax2. Notably, Tax1 expression uniquely sensitized primary human astrocytomas to apoptosis. A Tax2/Tax1 chimera encoding the C-terminal 53 amino acids of the Tax1 fused to the Tax2 gene (Tax(221)) demonstrated a phenotype that resembled Tax1, with respect to proinflammatory cytokine gene expression and sensitization to apoptosis. The patterns of differential cytokine induction and sensitization to apoptosis displayed by Tax1 and Tax2 may reflect differences relating to the heightened neuropathogenicity associated with HTLV-1 infection and the development of HAM/TSP.

Role of the human T-cell leukemia virus type 1 PTAP motif in Gag targeting and particle release

Human T-cell leukemia virus type 1 (HTLV-1) Gag is targeted to the plasma membrane for particle assembly and release. How HTLV-1 Gag targeting occurs is not well understood. The PPPY and PTAP motifs were previously shown to be involved in HTLV-1 particle release with PTAP playing a more subtle role in virus budding. These L domains function through the interaction with host cellular proteins normally involved in multivesicular body (MVB) morphogenesis. The plasma membrane pathway rather than the MVB pathway was found to be the primary pathway for HTLV-1 particle release in HeLa cells. Intriguingly, disruption of the PTAP motif led to a defect in the targeting of Gag from the plasma membrane to CD63-positive MVBs. Particles or particle buds were observed to be associated with MVBs by electron microscopy, implying that Gag targeting to the MVB resulted in particle budding. Blocking clathrin-dependent endocytosis was found not to influence localization of the HTLV-1 Gag PTAP mutant, indicating that Gag did not reach the MVBs through clathrin-dependent endocytosis. Our observations imply that the interaction between Gag and TSG101 is not required for Gag targeting to the MVB. Overexpression of dynamitin p50 increased particle release, suggesting that there was an increase in the intracellular transport of MVBs to the cell periphery by the utilization of the dynein-dynactin motor complex. Intriguingly, virus particle release with this mutant was reduced by 20-fold compared to that of wild type in HeLa cells, which is in marked contrast to the less-than-twofold defect observed for particle production of the HTLV-1 Gag PTAP mutant from 293T cells. These results indicate that the role of the PTAP motif in L domain function is cell type dependent.

Muscle wasting induced by HTLV-1 tax-1 protein: an in vitro and in vivo study

Besides tropical spastic paraparesis/human T-cell leukemia virus type-1 (HTLV-1)-associated myelopathy, the human retrovirus HTLV-1 causes inflammatory disorders such as myositis. Although the pathogenesis of HTLV-1-associated myositis is primarily unknown, a direct effect of cytokines or viral proteins in myocytotoxicity is suspected. We have developed an in vitro cell culture model to study the interactions between primary human muscle cells and HTLV-1 chronically infected cells. When HTLV-1-infected cell lines were added to differentiated muscle cultures, cytopathic changes such as fiber shrinking were observed as early as 1 day after contact. This was accompanied by alterations in desmin and vimentin organization, occurring in the absence of muscle cell infection but with Tax-1 present in myotubes. Cytopathic changes were also observed when infected culture supernatants were added to the muscle cells. Fiber atrophy and cytoskeletal disorganization were confirmed in muscle biopsies from two HTLV-1-infected patients with myositis. Transduction of cultured muscle cells with a lentiviral vector containing the HTLV-1 Tax gene reproduced such effects in vitro. The present data indicate that the myocytotoxicity that is observed in HTLV-1-associated myopathies can be due to a direct effect of the Tax-1 protein expressed in infected inflammatory cells, in the absence of muscle cell infection.

