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Background: Recently, Japanese Red Cross blood centers have changed the confirmatory test method from an indirect immunofluorescence (IF) technique to Western blotting (WB) for antibodies against human T-cell leukemia virus Type 1 (HTLV-1). In this study, these HTLV-1 tests were assessed using another sensitive method, that is, a luciferase immunoprecipitation system (LIPS), to identify a better confirmatory test for HTLV-1 infection., Study Design and Methods: Plasma samples from 54 qualified donors and 114 HTLV-1 screening-positive donors were tested by LIPS for antibodies against HTLV-1 Gag, Tax, Env, and HBZ recombinant proteins. The donors were categorized into six groups, namely, (Group I) qualified donors, screening positive; (Group II) IF positive; (Group III) IF negative; (Group IV) WB positive; (Group V) WB negative; and (Group VI) screening positive in the previous blood donation, but WB-indeterminate during this study period., Results: In Groups II and IV, all plasma samples tested positive by LIPS for antibodies against Gag and Env proteins. In Group V, all samples tested negative by LIPS, whereas some Group III samples reacted with single or double antigens in LIPS. In Group VI, the LIPS test identified a donor with suspected HTLV-1 infection. The first case of a blood donor with plasma that reacted with HBZ was identified by LIPS., Conclusion: Reevaluation of the current HTLV-1 screening method using the LIPS test showed that both confirmatory tests had similar sensitivity and specificity only when WB indeterminate results were eliminated. LIPS is a promising method for detecting and characterizing HTLV-1 antibodies., (© 2014 AABB.)

Expression of human T-cell leukemia virus type-1 (HTLV-1) in adult T-cell leukemia (ATL) cells is known to be marginal in vivo and inducible in short-term culture. In this study, we demonstrated that withdrawal of interleukin (IL)-2 from IL-2-dependent ATL cell lines resulted in induction of HTLV-1 mRNA and protein expression, and that viral induction was associated with phosphorylation of the stress kinase p38 and its downstream CREB. Pharmacological inhibitors of the p38 pathway suppressed viral expression induced by IL-2 depletion. These results indicate that the stress-induced p38 pathway might up-regulate HTLV-1 gene expression through at least CREB activation.

Human T-lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is an inflammatory neurologic disease caused by HTLV-1 infection, in which HTLV-1-infected CD4(+) T cells and HTLV-1-specific CD8(+) T cells may play a role in the disease pathogenesis. Patients with HAM/TSP have high proviral loads despite vigorous virus-specific CD8(+) T-cell responses; however, it is unknown whether the T cells are efficient in eliminating the virus in vivo. To define the dynamics of HTLV-1-specific CD8(+) T-cell responses, we investigated longitudinal alterations in HTLV-1 proviral load, amino acid changes in an immunodominant viral epitope, frequency of HTLV-1-specific T cells, and degeneracy of T-cell recognition in patients with HAM/TSP. We showed that the frequency and the degeneracy of the HTLV-1-specific CD8(+) T cells correlated well with proviral load in the longitudinal study. The proviral load was much higher in a patient with low degeneracy of HTLV-1-specific T cells compared to that in a patient with comparable frequency but higher degeneracy of the T cells. Furthermore, in a larger number of patients divided into 2 groups by the proviral load, those with high proviral load had lower degeneracy of T-cell recognition than those with low proviral load. Sequencing analysis revealed that epitope mutations were remarkably increased in a patient when the frequency and the degeneracy were at the lowest. These data suggest that HTLV-1-specific CD8(+) T cells with degenerate specificity are increased during viral replication and control the viral infection.

