Immunopathogenesis of human T cell lymphotropic virus type I-associated neurologic disease

Th17/IL-17 Axis in HTLV-1-Associated Myelopathy Tropical Spastic Paraparesis and Multiple Sclerosis: Novel Insights into the Immunity During HAMTSP

Human T lymphotropic virus-associated myelopathy/tropical spastic paraparesis (HTLV/TSP), also known as HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP), and multiple sclerosis (MS) are chronic debilitating diseases of the central nervous system; although the etiology of which is different, similarities have been observed between these two demyelinating diseases, especially in clinical manifestation and immunopathogenesis. Exorbitant response of the immune system to the virus and neurons in CNS is the causative agent of HAM/TSP and MS, respectively. Helper T lymphocyte-17 cells (Th17s), a component of the immune system, which have a proven role in immunity and autoimmunity, mediate protection against bacterial/fungal infections. The role of these cells has been reviewed in several CNS diseases. A pivotal role for Th17s is presented in demyelination, even more axial than Th1s, during MS. The effect of Th17s is not well determined in HTLV-1-associated infections; however, the evidence that we have supplied in this review illustrates the attendance, also the role of Th17 cells during HAM/TSP. Furthermore, for better conception concerning the trace of these cells in HAM/TSP, a comparative characterization with MS, the resembling disease, has been applied here.

Potential role of HTLV-1 Tax-specific cytotoxic t lymphocytes expressing a unique t-cell receptor to promote inflammation of the central nervous system in myelopathy associated with HTLV-1

Human T-lymphotropic virus 1 (HTLV-1) infection causes two serious diseases: adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy (HAM). Immunological studies have revealed that HTLV-1 Tax-specific CD8⁺ cytotoxic T-cells (Tax-CTLs) in asymptomatic carriers (ACs) and ATL patients play an important role in the elimination of HTLV-1-infected host cells, whereas Tax-CTLs in HAM patients trigger an excessive immune response against HTLV-1-infected host cells infiltrating the central nervous system (CNS), leading to local inflammation. Our previous evaluation of HTLV-1 Tax_301-309 (SFHSLHLLF)-specific Tax-CTLs (Tax_301-309-CTLs) revealed that a unique T-cell receptor (TCR) containing amino acid (AA)-sequence motif PDR, was shared among HLA-A*24:02⁺ ACs and ATL patients and behaved as an eliminator by strong activity against HTLV-1. However, it remains unclear whether PDR⁺Tax_301-309-CTLs also exist in HLA-A*24:02⁺ HAM patients and are involved in the pathogenesis of HAM. In the present study, by high-throughput TCR repertoire analysis technology, we revealed TCR repertoires of Tax_301-309-CTLs in peripheral blood (PB) of HLA-A*24:02⁺ HAM patients were skewed, and a unique TCR-motif PDR was conserved in HAM patients (10 of 11 cases). The remaining case dominantly expressed (-DR, P-R, and PD-), which differed by one AA from PDR. Overall, TCRs with unique AA-sequence motifs PDR, or (-DR, P-R, and PD-) accounted for a total of 0.3-98.1% of Tax_301-309-CTLs repertoires of HLA-A*24:02⁺ HAM patients. Moreover, TCR repertoire analysis of T-cells in the cerebrospinal fluid (CSF) from four HAM patients demonstrated the possibility that PDR⁺Tax_301-309-CTLs and (-DR, P-R, and PD-)⁺Tax_301-309-CTLs efficiently migrated and accumulated in the CSF of HAM patients fostering increased inflammation, although we observed no clear significant correlation between the frequencies of them in PB and the levels of CSF neopterin, a known disease activity biomarker of HAM. Furthermore, to better understand the potential function of PDR⁺Tax_301-309-CTLs, we performed immune profiling by single-cell RNA-sequencing of Tax_301-309-CTLs, and the result showed that PDR⁺Tax_301-309-CTLs up-regulated the gene expression of natural killer cell marker KLRB1 (CD161), which may be associated with T-cell activation and highly cytotoxic potential of memory T-cells. These findings indicated that unique and shared PDR⁺Tax_301-309-CTLs have a potential role in promoting local inflammation within the CNS of HAM patients.

Immunopathogenic CSF TCR repertoire signatures in virus-associated neurologic disease

In this study, we examined and characterized disease-specific TCR signatures in cerebrospinal fluid (CSF) of patients with HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP). TCR β libraries using unique molecular identifier–based methodologies were sequenced in paired peripheral blood mononuclear cells (PBMCs) and CSF cells from HAM/TSP patients and normal healthy donors (NDs). The sequence analysis demonstrated that TCR β repertoires in CSF of HAM/TSP patients were highly expanded and contained both TCR clonotypes shared with PBMCs and uniquely enriched within the CSF. In addition, we analyzed TCR β repertoires of highly expanded and potentially immunopathologic HTLV-1 Tax11-19–specific CD8⁺ T cells from PBMCs of HLA-A*0201⁺ HAM/TSP and identified a conserved motif (PGLAG) in the CDR3 region. Importantly, TCR β clonotypes of expanded clones in HTLV-1 Tax11-19–specific CD8⁺ T cells were also expanded and enriched in the CSF of the same patient. These results suggest that exploring TCR repertoires of CSF and antigen-specific T cells may provide a TCR repertoire signature in virus-associated neurologic disorders.

Expression of TSLC1 in patients with HAM/TSP

Human T-lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is chronic myelopathy characterized by slowly progressive spastic paraparesis and urinary dysfunction. A few biomarkers in the cerebrospinal fluid are known to be related to disease activity, but no biomarker has been reported in peripheral blood. This study aims to explore the expression level of the adhesion molecule during the expression level of the adhesion molecule among HAM/TSP disease activity. In lymphocyte function-associated antigen 1 and DNAX accessory molecule 1, no variation in expression levels specific to HTLV-1 infection was observed in CD4-positive T cells; however, TSLC1 expression was higher in HAM patients than in asymptomatic carriers and non-infected persons. TSLC1 tended to be higher in patients whose symptoms were worsening. On the contrary, the expression level of TSLC1 in CD8-positive T cells was lower in HAM patients than in asymptomatic carriers, and this tendency was stronger in patients whose symptoms had deteriorated. No significant correlation was found between TSLC1 and either of the transcription factors Tax or HBZ in any T cell group. Therefore, TSLC1 expression in CD4-positive T cells might be a useful biomarker of HAM/TSP disease activity.

Neuroimmunology of Human T-Lymphotropic Virus Type 1-Associated Myelopathy/Tropical Spastic Paraparesis

Human T-lymphotropic virus type 1 (HTLV-1) is the etiologic agent of both adult T-cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HAM/TSP is clinically characterized by chronic progressive spastic paraparesis, urinary incontinence, and mild sensory disturbance. Given its well-characterized clinical presentation and pathophysiology, which is similar to the progressive forms of multiple sclerosis (MS), HAM/TSP is an ideal system to better understand other neuroimmunological disorders such as MS. Since the discovery of HAM/TSP, large numbers of clinical, virological, molecular, and immunological studies have been published. The host-virus interaction and host immune response play an important role for the development with HAM/TSP. HTLV-1-infected circulating T-cells invade the central nervous system (CNS) and cause an immunopathogenic response against virus and possibly components of the CNS. Neural damage and subsequent degeneration can cause severe disability in patients with HAM/TSP. Little progress has been made in the discovery of objective biomarkers for grading stages and predicting progression of disease and the development of molecular targeted therapy based on the underlying pathological mechanisms. We review the recent understanding of immunopathological mechanism of HAM/TSP and discuss the unmet need for research on this disease.

