T-cell activation by autologous human T-cell leukemia virus type I-infected T-cell clones

XCL1, a serum biomarker in neurological diseases; HTLV-1-associated myelopathy and multiple sclerosis

The XCL1-XCR1 axis has a potential role in the recruitment of immune cells to the site of inflammation. The present study aimed to examine the relation of XCL1 serum levels with Multiple sclerosis (MS) and HTLV-1-associated myelopathy (HAM), as chronic inflammatory diseases of the central nervous system (CNS). DNA was extracted to evaluate HTLV-1 proviral load (PVL) using real-time PCR. Serum levels of XCL1 was determined by using an ELISA assay. The serum level of XCL1 was significantly higher in patients with HAM than that of asymptomatic carriers (ACs) and healthy controls (HCs) (p < 0.001 and p < 0.0001, respectively) and was also higher in MS patients compared to HCs (p < 0.0001). Moreover, the concentration of XCL1 serum level was significantly different between the ACs and HCs group (p < 0.0001). In conclusion, increased expression of XCL1 might contribute to the migration of autoreactive T cells to the central nervous system and play a critical role in the development and pathogenesis of inflammatory neurological diseases including HAM and MS.

NK Cells and Innate-Like T Cells After Autologous Hematopoietic Stem Cell Transplantation in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system, in which autoreactive T and B cells play important roles. Other lymphocytes such as NK cells and innate-like T cells appear to be involved as well. To name a few examples, CD56^bright NK cells were described as an immunoregulatory NK cell subset in MS while innate-like T cells in MS were described in brain lesions and with proinflammatory signatures. Autologous hematopoietic stem cell transplantation (aHSCT) is a procedure used to treat MS. This procedure includes hematopoietic stem/progenitor cell (HSPC) mobilization, then high-dose chemotherapy combined with anti-thymocyte globulin (ATG) and subsequent infusion of the patients own HSPCs to reconstitute a functional immune system. aHSCT inhibits MS disease activity very effectively and for long time, presumably due to elimination of autoreactive T cells. Here, we performed multidimensional flow cytometry experiments in peripheral blood lymphocytes of 27 MS patients before and after aHSCT to address its potential influence on NK and innate-like T cells. After aHSCT, the relative frequency and absolute numbers of CD56^bright NK cells rise above pre-aHSCT levels while all studied innate-like T cell populations decrease. Hence, our data support an enhanced immune regulation by CD56^bright NK cells and the efficient reduction of proinflammatory innate-like T cells by aHSCT in MS. These observations contribute to our current understanding of the immunological effects of aHSCT in MS.

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.

Macrophages Induce Long-Term Trapping of γδ T Cells with Innate-like Properties within Secondary Lymphoid Organs in the Steady State

So far, peripheral T cells have mostly been described to circulate between blood, secondary lymphoid organs (SLOs), and lymph in the steady state. This nomadic existence would allow them to accomplish their surveying task for both foreign Ags and survival signals. Although it is now well established that γδ T cells can be rapidly recruited to inflammatory sites or in certain tumor microenvironments, the trafficking properties of peripheral γδ T cells have been poorly studied in the steady state. In the present study, we highlight the existence of resident γδ T cells in the SLOs of specific pathogen-free mice. Indeed, using several experimental approaches such as the injection of integrin-neutralizing Abs that inhibit the entry of circulating lymphocytes into lymph nodes and long-term parabiosis experiments, we have found that, contrary to Ly-6C^-/+CD44^lo and Ly-6C⁺CD44^hi γδ T cells, a significant proportion of Ly-6C^-CD44^hi γδ T cells are trapped for long periods of time within lymph nodes and the spleen in the steady state. Specific in vivo cell depletion strategies have allowed us to demonstrate that macrophages are the main actors involved in this long-term retention of Ly-6C^-CD44^hi γδ T cells in SLOs.

ADAR1 enhances HTLV-1 and HTLV-2 replication through inhibition of PKR activity

Background

The role of innate immunity in general and of type I interferon (IFN-I) in particular in HTLV-1 pathogenesis is still a matter of debate. ADAR1-p150 is an Interferon Stimulated Gene (ISG) induced by IFN-I that can edit viral RNAs. We therefore investigated whether it could play the role of an anti-HTLV factor.

Results

We demonstrate here that ADAR1 is also expressed in the absence of IFN stimulation in activated primary T-lymphocytes that are the natural target of this virus and in HTLV-1 or HTLV-2 chronically infected T-cells. ADAR1 expression is also increased in primary lymphocytes obtained from HTLV-1 infected individuals. We show that ADAR1 enhances HTLV-1 and HTLV-2 infection in T-lymphocytes and that this proviral effect is independent from its editing activity. ADAR1 expression suppresses IFN-α inhibitory effect on HTLV-1 and HTLV-2 and acts through the repression of PKR phosphorylation.

Discussion

This study demonstrates that two interferon stimulated genes, i.e. PKR and ADAR1 have opposite effects on HTLV replication in vivo. The balanced expression of those proteins could determine the fate of the viral cycle in the course of infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-014-0093-9) contains supplementary material, which is available to authorized users.

Cellular Factors Involved in HTLV-1 Entry and Pathogenicit

Human T cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T cell leukemia (ATL) and HTLV-1 – associated myelopathy and tropical spastic paraparesis (HAM/TSP). HTLV-1 has a preferential tropism for CD4 T cells in healthy carriers and ATL patients, while both CD4 and CD8 T cells serve as viral reservoirs in HAM/TSP patients. HTLV-1 has also been detected other cell types, including monocytes, endothelial cells, and dendritic cells. In contrast to the limited cell tropism of HTLV-1 in vivo, the HTLV receptor appears to be expressed in almost all human or animal cell lines. It remains to be examined whether this cell tropism is determined by host factors or by HTLV-1 heterogeneity. Unlike most retroviruses, cell-free virions of HTLV-1 are very poorly infectious. The lack of completely HTLV-1-resistant cells and the low infectivity of HTLV-1 have hampered research on the HTLV entry receptor. Entry of HTLV-1 into target cells is thought to involve interactions between the env (Env) glycoproteins, a surface glycoprotein (surface unit), and a transmembrane glycoprotein. Recent studies have shown that glucose transporter GLUT1, heparan sulfate proteoglycans (HSPGs), and neuropilin-1 (NRP-1) are the three proteins important for the entry of HTLV-1. Studies using adherent cell lines have shown that GLUT1 can function as a receptor for HTLV. HSPGs are required for efficient entry of HTLV-1 into primary CD4 T cells. NRP-1 is expressed in most established cell lines. Further studies have shown that these three molecules work together to promote HTLV-1 binding to cells and fusion of viral and cell membranes. The virus could first contact with HSPGs and then form complexes with NRP-1, followed by association with GLUT1. It remains to be determined whether these three molecules can explain HTLV-1 cell tropism. It also remains to be more definitively proven that these molecules are sufficient to permit HTLV-1 entry into completely HTLV-1-resistant cells.

Cell surface markers in HTLV-1 pathogenesis

The phenotype of HTLV-1-transformed CD4⁺ T lymphocytes largely depends on defined viral effector molecules such as the viral oncoprotein Tax. In this review, we exemplify the expression pattern of characteristic lineage markers, costimulatory receptors and ligands of the tumor necrosis factor superfamily, cytokine receptors, and adhesion molecules on HTLV-1-transformed cells. These molecules may provide survival signals for the transformed cells. Expression of characteristic surface markers might therefore contribute to persistence of HTLV-1-transformed lymphocytes and to the development of HTLV-1-associated disease.

