[Immunodominance in CD8+ T cell responses to HIV-1 synthesized epitopes]

OBJECTIVE

To investigate immunodominance in CD8+ T cell responses to human immunodeficiency virus type 1 (HIV-1) epitopes.

METHODS

Frequency of Interferon-gamma (IFN-gamma) secreting cells and the proliferation percentage of CD8+ T cells in PBMC from an HIV-1-infected long term nonprogressor (LTNP) were assessed after stimulation with either the 34 pools of 701 overlapping peptides covering the regions of HIV-1 Env, Pol, Gag, Vif, Nef, Tat or some single peptides, by using various assays including enzyme-linked immunospot (ELISPOT) and CFSE Carboxy-fluorescein diacetate, succinimidyl ester (CFSE) labeling and flow cytometry.

RESULTS

HIV-1 Gag peptides induced the highest frequency of IFN-gamma secreting cells, followed by Nef, Tat, and Vif. Meanwhile, Env and Pol failed to induce significant responses. In the IFN-gamma ELISPOT assay, stimulation with single peptide and the corresponsive peptide pool generated analogous results. In addition, the frequencies of IFN-gamma secreting cells and the proliferation percentage of CD8+ T cells detected-ELISPOT and CFSE labeling and flow cytometry were proportional, when single peptides were used for stimulation.

CONCLUSION

CD8+ T cells can respond to some specific HIV-1 epitopes and induce immunodominant responses. As a complimentary approach to the standard of ELISPOT assay, We recommend a novel CFSE labeling and flow cytometry assay for the examination of immunodominance in studies of HIV-1 specific proliferation percentage of CD8+ T cell responses.

Soluble mannosylated myelin peptide inhibits the encephalitogenicity of autoreactive T cells during experimental autoimmune encephalomyelitis

We have previously shown that immunization with a mannosylated myelin peptide in complete adjuvant induces tolerance instead of disease in experimental autoimmune encephalomyelitis (EAE), a rodent model for multiple sclerosis. In this report we demonstrate that treatment with a soluble mannosylated epitope of proteolipid protein (M-PLP(139-151)) significantly inhibits disease mediated by autoreactive myelin-specific T cells during EAE. Treatment with M-PLP(139-151), applied in different EAE models, significantly reduced the incidence of disease and the severity of clinical symptoms. Delayed-type hypersensitivity responses were abolished after peptide treatment, emphasizing the impact on peripheral T-cell reactivity. Histological analysis of spinal cord tissue from mice treated with M-PLP(139-151) revealed the presence of only few macrophages and T cells. Moreover, little expression of interferon-gamma, interleukin-23, or major histocompatibility complex class II antigen was detected. Immune modulation by M-PLP(139-151) was primarily antigen-specific because an irrelevant mannosylated peptide showed no significant effect on delayed-type hypersensitivity responses or on the course of EAE. Therefore, mannosylated antigens may represent a novel therapeutic approach for antigen-specific modulation of autoreactive T cells in vivo.

T-cell responses directed against multiple HLA-A*0201-restricted epitopes derived from Wilms' tumor 1 protein in patients with leukemia and healthy donors: identification, quantification, and characterization

PURPOSE

Antigens derived from the Wilms' tumor (WT1) protein, which is overexpressed in leukemias, are attractive targets for immunotherapy. Four HLA-A*0201-restricted WT1-derived epitopes have been identified: WT37, WT126, WT187, and WT235. We determined the natural immunogenecity of these antigens in patients with hematologic malignancies and healthy donor.

EXPERIMENTAL DESIGN

To detect very low frequencies of WT1-specific CD8+ T cells, we used quantitative reverse transcription-PCR to measure IFN-gamma mRNA production by WT1 peptide-pulsed CD8+ T cells from 12 healthy donors, 8 patients with chronic myelogenous leukemia, 6 patients with acute myelogenous leukemia, and 8 patients with acute lymphoblastic leukemia.

RESULTS

Responses were detected in 5 of 8 chronic myelogenous leukemia patients, 4 of 6 patients with acute myelogenous leukemia, and 7 of 12 healthy donors. No responses were detected in patients with acute lymphoblastic leukemia. The magnitude and extent of these CD8+ T-cell responses was greater in patients with myeloid leukemias than in healthy donors. Clonotypic analysis of WT1-specific CD8+ T cells directly ex vivo in one case showed that this naturally occurring population was oligoclonal. Using fluorescent peptide-MHC class I tetramers incorporating mutations in the alpha3 domain (D227K/T228A) that abrogate binding to the CD8 coreceptor, we were able to confirm the presence of high-avidity T-cell clones within the antigen-specific repertoire.