[HTLV-1-associated myelopathy]

Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus that infects T lymphocytes. HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is an intractable neurodegenerative disease caused by HTLV-1 infection just like adult T cell leukemia/lymphoma (ATL) is, developing in a fraction of infected individuals. Here, we review the update information about the new drug development and therapeutic algorithm of HAM/TSP based on the resent research achievement in molecular pathogenesis and biomarkers.

In vivo and in vitro immunogenicity of novel MHC class I presented epitopes to confer protective immunity against chronic HTLV-1 infection

Human T-cell leukemia virus type 1 (HTLV-1) has infected as many as 10 million people worldwide. While 90% are asymptomatic, 5% develop severe diseases including adult T-cell leukemia/lymphoka (ATLL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). No vaccine against HTLV-1 exists, and screening programs are not universal. However, patients with chronic HTLV-1 infection have high frequencies of HTLV-1-activated CD8+ T cells, and the two main HLA alleles (A2, A24) are present in 88% of infected individuals. We thus utilized an immunoproteomics approach to characterize MHC-I restricted epitopes presented by HLA-A2+, A24+ MT-2 and SLB-1 cell lines. Unlike traditional motif prediction algorithms, this approach identifies epitopes associated with cytotoxic T-cell responses in their naturally processed forms, minimizing differences in antigen processing and protein expression levels. Out of nine identified peptides, we confirmed six novel MHC-I restricted epitopes that were capable of binding HLA-A2 and HLA-A24 alleles and used in vitro and in vivo methods to generate CD8+ T cells specific for each of these peptides. MagPix MILLIPLEX data showed that in vitro generated epitope-specific CD8+ T cells secreted IFN-ɣ, granzyme B, MIP-1α, TNF-α, perforin and IL-10 when cultured in the presence of MT-2 cell line. Degranulation assay confirmed cytotoxic response through surface expression of CD107 on CD8+ T cells when cultured with MT-2 cells. A CD8+ T-cell killing assay indicated significant antiviral activity of CD8+ T cells specific against all identified peptides. In vivo generated CD8+ T cells similarly demonstrated immunogenicity on ELISpot, CD107 degranulation assay, and MagPix MILLIPLEX analysis. These epitopes are thus candidates for a therapeutic peptide-based vaccine against HTLV-1, and our results provide preclinical data for the advancement of such a vaccine.

Plasma and cerebrospinal fluid levels of cytokines as disease markers of neurologic manifestation in long-term HTLV-1 infected individuals

AIM

The aim of this study is to evaluate the presence of a particular immunological profile in individuals long-term infected with HTLV-1, followed presenting different clinical courses.

MATERIALS & METHODS

Forty-eight individuals were evaluated for 19 cytokines analyzed in cerebrospinal fluid and plasma of patients with HTLV-1 presenting with and without neurological symptoms.

RESULTS

Proinflammatory cytokines and the chemokine ligand 11 (ITAC/CXCL11) were increased in individuals with HTLV-1 coursing with neurological symptoms.

CONCLUSION

Different cytokines' expression profile in the presence of neurological symptoms may help to understand and characterize the progression for severe clinical presentations.

Phylogenetic analysis of HTLV-1 in Iranian blood donors, HIV-1 positive patients and patients with beta thalassemia

Human T-cell lymphoma virus (HTLV) has been associated with various disease types. Since the discovery of the virus in 1980, seven subtypes of the virus have been identified. HTLV is widespread and endemic in some regions, such as Japan, Africa, South America, and northeast Iran. This study aimed to identify HTLV-1 genotype and also to analyze the nucleotide sequence of the LTR region in three groups, including blood donors, HIV-1+ patients, and β-thalassemia patients. In this cross-sectional study, 2200 samples were collected from blood donors in Tehran (2000 samples), HIV-1+ patients (100 samples) and β-thalassemia patients (100 samples). All samples were screened for anti-HTLV-I&II antibodies by ELISA. Then, genomic DNA was extracted from repeatedly positive samples, and nested PCR was performed for both the TAX and LTR regions. Purified PCR products were sequenced and analyzed, and finally, a phylogenetic tree was constructed using Mega7 software. The prevalence of the anti-HTLV-I&II antibody among blood donors and HIV-1+ patients was 1.7% (34/2000) and 12% (12/100), respectively. The PCR results confirmed that 0.05% (1/2000) of blood donors, 5% (5/100) of HIV-1+ patients, and 8% (8/100) of β-thalassemia patients were HTLV-I positive. All sequences were matched to HTLV-1 subtype a, subgroup A. Our phylogenetic analysis revealed that all sequenced samples belong to the endemic clusters of Iran. HTLV-1 genotypes in all samples were similar in three groups and were derived from the strains, which had been previously reported from Iran (AF00300/Mashhad and KT190712.1/Sabzevar).

The CC chemokine ligand (CCL) 1, upregulated by the viral transactivator Tax, can be downregulated by minocycline: possible implications for long-term treatment of HTLV-1-associated myelopathy/tropical spastic paraparesis

Background

Chemokine (C-C motif) ligand 1 (CCL1) is produced by activated monocytes/ macrophages and T-lymphocytes, and acts as a potent attractant for Th2 cells and a subset of T-regulatory (Treg) cells. Previous reports have indicated that CCL1 is overexpressed in adult T-cell leukemia cells, mediating an autocrine anti-apoptotic loop. Because CCL1 is also known as a potent chemoattractant that plays a major role in inflammatory processes, we investigated the role of CCL1 in the pathogenesis of human T-cell leukemia virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP).

Results

The results showed that: (1) CCL1 was preferentially expressed in HAM/TSP-derived HTLV-1-infected T-cell lines, (2) CCL1 expression was induced along with Tax expression in the Tax-inducible T-cell line JPX9, (3) transient Tax expression in an HTLV-1-negative T-cell line activated the CCL1 gene promoter, (4) plasma levels of CCL1 were significantly higher in patients with HAM/TSP than in HTLV-1-seronegative patients with multiple sclerosis and HTLV-1-infected asymptomatic healthy carriers, and (5) minocycline inhibited the production of CCL1 in HTLV-1-infected T-cell lines.

Conclusions

The present results suggest that elevated CCL1 levels may be associated with the pathogenesis of HAM/TSP. Although further studies are required to determine the in vivo significance, minocycline may be considered as a potential candidate for the long-term treatment of HAM/TSP via its anti-inflammatory effects, which includes the inhibition of CCL1 expression.

