Conformational melding permits a conserved binding geometry in TCR recognition of foreign and self molecular mimics.

Molecular mimicry between foreign and self Ags is a mechanism of TCR cross-reactivity and is thought to contribute to the development of autoimmunity. The αß TCR A6 recognizes the foreign Ag Tax from the human T cell leukemia virus-1 when presented by the class I MHC HLA-A2. In a possible link with the autoimmune disease human T cell leukemia virus-1-associated myelopathy/tropical spastic paraparesis, A6 also recognizes a self peptide from the neuronal protein HuD in the context of HLA-A2. We found in our study that the complexes of the HuD and Tax epitopes with HLA-A2 are close but imperfect structural mimics and that in contrast with other recent structures of TCRs with self Ags, A6 engages the HuD Ag with the same traditional binding mode used to engage Tax. Although peptide and MHC conformational changes are needed for recognition of HuD but not Tax and the difference of a single hydroxyl triggers an altered TCR loop conformation, TCR affinity toward HuD is still within the range believed to result in negative selection. Probing further, we found that the HuD-HLA-A2 complex is only weakly stable. Overall, these findings help clarify how molecular mimicry can drive self/nonself cross-reactivity and illustrate how low peptide-MHC stability can permit the survival of T cells expressing self-reactive TCRs that nonetheless bind with a traditional binding mode.

Development and Evaluation of a Novel ELISA for Detection of Antibodies against HTLV-I Using Chimeric Peptides.

We aimed to develope a peptide-based indirect ELISA to detect antibodies against Human T-lymphotropic virus type I (HTLV-I). Two chimeric peptides (CP-1 and CP-2) were designed using linear immunodominant epitopes of gp-46-I, and gp21-I proteins, according to the sequence from Uniprot database. These peptides were studied initially in the ELISA using infected sera. The most promising peptideCP-1, was used to develop a peptide ELISA for detection of HTLV-I infected sera. The optimal conditions for CP-1ELISA were: the optimum coating buffer was 100mM NaHCO3, pH 9.6; coating peptide concentration was 10 µg/mL; the optimal blocking buffer was5% fetal bovine serum (FBS); the secondary antibody concentration was 1:2000; and serum dilution was 1:20. 20serum samples from HTLV-I infected patients were evaluated by ELISA developed. CP-1 showed high antigenicity while lacking any cross-reactivity with normal human sera. The results of evaluations indicated that in comparison with commercial ELISA, CP-1 ELISA showed good sensitivity and specificity. With further validation, CP-1as described in the present study could be introduced as novel reliable and cost-effective candidates for the high-specific screening of HTLV-I/-II infections in endemic regions.

Structural analysis of the N-terminal domain of the human T-cell leukemia virus capsid protein.

The N-terminal domain of the retroviral capsid (CA) protein is one of the least conserved regions encoded in the genome. Surprisingly, the three-dimensional structures of the CA from different genera exhibit alpha-helical structural features that are highly conserved. The N-terminal residues of the human immunodeficiency virus type 1 (HIV-1) and Rous sarcoma virus (RSV) capsid proteins form a beta-hairpin. To determine if this feature is conserved in the retroviral family, we cloned, expressed, purified, and solved the structure of a N-terminal 134 amino acid fragment (CA(134)) from the human T-cell leukemia virus type 1 (HTLV-I) using high resolution nuclear magnetic resonance (NMR) spectroscopy. The CA(134) fragment contains an N-terminal beta-hairpin and a central coiled-coil-like structure composed of six alpha-helices. The N-terminal Pro1 residue contacts Asp54 in the helical cluster through a salt bridge. Thus, the beta-hairpin is conserved and the helical cluster is structurally similar to other retroviral CA domains. However, although the same Asp residue defines the orientation of the hairpin in both the HTLV-1 and HIV-1 CA proteins, the HTLV-I hairpin is oriented away, rather than towards, the helical core. Significant differences were also detected in the spatial orientation and helical content of the long centrally located loop connecting the helices in the core. It has been proposed that the salt bridge allows the formation of a CA-CA interface that is important for the assembly of the conical cores that are characteristic of HIV-1. As HTLV-I forms spherical cores, the salt-bridge feature is apparently not conserved for this function although its role in determining the orientation of the beta-hairpin may be critical, along with the central loop. Comparison of three-dimensional structures is expected to elucidate the relationships between the retroviral capsid protein structure and its function.

