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

Immunopathogenesis and Cellular Interactions in Human T-Cell Leukemia Virus Type 1 Associated Myelopathy/Tropical Spastic Paraparesis

HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP) is a neuropathological disorder in 1–3% of individuals infected with Human T-lymphotropic virus 1 (HTLV-1). This condition is characterized by progressive spastic lower limb weakness and paralysis, lower back pain, bladder incontinence, and mild sensory disturbances resembling spinal forms of multiple sclerosis. This disease also causes chronic disability and is therefore associated with high health burden in areas where HTLV-1 infection is endemic. Despite various efforts in understanding the virus and discovery of novel diagnostic markers, and cellular and viral interactions, HAM/TSP management is still unsatisfactory and mainly focused on symptomatic alleviation, and it hasn’t been explained why only a minority of the virus carriers develop HAM/TSP. This comprehensive review focuses on host and viral factors in association with immunopathology of the disease in hope of providing new insights for drug therapies or other forms of intervention.

Evaluation of T Regulatory Lymphocytes Transcription Factors in HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP) Patients

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is an aggressive neurological disease. The CD4⁺CD25⁺ T cell population plays pivotal roles in the maintenance of immunological tolerance and prevention of such autoimmune diseases. In the current study, proviral load (PVL), factor forkhead box p3 (Foxp3), and glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) gene expression and regulatory T cells (Tregs) counts of 21 HAM/TSP patients and 16 HTLV-1 healthy carriers (ACs) were measured using real-time PCR, TaqMan method, and flow cytometry. The demographic, history of disease, and severity of myelopathy were assessed by a checklist and the Osame motor disability score (OMDS). The mean OMDS for HAM/TSP was 4.82 ± 2.37 which had no significant correlation with Treg count or the expression of Foxp3, GITR, and PVL. The CD4⁺CD25⁺ cell counts had no significant differences between HAM/TSP and ACs. Findings revealed a higher PVL in HAM/TSPs (313.36 copies/10⁴) compared to ACs (144.93 copies/10⁴, p = 0.035). The Foxp3 and GITR mRNA levels were lower in HAM/TSP patients (11.78 and 13.80, respectively) than those in healthy carriers (18.44 and 21.00, p = 0.041 and 0.03, respectively). There was a significant correlation between Treg frequency and Foxp3 gene expression (R = 0.67, p = 0.006) and GITR and Foxp3 (R = 0.84, p = 0.042) in HAM/TSP patients. Furthermore, the transcription factors have strong correlations with CD4⁺CD25⁺ T cell frequencies. These findings suggest that HTLV-1 infection can modify the expression of main functional transcription factors, FOXP3 and GITR, which may lead to immune response deterioration of Tregs and consequently HAM/TSP manifestation.

Dynamic acquisition of HTLV-1 tax protein by mononuclear phagocytes: Role in neurologic disease

Pathology of HTLV-1 associated myelopathy/Tropical spastic paraparesis (HAM/TSP) is believed to be the result of "bystander damage" involving effector CD8 (+) T lymphocytes (CTLs) killing of virus infected cells. But the specific cellular events leading up to tissue injury are still unclear. Here, we developed the Microscopy Imaging of Cytotoxic T lymphocyte assay with Fluorescence emission (MI-CaFé), an optimized visualization analysis to explore the interactions between CTLs and virus infected or viral antigen presenting target cells. Various cell-to-cell formations can be observed and our results demonstrate elevated frequencies of CTL-target cell conjugates in HAM/TSP patient PBMCs compared to control PBMCs. Furthermore, HTLV-1 Tax protein expression can be localized at the cell-cell junctions and also tracked moving from an infected cell to a CD14 (+) mononuclear phagocyte (MP). Activation of CD14 (+) MPs in HAM/TSP patient PBMCs and antigenic presentation of HTLV-1 Tax by MPs can be inferred by their spontaneous cytotoxicity after 18h of in vitro culture. Given that CD4 (+) T lymphocytes are the primary reservoirs of HTLV-1 and MPs are scavenger cells responsible for pathogen clearance, spontaneous cytotoxicity against MPs in HAM/TSP PBMCs suggests a mechanism of chronic inflammation, secondary to low level of persistent virus infection within the central nervous system.