Human T cell leukemia virus type 1 infection drives spontaneous proliferation of natural killer cells

Most human T cell leukemia virus type 1 (HTLV-1) infected subjects remain asymptomatic throughout their lives, with a few individuals developing HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) or adult T cell leukemia. Lymphocytes from about half of HTLV-1 infected subjects spontaneously proliferate in vitro, and how this phenomenon relates to symptomatic disease outcome and viral burden is poorly understood. Spontaneous proliferation was measured in lymphocyte subsets, and these findings were correlated with HTLV-1 proviral load and Tax expression in PBMCs. We found that in addition to previously described vigorous CD8+ T cell spontaneous proliferation, natural killer (NK) cells spontaneously proliferated to a similar high level, resulting in expansion of CD56-expressing NK cells. Spontaneous NK cell proliferation positively correlated with HTLV-1 proviral load but not with Tax expression or the presence of HAM/TSP. The strongest correlate with clinical outcome in this cohort was the ability of cells to express Tax, while HTLV-1 proviral load was more closely related to spontaneous NK cell proliferation. These results demonstrate that spontaneous proliferation, Tax expression, and proviral load are inter-related but not equivalent, and that spontaneous lymphocyte proliferation is not restricted to T cells, the targets of HTLV-1 infection.

Human T Lymphotropic Virus Type 1 (HTLV-1): Molecular Biology and Oncogenesis

Human T lymphotropic viruses (HTLVs) are complex deltaretroviruses that do not contain a proto-oncogene in their genome, yet are capable of transforming primary T lymphocytes both in vitro and in vivo. There are four known strains of HTLV including HTLV type 1 (HTLV-1), HTLV-2, HTLV-3 and HTLV-4. HTLV-1 is primarily associated with adult T cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-2 is rarely pathogenic and is sporadically associated with neurological disorders. There have been no diseases associated with HTLV-3 or HTLV-4 to date. Due to the difference in the disease manifestation between HTLV-1 and HTLV-2, a clear understanding of their individual pathobiologies and the role of various viral proteins in transformation should provide insights into better prognosis and prevention strategies. In this review, we aim to summarize the data accumulated so far in the transformation and pathogenesis of HTLV-1, focusing on the viral Tax and HBZ and citing appropriate comparisons to HTLV-2.

Cathepsin S regulates class II MHC processing in human CD4+ HLA-DR+ T cells

Although it has long been known that human CD4(+) T cells can express functional class II MHC molecules, the role of lysosomal proteases in the T cell class II MHC processing and presentation pathway is unknown. Using CD4(+) T cell clones that constitutively express class II MHC, we determined that cathepsin S is necessary for invariant chain proteolysis in T cells. CD4(+)HLA-DR(+) T cells down-regulated cathepsin S expression and activity 18 h after activation, thereby ceasing nascent class II MHC product formation. This blockade resulted in the loss of the invariant chain fragment CLIP from the cell surface, suggesting that-like professional APC-CD4(+) HLA-DR(+) cells modulate self-Ag presentation as a consequence of activation. Furthermore, cathepsin S expression and activity, and concordantly cell surface CLIP expression, was reduced in HLA-DR(+) CD4(+) T cells as compared with B cells both in vitro and ex vivo.

[CCR4, HTLV-1 infection, and ATL oncogenesis]

Adult T-cell leukemia (ATL) is a malignancy of mature CD4+ T cells that is etiologically associated with the infection of human T-cell leukemia virus type 1 (HTLV-1), an exogenous human retrovirus. Previously, we have shown that leukemic cells of most ATL patients express CCR4, a chemokine receptor known to be selectively expressed by T cell subsets such as Th2 cells, skin-homing memory/effector T cells, and regulatory T cells. Therefore, the expression of CCR4 suggests that ATL cells are mostly derived from one of these T cell subsets. We have also shown that Tax, the HTLV-1-encoded potent transcriptional activator, strongly induces the expression of CCL22, a CCR4 ligand, which promotes the cell-dependent transmission of HTLV-1 from HTLV-1-infected T cells to CCR4+ target T cells by inducing close cell-to-cell interactions. We have also shown that ATL cells aberrantly express the AP-1 family member Fra-2 which, by forming the heterodimer with JunD, potently induces the expression of not only CCR4 but also the genes such as c-Myb, MDM2 and Bcl-6, the well-known proto-oncogenes. Thus, Fra-2 is a novel oncogene of ATL, and CCR4 may be regarded as a useful tumor marker of ATL.

Rapamycin-induced inhibition of HTLV-I LTR activity is rescued by c-Myb

Background

Rapamycin is an immunosuppressive which represses translation of transcripts harbouring a polypyrimidine motif downstream of the mRNA cap site through the mammalian target of rapamycin complex. It inhibits the abnormal autologous proliferation of T-cell clones containing a transcriptionally active human T-lymphotropic virus, type I (HTLV-I) provirus, generated from infected subjects. We showed previously that this effect is independent of the polypyrimidine motifs in the viral long terminal repeat (LTR) R region suggesting that HTLV-I transcription, and not translation, is being affected. Here we studied whether rapamycin is having an effect on a specific transcription factor pathway. Further, we investigated whether mRNAs encoding transcription factors involved in HTLV-I transcriptional activation, specifically CREB, Ets and c-Myb, are implicated in the rapamycin-sensitivity of the HTLV-I LTR.

Results

An in vitro analysis of the role of SRE- and NF-κB-mediated transcription highlighted the latter as rapamycin sensitive. Over-expression of c-Myb reversed the rapamycin effect.

Conclusion

The sensitivity of HTLV-I transcription to rapamycin may be effected through an NF-κB-pathway associated with the rapamycin-sensitive mTORC1 cellular signalling network.

HTLV-1 propels untransformed CD4 lymphocytes into the cell cycle while protecting CD8 cells from death

Human T cell leukemia virus type 1 (HTLV-1) infects both CD4+ and CD8+ lymphocytes, yet it induces adult T cell leukemia/lymphoma (ATLL) that is regularly of the CD4+ phenotype. Here we show that in vivo infected CD4+ and CD8+ T cells displayed similar patterns of clonal expansion in carriers without malignancy. Cloned infected cells from individuals without malignancy had a dramatic increase in spontaneous proliferation, which predominated in CD8+ lymphocytes and depended on the amount of tax mRNA. In fact, the clonal expansion of HTLV-1-positive CD8+ and CD4+ lymphocytes relied on 2 distinct mechanisms--infection prevented cell death in the former while recruiting the latter into the cell cycle. Cell cycling, but not apoptosis, depended on the level of viral-encoded tax expression. Infected tax-expressing CD4+ lymphocytes accumulated cellular defects characteristic of genetic instability. Therefore, HTLV-1 infection establishes a preleukemic phenotype that is restricted to CD4+ infected clones.

MHC Class II Expression Identifies Functionally Distinct Human Regulatory T Cells

It has been known for decades that circulating human CD4 cells can express functional MHC class II molecules that induce T cell nonresponsiveness with Ag presentation. Because there is significant expression of MHC class II (MHC-II) determinants (DR) on a subpopulation CD4+ CD25(high) regulatory T cells (Treg), we examined the function of CD4 cells expressing MHC-DR. We demonstrate that MHC-II expression on human CD4+ CD25(high) T cells identifies a functionally distinct population of Treg that induces early contact-dependent suppression that is associated with high Foxp3 expression. In striking contrast, MHC-II- CD4+ CD25(high) Treg induce early IL-4 and IL-10 secretion and a late Foxp3-associated contact-dependent suppression. The DR expressing CD25(high) Treg express higher levels of Foxp3 message and protein, compared with the DR- CD25(high) Treg population. Direct single-cell cloning of CD4+ CD25(high) Treg revealed that, regardless of initial DR expression, ex vivo expression of CD25(high), and not DR, predicted which clones would exhibit contact-dependent suppression, high levels of Foxp3 message, and an increased propensity to become constitutive for DR expression. Thus, the direct ex vivo expression of MHC-II in the context of CD25(high) identifies a mature, functionally distinct regulatory T cell population involved in contact-dependent in vitro suppression.

