HTLV-1 infection: what determines the risk of inflammatory disease?

The role of IFN-γ production during retroviral infections: an important cytokine involved in chronic inflammation and pathogenesis

Interferon-gamma (IFN-γ) plays a crucial role in viral infections by preventing viral replication and in the promotion of innate and adaptive immune responses. However, IFN-gamma can exert distinct effects in different persistent viral infections. The long-term overproduction of IFN-γ in retroviral infections, such as the human immunodeficiency virus (HIV), human T-lymphotropic virus type 1 (HTLV-1), and human endogenous retroviruses (HERVs), resulting in inflammation, may cause neuronal damage. This review is provocative about the role of IFN-γ during persistent retroviral infections and its relationship with the causation of some neurological disorders that are important for public health.

TAX-mRNA-Carrying Exosomes from Human T Cell Lymphotropic Virus Type 1-Infected Cells Can Induce Interferon-Gamma Production In Vitro

Human T cell lymphotropic virus type 1 (HTLV-1) is the etiological agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T cell leukemia/lymphoma. The development of HAM/TSP, a chronic neuroinflammatory disease, is correlated to complex interaction between the host immune response and the infecting virus. Tax expression plays an important role in HAM/TSP pathogenesis by activating various cellular genes, including the cytokines interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α). Exosomes have emerged as an important factor of cell-to-cell communication contributing to diverse cellular processes, including immune modulation. Considering the potential role of exosomes in modulating the immune response and inflammation, the main objective of this study was to examine if HTLV-1-infected cells produce exosomes carrying viral proteins or inflammatory molecules, which can participate in the chronic inflammation that is observed in patients with HAM/TSP. Exosomes were isolated from HTLV-1-infected cell line, evaluated for the tax mRNA presence, and tested for the ability to activate peripheral mononuclear cells (PBMC) in inducing an inflammatory immune response. We observed that the proinflammatory cytokines, IFN-γ and TNF-α, were upregulated in T cells after treatment of the PBMC with Tax-carrying exosomes compared to the negative control. Interleukin-4, Granzyme B, and Perforin did not show alterations. Taken together, these results suggest that exosomes carrying tax-mRNA isolated from HTLV-1-infected cells might induce the production of proinflammatory cytokines and activate T helper (Th)₁, and not Th₂-immune response. If this finding is further confirmed, this study may have impact on investigations on the pathogenesis of HAM-TSP and the inflammatory response involved in this disease.

The prevalence and clinical associations of HTLV-1 infection in a remote Indigenous community

OBJECTIVE

Hospital and laboratory data indicate that human T-lymphotropic virus type 1 (HTLV-1) is endemic to central Australia, but no community-based studies of its prevalence or disease burden have been reported. We determined the prevalence rates of HTLV-1 infection and of HTLV-1-associated diseases in a remote Indigenous community.

SETTING

A remote Northern Territory community.

DESIGN

All residents were asked to complete a health survey and offered a limited clinical examination, together with serological tests for HTLV-1 and Strongyloides, and HTLV-1 proviral load (PVL) assessment.

MAIN OUTCOME MEASURES

HTLV-1 seropositivity rates; HTLV-1 PVL (copies/105 peripheral blood leucocytes [PBL]); presentation with HTLV-1-related clinical disease.

RESULTS

HTLV-1 serostatus was determined for 97 of 138 residents (70%). The prevalence of HTLV-1 infection was significantly higher among adults (30 of 74 people tested) than children (1 of 23; P = 0.001). Nine of 30 HTLV-1-positive adults had a clinical syndrome that was potentially attributable to HTLV-1 infection (chronic lung disease, seven; symptomatic strongyloidiasis, two). The median HTLV-1 PVL was significantly higher for adults with chronic lung disease than for those who were asymptomatic (chronic lung disease, 649 copies/105 PBL [IQR, 162-2220]; asymptomatic adults, 40 copies/105 PBL [IQR, 0.9-229]; P = 0.017). Ten of 72 adults tested were seropositive for Strongyloides (six of 28 HTLV-1-positive participants and four of 44 HTLV-1-negative participants; P = 0.17), as were three of 15 children tested; the three children were HTLV-1-negative.

CONCLUSION

The prevalence of HTLV-1 infection and the rate of disease potentially attributable to HTLV-1 were high among adults in this remote community.