Human T Cell Leukemia Virus Type 1: Persistence and Pathogenesis

Human T cell leukemia virus type 1 (HTLV-1), also known as human T lymphotropic virus type 1, was the first exogenous human retrovirus discovered. Unlike the distantly related lentivirus HIV-1, HTLV-1 causes disease in only 5-10% of infected people, depending on their ethnic origin. But whereas HIV-1 infection and the consequent diseases can be efficiently contained in most cases by antiretroviral drug treatment, there is no satisfactory treatment for the malignant or inflammatory diseases caused by HTLV-1. The purpose of the present article is to review recent advances in the understanding of the mechanisms by which the virus persists in vivo and causes disabling or fatal diseases.

Association of Tuberculosis Status with Neurologic Disease and Immune Response in HTLV-1 Infection

The human T cell lymphotropic virus type 1 (HTLV-1) is the etiologic agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-1 infected individuals have increased susceptibility to Mycobacterium tuberculosis infection but the influence of tuberculosis (TB) on the course of HTLV-1 infection is unknown. The aim of this study was to evaluate the influence of TB on immunological, virologic, and neurologic features of HTLV-1 infection. This is a retrospective analysis of individuals enrolled in a cohort study from an HTLV-1 clinic who were evaluated for past or latent tuberculosis (LTB) and classified clinically as HTLV-1 carriers, probable HAM/TSP and definite HAM/TSP. Spontaneous cytokine production (interferon-gamma [IFN-γ], tumor necrosis factor [TNF], and interleukin[IL]-10), serum chemokines (CXCL9 and CXCL10) and HTLV-1 proviral load were evaluated. Of 172 participants, 64 did not have histories of TB (TB- group), 81 had LTB and 27 had TB in the past (TB+ group). In the TB+ group, there was a higher frequency of HAM/TSP patients (35%) than in HTLV-1 carriers (10%) (OR = 3.8, p = .0001). HAM/TSP patients with histories of TB had higher IFN-γ/IL-10 and TNF/IL-10 ratios when compared with HAM/TSP patients without histories of TB. There were no differences in serum chemokine production and proviral load across TB groups stratified on HTLV-1 clinical status. In conclusion, TB may influence the development of HAM/TSP, and patients with these two diseases have an impairment in the modulation of immune response.

Developing novel treatments for HTLV-1-associated myelopathy (HAM) by investigating molecular pathomechanisms

A small percentage of those infected with human T-lymphotropic virus type 1 (HTLV-1) develop HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a debilitating neurodegenerative disease. This disease impacts essential bodily functions, and since currently available treatments are considered to be poorly effective, there is a dire need to develop a truly effective treatment to suppress disease progression. Recently, the authors and others have determined that HTLV-1 in HAM/TSP patients primarily infects T cells expressing the chemokine receptor CCR4. The authors postulated that HTLV-1 causes these T cells to develop Th1-like functions that are critical for the pathogenesis of HAM/TSP. They described an inflammatory positive feedback loop in which cross-talk between these abnormal Th1-like cells and astrocytes produce and maintain spinal cord lesions in HAM/TSP patients. When an anti-CCR4 antibody was tested against cells from HAM/TSP patients, the antibody instigated the destruction of the CCR4-positive cells, reducing the number of infected cells and the amount of inflammatory activity. Thus, the anti-CCR4 antibody is expected to become a fundamentally new treatment for HAM/TSP that directly targets infected cells. The treatment is currently being tested in clinical trials.

Are lipid disorders involved in the predominance of human T-lymphotropic virus-1 infections in women?

INTRODUCTION

The human T-lymphotropic virus-1 (HTLV-1) is associated with chronic inflammatory diseases such as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic inflammatory disease. Disturbances in lipid metabolism are involved in inflammatory and demyelinating diseases.

METHODS

Plasma levels of triglycerides, total cholesterol, and fractions of HTLV-1-infected individuals of both sexes with different clinical progressions were determined.

RESULTS

Elevated levels of triglyceride and very low-density lipoproteins (VLDL) were exclusively detected in HTLV-1-infected women from asymptomatic and HAM/TSP groups compared with uninfected individuals (p = 0.02).

CONCLUSIONS

Elevated triglyceride and VLDL levels in HTLV-1-infected women may be related to the predominance of HAM/TSP in women.

How does HTLV-1 cause adult T-cell leukaemia/lymphoma (ATL)?

A typical person infected with the retrovirus human T-lymphotropic virus type 1 (HTLV-1) carries tens of thousands of clones of HTLV-1-infected T lymphocytes, each clone distinguished by a unique integration site of the provirus in the host genome. However, only 5% of infected people develop the malignant disease adult T cell leukaemia/lymphoma, usually more than 50 years after becoming infected. We review the host and viral factors that cause this aggressive disease.

Amyotrophic lateral sclerosis presentation of a human T-lymphotropic virus type-1 myelopathy--insight into pathogenesis

A 41-year-old human T-lymphotropic virus type 1-positive woman developed a syndrome with upper and lower motor neuron signs sometime after bilateral vertebral artery dissections. Over 2 years, she developed a progressive myelopathy affecting predominantly the motor system. She had the picture of a 'person in a barrel' and died from complications. At autopsy, spinal cord revealed inflammatory infiltrates and extensive gliosis involving mainly the anterior horns. The vertebral arterial dissections may have permitted the entry of infected lymphocytes and macrophages, secreting cytokines and metalloproteinases, into the medulla progressing to the spinal cord. Few cases with pathological correlation have been reported.

HTLV-1-associated myelopathy/tropical spastic paraparesis

Human T-lymphotropic virus 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a progressive disease of the CNS that causes weakness or paralysis of the legs, lower back pain and urinary symptoms. HAM/TSP was first described in Jamaica in the nineteenth century, but the aetiology of the condition, infection with the retrovirus HTLV-1, was only identified in the 1980s. HAM/TSP causes chronic disability and, accordingly, imposes a substantial health burden in areas where HTLV-1 infection is endemic. Since the discovery of the cause of HAM/TSP, considerable advances have been made in the understanding of the virology, immunology, cell biology and pathology of HTLV-1 infection and its associated diseases. However, progress has been limited by the lack of accurate animal models of the disease. Moreover, the treatment of HAM/TSP remains highly unsatisfactory: antiretroviral drugs have little impact on the infection and, although potential disease-modifying therapies are widely used, their value is unproved. At present, clinical management is focused on symptomatic treatment and counselling. Here, we summarize current knowledge on the epidemiology, pathogenesis and treatment of HAM/TSP and identify areas in which further research is needed. For an illustrated summary of this Primer, visit: http://go.nature.com/tjZCFM.

Neuroimmunological aspects of human T cell leukemia virus type 1-associated myelopathy/tropical spastic paraparesis

Human T cell leukemia virus type 1 (HTLV-1) is a human retrovirus etiologically associated with adult T cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Only approximately 0.25-4 % of infected individuals develop HAM/TSP; the majority of infected individuals remain lifelong asymptomatic carriers. Recent data suggest that immunological aspects of host-virus interactions might play an important role in the development and pathogenesis of HAM/TSP. This review outlines and discusses the current understanding, ongoing developments, and future perspectives of HAM/TSP research.