Visualization of HTLV-1-specific cytotoxic T lymphocytes in the spinal cords of patients with HTLV-1-associated myelopathy/tropical spastic paraparesis

Activated human T-lymphotropic virus type-1 (HTLV-1)–specific CD8-positive cytotoxic T lymphocytes (CTLs) are markedly increased in the periphery of patients with HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP), an HTLV-1–induced inflammatory disease of the CNS. Although virus-specific CTLs play a pivotal role to eliminate virus-infected cells, the potential role of HTLV-1–specific CTLs in the pathogenesis of HAM/TSP remains unclear. To address this issue, we evaluated the infiltration of HTLV-1–specific CTLs and the expression of HTLV-1 proteins in the spinal cords of 3 patients with HAM/TSP. Confocal laser scanning microscopy with our unique staining procedure made it possible to visualize HTLV-1–specific CTLs infiltrating the CNS of the HAM/TSP patients. The frequency of HTLV-1–specific CTLs was more than 20% of CD8-positive cells infiltrating the CNS. In addition, HTLV-1 proteins were detected in CD4-positive infiltrating T lymphocytes but not CNS resident cells. Although neurons were generally preserved, apoptotic oligodendrocytes were frequently in contact with CD8-positive cells; this likely resulted in demyelination. These findings suggest that the immune responses of the CTLs against HTLV-1–infected CD4-positive lymphocytes migrating into the CNS resulted in bystander neural damage.

Genes related to antiviral activity, cell migration, and lysis are differentially expressed in CD4(+) T cells in human t cell leukemia virus type 1-associated myelopathy/tropical spastic paraparesis patients

Human T cell leukemia virus type 1 (HTLV-1) preferentially infects CD4(+) T cells and these cells play a central role in HTLV-1 infection. In this study, we investigated the global gene expression profile of circulating CD4(+) T cells from the distinct clinical status of HTLV-1-infected individuals in regard to TAX expression levels. CD4(+) T cells were isolated from asymptomatic HTLV-1 carrier (HAC) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients in order to identify genes involved in HAM/TSP development using a microarray technique. Hierarchical clustering analysis showed that healthy control (CT) and HTLV-1-infected samples clustered separately. We also observed that the HAC and HAM/TSP groups clustered separately regardless of TAX expression. The gene expression profile of CD4(+) T cells was compared among the CT, HAC, and HAM/TSP groups. The paxillin (Pxn), chemokine (C-X-C motif ) receptor 4 (Cxcr4), interleukin 27 (IL27), and granzyme A (Gzma) genes were differentially expressed between the HAC and HAM/TSP groups, regardless of TAX expression. The perforin 1 (Prf1) and forkhead box P3 (Foxp3) genes were increased in the HAM/TSP group and presented a positive correlation to the expression of TAX and the proviral load (PVL). The frequency of CD4(+)FOXP3(+) regulatory T cells (Treg) was higher in HTLV-1-infected individuals. Foxp3 gene expression was positively correlated with cell lysis-related genes (Gzma, Gzmb, and Prf1). These findings suggest that CD4(+) T cell activity is distinct between the HAC and HAM/TSP groups.

The combination of arsenic, interferon-alpha, and zidovudine restores an "immunocompetent-like" cytokine expression profile in patients with adult T-cell leukemia lymphoma

BACKGROUND

HTLV-I associated adult T-cell leukemia/lymphoma (ATL) carries a dismal prognosis due to chemo-resistance and immuno-compromised micro-environment. The combination of zidovudine and interferon-alpha (IFN) significantly improved survival in ATL. Promising results were reported by adding arsenic trioxide to zidovudine and IFN.

RESULTS

Here we assessed Th1/Th2/T(reg) cytokine gene expression profiles in 16 ATL patients before and 30 days after treatment with arsenic/IFN/zidovudine, in comparison with HTLV-I healthy carriers and sero-negative blood donors. ATL patients at diagnosis displayed a T(reg)/Th2 cytokine profile with significantly elevated transcript levels of Foxp3, interleukin-10 (IL-10), and IL-4 and had a reduced Th1 profile evidenced by decreased transcript levels of interferon-γ (IFN-γ) and IL-2. Most patients (15/16) responded, with CD4⁺CD25⁺ cells significantly decreasing after therapy, paralleled by decreases in Foxp3 transcript. Importantly, arsenic/IFN/zidovudine therapy sharply diminished IL-10 transcript and serum levels concomittant with decrease in IL-4 and increases in IFN-γ and IL-2 mRNA, whether or not values were adjusted to the percentage of CD4⁺CD25⁺ cells. Finally, IL-10 transcript level negatively correlated with clinical response at Day 30.

CONCLUSIONS

The observed shift from a T(reg)/Th2 phenotype before treatment toward a Th1 phenotype after treatment with arsenic/IFN/zidovudine may play an important role in restoring an immuno-competent micro-environment, which enhances the eradication of ATL cells and the prevention of opportunistic infections.

