Differences in viral and host genetic risk factors for development of human T-cell lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis between Iranian and Japanese HTLV-1-infected individuals

Momordica charantia phytoconstituents can inhibit human T-lymphotropic virus type-1 (HTLV-1) infectivity in vitro and in vivo

There is an urgent need to find an effective therapy for life-threatening HTLV-1-associated diseases. Bitter melon (Momordica charantia) is considered a traditional herb with antiviral and anticancer properties and was tested in this study on HTLV-1 infectivity. GC-MS analyzed the alcoholic extract. In vitro assay was carried out using transfection of HUVEC cells by HTLV-1-MT2 cell line. The cells were exposed to alcoholic and aqueous extracts at 5,10, and 20 µg/mL concentrations. In vivo, mice were divided into four groups. Three groups were treated with HTLV-1-MT-2 cells as test groups and positive control, and PBS as the negative control group in the presence and absence of M. charantia extracts. Peripheral blood mononuclear cells (PBMCs), mesenteric lymph nodes (MLNs), and splenocytes were collected for HTLV-1-proviral load (PVL) assessment, TaqMan-qPCR. The GC-MS analysis revealed 36 components in M. charantia. The studies showed significant reductions in HTLV-1-PVL in the presence of extract in the HUVEC-treated groups (P = 0.001). Furthermore, the inhibitory effects of extracts on HTLV-1 infected mice showed significant differences in HTLV-1-PVL among M. charantia treated groups with untreated (P = 0.001). The T-cells in MLNs were significantly more susceptible to HTLV-1 than others (P = 0.001). There were significant differences among HTLV-1-infected cells in MLNs and splenocytes (P = 0.001 and 0.046, respectively). Also, aqueous and alcoholic extract-treated groups significantly affected HTLV-1-infected PBMCs (P = 0.002 and 0.009, respectively). M. charantia may have effective antiviral properties. The substantial compound of M. charantia could have inhibitory effects on the proliferation and transmission of HTLV-1 oncovirus.

Advances in the treatment of human T-cell lymphotropic virus type-I associated myelopathy

INTRODUCTION

Nearly 2-3% of those 10 to 20 million individuals infected with the Human T-cell lymphotropic virus type-1 (HTLV-1); are predisposed to developing HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). It is a neuro-inflammatory disease; differentiated from multiple sclerosis based on the presence of typical neurologic symptoms, confirmation of HTLV-1 infection, and other molecular biomarkers.

AREAS COVERED

A brief review of the epidemiology, host immune responses, and molecular pathogenesis of HAM/TSP is followed by detailed discussions about the host-related risk factors for developing HAM/TSP and success/failure stories of the attempted management strategies.

EXPERT OPINION

Currently, there is no effective treatment for HAM/TSP. Anti-retroviral therapy, peculiar cytokines (IFN-α), some anti-oxidants, and allograft bone marrow transplantation have been used for treating these patients with limited success. Under current conditions, asymptomatic carriers should be examined periodically by a neurologist for early signs of spinal cord injury. Then it is crucial to determine the progress rate to adapt the best management plan for each patient. Corticosteroid therapy is most beneficial in those with acute myelitis. However, slow-progressing patients are best managed using a combination of symptomatic and physical therapy. Additionally, preventive measures should be taken to decrease further spread of HTLV-1 infection.

Putative role of HLA polymorphism among a Brazilian HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) population

Around ten million people are infected with HTLV-1 worldwide, and 1-4% develop HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), characterized by an important degeneration of the spinal cord, which can lead to death. Distinct HLA alleles have been associated with either HAM/TSP susceptibility or protection. However, these HLA alleles set may change according to the population studied. Brazil is the second country in the number of HTLV-1-infected people and there are few reports addressing the HLA influence on HTLV-1 infection as well as on disease outcome. The objective of this study was to evaluate the influence of HLA alleles as a risk factor for HAM/TSP and the proviral load (PVL) levels, clinical progression, and death outcomes in an admixed Brazilian population. The HLA-A, -B, -C, and -DRB1 were genotyped in 375 unrelated HTLV-1-infected individuals divided into asymptomatic carriers (AC) (n = 165) and HAM/TSP (n = 210) in a longitudinal cohort from 8 to 22 years of follow-up. Because locus B deviated from Hardy-Weinberg Equilibrium for the study groups, the results represented for HLA-B alleles were inconclusive. The alleles HLA-A*68 and -C*07 were related to HAM/TSP risk in multivariate analysis. The alleles HLA-A*33, and -A*36 were associated with protection against disease progression in HAM/TSP patients, while -C*12, -C*14, and -DRB1*08 were associated with increased risk of death. In the AC group, the presence of, -C*06 and -DRB1*15 alleles influenced an increased PVL, in an adjusted linear regression model, while -A*30, -A*34, -C*06, -C*17 and -DRB1*09 alleles were associated with increased PVL in HAM/TSP group compared to HAM/TSP individuals not carrying these alleles. All these alleles were also related to increased PVL associated with clinical progression outcome. Increased PVL associated with the death outcome was linked to the presence of HLA-A*30. PVL has been associated with HLA, and several alleles were related in AC and HAM/TSP patients with or without interacting with clinical progression outcomes. Understanding the prognostic value of HLA in HAM/TSP pathogenesis can provide important biomarkers tools to improve clinical management and contribute to the discovery of new therapeutic interventions.

