Induction of tolerance to one determinant on a synthetic peptide does not affect the response to a second linked determinant. Implications for the mechanism of neonatal tolerance induction

In vivo immunogenicity of Tax(11-19) epitope in HLA-A2/DTR transgenic mice: implication for dendritic cell-based anti-HTLV-1 vaccine

Viral oncoprotein Tax plays key roles in transformation of human T-cell leukemia virus (HTLV-1)-infected T cells leading to adult T-cell leukemia (ATL), and is the key antigen recognized during HTLV-associated myelopathy (HAM). In HLA-A2+ asymptomatic carriers as well as ATL and HAM patients, Tax(11-19) epitope exhibits immunodominance. Here, we evaluate CD8 T-cell immune response against this epitope in the presence and absence of dendritic cells (DCs) given the recent encouraging observations made with Phase 1 DC-based vaccine trial for ATL. To facilitate these studies, we first generated an HLA-A2/DTR hybrid mouse strain carrying the HLA-A2.1 and CD11c-DTR genes. We then studied CD8 T-cell immune response against Tax(11-19) epitope delivered in the absence or presence of Freund's adjuvant and/or DCs. Overall results demonstrate that naturally presented Tax epitope could initiate an antigen-specific CD8T cell response in vivo but failed to do so upon DC depletion. Presence of adjuvant potentiated Tax(11-19)-specific response. Elevated serum IL-6 levels coincided with depletion of DCs whereas decreased TGF-β was associated with adjuvant use. Thus, Tax(11-19) epitope is a potential candidate for the DC-based anti-HTLV-1 vaccine and the newly hybrid mouse strain could be used for investigating DC involvement in human class-I-restricted immune responses.

Sercarzian immunology--In memoriam. Eli E. Sercarz, 1934-2009

During his long career as a principal investigator and educator, Eli Sercarz trained over 100 scientists. He is best known for developing hen egg white lysozyme (HEL) as a model antigen for immunologic studies. Working in his model system Eli furthered our understanding of antigen processing and immunologic tolerance. His work established important concepts of how the immune system recognizes antigenic determinants processed from whole protein antigens; specifically he developed the concepts of immunodominance and crypticity. Later in his career he focused more on autoimmunity using a variety of established animal models to develop theories on how T cells can circumvent tolerance induction and how an autoreactive immune response can evolve over time. His theory of "determinant spreading" is one of the cornerstones of our modern understanding of autoimmunity. This review covers Eli's entire scientific career outlining his many seminal discoveries.

Human cord blood CD4+CD25hi regulatory T cells suppress prenatally acquired T cell responses to Plasmodium falciparum antigens

In malaria endemic regions, a fetus is often exposed in utero to Plasmodium falciparum blood-stage Ags. In some newborns, this can result in the induction of immune suppression. We have previously shown these modulated immune responses to persist postnatally, with a subsequent increase in a child's susceptibility to infection. To test the hypothesis that this immune suppression is partially mediated by malaria-specific regulatory T cells (T(regs)) in utero, cord blood mononuclear cells (CBMC) were obtained from 44 Kenyan newborns of women with and without malaria at delivery. CD4(+)CD25(lo) T cells and CD4(+)CD25(hi) FOXP3(+) cells (T(regs)) were enriched from CBMC. T(reg) frequency and HLA-DR expression on T(regs) were significantly greater for Kenyan as compared with North American CBMC (p < 0.01). CBMC/CD4(+) T cells cultured with P. falciparum blood-stage Ags induced production of IFN-γ, IL-13, IL-10, and/or IL-5 in 50% of samples. Partial depletion of CD25(hi) cells augmented the Ag-driven IFN-γ production in 69% of subjects with malaria-specific responses and revealed additional Ag-reactive lymphocytes in previously unresponsive individuals (n = 3). Addition of T(regs) to CD4(+)CD25(lo) cells suppressed spontaneous and malaria Ag-driven production of IFN-γ in a dose-dependent fashion, until production was completely inhibited in most subjects. In contrast, T(regs) only partially suppressed malaria-induced Th2 cytokines. IL-10 or TGF-β did not mediate this suppression. Thus, prenatal exposure to malaria blood-stage Ags induces T(regs) that primarily suppress Th1-type recall responses to P. falciparum blood-stage Ags. Persistence of these T(regs) postnatally could modify a child's susceptibility to malaria infection and disease.