HTLV-1 induced molecular mimicry in neurological disease

As a model for molecular mimicry, we study patients infected with human T-lymphotropic virus type 1 (HTLV-1) who develop a neurological disease called HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a disease with important biological similarities to multiple sclerosis (MS) (Khan et al. 2001; Levin et al. 1998, 2002a; Levin and Jacobson 1997). The study of HAM/TSP, a disease associated with a known environmental agent (HTLV-1), allows for the direct comparison of the infecting agent with host antigens. Neurological disease in HAM/TSP patients is associated with immune responses to HTLV-1-tax (a regulatory and immunodominant protein) and human histocompatibility leukocyte antigen (HLA) DRB1*0101 (Bangham 2000; Jacobson et al. 1990; Jeffery et al. 1999; Lal 1996). Recently, we showed that HAM/TSP patients make antibodies to heterogeneous nuclear ribonuclear protein A1 (hnRNP A1), a neuron-specific autoantigen (Levin et al. 2002a). Monoclonal antibodies to tax cross-reacted with hnRNP A1, indicating molecular mimicry between the two proteins. Infusion of cross-reactive antibodies with an ex vivo system completely inhibited neuronal firing indicative of their pathogenic nature (Kalume et al. 2004; Levin et al. 2002a). These data demonstrate a clear link between chronic viral infection and autoimmune disease of the central nervous system (CNS) in humans and, we believe, in turn will give insight into the pathogenesis of MS.

Use of polarised equine endothelial cell cultures and an in vitro thrombosis model for potential characterisation of EHV-1 strain variation

Equine herpesvirus-1 (EHV-1) is responsible for respiratory disease and abortion in pregnant mares. Some high virulence isolates of EHV-1 also cause neurological disease. The pathogenesis of both abortion and neurological disease relates in part, to thrombus formation occurring in the pregnant uterus and central nervous system. The differences in disease outcome may relate to differing abilities of high and low virulence EHV-1 isolates to cause cell-associated viraemia, infect endothelial cells and cause thrombosis at sites distant from the respiratory tract. This study attempted to identify in vitro assays, which could be used to characterise the interaction between these isolates, equine endothelial cells and clotting factors. No significant difference was found between the growth kinetics of high and low virulence isolates of EHV-1 in polarised endothelial cells. For both isolates, virus was released preferentially from the apical surface of the polarised cells. The functional effects of viral infection on endothelial cells, with reference to virally-induced thrombosis were then investigated. Endothelial cells were grown on microcarrier beads, infected with EHV-1 and assayed for procoagulant activity. No significant difference in clotting time was observed between mock and EHV-1 infected endothelial cells in microcarrier cultures. Thus the degree of thrombosis may reflect a more complex interaction between endothelial cells, circulating leucocytes and other factors in the microenvironment.

Cells of the central nervous system as targets and reservoirs of the human immunodeficiency virus

The availability of highly active antiretroviral therapies (HAART) has not eliminated HIV-1 infection of the central nervous system (CNS) or the occurrence of HIV-associated neurological problems. Thus, the neurobiology of HIV-1 is still an important issue. Here, we review key features of HIV-1-cell interactions in the CNS and their contributions to persistence and pathogenicity of HIV-1 in the CNS. HIV-1 invades the brain very soon after systemic infection. Various mechanisms have been proposed for HIV-1 entry into the CNS. The most favored hypothesis is the migration of infected cells across the blood-brain barrier ("Trojan horse" hypothesis). Virus production in the CNS is not apparent before the onset of AIDS, indicating that HIV-1 replication in the CNS is successfully controlled in pre-AIDS. Brain macrophages and microglia cells are the chief producers of HIV-1 in brains of individuals with AIDS. HIV-1 enters these cells by the CD4 receptor and mainly the CCR5 coreceptor. Various in vivo and cell culture studies indicate that cells of neuroectodermal origin, particularly astrocytes, may also be infected by HIV-1. These cells restrict virus production and serve as reservoirs for HIV-1. A limited number of studies suggest restricted infection of oligodendrocytes and neurons, although infection of these cells is still controversial. Entry of HIV-1 into neuroectodermal cells is independent of the CD4 receptor, and a number of different cell-surface molecules have been implicated as alternate receptors of HIV-1. HIV-1-associated injury of the CNS is believed to be caused by numerous soluble factors released by glial cells as a consequence of HIV-1 infection. These include both viral and cellular factors. Some of these factors can directly induce neuronal injury and death by interacting with receptors on neuronal membranes (neurotoxic factors). Others can activate uninfected cells to produce inflammatory and neurotoxic factors and/or promote infiltration of monocytes and T-lymphocytes, thus amplifying the deleterious effects of HIV-1 infection. CNS responses to HIV-1 infection also include mechanisms that enhance neuronal survival and strengthen crucial neuronal support functions. Future challenges will be to develop strategies to prevent HIV-1 spread in the brain, bolster intrinsic defense mechanisms of the brain and to elucidate the impact of long-term persistence of HIV-1 on CNS functions in individuals without AIDS.

