Human T-cell lymphotropic virus type I and neurological diseases

Human T-cell lymphotropic virus type I (HTLV-I) infection is associated with a variety of human diseases. In particular, there are two major diseases caused by HTLV-I infection. One is an aggressive neoplastic disease called adult T-cell leukemia (ATL), and another is a chronic progressive inflammatory neurological disease called HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). It is still unknown why one virus causes these different diseases. With regard to HAM/TSP, virus-host immunological interactions are an considered to be important cause of this disease. Coexisting high HTLV-I proviral load and HTLV-I-specific T cells (CD4+ T cells and CD8+ T cells) is an important feature of HAM/TSP. Histopathological studies indicate the existence of an inflammatory reaction and HTLV-I-infected cells in the affected lesions of HAM/TSP. Therefore, the immune response to HTLV-I probably contributes to the inflammatory process of the central nervous system lesions in HAM/TSP patients.     

Reduced Foxp3 expression with increased cytomegalovirus-specific CTL in HTLV-I-associated myelopathy

Human T-lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients show high immune responses to HTLV-I. However, it is unclear whether the cytotoxic T lymphocyte (CTL) responses to other chronic viruses also increase. We investigated the responses in the peripheral blood by using HLA-A*0201/peptide pentamers. The frequency of cytomegalovirus (CMV)-specific CTL tended to be higher in HAM/TSP patients than in healthy controls (HCs). The frequency of CMV-specific CTL positively correlated with that of HTLV-I Tax-specific CTL. The frequency of Foxp3+ cells in CD4+ lymphocytes tended to be higher in HAM/TSP patients than in ACs and HCs. The expression level of Foxp3 was lower in HAM/TSP patients than in HCs and was inversely correlated with the CMV-specific CTL frequency. A percentage of Foxp3+ cells showed a positive correlation with the HTLV-I proviral load. These results suggest that a decrease in the Foxp3 expression may contribute to the high immune response to CMV and that the Foxp3+ regulatory T cells may play a role in the immune surveillance of HTLV-I.     

Pathogenesis of chronic progressive myelopathy associated with human T-cell lymphotropic virus type I

Human T-cell lymphotropic virus type I (HTLV-I) induces a chronic demyelinating disease known as HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). While only 0.25% of HTLV-I-infected individuals develop HAM/TSP, the mechanisms responsible for the progression of an HTLV-I carrier state to clinical disease are not clear. In particular, no specific sequence differences have been found between HTLV-I recovered from HAM patients and HTLV-I-infected carriers. Since CD4 T cells are the major reservoir of the virus, at least three hypotheses implicating CD4 T cells directly or indirectly have been proposed: 1) The cytotoxic hypothesis predicts that activated and HTLV-I-infected CD4 T cells migrate to the CNS and infect resident cells. Cytotoxic CD8 T cells may then recognize viral antigens on HTLV-I-infected CNS cells causing a cellularly mediated cytotoxic demyelination. 2) The autoimmune hypothesis predicts that either (a) virally reactive T cells cross-react with a CNS antigen, or (b) random infection of CD4 T cells eventually results in the infection of CNS-autoreactive CD4 T cells that, by virtue of the productive HTLV-I infection, become activated, expand and migrate to the CNS, where they encounter their antigen. This results in a specific immune response and demyelination, as is known to occur in experimental autoimmune encephalomyelitis. 3) The bystander damage hypothesis does not implicate a specific response against CNS cells. Instead this hypothesis suggests that the presence of IFN-γ-secreting HTLV-I-infected CD4 T cells and their recognition by virally specific CD8 T cells in the CNS induce microglia to secrete cytokines, such as TNF-α, which may be toxic for the myelin.     

