T cell clones specific for an amphipathic alpha-helical region of sperm whale myoglobin show differing fine specificities for synthetic peptides. A multiview/single structure interpretation of immunodominance

Selecting the Antigen

The classical method for generating polyclonal or monoclonal antibodies relies on the in vivo humoral response of animals. Here we describe the factors that antigens can have that might influence the strength and quality of an antibody response. This introduction is divided into three sections: (1) an overview of immunogenicity, (2) choosing the best form for the immunogen, and (3) methods for modifying antigens to make them more immunogenic.

Cryptosporidium spp. CP15 and CSL protein-derived synthetic peptides' immunogenicity and in vitro seroneutralisation capability

Cryptosporidium spp. is a zoonotic intracellular protozoan and a significant cause of diarrhoea in humans and animals worldwide. This parasite can cause high morbidity in immunocompromised people and children in developing countries, livestock being the main reservoir. This study was aimed at performing preliminary tests on Swiss albino weaned mice (ICR) to evaluate the humoral immune response induced against peptides derived from Cryptosporidium parvum CP15 (15 kDa sporozoite surface antigen) and CSL (circumsporozoite-like antigen) proteins. Peptides were identified and characterised using bioinformatics tools and were chemically synthesised. The antibody response was determined and the neutralising effect of antibodies was measured in cell culture. Despite all peptides studied here were capable of stimulating antibody production, neutralising antibodies were detected for just two of the CP15-derived ones. Additional studies aimed at evaluating further the potential of such peptides as vaccine candidates are thus recommended.

Structure of an α-Helical Peptide and Lipopeptide Bound to the Nonclassical Major Histocompatibility Complex (MHC) Class I Molecule CD1d

Mouse CD1d is a nonclassical MHC molecule able to present lipids and glycolipids to a specialized subset of T cells known as natural killer T cells. The antigens presented by CD1d have been shown to cover a broad range of chemical structures and to follow precise rules determining the potency of the antigen in the context of T cell activation. Together with lipids, initial reports suggested that CD1d can also bind and present hydrophobic peptides with (F/W)XX(I/L/M)XXW. However, the exact location of peptide binding and the molecular basis for the required motif are currently unknown. Here we present the crystal structure of the first peptide identified to bind CD1d, p99, and show that it binds in the antigen-binding groove of CD1d in a manner compatible with its presentation to T cell receptors. Interestingly, the peptide adopts an α-helical conformation, which orients the motif residues toward its deep binding groove, therefore explaining the molecular requirements for peptide binding. Moreover, we demonstrate that a lipopeptide version of the same peptide is able to bind CD1d in a similar conformation, identifying another class of molecules binding this antigen-presenting molecule.

3-Layer-based analysis of peptide-MHC interaction: in silico prediction, peptide binding affinity and T cell activation in a relevant allergen-specific model

CD4+ T cells recognize peptides bound to major histocompatibility complex (MHC) class II molecules on the surface of antigen presenting cells by their T cell receptor (TCR). Using a well-characterized allergen-specific model we studied peptide/MHC (pMHC) interactions by combining computational methods with experimental analyses. A 12-mer and an 18-mer peptide, both containing the human leukocyte antigen (HLA)-DR1-restricted, immunodominant T cell epitope of Art v 1, the major mugwort pollen allergen, were compared. A Molecular Dynamics simulation for a real time of 20 ns using GROMACS was performed. To this aim, the peptides were modelled into the binding groove of HLA-DRB1*0101 using different amino acid substitution tools. Binding of synthetic peptides to purified HLA-DRB1*0101 molecules was analysed in competition assays. The potency of the peptides to activate Art v 1-specific T cells was assessed using oligo- and monoclonal Art v 1-specific T cell cultures expanded from mugwort allergic individuals. All approaches revealed that the 18-mer peptide possessed higher HLA DR affinity as compared to the 12-mer. Computer modelling indicated that a loop-like structure within the additional N-terminal peptide flanking region of the 18-mer contributed to the pMHC interaction. Our approach, to combine computational methods validated by experimental results, demonstrates that Molecular Dynamics simulation may be a useful tool for the prediction of pMHC interactions in the future with possible applications in T cell-based immunotherapy e.g. in Type I allergy.

The Dermatophagoides pteronyssinus group 2 allergen contains a universally immunogenic T cell epitope

The use of T cell epitope-containing peptides for the induction of anergy in allergen sensitization is limited by genetic restriction that could be circumvented by using universally immunogenic epitopes. We attempted to identify such epitopes on Dermatophagoides pteronyssinus group 2 allergen (Der p 2), a major allergen of D. pteronyssinus T cells from BALB/c (H-2(d)), C57BL/6 (H-2(b)), C3H (H-2(k)), and SJL (H-2(s)) mice that were immunized with rDer p 2, recognized an immunodominant region encompassing residues 21-35. A synthetic 21-35 peptide (p21-35) induced strong dose-dependent in vitro T cell proliferation with cells of the four mouse strains and required processing for MHC class II presentation. Substitution of Ile(28) with Ala resulted in reduction of T cell proliferation in each strain. Ile(28) could represent an important MHC class II anchoring residue for T cell response to p21-35. An immunodominant T cell epitope of Der p 2 therefore behaves as a universal epitope and could be a suitable candidate for T cell anergy induction.

Differential regulation of Th1 and Th2 cells by p91-110 and p21-40 peptides of the 16-kD alpha-crystallin antigen of Mycobacterium tuberculosis

Permissively recognized peptides which can activate lymphocytes from subjects with a variety of class II HLA types are interesting diagnostic and vaccine candidates. In this study we generated T helper clones reactive to the permissively recognized p21-40 and p91-110 peptides of the 16-kD heat shock protein of Mycobacterium tuberculosis. All the clones specific for p91-110 secreted interferon-gamma (IFN-gamma) and were of the Th1 phenotype. By contrast, the p21-40 peptide favoured the generation of IL-4-producing clones. Antibody blockade established that the peptide-specific Th clones could either be DR-, DP- or DQ-restricted. Thus, two permissively recognized sequences p21-40 and p91-110 from the same mycobacterial antigen can drive the differentiation of functionally distinct T helper subsets. Attempts to immunize against tuberculosis should bear in mind epitope specificity if a favourable Th subtype response is to be generated.

Therapeutic vaccination of woodchucks against chronic woodchuck hepatitis virus infection

BACKGROUND/AIMS

Therapeutic vaccination is a new approach to treat patients with chronic hepatitis B virus infection. We have used the woodchuck model to examine the efficacy and safety of this approach.