Refining the risk of HTLV-1-associated myelopathy in people living with HTLV-1: identification of a HAM-like phenotype in a proportion of asymptomatic carriers

Up to 3.8% of human T-lymphotropic virus type-1 (HTLV-1)-infected asymptomatic carriers (AC) eventually develop HTLV-1-associated myelopathy (HAM). HAM occurs in patients with high (> 1%) HTLV proviral load (PVL). However, this cut-off includes more than 50% of ACs and therefore the risk needs to be refined. As HAM is additionally characterised by an inflammatory response to HTLV-1, markers of T cell activation (TCA), β₂-microglobulin (β₂M) and neuronal damage were accessed for the identification of ACs at high risk of HAM. Retrospective analysis of cross-sectional and longitudinal routine clinical data examining differences in TCA (CD4/CD25, CD4/HLA-DR, CD8/CD25 & CD8/HLA-DR), β₂M and neurofilament light (NfL) in plasma in ACs with high or low PVL and patients with HAM. Comparison between 74 low PVL ACs, 84 high PVL ACs and 58 patients with HAM revealed a significant, stepwise, increase in TCA and β₂M. Construction of receiver operating characteristic (ROC) curves for each of these blood tests generated a profile that correctly identifies 88% of patients with HAM along with 6% of ACs. The 10 ACs with this 'HAM-like' profile had increased levels of NfL in plasma and two developed myelopathy during follow-up, compared to none of the 148 without this viral-immune-phenotype. A viral-immuno-phenotype resembling that seen in patients with HAM identifies asymptomatic carriers who are at increased risk of developing HAM and have markers of subclinical neuronal damage.

Status of humoral and cellular immune markers in human T-cell lymphotropic virus type 1 (HTLV-1) asymptomatic carriers in northeastern Iran, Mashhad

It is estimated that about 10-20 million peoples are infected with human T-cell leukemia virus type 1 (HTLV-1) around the world and suffered from HTLV-related diseases. The present study was aimed to evaluate the cellular immunity, T-cell activation, humoral immunity, and inflammatory response hallmarks which affect HTLV-1-associated disease progression. A total of 78 participants were included in the study, comprising 39 HTLV-1 asymptomatic careers (ACs) and 39 healthy controls. The HTLV-proviral load (PVL) was determined via real-time PCR technique, and anti-HTLV antibody, sIL2R, sCD30, Neoptrin, hs-CRP, IgE, anti-VCA, anti-EBNA, and anti-EA were assessed by ELISA method. Mean PVL in ACs was 352.7 ± 418.7 copies/10⁴ PBMCs. A significant higher level of sIL-2R was observed in ACs (P < 0.0001). Anti-VCA antibody titer in ACs and healthy controls was 80.72 ± 105.95 and 156.05 ± 130.71, respectively (P = 0.007). Intriguingly, suppression in ACs immune response was not observed. Resultantly, HTLV-1 infection has no effect on the humoral immune response in ACs but greater T-cell activation and function cellular responses were detected. Finally, more studies on various immune markers in adult T-cell leukemia/lymphoma (ATLL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients are greatly needed to illuminate the association of ACs' immune status with the development of the related diseases.

HLA-B*35 as a new marker for susceptibility to human T-cell lymphotropic virus type 1 (HTLV-1) Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP) in patients living in Argentina

Background

Human T-cell lymphotropic virus type 1 (HTLV-1) is the etiological agent of HTLV associated myelopathy/ Tropical Spastic Paraparesis (HAM/TSP) and Adult T cell leukemia/lymphoma (ATLL), in around 2–5% of the infected individuals. Host genetic background might play a role in disease progression. Several previous studies across many countries report HLA haplotype to be one such factor. Here, we sequenced HLA-A, -B and -C of 66 individuals by Sequence-Based Typing (SBT), and compared the frequency of different alleles among ATLL patients, HAM/TSP patients, asymptomatic carriers and non-infected individuals living in Argentina.

Results

The frequency of HLA-A, -B and -C alleles largely matched that of the general population in Argentina. We identified HLA-A*02, HLA-B*35 and HLA-C*07 as associated to protection from ATLL (p = 0.031), susceptibility to HAM/TSP (p < 0.001) and susceptibility to ATLL (p = 0.017), respectively. We also found a strong correlation between high proviral load (PVL) and disease (p = 0.008), but were unable to identify any particular allele associated with high or low PVL.

Conclusions

We have found HLA-A*02, HLA-B*35 and HLA-C*07 to be associated to protection from ATLL (HLA-A*02) and susceptibility to HAM/TSP (HLA-B*35) or to ATLL (HLA-C*07), respectively. Whereas HLA-A*02 protection from ATLL has already been extensively described in other regions of the world, this is the first report that links HLA-B*35 and an increased susceptibility to HAM/TSP. As for HLA-C*07 it has previously been associated to susceptibility to HAM/TSP in other countries but in our population it has been linked to ATLL.

High proviral load of human T cell lymphotropic virus type-1 facilitates coronary artery diseases

Objective(s):

Coronary artery disease (CAD) is known as a life threatening disease, worldwide. In this study the role of HTLV-1 infection was evaluated on cardiac involvement in an endemic region of northeastern Iran.

Materials and Methods:

Serologic and molecular tests for HTLV-1 infection were carried out in subjects who had coronary angiography. A real-time PCR, TaqMan method, to quantify HTLV-1 proviral load (PVL), and routine hematological and biochemical tests were performed for study subjects.

Results:

Twenty nine patients were HTLV-1+CAD+ and 13 cases were HTLV-1+CAD-. Although, there were no significant differences for risk factors like FBS, HDL, triglyceride, systolic and diastolic blood pressure (Cbp, Dbp), waist circumference (WC), hip circumference (WL), cholesterol (P=0.003), and LDL (P=0.007) levels, and monocyte count (P=0.05) had meaningful differences. The mean HTLV-1 PVL in HTLV-1+CAD+ subjects was 992.62±120 which was higher compared with HTLV-1+CAD- group (406.54±302 copies/104 PBMCs). Moreover, HTLV-1 PVL in males (833±108) was lower compared with females (1218±141 copies/104 PBMCs) (P=0.05). Patients with HTLV-1-PVL of more than 500 copies/104 had more diffused atherosclerosis plaque than patients with less than 500 (OR=6.87, 95% CI=1.34-35.05; P=0.016). Furthermore, patients with diffused coronary atherosclerosis had significantly higher levels of HTLV-1 PVL than patients with middle, proximal, and normal location of coronary sclerotic lesions (P<0.05).

Conclusion:

Taken together, in endemic area, HTLV-1 infection, more likely is a facilitating factor for heart complications and the high HTLV-1 PVL might affect CAD manifestations.

