Rat lymphoid cell lines with HTLV-I production. III. Transmission of HTLV-I into rats and analysis of cell surface antigens associated with HTLV-I

Does HTLV-1 Infection Show Phenotypes Found in Sjögren's Syndrome?

Viruses are a possible cause for Sjögren's syndrome (SS) as an environmental factor related to SS onset, which exhibits exocrine gland dysfunction and the emergence of autoantibodies. Although retroviruses may exhibit lymphocytic infiltration into exocrine glands, human T-cell leukemia virus type 1 (HTLV-1) has been postulated to be a causative agent for SS. Transgenic mice with HTLV-1 genes showed sialadenitis resembling SS, but their phenotypic symptoms differed based on the adopted region of HTLV-1 genes. The dominance of tax gene differed in labial salivary glands (LSGs) of SS patients with HTLV 1-associated myelopathy (HAM) and adult T-cell leukemia. Although HTLV-1 was transmitted to salivary gland epithelial cells (SGECs) by a biofilm-like structure, no viral synapse formation was observed. After infection to SGECs derived from SS patients, adhesion molecules and migration factors were time-dependently released from infected SGECs. The frequency of the appearance of autoantibodies including anti-Ro/SS-A, La/SS-B antibodies in SS patients complicated with HAM is unknown; the observation of less frequent ectopic germinal center formation in HTLV-1-seropositive SS patients was a breakthrough. In addition, HTLV-1 infected cells inhibited B-lymphocyte activating factor or C-X-C motif chemokine 13 through direct contact with established follicular dendritic cell-like cells. These findings show that HTLV-1 is directly involved in the pathogenesis of SS.

Chimeric peptide vaccine composed of B- and T-cell epitopes of human T-cell leukemia virus type 1 induces humoral and cellular immune responses and reduces the proviral load in immunized squirrel monkeys (Saimiri sciureus)

A squirrel monkey model of human T-cell leukemia virus type 1 (HTLV-1) infection was used to evaluate the immunogenicity and protective efficacy of a chimeric peptide vaccine composed of a B-cell epitope from the envelope region (aa 175–218) and three HLA-A*0201-restricted cytotoxic T-lymphocyte epitopes derived from Tax protein (Tri-Tax). These selected Tax peptides induced secretion of gamma interferon (IFN-γ) in peripheral blood mononuclear cells obtained from monkeys chronically infected with HTLV-1. After immunization, a high titre of antibodies and a high frequency of IFN-γ-producing cells were detected against the Env and the Tri-Tax immunogens, but not against the individual Tax peptides. This might indicate that epitope(s) distinct from those recognized by humans are recognized by responder monkeys. After challenge, it was shown by competitive PCR that partial protection against HTLV-1 infection could be raised in immunized animals. Further studies should be developed to determine the duration of this protection.

The genetic background as a determinant of human T-cell leukemia virus type 1 proviral load

Human T-cell leukemia virus type 1 (HTLV-1) is etiologically linked with HTLV-1-associated diseases. HTLV-1 proviral load is higher in persons with adult T-cell leukemia and HTLV-1-associated myelopathy/tropical spastic paraparesis than in asymptomatic carriers. However there are little data available on the factors controlling HTLV-1 proviral load in carriers. To study the effect of genetic background on HTLV-1 proviral load, we employed a mouse model of HTLV-1 infection that we had established. Here we analyzed nine strains of mice and found there is a great variation of proviral load among mouse strains that is not necessarily dependent on major histocompatibility complex. The antibody response is also different among these strains. To our knowledge, this is the first demonstration of the importance of the genetic background other than major histocompatibility complex controlling the HTLV-1 proviral load.

HTLV type 1 infection in squirrel monkeys (Saimiri sciureus): a promising animal model for HTLV type 1 human infection

We show that the squirrel monkey Saimiri sciureus is susceptible to experimental infection with either syngeneic or allogeneic HTLV-1-immortalized cells. As in humans, such experimental inoculation leads to chronic infection, and HTLV-1 provirus was detected in PBMCs by PCR. Chronically infected monkeys developed high titers of antibodies against the structural proteins of the virus, as do HTLV-1-infected humans. Furthermore, in serially sacrificed squirrel monkeys infected with HTLV-1, proviral DNA was detected at primary phases of infection in PBMCs, spleens, and lymph nodes. Tax/rex mRNA was also detected by RT-PCR in the PBMCs of two monkeys at 12 days after inoculation and in the spleen and lymph nodes of the monkey sacrificed on Day 12. In this animal, scattered HTLV-1-tax/rex mRNA-positive lymphocytes were detected by in situ hybridization in frozen sections of the spleen. These results indicate that PBMCs, spleen, and lymph nodes serve as major reservoirs for HTLV-1 during the early phase of infection. To evaluate the relationship between viral expression and the immune response during infection, humoral and cytotoxic T cell responses (CTL) were studied at various times after inoculation. Antibodies to HTLV-1 were detected 3 weeks after infection and anti-p40Tax and anti-Env CTL activity was detected 2 months after infection and remained detectable thereafter. Our results indicate that the squirrel monkey provides a useful animal model for studying the pathogenesis of HTLV-1 and for evaluating new candidate vaccines.

