Induction of HLA class I and class II expression in human T-lymphotropic virus type I-infected neuroblastoma cells

STLV-1 Commonly Targets Neurons in the Brain of Asymptomatic Non-Human Primates

The human T-cell leukemia virus (HTLV)-1 is responsible for an aggressive neurodegenerative disease (HAM/TSP) and multiple neurological alterations. The capacity of HTLV-1 to infect central nervous system (CNS) resident cells, together with the neuroimmune-driven response, has not been well-established. Here, we combined the use of human induced pluripotent stem cells (hiPSC) and of naturally STLV-1-infected nonhuman primates (NHP) as models with which to investigate HTLV-1 neurotropism. Hence, neuronal cells obtained after hiPSC differentiation in neural polycultures were the main cell population infected by HTLV-1. Further, we report the infection of neurons with STLV-1 in spinal cord regions as well as in brain cortical and cerebellar sections of postmortem NHP. Additionally, reactive microglial cells were found in infected areas, suggesting an immune antiviral response. These results emphasize the need to develop new efficient models by which to understand HTLV-1 neuroinfection and suggest an alternative mechanism that leads to HAM/TSP.

Development of a cytotoxic T-cell assay in rabbits to evaluate early immune response to human T-lymphotropic virus type 1 infection

Human T-lymphotropic virus type 1 (HTLV-1) infection causes adult T-cell lymphoma/leukemia (ATL) following a prolonged clinical incubation period, despite a robust adaptive immune response against the virus. Early immune responses that allow establishment of the infection are difficult to study without effective animal models. We have developed a cytotoxic T-lymphocyte (CTL) assay to monitor the early events of HTLV-1 infection in rabbits. Rabbit skin fibroblast cell lines were established by transformation with a plasmid expressing simian virus 40 (SV40) large T antigen and used as autochthonous targets (derived from same individual animal) to measure CTL activity against HTLV-1 infection in rabbits. Recombinant vaccinia virus (rVV) constructs expressing either HTLV-1 envelope surface unit (SU) glycoprotein 46 or Tax proteins were used to infect fibroblast targets in a (51)Cr-release CTL assay. Rabbits inoculated with Jurkat T cells or ACH.2 cells (expressing ACH HTLV-1 molecule clone) were monitored at 0, 2, 4, 6, 8, 13, 21, and 34 wk post-infection. ACH.2-inoculated rabbits were monitored serologically and for viral infected cells following ex vivo culture. Proviral load analysis indicated that rabbits with higher proviral loads had significant CTL activity against HTLV-1 SU as early as 2 wk post-infection, while both low- and high-proviral-load groups had minimal Tax-specific CTL activity throughout the study. This first development of a stringent assay to measure HTLV-1 SU and Tax-specific CTL assay in the rabbit model will enhance immunopathogenesis studies of HTLV-1 infection. Our data suggest that during the early weeks following infection, HTLV-1-specific CTL responses are primarily targeted against Env-SU.

Role of resident CNS cell populations in HTLV-1-associated neuroinflammatory disease

Human T cell leukemia virus type 1 (HTLV-1), the first human retrovirus discovered, is the etiologic agent for a number of disorders; the two most common pathologies include adult T cell leukemia (ATL) and a progressive demyelinating neuroinflammatory disease, HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The neurologic dysfunction associated with HAM/TSP is a result of viral intrusion into the central nervous system (CNS) and the generation of a hyperstimulated host response within the peripheral and central nervous system that includes expanded populations of CD4+ and CD8+ T cells and proinflammatory cytokines/chemokines in the cerebrospinal fluid (CSF). This robust, yet detrimental immune response likely contributes to the death of myelin producing oligodendrocytes and degeneration of neuronal axons. The mechanisms of neurological degeneration in HAM/TSP have yet to be fully delineated in vivo and may involve the immunogenic properties of the HTLV-1 transactivator protein Tax. This comprehensive review characterizes the available knowledge to date concerning the effects of HTLV-1 on CNS resident cell populations with emphasis on both viral and host factors contributing to the genesis of HAM/TSP.