Expression of CCR4 in adult T-cell leukemia

Adult T-cell leukemia (ATL) is a malignancy of mature T cells that is etiologically associated with human T-cell leukemia virus type 1 (HTLV-1). The frequent manifestation of ATL is infiltration of leukemic cells into various organs. Besides certain cell adhesion molecules and matrix metalloproteineses, chemokine receptors may play important roles in tissue infiltration of ATL. Identification of a unique set of chemokine receptors expressed by ATL would thus provide valuable information about the molecular mechanism of tissue infiltration of ATL. This may also reveal that ATL frequently develops from a certain subset of T cells that express a particular set of chemokine receptors. Since HTLV-1 encodes a potent viral transcriptional activator Tax, which is known to induce various cellular genes, expression of some chemokine receptors may be affected by Tax. This, however, may relate more to HTLV-1-infected T cells, since ATL cells usually do not express Tax. Finally, identification of a unique set of chemokine receptors expressed by ATL may also provide a new therapeutic target. These considerations prompted us to examine the chemokine receptor expression in ATL. We found that in the majority of ATL cases, leukemic cells consistently express CCR4. Since CCR4 is known to be involved in T cell migration into skin, this may in part explain the frequent skin infiltration in ATL. Furthermore, CCR4 is known to be selectively expressed by Th2 and regulatory T cells. Thus, the majority of ATL may predominantly originate from either Th2 or regulatory T cells.

Impairment of blood-cerebrospinal fluid barrier properties by retrovirus-activated T lymphocytes: reduction in cerebrospinal fluid-to-blood efflux of prostaglandin E2

The choroid plexus epithelium forms the interface between the blood and the CSF. In conjunction with the tight junctions restricting the paracellular pathway, polarized specific transport systems in the choroidal epithelium allow a fine regulation of CSF-borne biologically active mediators. The highly vascularized stroma delimited by the choroidal epithelium can be a reservoir for retrovirus-infected or activated immune cells. In this work, new insight in the implication of the blood-CSF barrier in neuroinfectious and inflammatory diseases is provided by using a differentiated cellular model of the choroidal epithelium, exposed to infected T lymphocytes. We demonstrate that T cells activated by a retroviral infection, but not non-infected cells, reduce the transporter-mediated CSF-to-blood efflux of organic anions, in particular that of the potent pro-inflammatory prostaglandin PGE2, via the release of soluble factors. A moderate alteration of the paracellular permeability also occurs. We identified the viral protein Tax, oxygenated free radicals, matrix-metalloproteinases and pro-inflammatory cytokines as active molecules released during the exposure of the epithelium to infected T cells. Among them, tumour necrosis factor and interleukin 1 are directly involved in the mechanism underlying the decrease in some choroidal organic anion efflux. Given the strong involvement of CSF-borne PGE2 in sickness behaviour syndrome, these data suggest that the blood-CSF barrier plays an important role in the pathophysiology of neuroinflammation and neuroinfection, via changes in the transport processes controlling the CSF biodisposition of PGE2.

Epidemiological and clinical interaction between HTLV-1 and Strongyloides stercoralis

Strongyloides stercoralis is the most common human parasitic nematode that is able to complete a life cycle and proliferate within its host. The majority of patients with strongyloidiasis have an asymptomatic infection or mild disease. However, when autoinfection occurs, a high number of infecting larvae can gain access to the bloodstream by penetrating the colonic mucosa leading to a severe hyperinfection and the development of disseminated strongyloidiasis. The human T cell lymphotropic virus type 1 (HTLV-1) predominantly infects T cells and induces spontaneous lymphocyte proliferation and secretion of high levels of type 1 cytokines. Strongyloides stercoralis patients with HTLV-1 co-infection have a modified immunological responses against parasite antigens and co-infection has clinical implications for strongyloidiasis. The high production of IFN-gamma observed in patients co-infected with HTLV-1 and Strongyloides stercoralis decreases the production of IL-4, IL-5, IL-13 and IgE, molecules that participate in the host defence mechanism against helminths. Moreover, there is a decrease in the efficacy of treatment of Strongyloides stercoralis in patients co-infected with HTLV-1. Alterations in the immune response against Strongyloides stercoralis and the decrease in the efficacy of anti-parasitic drugs are responsible for the increased prevalence of Strongyloides stercoralis among HTLV-1 infected subjects and make HTLV-1 infection the most important risk factor for disseminated strongyloidiasis.

Human Dlg protein binds to the envelope glycoproteins of human T-cell leukemia virus type 1 and regulates envelope mediated cell-cell fusion in T lymphocytes

Human homologue of the Drosophila Dlg tumor suppressor (hDlg) is a widely expressed scaffold protein implicated in the organization of multi-protein complexes at cell adhesion sites such as the neuronal synapse. hDlg contains three PDZ domains that mediate its binding to the consensus motifs present at the C-termini of various cell surface proteins, thus inducing their clustering and/or stabilization at the plasma membrane. Using a yeast two-hybrid screen, we identified hDlg as a cellular binding partner of a viral membrane integral protein, the envelope glycoprotein (Env) of human T-cell leukemia virus type 1 (HTLV-1). HTLV-1 is a human retrovirus that infects CD4+ T lymphocytes and is preferentially transmitted via direct contacts between infected and target cells, through a structure referred to as the virological synapse. Here, we demonstrate that hDlg interacts with a classical PDZ domain-binding motif present at the C-terminus of the cytoplasmic domain of HTLV-1 Env and conserved in the related HTLV-2 virus. We further document that, in HTLV-1 infected primary T cells, hDlg and Env are concentrated in restricted areas of the plasma membrane, enriched in molecules involved in T-cell contacts. The presence of Gag proteins responsible for viral assembly and budding in these areas indicated that they constitute platforms for viral assembly and transmission. Finally, a mutant virus unable to bind hDlg exhibited a decreased ability to trigger Env mediated cell fusion between T lymphocytes. We thus propose that hDlg stabilizes HTLV-1 envelope glycoproteins at the virological synapse formed between infected and target cells, hence assisting the cell-to-cell transmission of the virus.

Increased expression of human T lymphocyte virus type I (HTLV-I) Tax11-19 peptide-human histocompatibility leukocyte antigen A*201 complexes on CD4+ CD25+ T Cells detected by peptide-specific, major histocompatibility complex-restricted antibodies in patients with HTLV-I-associated neurologic disease

Human T lymphocyte virus type I (HTLV-I)–associated chronic inflammatory neurological disease (HTLV-I–associated myelopathy/tropical spastic paraparesis [HAM/TSP]) is suggested to be an immunopathologically mediated disorder characterized by large numbers of HTLV-I Tax–specific CD8⁺ T cells. The frequency of these cells in the peripheral blood and cerebrospinal fluid is proportional to the amount of HTLV-I proviral load and the levels of HTLV-I tax mRNA expression. As the stimulus for these virus-specific T cells are immunodominant peptide–human histocompatibility leukocyte antigen (HLA) complexes expressed on antigen-presenting cells, it was of interest to determine which cells express these complexes and at what frequency. However, until now, it has not been possible to identify and/or quantify these peptide–HLA complexes. Using a recently developed antibody that specifically recognizes Tax11-19 peptide–HLA-A*201 complexes, the level of Tax11-19–HLA-A*201 expression on T cells was demonstrated to be increased in HAM/TSP and correlated with HTLV-I proviral DNA load, HTLV-I tax mRNA load, and HTLV-I Tax–specific CD8⁺ T cell frequencies. Furthermore, CD4⁺ CD25⁺ T cells were demonstrated to be the major reservoir of HTLV-I provirus as well as Tax11-19 peptide–HLA-A*201 complexes. These results indicate that the increased detection and visualization of peptide–HLA complexes in HAM/TSP CD4⁺ CD25⁺ T cell subsets that are shown to stimulate and expand HTLV-I Tax–specific CD8⁺ T cells may play an important role in the pathogenesis of HTLV-I–associated neurological disease.

