Non-specific peptide size effects in the recognition by site-specific T-cell clones. Demonstration with a T site of myoglobin

Regions of botulinum neurotoxin A light chain recognized by human anti-toxin antibodies from cervical dystonia patients immunoresistant to toxin treatment. The antigenic structure of the active toxin recognized by human antibodies

This work was aimed at determining the BoNT/A L-chain antigenic regions recognized by blocking antibodies in human antisera from cervical dystonia patients who had become immunoresistant to BoNT/A treatment. Antisera from 28 immunoresistant patients were analyzed for binding to each of 32 overlapping synthetic peptides that spanned the entire L-chain. A mixture of the antisera showed that antibodies bound to three peptides, L11 (residues 141-159), L14 (183-201) and L18 (239-257). When mapped separately, the antibodies were bound only by a limited set of peptides. No peptide bound antibodies from all the patients and amounts of antibodies bound to a given peptide varied with the patient. Peptides L11, L14 and L18 were recognized predominantly. A small but significant number of patients had antibodies to peptides L27 (365-383) and L29 (379-397). Other peptides were recognized at very low and perhaps insignificant antibody levels by a minority (15% or less) of patients or had no detectable antibody with any of the sera. In the 3-dimensional structure, antibody-binding regions L11, L14 and L18 of the L-chain occupy surface areas and did not correlate with electrostatic potential, hydrophilicity/hydrophobicity, or temperature factor. These three antigenic regions reside in close proximity to the belt of the heavy chain. The regions L11 and L18 are accessible in both the free light chain and the holotoxin forms, while L14 appears to be less accessible in the holotoxin. Antibodies against these regions could prevent delivery of the L-chain into the neurons by inhibition of the translocation.

Immune recognition of botulinum neurotoxin B: antibody-binding regions on the heavy chain of the toxin

The purpose of this work was to map the continuous regions recognized by human, horse and mouse anti-botulinum neurotoxin B (BoNT/B) antibodies (Abs). We synthesized a panel of sixty 19-residue peptides (peptide C31 was 24 residues) that overlapped consecutively by 5 residues and together encompassed the entire heavy chain of BoNT/B (H/B, residues 442-1291). Abs from the three host species recognized similar, but not identical, peptides. There were also peptides recognized by two or only by one host species. Where a peptide was recognized by Abs of more than one host species, these Abs were at different levels among the species. Human, horse and mouse Abs bound, although in different amounts, to regions within peptides 736-754, 778-796, 848-866, 932-950, 974-992, 1058-1076 and 1128-1146. Human and horse Abs bound to peptides 890-908 and 1170-1188. Human and mouse Abs recognized peptides 470-488/484-502 overlap, 638-656, 722-740, 862-880, 1030-1048, 1072-1090, 1240-1258 and 1268-1291. We concluded that the antigenic regions localized with the three antisera are quite similar, exhibiting in some cases a small shift to the left or to the right. This is consistent with what is known about protein immune recognition. In the three-dimensional structure, the regions recognized on H/B by anti-BoNT/B Abs occupied surface locations and analysis revealed no correlation between these surface locations and surface electrostatic potential, hydrophilicity, hydrophobicity, or temperature factor. A region that bound mouse Abs overlapped with a recently defined site on BoNT/B that binds to mouse and rat synaptotagmin II, thus providing a molecular explanation for the blocking (protecting) activity of these Abs. The regions thus localized afford candidates for incorporation into a synthetic vaccine design.