Immunogenicity of aggregates of recombinant human growth hormone in mouse models

Aggregation of recombinant therapeutic protein products is a concern due to their potential to induce immune responses. We examined the immunogenicity of protein aggregates in commercial formulations of recombinant human growth hormone produced by freeze-thawing or agitation, two stresses commonly encountered during manufacturing, shipping and handling of therapeutic protein products. In addition, we subjected each preparation to high-pressure treatment to reduce the size and concentration of aggregates present in the samples. Aggregates existing in a commercial formulation, as well as aggregates induced by freeze-thawing and agitation stresses enhanced immunogenicity in one or more mouse models. The use of high-pressure treatment to reduce size and concentrations of aggregates within recombinant human growth hormone formulations reduced their overall immunogenicity in agreement with the "immunon" hypothesis.

Phenotypic correction and long-term expression of factor VIII in hemophilic mice by immunotolerization and nonviral gene transfer using the Sleeping Beauty transposon system

Hemophilia A is a lead candidate for treatment by gene therapy because small increments in the missing secreted protein product, coagulation factor VIII (FVIII), would result in substantial clinical amelioration. Clinically relevant therapy might be achieved by stably delivering a human FVIII cDNA to correct the bleeding disorder. We used the Sleeping Beauty (SB) transposon, delivered as naked plasmid DNA by tail-vein injection, to integrate B-domain-deleted FVIII genes into the chromosomes of hemophilia A mice and correct the phenotype. Since FVIII protein is a neoantigen to these mice, sustaining therapeutic plasma FVIII levels was problematic due to inhibitory antibody production. We circumvented this problem by tolerizing 82% of neonates by a single facial-vein injection of recombinant FVIII within 24 hours of birth (the remaining 18% formed inhibitors). Achievement of high-level (10%-100% of normal) FVIII expression and phenotypic correction required co-injection of an SB transposase-expressing plasmid to facilitate transgene integration in immunotolerized animals. Linker-mediated polymerase chain reaction was used to clone FVIII transposon insertion sites from liver genomic DNA, providing molecular evidence of transposition. Thus, SB provides a nonviral means for sustained FVIII gene delivery in a mouse model of hemophilia A if the immune response is prevented.

Glycosylation of type II collagen is of major importance for T cell tolerance and pathology in collagen-induced arthritis

Type II collagen (CII) is a candidate cartilage-specific autoantigen, which can become post-translationally modified by hydroxylation and glycosylation. T cell recognition of CII is essential for the development of murine collagen-induced arthritis (CIA) and also occurs in rheumatoid arthritis (RA). The common denominator of murine CIA and human RA is the presentation of an immunodominant CII-derived glycosylated peptide on murine Aq and human DR4 molecules, respectively. To investigate the importance of T cell recognition of glycosylated CII in CIA development after immunization with heterologous CII, we treated neonatal mice with different heterologous CII-peptides (non-modified, hydroxylated and galactosylated). Treatment with the galactosylated peptide (galactose at position 264) was superior in protecting mice from CIA. Protection was accompanied by a reduced antibody response to CII and by an impaired T cell response to the glycopeptide. To investigate the importance of glycopeptide recognition in an autologous CIA model, we treated MMC-transgenic mice, which express the heterologous CII epitope with a glutamic acid in position 266 in cartilage, with CII-peptides. Again, a strong vaccination potential of the glycopeptide was seen. Hence CII-glycopeptides may be the optimal choice of vaccination target in RA, since humans share the same epitope as the MMC mouse.