Increased expression of OX40 is associated with progressive disease in patients with HTLV-1-associated myelopathy/tropical spastic paraparesis

Background

OX40 is a member of the tumor necrosis factor receptor family that is expressed primarily on activated CD4⁺ T cells and promotes the development of effector and memory T cells. Although OX40 has been reported to be a target gene of human T-cell leukemia virus type-1 (HTLV-1) viral transactivator Tax and is overexpressed in vivo in adult T-cell leukemia (ATL) cells, an association between OX40 and HTLV-1-associated inflammatory disorders, such as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), has not yet been established. Moreover, because abrogation of OX40 signals ameliorates chronic inflammation in animal models of autoimmune disease, novel monoclonal antibodies against OX40 may offer a potential treatment for HTLV-1-associated diseases such as ATL and HAM/TSP.

Results

In this study, we showed that OX40 was specifically expressed in CD4⁺ T cells naturally infected with HTLV-1 that have the potential to produce pro-inflammatory cytokines along with Tax expression. We also showed that OX40 was overexpressed in spinal cord infiltrating mononuclear cells in a clinically progressive HAM/TSP patient with a short duration of illness. The levels of the soluble form of OX40 (sOX40) in the cerebrospinal fluid (CSF) from chronic progressive HAM/TSP patients or from patients with other inflammatory neurological diseases (OINDs) were not different. In contrast, sOX40 levels in the CSF of rapidly progressing HAM/TSP patients were higher than those in the CSF from patients with OINDs, and these patients showed higher sOX40 levels in the CSF than in the plasma. When our newly produced monoclonal antibody against OX40 was added to peripheral blood mononuclear cells in culture, HTLV-1-infected T cells were specifically removed by a mechanism that depends on antibody-dependent cellular cytotoxicity.

Conclusions

Our study identified OX40 as a key molecule and biomarker for rapid progression of HAM/TSP. Furthermore, blocking OX40 may have potential in therapeutic intervention for HAM/TSP.

Altered expression of degranulation-related genes in CD8+ T cells in human T lymphotropic virus type I infection

Human T lymphotropic virus type I (HTLV-1) is the etiological agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). CD8+ T cells may contribute to the protection or development of HAM/TSP. In this study we used SAGE methodology to screen for differentially expressed genes in CD8+ T cells isolated from HTLV-1 asymptomatic carriers (HAC) and from HAM/TSP patients to identify genes involved in HAM/TSP development. SAGE analysis was conducted by pooling samples according to clinical status. The comparison of gene expression profiles between HAC and HAM/TSP libraries identified 285 differentially expressed tags. We focus on cytotoxicity and cytokine-related genes due to their potential biological role in HTLV-1 infection. Our results showed that patients with HAM/TSP have high expression levels of degranulation-related genes, namely GZMH and PRF1, and of the cytoskeletal adaptor PXN. We found that GZMB and ZAP70 were overexpressed in HTLV-infected patients compared to the noninfected group. We also detected that CCL5 was higher in the HAM/TSP group compared to the HAC and CT groups. Our findings showed that CD8+ T cells of HAM/TSP patients have an inflammatory and active profile. PXN and ZAP70 overexpression in HTLV-1-infected patients was described for the first time here and reinforces this concept. However, although active and abundant, CD8+ T cells are not able to completely eliminate infected cells and prevent the development of HAM/TSP and, moreover, these cells might contribute to the pathogenesis of the disease by migrating to the central nervous system (CNS). These results should be further tested with biological functional assays to increase our understanding on the role of these molecules in the development of HTLV-1-related diseases.

Influence of HTLV-1 on the clinical, microbiologic and immunologic presentation of tuberculosis

Background

HTLV-1 is associated with increased susceptibility to Mycobacterium tuberculosis infection and severity of tuberculosis. Although previous studies have shown that HTLV-1 infected individuals have a low frequency of positive tuberculin skin test (TST) and decreasing in lymphoproliferative responses compared to HTLV-1 uninfected persons, these studies were not performed in individuals with history of tuberculosis or evidence of M. tuberculosis infection. Therefore the reasons why HTLV-1 infection increases susceptibility to infection and severity of tuberculosis are not understood.The aim of this study was to evaluate how HTLV-1 may influence the clinical, bacteriologic and immunologic presentation of tuberculosis.

Methods

The study prospectively enrolled and followed 13 new cases of tuberculosis associated with HTLV-1 (cases) and 25 patients with tuberculosis without HTLV-1 infection (controls). Clinical findings, bacterial load in the sputum, x-rays, immunological response and death were compared in the two groups.

Results

There were no differences in the demographic, clinical and TST response between the two study groups. IFN-γ and TNF-α production was higher in unstimulated cultures of mononuclear cells of case than in control patients (p < 0.01). While there was no difference in IFN-γ production in PPD stimulated cultures, TNF-α levels were lower in cases than in controls (p = 0.01). There was no difference in the bacterial load among the groups but sputum smear microscopy results became negative faster in cases than in controls. Death only occurred in two co-infected patients.

Conclusion

While the increased susceptibility for tuberculosis infection in HTLV-1 infected subjects may be related to impairment in TNF-α production, the severity of tuberculosis in co-infected patients may be due to the enhancement of the Th1 inflammatory response, rather than in their decreased ability to control bacterial growth.

Ascorbic acid has superior ex vivo antiproliferative, cell death-inducing and immunomodulatory effects over IFN-α in HTLV-1-associated myelopathy

BACKGROUND

Clear therapeutic guidelines for HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) are missing due to the lack of randomized double-blind controlled clinical trials. Moderate yet similar clinical benefit has been demonstrated for IFN-α and high-dose ascorbic acid (AA) monotherapy in a large open clinical trial. However, there is a lack of in vivo and in vitro studies exploring and comparing the effects of high-dose AA and IFN-α treatment in the context of HAM/TSP. Therefore, we performed the first comparative analysis of the ex vivo and in vitro molecular and cellular mechanisms of action of IFN-α and high-dose AA in HAM/TSP.

PRINCIPAL FINDINGS

Through thymidine incorporation and quantification of Th1/Th2/Th17 cytokines, we demonstrate that high-dose AA displays differential and superior antiproliferative and immunomodulatory effects over IFN-α in HAM/TSP PBMCs ex vivo. In addition, high-dose AA, but not IFN-α, induced cell death in both HAM/TSP PBMCs and HTLV-1-infected T-cell lines MT-2 and MT-4. Microarray data combined with pathway analysis of MT-2 cells revealed AA-induced regulation of genes associated with cell death, including miR-155. Since miR-155 has recently been demonstrated to up-regulate IFN-γ, this microRNA might represent a novel therapeutic target in HAM/TSP, as recently demonstrated in multiple sclerosis, another neuroinflammatory disease. On the other hand, IFN-α selectively up-regulated antiviral and immune-related genes.

