Thymic selection and adaptability of cytotoxic T lymphocyte responses in transgenic mice expressing a viral protein in the thymus

α-NAC-Specific Autoreactive CD8+ T Cells in Atopic Dermatitis Are of an Effector Memory Type and Secrete IL-4 and IFN-γ

Autoreactivity may play a critical role in the chronification of atopic dermatitis (AD). Several studies showed that AD patients produce IgE Abs specific for autoantigens, and we described Th as well as CD8(+) T cells specific for the autoallergen Hom s 2, the α-chain of the nascent polypeptide-associated complex (α-NAC). This study aimed to investigate the frequency and inflammatory phenotype of autoallergen-specific CD8(+) T cells. CD8(+) T cell immunodominant epitopes of α-NAC were mapped by applying prediction softwares, and binding affinity was confirmed by stabilization of empty MHC complexes. MHC class I tetramers were assembled and binding cells were analyzed directly ex vivo by flow cytometry and in terms of single-cell assessment by ChipCytometry. We report significantly elevated numbers of α-NAC-specific peripheral T cells in sensitized patients compared with nonatopic controls. These cells secrete IL-4 and IFN-γ, and surface markers revealed significantly elevated frequencies of circulating terminally differentiated α-NAC-specific CD8(+) T cells in patients with AD compared with nonatopic donors. The observed phenotype of α-NAC-specific CD8(+) T cells indicates a role in the pathogenesis of AD.

Autoallergy in atopic dermatitis

The term autoallergy denotes autoimmunity accompanying an atopic disease, with antigen-specific IgE as a hallmark. This phenomenon is discussed to contribute to a chronification of the disease and to shape the immune response in chronic atopic dermatitis (AD). In this review, we highlight recent insights into the autoallergic inflammation in AD. Different mechanisms underlying the allergenicity of autoallergens are discussed at the moment: intrinsic functions modulating the immune system as well as molecular mimicry may influence the allergenic potential of these proteins. Finally, the role of specific T cells is discussed.

Cite this as: Hradetzky S, Werfel T, Roesner LM. Autoallergy in atopic dermatitis. Allergo J Int 2015; 24:16–22 DOI: 10.1007/s40629-015-0037-5

The rationale of vectored gene-fusion vaccines against cancer: evolving strategies and latest evidence

The development of vaccines that target tumor antigens in cancer has proven difficult. A major reason for this is that T cells specific for tumor self-antigens and neoantigens are eliminated or inactivated through mechanisms of tolerance. Antigen fusion strategies which increase the ability of vaccines to stimulate T cells that have escaped tolerance mechanisms, may have a particular potential as immunotherapies. This review highlights antigen fusion strategies that have been successful in stimulating the induction of T-cell immunity against cancer and counteracting tumor-associated tolerance. In preclinical studies, these strategies have shown to improve the potency of vectored vaccines through fusion of tumor antigen to proteins or protein domains that increase CD4+ T-cell help, CD8+ T-cell responses or both the CD4+ and CD8+ T-cell responses. However, in clinical trials such strategies seem to be less efficient when provided as a DNA vaccine. The first clinical trial using a viral vectored fusion-gene vaccine is expected to be tested as a partner in a heterologous prime-boost regimen directed against cervical cancer.

Promotion and prevention of autoimmune disease by CD8+ T cells

Until recently, little was known about the importance of CD8+ T effectors in promoting and preventing autoimmune disease development. CD8+ T cells can oppose or promote autoimmune disease through activities as suppressor cells and as cytotoxic effectors. Studies in several distinct autoimmune models and data from patient samples are beginning to establish the importance of CD8+ T cells in these diseases and to define the mechanisms by which these cells influence autoimmunity. CD8+ effectors can promote disease via dysregulated secretion of inflammatory cytokines, skewed differentiation profiles and inappropriate apoptosis induction of target cells, and work to block disease by eliminating self-reactive cells and self-antigen sources, or as regulatory T cells. Defining the often major contribution of CD8+ T cells to autoimmune disease and identifying the mechanisms by which they alter the pathogenesis of disease is a rapidly expanding area of study and will add valuable information to our understanding of the kinetics, pathology and biology of autoimmune disease.

Molecular anatomy and number of antigen specific CD8 T cells required to cause type 1 diabetes

We quantified CD8 T cells needed to cause type 1 diabetes and studied the anatomy of the CD8 T cell/beta (β) cell interaction at the immunologic synapse. We used a transgenic model, in situ tetramer staining to distinguish antigen specific CD8 T cells from total T cells infiltrating islets and a variety of viral mutants selected for functional deletion(s) of various CD8 T cell epitopes. Twenty percent of CD8 T cells in the spleen were specific for all immunodominant and subdominant viral glycoprotein (GP) epitopes. CTLs to the immunodominant LCMV GP33-41 epitope accounted for 63% of the total (12.5% of tetramers). In situ hybridization analysis demonstrated only 1 to 2% of total infiltrating CD8 T cells were specific for GP33 CD8 T cell epitope, yet diabetes occurred in 94% of mice. The immunologic synapse between GP33 CD8 CTL and β cell contained LFA-1 and perforin. Silencing both immunodominant epitopes (GP33, GP276–286) in the infecting virus led to a four-fold reduction in viral specific CD8 CTL responses, negligible lymphocyte infiltration into islets and absence of diabetes.

Insulin-dependent type 1 diabetes (T1D) is characterized by elevated blood sugar, lymphocytic infiltration into the islets of Langerhans and T cell destruction of beta (β) cells. β cells produce insulin whose function is to maintain and regulate glucose hemostasis. However, in vivo, the numbers of antigen specific T cells that migrate to the islets to cause T1D, the engagement of such T cells with β cells at the immunologic synapse and the molecules expressed at the synapse are not clear. Using a transgenic model of virus induced T1D, a panel of viruses with CD8 T cell epitope mutations and in situ tetramer hybridization, we note of the total CD8 T cells infiltrating the islets, only 1–2% are antigen specific recognizing the immunodominant virus CD8 T cell epitope expressed on β cells. Immunohistochemical analysis of the synapse found between antigen specific CD8 T cells and β cells displays attachment by LFA-1 and presence of perforin, the molecule indicative of lytic activity.