Mapping of the antibody-binding regions on the HN-domain (residues 449-859) of botulinum neurotoxin A with antitoxin antibodies from four host species. Full profile of the continuous antigenic regions of the H-chain of botulinum neurotoxin A

Previously, we mapped the antibody (Ab) and T-cell recognition regions on the HC domain (residues 855-1296) of the 848-residue heavy (H) chain of botulinum neurotoxin A (BoNT/A). We have mapped here the HN-domain (residues 449-859) regions that bind protective anti-BoNT/A Abs raised in four different species. We synthesized, purified, and characterized 29 19-residue peptides that spanned the entire HN and overlapped consecutively by 5 residues, and also region L218-231 around the L-chain's substrate-binding site. Human, horse, mouse, and chicken anti-BoNT/A Abs did not bind to the L-peptide but recognized similar HN regions within peptides 519-537/533-551/547-565/561-579 (with slight left- or right-shifts), 743-761, 785-803, and 813-831/827-845 overlap. Recognition of other peptides that bound lower Ab levels showed similarities and also some differences. Peptide 463-481, strongly immunodominant with horse antisera, did not bind human, mouse, and chicken Abs. However, peptide 449-467 bound Abs in these three antisera, and the region may have shifted to the right (peptide 463-481) with horse Abs. The overlap 659-677/673-691 reacted strongly with human Abs whereas with mouse and chicken antisera, only peptide 673-691 showed low reactivity. Horse antisera had no detectable Ab binding to region(s) 659-691. The Ab-recognition regions on the H chain occupy surface locations in BoNT/A three-dimensional structure, but the great part of the surface is not immunogenic. Regions recognized by the protective antisera of the four different species are prime candidates for inclusion in synthetic vaccine designs.

B-cell activation in vitro by helper T cells specific to a protein region that is recognized both by T cells and by antibodies

This laboratory had previously mapped the regions of T and B cell recognition on sperm whale myoglobin (Mb). Mb has five regions (E1-E5) that are recognized by both T cells and B cells (i.e. antibodies, Abs) and an additional region (E6) that is recognized exclusively by T cells (i.e., TE6) and to which no Abs are detectable. The responses to the site are each under separate genetic control. Recently, we showed in an H-2d haplotype that TE6 cells preferentially activated Mb-primed B cells (BMb) that made Abs against sites within E3 and E4 on the same protein. In the present work, we established, from Mb-primed SJL mice, an E4-specific T cell line (TE4) by passage in vitro with synthetic peptide E4. At relatively low numbers, these T cells activated syngeneic BMb cells in vitro to produce anti-Mb Abs that recognized each of the antigenic sites within regions E1, E2, E3, E4 and E5. We confirmed the ability of TE4 to activate B cells that produce Abs against each of these regions by allowing TE4 to activate in vitro syngeneic B cells that had been primed with E1, E2, E3, E4 or E5. The helper activity of TE4 cells was dependent on the in vitro concentration of the challenge Ag (intact Mb or peptide E4). Thus, T cells against an epitope may provide help restricted to B cells that make Abs against selected antigenic sites or they may activate B cells that make Abs against all the antigenic sites of a protein. This might depend on the site-specificity of the T cell and/or on the host.

Identification of core B cell epitope in the synthetic peptide inducing cross-inhibiting antibodies to a surface protein antigen of Streptococcus mutans

A surface protein antigen (PAc) of Streptococcus mutans, in particular, A-region of the molecule, has been considered as a possible target for the development of an effective anticaries vaccine. This region might be implicated in the induction of dental caries via interaction with salivary components. We have recently specified a unique peptide, TYEAALKQYEADL, as one of the minimum peptides that completely corresponds to the amino acid sequence of a part of the A-region. The unique peptide contains both T and B cell epitopes for the induction of cross-reacting antibodies to the PAc. In this study, we synthesized valine or glycine-substituted peptide analogs of this peptide and examined core B cell epitopes of this unique peptide by using ELISA inhibition assay. As a result, the core amino acid residues of -Y------Y---- for B cell recognition were found to likely be not only important amino acids stabilizing the structure, but also might be essential for induction of the cross-inhibiting antibodies against PAc. These results will hopefully provide us with useful information for the design of an effective anticaries peptide vaccine.