Study of the peptide length and amino acid specific substitution in the antigenic activity of the chimeric synthetic peptides, containing the p19 core and gp46 envelope proteins of the HTLV-I virus.

Four chimeric synthetic peptides (Q5, Q6, Q7(multiply sign in circle), and Q8(multiply sign in circle)), incorporating immunodominant epitopes of the core p19 (105-124 a.a.) and envelope gp46 proteins (175-205 a.a.), of HTLV-I were obtained. Also, two gp46 monomeric peptides M4 and M5(multiply sign in circle) (Ser at position 192) were synthesized. The analysis of the influence of the peptide lengths and the proline to serine substitution on the chimeric and monomeric peptides' antigenicity, with regard to the chimeric peptides Q1, Q2, Q3(multiply sign in circle), and Q4(multiply sign in circle), reported previously, for HTLV-I was carried out. The peptides' antigenicity was evaluated in an ultramicroenzyme-linked immunosorbent assay (UMELISA) using sera of HTLV-I/II. The peptides' antigenicity was affected appreciably by the change of the peptide length and amino acid substitutions into the immunodominant sequence of gp46 peptide.

Sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for (anti-human T-cell leukemia virus type I) IgG in serum using a synthetic peptide, Cys-env gp46(188-224), as antigen.

A sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for (anti-human T-cell leukemia virus type I) IgG (anti-HTLV-I IgG) in serum using a synthetic peptide, Cys-env gp46(188-224) of HTLV-I, is described. Anti-HTLV-I IgG in test serum, which had been incubated with excess of inactive beta-D-galactosidase to eliminate interference by anti-beta-D-galactosidase antibodies, was reacted simultaneously with 2,4-dinitrophenyl-bovine serum albumin-Cys-env gp46 (188-224) conjugate and Cys-env gp46 (188-224)-beta-D-galactosidase conjugate. The complex formed consisting of the three components was trapped onto polystyrene balls coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG. After washing to eliminate nonspecific IgG in the test serum and excess of the beta-D-galactosidase conjugate, the complex was eluted from the polystyrene balls with epsilon N-2,4-dinitrophenyl-L-lysine and transferred to polystyrene balls coated with affinity-purified (anti-human IgG gamma-chain) IgG. beta-D-Galactosidase activity bound to the (anti-human IgG gamma-chain) IgG-coated polystyrene balls was assayed by fluorometry. This assay was more sensitive and useful than the immune complex transfer enzyme immunoassay using Cys-Arg-env gp46(188-209) and other methods using HTLV-I as antigen.

Mouse monoclonal antibodies directed against the HTLV-I protease recognize epitopes internal to the dimer.

The proteases (PR) of retroviruses are expressed as gag-PR fused polyprotein. The active PR is a dimer obtained after the aggregation of the gag and gag-pro precursors, which leads to the formation and the release of the viral particle. Subsequently, in the cell, the PR is present essentially as a monomeric polyprotein. To mimic the antigenic properties of such an intracellular form of the PR, we produced a monomeric form of the HTLV-I (human T-cell leukemia virus, type-I) PR fused to the maltose binding protein (MBP-PR). Monoclonal antibodies (mabs) directed against MBP-PR were developed. Three mabs were obtained that recognized different epitopes. Two were directed against the NH2-terminus, a region that contributes to the dimerization interface. The other was specific to a peptide that lines the substrate binding pocket. This latter epitope is located just downstream of the D-T-G peptide of the catalytic site. The two identified regions contained the amino acids Asp6, Arg10 and Asp36, which were previously shown to be important in the stabilization of the dimer. In view of the localization of the recognized epitopes, these mabs will be useful for inhibition studies of the HTLV-I PR by intracellular immunization.

Improvement of gelatin particle agglutination test for detection of anti-HTLV-I antibody.

Partial modifications of antigen components were made to improve the gelatin particle agglutination (PA) test for the detection of antibodies against human T cell leukemia virus type-I. Envelope glycoproteins prepared by lentil lectin affinity chromatography were further added to the purified viral antigens to be coated on the gelatin particles. Comparative studies with a conventional PA test kit (Serodia ATLA) and indirect immunofluorescence assay showed that the specificity and sensitivity of the new PA test were increased and that abnormal agglutination such as the prozone phenomenon was abolished by this improvement.

Probing the conformation of the human T-lymphotropic virus I envelope protein complex with monoclonal antibodies.