CONCLUSION

The natural occurrence of high-avidity WT1-specific CD8+ T cells in the periphery could facilitate vaccination strategies to expand immune responses against myeloid leukemias.

Mapping the binding sites of anti-BP180 immunoglobulin E autoantibodies in bullous pemphigoid

Bullous pemphigoid (BP) is a subepidermal blistering disease characterized by autoantibodies against the hemidesmosomal protein BP180 (BPAg2, type XVII collagen). NC16A, a non-collagenous stretch of the BP180 ectodomain, is the primary target of pathogenic immunoglobulin (Ig)G autoantibodies and IgE class autoantibodies. This study further characterized the IgE-reactive regions of BP180. Of the ten sera from untreated BP patients, eight contained IgE reactive with the entire BP180 ectodomain. The IgE in four of these eight sera reacted with NC16A, whereas in the remaining four sera IgE immunoreactivity was restricted to sites downstream of NC16A. In contrast, IgG reactivity to NC16A was detected in nine of the ten BP sera, and in the remaining serum, IgG, as well as IgE, reacted exclusively with non-NC16A sites on the BP180 ectodomain. Fine mapping of the antigenic sites within NC16A revealed very similar reactivity patterns for IgE and IgG, with NC16A subregion-2 being the major site recognized by both isotypes. Eight of the untreated BP patients were tested for histamine release from their basophils in response to NC16A. Antigen-specific histamine release was observed only in those patients with detectable circulating IgE directed against NC16A (three of eight). Future studies will investigate the pathogenic relevance of anti-BP180 IgE.

In Vivo Modulation of T Cell Responses and Protective Immunity by TCR Antagonism during Infection

Infectious agents are known to express altered peptide ligands that antagonize T cells in vitro; however, direct evidence of TCR antagonism during infection is still lacking, and its importance in the context of infection remains to be established. In this study, we used a murine model of infection with recombinant Listeria monocytogenes and addressed three issues that are critical for assessing the role of TCR antagonism in the modulation of the immune response. First, we demonstrated that the antagonist peptide efficiently inhibited the ability of the agonist to prime naive TCR-transgenic T cells in vivo. Second, we showed clonal memory T cells were antagonized during recall responses, resulting in loss of protective immunity. Lastly, we observed that even in the context of a polyclonal response, TCR antagonism greatly inhibits the agonist-specific response, leading to altered hierarchy of immunodominance and reduced T cell memory and protective immunity. These results provide direct evidence of clonal TCR antagonism of naive and memory CD8 T cells during infection and demonstrate the effect of TCR antagonism on protective immunity. Thus, agonist/antagonist interactions may play an important role in determining the immunodominance and repertoire of T cell targets, and evaluation of immune responses and vaccine strategies may require examination of not only agonists but also antagonists and their interactions during an infection.

Myasthenia gravis patients, but not healthy subjects, recognize epitopes that are unique to the epsilon-subunit of the acetylcholine receptor

Myasthenia gravis (MG) is an autoimmune disease characterized by deficits in neuromuscular transmission due to antibody-mediated damage of the acetylcholine receptor (AChR). We examined the in vitro immune response of peripheral blood mononuclear cells isolated from MG patients (n=38) and healthy nonmyasthenic subjects (n=31) to epitopes on the alpha-, epsilon-, and gamma-chains of the AChR. The epsilon- and gamma-epitopes tested represent regions with little sequence homology to the alpha-chain, and little sequence homology between the epsilon- and gamma-chains. No differences were observed in the immune response of MG patients and healthy subjects to any of the alpha-chain epitopes tested. Serial studies of the immune response to the alpha-peptides suggest that epitope spread does occur over time. Cells from MG patients were stimulated by the epsilon- and gamma-chain peptides, although the response was weaker than that to the alpha-peptides. Cells from healthy subjects showed reactivity to gamma-chain peptides only; none of the healthy subjects responded to the epsilon-chain peptides tested. Differences between the epsilon- and gamma-chains may be important in the development of MG, because only MG patients respond to epitopes that are unique to the epsilon-subunit.