Rat brain endothelial cell lines for the study of blood-brain barrier permeability and transport functions

(1) In vitro models of the BBB have been developed from cocultures between bovine, porcine, rodent or human brain capillary endothelial cells with rodent or human astrocytes. Since most in vivo BBB studies have been performed with small laboratory animals, especially rats, it is important to establish a rat brain endothelial (RBE) cell culture system that will allow correlations between in vitro and in vivo results. The present review will constitute a brief description of the best characterized RBE cell lines (RBE4, GP8/3.9, GPNT, RBEC1, TR-BBBs and rBCEC4 cell lines) and will summarize their recent and important contribution to our current knowledge of the BBB transport functions and permeability to blood-borne solutes, drugs, and cells. (2) In most cases, primary cultures of RBE cells were transduced with an immortalizing gene (SV40 or polyoma virus large T-antigen or adenovirus E1A), either by transfection of plasmid DNA or by infection using retroviral vectors. In one case however, the conditionally immortalized TR-BBB cell line was derived from primary cultures of brain endothelial cells of SV40-T-expressing transgenic rats. (3) All cell lines appear to have an endothelial morphology. The absence of foci formation would mean that the cells are not transformed. The endothelial origin is shown by the expression of Factor VIII-related antigen. Immortalized RBE cells express all the enzymes and transporters that are considered as specific for the blood-brain barrier endothelium, with similar characteristics to those expected from in vivo analyses, but at a significantly lower level. Some RBE cell lines are responsive to astroglial factors, such as RBE4 cells, rBEC4, and TR-BBB cells. None of the immortalized RBE cell lines appear to generate the necessary restrictive paracellular barrier properties that would allow to use them in transendothelial permeability screening. (4) RBE cell lines have been used to demonstrate that transporters such as organic cation transporter/carnitine transporter, serotonin transporter, and the ATA2 system A isoform are expressed in rat brain endothelium. When the transporter is shown to be expressed with the same properties in the immortalized RBE cells as in vivo, regulation studies may be initiated even if the transporter is down-regulated. Pharmacological applications have been proposed with well-characterized transporters such as monocarboxylic acid transporter-1, large neutral amino acid tansporter-1, nucleoside carrier systems, and P-glycoprotein. RBE cell monolayers have also been used to investigate the mechanism of the transendothelial transport of large molecules, such as immunoliposomes or nanoparticles, potentially useful as drug delivery vectors to the brain. (5) RBE4 and GP8 cell lines have been extensively used to demonstrate that intercellular adhesion molecule-1 (ICAM-1) engagement in brain endothelial cells triggers multiple signal transduction pathways. Using functional assays, it was established that ICAM-1 signaling is intimately and actively involved in facilitating lymphocyte infiltration. (6) Several RBE cell lines have been described, which constitute tentative in vitro models of the rat BBB. The major limitation of these models generally appears to be due to their relatively high paracellular permeability to small molecules, thus limiting their use for permeability studies. The strategies developed for the production of these RBE cell lines will enable the characterization of still more efficient permeability models, as well as the immortalization of human brain endothelial cells.