The Role of Chemokines in the Pathogenesis of HTLV-1

Human T cell leukemia virus type 1 (HTLV-1) is a human retrovirus that is associated with two main diseases: HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T cell leukemia/lymphoma (ATL). Chemokines are highly specialized groups of cytokines that play important roles in organizing, trafficking, homing, and in the migration of immune cells to the bone marrow, lymphoid organs and sites of infection and inflammation. Aberrant expression or function of chemokines, or their receptors, has been linked to the protection against or susceptibility to specific infectious diseases, as well as increased the risk of autoimmune diseases and malignancy. Chemokines and their receptors participate in pathogenesis of HTLV-1 associated diseases from inflammation in the central nervous system (CNS) which occurs in cases of HAM/TSP to T cell immortalization and tissue infiltration observed in ATL patients. Chemokines represent viable effective prognostic biomarkers for HTLV-1-associated diseases which provide the early identification of high-risk, treatment possibilities and high-yielding clinical trials. This review focuses on the emerging roles of these molecules in the outcome of HTLV-1-associated diseases.

Influence of Immunogenetic Biomarkers in the Clinical Outcome of HTLV-1 Infected Persons

Human T-lymphotropic virus 1, a member of the Retroviridae family, causes a neglected, silent, persistent infection affecting circa 5 to 10 million people around the world, with biology, immune pathology, clinical diseases, epidemiology, and laboratory issues still unsolved. Most of the infected subjects are asymptomatic, but severe clinical disorders appear as a neurodegenerative disease (HTLV-1 associated myelopathy—HAM) or a lymphoprolipherative disorder (Adult T Leukemia/Lymphoma—ATLL) and in other target organs of the human body. HTLV-1 infections are frequently asymptomatic, but there is a large spectrum of diseases that have been described along the years. The mechanisms by which the virus interacts with the host, the different modes of response of the host to the infection, and the immunogenic characteristics of the host are some of the interesting and unanswered questions that may direct the outcome of the disease. The most relevant published results dealing with the genetic variations of the host, the immune response to HTLV-1 infection, and the outcome of the infection are presented herein, including Human Leucocyte Antigen (HLA), Killer Immunoglobulin-like Receptors (KIR), interleukin 6, 10, 28, Fas and Fas ligand, IFN-gamma, TNF-A, and Mannose-binding lectin. In summary, there are still several unmet research needs in the field of useful biomarkers on HTLV-1 pathogenesis.

Complete sequence of human T cell leukemia virus type 1 in ATLL patients from Northeast Iran, Mashhad revealed a prematurely terminated protease and an elongated pX open reading frame III

To gain insight into the origin, evolution, dissemination and viral factors affecting HTLV-1-associated diseases, knowing the complete viral genome sequences is important. So far, no full-length HTLV-1 genome sequence has been reported from Iran. Here we report the complete nucleotide sequence of HTLV-1 viruses isolated from adult T cell leukemia/lymphoma (ATLL) patients from this region. The genome size of HTLV-1-MhD (Mashhad) was found to be 9036 bp and sequence analysis of the LTR region showed that it belongs to cosmopolitan subtype A. Comparing the sequences with isolates from another endemic area (HTLV-1ATK) revealed variations in the U3 region (~3.4%), while there was 99.1% and 97.0% similarity in R and U5 regions, respectively. The nucleotide sequences of HTLV-1 gag, pro and pol genes had a difference of 1.1% compared with HTLV-1 ATK with 16 nucleotides replaced in the gag and 27 in the pol regions. There was no variability in the amino acid sequences in the p24^gag, however three residues were different in the p19^gag and one in the p15^gag. The nucleotide sequence of env showed a divergence of 1.5% compared to ATK with 22-nucleotide variation. The HTLV-1-MhD Tax, p13, p30, and p12 had 99.1, 100, 98.8, and 98%, respectively similarity with the prototype strain. Four amino acid changes were detected in ORF1 and ORF2 products p12 and p30, respectively, while the p13 region showed 100% conservation. The nucleotide identity between the isolates of Mashhad and those isolated from France, Germany, China, Canada and Brazil was 99.1%, 99.2%, 97.9%, 99% and 99.3%, respectively. Four amino acid changes compared with HTLV-1ATK from Japan were detected in ORF1 and ORF2 products p12 and p30, respectively, while the p13 region showed 100% conservation. This data could provide information regarding the evolutionary history, phylogeny, origin of the virus and vaccine design.

Association Between HTLV-1 Genotypes and Risk of HAM/TSP

Human T-cell leukemia virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a neurological disorder presenting with spastic paraparesis, sphincter dysfunction, and mild sensory disturbance in the lower extremities, which develops in a small minority of HTLV-1-infected individuals. HTLV-1-specific T cells are efficiently activated through dedicated human leukocyte antigen-mediated mechanisms, a process considered deeply involved with its pathogenesis. It has been reported that the lifetime risk of developing HAM/TSP differs between ethnic groups, and there is an association between HTLV-1 tax gene subgroups (i.e., tax subgroup-A or -B), which correspond to HTLV-1 “cosmopolitan subtype 1a subgroup A (i.e., transcontinental subgroup)” and “cosmopolitan subtype 1a subgroup B (i.e., Japanese subgroup),” respectively, and the risk of HAM/TSP in the Japanese population. These findings suggest that a given host’s susceptibility to HAM/TSP is deeply connected with both differences in genetically determined components of the host immune response and HTLV-1 subgroup. Therefore, it is crucial for ongoing work to focus on developing novel treatments and preventative approaches for HAM/TSP. In this review, based on an overview of the topic and our latest research findings, the role of the HTLV-1 subgroup on the effects of virus–host interactions in the pathogenesis of HAM/TSP is discussed.