Human T cell lymphotropic virus type I (HTLV-I)-specific CD4+ T cells: immunodominance hierarchy and preferential infection with HTLV-I

CD4(+) T cells predominate in early lesions in the CNS in the inflammatory disease human lymphotropic T cell virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP), but the pathogenesis of the disease remains unclear and the HTLV-I-specific CD4(+) T cell response has been little studied. We quantified the IFN-gamma-producing HTLV-I-specific CD4(+) T cells, in patients with HAM/TSP and in asymptomatic carriers with high proviral load, to test two hypotheses: that HAM/TSP patients and asymptomatic HTLV-I carriers with a similar proviral load differ in the immunodominance hierarchy or the total frequency of specific CD4(+) T cells, and that HTLV-I-specific CD4(+) T cells are preferentially infected with HTLV-I. The strongest CD4(+) T cell response in both HAM/TSP patients and asymptomatic carriers was specific to Env. This contrasts with the immunodominance of Tax in the HTLV-I-specific CD8(+) T cell response. The median frequency of HTLV-I-specific IFN-gamma(+) CD4(+) T cells was 25-fold greater in patients with HAM/TSP (p = 0.0023, Mann-Whitney) than in asymptomatic HTLV-I carriers with a similar proviral load. Furthermore, the frequency of CD4(+) T cells infected with HTLV-I (expressing Tax protein) was significantly greater (p = 0.0152, Mann-Whitney) among HTLV-I-specific cells than CMV-specific cells. These data were confirmed by quantitative PCR for HTLV-I DNA. We conclude that the high frequency of specific CD4(+) T cells was associated with the disease HAM/TSP, and did not simply reflect the higher proviral load that is usually found in HAM/TSP patients. Finally, we conclude that HTLV-I-specific CD4(+) T cells are preferentially infected with HTLV-I.

Simultaneous presence of endogenous retrovirus and herpes virus antigens has profound effect on cell-mediated immune responses: implications for multiple sclerosis

Retroviruses have been suggested as possible pathogenic factors in multiple sclerosis (MS), supported by the observation that endogenous retroviruses are activated in MS patients. Different members of the herpes family of which several are neurotropic have also been suggested as factors in MS pathogenesis. Further, interactions between retroviruses and herpes viruses have been implied in the development of MS. The objective of the study was investigation of cell-mediated immune responses of MS patients to retrovirus and herpes virus antigens, particularly antigen combinations, with analyses of the influence of retrovirus antigens on cellular immunological reactivity toward other viral antigens. Cellular immunity as measured by blast transformation assays was analyzed using freshly isolated peripheral blood mononuclear cells from 47 MS patients and 36 healthy volunteers. Combinations of the endogenous retrovirus HERV-H and herpes virus antigens resulted in highly increased cellular immune responses among both the MS patients and healthy subjects. The increase was synergistic in character in most samples. Very pronounced effects were obtained using HHV-6A and HSV-1 antigens. Blast transformation assays combining antigens from two different herpes viruses or combinations of measles and herpes antigens showed no synergy. The obtained data indicate a pronounced synergistic effect on the cellular immune response when retrovirus and herpes antigens are present together. The cause of the synergy is unknown so far. The effect on the immune response may influence the disease progression.

The protean immune cell synapse: a supramolecular structure with many functions

Heterogeneity in the supramolecular organization of immunological synapses arises from the involvement of different cells, distinct environmental stimuli, and varying levels of protein expression. There may also be heterogeneity in the types and amounts of cell surface proteins and lipids that transfer between lymphocytes during immune surveillance. In addition, immune cells can be involved in the assembly of a 'viral synapse', such that micrometer-scale organization of proteins at intercellular contacts occurs during transmission of a virus between T cells. Thus, while there may be unity in molecular mechanisms underlying the organization of cell surface receptors at immune cell synapses, there is diversity in their function.

The dynamics of T-cell fratricide: application of a robust approach to mathematical modelling in immunology

Fratricide between CD8(+) T lymphocytes is known to occur in HTLV-I and possibly HSV-1 and HIV-1 infection. However it is not known what effect, if any, T-cell fratricide has on the course of infection. Here we present simple mathematical techniques to investigate T-cell fratricide with particular reference to HTLV-I infection. Using a general model we predict the qualitative and quantitative effect of fratricide on HTLV-I equilibrium proviral load. We also investigate the effect of fratricide on the probability of viral clearance. We show that, surprisingly, fratricide can lead either to an increase or a decrease in equilibrium proviral load. We derive the conditions necessary for fratricide to cause a decrease in load and deduce that, for the five HTLV-I-positive patients considered here, fratricide has probably caused an increase in equilibrium load. We also estimate the percentage increase in load that is attributable to fratricide and determine the parameters that should be measured in order to improve this estimate. Finally, we show that fratricide reduces the probability of viral clearance. Mathematical modelling of HTLV-I infection, as is often the case in biology, is severely hampered by a lack of experimental data. Consequently it is difficult to know what functional form a model should take. The behaviour of complex nonlinear systems is highly model-dependent. Predictions based on theoretical models are therefore sensitive to the choice of model; this is a very severe problem that undermines and limits the success of the application of mathematics to immunology. In this paper we reduce the model dependency of the results in two ways-by considering (analytically) a general model with a minimal number of assumptions and, where this is not possible, by checking (numerically) that a wide range of models yield the same results. We therefore begin to develop two practical methods for dealing with the problem of robustness in mathematical models of the immune system.

Regulation of the cell-surface expression of an HTLV-I binding protein in human T cells during immune activation

Little is known about the requirements for human T-cell leukemia virus type I (HTLV-I) entry, including the identity of the cellular receptor(s). Recently, we have generated an HTLV-I surface glycoprotein (SU) immunoadhesin, HTSU-IgG, which binds specifically to cell-surface protein(s) critical for HTLV-I-mediated entry in cell lines. Here, expression of the HTLV-I SU binding protein on primary cells of the immune system was examined. The immunoadhesin specifically bound to adult T cells, B cells, NK cells, and macrophages. Cell stimulation dramatically increased the amount of binding, with the highest levels of binding on CD4(+) and CD8(+) T cells. Naive (CD45RA(high), CD62L(high)) CD4(+) T cells derived from cord blood cells, in contrast to other primary cells and all cell lines examined, bound no detectable HTLV-I SU. However, following stimulation, the level of HTSU-IgG binding was rapidly induced (fewer than 6 hours), reaching the level of binding seen on adult CD4(+) T cells by 72 hours. In contrast to HTLV-I virions, the soluble HTSU-IgG did not effect T-cell activation or proliferation. When incubated with human peripheral blood mononuclear cells in a mixed leukocyte reaction, HTSU-IgG inhibited proliferation at less than 1 ng/mL. These results indicate that cell-surface expression of the HTLV SU binding protein is up-regulated during in vitro activation and suggest a role for the HTLV-I SU binding proteins in the immunobiology of CD4(+) T cells.