Permeability studies on in vitro blood-brain barrier models: physiology, pathology, and pharmacology

(1) The specifically regulated restrictive permeability barrier to cells and molecules is the most important feature of the blood-brain barrier (BBB). The aim of this review was to summarize permeability data obtained on in vitro BBB models by measurement of transendothelial electrical resistance and by calculation of permeability coefficients for paracellular or transendothelial tracers. (2) Results from primary cultures of cerebral microvascular endothelial cells or immortalized cell lines from bovine, human, porcine, and rodent origin are presented. Effects of coculture with astroglia, neurons, mesenchymal cells, blood cells, and conditioned media, as well as physiological influence of serum components, hormones, growth factors, lipids, and lipoproteins on the barrier function are discussed. (3) BBB permeability results gained on in vitro models of pathological conditions including hypoxia and reoxygenation, neurodegenerative diseases, or bacterial and viral infections have been reviewed. Effects of cytokines, vasoactive mediators, and other pathogenic factors on barrier integrity are also detailed. (4) Pharmacological treatments modulating intracellular cyclic nucleotide or calcium levels, and activity of protein kinases, protein tyrosine phosphatases, phospholipases, cyclooxygenases, or lipoxygenases able to change BBB integrity are outlined. Barrier regulation by drugs involved in the metabolism of nitric oxide and reactive oxygen species, as well as influence of miscellaneous treatments are also listed and evaluated. (5) Though recent advances resulted in development of improved in vitro BBB model systems to investigate disease modeling, drug screening, and testing vectors targeting the brain, there is a need for checking validity of permeability models and cautious interpretation of data.

Autoimmunity and molecular mimicry in tropical spastic paraparesis/human T-lymphotropic virus-associated myelopathy

Viruses share antigenic sites with normal host cell components, a phenomenon known as molecular mimicry. It has long been suggested that viral infections might trigger an autoimmune response by several mechanisms including molecular mimicry. More than 600 antiviral monoclonal antibodies generated against 11 different viruses have been reported to react with 3.5% of cells specific for uninfected mouse organs. The main pathological feature of tropical spastic paraparesis/human T-lymphotropic virus type I (HTLV-I)-associated myelopathy (TSP/HAM) is a chronic inflammation of the spinal cord characterized by perivascular cuffing of mononuclear cells accompanied by parenchymal lymphocytic infiltration. We detected the presence of autoantibodies against a 98- to 100-kDa protein of in vitro cultured human astrocytes and a 33- to 35-kDa protein from normal human brain in the serum of HTLV-I-seropositive individuals. The two cell proteins exhibited molecular mimicry with HTLV-I gag and tax proteins in TSP/HAM patients, respectively. Furthermore, the location of 33- to 35-kDa protein cross-reaction correlated with the anatomical spinal cord areas (in the rat model) in which axonal damage has been reported in several cases of TSP/HAM patients. Our experimental evidence strongly suggests that the demyelinating process occurring in TSP/HAM may be mediated by molecular mimicry between domains of some viral proteins and normal cellular targets of the spinal cord sections involved in the neurodegeneration.

Establishing phenotypic features associated with morbidity in human T-cell lymphotropic virus type 1 infection

The human T-cell lymphotropic virus type 1 (HTLV-1) is the causative agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HT). Although it is widely believed that virus infection and host immune response are involved in the pathogenic mechanisms, the role of the immune system in the development and/or maintenance of HT remains unknown. We performed an analysis of the peripheral blood leukocyte phenotype for two different subcohorts of HTLV-1-infected individuals to verify the existence of similar immunological alterations, possible laboratory markers for HT. The leukocyte population balance, the activation status of the T lymphocytes, and the cellular migratory potential of T lymphocytes, monocytes, and neutrophils were evaluated in the peripheral blood of HTLV-1-infected individuals classified as asymptomatic individuals, oligosymptomatic individuals, and individuals with HT. Data analysis demonstrated that a decreased percentage of B cells, resulting in an increased T cell/B cell ratio and an increase in the CD8+ HLA-DR+ T lymphocytes, exclusively in the HT group could be identified in both subcohorts, suggesting its possible use as a potential immunological marker for HT for use in the laboratory. Moreover, analysis of likelihood ratios showed that if an HTLV-1-infected individual demonstrated B-cell percentages lower than 7.0%, a T cell/B cell ratio higher than 11, or a percentage of CD8+ HLA-DR+ T lymphocytes higher than 70.0%, this individual would have, respectively, a 12-, 13-, or 22-times-greater chance of belonging to the HT group. Based on these data, we propose that the T cell/B cell ratios and percentages of circulating B cells and activated CD8+ T lymphocytes in HTLV-1-infected patients are important immunological indicators which could help clinicians monitor HTLV-1 infection and differentiate the HT group from the asymptomatic and oligosymptomatic groups.