Mediators Go Together: High Production of CXCL9, CXCL10, IFN-γ, and TNF-α in HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic demyelinating and disabling syndrome caused by human T lymphotropic virus 1 (HTLV-1). Although the pathogenic mechanisms that lead to HAM/TSP outcome have not been elucidated, genetic and immunological factors may be involved in the myelopathy occurrence. This study aimed to compare cytokines, chemokines, and nitric oxide (NO) levels in asymptomatic and HAM/TSP HTLV-1-infected patients. The study group consisted of 21 HAM/TSP and 48 asymptomatic HTLV-1 patients. Chemokines (CCL5, CCL2, CXCL8, CXCL9, and CXCL10) and cytokines [IL-2, interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), IL-4, IL-6, and IL-10] were measured using cytometric bead array, whereas NO production was measured after reaction of supernatants with nitrate reduction solution. CXCL9 and CXCL10 chemokines levels were found to be higher in the HAM/TSP group. CXCL9 was also strongly correlated with CXCL10 and both CXCL9 and CXCL10 were moderately correlated with CCL2 and CCL5 levels, in both HAM/TSP and asymptomatic groups. There was no significant difference related to NO, IL-4, IL-6, and IL-10 levels between the clinical groups but TNF-α and IFN-γ levels were increased in HAM/TSP patients. Thus, factors such as CXCL9, CXCL10, TNF-α, and IFN-γ could be good prognostic biomarker candidates, and further studies may help to clarify their association with HAM/TSP immunopathogenesis.

Effects of host restriction factors and the HTLV-1 subtype on susceptibility to HTLV-1-associated myelopathy/tropical spastic paraparesis

BACKGROUND

Although human T-lymphotropic virus type 1 (HTLV-1) infection is a prerequisite for the development of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), specific provirus mutations in HAM/TSP have not yet been reported. In this study, we examined whether HAM/TSP patients had the disease-specific genomic variants of HTLV-1 by analyzing entire sequences of HTLV-1 proviruses in these patients, including familial cases. In addition, we investigated the genetic variants of host restriction factors conferring antiretroviral activity to determine which mutations may be related to resistance or susceptibility to HAM/TSP.

RESULTS

The subjects included 30 patients with familial HAM/TSP (f-HAM/TSP), 92 patients with sporadic HAM/TSP (s-HAM/TSP), and 89 asymptomatic HTLV-1 carriers (ACs). In all 211 samples, 37 samples (18%) were classified into transcontinental subtype and 174 samples (82%) were classified as Japanese subtype. Among three groups, the percentage of transcontinental subtype in f-HAM/TSP, s-HAM/TSP and ACs was 33, 23 and 7%, respectively. The frequency of transcontinental subtype was significantly higher in both f-HAM/TSP (p < 0.001) and s-HAM/TSP (p < 0.001) than in ACs. Fifty mutations in HTLV-1 sequences were significantly more frequent in HAM/TSP patients than in ACs, however, they were common only in transcontinental subtype. Among these mutations, ten common mutations causing amino acid changes in the HTLV-1 sequences were specific to the transcontinental subtype. We examined host restriction factors, and detected a rare variant in TRIM5α in HAM/TSP patients. The patients with TRIM5α 136Q showed lower proviral loads (PVLs) than those with 136R (354 vs. 654 copies/10⁴ PBMC, p = 0.003). The patients with the 304L variant of TRIM5α had significantly higher PVLs than those with 304H (1669 vs. 595 copies/10⁴ PBMC, p = 0.025). We could not find any HAM/TSP-specific mutations of host restriction factors.

CONCLUSIONS

Transcontinental subtype is susceptible to HAM/TSP, especially in familial cases. Ten common mutations causing amino acid changes in the HTLV-1 gene were specific to the transcontinental subtype. TRIM5α polymorphisms were associated with PVLs, indicating that TRIM5α could be implicated in HTLV-1 replication.

IL17A Polymorphism Is Not Associated with Human T-Lymphotropic Virus 1-Associated Myelopathy/Tropical Spastic Paraparesis

The human T-lymphotropic virus 1 (HTLV-1) is the causative agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The present study investigated the association between the rs2275913 polymorphism in the IL17A gene and the development of HAM/TSP. Peripheral blood samples were collected from 116 patients (29 symptomatic patients with HAM/TSP and 87 asymptomatic) with a positive diagnosis of HTLV-1. The single nucleotide polymorphism genotyping was carried out by real time PCR using TaqMan probes. In addition, serum levels of IL-2, IFN-γ, TNF-α, IL-4, IL-6, IL-10, and IL-17 were measured in 64 infected individuals from the study (47 asymptomatic and 17 HAM/TSP), using cytometric bead array technique. No significant differences were found in genotypic and allelic frequencies between the groups. Analysis of cytokine levels showed highest concentrations of IFN-γ and TNF-α in HAM/TSP patients. The results of the present study, therefore, suggest a lack of association between the rs2275913 polymorphism in the IL17A gene and the presence of HAM/TSP.

HLA-G 3'-untranslated region polymorphisms are associated with HTLV-1 infection, proviral load and HTLV-associated myelopathy/tropical spastic paraparesis development

Most human T-lymphotropic virus type 1 (HTLV-1)-infected patients remain asymptomatic throughout life. The factors associated with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) development have not been fully elucidated; immunological and genetic factors may be involved. The association of 14 bp INS/DEL HLA-G polymorphism with HTLV-1 infection susceptibility has been reported previously. Here, other polymorphic sites at the HLA-G 3'-UTR (14-bp D/I, +3003C/T, +3010C/G, +3027A/C, +3035C/T, +3142C/G, +3187A/G and +3196C/G) were evaluated in 37 HTLV-1-infected individuals exhibiting HAM/TSP, 45 HTLV-1 asymptomatic carriers (HAC) and 153 uninfected individuals, followed up at University Hospital of the Faculty of Medicine of Ribeirão Preto, University of São Paulo, Brazil. It was observed that: (i) 14bpDI genotype is a risk factor for HTLV-1 infection, while the 14bpDD and +3142CC genotypes were associated with protection against infection; (ii) the +3142C allele and the +3003CT and +3142CC genotypes were associated with susceptibility, while 14bpII and +3003TT genotypes were associated with protection against HAM/TSP development; and (iii) the 14bpII, +3010CC, +3142GG and +3187AA genotypes were associated with lower HTLV-1 proviral load compared to respective counterpart genotypes. Findings that HLA-G has a well-recognized immunomodulatory role and that the genetic variability at HLA-G 3'-UTR may post-transcriptionally modify HLA-G production indicate a differential genetic susceptibility to: (i) the development of HTLV-1 infection, (ii) the magnitude of HTLV-1 proviral load and (iii) HAM/TSP development.