HTLV-1-mediated immunopathological CNS disease

HAM/TSP is a chronic inflammatory disease of the spinal cord. It is rather rare in HTLV-1-infected individuals. Immunogenetic factors of the HLA complex have been identified that support or prevent the development of the disease. In HAM/TSP patients a characteristic constellation of high proviral loads and increased cellular and humoral immune responses have been established. Immune dysfunction in HAM/TSP patients might be partly explained by HTLV-1 tax p40 transactivation of cellular genes in infected CD4+ T lymphocytes. The oligoclonal expansion of infected T lymphocytes, the variation of tax p40 within HTLV-1 carriers, and the regulation of proviral gene expression are possible determinants for disease development and need to be clarified in future studies.

High frequencies of Th1-type CD4(+) T cells specific to HTLV-1 Env and Tax proteins in patients with HTLV-1-associated myelopathy/tropical spastic paraparesis

CD4(+) T cells are critical for inducing and maintaining efficient humoral and cellular immune responses to pathogens. The CD4(+) T-cell response in human T-lymphotropic virus 1 (HTLV-1) infection has not been studied in detail. However, CD4(+) T cells have been shown to predominate in early lesions in HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). We present direct estimates of HTLV-1 Env- and Tax-specific CD4(+) T-cell frequencies in patients infected with HTLV-1. We first showed that there was a strong bias toward the Th1 phenotype in these HTLV-1-specific CD4(+) T cells in patients with HAM/TSP. We then demonstrated significantly higher frequencies of HTLV-1-specific Th1-type CD4(+) T cells in HAM/TSP patients than in asymptomatic HTLV-1 carriers. The majority of these HTLV-1-specific CD4(+) T cells did not express HTLV-1 Tax and were therefore unlikely to be infected by HTLV-1. High frequencies of activated HTLV-1-specific CD4(+) T cells of the Th1 phenotype might contribute to the initiation or pathogenesis of HAM/TSP and other HTLV-1-associated inflammatory diseases.

In vitro spontaneous lymphoproliferation in patients with human T-cell lymphotropic virus type I-associated neurologic disease: predominant expansion of CD8+ T cells

Peripheral blood mononuclear cells (PBMCs) from patients with human T-cell lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) proliferate spontaneously in vitro. This spontaneous lymphoproliferation (SP) is one of the immunologic hallmarks of HAM/TSP and is considered to be an important factor related to the pathogenesis of HAM/TSP. However, the cell populations involved in this phenomenon have not yet been definitively identified. To address this issue, the study directly evaluated proliferating cell subsets in SP with a flow cytometric method using bromodeoxyuridine and Ki-67. Although both CD4+ and CD8+ T cells proliferated spontaneously, the percentage of proliferating CD8+ T cells was 2 to 5 times higher than that of CD4+ T cells. In addition, more than 40% of HTLV-I Tax11-19-specific CD8+ T cells as detected by an HLA-A*0201/Tax11-19 tetramer proliferated in culture. In spite of this expansion of HTLV-I-specific CD8+ T cells, HTLV-I proviral load did not decrease. This finding will help elucidate the dynamics of in vivo virus-host immunologic interactions that permit the coexistence of high HTLV-I-specific CD8+ cytotoxic T-lymphocyte responses and high HTLV-I proviral load in HAM/TSP.

Molecular biology and pathogenesis of the human T-cell leukaemia/lymphotropic virus Type-1 (HTLV-1)

Retroviruses are associated with a variety of diseases, including immunological and neurological disorders, and various forms of cancer. In humans, the Human T-cell Leukaemia/Lymphotropic virus type 1 (HTLV-1), which belongs to the Oncovirus family, is the aetiological agent of two diverse diseases: Adult T-cell leukaemia/lymphoma (ATLL) (Poiesz et al. 1980; Hinuma et al. 1981; Yoshida et al. 1982), as well as the neurological disorder tropical spastic paraparesis/HTLV-1-associated myelopathy (TSP/HAM) (Gessain et al. 1985; Rodgers-Johnson et al. 1985; Osame et al. 1986). HTLV-1 is the only human retrovirus known to be the aetiological agent of cancer. A genetically related virus, HTLV-2, has been identified and isolated (Kalyanaraman et al. 1982). However, there has been no demonstration of a definitive aetiological role for HTLV-2 in human disease to date. Simian T-cell lymphotropic viruses types 1 and 2 (STLV-1 and -2) and bovine leukaemia virus (BLV) have also been classified in same group, Oncoviridae, based upon their similarities in genetic sequence and structure to HTLV-1 and -2 (Burny et al. 1988; Dekaban et al. 1995; Slattery et al. 1999). This article will focus on HTLV-1, reviewing its discovery, molecular biology, and its role in disease pathogenesis.

Chromosomal positioning of human T-lymphotropic type 1 proviruses by fluorescence in situ hybridisation

Fluorescence in situ hybridisation (FISH) was employed to identify the chromosomal integration site of the human T-cell lymphotropic virus, type 1 (HTLV-1) present in T-cell clones derived from HTLV-1-infected individuals and a virally transformed cell line, C8166-45. Proviral sequences were detected in C8166-45 but not uninfected Jurkat cells. Integration sites were reliably detected in T-cell clones determined previously to be infected with HTLV-1. The results indicated that the transformed cell line and some of the T-cell clones possessed more than one proviral integration site. This hybridisation system is useful for determining the number of integration events and for localising proviruses to specific chromosomal regions.

Vascular cell adhesion molecule-1 induced by human T-cell leukaemia virus type 1 Tax protein in T-cells stimulates proliferation of human T-lymphocytes

Human T-cell leukaemia/lymphotropic virus type 1 (HTLV-1), aetiologically linked to lymphoproliferative as well as inflammatory diseases, infects and activates CD4(+) helper T-cells and thus alters immunoregulatory pathways. The viral regulatory Tax protein has been shown previously to induce the expression of vascular cell adhesion molecule-1 (VCAM-1) by T-cells. To determine the functional role of this adhesion molecule, Jurkat T-cells stably expressing either Tax or both Tax and Rex (another viral regulatory protein) were used in binding and coculture assays performed with either control Jurkat cells or primary human T-lymphocytes. Evidence was provided that VCAM-1 acting in synergy with leucocyte function-associated antigen-3 promotes T-cell-T-cell interactions and increases T-cell proliferation. Interestingly, Rex was found to modulate these events. These data establish that VCAM-1 induced by Tax on T-cells thus contributes to the immunopathological process triggered by HTLV-1 infection.

The rapamycin sensitivity of human T-cell leukaemia virus type I-induced T-cell proliferation is mediated independently of the polypyrimidine motifs in the 5' long terminal repeat

The immunosuppressant rapamycin can regulate the translation of a subset of messenger RNAs, a phenotype which has been linked to the presence of a polypyrimidine motif [C(N)(4-14)] downstream of the mRNA cap structure. T-cell clones naturally infected with transcriptionally active human T-cell leukaemia virus, type I (HTLV-I) undergo autologous proliferation; this phenotype is inhibited by rapamycin but not FK506, which reverses the rapamycin effect. Within the R region of the HTLV-I 5' long terminal repeat (LTR) there are seven polypyrimidine motifs. We sought to determine if these were involved in the sensitivity of proliferation to the presence of rapamycin. Here we illustrate the generation of an in vitro model of this rapamycin-sensitivity and the analysis of LTR mutants which were created to determine the importance of the polypyrimidine motifs. Reporter gene assays suggest the effect is independent of the polypyrimidine motifs in the virus leader sequence.