Possible etiologies for tropical spastic paraparesis and human T lymphotropic virus I-associated myelopathy

The epidemiology of tropical spastic paraparesis/human T lymphotropic virus I (HTLV-I)-associated myelopathy (TSP/HAM) is frequently inconsistent and suggests environmental factors in the etiology of these syndromes. The neuropathology corresponds to a toxometabolic or autoimmune process and possibly not to a viral disease. Some logical hypotheses about the etiology and physiopathology of TSP and HAM are proposed. Glutamate-mediated excitotoxicity, central distal axonopathies, cassava, lathyrism and cycad toxicity may explain most cases of TSP. The damage caused to astrocytes and to the blood-brain barrier by HTLV-I plus xenobiotics may explain most cases of HAM. Analysis of the HTLV-I/xenobiotic ratio clarifies most of the paradoxical epidemiology of TSP and HAM. Modern neurotoxicology, neuroimmunology and molecular biology may explain the neuropathology of TSP and HAM. It is quite possible that there are other xenobiotics implicated in the etiology of some TSP/HAMs. The prevention of these syndromes appears to be possible today.

Changes in cytoskeletal and tight junctional proteins correlate with decreased permeability induced by dexamethasone in cultured rat brain endothelial cells

The blood-brain barrier (BBB) plays an important role in controlling the passage of molecules from the blood to the extracellular fluid environment of the brain. An immortalised rat brain endothelial cell line (GPNT) was used to investigate the mechanisms underlying dexamethasone-induced decrease in paracellular permeability. Following treatment with 1 microM dexamethasone there was a decrease in transmonolayer paracellular permeability mainly to sucrose, fluorescein and dextrans of up to 20 KDa. According to pore theory, these differences in permeability were consistent with a decrease in the number of pores between brain endothelial cells. This effect was accompanied by a concentration of filamentous actin and cortactin to the cell periphery. Concomitantly, the continuity of the tight junctional protein ZO-1 at the cell borders was improved and was associated with an increase in both ZO-1 and occludin expression. By contrast, the expression and distribution of adherens junctional proteins such as beta-catenin and p100/p120 remained unchanged. These observations suggest that glucocorticoids induce a more differentiated BBB phenotype in cultured brain endothelial cells through modification of tight junction structure.

Pathogenesis of human immunodeficiency virus-induced neurological disease

Infection of the central nervous system by the type 1 human immunodeficiency virus (HIV-1) commonly results in a number of neurological impairments known, in their most severe form, as HIV-associated dementia (HAD). The persistence of HIV encephalitis (HIVE), the pathological correlate of HAD, in spite of highly active antiretroviral therapy (HAART) underscores the importance of continued research focused on the neurobiology of HIV. To elucidate direct and indirect mechanisms of HIV neuropathogenesis, current investigation is focused on neuroinvasion, HIV-1-mediated mechanisms of neuronal damage and apoptosis, and compartmentalized evolution of virus in the brain. The aim of this review is to provide a selective overview of the most recent research on the neurobiology of HIV, adding only a brief introduction regarding established principles.