Memory CD8+ T cells specific for a single immunodominant or subdominant determinant induced by peptide-dendritic cell immunization protect from an acute lethal viral disease

The antigens recognized by individual CD8(+) T cells are small peptides bound to major histocompatibility complex (MHC) class I molecules. The CD8(+) T cell response to a virus is restricted to several peptides, and the magnitudes of the effector as well as memory phases of the response to the individual peptides are generally hierarchical. The peptide eliciting a stronger response is called immunodominant (ID), and those with smaller-magnitude responses are termed subdominant (SD). The relative importance of ID and SD determinants in protective immunity remains to be fully elucidated. We previously showed that multispecific memory CD8(+) T cells can protect susceptible mice from mousepox, an acute lethal viral disease. It remained unknown, however, whether CD8(+) T cells specific for single ID or SD peptides could be protective. Here, we demonstrate that immunization with dendritic cells pulsed with ID and some but not all SD peptides induces memory CD8(+) T cells that are fully capable of protecting susceptible mice from mousepox. Additionally, while natural killer (NK) cells are essential for the natural resistance of nonimmune C57BL/6 (B6) to mousepox, we show that memory CD8(+) T cells of single specificity also protect B6 mice depleted of NK cells. This suggests it is feasible to produce effective antiviral CD8(+) T cell vaccines using single CD8(+) T cell determinants and that NK cells are no longer essential when memory CD8(+) T cells are present.

Transgenic expression of viral capsid proteins predisposes to axonal injury in a murine model of multiple sclerosis

We used transgenic expression of capsid antigens to Theiler's murine encephalomyelitis virus (TMEV) to study the influence of VP1, VP2 or VP2(121-130) to either protection or pathogenesis to chronic spinal cord demyelination, axonal loss and functional deficits during the acute and chronic phases of infection. We used both mice that are normally susceptible (FVB) and mice normally resistant (FVB.D(b) ) to demyelination. Transgenic expression of VP2(121-130) epitope in resistant FVB.D(b) mice caused spinal cord pathology and virus persistence because the VP2(121-130) epitope is the dominant peptide recognized by D(b) , which is critical for virus clearance. In contrast, all three FVB TMEV transgenic mice showed more demyelination, inflammation and axonal loss as compared with wild-type FVB mice, even though virus load was not increased. Motor function measured by rotarod showed weak correlation with total number of midthoracic axons, but a strong correlation with large-caliber axons (>10µm(2) ). This study supports the hypothesis that expression of viral capsid proteins as self influences the extent of axonal pathology following Theiler's virus-induced demyelination. The findings provide insight into the role of axonal injury in the development of functional deficits that may have relevance to human demyelinating disease.

Protective efficacy of serially up-ranked subdominant CD8+ T cell epitopes against virus challenges

Immunodominance in T cell responses to complex antigens like viruses is still incompletely understood. Some data indicate that the dominant responses to viruses are not necessarily the most protective, while other data imply that dominant responses are the most important. The issue is of considerable importance to the rational design of vaccines, particularly against variable escaping viruses like human immunodeficiency virus type 1 and hepatitis C virus. Here, we showed that sequential inactivation of dominant epitopes up-ranks the remaining subdominant determinants. Importantly, we demonstrated that subdominant epitopes can induce robust responses and protect against whole viruses if they are allowed at least once in the vaccination regimen to locally or temporally dominate T cell induction. Therefore, refocusing T cell immune responses away from highly variable determinants recognized during natural virus infection towards subdominant, but conserved regions is possible and merits evaluation in humans.

Adenovirus E3 MHC inhibitory genes but not TNF/Fas apoptotic inhibitory genes expressed in beta cells prevent autoimmune diabetes

To mimic events and molecules involved in type 1 insulin-dependent diabetes mellitus (T1D), we previously designed a transgenic (tg) mouse model where the viral nucleoprotein (NP) gene of lymphocytic choriomeningitis virus (LCMV) was expressed in the thymus to delete high affinity antiself (virus) T cells and in insulin-producing beta cells of the islets of Langerhans. Such tg mice, termed RIP-LCMV, fail to spontaneously develop diabetes. In contrast, when these mice are challenged with LCMV, they develop diabetes as they display hyperglycemia, low to absent levels of pancreatic insulin, and abundant mononuclear cell infiltrates in the islets. However, expressing the adenovirus early region (E3) gene in beta cells along with the LCMV transgene aborted the T1D. The present study utilizes this combined tg model (RIP LCMV x RIP E3) to define the requirement(s) of either pro-apoptotic TNF and Fas pathways or MHC class I up-regulation on beta cells for virus-induced T1D. Inhibitors to either pathway (TNF/Fas or MHC class I) are encoded in the E3 gene complex. To accomplish this task either the E3 region encoding the inhibitors of TNF and Fas pathways or the region encoding gp-19, a protein that inhibits transport of MHC class I molecules out of the endoplasmic reticulum were deleted in the RIP LCMV x RIP E3 model. Thus only the gp-19 is required to abort the virus-induced T1D. In contrast, removal of TNF- and Fas-pathway inhibitory genes had no effect on E3-mediated prevention of T1D.

Viral triggers for autoimmunity: is the 'glass of molecular mimicry' half full or half empty?

In this review we want to consider some of the requirements for autoimmune disease to develop and how this may be reproduced in animal models. Besides a genetic predisposition, environmental triggering factors seem to play a central role in the etiology of many autoimmune diseases. In theory, a structural similarity or identity between the host and an invading pathogen might cause the immune system of the host to react not only to the pathogen but also to self-components. However, in order for such a process of molecular mimicry to induce autoimmunity the mechanisms of maintaining tolerance or ignorance to the self-components need to be circumvented. Subsequently, in order to advance autoimmunity to overt autoimmune disease the frequency and avidity of autoaggressive lymphocytes has to be of sufficient magnitude. Intuitively, one would assume that tolerance might be stronger to identical structures than to structures that just share a certain degree of similarity. Self-reactive lymphocytes with high-avidity are more likely to be deleted or functionally silenced by central and/or peripheral tolerance mechanisms. Thus, perfect mimicry between identical structures might fail in inducing autoimmunity because of efficient tolerance mechanisms. In contrast, imperfect mimicry between similar but not identical structures might on one hand circumvent tolerance but on the other hand result in the generation of lymphocytes with only low- to intermediate avidity. Here we examine animal models that use the concept of molecular mimicry as a potential mechanism for inducing or accelerating autoimmunity. We focus on the RIP-LCMV model for type 1 diabetes and the novel cytochrome P450 2D6 (CYP2D6) model for autoimmune hepatitis, which use either identical or similar triggering and target antigens.