Revisiting tolerance induced by autoantigen in incomplete Freund's adjuvant

Injection of autoantigens in IFA has been one of the most effective ways of preventing experimental, T cell-mediated, autoimmune disease in mice. The mechanism that underlies this protection has, however, remained controversial, with clonal deletion, induction of suppressor cells or of type 2 immunity being implicated at one time or another. Using high resolution enzyme-linked immunospot (ELISPOT) analysis, we have revisited this paradigm. As models of autoimmunity against sequestered and readily accessible autoantigens, we studied experimental allergic encephalomyelitis, induced by myelin oligodendrocyte glycoprotein, proteolipid protein, myelin basic protein, and renal tubular Ag-induced interstitial nephritis. We showed that the injection of each of these Ags in IFA was immunogenic and CD4 memory cells producing IL-2, IL-4, and IL-5, but essentially no IFN-gamma. IgG1, but not IgG2a, autoantibodies were produced. The engaged T cells were not classic Th2 cells in that IL-4 and IL-5 were produced by different cells. The IFA-induced violation of self tolerance, including the deposition of specific autoantibodies in the respective target organs, occurred in the absence of detectable pathology. Exhaustion of the pool of naive precursor cells was shown to be one mechanism of the IFA-induced tolerance. In addition, while the IFA-primed T cells acted as suppressor cells, in that they adoptively transferred disease protection, they did not interfere with the emergence of a type 1 T cell response in the adoptive host. Both active and passive tolerance mechanisms, therefore, contribute to autoantigen:IFA-induced protection from autoimmune disease.

T cell receptor complementarity determining region 3 length analysis reveals the absence of a characteristic public T cell repertoire in neonatal tolerance. The response in the "tolerant" mouse within the residual repertoire is quantitatively similar but qualitatively different

All adult BALB/c mice immunized with hen egg white lysozyme (HEL) or its dominant determinant, peptide (p)106-116, mount a T cell response using a "public" Vbeta8.2Jbeta1.5 T cell clone. Neonatal exposure to tolerance-inducing doses of antigen can drastically diminish responsiveness in the draining lymph nodes but not in the spleens of animals challenged as adults with the cognate antigen. To determine the role of T cell deletion or anergy within the mechanisms of observed neonatal "tolerance," we treated neonatal BALB/c mice with HEL and directly followed the characteristic public clone using complementarity determining region 3 length T cell repertoire analysis. Our results confirm that despite intraperitoneal injection of neonates with a high dose of HEL emulsified in incomplete Freund's adjuvant, a strong splenic proliferative response to HEL was observed upon recall. However, the adult splenic T cell response of these neonatally treated mice lacked the usual Vbeta8.2Jbeta1.5 public clone characteristic of HEL-primed BALB/c mice. After challenge with HEL-complete Freund's adjuvant as adults, immunoglobulin (Ig)G2a isotype antibody was drastically reduced, and IgG1 was found to be the predominant anti-HEL IgG isotype expressed, indicating a deviation of cytokine response toward T helper type 2. 5-wk-old mice, nasally instilled with tolerogenic doses of HEL p106-116, also showed significant inhibition of this public T cell expansion. These results demonstrate that during neonatal and adult nasal tolerance induction, deletion/anergy removes the public clone, exposing a response of similar specificity but that is characterized by the T helper type 2 phenotype and a splenic residence.

Expansion of neonatal tolerance to self in adult life: II. Tolerance preferentially spreads in an intramolecular manner

Newborn rats exposed to a myelin basic protein determinant acquired long-lasting resistance to experimental autoimmune encephalomyelitis induced by another determinant only if both determinants are co-administered in adult life. We demonstrate here that during the course of disease both the anti-self response and the tolerant state spread in an intramolecular and not an intermolecular manner. Mechanisms involved in tolerance elicitation and expansion are then explored using an in vitro system in which indirect suppression could be measured.