Two chimeric synthetic peptides incorporating immunodominant sequences from HTLV-I virus were synthesized. Monomeric peptides P7 and P8 represent sequences from transmembrane protein (gp21) and envelope protein (gp46) of the virus. The peptide P7 is a gp21 (374-400) sequence and the peptide P8 is a gp46 (190-207) sequence. Those peptides were arranged in a way that permits one to obtain different combinations of chimeric peptides (P7-GG-P8 and P8-GG-P7), separated by two glycine residues as spacer arms. The antigenic activity of these peptides were evaluated by UltramicroEnzyme-linked immunosorbent assay (UMELISA) by using panels of anti-HTLV-I-positive sera (n = 22), anti-HTLV-I/II-positive sera (n = 2), HTLV-positive (untypeable) serum samples (n = 2), and anti-HTLV-II-positive sera (n = 11), while specificity was evaluated with anti-HIV-positive samples (n = 19) and samples from healthy blood donors (n = 30). The efficacy of the chimeric peptides in solid-phase immunoassays was compared with the monomeric peptides and monomeric peptides together. The chimeric peptide P7-GG-P8 proved to be the most reactive with anti-HTLV-I-positive sera. These results may be related to a higher peptide adsorption capacity to the solid surface and for epitope accessibility to the antibodies. This chimeric peptide would be very useful for HTLV-I diagnostics., (Copyright 2001 Academic Press.)

Partial sequences from the env(gp46) gene of two human T-lymphotropic virus type I (HTLV-I) isolates (LIN and WEN) obtained from inhabitants of Fujian Province in southeast China were analyzed. A phylogenetic tree was constructed from these sequence data and those of other known HTLV-I isolates from all over the world. Comparisons of the LIN and WEN nucleotide sequences with other HTLV-I isolates showed diversity ranging from 0.73 to 7.00% for LIN and from 0.87 to 7.00% for WEN. Sequences of isolates LIN, WEN, MT-2, TSP1, and CH were most closely related, and the phylogenetic tree showed that all belong to the widespread subtype A of the cosmopolitan group. These preliminary data indicate that HTLV-I isolates from Fujian Province, China are closely related to HTLV-I strains from Japan and the Caribbean.

We constructed a sensitive and quantitative assay system to examine human T-cell leukemia virus type I (HTLV-I) envelope (env) glycoprotein-mediated cell fusion in which T7 RNA polymerase in donor cells coexpressing env glycoproteins activates a reporter gene in recipient cells upon cell fusion. An efficient expression of HTLV-I env glycoproteins (gp46 and gp21) was observed in 293T cells transfected with an expression plasmid by both immunoblot and immunofluorescence analyses. The cells expressing env glycoproteins also exhibited self-fusion. By cocultivating the donor cells with recipient cells transfected with a reporter plasmid possessing the luciferase gene under the T7 promoter, the expression of luciferase was observed upon cell fusion. The activation of the luciferase gene was inhibited by either anti-env neutralizing antibody or synthetic peptide corresponding to env gp21, thus indicating the cell fusion to be specifically mediated by the HTLV-I env glycoproteins expressed in the donor cells. A broad range of cell lines exhibited susceptibility to HTLV-I env-mediated cell fusion by this assay. This newly established assay system may thus provide an efficient way both to study the fusion mechanisms mediated by HTLV-I env glycoproteins and to identify the HTLV-I receptor(s)., (Copyright 1999 Academic Press.)

To investigate the pathogenesis of human T lymphocyte virus type I (HTLV-I)- related diseases, the env-pX gene of HTLV-I was introduced into the germline of inbred Wistar-King-Aptekman-Hokudai rats. A wide spectrum of collagen vascular diseases was evident in the transgenic rats, including chronic destructive arthritis similar to rheumatoid arthritis, necrotizing arteritis mimicking polyarteritis nodosa, polymyositis, myocarditis, dermatitis, and chronic sialoadenitis and dacryoadenitis resembling Sjögren's syndrome in humans. Thymic atrophy with the depletion of CD4 and CD8 double-positive thymocytes was also observed. In these animals, a number of autoantibodies, including high titers of rheumatoid factor, were present in the serum. We propose that the HTLV-I env-pX gene region may play a pathogenetic role in the development of collagen vascular and autoimmune diseases associated with autoimmune phenomenon.