Effect of sex hormones on experimental autoimmune uveoretinitis (EAU)

PURPOSE

Sex hormones have been associated with the prevalence, susceptibility, and severity of autoimmune disease. Although the exact mechanism is unknown, sex hormones are reported to influence cytokine production, specifically by affecting the balance of Th1 and Th2 effector cells. We evaluated the effect of estrogen, progesterone, and testosterone in autoimmune uveoretinitis (EAU), a rodent model of human ocular autoimmune disease.

METHODS

Lewis rats implanted with either beta-estradiol (estrogen), 5-dihydrotestosterone (5-DHT), norgestrel (progesterone), or estrogen plus progesterone were immunized with the retinal antigen interphotoreceptor retinoid binding protein (IRBP) peptide. Evaluation of EAU was based on histology of the eyes and measurement of peripheral immunological responses of DTH and lymphocyte proliferation to S-antigen. Quantitative RT-PCR was used to measure IFN-gamma and IL-10 mRNA in the eyes.

RESULTS

In female rats 5-DHT significantly decreased, estrogen slightly enhanced, but progesterone or estrogen + progesterone did not affect EAU. In contrast, in male rats 5-DHT slightly decreased, estrogen moderately decreased, progesterone did not effect, but, estrogen + progesterone slightly decreased EAU. The results correlated with the ocular levels of Th1 (IFN-gamma) and Th2 (IL-10) cytokine messengers.

CONCLUSION

The data support the hypothesis that sex hormones may affect autoimmune diseases by inducing changes in the cytokine balance. This suggests that sex hormone therapy could be considered as an adjunct to anti-inflammatory agents to treat ocular autoimmune diseases in humans.

Therapeutic polypeptides based on HBcAg18-27 CTL epitope can induce antigen-specific CD8+ CTL-mediated cytotoxicity in HLA-A2 transgenic mice

AIM: To explore how to trigger an HLAI-restricted CD8⁺ T cell response to exogenously synthesized polypeptides in vivo.

METHODS: Three mimetic therapeutic polypeptides based on the immunodominant CTL epitope of HBcAg, the B- epitope of HBV PreS₂ region and a common T helper sequence of tetanus toxoid were designed and synthesized with Merrifield’s solid-phase peptide synthesis method. Their immunological properties of inducing T_H1 polarization, CD8⁺ HBV-specific CTL expansion and CD8⁺ T cell mediated cytotoxicity were investigated in HLA-A2 transgenic mice.

RESULTS: Results demonstrated that the mimetic polypeptides comprised of the immunodominant CTL, B-, and T helper epitopes could trigger specifically and effectively vigorous CD8⁺ HBV-specific CTL-mediated cytotoxicity and T_H1 polarization of T cells in HLA-A2 transgenic mice.

CONCLUSION: A designed universal T helper plus B-epitopes with short and flexible linkers could dramatically improve the immunogenicity of CTL epitopes in vivo. And that the mimetic therapeutic peptides based on the reasonable match of the above CTL, B- and T helper epitopes could be a promising therapeutic peptide vaccine candidate against HBV infection.

A disease-associated cellular immune response in type 1 diabetics to an immunodominant epitope of insulin

The 9-23 amino acid region of the insulin B chain (B9-23) is a dominant epitope recognized by pathogenic T lymphocytes in nonobese diabetic mice, the animal model for type 1 diabetes. We describe herein similar (B9-23)-specific T-cell responses in peripheral lymphocytes obtained from patients with recent-onset type 1 diabetes and from prediabetic subjects at high risk for disease. Short-term T-cell lines generated from patient peripheral lymphocytes showed significant proliferative responses to (B9-23), whereas lymphocytes isolated from HLA and/or age-matched nondiabetic normal controls were unresponsive. Antibody-mediated blockade demonstrated that the response was HLA class II restricted. Use of the highly sensitive cytokine-detection ELISPOT assay revealed that these (B9-23)-specific cells were present in freshly isolated lymphocytes from only the type 1 diabetics and prediabetics and produced the proinflammatory cytokine IFN-gamma. This study is, to our knowledge, the first demonstration of a cellular response to the (B9-23) insulin epitope in human type 1 diabetes and suggests that the mouse and human diseases have strikingly similar autoantigenic targets, a feature that should facilitate development of antigen-based therapeutics.