Is human T-cell lymphotropic virus type I really silent?

The role of the cellular immune response to human T-cell lymphotropic virus type I (HTLV-I) is not fully understood. The low level of HTLV-I protein expression in peripheral blood lymphocytes has led to the widely held belief that HTLV-I is transcriptionally silent in vivo. However, most HTLV-I-infected individuals mount a strong and persistently activated cytotoxic T-lymphocyte (CTL) response to the virus; this observation implies that there is abundant chronic transcription of HTLV-I genes. Here we show that HTLV-I Tax protein expression rises quickly in freshly isolated peripheral blood lymphocytes, but that expressing cells are rapidly killed by CTLs. Mathematical analysis of these results indicates that the CTL response is extremely efficient and that the half-life of a Tax-expressing cell is less than a day. We propose that HTLV-I protein expression in circulating lymphocytes is undetectable by current techniques because of the efficiency of the CTL-mediated immune surveillance in vivo.

The immune response to HTLV-I

A strong cytotoxic T lymphocyte response to HTLV-I protects against the associated inflammatory disease of the central nervous system, HAM/TSP (HTLV-I-associated myelopathy/tropical spastic paraparesis), by reducing the proviral load of HTLV-I; however, when the proviral load exceeds a threshold level, HTLV-I-specific cytotoxic T lymphocytes could contribute to inflammation.

Up-regulation of human T lymphotropic virus type 1 (HTLV-1) tax/rex mRNA in infected lung tissues

HTLV-1 has been implicated in certain pulmonary diseases. We previously demonstrated that expression of HTLV-1 tax/rex mRNA, encoding the transcriptional transactivator Tax, was closely associated with infiltration of activated T lymphocytes into lung tissue. To explore mechanisms of tax/rex expression in the lung, tax/rex mRNA expression and proviral DNA load were compared between peripheral blood mononuclear cells (PBMC) and bronchoalveolar lavage cells (BALC) from four patients with HTLV-1-associated myelopathy (HAM/TSP) and 13 carriers with various pulmonary symptoms. Semiquantitative detection of tax/rex mRNA strongly suggested that the lung was a preferential site for its expression. Proviral DNA loads in non-HAM/TSP carriers were variable but correlated well between PBMC and BALC in each individual, and revealed no relationship with tax/rex mRNA expression. In contrast, both cell groups from four HAM/TSP patients expressed detectable tax/rex mRNA accompanied by high proviral DNA load. The ratio of tax/rex mRNA expression to proviral DNA load was higher in BALC than in PBMC in three of four carriers and in three of four HAM/TSP patients, suggesting up-regulation of tax/rex mRNA in infected lung tissue. To analyse differences in distribution of HTLV-1 quasispecies between the two tissues, phylogenetic analysis was performed for sequence sets of the proviral tax open reading frame (ORF: 1059 bp) derived from PBMC and BALC of two infected individuals. Sequences derived from the two tissues distributed similarly to branches of phylogenetic trees, and there was no evidence of selective distribution of certain quasispecies in the lung. Our results suggest the presence of tissue-specific conditions that activate viral expression in infected cells in the lung. Constitutive exposure of this tissue to foreign antigens leading to up-regulation of basal viral promoter activity is likely to be one such mechanism.

Virus inactivation in a proportion of human T-cell leukaemia virus type I-infected T-cell clones arises through naturally occurring mutations

Human T-cell leukaemia virus type I (HTLV-I) is the aetiological agent of adult T-cell leukaemia/lymphoma and tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM). The trans-activating protein (Tax) of HTLV-I is strongly implicated in cellular proliferation. We examined the tax gene and 5' long terminal repeat (LTR) sequences in eight naturally infected T-cell clones derived from TSP/HAM-affected individuals who were either productively (proliferate spontaneously) or silently (do not proliferate spontaneously) infected. In two silently infected clones point mutations within the proviruses resulted in truncation of the Tax protein. One clone harboured both a deleterious tax gene mutation and a point mutation in an enhancer element of the 5' LTR. Sequence changes, immunological escape mutation, integration site context and host cell phenotype may all contribute to the high proportion of latently or silently infected T-cells found in vivo in virus carriers.

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) pathogenesis hypothesis. A shift of homologous peptides pairs, central nervous system (CNS)/HTLF-1, HTLV-1/thymus, thymus/CNS, in a thymus-like CNS environment, underlies the pathogenesis of HAM/TSP

Determinants shared by thymus, brain and HTLV-1 induce lymphocytic neurotropism and demyelinization in HAM/TSP, within the framework thymus-like brain environment. The disease evolves in two phases. The first phase of the disease would be dependent on CD4 T-lymphocytes specific for thymic autoantigens, reactivated by viral antigens homologous to thymus and CNS autoantigens. During this phase, demyelinization could be due initially to a stop in the synthesis of myelin following an altered expression of adhesion proteins at the surface of oligodendrocytes and neurons. The second phase, which covers the inflammatory and chronic character of the disease, would be dependent, on the one hand, on CD8 T-lymphocytes specific for viral peptides, and on the other hand, on CD8 T-lymphocytes specific for peptides arising from the cell-proteases induced progressive proteolysis of protein components from the myelin layers and other protein components of the CNS. Non-specific inflammatory and non-inflammatory cytokines keep the activation going of the different cellular types. The thoracic spinal cord cell-location specificity would be linked to a peptidic coherence between HTLV-1 (significant agent), thymus and thoracic spinal cord antigens, genetically peculiar to HAM/TSP patients.

Mechanisms of T-cell activation by human T-cell lymphotropic virus type I

The interactions between human T-cell lymphotropic virus type I (HTLV-I) and the cellular immune system can be divided into viral interference with functions of the infected host T cell and the subsequent interactions between the infected T cell and the cellular immune system. HTLV-I-mediated activation of the infected host T cell is induced primarily by the viral protein Tax, which influences transcriptional activation, signal transduction pathways, cell cycle control, and apoptosis. These properties of Tax may well explain the ability of HTLV-I to immortalize T cells. It is not clear, though, how HTLV-I induces T-cell transformation (interleukin-2 [IL-2] independence). Recent evidence suggests that Tax may promote the G1- to S-phase transition, although this may involve additional proteins. A role for other viral proteins that may constitutively activate the IL-2 receptor pathway has also been suggested. By virtue of their activated state, HTLV-I-infected T cells can nonspecifically activate resting, uninfected T cells via virus-mediated upregulation of adhesion molecules. This may favor viral dissemination. Moreover, the induction of a remarkably high frequency of antiviral CD8(+) T cells does not appear to eliminate the infection. Indeed, individuals with a high frequency of virus-specific CD8(+) T cells have a high viral load, indicating a state of chronic immune system stimulation. Thus, while an activated immune system is needed to eradicate the infection, the spread of the HTLV-I is also accelerated under these conditions. A detailed knowledge of the molecular interactions between virus-specific CD8(+) T cells and immunodominant viral epitopes holds promise for the development of specific antiviral therapy.