Heterologous expression of the human T-cell lymphotropic virus type 1 (HTLV-1) envelope surface glycoprotein (gp46) in a vaccinia virus/T7 polymerase system resulted in the production of authentic recombinant gp46. Five differentially glycosylated forms of the surface envelope protein were produced by this mammalian system, as demonstrated by tunicamycin inhibition of N-glycosylation and N-glycan removal with endoglycosidase H and glycopeptidase F. These studies revealed that all four potential N-glycosylation sites in gp46 were used for oligosaccharide modification and that the oligosaccharides were mannose-rich and/or hybrid in composition. Conformational integrity of the recombinant HTLV-1 envelope protein was determined by the ability to bind to various HTLV-1-infected human sera and a panel of conformational-dependent human monoclonal antibodies under nondenaturing conditions. Furthermore, this recombinant gp46 was recognized by a series of HTLV-2-infected human sera and sera from a Pan paniscus chimpanzee infected with the distantly related simian T-cell lymphotropic virus STLVpan-p. Maintenance of highly conserved conformational epitopes in the recombinant HTLV-1 envelope protein structure suggests that it may serve as a useful diagnostic reagent and an effective vaccine candidate.

A set of recombinant plasmids containing different fragments of HTLV-I env gene has been constructed on the basis of pUR290-pUR292 vectors. The hybrid proteins containing different fragments of ENV predecessor in the C-terminal of beta-galactosidase differed in stability in Escherichia coli cells. The presence of N-terminal of ENV predecessor in recombinant proteins considerably decreases their resistance to proteases of the bacterial cell. Elimination of this fragment led to obtaining of the recombinant plasmid pESG coding for the high level of synthesis of the env-specific hybrid polypeptide (up to 30% of the total cellular protein). This 134 Kda protein is able to interact efficiently with the HTLV-I positive sera and may be used in the diagnostic test-systems for identification of the HTLV-I infected patients.

To examine the immune response to retroviral gag sequences in autoimmune disease, we measured antibody levels to synthetic peptides representing the major epitopes on HTLV-1 p19 gag and a homologous sequence on the endogenous retrovirus, HRES-1, in sera from 121 patients with autoimmune disease and 52 healthy controls. In the absence of HTLV-1 antibodies, using a conventional diagnostic assay, significantly elevated levels of antibodies to the HTLV-1 peptide were found in 23% of multiple sclerosis and 20% of anti-Sm antibody positive systemic lupus erythematosus patients. Elevated antibody levels to HRES-1 were found in 32% of Sjögren's syndrome and 19% of multiple sclerosis patients. Evidence of reactivity with both HTLV-1 and HRES-1 was found in human sera and cross-reactivity demonstrated with affinity purified rabbit anti-peptide antibodies. Expression of HRES-1, detected by antibodies and Northern blots, was found in lymphoblastoid cells, salivary gland biopsy sections and salivary gland epithelial cells in culture. This study confirms previous reports of low levels of anti-retroviral gag antibodies in autoimmune disease. The cross-reactions support the concept that reports of elevated HTLV-1 antibodies may be due to an endogenous agent such as HRES-1. The expression of HRES-1 salivary gland may explain its antigenicity in a small proportion of Sjögren's syndrome patients as well as suggesting mechanisms whereby it may contribute to the chronic inflammation of autoimmune disease.

Monoclonal antibodies (MAbs) raised against human T-cell lymphotropic virus type I (HTLV-I) recognized five distinct antigenic domains of viral env gene-encoded proteins. By using recombinant env proteins and synthetic peptides as mapping antigens, it was determined that the most immunogenic region represented a central portion of the retroviral surface protein (domain 2; amino acids 165 to 191). However, only a single MAb was able to react strongly with native viral proteins. This antibody (clone 6C2) was directed to an epitope within domain 4 (amino acids 210 to 306) of the retroviral env gene and reacted with envelope proteins in both HTLV-I and HTLV-II, as determined by immunoprecipitation, solid-phase binding, and immunoblotting. No reactivity against envelope components of other human retroviruses, including human immunodeficiency virus types 1 and 2, was present. Flow cytometry data demonstrated that MAb 6C2 reacted with cell lines chronically infected with HTLV-I or HTLV-II and also with surface antigens expressed on fresh adult T-cell leukemia cells, following up-regulation with interleukin-2. By a chemiluminescence immunoassay procedure, picogram amounts of viral surface protein could be detected in the unconcentrated supernatants of HTLV-infected cell lines and in diagnostic cultures. Levels of env and gag proteins released by cells into culture supernatants were not directly related to percent expression of cell surface viral-coat proteins. Further, the molar ratio of p19 to gp46 in conditioned media varied from strain to strain, possibly reflecting differences in viral assembly or packaging mechanisms. MAb 6C2 will be of value in characterizing the biochemical and immunological behavior of retroviral env gene proteins and in studying the interaction of HTLV-I and HTLV-II with their receptors.