Localization of the regions on the C-terminal domain of the heavy chain of botulinum A recognized by T lymphocytes and by antibodies after immunization of mice with pentavalent toxoid

We have mapped the regions recognized by T and/or B cells (Abs) on the C-terminal domain (Hc) of the heavy chain of botulinum neurotoxin serotype A (BoNT/A) after immunization of two inbred mouse strains with pentavalent toxoid (BoNTs A, B, C, D and E). Using a set of synthetic overlapping peptides, encompassing the entire Hc domain (residues 855-1296), we demonstrated that T cells of Balb/c (H-2d) mice, primed with one injection of toxoid, recognized two major regions within residues 897-915 and 939-957. After multiple inoculations with toxoid, T cells of Balb/c expanded their recognition ability and responded very well to challenge with peptide 1261-1279 and moderately to stimulation with peptide 1149-1167. Unlike Balb/c T cells, those of toxoid-primed SJL (H-2s) mice exhibited a more complex profile and responded to challenge with a large number of overlapping peptides. After one toxoid injection, however, three peptides, 897-915, 939-957/953-971 overlap and 1051-1069, were the most potent T cells stimulators. After three toxoid injections, peptides 897-915 and 1051-1069 remained immunodominant while the third region was shifted upstream to 925-943/939-957 overlap. The immunodominant epitope within peptide 897-915 was recognized exclusively by T cells, since no Abs were detected against this region. The Ab binding profiles of the two mouse strains were quite similar, showing only small quantitative differences. Both, Balb/c and SJL anti-toxoid Abs displayed strong binding mainly to peptide 1177-1195, followed by peptides 869-887/883-901 overlap and 1275-1296. In addition, a significant amount of Balb/c anti-toxoid Abs was bound to peptide 1135-1153. Unlike Balb/c Abs, that interacted weakly with peptides 995-1013 and 1051-1069, the anti-toxoid Abs of SJL mice exhibited strong binding toward both peptides. The results showed that, in a given strain, the regions recognized by anti-toxoid Abs and T cells may coincide or may be uniquely B or T cell determinants.

Antibody and T-cell recognition of alpha-bungarotoxin and its synthetic loop-peptides

Peptides representing the loops and surface regions of alpha-bungarotoxin (BgTX) and control peptide analogs in which these sequences were randomized were synthesized and used to map the recognition profiles of the antibodies and T-cells obtained after BgTX immunization. Also, the abilities of anti-peptide antibodies and T-cells to recognize the immunizing peptide and BgTX were determined. Three regions of BgTX were immunodominant by both rabbit and mouse anti-BgTX antibodies. These regions resided within loops L1 (residues 3-16), L2 (residues 26-41) and the C-terminal tail (residues 66-74) of the toxin. The regions recognized by BgTX-primed T-lymphocytes were mapped in five mouse strains: C57BL/6(H-2b), Balb/c (H-2d), CBA (H-2k), C3H/He (H-2k) and SJL (H-2s). The H-2b and H-2d haplotypes were high responders to BgTX, while the H-2k and H-2s were intermediate responders. The T-cell recognition profile of the peptides varied with the haplotype, consistent with Ir gene control of the responses to the individual regions. The submolecular specificities of antibodies and T-cells were compared in three of the mouse strains (C57BL/6, Balb/c and SJL). In a given mouse strain, there were regions that were strongly recognized by both antibodies and T-cells as well as regions that were predominantly recognized either by antibodies or by T-cells. The peptides were used as immunogens in their free form (i.e. without coupling to any carrier) in two of the mouse strains, Balb/c and SJL. In both mouse strains, the peptides gave strong antibody responses. Antibodies against peptide L2 showed the highest binding to intact BgTX. Antibodies against the other peptides exhibited lower binding activity to the intact toxin, and this activity was dependent on the peptide and the mouse strain. The response of peptide-primed T-cells to a given immunizing peptide was not related to whether this region was immunodominant with BgTX-primed T-cells. The ability of peptide-primed T-cells to recognize the intact toxin varied with the peptide and was dependent on the host strain. These results indicate that anti-peptide antibody and T-cell responses are also under genetic control and that their ability to cross-react with the parent toxin is not only dependent on the conformational exposure of the correlate region in intact BgTX.