Human T-cell lymphotropic virus type 1 infection of CD34+ hematopoietic progenitor cells induces cell cycle arrest by modulation of p21(cip1/waf1) and survivin

Human T-cell lymphotropic virus type 1 (HTLV-1) is an oncogenic retrovirus and the etiologic agent of adult T-cell leukemia (ATL), an aggressive CD4(+) malignancy. HTLV-2 is highly homologous to HTLV-1; however, infection with HTLV-2 has not been associated with lymphoproliferative diseases. Although HTLV-1 infection of CD4(+) lymphocytes induces cellular replication and transformation, infection of CD34(+) human hematopoietic progenitor cells (HPCs) strikingly results in G(0)/G(1) cell cycle arrest and suppression of in vitro clonogenic colony formation by induction of expression of the cdk inhibitor p21(cip1/waf1) (p21) and concurrent repression of survivin. Immature CD34(+)/CD38(-) hematopoietic stem cells (HSCs) were more susceptible to alterations of p21 and survivin expression as a result of HTLV-1 infection, in contrast to more mature CD34(+)/CD38(+) HPCs. Knockdown of p21 expression in HTLV-1-infected CD34(+) HPCs partially abrogated cell cycle arrest. Notably, HTLV-2, an HTLV strain that is not associated with leukemogenesis, does not significantly modulate p21 and survivin expression and does not suppress hematopoiesis from CD34(+) HPCs in vitro. We speculate that the remarkable differences in the activities displayed by CD34(+) HPCs following infection with HTLV-1 or HTLV-2 suggest that HTLV-1 uniquely exploits cell cycle arrest mechanisms to establish a latent infection in hematopoietic progenitor/hematopoietic stem cells and initiates preleukemic events in these cells, which eventually results in the manifestation of ATL.

Human T-cell leukemia virus type 1 (HTLV-1) p12I down-modulates ICAM-1 and -2 and reduces adherence of natural killer cells, thereby protecting HTLV-1-infected primary CD4+ T cells from autologous natural killer cell-mediated cytotoxicity despite the reduction of major histocompatibility complex class I molecules on infected cells

Although natural killer (NK) cell-mediated control of viral infections is well documented, very little is known about the ability of NK cells to restrain human T-cell leukemia virus type 1 (HTLV-1) infection. In the current study we show that NK cells are unable to kill HTLV-1-infected primary CD4+ T cells. Exposure of NK cells to interleukin-2 (IL-2) resulted in only a marginal increase in their ability to kill HTLV-1-infected primary CD4+ T cells. This inability of NK cells to kill HTLV-1-infected CD4+ T cells occurred despite the down-modulation of major histocompatibility complex (MHC) class I molecules, one of the ligands for the major NK cell inhibitory receptor, by HTLV-1 p12(I) on CD4+ T cells. One reason for this diminished ability of NK cells to kill HTLV-1-infected cells was the decreased ability of NK cells to adhere to HTLV-1-infected cells because of HTLV-1 p12(I)-mediated down-modulation of intercellular adhesion molecule 1 (ICAM-1) and ICAM-2. We also found that HTLV-1-infected CD4+ T cells did not express ligands for NK cell activating receptors, NCR and NKG2D, although they did express ligands for NK cell coactivating receptors, NTB-A and 2B4. Thus, despite HTLV-1-mediated down-modulation of MHC-I molecules, HTLV-1-infected primary CD4+ T cells avoids NK cell destruction by modulating ICAM expression and shunning the expression of ligands for activating receptors.