Dominant CD8+ T-lymphocyte responses suppress expansion of vaccine-elicited subdominant T lymphocytes in rhesus monkeys challenged with pathogenic simian-human immunodeficiency virus

Emerging data suggest that a cytotoxic T-lymphocyte response against a diversity of epitopes confers greater protection against a human immunodeficiency virus/simian immunodeficiency virus infection than does a more focused response. To facilitate the creation of vaccine strategies that will generate cellular immune responses with the greatest breadth, it will be important to understand the mechanisms employed by the immune response to regulate the relative magnitudes of dominant and nondominant epitope-specific cellular immune responses. In this study, we generated dominant Gag p11C- and subdominant Env p41A-specific CD8(+) T-lymphocyte responses in Mamu-A*01(+) rhesus monkeys through vaccination with plasmid DNA and recombinant adenovirus encoding simian-human immunodeficiency virus (SHIV) proteins. Infection of vaccinated Mamu-A*01(+) rhesus monkeys with a SHIV Gag Deltap11C mutant virus generated a significantly increased expansion of the Env p41A-specific CD8(+) T-lymphocyte response in the absence of secondary Gag p11C-specific CD8(+) T-lymphocyte responses. These results indicate that the presence of the Gag p11C-specific CD8(+) T-lymphocyte response following virus challenge may exert suppressive effects on primed Env p41A-specific CD8(+) T-lymphocyte responses. These findings suggest that immunodomination exerted by dominant responses during SHIV infection may diminish the breadth of recall responses primed during vaccination.

Kinetics of expansion of epitope-specific T cell responses during primary HIV-1 infection

Multiple lines of evidence support a role for CD8(+) T cells in control of acute/early HIV replication; however, features of the primary HIV-specific CD8(+) T cell response that may impact on the efficiency of containment of early viral replication remain poorly defined. In this study, we performed a novel, comprehensive analysis of the kinetics of expansion of components of the HIV-specific CD8(+) T cell response in 21 acutely infected individuals. Epitope-specific T cell responses expanded asynchronously during primary infection in all subjects. The most rapidly expanded responses peaked as early as 5 days following symptomatic presentation and were typically of very limited epitope breadth. Responses of additional specificities expanded and contracted in subsequent waves, resulting in successive shifts in the epitope immunodominance hierarchy over time. Sequence variation and escape were temporally associated with the decline in magnitude of only a subset of T cell responses, suggesting that other factors such as Ag load and T cell exhaustion may play a role in driving the contraction of HIV-specific T cell responses. These observations document the preferential expansion of CD8(+) T cells recognizing a subset of epitopes during the viral burst in acute HIV-1 infection and suggest that the nature of the initial, very rapidly expanded T cell response may influence the efficiency with which viral replication is contained in acute/early HIV infection.

Genetic deletion of a single immunodominant T-cell response confers susceptibility to virus-induced demyelination

An important question in neuropathology involves determining the antigens that are targeted during demyelinating disease. Viral infection of the central nervous system (CNS) leads to T‐cell responses that can be protective as well as pathogenic. In the Theiler’s murine encephalomyelitis virus (TMEV) model of demyelination it is known that the immune response to the viral capsid protein 2 (VP2) is critical for disease pathogenesis. This study shows that expressing the whole viral capsid VP2 or the minimal CD8‐specific peptide VP2_121‐130 as “self” leads to a loss of VP2‐specific immune responses. Loss of responsiveness is caused by T cell‐specific tolerance, as VP2‐specific antibodies are generated in response to infection. More importantly, these mice lose the CD8 T‐cell response to the immunodominant peptide VP2_121‐130, which is critical for the development of demyelinating disease. The transgenic mice fail to clear the infection and develop chronic demyelinating disease in the spinal cord white matter. These findings demonstrate that T‐cell responses can be removed by transgenic expression and that lack of responsiveness alters viral clearance and CNS pathology. This model will be important for understanding the mechanisms involved in antigen‐specific T‐cell deletion and the contribution of this response to CNS pathology.

Modulation of DNA vaccine-elicited CD8+ T-lymphocyte epitope immunodominance hierarchies

Generating broad cellular immune responses against a diversity of viral epitopes is a major goal of current vaccine strategies for human immunodeficiency virus type 1 (HIV-1) and other pathogens. Virus-specific CD8(+) T-lymphocyte responses, however, are often highly focused on a very limited number of immunodominant epitopes. For an HIV-1 vaccine, the breadth of CD8(+) T-lymphocyte responses may prove to be critical as a result of the need to cover a wide diversity of viral isolates in the population and to limit viral escape from dominant epitope-specific T lymphocytes. Here we show that epitope modification strategies can alter CD8(+) T-lymphocyte epitope immunodominance hierarchies elicited by a DNA vaccine in mice. Mice immunized with a DNA vaccine expressing simian immunodeficiency virus Gag lacking the dominant D(b)-restricted AL11 epitope generated a marked and durable augmentation of responses specific for the subdominant D(b)-restricted KV9 epitope. Moreover, anatomic separation strategies and heterologous prime-boost regimens generated codominant responses against both epitopes. These data demonstrate that dominant epitopes can dramatically suppress the immunogenicity of subdominant epitopes in the context of gene-based vaccines and that epitope modification strategies can be utilized to enhance responses to subdominant epitopes.

CTL response compensation for the loss of an immunodominant class I-restricted HSV-1 determinant

The T-cell response to even complex pathogens is often focused on only a handful of immunodominant determinants. Such narrow responses provoke a selective pressure that can drive the emergence of CTL escape variants, raising the question of whether a broader response, targeting multiple non-dominant peptides may be more beneficial. To examine the ability of the T-cell repertoire to respond to non-dominant determinants, we have investigated how mutating the dominant peptide in HSV affects the magnitude of the CD8+ T-cell response. We found that the CTL response to HSV lacking the dominant peptide was only modestly reduced compared with the wild-type virus and, surprisingly, this compensation occurred without any enhancement in the response to an established minor epitope. These findings are supportive of a malleable T-cell repertoire that can elicit strong responses to alternate, unknown determinants in the absence of the dominant response.

The Unveiling of Hidden T-Cell Determinants of a Native Antigen by Defined Mediators of Inflammation: Implications for the Pathogenesis of Autoimmunity

A major hypothesis for the induction of autoimmunity invokes the enhanced display of previously hidden (cryptic) epitopes under inflammatory conditions leading to the activation of self-reactive T cells. However, there is meager data that directly validate the influence of specific immune mediators on the upregulation of the presentation of cryptic determinants in vivo. We tested the effect on well-defined cryptic epitopes of hen eggwhite lysozyme (HEL) of the availability locally of a cytokine (IL-2, IL-4, IL-6, IL-10, TNF-alpha or granulocyte-macrophage colony-stimulating factor) at the antigen delivery site, or of the pretreatment of the immunogen with a cathepsin (Cat B, D, L or S) prior to use in vivo. Each of the three mouse strains (H-2(b/d/k)) tested revealed a unique profile of T-cell reactivity to different cryptic epitopes of HEL in response to a particular cytokine or cathepsin. These results provide proof of principle for the reversal of crypticity of self-epitopes by immune mediators in the local milieu. Moreover, co-immunization with an antigen and a cytokine offers a simple and reliable tool for studying the role of cryptic epitopes in autoimmunity. Our results also strengthen the rationale for the use of inhibitors of cytokine/cathepsin activity in the treatment of autoimmune diseases.