Expansion of neonatal tolerance to self in adult life: I. The role of a bacterial adjuvant in tolerance spread

T cell neonatal tolerance to self evolves perturbation of the Th1/Th2 balance towards Th2-type self-specific T cells. In the current study we have demonstrated that a tolerant state could be extended to another encephalitogenic determinant only if the neonatally tolerizing determinant was co-administered in adult life with an emulsion of Mycobacterium tuberculosis (i.e. complete Freund's adjuvant). The mechanisms underlying tolerance elicitation and expansion were then explored by an in vitro system in which indirect suppression could be measured. Addition of a tolerizing epitope to splenic T cells from neonatally tolerized animals induced a marked suppression of the anti-MT response. This response could be restored by neutralizing antibodies to IL-4. In contrast, the neutralizing antibodies to IL-4 had no affect on the response of these cells to the tolerizing determinant. These findings are highly significant not only because they explore the important role of microbial antigens in neonatal tolerance, but also because they distinguish, for the first time, between tolerizing and tolerized T cells.

Induction of class II major histocompatibility complex blockade as well as T cell tolerance by peptides administered in soluble form

Peptides binding to a particular class II major histocompatibility complex (MHC) molecule can inhibit the activation of T cells by other peptides binding to the same molecule, a phenomenon termed class II MHC blockade. All class II-binding peptides exert MHC blockade in vivo in depot form with adjuvant, and some also retain their blocking properties in soluble form. We demonstrate here that soluble peptides, when used at doses causing short-term MHC blockade, can also induce long-term antigen-specific T cell tolerance to themselves. The tolerogenicity of soluble peptides correlates with their antigenicity in adjuvant, but it is not necessarily related to their capacity to act as class II blockers in vivo. The tolerant state is manifested in a decreased production of both T helper cell 1 (Th1)-type and Th2-type lymphokines, and it cannot be reversed by interleukin-2. Once T cells are primed with a peptide in complete Freund's adjuvant, they are resistant to tolerization with the same peptide applied in soluble form. Tolerance induction is partially impaired in B cell-deficient mu MT-/- mice, suggesting a role for B cell antigen presentation in this process. The results suggest that the potential immunogenicity of class II MHC blockers could be circumvented by choosing a tolerogenic mode of application.

Neonatal peptide exposure can prime T cells and, upon subsequent immunization, induce their immune deviation: implications for antibody vs. T cell-mediated autoimmunity

Neonatal exposure to antigen is believed to result in T cell clonal inactivation or deletion. Here we report that, contrary to this notion, neonatal injection of BALB/c mice with a hen egg lysozyme peptide 106-116 in putative "tolergenic" doses induced a T cell proliferative and an immunoglobulin G (IgG) antibody (Ab) response of both T helper cell 1 (Th1)- (IgG2a, IgG2b, and IgG 3) and Th2-dependent (IgG1) isotopes. Upon subsequent challenge with the peptide in complete Freund's adjuvant in adult life, although this neonatal regimen suppressed proliferation and the production of Th1 cytokines (interleukin[IL]-2 and interferon gamma), Th2 cytokine (IL-5, IL-4, and IL-10) secretion was increased, and the serum levels of Th1- and Th2-dependent isotypes of peptide-specific Ab remained elevated. The in vitro proliferative unresponsiveness in Th1 cells could be reversed by Abs to Th2 cytokines (IL-4 and IL-10). Thus, neonatal treatment with a peptide antigen induces T cell priming including production of IgG Abs of both Th1- and Th2-dependent isotypes. Upon subsequent peptide exposure, the peptide-specific T cell responses undergo an effective class switch in the direction of Th2, resulting in T cell proliferative unresponsiveness. Accordingly, this shift towards increased Ab production to autoantigen could be deleterious in individuals prone to antibody-mediated diseases. Indeed, neonatal treatment with a self-autoantigenic peptide from an anti-DNA monoclonal Ab (A6H 58-69) significantly increased the IgG anti-double-stranded DNA Ab levels in lupus-prone NZB/NZW F1 mice, despite suppressing peptide-specific T cell proliferation. This adverse clinical response is in sharp contrast to the beneficial outcome of neonatal treatment with autoantigens in Th1-mediated autoimmune diseases, such as autoimmune encephalomyelitis, as reported by others. A Th1 to Th2 immune deviation can explain the discordant biological responses after the presumed induction of neonatal tolerance in autoantibody- vs. Th-1 mediated autoimmune diseases.