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

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

Immunological homeostasis of the eye

Uveitis is a sight-threatening disease caused by autoimmune or infection-related immune responses. Studies in experimental autoimmune uveitis and in human diseases imply that activated CD4(+) T cells, Th1 and Th17 cells, play an effector role in ocular inflammation. The eye has a unique regional immune system to protect vision-related cells and tissues from these effector T cells. The immunological balance between the pathogenic CD4(+) T cells and regional immune system in the eye contributes to the maintenance of ocular homeostasis and good vision. Current studies have demonstrated that ocular parenchymal cells at the inner surface of the blood-ocular barrier, i.e. corneal endothelial (CE) cells, iris pigment epithelial (PE) cells, ciliary body PE cells, and retinal PE cells, contribute to the regional immune system of the eye. Murine ocular resident cells directly suppress activation of bystander T cells and production of inflammatory cytokines. The ocular resident cells possess distinct properties of immunoregulation that are related to disparate anatomical location. CE cells and iris PE cells, which are located at the anterior segment of the eye and face the aqueous humor, suppress activation of T cells via cell-to-cell contact mechanisms, whereas retinal PE cells suppress the activation of T cells via soluble factors. In addition to direct immune suppression, the ocular resident cells have another unique immunosuppressive property, the induction of CD25(+)Foxp3(+) Treg cells that also suppress the activation of bystander T cells. Iris PE cells convert CD8(+) T cells into Treg cells, while retinal PE cells convert CD4(+) T cells greatly and CD8(+) T cells moderately into Treg cells. CE cells also convert both CD4(+) T cells and CD8(+) T cells into Treg cells. The immunomodulation by ocular resident cells is mediated by various soluble or membrane-bound molecules that include TGF-β TSP-1, B7-2 (CD86), CTLA-2α, PD-L1 (B7-H1), galectin 1, pigment epithelial-derived factor PEDF), GIRTL, and retinoic acid. Human retinal PE cells also possess similar immune properties to induce Treg cells. Although there are many issues to be answered, human Treg cells induced by ocular resident cells such as retinal PE cells and related immunosuppressive molecules can be applied as immune therapy for refractive autoimmune uveitis in humans in the future.

Cytomegalovirus-specific T-cell reactivity in biliary atresia at the time of diagnosis is associated with deficits in regulatory T cells

Biliary atresia (BA) is a progressive, inflammatory cholangiopathy that culminates in fibrosis of extrahepatic and intrahepatic bile ducts. A leading theory on the pathogenesis of BA is that the bile duct damage is initiated by a virus infection, followed by a bile duct-targeted autoimmune response. One mechanism of autoimmunity entails a diminished number or function of regulatory T cells (Tregs). The aim of this study was to identify potential virus-specific liver T cells from infants with BA at the time of diagnosis, implicating the virus involved in early bile duct damage. A subaim was to determine if the presence of virus infection was associated with quantitative changes in Tregs. Liver T cells from BA and control patients were cultured with antigen-presenting cells in the presence of a variety of viral or control proteins. 56% of BA patients had significant increases in interferon-gamma-producing liver T cells in response to cytomegalovirus (CMV), compared with minimal BA responses to other viruses or the control group CMV response. In addition, a positive correlation between BA plasma CMV immunoglobulin M (IgM) and liver T-cell CMV reactivity was identified. Investigation of peripheral blood Tregs revealed significant deficits in Treg frequencies in BA compared with controls, with marked deficits in those BA patients who were positive for CMV.

CONCLUSION

Liver T-cell responses to CMV were identified in the majority of BA patients at diagnosis, suggesting perinatal CMV infection as a plausible initiator of bile duct damage. Deficiency of Tregs in BA implies decreased inhibition of inflammation and autoreactivity, potentially allowing for exaggerated bile duct injury.

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

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

Human T-lymphotropic virus type 1 (HTLV-1) and regulatory T cells in HTLV-1-associated neuroinflammatory disease

Human T-lymphotropic virus type 1 (HTLV-1) is a retrovirus that is the causative agent of adult T cell leukemia/lymphoma (ATL) and associated with multiorgan inflammatory disorders, including HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and uveitis. HTLV-1-infected T cells have been hypothesized to contribute to the development of these disorders, although the precise mechanisms are not well understood. HTLV-1 primarily infects CD4(+) T helper (Th) cells that play a central role in adaptive immune responses. Based on their functions, patterns of cytokine secretion, and expression of specific transcription factors and chemokine receptors, Th cells that are differentiated from naïve CD4(+) T cells are classified into four major lineages: Th1, Th2, Th17, and T regulatory (Treg) cells. The CD4(+)CD25(+)CCR4(+) T cell population, which consists primarily of suppressive T cell subsets, such as the Treg and Th2 subsets in healthy individuals, is the predominant viral reservoir of HTLV-1 in both ATL and HAM/TSP patients. Interestingly, CD4(+)CD25(+)CCR4(+) T cells become Th1-like cells in HAM/TSP patients, as evidenced by their overproduction of IFN-γ, suggesting that HTLV-1 may intracellularly induce T cell plasticity from Treg to IFN-γ(+) T cells. This review examines the recent research into the association between HTLV-1 and Treg cells that has greatly enhanced understanding of the pathogenic mechanisms underlying immune dysregulation in HTLV-1-associated neuroinflammatory disease.