Immunodomination in the evolution of dominant epitope-specific CD8+ T lymphocyte responses in simian immunodeficiency virus-infected rhesus monkeys

Because the control of HIV-1 replication is largely dependent on CD8+ T lymphocyte responses specific for immunodominant viral epitopes, vaccine strategies that increase the breadth of dominant epitope-specific responses should contribute to containing HIV-1 spread. Developing strategies to elicit such broad immune responses will require an understanding of the mechanisms responsible for focusing CD8+ T lymphocyte recognition on a limited number of epitopes. To explore this biology, we identified cohorts of rhesus monkeys that expressed the MHC class I molecules Mamu-A*01, Mamu-A*02, or both, and assessed the evolution of their dominant epitope-specific CD8+ T lymphocyte responses (Gag p11C- and Tat TL8-specific in the Mamu-A*01+ and Nef p199RY-specific in the Mamu-A*02+ monkeys) following acute SIV infection. The Mamu-A*02+ monkeys that also expressed Mamu-A*01 exhibited a significant delay in the evolution of the CD8+ T lymphocyte responses specific for the dominant Mamu-A*02-restricted SIV epitope, Nef p199RY. This delay in kinetics was not due to differences in viral load kinetics or magnitude or in viral escape mutations, but was associated with the evolution of the Mamu-A*01-restricted CD8+ T lymphocyte responses to the highly dominant SIV epitopes Gag p11C and Tat TL8. Thus, the evolution of dominant epitope-specific CD8+ T lymphocyte responses can be suppressed by other dominant epitope-specific responses, and this immunodomination is important in determining the kinetics of dominant epitope-specific responses.

Molecular and cellular mechanisms, pathogenesis, and treatment of insulin-dependent diabetes obtained through study of a transgenic model of molecular mimicry

The portrait of autoimmune diabetes mellitus or type I diabetes can be copied by a transgenic model in which either the nucleoprotein (NP) or glycoprotein (GP) of lymphocytic choriomeningitis virus (LCMV) is expressed in beta cells of the islets of Langerhans. In the absence of further environmental insult, diabetes does not occur. However, when LCMV or a dissimilar virus that shares cross-reactive T cell epitopes with LCMV initiates infection, diabetes ensues. If the self "viral" transgene is expressed only in the beta cells, then diabetes occurs acutely within 8 to 12 days. Specific antiviral (self) CD8 T cells are mandatory for disease, but CD4 T cells are not. In this instance, diabetes can occur in the absence of infection if interferon gamma or B7.1 molecules are also expressed in the islets but not when IL-2, IL-4, IL-10, or IL-12 is similarly expressed. In contrast, both CD8 and CD4 antiviral (self) specific T cells are required when the self "viral" transgene is expressed concomitantly in beta cells and in the thymus. In this instance, infection by LCMV or cross-reacting virus is essential to cause diabetes. Further, the time from onset of infection until disease depends, in part, on the host's MHC background and its quantitative influence on negative selection of high-avidity antiviral (self) T cells. Knowledge of the cells, their numbers, and the molecules required to cause diabetes allows the design of successful strategies to treat and prevent the autoimmune disease.

Islet-Specific Expression of CXCL10 Causes Spontaneous Islet Infiltration and Accelerates Diabetes Development

During inflammation, chemokines are conductors of lymphocyte trafficking. The chemokine CXCL10 is expressed early after virus infection. In a virus-induced mouse model for type 1 diabetes, CXCL10 blockade abrogated disease by interfering with trafficking of autoaggressive lymphocytes to the pancreas. We have generated transgenic rat insulin promotor (RIP)-CXCL10 mice expressing CXCL10 in the beta cells of the islets of Langerhans to evaluate how bystander inflammation influences autoimmunity. RIP-CXCL10 mice have islet infiltrations by mononuclear cells and limited impairment of beta cell function, but not spontaneous diabetes. RIP-CXCL10 mice crossed to RIP-nucleoprotein (NP) mice expressing the NP of the lymphocytic choriomeningitis virus in the beta cells had massively accelerated type 1 diabetes after lymphocytic choriomeningitis virus infection. Mechanistically, we found a drastic increase in NP-specific, autoaggressive CD8 T cells in the pancreas after infection. In situ staining with H-2D(b)(NP(396)) tetramers revealed islet infiltration by NP-specific CD8 T cells in RIP-NP-CXCL10 mice early after infection. Our results indicate that CXCL10 expression accelerates the autoimmune process by enhancing the migration of Ag-specific lymphocytes to their target site.

Strong memory CD8+ T cell responses against immunodominant and three new subdominant HLA-B27-restricted influenza A CTL epitopes following secondary infection of HLA-B27 transgenic mice

We previously showed that the known HLA-B27-restricted influenza A epitope identified from human studies, NP.383-391, was recognized by CTLs following influenza A infection of transgenic (Tg) HLA-B27/H2 class I-deficient (H2 DKO) mice. Here, we examined the kinetics of the primary NP.383-391-specific response in Tg HLA-B27/H2 DKO mice at the site of respiratory infection, along with the profile of additional influenza A epitopes recognized. While the temporal kinetics of the Tg HLA-B27/NP.383-391-specific CD8+ T cell response paralleled the H2-D(b)/NP.366-374-specific response of non-Tg H2b mice, the magnitude was less. Using epitope prediction programs, we identified three novel B27-restricted influenza A epitopes, PB2.702-710, PB1.571-579, and PB2.368-376, recognized during both the primary and secondary response to infection. Although the secondary NP.383-391-specific response was dominant, PB1.571-579 and PB2.368-376 stimulated stronger proliferative expansion in memory T cells. Our results indicate a broader B27/influenza A CTL repertoire than previously known. Together with results for other HLA class I alleles, this information will become important in improving vaccine strategies for influenza A and other human pathogens.

A viral epitope that mimics a self antigen can accelerate but not initiate autoimmune diabetes

We document here that infection of prediabetic mice with a virus expressing an H-2Kb-restricted mimic ligand to a self epitope present on beta cells accelerates the development of autoimmune diabetes. Immunization with the mimic ligand expanded autoreactive T cell populations, which was followed by their trafficking to the islets, as visualized in situ by tetramer staining. In contrast, the mimic ligand did not generate sufficient autoreactive T cells in naive mice to initiate disease. Diabetes acceleration did not occur in H-2Kb-deficient mice or in mice tolerized to the mimic ligand. Thus, arenavirus-expressed mimics of self antigens accelerate a previously established autoimmune process. Sequential heterologous viral infections might therefore act in concert to precipitate clinical autoimmune disease, even if single exposure to a viral mimic does not always cause sufficient tissue destruction.