T cell transformation with Herpesvirus saimiri: a tool for neuroimmunological research

Splice variants of CD44 molecule-harboring exon 10 (v6), often called v6 variants (v6v), are shown to confer tumor progressive, metastatic or invasive capacities. Furthermore, CD44 molecule on activated T-cells are shown to be required for infiltration of these cells into the inflammatory site and for accelerated immune response. Human T-cell lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is caused by HTLV-I infection and characterized by spastic paraparesis and urinary disturbance with perivascular HTLV-I-infected and activated CD4+ T-cell infiltration. In order to explore the underlying mechanism causing the disease after HTLV-I infection, we analyzed CD44 variant expression on peripheral blood mononuclear cells (PBMC) and in the spinal cord specimens from patients with HAM/TSP, and compared them with those from other HTLV-I-infected individuals and controls. We found that v6v expression with special direct link of exons 10 (v6) and 14(v10) was highly expressed in PBMC from patients with HAM/TSP and that v6v and CD4 double positive T-cell infiltration into the spinal cord lesion of HAM/TSP. This combination of CD44 splice variant has not been previously reported in the study of chronic inflammatory disorders and may be a marker molecule for T-cells infiltrating into the central nervous system (CNS), especially the spinal cord.     

Selected cytotoxic T lymphocytes with high specificity for HTLV-I in cerebrospinal fluid from a HAM/TSP patient

Human T lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic inflammatory disease of the spinal cord in which HTLV-I Tax-specific cytotoxic T lymphocytes (CTL) have been suggested to be immunopathogenic. However, it is unknown whether the HTLV-I-specific CTL in the central nervous system differ from those in the periphery. We investigated functional T-cell receptor diversity in HTLV-I Tax11-19-specific CTL clones derived from peripheral blood and cerebrospinal fluid (CSF) of a HAM/TSP patient using analogue peptides of the viral antigen. CTL responses to the analogue peptides varied between T-cell clones, however, CTL clones from CSF showed limited recognition of the peptides when compared to those from peripheral blood. This suggests that CTL with highly focused specificity for HTLV-I Tax accumulate in the CSF and may contribute to the pathogenesis of HAM/TSP. Furthermore, this study provides a rationale for analogue peptide-based immunotherapeutic strategies focusing on the immunopathogenic T-cells in HTLV-I-associated neurologic disease.     

Characterization of a unique T-cell clone established from a patient with HAM/TSP which recognized HTLV-I-infected T-cell antigens as well as spinal cord tissue antigens

Five T-cell clones reactive to autologous HTLV-I-infected T-cells (KODA-TV) were established from peripheral blood lymphocytes of a HAM/TSP patient (KODA) by the limiting dilution method. All the clones showed CD3⁺, CD4⁺ and CD25⁺ surface markers and expressed αβ⁺ T-cell receptors to recognize KODA-TV antigens. One of the five T-cell clones (KODA-408) was infected with HTLV-I but the remaining four clones (KODA-400, 404, 405 and 409) were free of HTLV-I infection. KODA-408 recognized both KODA-TV and spinal cord antigens, the latter being extracted from autopsy tissues of a HTLV-I seronegative donor. KODA-408 did not recognize either alloantigens of peripheral blood mononuclear cells extracted from unrelated HTLV-I seronegative donors or purified human myelin basic protein. KODA-408 T-cell clone produced a considerable amount of TNF-aβ, IFN-γ, and IL-6. The CDR3 motif of KODA-408 T-cell receptor showed a unique sequence CASSAGQS of Vβ8-Dβ-Jβ1.5. These results indicated that HAM/TSP CD4⁺ T-cells were polyclonally activated by HTLV-I infection and antigenic stimulation. The T-cell repertoire shaped by HTLV-I infection included T-cells which recognized HTLV-I-infected T-cell antigens as well as spinal cord antigen in particular.     

Pathogenetic significance of HTLV-I infection and immune surveillance in HAM]

HTLV-I proviral DNA load is significantly increased in HTLV-I associated myelopathy (HAM) compared with asymptomatic HTLV-I seropositive carriers (SPC), and this spread of HTLV-I infection seems to be critically important in the pathogenesis of HAM. Thus, in this report, cellular immune surveillance against HTLV-I was reviewed. (1) MHC class I-restricted cytotoxic T lymphocytes (CTL) activities are detected in peripheral blood mononuclear cells (PBMC) of HAM. CTL release various proinflammatory and cytotoxic cytokines, chemokines, and proteases. Since CTL are also found in the spinal lesions of HAM, CTL may contribute to the tissue damage. In spontaneous proliferation of PBMC in HAM, CD 4/CD 8 is decreased due to the proliferation of CD 8 + CTL. CD 4/CD 8 is inversely correlated with the clinical severity of HAM. Collectively, CTL may be involved in the pathogenesis of HAM. (2) Activity and subsets of natural killer (NK) cells are lower in HTLV-I-seropositive individuals. Moreover, NK have only a weak cytotoxicity against HTLV-I infected cells. (3) Antibody-dependent cell-mediated cytotoxicity (ADCC) are impaired in HAM compared with SPC due to the suppressed effector cell activity. Since ADCC effectively lyse HTLV-I infected cells in vitro, the impaired ADCC may in part allow the spread of HTLV-I infection in HAM, and potentiation of ADCC may have an anti-HTLV-I therapeutic effect.     