Update on Neurological Manifestations of HTLV-1 Infection

The human T cell lymphotropic virus type 1 (HTLV-1) is a retrovirus that infects 10-20 million persons around the world. Initially associated with the hematological malignancy adult T cell leukemia/lymphoma (ATLL), HTLV-1 is also the cause of a chronic progressive myelopathy named "HTLV-1-associated myelopathy/tropical spastic paraparesis" (HAM/TSP). HAM/TSP arises as the tip of the iceberg of an assortment of neurological syndromes triggered by the virus such as inflammatory myopathies, polyneuropathies, amyotrophic lateral sclerosis (ALS)-like syndromes, dysautonomia, and cognitive impairment. HAM/TSP typifies a chronic progressive spastic paraparesis with neurogenic bladder and minimal sensory signs. The neuropathology of HAM/TSP is concentrated in the thoracic spinal cord and is typically biphasic. Initially, there is a perivascular lymphocytic cuffing and mild parenchymal mononuclear infiltrates. Subsequently, this is replaced by gliosis and scarring. The neuropathogenesis of HTLV-1 is still partially understood. At present, the therapy of HAM/TSP remains basically symptomatic.

Higher human T-lymphotropic virus type 1 subtype C proviral loads are associated with bronchiectasis in indigenous australians: results of a case-control study

In this case-control study, HTLV-1 infection increased risk of bronchiectasis 1.84 times. HTLV-1 proviral loads for bronchiectasis patients were significantly higher than those of controls. HTLV-1 proviral loads correlated with the extent of radiologically determined pulmonary injury.

Background.

 We previously suggested that infection with the human T-lymphotropic virus type 1 (HTLV-1) subtype C is associated with bronchiectasis among Indigenous Australians. Bronchiectasis might therefore result from an HTLV-1-mediated inflammatory process that is typically associated with a high HTLV-1 proviral load (PVL). Human T-lymphotropic virus type 1 PVL have not been reported for Indigenous Australians.

Methods.

 Thirty-six Indigenous adults admitted with bronchiectasis from June 1, 2008, to December 31, 2009 were prospectively recruited and matched by age, sex, and ethno-geographic origin to 36 controls. Case notes and chest high-resolution computed tomographs were reviewed, and pulmonary injury scores were calculated. A PVL assay for the HTLV-1c subtype that infects Indigenous Australians was developed and applied to this study. Clinical, radiological, and virological parameters were compared between groups and according to HTLV-1 serostatus.

Results.

 Human T-lymphotropic virus type 1 infection was the main predictor of bronchiectasis in a multivariable model (adjusted risk ratio [aRR], 1.84; 95% confidence interval [CI], 1.19–2.84; P = .006). Moreover, the median HTLV-1c PVL (interquartile range) for cases was >100-fold that of controls (cases, 0.319 [0.007, 0.749]; controls, 0.003 [0.000, 0.051] per 100 peripheral blood lymphocytes; P = .007), and HTLV-1c PVL were closely correlated with radiologically determined pulmonary injury scores (Spearman's rho = 0.7457; P = .0000). Other predictors of bronchiectasis were positive Strongyloides serology (aRR, 1.69; 95% CI, 1.13–2.53) and childhood skin infections (aRR, 1.62; 95% CI, 1.07–2.44). Bronchiectasis was the major predictor of death (aRR, 2.71; 95% CI, 1.36–5.39; P = .004).

Conclusions.

 These data strongly support an etiological association between HTLV-1 infection and bronchiectasis in a socially disadvantaged population at risk of recurrent lower respiratory tract infections.

Clinical associations of Human T-Lymphotropic Virus type 1 infection in an indigenous Australian population

INTRODUCTION

In resource-poor areas, infectious diseases may be important causes of morbidity among individuals infected with the Human T-Lymphotropic Virus type 1 (HTLV-1). We report the clinical associations of HTLV-1 infection among socially disadvantaged Indigenous adults in central Australia.

METHODOLOGY AND PRINCIPAL FINDINGS

HTLV-1 serological results for Indigenous adults admitted 1(st) January 2000 to 31(st) December 2010 were obtained from the Alice Springs Hospital pathology database. Infections, comorbid conditions and HTLV-1 related diseases were identified using ICD-10 AM discharge morbidity codes. Relevant pathology and imaging results were reviewed. Disease associations, admission rates and risk factors for death were compared according to HTLV-1 serostatus. HTLV-1 western blots were positive for 531 (33.3%) of 1595 Indigenous adults tested. Clinical associations of HTLV-1 infection included bronchiectasis (adjusted Risk Ratio, 1.35; 95% CI, 1.14-1.60), blood stream infections (BSI) with enteric organisms (aRR, 1.36; 95% CI, 1.05-1.77) and admission with strongyloidiasis (aRR 1.38; 95% CI, 1.16-1.64). After adjusting for covariates, HTLV-1 infection remained associated with increased numbers of BSI episodes (adjusted negative binomial regression, coefficient, 0.21; 95% CI, 0.02-0.41) and increased admission numbers with strongyloidiasis (coefficient, 0.563; 95% CI, 0.17-0.95) and respiratory conditions including asthma (coefficient, 0.99; 95% CI, 0.27-1.7), lower respiratory tract infections (coefficient, 0.19; 95% CI, 0.04-0.34) and bronchiectasis (coefficient, 0.60; 95% CI, 0.02-1.18). Two patients were admitted with adult T-cell Leukemia/Lymphoma, four with probable HTLV-1 associated myelopathy and another with infective dermatitis. Independent predictors of mortality included BSI with enteric organisms (aRR 1.78; 95% CI, 1.15-2.74) and bronchiectasis (aRR 2.07; 95% CI, 1.45-2.98).