We synthesized 46 sequential peptides 21 to 39 amino acids long over the structural protein of human T-cell leukemia virus type I (HTLV-I; the p19 and p24 gag protein and the gp46 and p20E env proteins) and tested their reactivities against antibodies in sera from HTLV-I healthy carriers and patients diagnosed as having human T-cell leukemia-lymphoma (ATLL) and myelopathy (HAM) by using an enzyme-linked immunosorbent assay. Of the 46 synthetic peptides, 18 peptides (2 corresponding to the p19 gag protein, 2 corresponding to the p24 gag protein, 8 corresponding to the gp46 env protein, and 6 corresponding to the p20E env protein) reacted with antibodies in the sera from HTLV-I healthy carriers. In particular, the peptides comprising amino acids 100 to 119 and 119 to 130 of the gag and 175 to 199, 213 to 236, 253 to 282, and 288 to 317 of the env proteins reacted with antibodies in sera from more than 30% of HTLV-I healthy carriers. These peptides also showed high reactivities to the antibodies in the sera from patients with ATLL and HAM. The results indicate that the predominant antigenic regions of the structural protein of HTLV-I were located at the C-terminal end of the p19 gag protein and the C-terminal half of the gp46 env protein, and the corresponding peptides proved to be useful antigens in detecting antibodies in the sera from individuals infected with HTLV-I.

A 42-kDa recombinant protein, PX141, consisting of the trans-activator protein encoded by human T-cell leukemia virus (HTLV-1) (tax1 antigen) and the amino-terminal fusion peptide of 12 amino acid residues of the alpha-peptide encoded by the plasmid pUC19 was produced. In order to investigate the immunogenicity of the tax1 antigen, mice were immunized with the purified PX141 and 4 anti-tax1 monoclonal antibodies (MAbs) designated TAXY-1, TAXY-6, TAXY-7 and TAXY-8 were generated, and their reactivity was characterized along with another anti-tax1 MAb, Lt-4. Immunoblot assays showed that all the MAbs reacted with the PX141, the native tax1 antigen expressed in various HTLV-1-infected cell lines and the gp68 of MT-2 cells expressing the tax1 amino acids 94-353. Immunoblot assays using recombinant, truncated tax1 antigens, XD59 (expressing amino acids 180-338) and XD128 (expressing amino acids 1-47 and 286-353) showed that: (1) TAXY-1 and Lt-4 did not react with either antigen; (2) TAXY-6 and TAXY-8 reacted with only XD128: and (3) TAXY-7 reacted with both. In addition, TAXY-1, but not the other MAbs, reacted with a putative tax antigen of an STLV-I-infected cell line, designated RfM26-I. Competitive binding assays showed that TAXY-6 and TAXY-8 did not compete against each other. Sera from HTLV-I-infected humans interfered with the binding of all of these anti-tax1 MAbs. These results indicate that the tax1 antigen and the PX141 express at least 5 distinct epitopes recognized by human and mouse antibodies.

55 HTLV-I (human T-cell lymphotropic virus) and 45 HTLV-II carriers, confirmed by HTLV-type specific polymerase chain reaction (PCR), were distinguished by western blot assays with recombinant HTLV I or II envelope glycoproteins. Recombinant protein (RP) B1 contains aminoacids 166-201 from HTLV-I exterior glycoprotein gp46 and was reactive with HTLV-I samples only. RP-IIB, which contains aminoacids 96-235 from HTLV-II exterior glycoprotein gp52, was reactive with all HTLV-II samples. 39 patients (86.6%) had high reactivity by densitometry. Of 55 HTLV-I samples, 35 (65.5%) had antibody reactivity to RP-IIB, but only 1 (1.8%) had high reactivity by densitometry. RP B1 and IIB western blot assays may replace the PCR test in diagnosis of HTLV infection.