Induction of TH1 and TH2 immunity in neonatal mice

The neonatal period has been thought of as a window in ontogeny, during which the developing immune system is particularly susceptible to tolerization. In the present study, the classic system for induction of neonatal tolerance to protein antigens was reexamined in mice. The presumably tolerogenic protocol was found to trigger a vigorous T helper cell type 2 (TH2) immune response. Thus, neonatal "tolerization" induces immune deviation, not tolerance in the immunological sense. Neonates are not immune privileged but generate TH2 or TH1 responses, depending on the mode of immunization.

Difficulties in obtaining monoclonal antibodies to subsets of human leukocytes, using neonatal tolerance induction in mice

Many antigens are shared between different types of human leukocytes. In an effort to obtain new lineage-specific monoclonal antibodies, particularly antibodies to dendritic cells, we attempted to tolerize newborn mice to one type of leukocyte and then immunize the adults with another. We found that T cells, either unstimulated T cells or T blasts, were more effective at inducing neonatal tolerance than non-T cells or B cell lines. However, the tolerance that was achieved was not restricted to T cells, since we could not elicit from the tolerized mice a specific antibody response to a B cell line or to blood dendritic cells. Here we describe several efforts, all unsuccessful, to achieve cell specific immune responses in tolerant mice. The parameters we considered included the type of cell used to tolerize neonatal mice, the regimen of injections for inducing tolerance or eliciting immunity, and the use of several different adjuvants.

Neonatal tolerance to an immunodominant T cell reactivity does not confer resistance to EAMG induction in Lewis rats

The overall goal of this study was to determine, during induction of experimental autoimmune myasthenia gravis (EAMG) in Lewis rats, the relative importance of acetylcholine receptor (AChR)-reactive helper T cells associated with one particular immunodominant fine specificity. Thus, experiments presented below were designed to evaluate the immunopathological role played by helper T cells with reactivity against the AChR alpha subunit region associated with amino acid residues 100-116 (i.e., alpha 100-116); in particular, the relationship between T cell reactivity with this specificity and disease induction was assessed. In order to examine the importance of this T cell reactivity, Lewis rat neonates were made T cell tolerant to a synthetic peptide alpha 100-116 and subsequently evaluated for anti-AChR antibody production and resulting neuromuscular dysfunction. Results indicated that although T cell reactivity against the alpha 100-116 peptide could be effectively removed from the Lewis T cell repertoire, tolerized Lewis rats immunized with AChR could undergo an active anti-AChR antibody response that produced symptoms of EAMG. Thus, other AChR T cell reactivities appeared capable of providing adequate help to B cells leading to production of anti-AChR antibodies with pathogenic potential.

Orally administered myelin basic protein in neonates primes for immune responses and enhances experimental autoimmune encephalomyelitis in adult animals