METHODS

Seven woodchucks chronically infected with woodchuck hepatitis virus were immunized with surface antigen from this virus, purified from plasma, in conjunction with a peptide named FIS (encompassing amino acids 106-118: FISEAIIHVLHSR from sperm whale myoglobin), which is recognized by T helper lymphocytes. As controls, two woodchucks chronically infected with woodchuck hepatitis virus were immunized: one with FIS only and the other with surface antigen only.

RESULTS

Co-immunization with surface antigen and FIS, but not with FIS or surface antigen alone, induced anti-surface antibodies in 7/7 immunized woodchucks. In the two woodchucks in which the highest titer of anti-surface antibody was elicited, severe liver damage was observed: one died of fulminant hepatitis and the other became seriously ill with hepatic injury and had to be sacrificed.

CONCLUSIONS

Co-immunization of chronically infected woodchucks with surface antigen and a peptide recognized by T helper cells produces a good anti-surface antibody response. However, this strategy needs to be optimized before its implementation in humans. Although our experiments are not strictly comparable to vaccination of chronically hepatitis B virus-infected patients with recombinant or plasma-derived vaccines, we believe that precautions should be taken to avoid the risk of severe liver injury when immunizing hepatitis B virus carriers.

Peptide recognition by T-cell clones of an HLA-DRB1*1501/*0901 heterozygous donor is promiscuous only between parental alleles

The HLA class II isotype and allelic restrictions of peptide recognition were analyzed with T cells from a DRB1*1501/DRB1*0901 heterozygous donor. Nineteen T cell clones, all directed against the single mycobacterial epitope p21-40 were tested with HLA homozygous lymphoblastoid cell lines as antigen-presenting cells. The most striking finding has been, that several DR isotype restricted clones recognized the peptide in the context of both parental, but not of unrelated alleles. In contrast, DQ and DP restricted clones responded in the context of one parental allele only. Most DR promiscuous clones produced interferon-gamma but not IL-4, whereas most DQ and DP clones produced IL-4. We postulate that the confinement of DR promiscuity only to the parental alleles was established possibly during thymic maturation of T cells and that the proportions between monogamous and promiscuous T cells may play a role in the MHC mediated influences on host resistance to infections and other immune responses.

Interferon-gamma and interleukin-10 inhibit antigen presentation by Langerhans cells for T helper type 1 cells by suppressing their CD80 (B7-1) expression

CD80(B7-1) and CD86(B7-2) co-stimulatory molecules have been reported to activate Th1/Th2 development pathways differentially. It is well known that Langerhans cells (LC), potent antigen-presenting dendritic cells in the epidermis, express several co-stimulatory molecules and that this expression is modulated by several cytokines. Based on the recently reported effect of interferon (IFN)-gamma and interleukin (IL-)-10 on the expression of CD80 and CD86 by LC, we examined the effects of these cytokines on the expression of CD54 (intercellular adhesion molecule-1) and CD40 in addition to CD80 and CD86 on LC, and correlated the expression of each co-stimulatory molecule with antigen presentation for a Th1 clone by cultured LC (cLC) treated with these cytokines. LC cultured for 72 h significantly up-regulated MHC class II antigen expression and all the co-stimulatory molecules were examined. As previously reported, IL-10 or IFN-gamma inhibited the up-regulation of CD80 expression. Granulocyte/macrophage-colony-stimulating factor (GM-CSF) partially restored the suppression of CD80 expression induced by IFN-gamma on cultured LC, while it had virtually no effect on the inhibition induced by IL-10. Antigen presentation for the myoglobin-specific syngeneic Th1 clone by cLC, which were pre-incubated with these cytokines, correlated well with their CD80 expression. In addition, among the antibodies for CD80, CD86, CD28 or CD40, the suppression of the Th1 clone stimulation by LC was found to occur only with anti-CD80 and anti-CD28 antibodies. Finally, we studied the effects of IFN-gamma and IL-10 on GM-CSF production by epidermal keratinocytes (KC). We could show that only IFN-gamma, but not IL-10, suppressed GM-CSF production by KC. These findings suggest that both IFN-gamma and IL-10 suppress antigen presentation by LC for Th1 cells by suppressing their CD80 expression. The inhibitory effect of IFN-gamma on CD80 expression on LC appears to be partially mediated through the suppression of GM-CSF production by KC.

T cell receptor repertoire for a viral epitope in humans is diversified by tolerance to a background major histocompatibility complex antigen

Two unusual characteristics of the memory response to the immunodominant Epstein-Barr virus (EBV) epitope FLRGRAYGL, which associates with HLA B8, have provided an unique opportunity to investigate self tolerance and T cell receptor (TCR) plasticity in humans. First, the response is exceptionally restricted, dominated by cytotoxic T lymphocytes (CTL) with identical TCR protein sequences (Argaet, V. P., C. W. Schmidt, S. R. Burrows, S. L. Silins, M. G. Kurilla, D. L. Doolan, A. Suhrbier, D. J. Moss, E. Kieff, T. B. Sculley, and I. S. Misko. 1994. J. Exp. Med. 180:2335-2340). Second, CTL expressing this receptor are cross-reactive with the alloantigen HLA B* 4402 on uninfected cells (Burrows, S. R., R. Khanna, J. M. Burrows, and D. J. Moss. 1994. J. Exp. Med. 179:1155-1161). No CTL using this conserved public TCR could be reactivated from the peripheral blood of EBV exposed individuals expressing both HLA B8 and B*4402, demonstrating the clonal inactivation of potentially self-reactive T cells in humans. A significant FLRGRAYGL-specific response was still apparent, however, and TCR sequence analysis of multiple CTL clones revealed an oligoclonal TCR repertoire for this determinant within these individuals, using diverse V and J gene segments and CDR3 regions. In addition, a significant public TCR component was identified in which several distinct alpha/beta rearrangements are shared by CTL clones from a number of unrelated HLA B8+, B*4402+ donors. The striking dominance of public TCR in the response to this EBV epitope suggests a strong genetic bias in TCR gene recombination. Fine specificity analysis using peptide analogues showed that, of six different antigen receptors for FLRGRAYGL/HLA B8, none associate closely with the peptide's full array of potential TCR contact residues. Whereas the HLA B*4402-cross-reactive receptor binds amino acids toward the COOH terminus of the peptide, others preferentially favor an NH2-terminal determinant, presumably evading an area that mimics a structure presented on HLA B*4402. Thus, tolerance to a background major histocompatibility antigen can effectively diversify the TCR repertoire for a foreign epitope by deflecting the response away from an immunodominant combination of TCR-binding residues.