Mouse lysozyme-M knockout mice reveal how the self-determinant hierarchy shapes the T cell repertoire against this circulating self antigen in wild-type mice

We have studied T cell tolerance to defined determinants within ML-M using wild-type (WT; ML-M(+/+)) and LysMcre (ML-M(-/-)) C3H (H-2(k)) mice to determine the relative contribution of ML-M-derived epitopes vs those from other self Ags in selection of the ML-M-specific T cell repertoire. ML-M was totally nonimmunogenic in WT mice, but was rendered immunogenic in LysMcre mice. Most of the response to ML-M in LysMcre mice was directed to the immunodominant determinant region 105-119. This determinant is spontaneously displayed (without adding exogenous ML-M) by macrophages of WT, but not LysMcre, mice and is stimulatory for peptide 105-119 (p105-119)-primed T cells. Moreover, neonatal tolerization of LysMcre mice with p105-119 or ML-M abrogated the T cell response to subsequent challenge with ML-M or p105-119. Furthermore, p95-109 and p110-125 of ML-M were immunogenic in LysMcre mice, but not in WT mice, thereby representing subdominant, tolerance-inducing epitopes of ML-M. As expected, the T cell repertoire to cryptic ML determinants in WT mice was also intact in LysMcre mice. Furthermore, the pattern of response to the related homologue of ML-M, hen eggwhite lysozyme, was similar in these two groups of mice. Thus, several codominant T cell determinants within ML-M contribute significantly to tolerance induction, and the anti-cryptic T cell repertoire to ML-M was positively selected on non-ML-M self ligands. These results reveal that the induction of self tolerance to a multideterminant protein follows the quantitative hierarchy of self-determinant expression and are of relevance in understanding the pathogenesis of autoimmunity.

Intrathymic expression of neuromuscular acetylcholine receptors and the immunpathogenesis of myasthenia gravis

The thymus has been considered to play an important role in the pathogenesis of myasthenia gravis (MG), an autoimmune disease characterized by skeletal muscle weakness. However, the pathogenic role of the thymus still remains a mystery. The neuromuscular type of acetylcholine receptor (AChR) was the first self-protein associated with a defined autoimmune disease that was found to be expressed by thymic stromal populations. The studies described herein represent our efforts to determine how this "promiscuous" autoantigen expression may be involved in the immunopathogenesis of MG. We review our work, characterizating the expression of the alpha subunit of AChR (AChRalpha) in the thymus, and advance a new hypothesis that examines the intrathymic expression of this autoantigen in disease pathogenesis.

Peripheral antigen-expressing cells in type 1 diabetes

Studies in both humans and rodent models provide new insight into key mechanisms regulating tolerance to self-molecules. There is evidence that tissue-specific molecules are expressed in the thymus and peripheral lymphoid tissues (PLTs) by specialized antigen-presenting cells (APCs), and that such expression is critical for self-tolerance. Insulin, a key hormone exclusively produced by pancreatic beta cells and a critical autoantigen in type 1 diabetes, provides an excellent example of a molecule with tissue-restricted expression that is ectopically expressed by APCs in both thymus and PLTs. APCs may play a role in insulin presentation in both the central and peripheral immune system. Functional data from several transgenic and knockout mouse models, some specific for the expression of insulin, help dissect the significance of self-molecule presentation by APCs and its role in autoimmune diabetes.

Genetic variation in COL17A1 and the development of bullous pemphigoid

BACKGROUND

Bullous pemphigoid (BP) is an autoimmune blistering disease of the skin characterized by autoantibody attack on collagen XVII.

OBJECTIVES

To characterize the genetic complexity of COL17A1, the gene which encodes for the autoantigen collagen XVII. The data will be used to determine whether there is an association between polymorphisms and haplotypes of COL17A1 and genetic susceptibility to development of BP.

METHODS

The genetic complexity in COL17A1 was deduced by screening and then sequencing the gene. Haplotypes were constructed from the resulting polymorphisms using the statistical programme PHASE. The linkage disequilibrium (D') between the polymorphisms was deduced from haplotypic data using the statistical programme GOLD. Association of the polymorphisms and haplotypes was tested for, in a cohort of BP patients and controls.

RESULTS

Screening of COL17A1 for genetic variation was carried out in 29 individuals of North European caucasoid origin, and it revealed 19 single-nucleotide polymorphisms in approximately 14.7 kb of sequence. These variants resulted in 60 different haplotypes in 191 individuals, of which 13 occurred above 1% in the population. D' between the variants was found to be extensive, have a low correlation with physical distance and to extend over 33.8 kb. No association was found with any of the polymorphisms or haplotypes and development of BP, when tested for, in a cohort of patients and controls.

CONCLUSION

This study provides an extensive description of the genetic variation in COL17A1 and shows no association of the genetic variants with susceptibility to BP.

Preferential escape of subdominant CD8+ T cells during negative selection results in an altered antiviral T cell hierarchy

Negative selection is designed to purge the immune system of high-avidity, self-reactive T cells and thereby protect the host from overt autoimmunity. In this in vivo viral infection model, we show that there is a previously unappreciated dichotomy involved in negative selection in which high-avidity CD8(+) T cells specific for a dominant epitope are eliminated, whereas T cells specific for a subdominant epitope on the same protein preferentially escape deletion. Although this resulted in significant skewing of immunodominance and a substantial depletion of the most promiscuous T cells, thymic and/or peripheral deletion of high-avidity CD8(+) T cells was not accompanied by any major change in the TCR V beta gene family usage or an absolute deletion of a single preferred complementarity-determining region 3 length polymorphism. This suggests that negative selection allows high-avidity CD8(+) T cells specific for subdominant or cryptic epitopes to persist while effectively deleting high-avidity T cells specific for dominant epitopes. By allowing the escape of subdominant T cells, this process still preserves a relatively broad peripheral TCR repertoire that can actively participate in antiviral and/or autoreactive immune responses.

A unique mechanism for innate cytokine promotion of T cell responses to viral infections

The kinetics of CD8 T cell IFN-gamma responses as they occur in situ are defined here during lymphocytic choriomeningitis virus (LCMV) infections, and a unique mechanism for the innate cytokines IFN-alphabeta and IL-18 in promoting these responses is defined. Infections of mice with Armstrong or WE strains of LCMV induced an unexpectedly early day 4 IFN-gamma response detectable in serum samples and spleen and liver homogenates. Production of IFN-gamma was MHC class I/CD8 dependent, but did not require IL-12, NK cells, TCR-gammadelta T cells, MHC class II, or CD4 T cells. Peak response required specific Ag recognition, as administration of antagonist peptide partially impaired day 4 IFN-gamma induction, and viral peptide stimulation enhanced CD8 T cell IFN-gamma expression in culture. The IFN-gamma response was associated with IL-18 and IFN-alphabeta expression. Furthermore, both factors augmented peptide-driven IFN-gamma production in culture, and mice lacking IL-18 or IFN-alphabeta functions had reduced day 4 IFN-gamma. Collectively, these results demonstrate that during viral infections, there is a dramatic in vivo CD8 T cell response preceding maximal expansion of these cells, and that the mechanism supporting this response is dependent on endogenous innate cytokines. Because stimulation by microbial products is linked to innate cytokine expression, the studies also suggest a pathway for precisely limiting T cell functions to times of need.