Genetic Markers of the Host in Persons Living with HTLV-1, HIV and HCV Infections

Human T-cell leukemia virus type 1 (HTLV-1), hepatitis C virus (HCV) and human immunodeficiency virus type 1 (HIV-1) are prevalent worldwide, and share similar means of transmission. These infections may influence each other in evolution and outcome, including cancer or immunodeficiency. Many studies have reported the influence of genetic markers on the host immune response against different persistent viral infections, such as HTLV-1 infection, pointing to the importance of the individual genetic background on their outcomes. However, despite recent advances on the knowledge of the pathogenesis of HTLV-1 infection, gaps in the understanding of the role of the individual genetic background on the progress to disease clinically manifested still remain. In this scenario, much less is known regarding the influence of genetic factors in the context of dual or triple infections or their influence on the underlying mechanisms that lead to outcomes that differ from those observed in monoinfection. This review describes the main factors involved in the virus–host balance, especially for some particular human leukocyte antigen (HLA) haplotypes, and other important genetic markers in the development of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and other persistent viruses, such as HIV and HCV.

HTLV-1 subgroups associated with the risk of HAM/TSP are related to viral and host gene expression in peripheral blood mononuclear cells, independent of the transactivation functions of the viral factors

Among human T cell leukemia virus type 1 (HTLV-1)-infected individuals, the risk of developing HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) across lifetime differs between ethnic groups. There is an association between HTLV-1 tax gene subgroups (subgroup-A or subgroup-B) and the risk of HAM/TSP in the Japanese population. In this study, we investigated the full-length proviral genome sequences of various HTLV-1-infected cell lines and patient samples. The functional differences in the viral transcriptional regulators Tax and HTLV-1 bZIP factor (HBZ) between each subgroup and the relationships between subgroups and the clinical and laboratory characteristics of HAM/TSP patients were evaluated. The results of these analyses indicated the following: (1) distinct nucleotide substitutions corresponding to each subgroup were associated with nucleotide substitutions in viral structural, regulatory, and accessory genes; (2) the HBZ messenger RNA (mRNA) expression in HTLV-1-infected cells was significantly higher in HAM/TSP patients with subgroup-B than in those with subgroup-A; (3) a positive correlation was observed between the expression of HBZ mRNA and its target Foxp3 mRNA in HAM/TSP patients with subgroup-B, but not in patients with subgroup-A; (4) no clear differences were noted in clinical and laboratory characteristics between HAM/TSP patients with subgroup-A and subgroup-B; and (5) no functional differences were observed in Tax and HBZ between each subgroup based on reporter gene assays. Our results indicate that although different HTLV-1 subgroups are characterized by different patterns of viral and host gene expression in HAM/TSP patients via independent mechanisms of direct transcriptional regulation, these differences do not significantly affect the clinical and laboratory characteristics of HAM/TSP patients.

Inflammatory manifestations of HTLV-1 and their therapeutic options

Human T lymphotropic virus type 1 (HTLV-1) is one of the most intriguing retroviruses infecting humans. Most commonly, infection remains undetected, since it does not cause obvious harm, yet in 4-9% of patients, this infection can be devastating, causing adult T-cell leukemia/lymphoma and/or HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). This review concentrates on all inflammatory aspects of HTLV-1 infection: HAM/TSP, HTLV-1 associated uveitis, HTLV-1 associated conjunctivitis, sicca syndrome and interstitial keratitis, HTLV-1 associated Sjögren's syndrome, Hashimoto's thyroiditis and Graves' disease, HTLV-1 associated pulmonary disease, infective dermatitis associated with HTLV-1, HTLV-1 associated inflammatory myositis and HTLV-1 associated arthritis. With the exception of HAM/TSP treatment, studies of these conditions are sparse and even for HAM/TSP, the level of evidence is limited. While control or elimination of infection remains a goal, most therapy beyond symptomatic management is directed at the immune response to HTLV-1.

HTLV-1 specific CD8+ T cell function augmented by blockade of 2B4/CD48 interaction in HTLV-1 infection

CD8+ T cell response is important in the response to viral infections; this response though is regulated by inhibitory receptors. Expression of inhibitory receptors has been positively correlated with CD8+ T cell exhaustion; the consequent effect of simultaneous blockade of these inhibitory receptors on CD8+ T cell response in viral infections have been studied, however, the role of individual blockade of receptor-ligand pair is unclear. 2B4/CD48 interaction is involved in CD8+T cell regulation, its signal transducer SAP (signaling lymphocyte activation molecule (SLAM)-associated protein) is required for stimulatory function of 2B4/CD244 on lymphocytes hence, we analyzed 2B4/CD244 (natural killer cell receptor) and SAP (signaling lymphocyte activation molecule(SLAM)-associated protein) on total CD8+ and HTLV-1 specific CD8+T cells in HTLV-1 infection and the effect of blockade of interaction with ligand CD48 on HTLV-1 specific CD8+ T cell function. We observed a high expression of 2B4/CD244 on CD8+ T cells relative to uninfected and further upregulation on HTLV-1 specific CD8+ T cells. 2B4+ CD8+ T cells exhibited more of an effector and terminally differentiated memory phenotype. Blockade of 2B4/CD48 interaction resulted in improvement in function via perforin expression and degranulation as measured by CD107a surface mobilization on HTLV-1 specific CD8+ T cells. In the light of these findings, we thus propose an inhibitory role for 2B4/CD48 interaction on CD8+T cell function.

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.