Proinflammatory cytokine gene induction by human T-cell leukemia virus type 1 (HTLV-1) and HTLV-2 Tax in primary human glial cells

Infection with human T-cell leukemia virus type 1 (HTLV-1) can result in the development of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic inflammatory disease of the central nervous system (CNS). HTLV-2 is highly related to HTLV-1 at the genetic level and shares a high degree of sequence homology, but infection with HTLV-2 is relatively nonpathogenic compared to HTLV-1. Although the pathogenesis of HAM/TSP remains to be fully elucidated, previous evidence suggests that elevated levels of the proinflammatory cytokines in the CNS are associated with neuropathogenesis. We demonstrate that HTLV-1 infection in astrogliomas results in a robust induction of interleukin-1beta (IL-1beta), IL-1alpha, tumor necrosis factor alpha (TNF-alpha), TNF-beta, and IL-6 expression. HTLV encodes for a viral transcriptional transactivator protein named Tax that also induces the transcription of cellular genes. To investigate and compare the effects of Tax1 and Tax2 expression on the dysregulation of proinflammatory cytokines, lentivirus vectors were used to transduce primary human astrocytomas and oligodendrogliomas. The expression of Tax1 in primary human astrocytomas and oligodendrogliomas resulted in significantly higher levels of proinflammatory cytokine gene expression compared to Tax2. Notably, Tax1 expression uniquely sensitized primary human astrocytomas to apoptosis. A Tax2/Tax1 chimera encoding the C-terminal 53 amino acids of the Tax1 fused to the Tax2 gene (Tax(221)) demonstrated a phenotype that resembled Tax1, with respect to proinflammatory cytokine gene expression and sensitization to apoptosis. The patterns of differential cytokine induction and sensitization to apoptosis displayed by Tax1 and Tax2 may reflect differences relating to the heightened neuropathogenicity associated with HTLV-1 infection and the development of HAM/TSP.

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.

Simian retrovirus infections: potential confounding variables in primate toxicology studies

Various species of nonhuman primates are natural hosts for 6 exogenous retroviruses, including gibbon-ape leukemia virus (GaLV), simian sarcoma virus, simian T-lymphotropic virus (STLV), simian immunodeficiency virus (SIV), simian type D retrovirus (SRV), and simian foamy virus (SFV). These viruses establish persistent infections with a broad spectrum of pathogenic potential, ranging from highly pathogenic to nonpathogenic, depending on various host, virus, and environmental factors. Latent or subclinical infections are common, and various procedures associated with experimental protocols may lead to virus reactivation and disease. Adverse effects on toxicologic research by undetected retroviral infections can occur in several ways, including loss of experimental subjects (and statistical power) due to increased morbidity and mortality. In addition, results may be confounded by virus-induced clinical abnormalities, histologic lesions, alteration of physiologic parameters and responses, and interference with in vitro assays and/or destruction of primary cell cultures. Key clinical and epidemiological features of several important retroviruses are reviewed, with emphasis on viruses infecting species of macaques most commonly used as research subjects in primate toxicology studies. Examples of actual and potential confounding of toxicologic studies by retroviruses are discussed, including altered cytokine profiles in healthy STLV carriers, and clinical and pathological abnormalities induced by SRV infection. Adequate prestudy viral screening is critical to exclude retrovirus-infected primates from toxicologic research protocols and prevent potential confounding of research results.

Immunopathogenesis of human T cell lymphotropic virus type I-associated neurologic disease

This review focuses on current approaches to understanding the immunopathogenesis of human T cell lymphotropic virus (HTLV) type I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) based on newly developed molecular and immunologic techniques that have been adapted to studies of HTLV-I proviral load, HTLV-I mRNA, and HTLV-I tax-specific CD8 T cells. These methods enable researchers to study previously inaccessible aspects of this disease and allow a more detailed analysis of virus/host immune responses as they relate to disease specificity in this disorder. The role of HTLV-I-specific CD8 T cell immune responses is highlighted. The elucidation of the immunopathology of HAM/TSP will enhance our understanding of other HTLV-I-associated disorders plus other neurologic, hematologic, and inflammatory diseases for which viral etiologies have been suggested.