We established rat T cell lines expressing human T cell leukemia virus type I (HTLV-I) Ag from inbred strains of rats, WKA/H, DA, and F344, to study CTL response against the HTLV-I-infected cells. HTLV-I-specific Ag expressed in these rat cells were HTLV-I gag Ag, p19, p24, and p15, and pX Ag, p40tax and p27rex, but not env Ag, as determined by immunofluorescence and immunoblot assays. By immunization of rats with syngeneic HTLV-I-infected cells, CTL against syngeneic HTLV-I-infected cells and antibodies to HTLV-I Ag were generated in WKA/H and DA rats. The bulk CTL cultures from WKA/H and DA rats lysed specifically syngeneic SV40-transformed kidney cells infected with recombinant vaccinia viruses (RVV) expressing HTLV-I gag and pX Ag, but not those infected with RVV expressing HTLV-I env Ag or a control vaccinia virus. From WKA/H rat CTL cultures, four CTL clones reactive with syngeneic HTLV-I-infected cells were isolated, three of which were specific for p27rex/p21x, but the Ag recognized by the other CTL clone was not defined with any RVV used. These results indicate that HTLV-I gag and pX gene products are recognized by MHC-restricted rat CTL specific for syngeneic HTLV-I-infected cells.

HTLV-I particles grown in 4 human lymphocyte cultures were observed by electron microscopy. Particles in all cell lines showed marked size and structural variations that were characteristic of each cell line. Profiles of size-distributions were found to be similar among virus particles of the same origin in different cell lines. Immunogold electron microscopy using monoclonal antibody to HTLV-I-p15, -p19, or -p24 revealed varying reactivities of individual particles. By double-labeling technique using antibody to HTLV-I-p19 or -p24, particles were found to be classifiable into 4 groups: p19+p24+, p19+p24-, p19-p24%, and p19-p24-. Each cell line showed the characteristic profile of distributions of virus particles of each group as observed at different in vitro passage levels. These antibodies reacted with certain structures in the extracellular space and in the cytoplasm. Results of this study demonstrate variations in morphology and antigenicity, as well as the morphogenesis of HTLV-I particles in different host cells.

T cell immune responses in syngeneic WKA/H rats were analyzed by using lymphoid cell lines, TARS-1, TART-1, and TARL-2, infected with human T-lymphotropic virus type 1 (HTLV-1). Spleen cells of rats in which these cell lines had been rejected were sensitized in vitro with the same cell lines, and cells cytotoxic to these HTLV-1+ cell lines, and cells cytotoxic to these HTLV-1+ cell lines were generated. The effector cells were CTL of the CD5+ CD8+ phenotype and showed restriction of MHC class I Ag. Direct tests as well as cold target cell inhibition tests with an array of cell populations showed that these CTL reacted only with syngeneic HTLV-1+ cell lines. When xenogeneic HTLV-1+ cell lines were similarly utilized for in vitro sensitization, rat CTL specific for syngeneic HTLV-1+ cells were generated. They were not, however, reactive with xenogeneic HTLV-1+ cells used for sensitization. Syngeneic rat cells selectively expressing gag, env, or pX gene coded Ag were prepared by infection of recombinant vaccinia viruses. In cold target cell inhibition tests of anti-HTLV-1 CTL with thus prepared cells, cytotoxicity against the syngeneic HTLV-1+ cells line, TARS-1, was inhibited by syngeneic cells expressing gag gene or env gene coded Ag. Inhibition was, however, more consistent and more dominant by cells with gag gene than those with env gene. Syngeneic cells with pX gene and MHC class I incompatible cells with gag, env, or pX gene did not inhibit cytotoxicity.