The impact of interferon-alpha treatment on clinical and immunovirological aspects of HTLV-1-associated myelopathy in northeast of Iran

Human T-lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic inflammatory myelopathy. The pathophysiology of HAM/TSP is not yet fully understood; therefore, effective therapy remains a challenging issue. This study was designed to evaluate the efficacy of interferon-alpha (IFN-α) in HAM/TSP patients in the Northeast of Iran. Forty-nine patients with a definite diagnosis of HAM/TSP were enrolled in this clinical trial. For six months, the patients received three million international units of subcutaneous IFN-α-2b per each injection. The dose regimen was daily injection for the first month, three times administration per week for the months 2 and 3, twice weekly injection for the months 4 and 5 and weekly injection for the sixth month. The clinical and laboratory responses were evaluated based on neurologic examinations and immunovirological markers. IFN-α had significant but temporary effect on the motor and urinary functions of the patients. Comparing to the baseline values, proviral load was significantly decreased one month after treatment in responders (495.20±306.87 to 262.69±219.24 p=0.02) and non-responders (624.86±261.90 to 428.28±259.88 p=0.03). Anti-HTLV-1 antibody titers were significantly decreased among responders (1152.1±200.5 to 511.6±98.2 p=0.009) and non-responders (1280.1±368.1 to 537.6±187 p=0.007). Flow cytometry showed no significant changes in CD4, CD8, CD4CD25 and CD16CD56 counts with IFN-α. The positive impact of IFN-α was observed during the treatment period with significant effects on some clinical aspects of HAM/TSP.

Possible implication of NFKB1A and NKG2D genes in susceptibility to HTLV-1-associated myelopathy/tropical spastic paraparesis in Peruvian patients infected with HTLV-1

The human T-cell lymphotropic virus type 1 (HTLV-1) is the etiological agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a progressive disease causing paraparesis of the lower limbs. Only a minority of persons infected with HTLV-1 develop HAM/TSP. Universal susceptibility factors for HAM/TSP are not known. The viral genotype is similar in asymptomatic carriers and HAM/TSP patients. High proviral load has been associated consistently with HAM/TSP, but this factor does not explain fully the presence of disease in HTLV-1-infected subjects. Most likely, host genetic factors will play an important role in HAM/TSP development. A two-stage case-control study was carried out to evaluate the association between HAM/TSP and candidate single nucleotide polymorphisms (SNPs) from 45 genes in addition to six human leukocyte antigen (HLA) alleles. Ancestry-informative markers were used to correct for population stratification. Several SNPs belonging to NFKB1A and NKG2D showed a trend of association in both stages. The fact that the direction of the association observed in the first stage was the same in the second stage suggests that NFKB1A and NKG2D may be implicated in the development of HAM/TSP. Further replication studies in independent HTLV-1 patient groups should validate further these associations.

Interleukin-18 and interferon-gamma polymorphisms are implicated on proviral load and susceptibility to human T-lymphotropic virus type 1 infection

Interleukin-18 (IL-18) and interferon-gamma (IFN-γ) exert important functions in both innate and adaptive immune responses against intracellular pathogens and viruses. Previous studies suggested that host genetic factors, including cytokines gene polymorphisms, could be involved in the pathogenesis of human T-cell leukemia virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Thus, we analyzed -137C/G and -607A/C of the IL-18 promoter and +874T/A of the IFN-γ in DNA samples from 98 HTLV-1-infected individuals exhibiting or not clinical symptoms and 150 healthy control individuals. The IL-18 promoter -607CC genotype was significantly lower in HTLV-1 asymptomatic carriers (HAC) and HTLV-1-infected individuals (HAC + HAM/TSP) than healthy control group. In contrast, the -607AC genotype was significantly higher in HAC and HTLV-1-infected individuals group compared to the healthy control group. The -137G/-607A IL-18 haplotype was higher in infected group than healthy control group, and the -137C/-607C IL-18 haplotype was increased in the healthy control group compared to the others. Finally, the IFN-γ polymorphism analysis showed that the HTLV-1-infected individuals with +874AT genotype presented higher proviral load than +874AA genotype. These data indicate that the IL-18-607AC genotype and -137G/-607A haplotype could be a risk factor for HTLV-1 infection, whereas the protective effect could be conferred by -607CC genotype and -137C/-607C haplotype. Also, the IFN-γ could be implicated on the proviral load levels.

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.

Ethnoepidemiology of HTLV-1 related diseases: ethnic determinants of HTLV-1 susceptibility and its worldwide dispersal

Human T-cell lymphotropic virus type 1 is vertically transmitted in neonatal life and is causatively associated with adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) in adults. Persistence of HTLV-1 in host T cells, clonal expansion of the HTLV-1 carrying T cells, and emergence of malignantly transformed T cells are in accord with the multistep model of human cancer and roles for continuous interaction between host genes and environmental factors. This article reviews two lines of HTLV-1 investigation, one regarding worldwide surveillance of HTLV-1 infection foci by serological testing and molecular analysis of HTLV-1 isolates, and the other focusing on genetics of the human leukocyte antigen (HLA) that determines the ethnic background of HTLV-1 permissiveness and susceptibility to ATL or HAM/TSP. The serological surveillance revealed transcontinental dispersal of HTLV-1 in the prehistoric era that started out of Africa, spread to Austro-Melanesia and the Asian continent, then moved to North America and through to the southern edge of South America. This was highlighted by an Andean mummy study that proved ancient migration of paleo-mongoloid HTLV-1 from Asia to South America. Phylogenetic analysis of HLA alleles provided a basis for ethnic susceptibility to HTLV-1 infection and associated diseases, both ATL and HAM/TSP. Ethnicity-based sampling of peripheral blood lymphocytes has great potential for genome-wide association studies to illuminate ethnically defined host factors for viral oncogenesis with reference to HTLV-1 and other pathogenic elements causatively associated with chronic disease and malignancies.

HTLV infection and its implication in gynaecology and obstetrics

INTRODUCTION

Worldwide, 20-30 million people are estimated to be infected with HTLV. HTLV-1 is endemic in Western Africa and Southern Japan, whereas HTLV-2 is considered to be spread among native American people.

MATERIALS AND METHODS

The impact of HTLV in gynaecology and obstetrics is being reviewed. Search strategy and selection criteria for identifying relevant data were performed by searching Medline, Current Contents, Web of Science, Embase and references from relevant articles. English and German gynaecological and infectious diseases textbooks as well as national and international guidelines and recommendations were also reviewed.