CONCLUSIONS

In comparison to IFN-α, high-dose AA treatment has superior ex vivo and in vitro cell death-inducing, antiproliferative and immunomodulatory anti-HTLV-1 effects. Differential pathway activation by both drugs opens up avenues for targeted treatment in specific patient subsets.

[HTLV-1-associated myelopathy/tropical spastic paraparesis: a differential diagnosis in multiple sclerosis]

Human T-cell lymphotropic virus 1 (HTLV-1) associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a neurological disease caused by infection with HTLV-1. The disorder is very rare in Europe but endemic in many parts of the world. The pathogenesis is not clearly characterized but is based on a possibly immune-mediated injury of the cervicothoracic spinal cord. Clinically, HAM/TSP constitutes a slowly progressive spastic paraparesis associated with bladder dysfunction and often mimics the course of autoimmune and neurodegenerative diseases. The diagnosis is based on typical symptoms as well as detection of HTLV-1 specific antibodies and proviral HTLV-1 DNA or HTLV-1 RNA. The therapy is limited to symptomatic treatment. Transmission of HTLV-1 can occur vertically by breast feeding, through sexual contact or via infected blood products. Based on a clinical case report, we present here a current review on the pathophysiology, epidemiology, clinical manifestations, diagnosis and treatment of HAM/TSP.

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.

Immunopathogenesis of human T-cell leukemia virus type-1-associated myelopathy/tropical spastic paraparesis: recent perspectives

Human T-cell leukemia virus type-1 (HTLV-1) is a replication-competent human retrovirus associated with two distinct types of disease only in a minority of infected individuals: the malignancy known as adult T-cell leukemia (ATL) and a chronic inflammatory central nervous system disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HAM/TSP is a chronic progressive myelopathy characterized by spastic paraparesis, sphincter dysfunction, and mild sensory disturbance in the lower extremities. Although the factors that cause these different manifestations of HTLV-1 infection are not fully understood, accumulating evidence from host population genetics, viral genetics, DNA expression microarrays, and assays of lymphocyte function suggests that complex virus-host interactions and the host immune response play an important role in the pathogenesis of HAM/TSP. Especially, the efficiency of an individual's cytotoxic T-cell (CTL) response to HTLV-1 limits the HTLV-1 proviral load and the risk of HAM/TSP. This paper focuses on the recent advances in HAM/TSP research with the aim to identify the precise mechanisms of disease, in order to develop effective treatment and prevention.

Bronchiectasis is associated with human T-lymphotropic virus 1 infection in an Indigenous Australian population

BACKGROUND

Recent studies suggest that infection with human T-lymphotropic virus 1 (HTLV-1) might be associated with bronchiectasis among Indigenous Australians. The present study compared the clinical characteristics and outcomes of bronchiectasis in this population, according to HTLV-1 serologic status.

METHODS

We performed a retrospective cohort study of Indigenous adults with bronchiectasis and known HTLV-1 serologic status admitted to Alice Springs Hospital, central Australia, from January 2000 through December 2006.

RESULTS

Among 89 Indigenous adults whose HTLV-1 serologic status was confirmed, 52 (58.4%) were HTLV-1 seropositive. Differences between HTLV-1-seropositive and HTLV-1-seronegative groups were apparent in childhood presentations and adult outcomes. Among adults, an increasing number of bronchiectatic lobes (univariable odds ratio [OR], 1.51; 95% confidence interval [CI]; 1.03-2.20; P = .033) and the presence of ground-glass opacities at chest high-resolution computed tomography (univariable OR, 8.54; 95% CI, 1.04-70.03; P = .046) predicted HTLV-1 infection. Cor pumonale (HTLV-1-positive group, 10/52; HTLV-1-negative group, 1/37; P = .023) was more frequent among HTLV-1-seropositive adults, who also experienced a higher disease-specific mortality (univariable OR, 5.78; 95% CI, 1.17-26.75; P = .028). Only HTLV-1-seropositive patients were admitted specifically for the treatment of infected skin lesions, and this finding predicted death (multivariable OR, 6.77; 95% CI, 1.46-31.34; P = .014). Overall mortality was high; 34.2% of the cohort died at a median age of 42.5 years.

CONCLUSIONS

HTLV-1 infection contributes to the risk of developing bronchiectasis and worsens outcomes among Indigenous Australians.

A crippling virus: diagnosing tropical spastic paraparesis

PURPOSE

To provide nurse practitioners (NPs) with an overview of the pathogenesis, mode of transmission, clinical presentation, diagnosis, management, and treatment of tropical spastic paraparesis (TSP) caused by the human T-lymphotropic virus type I (HTLV-I).

DATA SOURCES

A review of the scientific literature on tropical spastic paraparesis and HTLV I-associated myelopathy was conducted using PubMed and Medline. A case study was used to illustrate the complexity of the disease.

CONCLUSIONS

NPs should be aware of the clinical features of TSP to improve diagnostic accuracy of symptomatic patients, reduce transmission rates, and provide appropriate patient counseling. The ability to accurately diagnose TSP early in the disease process and differentiate it from other neurological diseases will lead to improved patient outcomes. Timely diagnosis is important to maximize patient response to pharmacological interventions that are used to treat the clinical manifestations of TSP.

IMPLICATIONS FOR PRACTICE

In this globalized society, NPs will need to be prepared to care for patients who have immigrated to the United States from parts of the world where the HTLV-I virus is endemic.

Effect of TNF-α production inhibitors on the production of pro-inflammatory cytokines by peripheral blood mononuclear cells from HTLV-1-infected individuals

Human T lymphotropic virus type 1 (HTLV-1) is the causal agent of myelopathy/tropical spastic paraparesis (HAM/TSP), a disease mediated by the immune response. HTLV-1 induces a spontaneous proliferation and production of pro-inflammatory cytokines by T cells, and increasing interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) levels are potentially involved in tissue damage in diseases related to HTLV-1. This exaggerated immune response is also due to an inability of the natural regulatory mechanisms to down-modulate the immune response in this group of patients. TNF-α inhibitors reduce inflammation and have been shown to improve chronic inflammatory diseases in clinical trials. The aim of this study was to evaluate the ability of pentoxifylline, forskolin, rolipram, and thalidomide to decrease in vitro production of TNF-α and IFN-γ in cells of HTLV-1-infected subjects. Participants of the study included 19 patients with HAM/TSP (mean age, 53 ± 11; male:female ratio, 1:1) and 18 HTLV-1 carriers (mean age, 47 ± 11; male:female ratio, 1:2.6). Cytokines were determined by ELISA in supernatants of mononuclear cell cultures. Pentoxifylline inhibited TNF-α and IFN-γ synthesis with the minimum dose used (50 µM). The results with forskolin were similar to those observed with pentoxifylline. The doses of rolipram used were 0.01-1 µM and the best inhibition of TNF-α production was achieved with 1 µM and for IFN-γ production it was 0.01 µM. The minimum dose of thalidomide used (1 µM) inhibited TNF-α production but thalidomide did not inhibit IFN-γ production even when the maximum dose (50 µM) was used. All drugs had an in vitro inhibitory effect on TNF-α production and, with the exception of thalidomide, all of them also decreased IFN-γ production.