Expression of complement inhibitor protein CD59 in human neuronal and glial cell lines treated with HIV-1 gp41 peptides

In attempts to elucidate the pathogenic mechanisms involved in neurodegeneration in AIDS patients with cognitive deficits, the possible effect of HIV-1 transmembrane envelope protein gp41 on expression of the membrane inhibitor of complement mediated cytolysis (CD59) was assessed in human neuronal (SK-N-SH) and astroglial (T98G) cell lines. Western blotting analyses demonstrated that an immunodominant (ID, aa 598-613) gp41 peptide as well as the recombinant gp41 protein encompassing this domain markedly reduced CD59 level in a dose dependent manner whereas p24 and control peptide had little effect. RT-PCR showed that ID peptide also elicited a reduction in the expressed CD59 mRNA level. This gp41 peptide apparently down-regulated phorbol 12,13-dibutyrate induced elevation of CD59 at the protein and mRNA levels in a manner similar to that conferred by protein kinase C inhibitor, H-7 or staurosporine in SK-N-SH. Interestingly, proinflammatory cytokines such as IL-1beta or IFN-gamma as well as LPS greatly decreased CD59 in SK-N-SH and to a lesser extent in T98G whereas TNF-alpha did not significantly alter it. In contrast, antioxidants and anti-inflammatory agents enhanced CD59 expression reversing gp41 peptide mediated inhibitory effect in SK-N-SH. Our data suggest that high level of gp41 or its metabolites as well as impaired protein kinase response, chronic inflammation or antioxidant depletion within HIV-1 infected brains may be associated with a diminished expression of CD59 which would render neuronal cells to susceptible to indirect bystander lysis in the presence of autologous complement.

Opposite effects of immunotherapy with ovalbumin and the immunodominant T-cell epitope on airway eosinophilia and hyperresponsiveness in a murine model of allergic asthma

In the present study, we investigated immunotherapy using an entire protein or an immunodominant epitope in a murine model of allergic asthma. Immunotherapy was performed in ovalbumin (OVA)-sensitized mice before OVA challenge. Mice were treated subcutaneously with OVA, the immunodominant epitope OVA323-339, or vehicle. In vehicle-treated animals, repeated OVA challenge induced increased serum levels of OVA-specific immunoglobulin (Ig)G1, IgE, airway eosinophilia, and hyperresponsiveness, compared with saline-challenged animals. In addition, interleukin (IL)-4 and IL-5 production upon OVA restimulation of lung-draining lymph node cells in vitro were significantly increased in OVA-challenged animals. Immunotherapy using OVA significantly reduced airway eosinophilia and hyperresponsiveness. This finding was accompanied by significantly reduced OVA-specific IL-4 and IL-5 production. Further, OVA immunotherapy induced increased serum levels of OVA-specific IgG1, whereas OVA-specific IgG2a and IgE levels were not affected. In contrast to OVA immunotherapy, immunotherapy with OVA323-339 aggravated airway eosinophilia and hyperresponsiveness. OVA-specific IgG1, IgG2a, and IgE serum levels, and in vitro IL-4 and IL-5 production, were not affected. Thus, immunotherapy with protein resulted in beneficial effects on airway eosinophilia and hyperresponsiveness, which coincided with a local reduced T-helper 2 (Th2) response. In contrast, peptide immunotherapy aggravated airway hyperresponsiveness and eosinophilia, indicating a local enhanced Th2 response.

Mutations in immunodominant T cell epitopes derived from the nonstructural 3 protein of hepatitis C virus have the potential for generating escape variants that may have important consequences for T cell recognition

One of the most disturbing features of hepatitis C virus (HCV) is its long-term persistence in the host. One hypothesis to explain this phenomenon is that HCV escapes immune recognition through its intrinsic hypermutability. To determine whether immunodominant T cell epitopes derived from HCV nonstructural 3 (NS3) protein might be subject to sequence variations leading to escape mutants, we examined sequence variations of one IL-2-producing epitope, NS3358-375, and one IL-10-producing epitope, NS3505-521. By PCR amplification, cloning, and sequencing, we observed significant sequence variations in the two epitopes, although the selection intensity for each epitope was different. For NS3358-375, more variants were observed, and for NS3505-521, fewer mutations were observed. Moreover, functional studies revealed that three NS3358-375 and one NS3505-521 variants failed to stimulate T cell proliferation, and two other NS3358-375 and NS3505-521 variants weakly stimulated T cell responses. Our results are consistent with immune selection of viral variants at the epitope level, which may enable HCV to evade host defenses over time.