HTLV-I alters the multidrug resistance associated protein 1 (ABCC1/MRP1) expression and activity in human T cells

The human T cell lymphotropic/leukaemia virus type I (HTLV-I) causes HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The multidrug resistance associated protein 1 (ABCC1) plays multiple functions in physiopathologic responses. The expression and activity of ABCC1 was studied in T lymphocytes from uninfected and HTLV-I-infected individuals (both asymptomatic and symptomatic/HAM/TSP). ABCC1 expression and activity was reduced to nearly half in T lymphocytes from infected patients compared to control lymphocytes. Only 51.6% of CD4(+) cells from HAM/TSP patients expressed ABCC1 whereas this was seen in 60.3% from asymptomatic individuals, compared to an expression of around 86% in controls. Our results suggest that ABCC1 is negatively regulated in HTVL-I infection, supplying a novel target to investigate the pathogenesis of HTLV-I.     

Interferon-beta1a therapy in human T-lymphotropic virus type I-associated neurologic disease

Human T-lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is an immune-mediated inflammatory disorder of the central nervous system. Immune activation in the host, which results from high levels of persistent antigenic stimulation and from transactivation of host immunoregulatory genes by HTLV-I, appears important in the pathogenesis of HAM/TSP. In a single-center, open-label trial, 12 patients with HAM/TSP were treated with doses of interferon-beta1a of up to 60mug twice weekly, based on its antiviral and immunomodulatory effects. Primary end points were immunological and virological measures that are potential biomarkers for HAM/TSP. Interferon-beta1a therapy reduced the HTLV-I tax messenger RNA load and the frequency of potentially pathogenic HTLV-I-specific CD8(+) cells. The HTLV-I proviral DNA load remained unchanged. Spontaneous lymphoproliferation, a marker of T-cell activation in HAM/TSP, also was reduced. Some measures of motor function were improved, and no significant clinical progression occurred during therapy. These results indicate that interferon-beta1a may beneficially affect the immune mechanisms central to the pathogenesis of HAM/TSP.     

Involvement of p38 MAPK signaling pathway in IFN-gamma and HTLV-I expression in patients with HTLV-I-associated myelopathy/tropical spastic paraparesis

We analyzed the relationship between the expression of interferon (IFN)-gamma and HTLV-I p19 antigen and activation of p38 mitogen-activated protein kinase (p38 MAPK) in two HTLV-I-infected T cell lines derived from two patients (HCT-1 and HCT-4) with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), and three HTLV-I-infected T cell lines derived from three patients with adult T cell leukemia (ATL). Expression of phosphorylated (activated)-p38 MAPK was markedly increased concomitant with high levels of both IFN-gamma and HTLV-I p19 antigen expression in both HCT-1 and HCT-4 compared with cell lines derived from ATL patients. Treatment with SB203580, a specific inhibitor of p38 MAPK, suppressed IFN-gamma and HTLV-I p19 antigen expression levels in HCT-1, HCT-4 and peripheral blood CD4(+) T cells of HAM/TSP patients. These findings strongly suggest that activation of p38 MAPK signaling pathway is involved in the up-regulation of IFN-gamma expression with high HTLV-I proviral load in HAM/TSP patients.     