Stable and transient periodic oscillations in a mathematical model for CTL response to HTLV-I infection

The cytotoxic T lymphocyte (CTL) response to the infection of CD4+ T cells by human T cell leukemia virus type I (HTLV-I) has previously been modelled using standard response functions, with relatively simple dynamical outcomes. In this paper, we investigate the consequences of a more general CTL response and show that a sigmoidal response function gives rise to complex behaviours previously unobserved. Multiple equilibria are shown to exist and none of the equilibria is a global attractor during the chronic infection phase. Coexistence of local attractors with their own basin of attractions is the norm. In addition, both stable and unstable periodic oscillations can be created through Hopf bifurcations. We show that transient periodic oscillations occur when a saddle-type periodic solution exists. As a consequence, transient periodic oscillations can be robust and observable. Implications of our findings to the dynamics of CTL response to HTLV-I infections in vivo and pathogenesis of HAM/TSP are discussed.

HTLV-1 tax specific CD8+ T cells express low levels of Tim-3 in HTLV-1 infection: implications for progression to neurological complications

The T cell immunoglobulin mucin 3 (Tim-3) receptor is highly expressed on HIV-1-specific T cells, rendering them partially "exhausted" and unable to contribute to the effective immune mediated control of viral replication. To elucidate novel mechanisms contributing to the HTLV-1 neurological complex and its classic neurological presentation called HAM/TSP (HTLV-1 associated myelopathy/tropical spastic paraparesis), we investigated the expression of the Tim-3 receptor on CD8(+) T cells from a cohort of HTLV-1 seropositive asymptomatic and symptomatic patients. Patients diagnosed with HAM/TSP down-regulated Tim-3 expression on both CD8(+) and CD4(+) T cells compared to asymptomatic patients and HTLV-1 seronegative controls. HTLV-1 Tax-specific, HLA-A*02 restricted CD8(+) T cells among HAM/TSP individuals expressed markedly lower levels of Tim-3. We observed Tax expressing cells in both Tim-3(+) and Tim-3(-) fractions. Taken together, these data indicate that there is a systematic downregulation of Tim-3 levels on T cells in HTLV-1 infection, sustaining a profoundly highly active population of potentially pathogenic T cells that may allow for the development of HTLV-1 complications.

Effects of valproate on Tax and HBZ expression in HTLV-1 and HAM/TSP T lymphocytes

A determinant of human T-lymphotropic virus-1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) development is the HTLV-1-infected cell burden. Viral proteins Tax and HBZ, encoded by the sense and antisense strands of the pX region, respectively, play key roles in HTLV-1 persistence. Tax drives CD4(+)-T cell clonal expansion and is the immunodominant viral antigen recognized by the immune response. Valproate (2-n-propylpentanoic acid, VPA), a histone deacetylase inhibitor, was thought to trigger Tax expression, thereby exposing the latent HTLV-1 reservoir to immune destruction. We evaluated the impact of VPA on Tax, Gag, and HBZ expressions in cultured lymphocytes from HTLV-1 asymptomatic carriers and HAM/TSP patients. Approximately one-fifth of provirus-positive CD4(+) T cells spontaneously became Tax-positive, but this fraction rose to two-thirds of Tax-positive-infected cells when cultured with VPA. Valproate enhanced Gag-p19 release. Tax- and Gag-mRNA levels peaked spontaneously, before declining concomitantly to HBZ-mRNA increase. VPA enhanced and prolonged Tax-mRNA expression, whereas it blocked HBZ expression. Our findings suggest that, in addition to modulating Tax expression, another mechanism involving HBZ repression might determine the outcome of VPA treatment on HTLV-1-infected-cell proliferation and survival.

Clinical manifestations in individuals with recent diagnosis of HTLV type I infection

BACKGROUND

Human T-lymphotropic virus type 1 (HTLV-1) is known to cause HTLV-associated myelopathy (HAM)/tropical spastic paraparesis and adult T cell leukemia. A growing body of evidence links HTLV-1 infection with an increasing spectrum of disease, including uveitis, periodontal disease, arthropathy, sicca syndrome, and neurologic deficits.

OBJECTIVES

Despite recent findings, the natural history of HTLV-1 infection remains poorly defined. This study was designed to better characterize initial clinical and neurological findings in individuals diagnosed with HTLV-1 infection.

STUDY DESIGN

We conducted a cross-sectional study of 71 individuals recently diagnosed with HTLV-1 and 71 uninfected age- and sex-matched blood donors in Salvador, Brazil. Subjects were administered a standardized questionnaire and underwent physical exam.

RESULTS

HTLV-1 infected subjects were significantly more likely than controls to report complaints of hand and foot numbness (OR=5.3; 95% CI: 1.8-15.3; p=0.002 and OR=4.0; 95% CI: 1.3-12; p=0.013 respectively), difficulty running (OR=4.0; 95% CI: 1.1-14.2; p=0.032), nocturia (OR=5.0; 95% CI: 1.1-22.8; p=0.038), arthralgia (OR=3.3; 95% CI: 1.4-7.7; p=0.006), and photophobia (OR=3.3; 95% CI: 1.4-7.7; p=0.006).

CONCLUSIONS

Neurologic, ocular and rheumatologic complaints may be the first manifestations of HTLV-1 infection. Therefore, all patients presenting with initial diagnosis should be rigorously screened for these symptoms.

Design and synthesis of several small-size HTLV-I protease inhibitors with different hydrophilicity profiles

The human T cell leukemia/lymphotropic virus type 1 (HTLV-I) is clinically associated with adult T cell leukemia/lymphoma, HTLV-I associated myelopathy/tropical spastic paraparesis, and a number of other chronic inflammatory diseases. To stop the replication of the virus, we developed highly potent tetrapeptidic HTLV-I protease inhibitors. In a recent X-ray crystallography study, several of our inhibitors could not form co-crystal complexes with the protease due to their high hydrophobicity. In the current study, we designed, synthesized and evaluated the HTLV-I protease inhibition potency of compounds with hydrophilic end-capping moieties with the aim of improving pharmaceutic and pharmacokinetic properties.

Maintaining potent HTLV-I protease inhibition without the P3-cap moiety in small tetrapeptidic inhibitors

The human T cell lymphotropic/leukemia virus type 1 (HTLV-I) causes adult T cell lymphoma/leukemia. The virus is also responsible for chronic progressive myelopathy and several inflammatory diseases. To stop the manufacturing of new viral components, in our previous reports, we derived small tetrapeptidic HTLV-I protease inhibitors with an important amide-capping moiety at the P(3) residue. In the current study, we removed the P(3)-cap moiety and, with great difficulty, optimized the P(3) residue for HTLV-I protease inhibition potency. We discovered a very potent and small tetrapeptidic HTLV-I protease inhibitor (KNI-10774a, IC(50)=13 nM).