Tolerization of adult mice to immunodominant proteins before monoclonal antibody production

Generating monoclonal antibodies (mAbs) against one polypeptide chain of a heterodimeric protein can be difficult when the other chain is more immunogenic. To influence the immune response in favor of the less immunogenic protein, we rendered adult mice tolerant to the immunodominant protein using a procedure based on the phenomenon of high zone tolerance. We then immunized the tolerized mice with a heterodimeric protein containing the immunogenic protein and produced hybridomas in the usual way. Screening the hybridomas for reactivity against the immunodominant protein and against the heterodimer revealed that this tolerization procedure can result in an increase of hybridomas producing mAbs against the protein of interest by up to 90-fold. This method should be of general utility for the production of mAbs against weakly antigenic proteins in mixtures of antigens.

Bacterial surface proteins recognized by CD4+ T cells during murine infection with Listeria monocytogenes

Optimal immunity to the Gram-positive pathogen Listeria monocytogenes (LM) requires both CD8+ and CD4+ antigen-specific T cell responses. Understanding how CD4+ T cells function in an immune response to LM and how bacterial proteins are processed to peptide/MHC class II complexes in infected cells requires identification of these proteins. Using LacZ-inducible, LM-specific CD4+ T cells as probes, we identified two immunogenic LM proteins by a novel expression cloning strategy. The antigenic peptides contained within these proteins were defined by deletion analysis of the genes, and their antigenicity was confirmed with synthetic peptides. The nucleotide sequences of the genes showed that they encode previously unknown LM proteins that are homologous to surface proteins in other bacterial species. Consistent with their surface topology, mild trypsin treatment of LM protoplasts ablated T cell recognition of these Ags. These findings establish a general strategy for identifying unknown CD4+ T cell Ags and demonstrate that LM surface proteins can provide the peptides for presentation by MHC class II molecules that are specific targets for CD4+ T cells during murine LM infection.

On the mechanisms by which transforming growth factor-beta 2 alters antigen-presenting abilities of macrophages on T cell activation

Peritoneal exudate cells (PEC) incubated with antigen in the presence of transforming growth factor-(TGF)-beta 2 selectively suppress delayed hypersensitivity and IgG2a antibody production when injected intravenously into naive syngeneic recipients. In this study, we have examined in vitro the effects of TGF-beta 2 on the antigen presenting abilities of PEC to activate DO11.10 T cells that express a transgenic T cell receptor that recognizes ovalbumin peptide fragment 323-339 in the context of I-Ad. PEC were pretreated overnight with TGF-beta 2, washed extensively, then co-cultured with DO11.10 T cells in the presence of native OVA or P323-339. We found that TGF-beta 2-treated PEC induced the production of the T helper type 2 (Th2) cytokine, interleukin-4 (IL-4), but unlike untreated PEC, were unable to stimulate the Th1 cytokines, IL-2 and interferon-gamma (IFN-gamma). Furthermore, TGF-beta 2 was produced in an autocrine fashion by TGF-beta 2-treated PEC and was responsible for this shift to a Th2 response. This conclusion was supported by the following results. First, TGF-beta 2-treated PEC were found to express much more TGF-beta 1 and TGF-beta 2 mRNA than untreated PEC. Second, TGF-beta 2-treated PEC secreted large amounts of TGF-beta including its mature form. Third, addition of neutralizing anti-TGF-beta 2 antibodies, but not neutralizing anti-TGF-beta 1 antibodies, restored the ability of antigen-pulsed, TGF-beta 2-pretreated PEC to stimulate DO11.10 T cells to secrete IL-2 and IFN-gamma. These results indicate that antigen-presenting cells that encounter antigen in a TGF-beta-enriched environment (e.g., in the eye) shift responding native T cells toward Th2 responses by producing TGF-beta during antigen presentation.

Role of a C-terminal residue of an immunodominant epitope in T cell activation and repertoire diversity

In the present study, the extent of heterogeneity in the high responder T cell response to the predominant epitope region of hen egg white lysozyme (HEL46-61) was examined. Through analyses of T cell proliferation and precursor frequency, the C3H T cell response is shown not to be limited to peptides containing the previously defined minimal epitope of residues 52-61, but rather is quite heterogeneous, encompassing much of the 46-61 sequence. Further characterization using a panel of T cell hybridoma clones revealed T cell recognition of diverse minimal epitopes within this region. Interestingly, these T hybridomas could be grouped into three distinct categories based on the ability to respond to peptides with or without the native arginine residue at position 61 (61-required, 61-inhibitory, dual responders). Using analogue peptides containing single amino acid substitutions at position 61, further heterogeneity within these hybridoma groups was identified, suggesting the presence of an extremely diverse T cell repertoire for the epitope region. The charge and/or size of the C-terminal residue appears to be a critical factor for certain clones; replacement of the native arginine residue with aspartic acid or glutamic acid enabled a nonstimulatory ligand to specifically antagonize a T cell hybridoma response. Collectively, these results strongly suggest that the C-terminal residue of the predominant epitope in high responder mice plays a critical role in T cell diversity and activation.