HTLV type 1 Tax transduction in microglial cells and astrocytes by lentiviral vectors

Infection with human T cell leukemia virus type 1 (HTLV-1) can result in the development of HAM/TSP, a nonfatal, chronic inflammatory disease involving neuronal degeneration and demyelination of the central nervous system. Elevated levels of the proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), and IL-1 observed in the cerebrospinal fluid of HAM-TSP patients suggest that cytokine dysregulation within the CNS is involved in neuropathogenesis. HTLV-1 infection and enhanced expression of TNF-alpha by microglial cells, astrocytes, and macrophages has been hypothesized to lead to the destruction of myelin and oligodendrocytes in the CNS. Although the association of HTLV-2 infection and development of neurological disease is more tenuous, HTLV-2 has also been found to be associated with peripheral neuropathies. To investigate the roles of HTLV Tax(1) and Tax(2) in the induction of cytokine disregulation in these cell types, we are currently developing gene delivery vectors based on human immunodeficiency virus type-1 (HIV-1) capable of stably coexpressing the HTLV-1 or -2 tax and eGFP reporter genes in primary human cells. Transduction frequencies of up to 50%, as assessed by eGFP expression, can be achieved in human monocyte-derived macrophages and in explanted cultures of human microglia. Preliminary data suggest that Tax(1) expression is sufficient to up-regulate the proinflammatory cytokine profile in explanted human microglial cells. Future experiments will compare and evaluate the effect of tax(1) and tax(2) gene expression on the cellular proinflammatory cytokine expression profile, as well as demonstrate the effects of transducing human fetal astrocytes and PBMC-derived macrophages.

Human T cell leukemia virus type-I and rheumatoid arthritis

HTLV-I is a retrovirus known as an oncogenic virus for human. This virus, initially found as a causative agent for adult T cell leukemia, has been lately focused as a causative virus for several autoimmune disorders. Here we described the characteristics of polyarthritis in HTLV-I careers, which is indistinguishable from idiopathic rheumatoid arthritis (RA). The relationship between arthritis and this virus was clearly proved by epidimiological study. Moreover, we presented transactivating gene of this virus, tax, is responsible for proliferation of synovial cells. This was proved by Tax transgenic mice, which present chronic destructive arthritis resembling human RA. Other autoimmune disorders, such as Sjögren's syndrome and uveitis, are also reviewed.

Syncytium-inhibiting monoclonal antibodies produced against human T-cell lymphotropic virus type 1-infected cells recognize class II major histocompatibility complex molecules and block by protein crowding

Four new monoclonal antibodies (MAbs) that inhibit human T-cell lymphotropic virus type 1 (HTLV-1)-induced syncytium formation were produced by immunizing BALB/c mice with HTLV-1-infected MT2 cells. Immunoprecipitation studies and binding assays of transfected mouse cells showed that these MAbs recognize class II major histocompatibility complex (MHC) molecules. Previously produced anti-class II MHC antibodies also blocked HTLV-1-induced cell fusion. Coimmunoprecipitation and competitive MAb binding studies indicated that class II MHC molecules and HTLV-1 envelope glycoproteins are not associated in infected cells. Anti-MHC antibodies had no effect on human immunodeficiency virus type 1 (HIV-1) syncytium formation by cells coinfected with HIV-1 and HTLV-1, ruling out a generalized disruption of cell membrane function by the antibodies. High expression of MHC molecules suggested that steric effects of bound anti-MHC antibodies might explain their inhibition of HTLV-1 fusion. An anti-class I MHC antibody and a polyclonal antibody consisting of several nonblocking MAbs against other molecules bound to MT2 cells at levels similar to those of class II MHC antibodies, and they also blocked HTLV-1 syncytium formation. Dose-response experiments showed that inhibition of HTLV-1 syncytium formation correlated with levels of antibody bound to the surface of infected cells. The results show that HTLV-1 syncytium formation can be blocked by protein crowding or steric effects caused by large numbers of immunoglobulin molecules bound to the surface of infected cells and have implications for the structure of the cellular HTLV-1 receptor(s).