We are investigating the binding of a series of monoclonal antibodies to native and detergent-treated human T-lymphotropic virus I (HTLV-I) envelope proteins to explore their conformation. A comparison of our data with previously published findings suggests that a central neutralization domain (aa 175-200) is folded such that only short stretches are exposed at the surface of the native envelope protein complex. However, the complete domain becomes accessible after treatment with mild non-ionic detergents, suggesting that envelope subunit interaction may partially obscure this domain. We further provide immunochemical evidence that a region containing a heptad repeat in the extracellular part of the transmembrane protein is folded towards the interior of the HTLV-I envelope complex.

Segregation of human T cell lymphotropic virus type I and II infections by antibody reactivity to unique viral epitopes.

A recombinant protein of the human T cell lymphotropic virus type I (HTLV-I) gp46 outer membrane envelope, MTA-4 (residues 129-203), reacted by Western blot with sera from HTLV-I-infected individuals from the United States and Jamaica but not with 24 (10%) of 242 Japanese sera. A related gp46 recombinant protein, MTA-1 (residues 162-209), reacted with all 58 sera from HTLV-I-infected US and Jamaican individuals and 238 of 242 sera from infected Japanese (combined sensitivity of 99%). Neither recombinant showed reactivity to sera from HTLV-II-infected individuals or uninfected controls. The reactivity of recombinant proteins containing the region of HTLV-II gp46 analogous to MTA-1 was also evaluated by Western blot: GH2-K15 (residues 157-205) and GH2-K55 (residues 162-205) reacted with 88 (98%) and 89 (99%), respectively, of 90 sera from HTLV-II-infected individuals but not with sera from HTLV-I-infected individuals or uninfected controls. These recombinant proteins should permit the development of assays to unambiguously confirm and differentiate HTLV-I and HTLV-II infections.

Sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for (antihuman T-cell leukemia virus type I) immunoglobulin G in serum using a synthetic peptide, Ala-Cys-Env gp46(237-262), as antigen.

A sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for (antihuman T-cell leukemia virus type I) IgG (anti-HTLV-I IgG) in serum using a synthetic peptide, Ala-Cys-env gp46(237-262), of HTLV-I is described. Anti-HTLV-I IgG in test serum, which had been incubated with excess of inactive beta-D-galactosidase to eliminate interference by anti-beta-D-galactosidase antibodies, was reacted simultaneously with 2,4-dinitrophenyl-bovine serum albumin-Ala-Cys-env gp46(237-262) conjugate and Ala-Cys-env gp46(237-262)-beta-D-galactosidase conjugate. The complex formed consisting of the three components was trapped onto polystyrene balls coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG. After washing to eliminate nonspecific IgG in the test serum and excess of the beta-D-galactosidase conjugate, the complex was eluted from the polystyrene balls with epsilon N-2,4-dinitrophenyl-L-lysine and transferred to polystyrene balls coated with affinity-purified (anti-human IgG gamma-chain) IgG. beta-D-galactosidase activity bound to the (anti-human IgG gamma-chain) IgG-coated polystyrene balls was assayed by fluorometry. This assay was more sensitive than other methods using HTLV-I as antigen, and most negative and positive sera were discriminated. However, some results appeared to be false positive or false negative, and the peptide, Ala-Cys-env gp46(237-262), was suggested to be useful, in combination with other peptides, for improving the reliability of serodiagnosis by separately demonstrating antibodies against as many different epitopes of HTLV-I as possible.

Antigenic mixture of synthetic peptides for the immunodiagnosis of HTLV I/II infection.

Monomeric and chimeric synthetic peptides were used as coating antigens in four different mixtures in a solid phase immunoassay to select an optimal combination for the detection of antibodies to human T-cell lymphotropic virus (HTLV) in serum samples. The peptides, P-13 (gp21 I), Q5 (gp21 II)-GG-(gp46 II), and Q (gp46 I)-GG-(p19 I), represent immunodominant sequences from transmembrane protein (gp21), envelope protein (gp46), and core protein (p19) of HTLV I/II viruses; they were the most antigenic and specific peptides in previous studies. The sequences of the chimeric peptides were separated by two glycine residues. An indirect UltramicroEnzyme-linked immunosorbent assay (UMELISA) was used to evaluate the antigenicity of these peptide mixtures by using samples from anti-HTLV I/II PRP205(M), (n = 20), HTLV I-infected individuals from Cuba (n = 7), and HTLV I-positive sera from Colombia and Chile (n = 9). The specificity was evaluated with healthy blood donor sera (n = 300), anti-HIV 1-positive samples (n = 10), and other seropositive samples to different infectious agents. The highest sensitivity and specificity was obtained with mixture 1, which could be very useful in the immunodiagnostic of HTLV infection.