Immunodominance of cytotoxic T lymphocyte epitopes co-injected in vivo and modulation by interleukin-12

Immunodominance (ID) of T cell epitopes is a well-documented phenomenon that might have profound significance in the evolution of T cell responses to pathogens, tumors, autoantigens and vaccines. With the intention of developing vaccines composed of several cytotoxic T cell (CTL) epitopes, we injected mice with peptide mixtures containing two to five CTL epitopes and observed clear patterns of ID. In a first case, ID strictly correlated with the competitor activity of the individual peptides for H-2Kd, whereas in a second case, the absence of correlation between ID and competitor activity, binding affinity, half-life of the peptides in serum, induction of proliferation in vitro and the individual immunogenicity of the peptides, suggested to us that ID of co-injected CTL epitopes can be determined both at the peptide level (binding affinity to H-2Kd) and at the T cell level. This hypothesis is supported by our finding that interleukin-12 strongly modulates ID when it is not correlated with MHC binding.

Intraocular injection of class II-restricted peptide induces an unexpected population of CD8 regulatory cells

Intraocular injection of exogenous protein induces an Ag-specific impairment of systemic delayed hypersensitivity (DH), termed anterior chamber associated immune deviation (ACAID). The ACAID-inducing signal is carried by blood-borne cells from the eye to the spleen and can also be generated in vitro by incubating APCs with Ag plus TGF-beta. Paradoxically, class I-restricted CD8 regulatory cells are induced in the spleens of mice with ACAID, and previous studies suggest that CD8 cells are important, and even necessary, for the expression of ACAID. To explore this issue further, we asked whether ACAID could be induced with a class II-restricted peptide, and if so, what type of regulatory cells are generated. An intraocular, but not an i.v., injection of OVA (323-339) peptide resulted in impairment of native OVA-specific DH in both naive and previously sensitized mice. Furthermore, i.v. injection of APCs pretreated with TGF-beta plus OVA peptide also prevented native OVA-specific DH. Surprisingly, both CD8+ and CD4+ spleen cells capable of impairing expression of DH were induced by either intraocular injection of peptide or i.v. injection of APCs pretreated with peptide plus TGF-beta. In summary, ACAID can be induced by a class II-restricted peptide and is accompanied by the generation of two unusual populations of cells: 1) CD8+ regulatory cells unexpectedly induced by class II-restricted peptide; and 2) a novel population of CD4 regulatory cells induced by peptide, but not native protein. Potential mechanisms involved in the processing and presentation of exogenous protein in the ACAID model are discussed in light of the present data.

Inhibition of relapsing experimental autoimmune encephalomyelitis in SJL mice by feeding the immunodominant PLP139-151 peptide

Peripheral antigen-specific tolerance can be induced by feeding protein antigens. The mechanism has been described as either clonal anergy/deletion or induction of antigen-specific regulatory cells that produce transforming growth factor-beta (TGF-beta). These two mechanisms have been linked to the magnitude and frequency of the dose of antigen fed; a single high dose induces anergy/deletion, whereas multiple low doses of antigen induce TGF-beta-secreting regulatory cells. In the present study, we investigated the mechanisms of feeding soluble peptides of proteolipid protein (PLP) for prevention of experimental autoimmune encephalomyelitis (EAE) induced by either intact PLP or the immunodominant PLP139-151 peptide. Feeding PLP139-151 prevented acute and relapsing EAE induced by either PLP139-151 or intact PLP. PLP139-151 feeding induced anergy in the T helper 1 (Th1) population as measured by an inhibition of both proliferation and interferon-gamma (IFN-gamma) production. Interleukin-4 (IL-4) production was increased, but increased TGF-beta production was not observed. Importantly, PLP139-151 feeding induced anergy in peripheral and central nervous system (CNS)-in-filtrating T cells. Feeding of the subdominant PLP epitope (PLP178-191) failed to inhibit EAE induced by PLP139-151; therefore, oral tolerance was not due to induction of bystander suppression. These results demonstrate that both acute and relapsing paralysis in EAE can be prevented by feeding the immunodominant peptide of PLP.