Usefulness of proviral load measurement for monitoring of disease activity in individual patients with human T-lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis

High human T-lymphotropic virus type I (HTLV-I) proviral load in peripheral blood mononuclear cells (PBMCs) has been reported in patients with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and the proviral load has been reported to fluctuate in individual patients during the course of the disease. Clinical symptoms usually became stable after a prolonged period of symptom progression. However, the authors have experienced having some patients whose clinical manifestations suddenly became worse during the course of the disease. To clarify the role of high proviral load and its fluctuation in the pathogenesis of HAM/TSP, the authors measured the proviral load of serially taken PBMCs as well as of cerebrospinal fluid (CSF) cells from patients with HAM/TSP on long-term follow-up and compared these with their clinical manifestations. There was a wide distribution of proviral load, from 0.3 to 37.8 copies/100 PBMCs; however, the proviral load in individual patients was relatively stable during the course of the disease. Eighty-three percent of the patients with clinical worsening showed an increase in proviral load at the time point when clinical worsening was recorded, or at the preceding time point. The proviral loads in CSF cells were higher than those in PBMCs in individual patients. The ratio of proviral loads in CSF cells/in PBMCs, but not the absolute load, in either compartment, was significantly associated with clinically progressive disease and with recent onset of HAM/TSP. These findings indicate that clinical progression of HAM/TSP is associated with increased proliferation or immigration of HTLV-I-infected lymphocytes in the central nervous system.

Efficient transfer of HTLV-1 tax gene in various primary and immortalized cells using a flap lentiviral vector

Human T cell leukemia virus type 1 (HTLV-1) causes two major diseases: adult T-cell leukemia-lymphoma and tropical spastic paraparesis/HTLV-1 associated myelopathy (TSP/HAM). In order to understand the involvement of Tax protein in HTLV-1 pathogenesis, we constructed a HIV-1 based lentiviral vector containing the central DNA flap sequence and either the green fluorescent protein (GFP) or the HTLV-1 tax genes. Using these vectors, GFP and tax genes were introduced in several primary and immortalized cells of endothelial, lymphoid, astrocytic or macrophagic origin. As assessed by GFP expression, up to 100% efficiency of transduction was obtained for all cell types tested. Tax expression was detected by Western blot and immuno-fluorescence in the transduced cells. After transduction, the Tax transcriptional activity was confirmed by the transactivation of HTLV-1 LTR-lacZ or HTLV-1 LTR-GFP reporter genes. Increased CD25 and HLA DR expression was observed in human peripheral blood lymphocytes transduced with the Tax vector. These results indicate that both pathways of Tax transactivation, CREB (viral LTR) and NF-kappa B (CD25 and HLA DR), are functional after transduction by TRIP Tax vector. Therefore, this vector provides a useful tool for investigating the role of the Tax viral protein in the pathogenesis of diseases linked to HTLV-1 infection.

Human immunodeficiency virus type 1 enters brain microvascular endothelia by macropinocytosis dependent on lipid rafts and the mitogen-activated protein kinase signaling pathway

Brain microvascular endothelial cells (BMVECs) present an incomplete barrier to human immunodeficiency virus type 1 (HIV-1) neuroinvasion. In order to clarify the mechanisms of HIV-1 invasion, we have examined HIV-1 uptake and transcellular penetration in an in vitro BMVEC model. No evidence of productive infection was observed by luciferase, PCR, and reverse transcriptase assays. Approximately 1% of viral RNA and 1% of infectious virus penetrated the BMVEC barrier without disruption of tight junctions. The virus upregulated ICAM-1 on plasma membranes and in cytoplasmic vesiculotubular structures. HIV-1 virions were entangled by microvilli and were taken into cytoplasmic vesicles through surface invaginations without fusion of the virus envelope with the plasma membrane. Subsequently, the cytoplasmic vesicles fused with lysosomes, the virions were lysed, and the vesicles diminished in size. Upon cell entry, HIV-1 colocalized with cholera toxin B, which targets lipid raft-associated GM1 ganglioside. Cholesterol-extracting agents, cyclodextrin and nystatin, and polyanion heparin significantly inhibited virus entry. Anti-CD4 had no effect and the chemokine AOP-RANTES had only a slight inhibitory effect on virus entry. HIV-1 activated the mitogen-activated protein kinase (MAPK) pathway, and inhibition of MAPK/Erk kinase inhibited virus entry. Entry was also blocked by dimethylamiloride, indicating that HIV-1 enters endothelial cells by macropinocytosis. Therefore, HIV-1 penetrates BMVECs in ICAM-1-lined macropinosomes by a mechanism involving lipid rafts, MAPK signaling, and glycosylaminoglycans, while CD4 and chemokine receptors play limited roles in this process.