HTLV-I-infected T cells evade the antiproliferative action of IFN-beta

Human T-cell lymphotropic virus type I (HTLV-I)-infected T-cell clones enter the S-phase of the cell cycle in the absence of exogenous IL-2. The pathway by which HTLV-I activates the host T cell may circumvent normal immunoregulatory mechanisms and thus be important for the pathogenesis of HTLV-I-induced diseases. The early control of viral infections is in part mediated by interferons (IFNs), which possess both antiviral and antiproliferative functions. In order to investigate the antiproliferative effect of IFN-beta on HTLV-I-induced T-cell activation, we generated T-cell clones from patients with HTLV-I-associated myelopathy/tropical spastic paraparesis by single-cell cloning under limiting dilution conditions. Here we demonstrate that HTLV-I-induced T-cell proliferation is resistant to the antiproliferative action of IFN-beta. Moreover, HTLV-I-infected T-cell clones continue to constitutively secrete IFN-gamma in the presence of high doses of IFN-beta. HTLV-I-infected T cells express normal levels of IFNAR1 and are able to respond to IFN-beta by phosphorylation of STAT1 on Tyr701, although they display a relative increase in phosphorylation of the transcriptionally inactive STAT1beta when compared with STAT1alpha. Thus, HTLV-I promotes cell cycle progression in G1 by a mechanism that overcomes inhibitory signals, thereby circumventing an innate immune defense mechanism.

Marked suppression of T cells by a benzothiophene derivative in patients with human T-lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis

In a search for new anti-autoimmune agents that selectively suppress activation of autoreactive T cells, one such agent, 5-methyl-3-(1-methylethoxy)benzo[b]thiophene-2-carboxamide (CI-959-A), was found to be effective. This compound, which is known to suppress tumor necrosis factor alpha (TNF-alpha)-induced CD54 expression, inhibited the primary proliferative response of the T cell to antigen (Ag)-presenting cells (APCs) including allogenic dendritic cells (DCs), autologous Epstein-Barr virus-infected B cells, and human T lymphotropic virus type I (HTLV-I)-infected T cells. Autoreactive T cells from patients with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) spontaneously proliferate in vitro, and their activation is reported to be associated with CD54 expression. The spontaneous proliferation of T cells from patients with HAM/TSP was entirely blocked by CI-959-A. However, in this study, the T-cell proliferation in 15 patients with HAM/TSP was found to depend more extensively on major histocompatibility complex (MHC) class II and CD86 than on CD54 Ags. Since most important APCs for the development of HAM/TSP are DCs and HTLV-I-infected T cells, the effect of CI-959-A on DC generation and on the expression of surface molecules on activated T cells is examined. CI-959-A suppressed recombinant granulocyte-macrophage colony stimulating factor (GM-CSF)- and recombinant interleukin-4-dependent differentiation of DCs from monocytes and inhibited the expression of CD54 and, more extensively, MHC class II and CD86 Ags. CI-959-A showed little toxicity toward lymphoma or HTLV-I-infected T-cell lines or toward monocytes and cultured DCs. These results suggest that CI-959-A might be a potent anti-HAM/TSP agent.

Genetic control and dynamics of the cellular immune response to the human T-cell leukaemia virus, HTLV-I

About 1% of people infected with the human T-cell leukaemia virus, type 1 (HTLV-I) develop a disabling chronic inflammatory disease of the central nervous system known as HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Patients with HAM/TSP have a vigorous immune response to HTLV-I, and it has been widely suggested that this immune response, particularly the HTLV-I-specific cytotoxic T-lymphocyte (CTL) response, causes the tissue damage that is seen in HAM/TSP. In this paper we summarize recent evidence that a strong CTL response to HTLV-I does in fact protect against HAM/TSP by reducing the proviral load of HTLV-I. We conclude that HTLV-I is persistently replicating at a high level, despite the relative constancy of its genome sequence. These results imply that antiretroviral drugs could reduce the risk of HAM/TSP by reducing the viral load, and that an effective anti-HTLV-I vaccine should elicit a strong CTL response to the virus. The dynamic nature of the infection also has implications for the epidemiology and the evolution of HTLV-I.

Activation of human T-cell leukemia virus type 1 tax gene expression in chronically infected T cells

Expression of human T-cell leukemia virus type 1 (HTLV-1) is regulated both by the HTLV-1 Tax transactivator and by cellular transcriptional factors binding to the viral long terminal repeat (LTR), suggesting that cellular signals may play a role in regulating viral expression. Treatment of cells chronically infected with HTLV-1, which express low levels of HTLV-1 RNAs and Tax protein, with phorbol esters (i.e., phorbol12-myristate 13- acetate [PMA]), phytohemagglutinin (PHA), sodium butyrate, or combinations of cytokines resulted in induction of HTLV- 1 gene expression. PMA or PHA treatment following cotransfection of HTLV-1 Tax expression plasmids resulted in synergistic activation of HTLV-1 LTR-directed gene expression, apparently involving tyrosine ki- nase- mediated pathways. These results suggest that cellular activation stimuli may cooperate with HTLV-1 Tax to enhance expression of integrated HTLV-1 genomes and thus may play a role in the pathogenesis of HTLV-1 disease.

Elevated serum levels of soluble E- and L-selectin in patients with human T-cell lymphotropic virus type I-associated myelopathy

We compared soluble E-selectin (sE-selectin) and L-selectin (sL- selectin) levels in sera and cerebrospinal fluid (CSF) of 30 patients with human T-lymphotropic virus type I (HTLV-I)-associated myelopathy (HAM), with those of 10 patients with the relapsing-remitting form of multiple sclerosis (MS), and 16 patients with other neurological diseases (OND). Serum levels of both sE-selectin and sL-selectin, as measured by enzyme-linked immunosorbent assay, were significantly elevated in patients with HAM, compared to patients with OND. In addition, serum levels of sL-selectin were significantly elevated in HAM patients compared to MS patients. No significant difference was found in CSF levels of sL-selectin between HAM patients and controls. However, HAM patients who had received blood transfusions had significantly higher CSF levels of sL-selectin than HAM patients without a past history of transfusions, suggesting that HAM patients with past history of transfusion have a more active immunological state in the central nervous system. sE-selectin was not detected in CSF of HAM patients and controls. This finding might be based on exaggerated inflammatory conditions following increased attachment of lymphocytes to activated endothelial cells in HAM patients.

Transcriptional activation of the intercellular adhesion molecule 1 (CD54) gene by human T lymphotropic virus types I and II Tax is mediated through a palindromic response element

In vitro infection of T cells with human T lymphotropic virus types I and II (HTLV-I and HTLV-II) resulted in constitutive expression of ICAM-1. Higher levels of ICAM-1 mRNA were expressed in HTLV-transformed cell lines (MT-2, MoT, C8166) when compared with uninfected T cell lines (A301). We demonstrate that this activation is conferred through a site on the ICAM-1 promoter that is activated in trans by the Tax protein of HTLV-I and HTLV-II. Enhanced promoter activity was detected when the ICAM-1 construct (-1162/+1) was transfected into HTLV-I-infected (MT-2), HTLV-II-infected (MoT, AI 1050), or an HTLV-I Tax-only-expressing (C8166) cell line as compared to the uninfected T cell line (A3.01). Cotransfection of the uninfected T cell line A3.01 with the ICAM construct along with Tax-I and Tax-II expression plasmid also resulted in increased promoter activity. Furthermore, experiments with deletion constructs of the ICAM-1 promoter region indicated that a region between -88 and -53 bp relative to the transcription start site is sufficient for Tax-inducible CAT expression. This segment includes an 11-bp palindromic segment (TTTCCGGGAAA) that has homology with the IFN-gamma and IL-6 response element. An 11-bp segment containing this regulatory region proved to be sufficient to confer Tax-I and Tax-II inducibility on a heterologous promoter (TK-CAT). Taken together these findings indicate that constitutive expression of ICAM-1 by HTLV-infected cells is influenced by the viral trans-activator protein Tax. This increased expression of ICAM-1 in response to the Tax protein may play an important role in the lymphoproliferation associated with HTLV infection.