Quaternary structure of a carrier protein influences antigenicity and immunogenicity of an inserted T cell determinant

To study the influence of the quaternary structure of the outer membrane protein PhoE of Escherichia coli on the presentation of an inserted T cell epitope, an epitope comprising amino acid residues 72-85 of myelin basic protein (MBP) was inserted at different sites in PhoE. This sequence is the critical T cell epitope in experimental autoimmune encephalomyelitis (EAE) in Lewis rats. The antigenicity and immunogenicity of two different conformational forms of the chimeric PhoE constructs, i.e. the denatured monomeric form and the native trimeric form, were studied. It appeared that the monomeric form, but not the native trimeric form of such PhoE constructs induced proliferation of the MBP72-85-specific T cell line Z1a. This conformational discrepancy was independent of the site in PhoE in which the epitope was inserted. Immunization with the monomeric form of PhoE constructs resulted in the priming of MBP72-85-specific T cells. In contrast, the trimeric form of these constructs was much less efficient in priming such cells. The differences between the monomeric and trimeric forms were most apparent when induction of EAE was studied. The monomeric form was encephalitogenic while the trimeric form was not. Furthermore, the antigen fine specificity, Vbeta usage and encephalitogenicity of T cells triggered by immunization with a monomeric PhoE construct appeared to be the same as those of T cell line Z1a, which was obtained after immunization with MBP, indicating that similar cells are triggered by immunization with the epitope either in PhoE or in its native context.

Receptor binding and biologic activity of synthetic ET-1 peptides in the retinal pericyte

PURPOSE

The purpose of this study was to examine the effect of synthetic endothelin (ET)-1 peptides with antigenic potential for binding and biologic activity using an in vitro model of microvascular pericytes.

METHODS

All possible sequential hexapeptide fragments of endothelins -1, -2, and -3 were synthesized on polyethylene rods and tested for reactivity with antibodies for ET-1 and ET-3. The most highly antigenic peptide ET-1[3-8] and the least antigenic ET-1[1-6], which gave low reactivity in the enzyme-linked immunosorbent assay (ELISA), were synthesized. The C-terminal hexapeptide ET-1[16-21], which has been reported as an ETB receptor agonist but which gave no reactivity in the ELISA, also was investigated. The synthesized ET analogues were tested for receptor binding, inositol phosphate generation, and mitogenesis in bovine retinal pericytes.

RESULTS

ET-1[16-21] partially inhibited both [125I]-ET-3 binding at high concentrations, as did ET-1[1-6]. In contrast, ET-1[3-8] displaced labeled ET-1 binding but not labeled ET-3 binding. None of the peptides had any significant mitogenic or second-messenger responses when compared to those elicited by the full ET-1 molecule.

CONCLUSIONS

The result of the current work shows that the sequence, ET[3-8], is involved in isopeptide-specific binding to ETA receptors, but it suggests that other regions of the molecule are necessary for full bioactivity in microvascular pericytes.

Hapten-carrier interactions and their role in the production of monoclonal antibodies against hydrophobic haptens

The coupling of haptens to carrier proteins is required for the generation of antihapten antibody response. To date, different polypeptides (such as gelatin, albumin, and keyhole limpet hemocyanin) have been used to increase the immune response against haptens. Different methods of conjugation have also been used to increase the specificity of the antibody response. Our results, obtained through an analysis of the antibody response at both the polyclonal and the monoclonal levels, show that carrier proteins specifically modulate the antibody titer, the specificity of the response, the fusion efficiency, and the number of specific clones. Moreover, the affinity constants of both serum and randomly selected hybridomas directed against different haptens have been found to be exclusively modulated by carrier proteins. In addition, the results show that the carrier protein should be selected considering its possible physicochemical interaction with haptens. Data obtained suggested that any carrier is suitable for hydrophilic haptens, while the choice of the carrier for hydrophobic haptens is critical in obtaining a specific immune response. The use of specific carriers allowed the production of highly specific antibodies: even IgMs, obtained by using these carriers, were able to specifically react with hydrophobic haptens; the case of some IgM monoclonal antibodies specifically reacting with protoporphyrin IX is reported.