Antigen-driven tolerance is an effective method for suppression of autoimmune diseases. Adult animals can be tolerized against the induction of experimental autoimmune encephalomyelitis (EAE) by both oral and parenteral administration of myelin basic protein (MBP). We have found that in contrast to previous studies of neonatal tolerance in which parenterally administered autoantigens induced tolerance, the oral administration of MBP in neonatal rats did not result in tolerization to MBP, but instead, primed for immunologic responses. Proliferative responses to MBP and its encephalitogenic epitope were present in animals fed with MBP as neonates and co-culture of encephalitogenic T cells with cells from neonatal rats fed with MBP were associated with enhanced MBP responses rather than the suppression observed with cells from adult rats fed with MBP. Furthermore, neonates fed with MBP and immunized 6-8 weeks later with MBP in adjuvant to induce EAE revealed enhancement of disease severity, and were not protected from a second attack upon active reinduction of EAE. Subcutaneous injection of soluble MBP into neonates had no effect on EAE induction as adults, whereas intraperitoneal injection of MBP in neonates was associated with marked suppression of disease in adults. Suppression of EAE began to appear in animals fed with MBP at 4 weeks of age, and was similar to oral tolerance in adult animals when animals were fed at 6 weeks of age. These results suggest that immaturity of the immunoregulatory network associated with oral tolerance and sensitization to autoantigens via the gut in the neonatal period may contribute to the pathogenesis of autoimmune diseases.

Examination of characteristics that may distinguish disease-causing from benign AChR-reactive antibodies in experimental autoimmune myasthenia gravis

In summary, the strategies of the experimentation described above were designed to address the confusion resulting from observations concerning the lack of correlation between antibody titers and disease severity in MG patients. Lessons learned from these studies of EAMG suggest that if the proportion of the total expressed/produced anti-AChR antibody repertoire with disease-causing potential differs from patient-to-patient with MG, then assessment of the total antibody titer becomes meaningless unless a particular patient produces disease-causing reactivities that make up a major portion of the total titer. Not only may disease severity depend on the titer of a small subset of disease-causing antibody(s) reactive with a particular conformation-dependent AChR region, but may also depend on the relative contribution of additional subsets of antibody with functionally irrelevant or potentially protective activity. The key to exploiting the existence of antibody subsets with differing disease-causing potential will be to create probes that would allow the easy monitoring of the relevant reactivities. For instance, carefully selected anti-idiotypic antibodies (such as the 11E10 monoclonal antibody described above) may be of great value when specifically capable of recognizing idiotypes that are selectively associated with disease-causing anti-AChR antibodies and under-represented on antibodies lacking disease-causing capability. If, in addition, characteristics of helper T cells are identified that allow more accurate prediction of D+ Id production, exciting opportunities would become available to more directly evaluate disease mechanisms and to develop more highly efficacious immunotherapeutic strategies.

Prevention of experimental autoimmune arthritis with a peptide fragment of type II collagen

Collagen arthritis is induced in inbred rats with the injection of native type II collagen. The pathogenesis of this experimental autoimmune disease is T cell dependent. This study demonstrates that collagen-specific T cells, derived from pathogenic and nonpathogenic rat T cell lines, both recognize the same peptide epitope. The epitope, consisting of amino acids 58-73 of cyanogen bromide fragment 11 of type II collagen, was as effective as whole collagen in stimulating a panel of collagen-specific rat/mouse T cell hybridomas. This peptide may, therefore, constitute a dominant epitope for CD4+ rat T cells in their response to type II collagen. Administration of the peptide to either neonatal or adult rats prevented the subsequent induction of experimental arthritis with whole collagen, demonstrating that the in vivo response to this dominant epitope is, therefore, relevant in the pathogenesis of arthritis. Despite its ability to prevent collagen-induced arthritis, administration of this peptide in incomplete Freund's adjuvant intradermally did not induce disease.

Alternative patterns of MHC-restricted antibody responsiveness following intraperitoneal immunization of inbred mice with different preparations of an 86 kilodalton antigen of Schistosoma mansoni

The investigation of MHC restricted antibody responses to an 86 kDa antigen (p86) during chronic Schistosoma mansoni infection has been extended to immunization with this antigen. In the absence of adjuvant, a similar pattern of responsiveness by mice expressing H-2k and H-2d but not H-2b was observed following immunization with unpurified adult worm homogenate. Adjuvant selectively abrogated the capacity of H-2d mice to respond and this was also the case when purified p86 with adjuvant was injected. Immunization with purified subfragments of p86 again demonstrated MHC restriction in the capacity to immunoprecipitate p86 in vitro translation product, the pattern varying according to the fragment used. Western blot analysis showed that in some, but not all instances of apparent 'non-responsiveness' characterized by immunoprecipitation, antibody specificities capable of recognizing p86 epitopes on the nitrocellulose bound p86 were, indeed, present. Thus the fine specificity as well as the absolute capacity to respond is influenced by both the MHC haplotype of the host and the nature of the immunizing antigen.