CONCLUSION

HTLV-1 infection contributes to morbidity among socially disadvantaged Indigenous adults in central Australia. This is largely due to an increased risk of other infections and respiratory disease. The spectrum of HTLV-1 related diseases may vary according to the social circumstances of the affected population.

Type I Interferon at the Interface of Antiviral Immunity and Immune Regulation: The Curious Case of HIV-1

Type I interferon (IFN-I) play a critical role in the innate immune response against viral infections. They actively participate in antiviral immunity by inducing molecular mechanisms of viral restriction and by limiting the spread of the infection, but they also orchestrate the initial phases of the adaptive immune response and influence the quality of T cell immunity. During infection with the human immunodeficiency virus type 1 (HIV-1), the production of and response to IFN-I may be severely altered by the lymphotropic nature of the virus. In this review I consider the different aspects of virus sensing, IFN-I production, signalling, and effects on target cells, with a particular focus on the alterations observed following HIV-1 infection.

Animal models of bovine leukemia virus and human T-lymphotrophic virus type-1: insights in transmission and pathogenesis

Bovine leukemia virus (BLV) and human T-lymphotrophic virus type-1 (HTLV-1) are related retroviruses associated with persistent and lifelong infections and a low incidence of lymphomas within their hosts. Both viruses can be spread through contact with bodily fluids containing infected cells, most often from mother to offspring through breast milk. Each of these complex retroviruses contains typical gag, pol, and env genes but also unique, nonstructural proteins encoded from the pX region. These nonstructural genes encode the Tax and Rex regulatory proteins, as well as novel proteins essential for viral spread in vivo. Improvements in the molecular tools to test these viral determinants in cellular and animal models have provided new insights into the pathogenesis of each virus. Comparisons of BLV and HTLV-1 provide insights into mechanisms of spread and tumor formation, as well as potential approaches to therapeutic intervention against the infections.

Commensal microbiota contributes to chronic endocarditis in TAX1BP1 deficient mice

Tax1-binding protein 1 (Tax1bp1) negatively regulates NF-κB by editing the ubiquitylation of target molecules by its catalytic partner A20. Genetically engineered TAX1BP1-deficient (KO) mice develop age-dependent inflammatory constitutions in multiple organs manifested as valvulitis or dermatitis and succumb to premature death. Laser capture dissection and gene expression microarray analysis on the mitral valves of TAX1BP1-KO mice (8 and 16 week old) revealed 588 gene transcription alterations from the wild type. SAA3 (serum amyloid A3), CHI3L1, HP, IL1B and SPP1/OPN were induced 1,180-, 361-, 187-, 122- and 101-fold respectively. WIF1 (Wnt inhibitory factor 1) exhibited 11-fold reduction. Intense Saa3 staining and significant I-κBα reduction were reconfirmed and massive infiltration of inflammatory lymphocytes and edema formation were seen in the area. Antibiotics-induced ‘germ free’ status or the additional MyD88 deficiency significantly ameliorated TAX1BP1-KO mice's inflammatory lesions. These pathological conditions, as we named ‘pseudo-infective endocarditis’ were boosted by the commensal microbiota who are usually harmless by their nature. This experimental outcome raises a novel mechanistic linkage between endothelial inflammation caused by the ubiquitin remodeling immune regulators and fatal cardiac dysfunction.

Virus induced inflammation and cancer development

Chronic inflammation as a result of viral infection significantly increases the likelihood of cancer development. A handful of diverse viruses have confirmed roles in cancer development and progression, but the list of suspected oncogenic viruses is continually growing. Viruses induce cancer directly and indirectly, by activating inflammatory signalling pathways and cytokines, stimulating growth of infected cells and inhibiting apoptosis. Although oncogenic viruses induce inflammation by various mechanisms, it is generally mediated by the MAPK, NFκB and STAT3 signalling pathways. This review will explore the unique mechanisms by which different oncogenic viruses induce inflammation to promote cancer initiation and progression.