Demonstration of human T lymphotropic virus type I (HTLV-I)-specific T cell responses from seronegative and polymerase chain reaction-negative persons exposed to HTLV-I.

Human T lymphotropic virus type I (HTLV-I) is a human retrovirus etiologically linked to adult T cell leukemia and the progressive chronic neurologic disease HTLV-I-associated myelopathy/tropical spastic paraparesis. Described is a method that measures the production of interleukin-2 from HTLV-I synthetic peptide-stimulated peripheral blood lymphocytes (PBL) of HTLV-I-infected persons. The peptides correspond to immunogenic regions of the HTLV-I Env and Tax proteins. Significantly, this assay demonstrated T cell responses to these HTLV-I peptides from coded PBL samples in 7 of 19 HTLV-I-seronegative polymerase chain reaction-negative persons known to have been exposed to HTLV-I but in none of 16 matched controls without risk factors for exposure (P = .007). The implications of this finding are discussed.

Immunogenicity and conformational properties of an N-linked glycosylated peptide epitope of human T-lymphotropic virus type 1 (HTLV-I).

The identification and characterization of epitopes of human T-lymphotropic virus type 1 (HTLV-I), which elicit an effective humoral or cell-mediated immune response, remains a central obstacle to the development of a peptide-based vaccine against the virus infection. The objective of the studies presented here was to examine the influence of N-linked glycosylation on peptide structure and immunogenicity. We engineered the 233-253 sequence of gp46 of HTLV-I to contain an N-acetylglucosamine (GlcNAc) residue at Asn244. Secondary structure prediction using computer algorithms indicated that this peptide may contain a beta-turn at residues 242-246. Recent work with model glycopeptides suggests that beta-turn conformation in peptides may be induced, and probably is stabilized, by the presence of even a single sugar residue. In the present study, the structures of the 233-253 peptide, SC1, and the 233-253(Asn244-GlcNAc) glycopeptide, SC2, were determined. Similar conformation was exhibited by both the glycosylated and nonglycosylated peptide displaying a beta-turn at residues 243-246 and extended-chain structure at the peptide/glycopeptide termini. Both peptides were engineered into chimeric constructs with a promiscuous T-cell epitope from measles virus and were used as immunogens in rabbits. Both chimeric peptides were highly immunogenic in rabbits, producing high-titered antibodies as early as primary + three weeks. The antibodies generated against either construct were able to bind to whole virus (ELISA) and to gp46 (radioimmunoprecipitation assay). Additionally, human sera of individuals known to be positive for HTLV-I recognized both the glycosylated and nonglycosylated constructs. It appears that the 233-253 peptide is able to adopt a conformation that mimics the structure in native gp46, and addition of a GlcNAc residue at Asn244 does not affect the conformational preference or stability of this construct; nor does glycosylation alter immunogenicity but instead appears to enhance immune recognition.

Characterization of an antigen shared by human thymic epithelium and human T cell leukemia virus p19 Gag protein.

The molecular basis for cross-reactive antibody binding to human T cell leukemia virus type I (HTLV-I) p19 core protein and human thymic epithelium has been defined with two monoclonal antibodies (mAbs), 12/1-2 and 13B12, raised to HTLV-I p19. The mAb 12/1-2 has previously been shown to react with HTLV-I p19, HTLV-II p22, and antigens of normal human thymic epithelium, placenta, and foreskin, whereas mAb 13B12 binds only to the carboxyl terminus of HTLV-I p19. In the present study, mAb 12/1-2 bound to a subset of Triton X-100-insoluble intermediate filaments in human thymic epithelium also recognized by antikeratin antibodies AE1 and AE3. The mAb 12/1-2 also reacted in Western blot assays with proteins of 54, 46, and 40 kDa present in extracts of human thymic epithelium and with hexameric peptides containing overlapping sequences of HTLV-I p19 with the amino acids IPP (amino acids 117-119). In contrast, the HTLV-I-specific mAb 13B12 did not bind to human thymic epithelium and reacted with a single hexameric peptide containing the carboxy-terminal HTLV-I p19 sequence IPPPYV (amino acids 117-122). Binding of mAb 12/1-2 to thymic epithelium could be inhibited by adsorption with peptide SP-79 containing a C-terminal sequence (amino acids 112-125) of p19. The crossreactive IPP site is within a region of p19 that has been previously shown to be highly immunogenic in HTLV-I-infected individuals and that is also encoded by genes or mRNA of human cytokeratin 17, keratin 4, epidermal cytokeratin 2, and 50-kDa type I epidermal keratin. Thus, our studies define the sequence of a cross-reactive antigen on HTLV-I p19 that is also associated with keratin intermediate filaments from human thymic epithelium and other normal human tissues and that could serve as a focus of an autoimmune response during HTLV-I infection.