Phenotypic study of peripheral blood leucocytes in HTLV-I-infected individuals from Minas Gerais, Brazil

The human T-cell lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) associated with the HTLV-I is a well-defined clinical-pathological entity in which the virus and host immune responses contribute to the pathological mechanism. In this study, flow cytometric analysis of whole peripheral blood leucocytes (PBL) was performed to evaluate the immunological status of HTLV-I-infected individuals in an effort to better understand the role of the immune system in the development of HAM/TSP. We have evaluated three groups of infected patients including asymptomatic (AS = 18), ambulatory/oligosymptomatic (AM = 14) and hospitalized HAM/TSP individuals (HO = 42). Noninfected healthy blood donors were used for the control group (NI = 32). Our results demonstrated that the HO group presents an increased percentage of circulating T cells and a decreased percentage of B and natural killer (NK) cells, leading to the highest T/B-cell ratio in comparison with the other groups. Interestingly, while an increased percentage of activated CD4+HLA-DR+ T lymphocytes was observed in both AM and HO, only HO presented higher percentage of activated CD8+HLA-DR+ in combination with the highest CD18 surface expression. This was true for all cell populations analysed, including T lymphocytes, monocytes and neutrophils. Moreover, the HO group was distinguished by a dramatic decrease in the percentage of CD8+CD28+ lymphocytes. Taken together, these findings demonstrate a potent cellular immune activation response involving primarily CD8+ T cells that is concomitant with disease progression in HAM/TSP. We also show that an upregulation of CD18 expression, a hallmark for increased cell migratory potential, might play a critical role in the development/maintenance of HAM/TSP.

Autoimmunity due to molecular mimicry as a cause of neurological disease

One hypothesis that couples infection with autoimmune disease is molecular mimicry. Molecular mimicry is characterized by an immune response to an environmental agent that cross-reacts with a host antigen, resulting in disease. This hypothesis has been implicated in the pathogenesis of diabetes, lupus and multiple sclerosis (MS). There is limited direct evidence linking causative agents with pathogenic immune reactions in these diseases. Our study establishes a clear link between viral infection, autoimmunity and neurological disease in humans. As a model for molecular mimicry, we studied patients with human T-lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a disease that can be indistinguishable from MS (refs. 5,6,7). HAM/TSP patients develop antibodies to neurons. We hypothesized these antibodies would identify a central nervous system (CNS) autoantigen. Immunoglobulin G isolated from HAM/TSP patients identified heterogeneous nuclear ribonuclear protein-A1 (hnRNP-A1) as the autoantigen. Antibodies to hnRNP-A1 cross-reacted with HTLV-1-tax, the immune response to which is associated with HAM/TSP (refs. 5,9). Immunoglobulin G specifically stained human Betz cells, whose axons are preferentially damaged. Infusion of autoantibodies in brain sections inhibited neuronal firing, indicative of their pathogenic nature. These data demonstrate the importance of molecular mimicry between an infecting agent and hnRNP-A1 in autoimmune disease of the CNS.

Human T cell leukemia virus type I and neurologic disease: events in bone marrow, peripheral blood, and central nervous system during normal immune surveillance and neuroinflammation