Pathological mechanisms of human T-cell lymphotropic virus type I-associated myelopathy (HAM/TSP)

The recent studies have greatly improved our understanding of the pathological mechanisms of human T cell lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The pathological mechanisms of HAM/TSP based on the histopathological, immunological, and molecular analysis with emphasis on the longitudinal alterations of the disease will be discussed. Immunohistological examination revealed the existence and the activation both of HTLV-I-infected CD4+ cells and HTLV-I-specific CD8+ cytotoxic T lymphocytes in the spinal cord lesions, which suggest that they play an important role in the pathogenesis. Increased expression of several cytokines, Fas/Fas ligand, adhesion molecules, and molecules influencing T cell migration in the lesions have been reported. These cell infiltrates and cytokines they secrete in the lesions may damage bystander neural tissue. Furthermore, longitudinal alterations in the affected spinal cords suggest that the inflammatory process is gradually decreased. Epidemiological studies show that less than 5% of infected individuals develop HAM/TSP and indicate that increased proviral load of HTLV-I is a strong predictor for the development of HAM/TSP. A recent study has shown that the autoantibody for the ribonuclear protein-A1 can cross-react with HTLV-I Tax protein and inhibit neuronal firing ex vivo, indicating that a molecular mimicry of the humoral immune response may be involved in the pathogenesis of HAM/TSP. Based on these studies, two hypotheses can be proposed for the pathogenesis of HAM/TSP, where cellular and humoral immune responses both play important roles.     

Retrovirus infection and neurological disorders]

Our series of neuropathologic studies on HAM/TSP and AIDS dementia were reviewed. Studies on HAM/ TSP demonstrated chronic inflammatory process in the spinal cord, accentuated inflammation in the area with slow blood flow in the spinal cord, characteristic adhesion molecule expression for T-cell migration, apoptosis of helper T-cells in active inflammatory lesion, correlation of HTLV-I provirus amount with disease activity, and HTLV-I infection and expression of HTLV-I gene on infiltrated T-cells in the spinal cord lesion. Based on these findings, we have proposed a by-stander mechanism as a pathogenesis of HAM/TSP. HIV-1 also involves the CNS, however, its pathogenesis has not been fully studied yet. To understand the pathogenesis of AIDS dementia, we used a SIV-macaque model and demonstrated that there are two independent pathogenic processes in AIDS dementia; AIDS-dependent neuropil degeneration in the cortex caused by T-cell tropic virus, and immune response against invading virus-infected cells in the white matter caused by macrophage tropic virus. The latter mechanism is similar to that of HAM/TSP. Invasion of virus-infected blood cells inside the CNS and a gradual damage of surrounding CNS tissues caused by prolonged immune attack to these virus-infected cells may be a common pathogenic process of retrovirus induced CNS diseases.     

Cellular immune surveillance against HTLV-I infected T lymphocytes in HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP).

To investigate the cellular immune surveillance against HTLV-I infected T lymphocytes in HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP), we studied the cytotoxic T lymphocytes (CTL) activity against an HTLV-I infected human T cell line (MT-2) and the natural killer (NK) cell activity in 15 HAM patients, 6 HTLV-I carriers, and 15 controls. The activity of CTL against MT-2 cells was found to be significantly elevated in HAM compared with that in the controls. This cytotoxicity in HAM was higher than in HTLV-I carriers, although the difference was not statistically significant. There was an HLA class I restriction in this CTL activity against MT-2 cells in HAM. On the other hand, NK cell activity was significantly lower in HAM than in controls. Cold target inhibition studies suggested that NK cells could not lyse MT-2 cells effectively. There was a positive correlation between the CTL activity against MT-2 cells and the serum antibody titers to HTLV-I in HAM.     

Downregulation of IL-10 secretion and enhanced antigen-presenting abilities following HTLV-I infection of T cells