Simple strategy to induce antibodies of distinct specificity: application to the mapping of gp120 and inhibition of HIV-1 infectivity

In this study 96 15-mer peptides encompassing the entire sequence of HIV-1 gp120 were synthesized and used to immunize BALB/c mice (i) alone or (ii) in conjunction with the T helper cell determinant FISEAIIHVLHSR (FIS) from sperm whale myoglobin, which is well recognized by major histocompatibility complex (MHC) class II molecules of BALB/c. Of these peptides 39 were immunogenic per se and 57 were not. Out of the 57 non-immunogenic peptides 53 could be rendered immunogenic with the second immunization protocol. With the exception of 4 cases, the anti-peptide antibody titers induced in (ii) were equal (14 cases) or higher (78 cases) than those induced in (i). From the 96 anti-peptide antibodies tested, 12 were able to recognize recombinant gp120 with good antibody titers, a result in agreement with previously identified B cell epitopes from gp120 by anti-peptide antibodies induced with longer peptides conjugated to a carrier protein. Moreover, 4 of the 12 anti-peptide antisera that recognized gp120 were able to neutralize HIV-1 infectivity in vitro, showing that the strategy of co-immunization with FIS may afford functional antibodies.

In vivo cytotoxic T-lymphocyte induction may take place via CD8 T helper lymphocytes

Immunization of mice with peptide constructs, consisting of a determinant recognized by T cytotoxic cells colinearly linked to a determinant recognized by T helper cells (TDc-TDh) was able to induce cytotoxic T lymphocytes in vivo. Interestingly, this induction could be achieved in the absence of adjuvant in non-depleted as well as in CD4(+)-cell-depleted BALB/c mice. In the latter case, induction took place simultaneously with the activation of CD8+ T helper cells specific for a TDh contained within the sequence of the TDc RIQRGPGRAFVTIGK from the immunodominant V3 loop of HIV1 gp120. The possible implications of these findings in HIV infection and AIDS disease are discussed.

The importance of extended conformations and, in particular, the PII conformation for the molecular recognition of peptides

Crystallographic, isotopic labeling nmr and transferred nuclear Overhauser effect studies have highlighted the extended conformation as a very important element of secondary structure at the binding site of many peptide/protein complexes including peptide inhibitors-enzymes, B-cell epitopes-antibodies, and T-cell epitopes-major histocompatibility complex (MHC) of class I and II complexes. This paper discusses the peptide ligand conformation consequences of these findings particularly in view of the identification of the PII conformation (left-handed extended polyproline II) in free solution.

Overcoming class II-linked non-responsiveness to hepatitis B vaccine

This work shows that class II-linked humoral lack of response to an antigen can be overcome by joint immunization with the antigen and a T-helper cell determinant (TDh) well recognized by class II molecules of a non-responder individual. Thus, SJL/J mice (H-2s), which are non-responders to the S region of hepatitis B virus surface antigen (HBsAg), were rendered responders by joint immunization with a recombinant surface antigen, only composed of the S region, and a short synthetic TDh peptide well recognized by the H-2s restriction. By contrast, when this peptide is not recognized as TDh, as in B10M mice (H-2f restricted and also non-responders to the S region), no humoral response could be induced against the S region. These results have important implications for therapy and vaccination against hepatitis B virus as well as in enhancing the immunogenicity of other antigens.

Naturally processed heterodimeric disulfide-linked insulin peptides bind to major histocompatibility class II molecules on thymic epithelial cells

We determined whether disulfide-linked insulin peptides that are immunogenic in vitro for CD4+ T cells bind to major histocompatibility complex class II in vivo. Radiolabeled recombinant human insulin (rHI) was injected into BALB/c mice, and processed rHI peptides bound to I-Ad molecules on different thymic antigen-presenting cells were characterized. The A6-A11/B7-B19 and A19-A21/B14-B21 disulfide-linked I-Ad-bound rHI peptides were isolated from thymic epithelial cells but not dendritic cells. While both thymic epithelial cells and dendritic cells present rHI to HI/I-Ad-specific T cells, these antigen-presenting cells do not present the reduced or nonreduced forms of the disulfide-linked rHI peptides. Thus, a naturally processed disulfide-linked peptide can bind to major histocompatibility complex class II in vivo. The potential role of these peptides in immunological tolerance is discussed.

Sequence features that correlate with MHC restriction

Identification of common sequence motifs in antigenic peptides restricted to a specific class II molecule has not been easy due to the large variation in length and sequence that is observed in these peptides. The goal of this study is to develop an automated computerized method for the identification of sequence features and structural determinants that play a role in the MHC restriction of helper T-cell antigenic peptides. For this, we compiled an extended database of helper T-cell sites, including the information on MHC restriction, when available. Two groups of peptides are assigned to each MHC type: (1) peptides that bind to that MHC molecule to elicit a T-cell response, and (2) peptides that were shown experimentally either not to bind to or not to elicit a T-cell proliferative response in association with that MHC molecule. We search for common motifs in the group of binding peptides, and identify significant motifs that are frequent among these peptides but almost absent in the group of non-binding peptides. A motif consists of physical-chemical and structural properties that may be responsible for binding specificity and can be extracted from sequence data, such as, hydrophobicity, charge, hydrogen bonding capability, etc. The first search is performed on the non-aligned binding peptides. Next, the sequences are aligned according to an identified motif and a search for additional, conserved, properties is performed. The statistical significance of the motifs is evaluated as well as their compatibility with published experimental results on substitution effects. Here we demonstrate the general scheme of the analysis and results for I-Ek and I-Ak associated peptides.

Enhancement of peptide immunogenicity by insertion of a cathepsin B cleavage site between determinants recognized by B and T cells

The insertion of two lysine residues (cleavage sites of cathepsin B) at the boundary of a peptide recognized by B cells (BD) and a class-II- presentable sequence (TDh) enhanced the anti-BD antibody induction capacity of this type of peptide construct, as well as production of IL2. It is postulated that these lysines generate a neoprocessable site which helps in release of the TDh moiety from the construct, enabling its presentation to class II molecules, an essential step in clonal expansion of the antibody-producing B cell after internalization of the construct via the BD moiety.