Human T cell lymphotropic/leukemia virus type I (HTLV-I) has been identified as the causative agent of both adult T cell leukemia (ATL) and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Although the exact sequence of events that occur during the early stages of infection are not known in detail, the initial route of infection may predetermine, along with host, environmental, and viral factors, the subset of target cells and/or the primary immune response encountered by HTLV-I, and whether an HTLV-I-infected individual will remain asymptomatic, develop ATL, or progress to the neuroinflammatory disease, HAM/TSP. Although a large number of studies have indicated that CD4(+) T cells represent an important target for HTLV-I infection in the peripheral blood (PB), additional evidence has accumulated over the past several years demonstrating that HTLV-I can infect several additional cellular compartments in vivo, including CD8(+) T lymphocytes, PB monocytes, dendritic cells, B lymphocytes, and resident central nervous system (CNS) astrocytes. More importantly, extensive latent viral infection of the bone marrow, including cells likely to be hematopoietic progenitor cells, has been observed in individuals with HAM/TSP as well as some asymptomatic carriers, but to a much lesser extent in individuals with ATL. Furthermore, HTLV-I(+) CD34(+) hematopoietic progenitor cells can maintain the intact proviral genome and initiate viral gene expression during the differentiation process. Introduction of HTLV-I-infected bone marrow progenitor cells into the PB, followed by genomic activation and low level viral gene expression may lead to an increase in proviral DNA load in the PB, resulting in a progressive state of immune dysregulation including the generation of a detrimental cytotoxic Tax-specific CD8(+) T cell population, anti-HTLV-I antibodies, and neurotoxic cytokines involved in disruption of myelin-producing cells and neuronal degradation characteristic of HAM/TSP.

Activation of HTLV-I long terminal repeat by stress-inducing agents and protection of HTLV-I-infected T-cells from apoptosis by the viral tax protein

HTLV-I is etiologically implicated with tropical spastic paraparesis/HTLV-I associated myelopathy, adult T-cell leukemia and certain other diseases. However, after infection the virus enters into a dormant state, whereas the characteristics of the HTLV-I related diseases indicate that their genesis requires activation of the dormant virus by a Tax-independent mechanism. In the present study we demonstrate that a variety of stress-inducing agents (TPA, cisplatin, etoposide, taxol, and 3-methylcholanthrene) are capable of Tax-independent activation of HTLV-I LTR and that this activation is detected mainly in cells that are undergoing through the apoptotic process. Furthermore, it is demonstrated that both apoptosis induction and HTLV-I LTR activation are inhibited by Bcl-2 and by PKC, indicating that these two processes are mechanistically cross-linked. In addition, using an HTLV-I producing human T-cell line which permanently express the negatively transdominant tax mutant, Delta58tax, under the Tet-Off control system, we prove that the virally encoded Tax protein protects the host cells from apoptosis. Together, these data suggest that activation of the dormant virus in the carriers' infected T-cells by certain stress-inducing conditions and protecting these cells from the consequent apoptotic death by the viral Tax protein emerging after this activation, might be the basis for switching the virus from latency to a pathogenic phase.

HTLV-1 and its neurological complications

BACKGROUND

Since its discovery in 1980, human T-cell lymphotropic virus type-1 (HTLV-1) has been associated with a number of neurological diseases. The distribution of HTLV-1-associated neurological disease is worldwide. In endemic areas, up to 30% of the population may be infected with HTLV-1; however, only a small percentage of infected persons develops neurological disease.

REVIEW SUMMARY

In 1986, HTLV-1 infection was reported in patients of chronic progressive myelopathy of uncertain etiology, and the disease entity was called HTLV-1-associated myelopathy/tropical spastic paraparesis. Recently, HTLV-1 infection has been associated with polymyositis and uveitis. Interestingly, a single patient may display more than one syndrome. Although other neurological syndromes occur in HTLV-1-infected individuals, there is not enough epidemiologic data that show a strong association. Treatment of HTLV-1-associated neurological disease is challenging, and well-controlled studies are lacking.

CONCLUSION

As neurologists and other scientists begin to understand the pathophysiology of HTLV-1 infection, improved therapies should be developed. Randomized trials with longer follow-up are required to understand the effect of treatment on disability and quality of life.

Immunopathogenesis of human T cell lymphotropic virus type I-associated myelopathy

Human T cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis is a chronic progressive inflammatory neurological disease. Aspects of human T cell lymphotropic virus type I biology, host genetic susceptibility, and immune responses to this agent are important factors that are associated with disease progression. The use of novel immunological and molecular methods has improved our understanding of the pathophysiological mechanisms that are operative in human T cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis. Co-existing high proviral loads and virus-specific CD8 T cells are important features of this disorder, in which a high cellular immune response continuously driven by this virus may contribute to the inflammatory process within central nervous system lesions in patients with this disease.