Role of the genetic background of rats in infection by HTLV-I and HTLV-II and in the development of associated diseases

Three aspects of the rat model of HTLV-I/II infection were investigated. (i) The efficacy of HTLV-I-transformed rat cell lines in infecting different strains of rats: WKY and Lewis HTLV-I-transformed cell lines were injected into adult WKY, Lewis and Brown Norway rats, representing syngeneic and allogeneic combinations. The HTLV-I provirus was not detected in peripheral-blood mononuclear cells (PBMC) from these rats 18 weeks after inoculation, showing that HTLV-I-transformed rat cells are not suitable for virus challenge in vaccination experiments. Rats inoculated with Lewis HTLV-I-transformed cells produced an antibody response to HTLV-I, which was higher in allogeneic (WKY and Brown Norway) than in syngeneic rats. (ii) The susceptibility of rats to HTLV-II infection: After human HTLV-II-producing cells (MO) were injected into adult WKY rats, the HTLV-II provirus was detected in PBMC 12 weeks later. Sequencing of a portion of this provirus confirmed its identity with the HTLV-II from MO cells. (iii) The role of MHC haplotype in susceptibility to neurological disease in rats inoculated as newborns with HTLV-I: The hypothesis that the RT-Ik haplotype confers susceptibility was tested by inoculating newborn OKA (RT-Ik), WKY (RT-Il), Lewis (RT-Il) and Fischer 344 (RT-I lvl) rats with human HTLV-I-producing cells (MT-2). Eighteen months later, only the WKY rats showed histological abnormality of the spinal cord, without clinical paralysis. Fischer 344 rats developed cutaneous tumors and OKA rats mammary tumors. The HTLV-I provirus was not detected in these tumors.

HTLV-I infection in squirrel monkeys (Saïmiri sciureus) using autologous, homologous, or heterologous HTLV-I-transformed cell lines

Peripheral blood mononuclear cells (PBMC) from three adult male squirrel monkeys (Saïmiri sciureus) were transformed by human T-cell leukemia/lymphoma virus type I (HTLV-I) by cocultivation with lethally irradiated human MT-2 cells. Three permanent monkey T-cell lines producing HTLV-I were obtained and characterized. Six weeks after inoculation seroconversion was observed in three of three monkeys inoculated with autologous transformed T cells and in two of three monkeys receiving homologous cells. Proviral DNA was detected in their PBMC at various times after inoculation, with the highest proviral load and antibody titers being found in monkeys infected with homologous cells. Monkeys inoculated with heterologous MT-2 cells did not seroconvert, and HTLV-I provirus was detected only transiently in their PBMC. To determine whether in vitro and in vivo HTLV-I infection of squirrel monkey cells led to a selection of monkey-adapted viral mutants, comparative sequencing of the proviral gp21 env between ex vivo monkey HTLV-I-infected PBMC, the inoculum, and MT-2 cells was done and no significant differences were detected. The squirrel monkey, which is naturally free of simian T-cell leukemia/ lymphoma virus, thus appears to be a suitable model for evaluating HTLV-I candidate vaccines and for studying the pathogenesis of HTLV-I.

Infection of rats with human T-cell leukemia virus type-I: susceptibility of inbred strains, antibody response and provirus location

The susceptibilities of different strains of inbred rats to infection with the human T-cell leukemia virus (HTLV-I) after inoculation of human HTLV-I producer cell lines were compared. The Fisher F344 and Brown Norway strains developed the highest antibody response to HTLV-I, while the Lewis and BB strains were low responders. Antibodies against the HTLV-I gag proteins, and env gp21 but not env gp46, were detected in Western blots with sera from HTLV-I-infected Fischer F344 and Brown Norway rats. These sera were inactive in an in vitro syncytium-formation inhibition test. The HTLV-I provirus was detected by polymerase chain reaction in all Fischer F344, and some Lewis and Brown Norway rats, but not in the BB, which lack CD8+ T lymphocytes. The most frequent locations of the HTLV-I provirus in the Fischer F344, Lewis and Brown Norway rats at 12 weeks after infection were the peripheral blood mononuclear cells (PBMC) and spinal cord. In a second experiment in Brown Norway rats, the provirus was again detected in the PBMC of rats at 12 weeks, but not at 22 weeks, and among the other organs tested at 22 weeks the sympathetic nerve ganglia were positive. It is concluded that HTLV-I infection occurs in adult rats, but is suppressed with time.