Phylogeny of immune recognition: fine specificity of fish immune repertoires to cytochrome C

Using the structurally defined protein antigen cytochrome C, studies were conducted in an attempt to delineate the fine specificities of channel catfish immune repertoires. We have previously reported that species variants of cytochrome C were cross-stimulatory to peripheral blood leukocytes (PBL) from catfish immunized with the pigeon variant. Molecular database analyses revealed the existence of overlapping epitopes that appear to define the specificity of the immune response to a "family" of closely related antigens. To further explore these observations, studies were conducted to determine the contribution of peptide 81-104 to the immunogenicity of cytochrome C. Current data showed that peptide 81-104 and intact cytochrome C were stimulatory to PBL from fish previously immunized with the native molecule. In contrast, PBL from fish previously primed with the peptide 81-104 responded only to the immunizing peptide as well as to some, but not all, variants of the peptide 81-104. The differences in the stimulatory capacities of the peptide variants appeared to correlate with amino acid substitutions at various positions of the peptide and changes in their predicted secondary structures.

Human HLA class I- and HLA class II-restricted cloned cytotoxic T lymphocytes identify a cluster of epitopes on the measles virus fusion protein

The transmembrane fusion (F) glycoprotein of measles virus is an important target antigen of human HLA class I- and class II-restricted cytotoxic T lymphocytes (CTL). Genetically engineered F proteins and nested sets of synthetic peptides spanning the F protein were used to determine sequences of F recognized by a number of F-specific CTL clones. Combined N- and C-terminal deletions of the respective peptides revealed that human HLA class I and HLA class II-restricted CTL efficiently recognize nonapeptides or decapeptides representing epitopes of F. Three distinct sequences recognized by three different HLA class II (DQw1, DR2, and DR4/w53)-restricted CTL clones appear to cluster between amino acids 379 and 466 of F, thus defining an important T-cell epitope area of F. Within this same region, a nonamer peptide of F was found to be recognized by an HLA-B27-restricted CTL clone, as expected on the basis of the structural homology between this peptide and other known HLA-B27 binding peptides.

Microheterogeneity in the recognition of a HLA-DR2-restricted T cell epitope from a meningococcal outer membrane protein

The trimolecular interaction of T cell receptor (TcR), antigen and major histocompatibility complex (MHC) class II was analyzed using a panel of HLA-DR2-restricted T cell clones recognizing the 49-61 region of a meningococcal class I outer membrane protein (OMP). The clones, all CD3+CD4+CD8-TcR alpha/beta+, were selected by restimulation with the synthetic peptide OMP(49-61), which contains an immunodominant T helper determinant. Using a series of peptides that were sequentially truncated from the N or C terminus, four different epitope fine-specificity patterns were identified. Furthermore, each clone was found to exhibit a distinct recognition pattern for a panel of 20 single-residue substitution analogues of the minimal epitope OMP(50-58). Most substitutions that were not tolerated in the nonamer were allowed when the analogues were prepared departing from the native peptide OMP(49-61). Obviously, the residues outside the minimal epitope contribute to stabilization of the trimolecular complex. These findings suggest that defining the minimal size of T cell determinants may be of limited value. By performing proliferation competition assays putative MHC and TcR contact residues were identified in the peptide. Most likely, Ile 51 and Phe 54 act as MHC-anchoring residues, whereas Asp 53 represents a critical TcR contact residue for all of the clones. MHC anchoring may be provided by other residues as well, since Ile 51 and Phe 54 can be substituted by conservative residues [as OMP(50-58) and OMP(49-61) analogues] and with Ala [as OMP(49-61) analogues only]. Some evidence was found for interaction of particular side chains at other positions with TcR molecules, but this contribution was not equally important for all clones. Apparently, the clonotypic TcR can see a single epitope in different ways in the context of the same MHC restriction element. Since most clones use different V alpha and V beta genes (which encompass the putative MHC-binding regions first and second complementarity-determining regions, CDR1 and CDR2) different modes of interaction with the HLA-DR2 molecule indeed are likely to occur.

Fine specificity of the human T-cell response to the hepatitis B virus preS1 antigen

The T-cell response to hepatitis B virus envelope antigens was studied in 11 hepatitis B vaccine recipients; 7 were selected to analyze the fine specificity of the T-cell response to the preS1 antigen. Four distinct T-cell epitopes were identified by peripheral blood lymphomononuclear cell stimulation with a panel of short synthetic peptides covering the preS1 sequence. The immunodominance of the preS1 epitopes included within peptides 21-30 and 29-48 was shown by their capacity to restimulate an HLA class II restricted proliferative response of T cells primed with the whole preS1 antigen. Conversely, peptide-specific T cells selected by peripheral blood lymphomononuclear cell stimulation with peptides 21-30 and 29-48 were able to recognize the native preS1 molecule, confirming that these epitopes are actually generated by the intracellular processing of preS1. Finally, amino acid residues essential for T-cell activation by peptide 21-30 were identified using 10 analogues of the stimulatory peptide containing single alanine substitutions. These results may be relevant to the design of efficient synthetic vaccines against hepatitis B virus infection.

Unusually diverse T cell response to a repeating tripeptide epitope

The immune system utilizes a diverse T cell repertoire for the recognition of foreign antigens in the context of self MHC gene products. We have examined the potential diversity of the T cell response directed to a immunodominant repeating tripeptide epitope (EYA)5. This peptide represents one of the two T cell epitopes on the synthetic alpha-helical polypeptide antigen Poly 18, Poly EYK(EYA)5 in H-2d mice and does not require antigen processing prior to presentation to Poly 18-specific T cell hybridomas. The T cell response directed to the repeating tripeptide epitope (EYA)5 is extremely heterogenous even though the epitope has a relatively simple amino acid sequence. We have analyzed the fine specificity of 21 randomly chosen Poly 18-reactive, (EYA)5-specific and H-2d-restricted T cell hybridomas derived from H-2d, H-2bxd, and H-2b----H-2bxd Poly 18-responding mice to determine the number of unique antigen reactivity patterns represented by this T cell population. We used alanine- and/or lysine-substituted (EYA)5 peptides and a panel of haplotype-varied splenocytes and observed a great deal of microheterogeneity in response. We find that 13 of the 21 hybridomas have a distinct fine antigen specificity and T cell receptors. The binding of (EYA)5 to the antigen-binding groove of I-Ad appears to generate a highly diversified T cell response. Therefore, (EYA)5-I-Ad complex allows the activation of unrelated T cell clonotypes with the same overall antigen specificity and MHC restriction, but with distinct microheterogeneity in response and receptor usage.