Astrocyte-specific expression of human T-cell lymphotropic virus type 1 (HTLV-1) Tax: induction of tumor necrosis factor alpha and susceptibility to lysis by CD8+ HTLV-1-specific cytotoxic T cells

Human T-cell lymphotropic virus type 1 (HTLV-1) is associated with a chronic neurological disease termed HTLV-1-associated myelopathy/tropical spastic paraperesis (HAM/TSP). Although the pathogenesis of this disease remains to be elucidated, the evidence suggests that immunopathological mechanisms are involved. Since HTLV-1 tax mRNA was colocalized with glial acidic fibrillary protein, a marker for astrocytes, we developed an in vitro model to assess whether HTLV-1 infection activates astrocytes to secrete cytokines or present viral immunodominant epitopes to virus-specific T cells. Two human astrocytic glioma cell lines, U251 and U373, were transfected with the 3' portion of the HTLV-1 genome and with the HTLV-1 tax gene under astrocyte-specific promoter control. In this study, we report that Tax-expressing astrocytic glioma transfectants activate the expression of tumor necrosis factor alpha mRNA in vitro. Furthermore, these Tax-expressing glioma transfectants can serve as immunological targets for HTLV-1-specific cytotoxic T lymphocytes (CTL). We propose that these events could contribute to the neuropathology of HAM/TSP, since infected astrocytes can become a source for inflammatory cytokines upon HTLV-1 infection and serve as targets for HTLV-1-specific CTL, resulting in parenchymal damage by direct lysis and/or cytokine release.

Physical and functional interaction between the human T-cell lymphotropic virus type 1 Tax1 protein and the CCAAT binding protein NF-Y

Tax1, a potent activator of human T-cell lymphotropic virus type 1 (HTLV-1) transcription, has been shown to modulate expression of many cellular genes. Tax1 does not bind DNA directly but regulates transcription through protein-protein interactions with sequence-specific transcription factors. Using the yeast two-hybrid system to screen for proteins which interact with Tax1, we isolated the B subunit of the CCAAT binding protein NF-Y from a HeLa cDNA library. The interaction of Tax1 with NF-YB was specific in that NF-YB did not interact with a variety of other transcription factors, including human immunodeficiency virus Tat, human papillomavirus E6, and Bicoid, or with the M7 (amino acids 29CP-AS) Tax1 mutant. However, NF-YB did interact with the C-terminal Tax1 mutants M22 (130TL-AS) and M47 (319LL-RS). We also show that in vitro-translated NF-YB specifically bound to a glutathione S-transferase-Tax1 fusion protein. Further, Tax1 coimmunoprecipitated with NF-Y from nuclear extracts of HTLV-1-transformed cells, providing evidence for in vivo interaction of Tax1 and NF-YB. We further demonstrate that Tax1 specifically activated the NF-Y-responsive DQbeta promoter, as well as a minimal promoter which contains only the Y-box element. In addition, mutation of the Y-box element alone abrogated Tax1-mediated activation. Taken together, these data indicate that Tax1 interacts with NF-Y through the B subunit and that this interaction results in activation of the major histocompatibility complex class II promoter. Through activation of this and other NF-Y driven promoters, the Tax1-NF-Y interaction may play a critical role in causing cellular transformation and HTLV-1 pathogenesis.

Detection of HTLV-I in Peripheral Blood Lymphocytes from Patients with Chronic HTLV-I-Associated Myelopathy/Tropical Spastic Paraparesis and Asymptomatic Carriers by PCR-in situ Hybridization

Less than 5% of people infected with human T-lymphotropic virus type I (HTLV-I) develop HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic progressive neurologic disease. A number of factors have been implicated in the development of HAM/TSP including heterogeneity of viral sequences, host-genetic background, viral-specific cellular immune responses and viral load. This study examined the presence of HTLV-1 tax DNA in peripheral blood lymphocytes (PBL) from 2 chronic HAM/TSP patients and 2 asymptomatic HTLV-I carriers by using PCR-in situ hybridization (PCR-ISH) for the in situ presence of proviral HTLV-I tax DNA. By this technique, rare PBL from these HTLV-I-infected individuals contained HTLV-I DNA. PCR-ISH did not detect any difference in the number of infected cells between HAM/TSP patients and asymptomatic carriers. Copyright 1997 S. Karger AG, Basel