Isolation of sooty mangabey simian T-cell leukemia virus type I [STLV-I(sm)] and characterization of a mangabey T-cell line coinfected with STLV-I(sm) and simian immunodeficiency virus SIVsmmPBj14

It has been postulated that dual infections of humans with human immunodeficiency virus (HIV) and human T-cell leukemia/lymphotropic virus (HTLV) may potentiate disease progression. Counterparts of both of these pathogenic human retroviruses have been identified in various simian species indigenous to Asia and Africa, including sooty mangabey monkeys (Cercocebus atys). Using peripheral blood mononuclear cells (PBMC) from a mangabey naturally infected with both SIV and STLV-I, T-cell lines were established and maintained continuously for more than 3 years; these cell lines harbored only a newly identified mangabey STLV-I(sm) or both STLV-I(sm) and the acutely lethal variant SIVsmmPBj14. The dually infected cell line (FEd-P14) was established by de novo infection of mangabey PBMC with SIVsmmPBj14. This cell line was characterized by multiple assays which showed that structural proteins encoded by both viruses were produced in large quantities, but that the predominant viral glycoprotein on the cell surface was the STLV-I(sm) Env. Unusual interactions of the two retroviral glycoproteins were suggested by the formation of syncytia between Raji and the FEd-P14 cells, but not between Raji and simian cells infected with only one retrovirus or human cells infected with HTLV-I. The STLV-I(sm) strain obtained from the sooty mangabey was transmitted to normal macaque and mangabey PBMC and was shown to be unique by sequencing of the entire env gene. STLV-I(sm) from this African species was more closely related to "cosmopolitan" HTLV-I strains than to the prototypic STLV-I from an Asian pig-tailed macaque. In vitro and in vivo studies of STLV-I(sm) and SIVsmm, both isolated from a naturally infected mangabey monkey, may provide insight into disease induction and manifestations associated with coinfection by their human counterparts.

HIV viral load and CD4+ lymphocyte counts in subjects coinfected with HTLV-I and HIV-1

Reports indicate that there is a dissociation between markers of HIV disease progression and clinical stage among subjects coinfected with human T-cell lymphotropic virus type I (HTLV-I) and HIV. HTLV-I coinfection does not appear to affect HIV viral load, currently considered to be the best marker of HIV disease progression. We measured HIV RNA levels in stored serum samples from 23 subjects with coinfection and 92 subjects with HIV single infection and examined the correlation with the CD4+ lymphocyte count. Subjects were recruited from an ongoing HIV cohort study in Rio de Janeiro, Brazil. In both groups, CD4+ lymphocyte counts declined with increasing levels of HIV RNA. In a linear regression analysis adjusting for HIV RNA serum level, coinfected individuals had an estimated 78% higher CD4+ lymphocyte count than those with single infection. Simultaneous adjustment for beta2-microglobulin level increased the difference, with coinfected individuals having 146% (p = 0.005, 95% CI: 32% to 359%) higher CD4+ counts. These data suggest that the higher CD4+ lymphocyte counts associated with coinfection do not provide immunologic benefit and may reflect HTLV-I-associated nonspecific lymphocyte proliferation. The results of this and other studies suggest that the CD4+ count cutoff values used in making clinical decisions in HIV infection may not be appropriate in coinfection. As with HIV single infection, HIV virus load may be the optimal surrogate marker for subjects with coinfection.

HTLV-I-infected T cells activate autologous CD4+ T cells susceptible to HTLV-I infection in a costimulatory molecule-dependent fashion

A vigorous production of human T lymphotropic virus type I (HTLV-I)-infected CD4+ T cells is closely associated with the development of adult T cell leukemia (ATL) and neurological disease. However, the immunological mechanisms leading to generation of the HTLV-I-infected cells are not fully clarified. The modulation of CD80 and CD86 expression on the HTLV-I-infected cells and its physiological role in the interaction of infected CD4+ T cells with uninfected CD4+ T cells was examined. The HTLV-I-infected CD4+ T cell lines established from ATL patients and normal donors by infecting their CD4+ T cells with the virus expressed CD80, CD86, and HLA-DR, and induced a proliferation of autologous and allogenic CD4+ T cells. While the CD4+ T cells stimulated with the autologous HTLV-I-infected cells for 7 days expressed CD80 and CD86 but not HTLV-I gene products, they expressed HTLV-I gag antigen after 4 weeks. The interaction of HTLV-I-infected and -uninfected CD4+ T cells was profoundly suppressed by a combination of CD80 and CD86 monoclonal antibodies. These results suggest that the induction of CD80 and CD86 on HTLV-I-infected CD4+ T cells participates actively in the generation of the virus-infected progenitor cells.

Variable Immortalizing Potential and Frequent Virus Latency in Blood-Derived T-Cell Clones Infected With Human T-Cell Leukemia Virus Type I

Human T-cell leukemia virus type I (HTLV-I)-infected T cells expanded in vitro by single-cell cloning provide a unique system for investigating virus-cell interactions in nonimmortalized T cells. By analysis of clones generated randomly from the blood of virus carriers, we confirm that CD4 T cells are the major reservoir of HTLV-I in vivo and show that most infected cells contain a single integrated provirus. Contrary to the situation in HTLV-I immortalized cell lines, the HTLV-I provirus was found to be transcriptionally silent in a high proportion of randomly generated T-cell clones and could not be reactivated by mitogenic stimulation. The spontaneous proliferation previously documented in HTLV-I–infected T-cell clones was not observed in silently infected cells, and therefore correlates directly with the expression of tax and other viral genes. The only cytokine mRNA found to be significantly elevated in the virus-producing clones was interleukin-6; however, receptor-blocking experiments argue against a role for IL-6 in the virus-induced cell proliferation. We observed a striking variation in the ability of individual HTLV-I–producing clones to immortalize fresh peripheral blood lymphocytes. This ability did not correlate with the levels of viral mRNA expression, gag p24 production, spontaneous proliferation, or tax-transactivation, possibly suggesting a role for host cell factors as determinants of viral infectivity or immortalization. Studies to elucidate the basis of this phenotypic heterogeneity should enhance our understanding of viral spread and pathogenesis.

Pentoxifylline down-regulates adhesion molecule expression and inflammatory cytokine production in cultured peripheral blood mononuclear cells from patients with HTLV-I-associated myelopathy

To clarify if pentoxifylline (PTX) may have therapeutic potential for human T-cell lymphotropic virus type I (HTLV-I)-associated myelopathy (HAM), we investigated the in vitro effect of PTX on spontaneous proliferation of peripheral blood lymphocytes (SPP), as well as on the expression of adhesion molecules, such as lymphocyte function antigen-1 (LFA-1) and very late activation antigen-4 (VLA-4), and the production of inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma) and granulocyte-monocyte colony stimulating factor (GM-CSF), in cultured PBMC from 10 HAM patients, compared with control subjects. SPP in HAM patients was significantly suppressed in a dose-dependent manner with PTX. Using flow cytometry, PTX was found to down-regulate the expression of LFA-1 and VLA-4 on CD4+ and CD8+ T cells in HAM patients as well as control subjects. However, the fall in the expression of LFA-1 and VLA-4 on CD4+ T cell population in HAM patients was higher than that of control subjects. PTX caused a significant suppression of spontaneous production of TNF-alpha by cultured PBMC of HAM patients. It also caused a small but significant suppression GM-CSF and IFN-gamma production. Collectively, our results suggest that PTX might be therapeutically effective at critical points in the immunopathogenesis of HAM.