Reduction of antiviral CD8 lymphocytes in vivo with dendritic cells expressing Fas ligand-increased survival of viral (lymphocytic choriomeningitis virus) central nervous system infection

In vivo administration of APC expressing Fas ligand (Fas-L(+) dendritic cells (DCs)) has shown promise in dampening allergic reactions and transplant rejection. Since the effect in these studies was mainly on CD4 lymphocytes, our goal was to evaluate the ability of such killer DCs to eliminate antiviral CD8 lymphocytes and in this way ameliorate viral immunopathology or, conversely, impede viral clearance. Intravenous administration of Fas-L(+) DCs resulted in a 50% reduction of lytic CD8 precursors following intracerebral infection with lymphocytic choriomeningitis virus (LCMV), and accordingly, immunopathology and survival of LCMV meningitis were improved, whereas viral clearance remained unaffected. In transfer studies the effect of the Fas-L(+) DCs was only quantifiable on experienced, not naive, CD8 lymphocytes. Importantly, loading of Fas-L(+) DCs with viral Ag before therapy was not necessary to achieve this effect, indicating that non-LCMV-infected Fas-L(+) DCs acquired viral Ag during acute LCMV infection in vivo. Our studies delineate important aspects for the clinical use of Fas-L(+) DCs in vivo. One should expect that they acquire viral Ags and suppress antiviral CD8 responses to some degree when given while an acute infection is ongoing. In terms of safety it is encouraging that resolution of the infection, at least in the case of LCMV, is not inhibited.

Lymphotoxin-alpha- and lymphotoxin-beta-deficient mice differ in susceptibility to scrapie: evidence against dendritic cell involvement in neuroinvasion

Transmissible spongiform encephalopathy or prion diseases are fatal neurodegenerative disorders of humans and animals often initiated by oral intake of an infectious agent. Current evidence suggests that infection occurs initially in the lymphoid tissues and subsequently in the central nervous system (CNS). The identity of infected lymphoid cells remains controversial, but recent studies point to the involvement of both follicular dendritic cells (FDC) and CD11c(+) lymphoid dendritic cells. FDC generation and maintenance in germinal centers is dependent on lymphotoxin alpha (LT-alpha) and LT-beta signaling components. We report here that by the oral route, LT-alpha -/- mice developed scrapie while LT-beta -/- mice did not. Furthermore, LT-alpha -/- mice had a higher incidence and shorter incubation period for developing disease following inoculation than did LT-beta -/- mice. Transplantation of lymphoid tissues from LT-beta -/- mice, which have cervical and mesenteric lymph nodes, into LT-alpha -/- mice, which do not, did not alter the incidence of CNS scrapie. In other studies, a virus that is tropic for and alters functions of CD11c(+) cells did not alter the kinetics of neuroinvasion of scrapie. Our results suggest that neither FDC nor CD11c(+) cells are essential for neuroinvasion after high doses of RML scrapie. Further, it is possible that an as yet unidentified cell found more abundantly in LT-alpha -/- than in LT-beta -/- mice may assist in the amplification of scrapie infection in the periphery and favor susceptibility to CNS disease following peripheral routes of infection.

Constitutive beta cell expression of IL-12 does not perturb self-tolerance but intensifies established autoimmune diabetes

To analyze the function of the Th1-promoting cytokine IL-12 in vivo, we generated transgenic (tg) mice (RIP-IL12 mice) whose pancreatic beta cells constitutively express bioactive IL-12 or one of its components, p35 or p40. In contrast to non-tg littermates or single-tg RIP-p35 and RIP-p40 mice, RIP-IL12 mice developed a marked pancreatic infiltration of lymphocytes and macrophages, mainly around islets. Expression of bioactive IL-12 primarily upregulated transcript levels of IFN-inducible protein-10 (IP-10), RANTES, IFN-gamma, and TNF-alpha in the pancreas. Despite the substantial recruitment of mononuclear cells, no biochemical or clinical disease was evident in the exocrine or endocrine pancreas. Coexpression of lymphocytic choriomeningitis virus (LCMV) proteins with IL-12 in the beta cells failed to spontaneously activate or expand antigen-specific anti-self/viral T cells in uninfected tg animals. However, when RIP-IL12 x RIP-LCMV tg mice were infected with LCMV, antigen-specific anti-self/viral T cells were induced, which led to an acceleration in the kinetics and severity of insulin-dependent diabetes mellitus (IDDM). Thus, the ectopic expression of IL-12 does not spontaneously break tolerance and activate antigen-specific T cells in the periphery, but it does worsen ongoing autoimmune disease.

Protection from type 1 diabetes in the face of high levels of activated autoaggressive lymphocytes in a viral transgenic mouse model crossed to the SV129 strain

In comparing the incidence of virally induced type 1 diabetes in F(1) crosses of RIP-LCMV mice to three different mouse strains identical at the major histocompatibility complex H-2D(b) locus, we surprisingly found that disease development was reduced by 80% in F(1) crosses to the SV129 genetic background and by 60% after eight backcrosses to the original C57BL/6 RIP-LCMV mice. In this model, diabetes is strongly dependent on a virally induced H-2D(b)-restricted cytotoxic T-cell (CTL) response. Importantly, numbers and effector functions of autoaggressive CD4 and CD8 lymphocytes were not decreased in the protected mice, and CTLs were still able to kill syngeneic islet cells in vitro with equal efficacy compared with CTLs from the original RIP-LCMV strain. Furthermore, CTLs were able to extravasate into islets in vivo, and no evidence for induction of regulatory cells was observed. However, regeneration of beta-cells in islets under "attack" occurred only in the protected SV129-crossed animals, whereas it was not evident at any time in any mice that developed diabetes. Thus, genetic factors can "override" the diabetogenic potential of high numbers of autoaggressive lymphocytes through, for example, increased islet regeneration. This finding has important implications for interpreting numbers and pathogenicity of autoreactive lymphocytes in prediabetic patients of genetically diverse backgrounds.