Sequence analysis of peptides bound to MHC class II molecules

CD4 T cells recognize peptide fragments of foreign proteins bound to self class II molecules of the major histocompatibility complex (MHC). Naturally processed peptide fragments bound to MHC class II molecules are peptides of 13-17 amino acids which appear to be precessively truncated from the carboxy terminus, perhaps after binding to the MHC class II molecule. The finding of predominant self peptides has interesting implications for antigen processing and self-non-self discrimination.

Analysis of human T-cell epitopes in the 19,000 MW antigen of Mycobacterium tuberculosis: influence of HLA-DR

The potential number of T-cell epitopes in the 19,000 molecular weight (MW) antigen has been investigated using overlapping peptides which comprise the complete sequence. Sixteen potential epitopes could be deduced from the responses to these peptides by polyclonal T cells derived from 22 antigen-responsive donors. The majority of epitopes were not predicted by either of the major paradigms, the Rothbard motif and the amphipathic helix. A hierarchy of epitopes was indicated by the responses, which ranged from strong and frequent in the N-terminal region, to moderate or weak elsewhere. Some epitopes were restricted by single HLA-DR determinants, or families of determinants sharing structural features in common, whilst the two N-terminal peptides were recognized by donors with a diversity of DR types. The high degree of T-cell recognition of the N-terminal region may be of relevance to the design of a sub-unit vaccine capable of priming T cells against Mycobacterium tuberculosis.

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.

The T cell receptor repertoire influences V beta element usage in response to myoglobin

T cell clones recognizing the sperm whale myoglobin (SpWMb) epitope 110-121 in association with H-2d major histocompatibility complex class II molecules display a very limited heterogeneity of T cell receptor (TCR) V beta usage in DBA/2 mice. All clones previously tested used the same V beta 8.2 gene segment and very restricted junctional regions. To investigate the significance of this observation in vivo, we immunized DBA/2 mice with the intact SpW Mb protein or peptide 110-121. Only the V beta 8+ T cells showed any significant response to the 110-121 epitope. The response to peptide 110-121 was then analyzed in mice which, either as a consequence of antibody depletion or through genetic deletion of TCR V beta genes, lacked V beta 8+ peripheral T cells. DBA/2 mice depleted of V beta 8+ T cells by antibody treatment responded poorly to the 110-121 peptide, and only at high antigen concentrations. In contrast, DBA/2V beta a mice (homozygous for a deletion of multiple V beta gene segments including the V beta 8 family) made a response at least as great as that made by DBA/2 mice, even though the DBA/2V beta a mice had a very restricted TCR V beta repertoire compared with DBA/2 mice. Mechanisms which might determine differences in the 110-121 specific response of DBA/2, DBA/2V beta a and F23.1-treated DBA/2 mice are discussed.

Induction of antibodies against a peptide hapten does not require covalent linkage between the hapten and a class II presentable T helper peptide

Following immunization with a complex antigen, a B cell internalizes this antigen through an interaction between its surface immunoglobulins and an epitope of the antigen. Enzymatic processing of the antigen frees one or more short peptide determinants (TD) which bind to class II molecules of the B cell. If the complex TD-MHC II is recognized by the receptor of a T helper cell, T cell help is provided leading to the expansion of an antibody-producing B cell clone specific for the epitope. We present experimental evidence proving that the induction of anti-peptide hapten antibodies does not require covalent linkage between the peptide hapten and the peptide behaving as TD. Indeed, high anti-peptide hapten antibody titers are induced if an emulsion of TD and hapten are injected in the same immunization site. This result suggests a way to manipulate antibody production with useful applications to research and therapy.

Mechanisms of T cell recognition with application to vaccine design

Both helper and cytotoxic T lymphocytes generally recognize protein antigens not in their intact form, as antibodies do, but on the surface of another cell, after "processing" by that cell to unfold or cleave the protein into fragments and after association of the processed antigen with major histocompatibility complex (MHC) molecules on that cell. This complex process leads to immunodominance of certain segments from the protein, which depends not only on structural features intrinsic to the antigenic segment itself, but also on antigen processing and on the structure of the MHC molecules of the responding individual. We have explored all three of these factors, including the enzymes involved in processing, the way peptides bind to MHC molecules, and structural features such as helical amphipathicity that seem to favour T cell recognition. We have used this information to locate and characterize antigenic sites of proteins of interest for vaccine development, including proteins from the malaria parasite and the AIDS virus, HIV. For HIV, we have identified both helper and cytotoxic T cell sites, coupled a helper site to a B cell site to produce a synthetic immunogen that elicits neutralizing antibodies, and studied the effect of viral sequence variation on cytotoxic T cell recognition and binding of the immunodominant peptide to MHC molecules. This information suggests strategies for the rational design of synthetic or recombinant vaccines.

Structural aspects of a protein epitope and their role in the major histocompatibility complex control of T cell responsiveness

We have previously shown that immunization of C57BL/10 (H-2b) mice with the tobacco mosaic virus protein (TMVP) or with its tryptic peptide number 8, representing residues 93-112 of TMVP, induces T cells which proliferate in vitro in response to TMVP and peptide 8. In contrast, immunization of congenic B10.BR (H-2k) mice with either TMVP or with peptide 8 induces T cells which respond in vitro to the homologous but not the heterologous antigen. The capacity to exhibit cross-reactivity between TMVP and peptide 8 on the T cell level has been shown to be under major histocompatibility complex (MHC)-linked genetic control. The lack of cross-reactivity has been attributed to the inability of the H-2k APC to present the appropriate epitope to T cells. In the present paper, we report results of a comparative analysis of the role of structural aspects of the epitope on the proliferative T cell responses from TMVP and peptide 8-immune C57BL/10 (H-2b) and B10.BR (H-2k) mice. Utilizing a panel of synthetic peptides representing portions of peptide 8 and a panel of peptide-protein conjugates, we have determined that peptide 8-immune T cells of the H-2k strain appear to recognize a single epitope within peptide 8, located at its N-terminus. In contrast, in the H-2b strain, both TMVP and peptide 8-immune T cells appear to recognize two overlapping epitopes within peptide 8; one located in the middle region and the other toward the N-terminus. Experiments with H-2b T cells revealed that random amino acids added to the carboxyl or amino-terminus of nonstimulatory peptides can confer activity to these peptides, demonstrating limited specificity of interaction between antigen and Iab. Results of experiments dealing with fixation of antigen-presenting cells suggest that TMVP requires processing in order to be recognized by peptide 8-immune H-2b proliferative T cells whereas peptide 8 does not. Taken together the results suggest that the T cell responsiveness to TMVP and peptide 8 exhibited by these two congenic strains H-2b and H-2k is not only controlled by the strains MHC but is also influenced by antigen processing. Antigen processing may eliminate a potential epitope for the primary induction and the secondary stimulation of B10.BR T cells.