Profile of the regions on the alpha-chain of human acetylcholine receptor recognized by autoantibodies in myasthenia gravis

Eighteen synthetic overlapping peptides encompassing the entire extracellular part (residues alpha 1-210) of the alpha-chain of human acetylcholine receptor (AChR) and a 19th peptide (residues alpha 262-276) corresponding to an extracellular connection between two transmembrane regions were prepared and used for the measurement, by solid-phase radioimmunoassay, of the binding of autoantibodies in plasma from myasthenia gravis (MG) patients. Autoantibodies were found to recognize only a limited number of the synthetic peptides. The regions recognized resided predominantly within the areas alpha 10-30, alpha 111-145 and alpha 175-198 and, less frequently, region alpha 45-77. Differences in the recognition profile of the peptides from patient to patient indicated that the autoantibody responses were under genetic control. However, by using a mixture of the appropriate peptides, it was possible to determine autoantibodies in all 15 myasthenia sera and to distinguish between these, normal human sera and other neurological or autoimmune diseases. The mapping of the continuous antigenic regions recognized by autoantibodies on the alpha-chain of human AChR has permitted a comparison of the regions recognized by autoantibodies and autoimmune T-cells from the same donor. It also provided a peptide-based direct antibody binding method for diagnosis of MG.

HIV envelope protein is recognized as an alloantigen by human DR-specific alloreactive T cells

Recent studies from this laboratory reported the mapping of the full profile of T-cell allorecognition regions of HLA-DR2 beta subunit. The results indicated the presence of an allodeterminant within DR2 beta regions 141-156. In another study, we have shown that this allodeterminant is one of five regions of structural homology between the DR2 beta molecule and the HIV-envelope protein gp120 region 254-268. The fact that gp120 peptide 254-268 is homologous to the allodeterminant within the DR2 beta region 141-156 prompted us to investigate whether synthetic gp120 peptide 254-272 is recognized by human DR2-specific alloreactive T-cell lines. Five human alloreactive T-cell lines were prepared that were specific for the DR2 molecule and did not recognize DR1. These lines mounted in vitro proliferative responses to the allodeterminant peptide DR141-156 and also responded to the DR-similar peptide gp254-272. Removal of the residues 262-272 from the gp120 peptide (i.e., peptide 254-263) resulted in essentially complete loss of its proliferative activity. The effect of deletion of three residues of homology (Val-Val-Ser) at the N terminal (i.e., peptides DR145-156 and gp257-272) was examined. Peptide DR2 beta 145-156 exhibited very low stimulating activity, whereas peptide gp 257-272 did not cause T-cell proliferative responses in any of the alloreactive T-cell lines. The T-cell lines did not respond to unrelated peptide controls, thus further confirming the specificity of these responses. These findings indicate that the virus is recognized as an alloantigen by human alloreactive DR2-specific T cells.

Antigen processing by endosomal proteases determines which sites of sperm-whale myoglobin are eventually recognized by T cells

This study reports an identification of the major processing products of an exogenous protein antigen, viz, sperm-whale myoglobin, as obtained after cell-free processing with partially purified macrophage endosomes. It is demonstrated that such a system yields fragments that are indistinguishable by high performance liquid chromatography analysis from those generated after uptake of myoglobin inside live macrophages. The concerted action of the endosomal proteases cathepsin D and cathepsin B can account for nearly all cleavages observed. Cathepsin D appears to be mainly responsible for the initial cleavage of myoglobin, while cathepsin B catalyzes the C-terminal trimming of initially released fragments. The fragments released by cathepsin D contain most, if not all, major epitopes for murine myoglobin-specific helper T cells. Interestingly, each known T cell epitope of myoglobin is located at the very N terminus of a different myoglobin fragment released upon processing. In order to explain this correspondence, noted also in several other protein antigens, a structural relationship is proposed between antigen processing by cathepsin D and antigen recognition by major histocompatibility complex (MHC) class II products. As is demonstrated here, this relationship may be used as a predictive tool for the identification of MHC-binding sequences as well as of T cell epitopes in their naturally occurring form.