We examined the ability of the trans-acting factor p40tax of human T-cell leukemia virus type I (HTLV-I), which is thought to be a crucial molecule in T-cell transformation by HTLV-I, to activate expression of a set of endogenous cellular genes related to T-cell proliferation. For this purpose we established a subclone (JPX-9) of Jurkat cells that was stably transfected with an expression plasmid containing the p40tax gene, whose expression is definitely dependent on heavy-metal ions. Expression of the interleukin-2 receptor alpha chain in JPX-9 cells was induced in response to the induction of p40tax expression, as has been demonstrated by others in transient transfection experiments with Jurkat cells. In addition, we found that significant enhancement of expression of the nuclear proto-oncogene c-fos was closely associated with expression of p40tax. Continous enhancement in the level of c-fos mRNA was observed in the presence of p40tax. In contrast, mRNA levels of other nuclear proto-oncogenes (c-myc, c-myb, and c-jun) were not appreciably effected by the expression of p40tax. These results suggest that (i) in addition to the interleukin-2-interleukin-2 receptor system, cellular genes such as c-fos, which regulate normal T-cell growth, are also activated directly or indirectly by p40tax and (ii) p40tax-induced modulation of gene expression plays a crucial role in T-cell transformation by HTLV-I.

Expression of human T-cell leukemia virus type I (HTLV-I) is not detectable by immunofluorescence analysis or RNA blot analysis in most fresh peripheral blood mononuclear cells of patients with adult T-cell leukemia or of asymptomatic HTLV-I carriers. However, in this work, mRNA for the HTLV-I tax1/rex1 genes was detected in fresh peripheral blood mononuclear cells of adult T-cell leukemia patients and asymptomatic HTLV-I carriers by using reverse transcription followed by the polymerase chain reaction. By using fresh peripheral blood mononuclear cells, the expression of tax1/rex1 mRNA was detected in five of the six adult T-cell leukemia patients and four of the eight HTLV-I carriers examined. The amounts of tax1/rex1 mRNA detected corresponded to approximately 10(5) to 10(6) times less than that in the HTLV-I-infected MT-2 cell line. These results indicate that, in some individuals infected with HTLV-I, the provirus in circulating blood cells is transcribed in vivo. Thus the expression of viral antigens in circulating blood cells in vivo is suggested.

Production of granulocyte-macrophage colony-stimulating factor (GM-CSF) by normal T lymphocytes requires activation by antigen, mitogen or lectin, whereas T-cell lines transformed by human T-cell leukemia virus type I (HTLV-I) or type II (HTLV-II) constitutively produce high levels of GM-CSF. Using transient cotransfection assays, we demonstrate that introduction of the tax gene of either HTLV-I or HTLV-II is sufficient to activate GM-CSF promoter constructs in an unstimulated T-cell line. The GM-CSF 5' flanking sequences previously shown to be sufficient for GM-CSF induction following T-cell activation are also sufficient for activation by the HTLV tax proteins. The sequences required for trans-activation of GM-CSF are distinct from those required for the activation of other T-cell-inducible genes (IL-2R alpha, IL-2) by tax, suggesting that tax can have pleiotropic effects on gene expression in T cells. Constitutive GM-CSF production by HTLV-infected T cells may therefore be due to trans-activation of its promoter by tax. Expression of GM-CSF by HTLV-I infected lymphocytes may be important in the granulocytosis and eosinophilia frequently seen in patients with HTLV-I-induced adult T-cell leukemia/lymphoma.

Transcriptional activation of the human T-cell leukemia virus type I (HTLV-I) long terminal repeat (LTR) by viral protein p40x requires a 21-base-pair (bp) sequence which is repeated three times within the LTR. This sequence contains a core octanucleotide (TGACGTCT) which has been attributed to be a cyclic-AMP (cAMP)-responsive element. We demonstrate here that the HTLV-I LTR can be specifically stimulated by cAMP regulators and have identified four proteins in HeLa cells that bind to the HTLV-I 21-bp sequence. We correlated the in vitro binding and transcriptional activity of one of these cellular factors (Mr, 180,000) to the trans-activation of the HTLV-I LTR by p40x. Point mutations were generated within the cAMP octanucleotide of the HTLV-I 21-bp sequence that simultaneously abolished biological responsiveness to trans-activation by p40x and to stimulation by cAMP. We found that these mutations also eliminated the binding of the 180-kilodalton HeLa factor to the HTLV-I 21-bp element. In the absence of a demonstrable DNA-binding property for p40x, we hypothesize that cellular proteins are involved, possibly through signal transduction pathways, in its trans-activation of responsive promoters.