Human T-cell lymphotropic virus type I (HTLV-I) may infect up to 10% of peripheral blood T cells in patients with HTLV-I myelopathy. To examine the impact of HTLV-I infection on the abilities of T cells to present and respond to peptide antigen, we HTLV-I infected and subcloned a myelin basic protein peptide 84-102 (MBP p84-102)-specific T-cell clone. The HTLV-I-infected subclones displayed spontaneous clonal proliferation, as observed in T-cell clones from HTLV-I myelopathy patients, indicating virally induced T-cell activation. In the presence of soluble peptide antigen, the HTLV-I-infected T cells responded to a 100-fold lower peptide concentration than did the uninfected parental T-cell clone. This response was not mediated by virally induced priming for hyperresponsiveness because peptide-pulsed Epstein-Barr Virus (EBV)-transformed B cells or HLA-DR2/B7-1 or B7-2 transfected Chinese hamster ovary (CHO) cells activated uninfected T cells at least twofold better than HTLV-I-infected T cells. Instead, the HTLV-I-infected T cells were better antigen-presenting cells when compared to activated, uninfected T cells and the enhanced ability to present antigen correlated with a marked upregulation in surface expression of major histocompatibility complex (MHC) class II and LFA-3. The ability of HTLV-I-infected T cells to activate other T cells was not simply caused by their state of activation. In contrast with activated and uninfected parental T cells, HTLV-I-infected T cells had downregulated secretion of the immunosuppressive cytokine IL-10, whereas interferon-γ secretion was significantly increased. Because IL-10 inhibits human CD8 T-cell proliferation, the enhanced antigen-presenting abilities of HTLV-I-infected T cells and the downregulation of IL-10 may be important contributors to the general immune activation and potentially to the remarkably high frequency of cytotoxic T cells observed in HTLV-I myelopathy patients. © 1996 Wiley-Liss, Inc.     

Limited T cell receptor usage by HTLV-I tax-specific, HLA class I restricted cytotoxic T lymphocytes from patients with HTLV-I associated neurological disease

T cell receptor (TCR) Vα and Vβ chain usage of HTLV-I tax-specific, HLA class I restricted CD8⁺ cytotoxic T cells (CTL) was determined from lymphocytes obtained from peripheral blood of patients with HTLV-I associated neurological disease. To characterize TCR repertoire, CD8⁺ lymphocytes from peripheral blood were cloned in limiting dilution, and the resulting wells were screened for HTLV-I-specific precursor CTL activity. RNA was isolated from HLA-A2 restricted HTLV-I tax peptide-specific (tax 11–19; LLFGYPVYV) CD8⁺ CTL lines and cDNA was analyzed by PCR amplification using Vα and Vβ chain family-specific oligonucleotide primers. The results indicate that CD8⁺ cytotoxic T cell lines from HLA-A2 HAM/TSP patients express a limited repertoire of T cell receptor chains which may correlate with duration and severity of disease. The restricted use of TCR genes expressed by antigen-specific CTL may play a critical role in the pathogenesis of HAM/TSP and may be of value in developing immunotherapeutic strategies that focus on eliminating these cells or inhibiting their activity.     

Neuronal molecular mimicry in immune-mediated neurologic disease

Molecular mimicry is implicated in the pathogenesis of autoimmune diseases such as diabetes mellitus, rheumatoid arthritis, and multiple sclerosis (MS). Cellular and antibody-mediated immune responses to shared viral-host antigens have been associated with the development of disease in these patients. Patients infected with human T-lymphotropic virus type I (HTLV-I) develop HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), an immunemediated disorder of the central nervous system (CNS) that resembles some forms of MS. Damage to neuronal processes in the CNS of HAM/TSP patients is associated with an activated cellular and antibody-mediated immune response. In this study, IgG isolated from HAM/TSP patients was immunoreactive with uninfected neurons and this reactivity was HTLV-I specific. HAM/TSP IgG stained uninfected neurons in human CNS and cell lines but not nonneuronal cells. Neuronal western blots showed IgG reactivity with a single 33-kd band in all HAM/TSP patients tested. By contrast, no neuron-specific IgG reactivity could be demonstrated from HTLV-I seronegative controls and, more important, from HTLV-I seropositive, neurologically asymptomatic individuals. Both immunocytochemical staining and western blot reactivity were abolished by preincubating HAM/TSP IgG with HTLV-I protein lysate but not by control proteins. Staining of CNS tissue by a monoclonal antibody to HTLV-I tax (an immunodominant HTLV-I antigen) mimicked HAM/TSP IgG immunoreactivity. There was no staining by control antibodies. Absorption of HAM/TSP IgG with recombinant HTLV-I tax protein or preincubation of CNS tissue with the monoclonal antibody to HTLV-I tax abrogated the immunocytochemical and western blot reactivity of HAM/TSP IgG. Furthermore, in situ human IgG localized to neurons in HAM/TSP brain but not in normal brain. These data indicate that HAM/TSP patients develop an antibody response that targets uninfected neurons, yet reactivity is blocked by HTLV-I, suggesting viral-specific autoimmune reactivity to the CNS, the damaged target organ in HAM/TSP.