T helper cell activation and human retroviral pathogenesis

T helper (Th) cells are of central importance in regulating many critical immune effector mechanisms. The profile of cytokines produced by Th cells correlates with the type of effector cells induced during the immune response to foreign antigen. Th1 cells induce the cell-mediated immune response, while Th2 cells drive antibody production. Th cells are the preferential targets of human retroviruses. Infections with human T-cell leukemia virus (HTLV) or human immunodeficiency virus (HIV) result in the expansion of Th cells by the action of HTLV (adult T-cell leukemia) or the progressive loss of T cells by the action of HIV (AIDS). Both retrovirus infections impart a high-level activation state in the host immune cells as well as systemically. However, diverging responses to this activation state have contrasting effects on the Th-cell population. In HIV infection, Th-cell loss has been attributed to several mechanisms, including a selective elimination of cells by apoptosis. The induction of apoptosis in HIV infection is complex, with many different pathways able to induce cell death. In contrast, infection of Th cells with HTLV-1 affords the cell a protective advantage against apoptosis. This advantage may allow the cell to escape immune surveillance, providing the opportunity for the development of Th-cell cancer. In this review, we will discuss the impact of Th-cell activation and general immune activation on human retrovirus expression with a focus upon Th-cell function and the progression to disease.

Human T-cell lymphotropic virus type II-associated myelopathy: clinical and immunologic profiles

Human T-cell lymphotropic virus type II (HTLV-II) is endemic in several ethnic tribes and among intravenous drug users in metropolitan areas. Despite the presence of HTLV-II in these various populations, the association of HTLV-II with disease is sparse and mainly limited to isolated case reports. This study is an extension of an earlier description of an HTLV-II-infected patient with neurologic disease and presents the clinical and immunologic findings of 4 patients with HTLV-II seropositivity and spastic paraparesis. The patients are of African-American origin with 3 of the patients being of Amerindian descent. All of the patients are seronegative for the human immunodeficiency virus (HIV). The patients progressed to a nonambulatory state in less than 5 years. Magnetic resonance imaging studies obtained from 3 of the patients demonstrated white matter disease in the cerebrum and spinal cord. The cerebrospinal fluid and serum contained antibodies to HTLV-II. The presence of proviral HTLV-II was confirmed by polymerase chain reaction analysis of peripheral blood lymphocytes (PBLs). A spinal cord biopsy from 1 patient demonstrated HTLV RNA within a lesion. Immunologic studies on 2 patients demonstrated that spontaneous lymphoproliferation of PBLs was present but decreased relative to HTLV-I-infected patients. The clinical and immunologic findings from these HTLV-II-infected patient resemble those found in HTLV-I-associated myelopathy/tropical spastic paraparesis.

Human T lymphotropic virus type I in arthropathy and autoimmune disorders

The progressive nature of the disease and the persistent inflammation affecting various organs are common features of idiopathic autoimmune disorders of unknown etiology. Therefore, the HTLV-I-associated disorders described in the present review are outstandingly important models for our understanding of the pathologic mechanisms of organ-specific immune disorders. HTLV-I arthropathy is characterized by chronic inflammatory and proliferative synovitis with lymphoid follicles and pannus formation in the affected joints, indistinguishable from the findings in idiopathic RA. The presence of the tax gene in HTLV-I-negative SS patients suggests that it is responsible for the exocrine gland abnormality, characterized by extensive lymphoproliferative epithelial lesions. Furthermore, the pulmonary lesions of HTLV-I bronchopneumonopathy are similar to those of idiopathic interstitial pneumonitis. Based on these observations, the clinical findings associated with the immunologic abnormalities in HTLV-I-infected patients provide us with valuable information for understanding the pathogenetic mechanisms of chronic inflammatory conditions associated with immune regulatory disorders. Although the clinical and pathologic features of the 2 common HTLV-I-associated disorders, ATL and HAM/TSP, have been well characterized and are clearly distinguishable from those of the idiopathic forms of these disorders, other HTLV-I-related autoimmune diseases, e.g., arthropathy, SS, or bronchopneumonopathy, are clinically indistinguishable from the idiopathic forms of the diseases. Such similarity may serve as a clue to the pathogenetic mechanisms of idiopathic autoimmune disorders.