Neuroimmunity of HTLV-I Infection

Human T-lymphotrophic virus type I (HTLV-I) is an oncogenic retrovirus and its infection is associated with a variety of human diseases including HTLV-I-associated myelopathy/tropic spastic paraparesis (HAM/TSP). Large numbers of epidemiological, virological, immunological, and clinical studies on HTLV-I- and HTLV-I-associated diseases have been published, although the pathogenesis of HAM/TSP remains to be fully understood. In the last several years, researchers have shown that several key factors are important in HTLV-I-associated neurologic disease including high HTLV-I proviral load and a strong immune response to HTLV-I. Here, we review pathophysiological findings on HAM/TSP and focus on viral-host immune responses to the virus in HTLV-I infected individuals. In particular, the role of HTLV-I-specific CD8+ T cell response is highlighted.

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

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

Changes in T cell phenotype and activated MAPKs are correlated to impaired cellular responses to antigens and glucocorticoids during HTLV-I infection

Lymphocytes of human T-lymphotropic virus type-I (HTLV-I) infected patients were previously found tolerant to mitogenic stimuli as well as glucocorticoid treatment. These data suggest that common signaling events are impaired during this infection. The underlying mechanisms of these phenomena may include changes in cellular composition, cytokine milieu and the differential activation of mitogen-activated protein kinases (MAPKs). We investigated the role of (i) p38 and ERK MAPKs, (ii) lymphocyte subpopulations, (iii) and cytokines implicated in antigen or glucocorticoid-induced immunomodulation. Twenty-one asymptomatic carriers (AC), 19 patients with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and 21 healthy subjects took part in this study. Lymphocytes were isolated and cultured in vitro to assess lymphocyte proliferation and sensitivity to dexamethasone. The expression of phospho-MAPKs, lymphocyte subsets and cytokines were assessed by flow cytometry. Patients with HAM/TSP had a higher p38/ERK ratio (p<0.05) associated with a reduced response to mitogens (phytohaemagglutinin or PMA+ionomycin) (p<0.001) and higher sensitivity to dexamethasone (p<0.05). HAM/TSP patients presented increased frequency of activated T cells and CD8(+)CD28(-) regulatory T cells, being negatively related to the mitogenic response. These data suggest that multiple underlying mechanisms could be involved with HTLV-related changes in cellular response to mitogens and glucocorticoids.

Abnormally high levels of virus-infected IFN-gamma+ CCR4+ CD4+ CD25+ T cells in a retrovirus-associated neuroinflammatory disorder

Background

Human T-lymphotropic virus type 1 (HTLV-1) is a human retrovirus associated with both HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), which is a chronic neuroinflammatory disease, and adult T-cell leukemia (ATL). The pathogenesis of HAM/TSP is known to be as follows: HTLV-1-infected T cells trigger a hyperimmune response leading to neuroinflammation. However, the HTLV-1-infected T cell subset that plays a major role in the accelerated immune response has not yet been identified.

Principal Findings

Here, we demonstrate that CD4⁺CD25⁺CCR4⁺ T cells are the predominant viral reservoir, and their levels are increased in HAM/TSP patients. While CCR4 is known to be selectively expressed on T helper type 2 (Th2), Th17, and regulatory T (Treg) cells in healthy individuals, we demonstrate that IFN-γ production is extraordinarily increased and IL-4, IL-10, IL-17, and Foxp3 expression is decreased in the CD4⁺CD25⁺CCR4⁺ T cells of HAM/TSP patients as compared to those in healthy individuals, and the alteration in function is specific to this cell subtype. Notably, the frequency of IFN-γ-producing CD4⁺CD25⁺CCR4⁺Foxp3⁻ T cells is dramatically increased in HAM/TSP patients, and this was found to be correlated with disease activity and severity.

Conclusions

We have defined a unique T cell subset—IFN-γ⁺CCR4⁺CD4⁺CD25⁺ T cells—that is abnormally increased and functionally altered in this retrovirus-associated inflammatory disorder of the central nervous system.