The HTLV-I tax gene protein (Tax) is not packaged within the mature viral particle from which the proteins for the commercially available enzyme-linked immunosorbent assay (ELISA) are derived. Screening of 162 individuals within a cohort of white intravenous (IV) drug abusers, previously identified as having an increased incidence of HTLV-I infection, demonstrated that seven of them had antibodies to the HTLV-I Tax protein but tested negative in HTLV-I ELISAs and Western blots prepared from purified virion proteins. Three out of 35 individuals in other behaviorally defined high-risk groups also displayed this limited pattern of reactivity to HTLV-I proteins. The presence of the anti-HTLV-I p40/Tax antibodies was determined by radioimmunoprecipitation assay (RIPA), which also revealed low levels of anti-env reactivity. The specificity of the anti-p40 reactivity was confirmed on specific Tax ELISAs and Western blots prepared from recombinantly produced Tax. In vitro gene amplification by the polymerase chain reaction (PCR) was used to establish the presence of sequences homologous to HTLV-I proviral DNA in four/four of these HTLV-I ELISA negative, Tax ELISA/Tax western blot/RIPA positive individuals. These data suggest that the true incidence of HTLV-I infection within high-risk cohorts is greater than previously reported.

The tax gene of the human T-cell leukemia virus types I and II (HTLV-I and HTLV-II) is essential for viral replication and acts by increasing the level of RNA transcription. The tax genes of HTLV-I and HTLV-II encode proteins of 40 and 37 kilodaltons, respectively. By in vitro mutagenesis of the tax gene, we have investigated those regions of the protein which are essential for its function. Mutation of either the amino- or carboxy-terminal domain of the protein resulted in loss of trans-activation ability. In addition, specificity of its activity with regard to trans-activation of either the HTLV-I or HTLV-II long terminal repeats was conferred by the first 59 amino acids.

One potent transcriptional activator of human T-cell leukemia virus type I (HTLV-I) is virally encoded protein Tax (p40x). p40x trans-activates HTLV-I through the long terminal repeat (LTR) by using a triply repeated 21-base-pair sequence as the target. In this report we have characterized the induction of the HTLV-I LTR by 12-O-tetradecanoylphorbol-13-acetate (TPA). By assaying progressively deleted mutations in the HTLV-I LTR, we have delimited a 60-base-pair sequence in the LTR which is capable of conferring TPA responsiveness, but not p40x responsiveness, to heterologous promoters in a position-independent fashion. This HTLV-I TPA-responsive element is specifically recognized by preexisting factors from uninfected cells. We show that activation of this sequence by phorbol ester does not require de novo cellular protein synthesis. When the HTLV-I LTR was simultaneously activated by both Tax and TPA, an additive effect was seen. This suggests the use of distinct regulatory pathways by the two respective trans-activators.

The trans activator (p40tax) of human T-cell leukemia virus type I (HTLV-I) is a transcriptional factor that activates the long terminal repeat (LTR) of HTLV-I and interleukin-2 receptor alpha. We examined the HTLV-I enhancer responsible for tax-mediated trans activation and identified (A/T)(G/C)(G/C)CNNTGACG(T/A) as a plausible tax-responsive element (TRE). The putative TRE in the LTR was found to be different from the elements required for activation by cycle AMP and 12-O-tetradecanoylphorbol-13-acetate, although these elements overlapped each other. The TRE was also different from a binding site of an NF-kappa B-like factor that was identified in the interleukin-2 receptor alpha promoter and human immunodeficiency virus LTR as a TRE. The latter result was further demonstrated by the failure of the NF-kappa B sequence to compete with the TRE of the LTR in a protein-binding assay. These findings indicate that tax function and its cascade can modulate activities of various enhancer sequences, which are probably regulated by distinct DNA-binding factors.