Pathways for self-tolerance and the treatment of autoimmune diseases

Antigen delivers both immunogenic and tolerogenic signals to lymphocytes. The outcome of antigen exposure represents a complex integration of the timing of antigen binding with signals from many other immunogenic and tolerogenic costimulatory pathways. A road map of these signalling pathways is only beginning to be charted, revealing the mechansim of action and limitations of current immunotherapeutic agents and the points of attack for new agents. Ciclosporin and tacrolimus interfere with tolerogenic signals from antigen in addition to blocking immunogenic signals, thus preventing active establishment of tolerance. Corticosteroids inhibit a key immunogenic pathway, NFkappaB, and more specific inhibitors of this pathway may allow tolerance to be actively established while immune responses are blocked. New experimental therapies aim to mimic tolerogenic antigen signals by chronically stimulating antigen receptors with antigen or antibodies to the receptor, or aim to block costimulatory pathways involving CD40 ligand, B7, or interleukin 2. Obtaining the desired response with these strategies is unpredictable because many of these signals have both tolerogenic and immunogenic roles. The cause of autoimune diseases has been determined for several rare monogenic disorders, revealing inherited deficiencies in tolerogenic costimulatory pathways such as FAS. Common autoimmune disorders may have a biochemically related pathogenesis.

Lessons from BXSB and related mouse models

The BXSB murine strain spontaneously develops an autoimmune syndrome with features of systemic lupus erythematosus (SLE) that affects males much earlier than females, due to the presence of an as yet unidentified mutant gene located on its Y chromosome, designated Yaa (Y-linked autoimmune acceleration). The Yaa gene by itself is unable to induce significant autoimmune responses in mice without an apparent SLE background, while it can induce and accelerate the development of an SLE in combination with autosomal susceptibility alleles present in lupus-prone mice. Although the genes encoded within or closely linked to the MHC locus play an important role in the development or protection of SLE, the MHC effect can be completely masked by the presence of the Yaa gene in mice highly predisposed to SLE. The role of the Yaa gene for the acceleration of SLE is apparently two-fold; it enhances overall autoimmune responses against autoantigens to which mice respond relatively weakly, and promotes Th 1 responses against autoantigens to which mice respond relatively well, leading to the production of more pathogenic autoantibodies, i.e., FcgammaR-fixing IgG2a and cryoglobulin IgG3 autoantibodies. Yaa+ - Yaa- double bone marrow chimera experiments revealed that the Yaa defect is expressed in B cells, but not in T cells, and that T cells from non-autoimmune mice are capable of providing help for autoimmune responses by collaborating Yaa+ B cells. We speculate that the Yaa defect may decrease the threshold for antigen receptor-dependent stimulation, leading to the triggering and excessive stimulation of autoreactive T and B cells.

Overcoming T cell tolerance to the hepatitis B virus surface antigen in hepatitis B virus-transgenic mice

The sequence of the hepatitis B virus (HBV) major envelope (Env) protein (ayw subtype) was scanned for the presence of H-2(d,b) motifs. Following binding and immunogenicity testing, two new H-2(d)-restricted epitopes (Env.362 and Env.364) were identified. These epitopes induced CTLs capable of recognizing naturally processed HBV-Env, but were apparently generated with lower efficiency than the previously defined dominant Env.28 epitope. Next, HBV-transgenic mice that express all of the HBV proteins and produce fully infectious particles were immunized with a mixture of lipopeptides encompassing the Env.28, Env.362, and Env.364 epitopes. Significant CTL responses were obtained, but they had no effect on viral replication in the liver, nor did they induce an inflammatory liver disease. However, in adoptive transfer experiments, CTL lines generated from the HBV-transgenic mice following immunization were able to inhibit viral replication in vivo without causing hepatitis. This is in contrast to CTL lines derived from nontransgenic mice that displayed both antiviral and cytopathic effects, presumably because they displayed higher avidity for the viral epitopes than the transgenic CTLs. These results suggest that T cell tolerance to HBV can be broken with appropriate immunization but the magnitude and characteristics of the resultant T cell response are significantly different from the response in HBV-naive individuals since their antiviral potential is stronger than their cytotoxic potential. This has obvious implications for immunotherapy of chronic HBV infection.

Transgenic mice expressing human HLA and CD8 molecules generate HLA-restricted measles virus cytotoxic T lymphocytes of the same specificity as humans with natural measles virus infection

Control of primary measles virus (MV) infection in humans and continued maintenance of immune memory that protects against reinfection are mediated primarily through the anti-MV T cell response, as judged by observations of children with defects in antibody formation but competency in making T cells. Further, the failure of T cell responses in those infected with MV most often leads to overwhelming infection. To better define and manipulate the elements involved in human T cell responses to MV, we analyzed the generation of HLA-restricted cytotoxic T lymphocytes (CTL) in a small animal model. Transgenic mice expressing the human class I MHC antigen HLA-B27 in conjunction with human CD8 molecules produced vigorous HLA-restricted CTL responses to MV antigens, paralleling those in MV infection of humans. In addition, such humanized mice generated human CD8 coreceptor-dependent HLA-B27-restricted CTL with the same specificity for recognition of MV fusion (F) peptide RRYPDAVYL as reported for humans during natural MV infection. Neither murine beta(2)-microglobulin nor murine CD8 substituted adequately as coreceptors for the HLA-B27 heavy chain. By contrast, HLA-A2.1-restricted responses to measles could be generated in the absence of expression of human beta(2)-microglobulin or CD8(+) molecules in HLA-A2.1/K(b) transgenic mice. Thus a small animal model is now available for studying strategies for optimizing human CD8(+) T cell responses and for testing vaccines. This model offers the potential, when combined with the newly reported CD46 transgenic mouse model in which MV replicates in cells of the immune system, for uncoding the molecular mechanism of MV-induced immunosuppression.

Evolution of the CD8 T-cell repertoire during infections

CD8 T cells exist in a dynamic network whose repertoire remains static in the absence of infection but changes in the presence of foreign antigens. Individuals each have unique T-cell repertoires that continually evolve in the presence of antigen and of cross-reactive heterologous antigens, and homeostatic forces drive deletions in T-cell memory pools to accommodate the entry of new memory cells into a finite immune system.

Virus-induced diabetes in a transgenic model: role of cross-reacting viruses and quantitation of effector T cells needed to cause disease

Virus-specific cytotoxic T lymphocytes (CTL) at frequencies of >1/1, 000 are sufficient to cause insulin-dependent diabetes mellitus (IDDM) in transgenic mice whose pancreatic beta cells express as "self" antigen a protein from a virus later used to initiate infection. The inability to generate sufficient effector CTL for other cross-reacting viruses that fail to cause IDDM could be mapped to point mutations in the CTL epitope or its COO(-) flanking region. These data indicate that IDDM and likely other autoimmune diseases are caused by a quantifiable number of T cells, that neither standard epidemiologic markers nor molecular analysis with nucleic acid probes reliably distinguishes between viruses that do or do not cause diabetes, and that a single-amino-acid change flanking a CTL epitope can interfere with antigen presentation and development of autoimmune disease in vivo.