Structure-function relationships among highly diverse T cells that recognize a determinant from influenza virus hemagglutinin

We have analyzed the structural and genetic basis for T cell recognition of the complex formed between antigen and class II products of the major histocompatibility complex by performing sequence analysis of T cell receptors (TCRs) induced in response to the helper T cell site 1 of the influenza virus hemagglutinin. The results demonstrate, first, that structurally highly diverse TCRs can be utilized in recognition of the same antigen/I-Ed complex: 12 of 13 TCRs utilize unique V alpha/V beta gene segment combinations, suggesting that approximately 70 different V alpha/V beta combinations are available to BALB/c mice in response to this determinant. Second, comparison of these sequences with the ability of each hybridoma to recognize a panel of peptide analogues suggests that alpha and beta chains of these TCRs frequently determine specificity for the NH2-terminal and the COOH terminal portions, respectively, of the site 1 determinant.

The presumptive CDR3 regions of both T cell receptor alpha and beta chains determine T cell specificity for myoglobin peptides

The T cell receptor alpha/beta (TCR-alpha/beta) is encoded by variable (V), diversity (D), joining (J), and constant (C) segments assembled by recombination during thymocyte maturation to produce a heterodimer that imparts antigenic specificity to the T cell. Unlike immunoglobulins (Igs), which bind free antigen, the ligands of TCR-alpha/beta are cell surface complexes of intracellularly degraded antigens (i.e., peptides) bound to and presented by polymorphic products of the major histocompatibility complex (MHC). Therefore, antigen recognition by T cells is defined as MHC restricted. A model has been formulated based upon the similarity between TCR-alpha/beta V region and Ig Fab amino acid sequences, and the crystal structure of the MHC class I and Ig molecules. This model predicts that the complementarity determining regions (CDR) 1 and 2, composed of TCR V alpha and V beta segments, primarily contact residues of the MHC alpha helices, whereas V/J alpha and V/D/J beta junctional regions (the CDR3 equivalent) contact the peptide in the MHC binding groove. Because polymorphism in MHC proteins is limited relative to the enormous diversity of antigenic peptides, the TCR may have evolved to position the highly diverse junctional residues (CDR3), where they have maximal contact with antigen bound in the MHC peptide groove. Here, we demonstrate a definitive association between CDR3 sequences in both TCR alpha and beta chains, and differences in recognition of antigen fine specificity using a panel of I-Ed-restricted, myoglobin-reactive T cell clones. Acquisition of these data relied in part upon a modification of the polymerase chain reaction that uses a degenerate, consensus primer to amplify TCR alpha chains without foreknowledge of the V alpha segments they utilize.

The role of polymorphic HLA-DR beta chain residues in presentation of viral antigens to T cells

The relative importance of 11 polymorphic positions in the HLA-DR7 beta 1 chain in T cell recognition of foreign antigens was investigated using transfectants expressing mutant DR7 beta 1 chains as APC for five rabies virus-specific T cell clones. The results indicate that multiple amino acids, located in both the beta-strands and alpha-helix of DR7 beta 1 in the model of a class II molecule, are involved in DR7-restricted T cell recognition of these antigens. Many of the substitutions appeared to reduce the affinity of an antigenic peptide for the mutant DR7 molecules but did not prevent binding. The heterogeneity of responses of the three G-specific T cell clones to presentation of the G11.3 peptide by several of the mutant DR7 molecules indicates that the T cell receptor (TCR) of each these clones requires a different view of the G11.3/DR7 complex and raises the possibility that the G11.3 peptide may bind to the DR7 molecule in more than one conformation.

Repeated determinants within the retinal interphotoreceptor retinoid-binding protein (IRBP): immunological properties of the repeats of an immunodominant determinant

Interphotoreceptor retinoid-binding protein (IRBP), a glycoprotein which localizes in the retina and pineal gland, induces inflammatory changes in these organs (EAU and EAP, respectively) when injected into various mammals. We have previously identified a determinant (residues 1169-1191) in bovine IRBP which is immunodominant and highly immunogenic and immunopathogenic in Lewis rats. IRBP exhibits a fourfold repeat structure and we report here on the comparison between the active sequence 1179-1191 and its three repeat peptides. Only one of the repeats, 271-283, cross-reacted with 1179-1191 and exhibited immunodominance, albeit of a low level. Peptide 271-283 was also immunogenic and immunopathogenic in Lewis rats, but with a minimal dose approximately 100 times higher than that of 1179-1191. Peptide 880-892, a nondominant determinant, resembled 271-283 in its immunogenicity, but was markedly less immunopathogenic. No immunological activity was detected in the fourth repeat peptide, 579-591. Peptide 1179-1191 was superior to the other repeats also in its antigenicity, i.e., the capacity to stimulate presensitized lymphocytes in culture: the minimal stimulatory concentrations of 1179-1191 was greater than 1000 times lower than those of 271-283 or 880-892. Furthermore, 1179-1191 was stimulatory at concentrations lower than those of 271-283 even when tested with lymphocytes sensitized against 271-283. A correlation was also found between the immunological activities of the repeat peptides and their amphipathicity. This study thus identifies two new immunopathogenic determinants of IRBP and provides additional data to show the association between immunodominance of peptides and their various immunological activities.

Polyvalent synthetic vaccines: relationship between T epitopes and immunogenicity

Three different synthetic polyvalent vaccines have been constructed by conjugating four synthetic peptides without any carrier protein. The peptides were copy fragments of two bacterial antigens (Streptococcus pyogenes M protein and diphtheria toxin), two parasitic antigens (circumsporozoite protein of Plasmodium falciparum and Plasmodium knowlesi), and one viral antigen (hepatitis B surface antigen). Outbred guinea-pigs immunized with polyvalent vaccine containing streptococcal, diphtheric, P. knowlesi and hepatitis peptides raised high specific antibody response against the four specificities. Individual T cell analysis demonstrated that hepatitis peptide bears T dominant epitope. A similar immune response was obtained with a second polyvalent vaccine where the P. knowlesi peptide had been replaced by the P. falciparum peptide. In both experiments the malarial peptides behave like pure B epitopes. Prediction of immunodominant helper T-cell antigenic sites were performed with the five peptides using computer algorithm. Hepatitis and diphtheric peptides were selected whereas the streptococcal peptide was rejected although it can experimentally contain a T epitope. To confirm this result animals were immunized with a third polyvalent vaccine which does not contain the hepatitis peptide. No T cell proliferation or antipeptide antibodies were detected. These results demonstrate that the cooperative immune response requires a certain degree of antigenic complexity for the induction of antibody response.