Autoimmune T cell recognition of human acetylcholine receptor: the sites of T cell recognition in myasthenia gravis on the extracellular part of the alpha subunit

Autoimmune T cell lines were prepared from peripheral blood lymphocytes of five myasthenia gravis patients by passage in vitro with an equimolar mixture of 18 overlapping synthetic peptides corresponding to the entire extracellular region (residues alpha 1-210) of the alpha subunit of human acetylcholine receptor (AChR). The proliferative responses of the human AChR-specific T cell lines to each of the individual peptides were determined. It was found that the profiles of the peptides recognized by the T cells were different among the five T cell lines, consistent with genetic control operating at the recognition site level. However, other regulatory influences may play important roles in the triggering of the autoimmune responses. These results suggest that the pathogenesis of this autoimmune disease is variable at the cellular-molecular level.

Characteristics of peptides which compete for presented antigen-binding sites on antigen-presenting cells

The T cell recognition of globular protein antigens requires the cell surface presentation of the protein by Ia-expressing antigen-presenting cells (APC). The mechanisms by which APC function remain to be elucidated. To gain a better understanding of association of antigen with APC surfaces, a large panel of peptides of diverse physicochemical properties was assayed for the ability to compete with presented antigen for binding sites on the APC surface. Competition was measured by the ability of a peptide to block the I-Ek-restricted T cell response to pigeon cytochrome c (Pc) as presented by APC. The panel assayed included overlapping peptides representing the entire length of sperm whale myoglobin and the alpha and beta chains of human adult hemoglobin as well as synthetic conformational peptides of lactate dehydrogenase C4 exhibiting stable secondary, alpha-helical structures. The results presented here show that several peptides of this group compete with the presented form of Pc for binding sites on the APC. However, there is no single biochemical property or amino acid sequence algorithm which predicts the blocking ability. The peptides which compete with presented Pc are not predicted to assume the amphipathic alpha-helical conformation hypothesized by De Lisi and Berzofsky (Proc. Natl. Acad. Sci. USA 1986. 82: 7048) for T cell antigenic peptides. However, peptides designed and synthesized to adopt a stable alpha-helical secondary structure show more potent blocking activity than the corresponding linear peptides, suggesting that the secondary structure may indeed be a contributing factor in the ability of presented antigenic peptides to be bound by the APC. The results with the myoglobin and hemoglobin peptides show no connection between any particular secondary structure of the peptide in the native proteins and the ability of the peptides to block presentation. Further, there is no correlation between the major histocompatibility complex restriction of the competing peptides and their ability to block the I-Ek-restricted Pc-specific T cell response. This suggests that antigen presented by the APC may be bound to APC structures other than Ia prior to association with Ia. Such additional binding sites for presented antigen may be necessary to facilitate association with Ia.

Mapping of the full profile of T cell allorecognition regions on HLA-DR2 beta subunit

Alloreactive human T cell lines were developed by repeated in vitro restimulation with alternate allogeneic cells of similar DR2 serotype, but differing at other HLA loci. These polyclonal T cells recognized DR specificities in common with all DR2 serotypes. The allorecognition profiles of DR2 beta by the T cell lines were mapped by consecutive uniform-sized overlapping peptides encompassing the entire extracellular and intracellular regions of the DR beta subunit. It was found that the T cell allorecognition sites are focused around the first and third polymorphic regions of the N-terminal domain, and interestingly, include conserved areas in the DR beta second domain as well as the intracellular segment beta 222-237. These findings have important implications for allorecognition. Comparison with the previous analysis of antibody-binding regions of DR2 beta revealed some similarities and differences in the antibody and T cell alloresponses to this histocompatibility antigen.