Induction of tumor-reactive CTL from peripheral blood and tumor-infiltrating lymphocytes of melanoma patients by in vitro stimulation with an immunodominant peptide of the human melanoma antigen MART-1

MART-1 is an Ag expressed on melanomas and melanocytes, and is recognized by the majority of HLA-A2-restricted tumor-specific tumor-infiltrating lymphocytes (TIL) from melanoma patients. In the present study we have analyzed 10 potential 9-mer epitopes containing the HLA-A2.1 binding motifs for their ability to induce melanoma-specific T cell lines. Antimelanoma CTL could be generated only with MART-1(27-35) peptide, which has been previously shown to be recognized by a majority of HLA-A2-restricted TIL. Anti-MART-1(35-43)-specific CTL could also be induced, but these T cells did not recognize melanoma cells. MART-1(27-35)-specific CTL could be effectively generated from a total of 11 of 12 PBL and from 3 of 3 TIL derived from HLA-A2+ melanoma patients, as well as from 2 of 4 PBL from HLA-A2+ healthy donors by in vitro stimulation with autologous PBMC pulsed with the synthetic MART-1(27-35) peptide. These CTL lines specifically lysed and release cytokines (TNF-alpha, IFN-gamma, and GM-CSF) in response to T2 cells pulsed with MART-1(27-35), as well as to HLA-A2+ MART-1+ melanoma cells. CTL generated with MART-1(27-35) also lysed uncultured HLA-A2+ melanoma cells derived from tumor biopsies, indicating that this MART-1 epitope is likely to be expressed in association with HLA-A2 on the surface of tumor cells in vivo. CTL lines generated with MART-1(27-35) mediated 25- to 100-fold higher lytic activity than MART-1-reactive CTL grown from TIL in the presence of high dose IL-2. These results demonstrate that MART-1(27-35) peptide may represent an ideal candidate for Ag-specific immunotherapy in melanoma patients.

Induction of unresponsiveness in adult rats by immunodominant and nondominant peptides

Intravenous (i.v.) administration of antigens in aqueous solution is an efficient procedure for inducing unresponsiveness in adult animals. Using this procedure, we have compared the unresponsiveness-inducing capacity of an immunodominant and a nondominant peptide derived from the sequence of a retinal antigen, interphotoreceptor retinoid-binding protein (IRBP). The immunodominant peptide, R16, is highly immunogenic in the Lewis rat, while the nondominant peptide, R4, is much less immunogenic and requires higher doses to induce immune response. Pretreatment of Lewis rats with peptides R4 or R16 effectively induced unresponsiveness, shown by the reduced lymphocyte responses following the challenge with the same peptide in adjuvant emulsion. A correlation was found between the doses of each peptide needed to induce immunity or unresponsiveness: both of these doses had to be higher for peptide R4 than for R16. Remarkably, the minimal unresponsiveness-inducing doses of both peptides were lower than those used for the challenge. Pretreatment with the immunodominant peptide, R16, readily inhibited the response to this peptide by lymphocytes from rats challenged with whole IRBP and excessive doses of R16 even affected the response of these rats against whole IRBP. In contrast, R4, which is not recognized by cells of rats challenged with whole IRBP, had no effect on the responses of these rats. The data thus underscore the relationship between immunodominance and unresponsiveness-inducing capacity of peptides and support the notion that the processes of unresponsiveness induction are related to those that produce immunity.

Lymphocyte responses to DR4/1-restricted peptides in rheumatoid arthritis. The immunodominant T cell epitope on the 19-kd Mycobacterium tuberculosis protein

OBJECTIVE

Peptides presented by DR4/1 may be involved in the pathogenesis of rheumatoid arthritis (RA). T cell responses to DR4/1-restricted peptides unrelated to the causative antigen may be altered in RA. Thus, DR4/1-restricted lymphocyte responses in healthy volunteers and patients with RA were determined.

METHODS

Peripheral blood lymphocytes (PBL) and synovial lymphocytes were cultured with synthetic peptides spanning the 19-kd Mycobacterium tuberculosis (MT) protein.

RESULTS

3H-thymidine uptake by PBL from 5 of 7 healthy individuals and 5 of 7 RA patients increased in response to the N-terminal peptide (residues 1-20). Eleven fresh synovial fluid and 4 fresh synovial tissue (ST) lymphocyte samples did not proliferate in response to any of the peptides. However, the same T cell epitope was identified by ST lymphocytes when these were precultured. The N-terminal peptide was not a common antibody-binding site, unlike several of the other peptides.

CONCLUSION

Similar responses by RA and normal PBL to a DR4/1-restricted immunodominant T cell epitope on the 19-kd MT protein were observed. The responses were more readily detected in PBL than in synovial lymphocytes. These observations may be relevant for assessing unrelated synthetic peptides in the development of DR4/1-restricted peptide immunotherapy.