Evidence of HTLV-I in thyroid tissue in an HTLV-I carrier with Hashimoto's thyroiditis

Human T-lymphotropic virus type l (HTLV-I) protein and messenger RNA (mRNA) for HTLV-I were examined in thyroid tissues from two patients with Hashimoto's thyroiditis and serum anti-thyroid antibody. The virus envelope protein and signals for the mRNA were detected in many of the follicular epithelial cells of the thyroid tissue from one of the patients, respectively, by immunohistochemistry and in situ hybridization. PCR-Southern blotting revealed the presence of HTLV-I DNA in the thyroid tissue, in which the viral protein and mRNA were detected, although no virus particles were found in the epithelial cells by electron microscopy. HTLV-I virus was not present in the thyroid tissue from the second patient. The present findings suggest that infection of thyroid tissue with HTLV-I is associated with the pathogenesis of Hashimoto's thyroiditis in some patients.

HTLV-I arthropathy and Sjögren syndrome

Human T-cell lymphotropic virus type I (HTLV-I) was initially detected as the causative agent of adult T-cell leukemia (ATL). However, recent studies have revealed that HTLV-I may disrupt the immune system and lead to the development of rheumatoid arthritis and Sjögren syndrome. A current study in our laboratory has revealed that HTLV-I tax gene, known as the transregulatory gene, contributes not only to the induction of synovial cell hyperplasia but also the immune response, both in vivo and in vitro. In this report, the role of HTLV-I in the pathogenesis of chronic destructive arthropathy and Sjögren syndrome is discussed.

Interpreting MHC class I expression and class I/class II reciprocity in the CNS: reconciling divergent findings

MHC-restricted T cells are thought to contribute to clinical demyelination in MS and other circumstances. The step-by-step mechanisms involved and ways of controlling them are still being defined. Identification of the MHC+ cells in the CNS in situ has been controversial. This chapter reviews MHC expression in neural tissue, including normal, pathological, experimental, and developing tissue in situ and isolated cells in vitro. A basic pattern is defined, in which MHC expression is limited to nonneural cells and strongest class I and II expression are on different cell types. Variations from the basic pattern are reviewed. Ways of reconciling divergent findings are discussed, including the use of "mock tissue" to help choose between technical and biological bases for divergent findings, the potential contribution of internal antigen to the in situ staining patterns, and the possibility that class I upregulation is actively suppressed in situ. Functional implications of the observed patterns of MHC expression and ways of confirming the function of each MHC+ cell type in situ are described. It is suggested that modulating MHC expression in different cell types at different times or in different directions might be desirable.

Detection of human T-lymphotropic virus type I (HTLV-I) tax RNA in the central nervous system of HTLV-I-associated myelopathy/tropical spastic paraparesis patients by in situ hybridization

Autopsy specimens from 3 patients with human T-lymphotropic virus (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) were examined for the presence of HTLV-I in the central nervous system (CNS). In situ hybridization using an HTLV-I tax RNA probe detected cells containing HTLV-I RNA in spinal cord and cerebellar sections. HTLV-I infected cells were located within the white matter and, in particular, within the anterior and lateral funiculi of the spinal cord. Consistent with previously described HAM/TSP pathology, there were perivascular infiltrates in these CNS specimens. Significantly, HTLV-I RNA was not localized to these infiltrates but was detected deeper within the neural tissue. Furthermore, phenotypic analysis demonstrated that at least some of the infected cells were astrocytes. While previous polymerase chain reaction studies have demonstrated the presence of proviral HTLV-I in CNS specimens, here we provide evidence for the in situ expression of HTLV-I RNA in the CNS of HAM/TSP patients.