Inhibition of immune activation by a novel nuclear factor-kappa B inhibitor in HTLV-I-associated neurologic disease

The human T-lymphotropic virus type I (HTLV-I) causes a chronic inflammatory disorder of the central nervous system termed HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-I encodes a protein known to activate several host-signaling pathways involved in inflammation, such as the nuclear factor-κB (NF-κB). The contribution of the NF-κB pathway to the pathogenesis of HAM/TSP, however, has not been fully defined. We show evidence of canonical NF-κB activation in short-term cultures of peripheral blood mononuclear cells (PBMCs) from subjects with HAM/TSP. NF-κB activation was closely linked to HTLV-I viral protein expression. The NF-κB activation in HAM/TSP PBMCs was reversed by a novel small-molecule inhibitor that demonstrates potent and selective NF-κB antagonist activity. Inhibition of NF-κB activation led to a reduction in the expression of lymphocyte activation markers and resulted in reduced cytokine signaling in HAM/TSP PBMCs. Furthermore, NF-κB inhibition led to a reduction in spontaneous lymphoproliferation, a key ex vivo correlate of the immune activation associated with HAM/TSP. These results indicate that NF-κB activation plays a critical upstream role in the immune activation of HAM/TSP, and identify the NF-κB pathway as a potential target for immunomodulation in HAM/TSP.

Multiple stable periodic oscillations in a mathematical model of CTL response to HTLV-I infection

Stable periodic oscillations have been shown to exist in mathematical models for the CTL response to HTLV-I infection. These periodic oscillations can be the result of mitosis of infected target CD4(+) cells, of a general form of response function, or of time delays in the CTL response. In this study, we show through a simple mathematical model that time delays in the CTL response process to HTLV-I infection can lead to the coexistence of multiple stable periodic solutions, which differ in amplitude and period, with their own basins of attraction. Our results imply that the dynamic interactions between the CTL immune response and HTLV-I infection are very complex, and that multi-stability in CTL response dynamics can exist in the form of coexisting stable oscillations instead of stable equilibria. Biologically, our findings imply that different routes or initial dosages of the viral infection may lead to quantitatively and qualitatively different outcomes.

Anti-Tax antibody levels in asymptomatic carriers, oligosymptomatic carriers, patients with rheumatologic disease or with HAM/TSP do not correlate with HTLV-1 proviral load

BACKGROUND

HTLV-1 infects millions of people around the world and induces myelopathy (HAM/TSP), adult T-cell leukemia (ATL) or other inflammatory or rheumatologic diseases. The host-virus interaction causes asymptomatic carriers to develop HAM/TSP. Biomarkers are needed to predict patients who are at risk for HAM/TSP. Tax is highly immunogenic and is a major target protein recognized by cytotoxic T lymphocytes. Anti-Tax antibodies are involved in HAM/TSP pathogenesis.

OBJECTIVES

To assess anti-Tax IgG reactivity with a flow cytometry assay (FCA) using an infection/transfection system with Vaccinia virus and pLW44/Tax-expressing Tax and to correlate the anti-Tax response and the HTLV-1 proviral load.

STUDY DESIGN

: We enrolled 81 individuals: 9 HTLV-1 seronegative (NP) and 72 HTLV-1 positive (23 HTLV-1 asymptomatic carriers (AC), 12 oligosymptomatic patients (OL), 7 with rheumatologic diseases (DR) and 30 with HAM/TSP (HT)). Anti-Tax reactivity was assessed by FCA, and HTLV-1 proviral load was measured with real time PCR.

RESULTS

The HT and DR groups showed greater anti-Tax IgG reactivity (p<0.001 and p<0.05 comparing HT to the OL and AC group, respectively; p<0.05 comparing DR to the OL group), and the reactivity in the DR+HT group was significantly different when compared to the AC group (p<0.05) and to the OL group (p<0.001). The proviral load was higher in the HT group compared to the OL (p<0.001) and in the HT+DR group compared to OL (p<0.001). There was no correlation between anti-Tax IgG reactivity and proviral load in any of the HTLV-1-infected groups.

CONCLUSION

These findings suggest that although anti-Tax IgG reactivity and the HTLV-1 proviral load are important markers of the development of HTLV-1-associated diseases, their levels are not correlated.

HLA class I binding of HBZ determines outcome in HTLV-1 infection

CD8(+) T cells can exert both protective and harmful effects on the virus-infected host. However, there is no systematic method to identify the attributes of a protective CD8(+) T cell response. Here, we combine theory and experiment to identify and quantify the contribution of all HLA class I alleles to host protection against infection with a given pathogen. In 432 HTLV-1-infected individuals we show that individuals with HLA class I alleles that strongly bind the HTLV-1 protein HBZ had a lower proviral load and were more likely to be asymptomatic. We also show that in general, across all HTLV-1 proteins, CD8(+) T cell effectiveness is strongly determined by protein specificity and produce a ranked list of the proteins targeted by the most effective CD8(+) T cell response through to the least effective CD8(+) T cell response. We conclude that CD8(+) T cells play an important role in the control of HTLV-1 and that CD8(+) cells specific to HBZ, not the immunodominant protein Tax, are the most effective. We suggest that HBZ plays a central role in HTLV-1 persistence. This approach is applicable to all pathogens, even where data are sparse, to identify simultaneously the HLA Class I alleles and the epitopes responsible for a protective CD8(+) T cell response.

Human T-lymphotropic virus type I or II (HTLV-I/II) associated with recurrent longitudinally extensive transverse myelitis (LETM): two case reports

We describe two patients with recurrent longitudinally extensive transverse myelitis (LETM) associated with human T-lymphotropic virus type I or II (HTLV-I/II) exposure, and with neuromyelitis optica (NMO) immunoglobulin G (IgG) antibody in one case. HTLV-I/II are well known retroviral agents of myelopathy and B-cell dysfunction in humans. NMO is an autoimmune, demyelinating disorder of the central nervous system (CNS), also linked to B-cell dysfunction. Therefore, the immunopathogenesis of NMO may in some cases be linked to human HTLV exposure. Awareness of a possible association with human retroviral exposure will contribute to the optimal diagnosis and management of patients presenting with LETM or NMO.

Cytotoxic responses to BLV tax oncoprotein do not prevent leukemogenesis in sheep

Delta retrovirus-mediated leukemogenesis is dependent on the oncogenic potential of Tax. It is not clear, however, whether Tax-specific immune responses play a role in leukemia onset and progression. Using the BLV-associated leukemia model in sheep, we found that Tax-specific cytotoxic responses induced by DNA immunization or viral infection of naïve animals were not predictive of disease outcome and did not prevent tumor development. Furthermore, provirus and tax may be absent from blood for extended periods, emphasizing the relevance of surveying other compartments during chronic lymphoproliferative disorders. Our results support the conclusion that Tax-specific cytotoxic responses, even during the initial phase of infection, are not sufficient to prevent leukemogenesis.