Immunological features of synthetic peptides derived from the retinal protein IRBP: differences between immunodominant and non-dominant peptides

Interphotoreceptor retinoid-binding protein (IRBP) is a glycoprotein of 1264 residues (bovine) which localizes specifically in the retina and pineal gland and induces inflammatory changes in these organs (EAU and EAP, respectively) in immunized animals. We report here on differences between the immunological activities in Lewis rats of four IRBP-derived synthetic peptides. Only one of these peptides, designated R14 (residues: 1169-1191) is immunodominant, i.e., it has the capacity to stimulate lymphocytes sensitized against whole IRBP. The remaining peptides, R4 (1158-1180), R8 (1197-1209), and R12 (248-266), are non-dominant and are not recognized by IRBP-sensitized lymphocytes. R14 differed profoundly from the other peptides in its immunogenicity, inducing cellular immunity at the low dose of 0.1 nmol/rat, whereas the non-dominant peptides initiated immune responses at doses approximately 100 times higher. R14 was also superior to the non-dominant peptides in its antigenicity, as determined by the lowest concentration required to induce sensitized lymphocytes to proliferate. Responses were stimulated by R14 at a concentration of 10(-6) microM, while the three non-dominant peptides were stimulatory at the much higher concentration of 10(-1) microM. These data support the concept that immunodominance is linked to a high binding affinity of the peptide determinant to the major histocompatibility complex antigens on antigen-presenting cells.

Analysis of peptide binding patterns in different major histocompatibility complex/T cell receptor complexes using pigeon cytochrome c-specific T cell hybridomas. Evidence that a single peptide binds major histocompatibility complex in different conformations

The interaction of TCR, antigen, and MHC complex has been analyzed using synthetic peptide antigens and a series of single amino acid-substituted analogues. Two similar antigens, mouse cytochrome c (mcyt c) and pigeon cytochrome c (pcyt c), elicit T cell responses in strains of mice bearing MHC class II Ek beta Ek alpha (B10.A), Eb beta Ek alpha [B10.A(5R)], and Es beta Ek alpha [B10.S(9R)]. The immunogenic regions of these antigens are located in the peptide sequence p88-104 for pcyt c and m88-103 for mcyt c. The limited T cell repertoire for these antigens is comprised of four groups of T cell phenotypes that have very few differences in their TCR gene make up. In this paper, we examine the diversity in their fine specificity for each of the antigens, m88-103 and p88-104, complexed with each of the I-Ek haplotypes. Epitopes, i.e., residues that interact with the TCR, and agretopes, i.e., residues in the MHC-binding site, were assigned for the two peptide antigens in the presence of APC bearing E beta kEk alpha, Eb beta Ek alpha, or Eb beta Ek alpha using T cell hybridomas of the phenotypes I, IIIa, and IV. From our results, we conclude that first, the substitution of any residue between 95 and 104 of the cytochrome c peptide changed the antigenic potency of the peptide for at least one of the hybridomas. Second, each T cell type has a different recognition pattern of epitopes and agretopes for a particular antigen-MHC complex, thus, ruling out a static model of T cell recognition, which assigns certain, invariant agretopic residues to the peptide by which it interacts with the MHC molecule independently of the TCR. Third, the same T cell hybridoma responded to the antigens differently when presented on various MHC molecules, implying that overall changes in the MHC groove, as displayed by the three haplotypes, may affect the efficiency in binding the peptide. Fourth, since most of the residues are used as epitopes by at least one of the T cell specificities, the peptide appears to be recognized in a different conformation by each T cell hybridoma phenotype; and, finally, the epitopic and agretopic residues do not segregate, for any one of the T cell specificities, in such a way that suggests they are recognized in a helical conformation. In summary, our results suggest that a single peptide may generate diversity in the T cell response by virtue of its conformational flexibility within the TCR-MHC-antigen complex.

Molecular analyses of a five-amino-acid cytotoxic T-lymphocyte (CTL) epitope: an immunodominant region which induces nonreciprocal CTL cross-reactivity

The cytotoxic T-lymphocyte (CTL) response to lymphocytic choriomeningitis virus infection determines the outcome of infection. Here we show that this response in BALB/c mice (H-2d), when analyzed both at the primary CTL level and using CTL clones, is predominantly monospecific. The vast majority of CTL have a common specificity for a single epitope in the virus nucleoprotein, which can be minimally identified by amino acids GVYMG. This epitope is presented by the Ld class I glycoprotein. We used these data to design a subunit CTL vaccine, whose effectiveness is demonstrated in the accompanying report (L. S. Klavinskis, J. L. Whitton, and M. B. A. Oldstone, J. Virol. 63:4311-4316, 1989). Further analysis indicates that, while CTL clones share a common minimal epitope, they differ in their ability to recognize cells infected with a related but distinct strain of lymphocytic choriomeningitis virus. Studies on the molecular nature of CTL cross-reactivity indicate that CTL induced by similar sequences may cross-react in a unidirectional manner. These novel observations suggest that CTL vaccines, to achieve optimal effectiveness, should not simply include virus sequences which will yield a CTL response; the immunizing sequences should also be selected to ensure that the fine specificities of the induced CTL are such that they maximize the chance of recognizing serotypically diverse strains.

Class II-restricted T-cell clones to a synthetic peptide of influenza virus hemagglutinin differ in their fine specificities and in the ability to respond to virus

Fifteen T-cell clones were derived from BALB/c or DBA/2 mice immunized with a synthetic peptide corresponding to the C-terminal 24 residues (residues 305 to 328) of the HA1 chain of H3 subtype influenza virus hemagglutinin. All of the clones proliferated when the peptide was presented in association with I-Ed. By using shorter homologs, it was shown that the T-cell response was focused predominantly on the region at the N-terminal end of the peptide encompassed by residues 306 to 319. Individual clones recognizing this region differed in their absolute requirements for residues at the extremities of the site and also in their patterns of efficiency of recognition of shorter homologs. One particular clone defined another site of T-cell recognition within residues 314 to 328. The response of the clones to peptide analogs identified certain residues within the sites that were critical for recognition, with the substitution Gln-311----Ser having a differential effect on clones responding to the N-terminal site. Only one of the clones responded well to influenza virus itself. This clone also required relatively low concentrations of the parent peptide for optimum stimulation and was suppressed by higher concentrations. The data demonstrate striking heterogeneity in the T-cell response even to a short synthetic peptide, with different T-cell clones recognizing slightly different but overlapping areas of the molecule.