Antigen presentation by non-immune B-cell hybridoma clones: presentation of synthetic antigenic sites reveals clones that exhibit no specificity and clones that present only one epitope

Recently, we reported the preparation and antigen-presenting properties of hybridoma B-cell clones obtained after fusing non-secreting, non-antigen presenting Balb/c 653-myeloma cells with non-immune SJL spleen cells. It was found that antigen presentation at the clonal level can be specific or non-specific, depending on the particular B-cell clone. In the present work, one specific and one general presenter B-cell clones were tested for their epitope presentation ability to SJL T-cells that were specific to lysozyme or myoglobin. B-cell clone A1G12, a general presenter which presented both lysozyme and myoglobin to their respective T-cell lines, was found to present all five myoglobin epitopes while clone A1L16, a lysozyme specific presenter presented only one of the three epitopes of lysozyme. The latter reveals a hitherto unknown submolecular specificity (to a given epitope within a protein) for antigen presenting cells at the clonal level. Therefore, the specificity of T-cell recognition does not only derive from the T-cell but may also be dependent on the epitope specificity of the antigen-presenting B-cell.

Conformation-dependent recognition of a protein by T cells requires presentation without processing

Presentation of a protein antigen to T cells is believed to follow its intracellular breakdown by the antigen-presenting cell, with the fragments constituting the trigger of immune recognition. It should then be expected that T-cell recognition of protein antigens in vitro will be independent of protein conformation. Three T-cell lines were made by passage in vitro with native lysozyme of T cells from two mouse strains (B10.BR and DBA/1) that had been primed with the same protein. These cell lines responded well to native lysozyme and very poorly to unfolded (S-sulphopropyl) lysozyme. The response of the T-cell lines to the antigen was major histocompatibility complex (MHC)-restricted. A line from B10.BR was selected for further studies. This line responded to the three surface-simulation synthetic sites of lysozyme (representing the discontinuous antigenic, i.e. antibody binding, sites) and analogues that were extended to a uniform size by a nonsense sequence. T-cell clones prepared from this line were specific to native lysozyme and did not respond to the unfolded derivative. Furthermore, several of these clones showed specificity to a given surface-simulation synthetic site. The exquisite dependency of the recognition by the clones on the conformation of the protein antigen and their ability to recognize the surface-simulation synthetic sites indicate that the native (unprocessed) protein was the trigger of MHC-restricted T-cell recognition.

T-cell recognition and antigen presentation of myoglobin. Protein recognition by site-specific T-cell clones is influenced by amino acid substitutions outside the site

Six T-cell clones from SJL mice were prepared from T-cell lines that were obtained by passage with synthetic myoglobin (Mb) peptide 107-120. In addition, a T-cell clone, specific to this region of Mb, was isolated from a Mb-passaged T-cell culture. The proliferative responses of these clones to Mb variants from 14 different species were studied. It was found, as expected, that amino acid replacements within the site affected its recognition by the T-cell clones. In addition to these effects, the T-cell recognition site, like the sites recognized by antibodies, was also influenced by substitutions of residues that are close to site residues in three-dimensional structure but are otherwise distant in sequence. This is noteworthy in view of the fact that six of the clones were selected with a free peptide, and thus the environmental residues are clearly not part of the 'contact' residues of the site. These findings are discussed in relation to the presentation of the antigen and are interpreted as indicating that Mb is presented in its intact form to the T-cells in vitro.

T lymphocyte recognition of acetylcholine receptor: localization of the full T cell recognition profile on the extracellular part of the alpha chain of Torpedo californica acetylcholine receptor

A series of eighteen consecutive overlapping synthetic peptides, of uniform size and overlaps, which encompass the entire extracellular part (residues 1-210) of the Torpedo californica acetylcholine receptor alpha chain were examined in vitro for their ability to stimulate lymph node cells from acetylcholine receptor-primed C57BL/6 (H-2b), C3H/He (H-2k), SWR (H-2q) and SJL (H-2s) mice. The recognition sites (T sites) by acetylcholine receptor-primed lymph node cells from these mouse strains resided within six regions on the extracellular part of the alpha chain. Three of the regions recognized by T cells coincided with regions recognized by antibodies (i.e. B cells) and one of these three regions also coincided with an alpha-neurotoxin-binding region. It is noteworthy that, in addition to sites recognized by both T and B cells, the protein has at least two sites which are recognized exclusively by T cells and to which no detectable antibody responses are directed.