Synthesis and CD studies of an 88-residue peptide containing the main receptor binding site of HTLV-I SU-glycoprotein.

Essential HTLV-1 biological functions, like host-cell receptor recognition, depend on the structural motives on the surface glycoprotein gp46. We defined a peptide of 88 amino acids [Arg147-Leu234] corresponding to the central part of the protein sequence, where major neutralizing epitopes are localized. After evaluating the feasibility of its chemical synthesis, the chosen sequence was realized using the stepwise solid-phase methodology. Multiple chromatographic purification steps were required to obtain a sample suitable for structural analysis. Correct folding was supported by strong binding of monooclonal antibodies, recognizing known exposed immunodominant regions. Circular dichroism studies confirmed a non-random conformation of at least 70-80% of the synthetic peptide. Investigation of the 3D-structure of the synthetic peptide will provide useful information for future vaccine and drug-design strategies.

Antigenicity of chimeric synthetic peptides based on HTLV-1 antigens and the impact of epitope orientation.

The present study evaluated four chimeric synthetic peptides incorporating immunodominant sequences from HTLV-1 virus. Monomeric peptides M1, M2, and M3 represent sequences from core (p19) and envelope (gp46) of the virus. The peptide M1 is a p19 (105-124) sequence, the peptide M2 is a gp46 (190-207) sequence, and the peptide M3 is a gp 46 sequence with substitution of proline at position 192 by serine. Those peptides were arranged in such a way that permits one to obtain different combinations of chimeric peptides (M1-M2, M2-M1, M1-M3, and M3-M1). Two glycine residues were used as arm spacers for separating the two sequences. The antigenicity of these peptides was evaluated in an ultramicroenzyme-linked immunosorbent assay (UMELISA) using sera of human T cell leukemia virus type I (HTLV-I)-infected individuals (n = 24), while specificity was evaluated with anti-HTLV-II-positive samples (n = 11) and healthy blood donors (n = 25). The results were compared to plates coated with monomeric peptides M1, M2, and M3. The chimeric peptide orientation (M1-M2) and the proline at position 192 of the gp46 peptide showed higher sensitivity.

Chimeric synthetic peptides containing two immunodominant epitopes from the envelope gp46 and the transmembrane gp21 glycoproteins of HTLV-I virus.

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.

A source of glycosylated human T-cell lymphotropic virus type 1 envelope protein: expression of gp46 by the vaccinia virus/T7 polymerase system.

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.

Structural and immunogenicity analysis of chimeric B-cell epitope constructs derived from the gp46 and gp21 subunits of the envelope glycoproteins of HTLV-1.

B-cell epitopes were selected from the gp21 and gp46 subunits of the envelope glycoprotein of human T-cell lymphotropic virus type 1 (HTLV-1) by computer-aided analyses of protein antigenicity. Molecular modeling was used to design and synthesize the epitopes as chimeric constructs with promiscuous T-helper epitopes derived either from the tetanus toxoid (amino acids 947-967) or measles virus fusion protein (amino acids 288-302). Circular dichroism measurements revealed that the peptides had a secondary structure that correlated well with the crystal structure data or predicted structure. The chimeric peptides were then evaluated for their immunogenicity in rabbits or mice. Antibodies against one of the epitopes derived from the gp21 subunit were found to be neutralizing in its ability to inhibit the formation of virus-induced syncytia. These studies underscore the importance of the gp21 transmembrane region for the development of vaccine candidates. The applicability of a chimeric approach is discussed in the context of recent findings regarding the role of gp21 transmembrane region in the viral fusion process.