Autoantigen-induced self lysis of human myelin basic protein-specific T lymphocytes

Cytotoxic T cells reactive with myelin basic protein (MBP) may be isolated from most human subjects. Since activated T cells express major histocompatibility complex (MHC) class II antigens, we assessed whether MBP-specific, CD4+ T cells could present MBP or synthetic MBP peptides to themselves and whether this provoked self lysis. We examined two MBP-specific cell lines and eight T cell clones recognizing four different MBP epitopes. All T cell populations presented MBP as well as synthetic peptides to themselves eliciting self lysis of the T cell clones. CD4+ T cell populations recognizing another central nervous system (CNS) protein, proteolipid protein (PLP), or the recall antigen, Candida, did not exhibit this antigen-induced, autocytolytic activity. However, activated, PLP-reactive T cells were susceptible to lysis by cytotoxic MBP-specific T cells in the presence of MBP. These results suggest that antigen-induced self lysis of activated human T cells might limit an autoimmune response within a target organ independent of other immunoregulatory mechanisms.

Does the presence of self-reactive T cells indicate the breakdown of tolerance?

There are many experimental systems in which autoreactive T cells can easily be demonstrated but where the host does not normally develop autoimmune disease. How do these animals avoid autoimmunity? Does the presence of these self-reactive cells indicate the failure of self-tolerance? To answer these questions it is necessary to consider how some T cells might escape tolerance induction and why they are not activated in the host. There are several different explanations which can be broadly placed into one of two categories. First, although autoreactive cells may be easily stimulated under experimental conditions, the requirements for activation and likewise deletion may not be met under physiological conditions. The self-antigen may be poorly presented by APC or sequestered in a particular body compartment; alternatively, these T cells may have low affinity receptors needing high levels of antigen. The second category is characterized by the need for immunoregulation. A random selection of T cells may escape clonal inactivation in the thymus but may be kept under constant suppression, which provides a fail-safe mechanism for deletional tolerance. In this review we will discuss these mechanisms and their possible importance in the prevention of autoimmunity.

Identification of an immunosuppressive epitope of type II collagen that confers protection against collagen-induced arthritis

We have previously reported that collagen-induced arthritis can be suppressed by intravenous injection of native type II (CII) but not type I collagen. We have now identified denatured fragments of CII capable of suppressing collagen-induced arthritis and inducing tolerance. Purified CII was cleaved with cyanogen bromide (CB), and the major resulting peptides were isolated. Female DBA/1 mice were administered OVA, native CII, or one of the CB peptides, intravenously, before immunization with native CII, 6 wk after immunization, mice tolerized with CII and CB11 had a markedly lower incidence of arthritis compared with controls. There was a correlation between the overall antibody response and the incidence of arthritis. In addition, animals tolerized with either CII or CB11 had a decreased antibody response not only to CII, but also to each of the other CB peptides tested. To identify the epitope involved in suppression of arthritis, five synthetic peptides, 21-26 amino acids in length, corresponding to selected regions of CB11, were generated. Each of the peptides was injected intravenously into mice before immunization. Only one of these, CB11 122-147, was capable of suppressing arthritis. In addition, mice given the synthetic peptide CB11 122-147 neonatally were suppressed for arthritis and antibody responsiveness when immunized with CII at 8 wk of age. Thus, we have identified CB11 122-147 as an epitope of CII important in induction of tolerance and suppression of disease. Further experiments narrowing down the pivotal amino acids for the immunogenicity of this epitope and the role this epitope plays in induction and regulation of disease will enhance our understanding of how the immune response to collagen affects autoimmune arthritis.