HERVs in neuropathogenesis

In humans, exogenous retroviruses are known to cause immunodeficiency and neurological disease. While endogenous retroviruses are firmly established pathogens in other species, the human endogenous retroviruses (HERVs) may well be considered as emerging pathogens. HERVs also exhibit complex interactions with exogenous retroviruses and herpesviruses. Two neurological disorders in particular are associated with HERVs: multiple sclerosis (MS) and schizophrenia. HERV-H/F and HERV-W are specifically activated both in the circulation and the central nervous system (CNS) in a majority of MS patients, and particularly, the envelopes (env transcription and Env proteins) appear strongly associated with disease activity. Interferon beta (IFN-beta) therapy is well-established for MS. IFN-beta is also known to have anti-retroviral activities toward exogenous retroviruses (HIV and HTLV-I). New reports show that IFN-beta also mediate down-regulation of HERV-H/F and HERV-W in MS patients. HERV-W and HERV-K transcription (gag and pol) appears, to some extent, to be up-regulated in the circulation and the CNS of patients with schizophrenia. The expression of anti-HERV-W Gag reactive epitopes is reported to be down-regulated in the brain but up-regulated in the blood from schizophrenia patients. The pathogenic potential of HERVs certainly merits further studies.

Immunogenetics and the Pathological Mechanisms of Human T-Cell Leukemia VirusType 1- (HTLV-1-)Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP)

Human T-cell leukemia virus type 1 (HTLV-1) is a replication-competent human retrovirus associated with two distinct types of disease only in a minority of infected individuals: the malignancy known as adult T-cell leukemia (ATL) and a chronic inflammatory central nervous system disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Although the factors that cause these different manifestations of HTLV-1 infection are not fully understood, accumulating evidence suggests that complex virus-host interactions play an important role in determining the risk of HAM/TSP. This review focuses on the role of the immune response in controlling or limiting viral persistence in HAM/TSP patients, and the reason why some HTLV-1-infected people develop HAM/TSP whereas the majority remains asymptomatic carriers of the virus.

Multistability in a model for CTL response to HTLV-I infection and its implications to HAM/TSP development and prevention

Human T-cell leukaemia/lymphoma virus type I (HTLV-I) is a retrovirus that has been identified as the causative agent of HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and other illnesses. HTLV-I infects primarily CD4(+) T cells and the transmission occurs through direct cell-to-cell contact. HAM/TSP patients harbor higher proviral loads in peripheral blood lymphocytes than asymptomatic carriers. Also, HAM/TSP patients exhibit a remarkably high number of circulating HTLV-I-specific CD8(+) cytotoxic T lymphocytes (CTLs) in the peripheral blood. While CTLs have a protective role by killing the infected cells and lowering the proviral load, a high level of CTLs and their cytotoxicity are believed to be a main cause of the development of HAM/TSP. A mathematical model for HTLV-I infection of CD4(+) T cells that incorporates the CD8(+) cytotoxic T-cell (CTL) response is investigated. Our mathematical analysis reveals that the system can stabilize at a carrier steady-state with persistent viral infection but no CTL response, or at a HAM/TSP steady-state at which both the viral infection and CTL response are persistent. We also establish two threshold parameters R(0) and R(1), the basic reproduction numbers for viral persistence and for CTL response, respectively. We show that the parameter R(1) can be used to distinguish asymptomatic carriers from HAM/TSP patients, and as an important control parameter for preventing the development of HAM/TSP.

The elevated interferon gamma production is an important immunological marker in HAM/TSP pathogenesis

Human T-lymphotropic virus type 1 (HTLV-1) is the agent of the HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), which may occur in >5% of patients during their lifetime. HTLV-1-infection causes disturbances in the immune system, and the viral load may also play an important role in the pathogenesis of HAM/TSP. Some cytokines are involved in the pathogenesis of this disorder. We have determined IL-2, IL-4, IL-10, IL-12 p70, IFN-gamma and TNF-alpha production among HTLV-1-infected subjects from our HTLV-out Clinic in Institute of Infectious 'Emílio Ribas' in Sao Paulo city, Brazil. PBMC obtained from healthy controls (n = 32), asymptomatic HTLV-1 carriers (n = 68) and HAM/TSP patients (n = 44) were grown in the absence and in the presence of phytohaemagglutinin (PHA), and the supernatants' fluids were measured for cytokines production. IL-2 levels were increased in the asymptomatic HTLV-1 carriers, and IFN-gamma was increased in both groups of patients (asymptomatic HTLV-1 carriers and more significantly among HAM/TSP patients). IL-4, IL-10, TNF-alpha and IL-12 p70 levels were not significantly increased on both groups of patients, as compared with controls. The major finding of this study is that IFN-gamma was an important cytokine for the HAM/TSP pathogenesis. Therefore, immune modulation of IFN-gamma may be critical to treat of HAM/TSP patients.

Lower numbers of circulating Natural Killer T (NK T) cells in individuals with human T lymphotropic virus type 1 (HTLV-1) associated neurological disease

Human T lymphotropic virus type 1 (HTLV-1) infects 10-20 million people worldwide. The majority of infected individuals are asymptomatic; however, approximately 3% develop the debilitating neurological disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). There is also currently no cure, vaccine or effective therapy for HTLV-1 infection, and the mechanisms for progression to HAM/TSP remain unclear. NK T cells are an immunoregulatory T cell subset whose frequencies and effector functions are associated critically with immunity against infectious diseases. We hypothesized that NK T cells are associated with HAM/TSP progression. We measured NK T cell frequencies and absolute numbers in individuals with HAM/TSP infection from two cohorts on two continents: São Paulo, Brazil and San Francisco, CA, USA, and found significantly lower levels when compared with healthy subjects and/or asymptomatic carriers. Also, the circulating NK T cell compartment in HAM/TSP subjects is comprised of significantly more CD4(+) and fewer CD8(+) cells than healthy controls. These findings suggest that lower numbers of circulating NK T cells and enrichment of the CD4(+) NK T subset are associated with HTLV-1 disease progression.

Severe loss of invariant NKT cells exhibiting anti-HTLV-1 activity in patients with HTLV-1-associated disorders

Invariant natural killer T (iNKT) cells are unique T cells that regulate the immune response to microbes, cancers, and autoimmunity. We assessed the characteristics of iNKT cells from persons infected with human T-lymphotropic virus type 1 (HTLV-1). Whereas most infected persons remain asymptomatic carriers (ACs) throughout their lives, a small proportion, usually with high equilibrium proviral loads,develop 2 diseases: HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T-cell leukemia (ATL). We demonstrated that the frequency of iNKT, NK, and dendritic cells in the peripheral blood of HAM/TSP and ATL patients is decreased. We also observed an inverse correlation between the iNKT cell frequency and the HTLV-1 proviral load in the peripheral blood of infected persons. Notably, in vitro stimulation of peripheral blood cells with alpha-galactosylceramide led to an increase in the iNKT cell number and a subsequent decrease in the HTLV-1-infected T-cell number in samples from ACs but not HAM/TSP or ATL patients. Our results suggest that iNKT cells contribute to the immune defense against HTLV-1, and iNKT-cell depletion plays an important role in the pathogenesis of HAM/TSP and ATL. Therefore, iNKT cell-based immunotherapy may be an effective strategy for preventing these HTLV-1-associated disorders.