Phenotypic progression of a rat lymphoid cell line immortalized by human T-lymphotropic virus type I to induce lymphoma/leukemia-like disease in rats

Rat lymphoid cells, TARS-1, immortalized by coculture with adult T-cell leukemia cells, were intraperitoneally injected into 65 newborn, inbred WKAH/Hkm rats. In most of the rats, tumor nodules were discernible 7 to 15 days after transplantation but were completely rejected within 5 to 6 weeks. Two rats with no tumor nodules exhibited gait disturbances and paralysis of the hind legs 3 to 4 weeks after transplantation. Histological and hematological examinations revealed that a lymphoma/leukemia-like disease had developed in one of the two rats, and the T-lymphoid cell line WLeuk-1 was established from peripheral blood mononuclear cells from this rat. When the WLeuk-1 cells were transplanted into newborn WKAH/Hkm rats, the animals died of a lymphoma/leukemia-like disease within several weeks after transplantation, in contrast to their rejection of the TARS-1 cells. Southern blot and karyotype analyses revealed that WLeuk-1 cells had retained the marker chromosomes and human T-lymphotropic virus type I (HTLV-I) integration patterns of the parent cell line, TARS-1. The additional specific chromosome abnormalities 3p+,t (12;13), and Xq+ were found in the WLeuk-1 cells. Moreover, the expression of HTLV-I structural proteins was slightly depressed in WLeuk-1 cells, while that of the transacting factors p40tax and p21x, but not that of p27rex, was enhanced about fivefold compared with that in TARS-1. The transactivating function of p40tax was intact in WLeuk-1, as evidenced by enhanced interleukin-2 receptor alpha chain expression. These results suggest that aberrant expression of HTLV-I regulatory genes and alteration of cellular genes were associated with the phenotypic progression of the WLeuk-1 cell line.

A rat model of human T lymphocyte virus type I (HTLV-I) infection. 1. Humoral antibody response, provirus integration, and HTLV-I-associated myelopathy/tropical spastic paraparesis-like myelopathy in seronegative HTLV-I carrier rats

Human T lymphocyte virus type I (HTLV-I) can be transmitted into several inbred strains of newborn and adult rats by inoculating newly established HTLV-I-immortalized rat T cell lines or the human T cell line MT-2. The transmission efficiency exceeds 80%, regardless of strain differences or the age at transmission. The production of anti-HTLV-I antibodies significantly differs among the strains and depends on the age at the time of transmission. Rats neonatally inoculated with HTLV-I-positive rat or human cells generally become seronegative HTLV-I carriers throughout their lives, whereas adult rats inoculated with HTLV-I-positive cells at 16 wk of age become seropositive HTLV-I carriers. The HTLV-I provirus genome is present in almost all organs, regardless of whether the carriers are seronegative or seropositive. According to antibody titers to HTLV-I, there are three groups of inbred rat strains: ACI, F344, and SDJ (high responders); WKA, BUF, and LEJ (intermediate responders); and LEW (low responder). Three of three 16-mo-old seronegative HTLV-I carrier rats of the WKA strain developed spastic paraparesis of the hind legs. Neuropathological examinations revealed that the lesions were confined primarily to the lateral and anterior funiculi of the spinal cord. Both myelin and axons were extensively damaged in a symmetrical fashion, and infiltration with massive foamy macrophages was evident. The most severe lesions were at levels of the thoracic cord and continued from the cervical to the lumbar area. These histopathological features as well as clinical symptoms largely parallel findings in humans with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). These HTLV-I carrier rats, in particular the WKA rats described above, can serve as a useful animal model for investigating virus-host interactions in the etiopathogenesis of HTLV-I-related immunological diseases, particularly HAM/TSP.

Infection of rats with HTLV-1: a small-animal model for HTLV-1 carriers

A human T-cell line producing human T-cell leukemia virus type I (HTLV-I), MT-2, was injected intravenously into female F344 rats aged 5 weeks to make HTLV-I carrier rats. Antibody against HTLV-I was detected at the 5th week after MT-2 injection, and its titer reached a high plateau which continued from the 15th to the 27th week. The antibodies were against p19, p24, p28 and p53 of HTLV-I antigens from MT-2 cells. The gag, pX and LTR nucleotide sequences of HTLV-I provirus were demonstrated by using polymerase chain reaction (PCR) in the peripheral-blood mononuclear cells of 3 rats at the 44th week and 2 at the 66th to 68th week out of 8 F344 rats injected with MT-2 cells. Quantification of the HTLV-I proviral sequence revealed that 30 to 60 molecules were present in 10(5) peripheral-blood mononuclear cells, indicating that the rats were chronically infected with HTLV-I. HTLV-I-infected rats could serve as a small-animal model for studying the pathophysiological state of HTLV-I carriers and also that of HTLV-I infection on various HTLV-I-related diseases, including adult T-cell leukemia and HTLV-I-associated myelopathy.