How some T cells escape tolerance induction

A feature common to many animal models of autoimmune disease, for example, experimental allergic encephalomyelitis, experimental autoimmune myasthenia gravis and collagen-induced arthritis, is the presence of self-reactive T cells in healthy animals, which are activated to produce disease by immunization with exogenous antigen. It is unclear why these T cells are not deleted during ontogeny in the thymus and, having escaped tolerance induction, why they are not spontaneously activated by self-antigen. To investigate these questions, we have examined an experimental model in which mice are tolerant to an antigen despite the presence of antigen-reactive T cells. We find that the T cells that escape tolerance induction are specific for minor determinants on the antigen. We propose that these T cells evade tolerance induction because some minor determinants are only available in relatively low amounts after in vivo processing of the whole antigen. For the same reason, these T cells are not normally activated but can be stimulated under special circumstances to circumvent tolerance.

In vivo-induced suppression of T cell proliferation: the relationship between the specificity of induction and control

We have previously shown that sc 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 to peptide 8. In contrast, immunization of B10.BR (H-2k) mice either with TMVP or with peptide 8 induces T cells which respond in vitro to the homologous but not the heterologous Ag. In the present article , we report that in the B10.BR (H-2k) strain, ip prepriming with (TMVP) 7 days prior to sc immunization with peptide 8 causes a drastic reduction in the in vitro proliferative response of peptide 8-specific T cells while no such effect is seen in the congenic C57BL/10 (H-2b) strain. This suppression of T cell responsiveness can be transferred with TMVP-primed spleen cells. Moreover, deleting T cells from the transferred spleen cells abrogates the suppressive effect. In both H-2 haplotypes, ip prepriming with peptide 8 causes suppression of the proliferative T cell response induced by subsequent immunization with peptide 8. This prepriming has no effect on the response to TMVP immunization of B10.BR mice but does effect the response of C57BL/10 mice. Using various synthetic peptides to analyze the specificity of the suppression, we have determined that (1) T cells involved in the suppression of the proliferative T cell response to a single peptide determinant do not suppress the proliferative T cell response to other determinants on the protein antigen and (2) these T cells with suppressor function, and proliferating T cells which are ultimately regulated, can exhibit specificity for the same epitope. These studies suggest that there may exist fundamental differences as to how T cells which participate in suppression an proliferating T cells (which include mainly T helper cells) recognize protein antigens.

Peptide-specific prevention of experimental allergic encephalomyelitis. Neonatal tolerance induced to the dominant T cell determinant of myelin basic protein

Experimental allergic encephalomyelitis (EAE) is a model of antigen-specific T cell-mediated autoimmune disease. The alpha-acetylated, NH2-terminal nine amino acids (1-9NAc) of myelin basic protein (MBP) represents the dominant T cell epitope for the induction of EAE in the B10.PL (H-2u) strain. We tolerized neonatal B10.PL mice to 1-9NAc and studied the proliferative responses to this peptide and to whole MBP. Mice exposed to 1-9NAc in the neonatal period were tolerant to subsequent challenge at the proliferative T cell level. Similarly, in the 1-9NAc-tolerant group, both the incidence and severity of 1-9NAc induced EAE were greatly reduced. The fact that we were able to tolerize mice normally responsive to MBP suggests that this self antigen is sequestered (within the central nervous system) and hence tolerance to it is not normally induced. No significant difference in disease incidence was seen in response to rat MBP between control animals and 1-9NAc-tolerized mice (50% in both groups), demonstrating the presence of at least one additional encephalitogenic determinant elsewhere on the molecule. We have successfully prevented disease induction by peptide-induced tolerization. Tolerance induction by peptides provides a new and specific strategy in the prevention of autoimmunity. However, it will be clearly necessary to fully define all epitopes potentially capable of inducing pathogenic T cells to ensure complete and effective therapy of T cell-mediated autoimmune disease.