RESULTS

Transmission may occur by sexual intercourse or cellular blood products. Although materno-fetal transmission is debated, transmission through maternal breast milk has been confirmed. An HTLV-infection can lead to adult T-cell leukaemia (ATL) or cumulative opportunistic and neurological disorders that can occur with varying degrees of severity. Diagnosis can be done by antibody detection via the use of ELISA and western blot analysis as well as PCR diagnosis.

CONCLUSION

Due to inadequate treatment options and the lack of an effective vaccination, prevention is currently only possible by restricting transmission, including the usage of condoms during sexual intercourse or avoiding breastfeeding in HTLV-seropositive mothers. If, due to socio-economic reasons, breastfeeding cannot be avoided, short-term breastfeeding for a maximum of up to 6 months is suggested.

Role of killer cell immunoglobulin-like receptor gene content and human leukocyte antigen-C group in susceptibility to human T-lymphotropic virus 1-associated myelopathy/tropical spastic paraparesis in Peru

Human T-lymphotropic virus 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) affects approximately 5% of HTLV-1-infected individuals. It is poorly understood why only some infected subjects develop this disease, but host genetic factors may determine susceptibility. The innate immune system may influence disease outcome in HTLV-1-infected individuals because of its role in early immune responses to viral infections. Variation in genes encoding killer cell immunoglobulin-like receptors (KIR) and their human leukocyte antigen (HLA) molecule ligands may affect the risk of HAM/TSP. We performed a two-stage case-control study to examine the distribution of KIR genes and HLA-Cw groups in Peruvian HTLV-1-infected HAM/TSP individuals and asymptomatic carriers. We also tested for epistatic effects between specific KIR genes and HLA-Cw groups. In the first stage, we found several trends toward association with HAM/TSP or proviral load (PVL). However, these results were not replicated in the second stage. In conclusion, this is the first report on KIR gene frequencies in the Peruvian population and may be of significance in hematopoietic stem-cell transplants. Our study did not reveal significant associations between KIR genes and HLA-Cw groups and HAM/TSP or PVL. However, because our study was powered to detect only larger effects, additional studies using larger cohorts are needed.

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.

Evaluation of host genetic and viral factors as surrogate markers for HTLV-1-associated myelopathy/tropical spastic paraparesis in Peruvian HTLV-1-infected patients

Human T-lymphotropic virus 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a complication that affects up to 5% of HTLV-1-infected individuals. Several host genetic and viral factors have been associated with the risk of HAM/TSP. The aim of this study was to evaluate the performance of a prognostic model for HAM/TSP developed in Japan in a Peruvian population of 71 HAM/TSP patients and 94 asymptomatic carriers (ACs). This model included age, proviral load (PVL), the presence of HLA-A*02 and HLA-Cw*08 alleles, SDF-1 +801, and TNF-alpha -863 polymorphisms, and viral subgroup. We describe frequencies for the four host genetic markers and demonstrate the presence of the HTLV-1 tax B subgroup in Peru. Using cross-validation, we show that the predictive ability of the prognostic model, as characterized by the area under the receiver-operating characteristic curve (AUC), does not differ from a model containing PVL only (both AUC = 0.74). We found some suggestive evidence of a protective effect of the HLA-A*02 allele but failed to replicate the associations with the other three genetic markers and with viral subgroup. A logistic model containing PVL, age, gender, and HLA-A*02 provided the best predictive ability in the Peruvian cohort (AUC = 0.79). J. Med. Virol. 82:460-466, 2010. (c) 2010 Wiley-Liss, Inc.

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.

In vivo expression of the HBZ gene of HTLV-1 correlates with proviral load, inflammatory markers and disease severity in HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP)

Background

Recently, human T-cell leukemia virus type 1 (HTLV-1) basic leucine zipper factor (HBZ), encoded from a minus strand mRNA was discovered and was suggested to play an important role in adult T cell leukemia (ATL) development. However, there have been no reports on the role of HBZ in patients with HTLV-1 associated inflammatory diseases.

Results

We quantified the HBZ and tax mRNA expression levels in peripheral blood from 56 HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients, 10 ATL patients, 38 healthy asymptomatic carriers (HCs) and 20 normal uninfected controls, as well as human leukemic T-cell lines and HTLV-1-infected T-cell lines, and the data were correlated with clinical parameters. The spliced HBZ gene was transcribed in all HTLV-1-infected individuals examined, whereas tax mRNA was not transcribed in significant numbers of subjects in the same groups. Although the amount of HBZ mRNA expression was highest in ATL, medium in HAM/TSP, and lowest in HCs, with statistical significance, neither tax nor the HBZ mRNA expression per HTLV-1-infected cell differed significantly between each clinical group. The HTLV-1 HBZ, but not tax mRNA load, positively correlated with disease severity and with neopterin concentration in the cerebrospinal fluid of HAM/TSP patients. Furthermore, HBZ mRNA expression per HTLV-1-infected cell was decreased after successful immunomodulatory treatment for HAM/TSP.

Conclusion

These findings suggest that in vivo expression of HBZ plays a role in HAM/TSP pathogenesis.

Increased frequency of CD4+T cells expressing fractalkine receptor CX3CR1 in patients with HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP), but its AIDS susceptible polymorphisms are not associated with the disease

To investigate whether fractalkine receptor CX3CR1 polymorphisms that have been associated with rapid progression to AIDS among HIV-1 positive individuals also affects the risk of human T cell lymphotropic virus type 1 (HTLV-1) associated myelopathy/tropical spastic paraparesis (HAM/TSP), we compared the allele frequencies of V249I and T280M between 233 HAM/TSP patients and 213 HTLV-1 seropositive asymptomatic carriers (HCs). Although the frequency and absolute number of peripheral blood CX3CR1+CD4+T cells were significantly increased in HAM/TSP patients compared to HCs and uninfected controls independent of HTLV-1 trans-activator protein Tax, we could not observe any association between the two polymorphisms and the risk of HAM/TSP in our cohort.