Identification of an immunodominant and highly immunopathogenic determinant in the retinal interphotoreceptor retinoid-binding protein (IRBP)

Interphotoreceptor retinoid-binding protein (IRBP), a glycoprotein specific for the retina and pineal gland, induces inflammatory changes in these two organs in immunized animals. We report here on the identification of an immunodominant determinant of bovine IRBP that is highly immunogenic and immunopathogenic in the Lewis rat. The peptide, which comprises the sequence 1169-1191 of bovine IRBP, was shown to be immunodominant by its capacity to stimulate lymphocytes sensitized against whole IRBP. A comparison was made between peptide 1169-1191 and another peptide, 1158-1180, which is nondominant but is immunogenic and immunopathogenic in the Lewis rat. Peptide 1169-1191 was found to be superior in its immunological capacities; the minimal dose of 1169-1191 needed to induce cellular immune response or disease in Lewis rats (0.02-0.1 nmol/rat) is congruent to 1,000 times smaller than that of 1158-1180. In addition, unlike the ocular disease induced by 1158-1180, the disease produced by 1169-1191 resembled that induced by whole IRBP in its kinetics and histopathological features. The immunological activity of 1169-1191 in the Lewis rat was localized to the 10 residues at the COOH terminus; no such activity was exhibited by the truncated peptide 1169-1188, which comprises the 20 residues at the NH2 terminus of the full peptide. The usefulness of this unique experimental system in analyzing the role of immunodominance in peptide immunogenicity and immunopathogenicity is underscored.

Identification of T-cell epitopes and use in construction of synthetic vaccines

The T cell is central to the immune system response to foreign antigens, and understanding the mechanism of T cell response to antigen is crucial for vaccine development. Short subpeptides of foreign antigen can prime the T cells to respond to the whole antigen, in some cases as well as or better than immunization with the whole antigen itself. Antigenic sites located first in the murine model are also antigenic in the human, suggesting that the structural features of antigenic sites are species-independent. The amphipathic helix hypothesis has proven useful in developing an algorithm that has successfully located immunodominant sites in important proteins, thus reducing substantially the experimental time and effort required to locate those sites. Other algorithms have also been used successfully, but in all cases there are proven T-cell sites not accounted for by the algorithm. A data base showing T-cell response to collections of peptides uniformly distributed along protein antigens would be very useful in subsequent efforts to characterize the physical and chemical properties of T-cell antigenic sites.

Antigen processing for presentation to T lymphocytes: function, mechanisms, and implications for the T-cell repertoire

Antigen processing encompasses the metabolic events that a protein antigen must undergo in or on the antigen-presenting cell before it can be recognized by the T lymphocyte. It appears that a primary goal of these events is to unfold the protein to expose residues that are buried in the native conformation, which is designed to be soluble in water. The APC usually accomplishes this task by proteolytic cleavage of the protein, but we have found that artificial unfolding without proteolysis is sufficient. The purpose of unfolding may be to allow different faces of the antigenic site to bind simultaneously to the T-cell receptor and the MHC molecule on the APC, or to interact with other structures on the membrane of the APC. This requirement for unfolding appears to apply to everything from small peptides to large multimeric proteins. We have found that the way the antigen is processed and the structure of the fragments produced can greatly affect the availability of antigenic sites. For instance, some antigenic sites are not recognized when the native protein is used as immunogen, despite the fact that immunization with a small peptide corresponding to that site reveals both the ability of the site to bind to MHC molecules of the animal in question and the presence of a T-cell repertoire specific for that site. The antigenic site is not destroyed by processing, since it can be presented by the same F1 APC to T cells of another MHC type. Similarly, cross-reactivity between homologous epitopes of related proteins may occur at the peptide level even though the native proteins do not crossreact for the same T-cell clone. Since these events occur with monoclonal T cells, they cannot be due to suppressor cells specific for other sites on the native molecule. The best explanation is that the products of natural processing of the protein are larger than the peptides corresponding to the minimal antigenic sites, and contain hindering structures that interfere with binding to some MHC molecules and not others, or to some T-cell receptors and not others. Thus, antigen processing is a third factor that can lead to apparent Ir gene defects - in addition to MHC specificity and holes in the T-cell repertoire - and can significantly influence which antigenic sites are immunodominant.(ABSTRACT TRUNCATED AT 400 WORDS)

T cell response to myoglobin: a comparison of T cell clones in high-responder and low-responder mice

Mice carrying the H-2b haplotype (e.g., inbred strains C57BL/6 and C57BL/10) are low responders to sperm whale myoglobin when tested in the T cell proliferation assay. Their response is improved by the removal of the Ly-2+ cells from the lymph node population, but it still remains significantly lower than that of cells cells from high-responder strains (e.g., DBA/2, H-2d). To determine whether T cells from the low and high-responder mice recognize the same or different epitopes on the immunizing antigen, we obtained sets of T cell clones from both strains and tested them against peptides representing different regions of the myoglobin molecule, as well as against myoglobins from species other than the sperm whale. Four types of T cell clones were obtained from the DBA/2 mice: 3 types responded to the peptide 107-120 (9 clones altogether), and 1 type responded to the peptide 133-149 (4 clones altogether). The 3 types responding to the peptide 107-120 could be distinguished by their response to horse myoglobin or by the restriction of the response (Ad vs. Ed). Similarly, 5 types of T cell clones were obtained from the C57BL/6 mice: 2 types responded to the peptide 10-22 (1 type, but not the other, responded to horse myoglobin); 1 type responded to the peptide 133-149; and 2 types did not respond to any of the peptides used (1 type, but not the other, responded to dog myoglobin). All 5 types (13 clones altogether) were presumably Ab restricted. These results demonstrate the diversity of epitopes in single antigenic regions and show equivalent heterogeneity of T cell repertoires in high and low responder mice. Attempts to demonstrate specific T cell suppression in the low responder mice failed; only partial, nonspecific suppression was observed.