Ex vivo analysis of human T lymphotropic virus type 1-specific CD4+ cells by use of a major histocompatibility complex class II tetramer composed of a neurological disease-susceptibility allele and its immunodominant peptide

HLA-DRB1*0101 is associated with susceptibility to human T lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Here, we used a synthetic tetramer of DRB1*0101 and its epitope peptide to analyze HTLV-1-specific CD4(+) T cells ex vivo. The frequency of tetramer(+)CD4(+) T cells was significantly greater in patients with HAM/TSP than in healthy HTLV-1 carriers (HCs) at a given proviral load and correlated with HTLV-1 tax messenger RNA expression in HCs but not in patients with HAM/TSP. These cells displayed an early to intermediate effector memory phenotype and were preferentially infected by HTLV-1. T cell receptor gene analyses of 2 unrelated DRB1*0101-positive patients with HAM/TSP showed similar Vbeta repertoires and amino acid motifs in complementarity-determining region 3. Our data suggest that efficient clonal expansion of virus-specific CD4(+) T cells in patients with HAM/TSP does not simply reflect higher viral burden but rather reflects a rapid turnover caused by preferential infection and/or in vivo stimulation by major histocompatibility complex-peptide complexes.

Human T-lymphotropic virus 1: recent knowledge about an ancient infection

Human T-lymphotropic virus 1 (HTLV-1) has infected human beings for thousands of years, but knowledge about the infection and its pathogenesis is only recently emerging. The virus can be transmitted from mother to child, through sexual contact, and through contaminated blood products. There are areas in Japan, sub-Saharan Africa, the Caribbean, and South America where more than 1% of the general population is infected. Although the majority of HTLV-1 carriers remain asymptomatic, the virus is associated with severe diseases that can be subdivided into three categories: neoplastic diseases (adult T-cell leukaemia/lymphoma), inflammatory syndromes (HTLV-1-associated myelopathy/tropical spastic paraparesis and uveitis among others), and opportunistic infections (including Strongyloides stercoralis hyperinfection and others). The understanding of the interaction between virus and host response has improved markedly, but there are still no clear surrogate markers for prognosis and there are few treatment options.

The HTLV-1 neurological complex

Human T-cell lymphotropic virus type 1 (HTLV-1) is a retrovirus that infects about 20 million people worldwide and causes immune-mediated diseases of the nervous system. The classic neurological presentation of HTLV-1 infection is a myelopathy called HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). However, HAM/TSP is not the only neurological outcome that can result from HTLV-1 infection. In this Personal View, we show that HTLV-1 has a broader neurological spectrum than the names HAM/TSP suggest and that people infected with this virus can present with various isolated or assorted syndromes.

Risk of human T-lymphotropic virus type I-associated diseases in Jamaica with common HLA types

Human T-lymphotropic virus-I (HTLV-I) causes adult T-cell leukemia/lymphoma (ATL) and HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP). We postulated a higher disease risk for people with common human leukocyte antigen (HLA) types, due to a narrower immune response against viral or neoplastic antigens, compared to people with uncommon types. HLA class-I (A,B) and class-II (DRB1, DQB1) allele and haplotype frequencies in 56 ATL patients, 59 HAM/TSP patients and 190 population-based, asymptomatic HTLV-I-infected carriers were compared by logistic regression overall (score test) and with odds ratios (ORs) for common types (prevalence >50% of asymptomatic carriers) and by prevalence quartile. HTLV-I proviral load between asymptomatic carriers with common versus uncommon types was compared by t-test. ATL differed from asymptomatic carriers in overall DQB1 allele and class-I haplotype frequencies (p </=</= 0.04). ATL risk was increased significantly with common HLA-B (OR 2.25, 95% CI 1.19-4.25) and DRB1 (OR 2.11, 95% CI 1.13-3.40) alleles. Higher prevalence HLA-B alleles were associated with higher ATL risk (OR 1.14 per quartile, p(trend) = 0.02). Asymptomatic carriers with common HLA-B alleles had marginally higher HTLV-I proviral load (p = 0.057). HAM/TSP risk did not differ consistently with common HLA types. Thus, ATL risk, but not HAM/TSP risk, was increased with higher prevalence HLA-B alleles. Perhaps breadth of cellular immunity affects risk of this viral leukemia/lymphoma.

Cellular immune response to HTLV-1

There is strong evidence at the individual level and the population level that an efficient cytotoxic T lymphocyte (CTL) response to HTLV-1 limits the proviral load and the risk of associated inflammatory diseases such as HAM/TSP. This evidence comes from host population genetics, viral genetics, DNA expression microarrays and assays of lymphocyte function. However, until now there has been no satisfactory and rigorous means to define or to measure the efficiency of an antiviral CTL response. Recently, methods have been developed to quantify lymphocyte turnover rates in vivo and the efficiency of anti-HTLV-1 CTLs ex vivo. Data from these new techniques appear to substantiate the conclusion that variation between individual hosts in the rate at which a single CTL kills HTLV-1-infected lymphocytes is an important determinant, perhaps the decisive determinant, of the proviral load and the risk of HAM/TSP. With these experimental data, it is becoming possible to refine, parameterize and test mathematical models of the immune control of HTLV-1, which are a necessary part of an understanding of this complex dynamic system.

Cell-mediated immune response to human T-lymphotropic virus type I

Human T-lymphotropic virus type I (HTLV-I) is a retrovirus that causes persistent infection in many populations in tropical and subtropical regions. HTLV-I chronically activates the cell-mediated arm of the host adaptive immune response. There has been much debate about the role of the immune response in determining the outcome of HTLV-I infection: most seropositive individuals remain lifelong asymptomatic carriers of the virus, whereas a small proportion-usually those with higher equilibrium proviral loads-develop an inflammatory disease of the central nervous system known as HAM/TSP. Here we discuss the cell-mediated immune response to HTLV-I infection. We summarize recent data on the HTLV-I-specific CD4(+) cell response and explore its potential role in HAM/TSP pathogenesis. We also explore the controversy surrounding the role of the CD8(+) cell response in controlling HTLV-I infection and/or contributing to HAM/TSP disease, highlighting recent studies of T cell gene expression profiles and a newly developed assay of CD8(+) cell functional efficiency. Finally, we introduce a possible role for cellular innate immune effectors in HTLV-I infection.