Vaccination to treat persistent viral infection

Persistent infections caused by such agents as the human immunodeficiency virus, hepatitis B virus, Epstein-Barr virus, etc., present formidable medical problems. A defining characteristic of these infections is that anti-viral cytotoxic T lymphocytes (CTL) may be lost or, if present, fail to clear the infection. Here we report a vaccination strategy which was successful in generating lytic CTL in persistently infected mice. Vaccination with an immunodominant CTL epitope derived from the nucleoprotein of lymphocytic choriomeningitis virus (LCMV) delivered in the form of a lipopeptide incorporating a universal CD4 helper epitope successfully induced lytic MHC-restricted CTL in mice persistently infected with LCMV since birth. However, induction of such CTL did not eliminate the virus, most likely because the CTL were generated at low frequencies and had 2 to 3 logs lower affinity than CTL generated in uninfected mice inoculated with the vaccine. Both CTL populations from either uninfected or persistently infected mice produced significant and similar amounts of interferon-gamma and IL-6. Vaccine-induced low-affinity CTL were still inadequate at complete removal of the virus when combined with LCMV-specific CD4 helper T lymphocytes. Thus, our results establish that CTL can be generated in persistently infected mice and that a crucial factor for clearing viral infection is the affinity of the CTL.

Disruption of the STAT4 Signaling Pathway Protects from Autoimmune Diabetes While Retaining Antiviral Immune Competence

The role of the STAT4 signaling pathway in autoimmune diabetes was investigated using the rat insulin promoter lymphocytic choriomeningitis virus model of virally induced autoimmune diabetes. Abrogation of STAT4 signaling significantly reduced the development of CD4+-T cell-dependent but not CD4+-T cell-independent diabetes, illustrating the fine-tuned kinetics involved in the pathogenesis of autoimmunity. However, the absence of STAT4 did not prevent the generation of autoreactive Th1/Tc1 T cell responses, as well as protective antiviral immunity. Protection from insulin-dependent diabetes mellitus was associated with decreased numbers of autoreactive CTL precursors in the pancreas and the spleen and a general as well as Ag-specific reduction of IFN-γ secretion by T lymphocytes. A shift from Th1 to Th2 T cell immunity was not observed. Hence, our results implicate both CTL and cytokines in β cell destruction. Selective inhibition of the STAT4 signal transduction pathway might constitute a novel and attractive approach to prevent clinical insulin-dependent diabetes mellitus in prediabetic individuals at risk.

Autoreactive CD4+ T cells protect from autoimmune diabetes via bystander suppression using the IL-4/Stat6 pathway

Targeted immune regulation can be achieved by use of tissue-specific T cells and offers the potential for organ-specific suppression of destructive autoimmune processes. Here, we report the generation and characterization of insulin B chain-specific "autoreactive" CD4+ regulatory T cells that locally suppress diabetogenic T cell responses against an unrelated self-antigen (viral transgene) in a virus-induced model for type 1 diabetes. Interleukin 4 (IL-4) is essential for prevention of diabetes since regulatory T cells cannot be induced in the absence of IL-4 or stat6 (IL-4 signaling pathway). Our observations demonstrate that autoreactive regulatory T cells can suppress autoreactive destructive T cell activity of differential antigenic specificity locally in the pancreatic draining lymph node, probably via cytokine-mediated modulation of antigen-presenting cells.

Thymic tolerance to only one viral protein reduces lymphocytic choriomeningitis virus-induced immunopathology and increases survival in perforin-deficient mice

The outcome of viral infections is dependent on the amount of tissue destruction caused either by direct lysis of infected cells and/or by immunopathology resulting from the immune response to the virus. We investigated whether induction of tolerance to only one viral protein could reduce immunopathology caused by nonlytic lymphocytic choriomeningitis virus (LCMV) in perforin-deficient hosts. Earlier studies had shown that LCMV infection results in aplastic anemia and death in most of these mice and that this is associated with bone marrow infiltration by antiviral cytotoxic T lymphocytes (CTL) that secrete inflammatory cytokines. We report here that perforin-deficient mice exhibit severe immunopathology in multiple organs that is characterized by infiltration of anti-LCMV CTL that secrete large amounts of gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha). Importantly, this immunopathology is significantly reduced and long-term survival of LCMV infection is increased in perforin-deficient mice expressing LCMV nucleoprotein (NP) in the thymus (and therefore deleting most of their LCMV-NP CTL) compared to the situation in thymus nonexpressors. This is due to the selective reduction of NP-specific CTL responses and their inflammatory-cytokine (IFN-gamma and TNF-alpha) secretion and to a lack of pathogenetically relevant compensatory responses to other viral proteins. Thus, "selective reduction" of the antiviral immune response to only one viral protein can significantly reduce inflammatory immunopathology and might be a therapeutic possibility for certain nonlytic infections.

Immunodominance in major histocompatibility complex class I-restricted T lymphocyte responses

Of the many thousands of peptides encoded by a complex foreign antigen that can potentially be presented to CD8+ T cells (TCD8+), only a small fraction induce measurable responses in association with any given major histocompatibility complex class I allele. To design vaccines that elicit optimal TCD8+ responses, a thorough understanding of this phenomenon, known as immunodominance, is imperative. Here we review recent progress in unraveling the molecular and cellular basis for immunodominance. Of foremost importance is peptide binding to class I molecules; only approximately 1/200 of potential determinants bind at greater than the threshold affinity (Kd > 500 nM) associated with immunogenicity. Limitations in the TCD8+ repertoire render approximately half of these peptides nonimmunogenic, and inefficient antigen processing further thins the ranks by approximately four fifths. As a result, only approximately 1/2000 of the peptides in a foreign antigen expressed by an appropriate antigen presenting cell achieve immunodominant status with a given class I allele. A roughly equal fraction of peptides have subdominant status, i.e. they induce weak-to-nondetectable primary TCD8+ responses in the context of their natural antigen. Subdominant determinants may be expressed at or above levels of immunodominant determinants, at least on antigen presenting cells in vitro. The immunogenicity of subdominant determinants is often limited by immunodomination: suppression mediated by TCD8+ specific for immunodominant determinants. Immunodomination is a central feature of TCD8+ responses, as it even occurs among clones responding to the same immunodominant determinant. Little is known about how immunodominant and subdominant determinants are distinguished by the TCD8+ repertoire, or how (and why) immunodomination occurs, but new tools are available to address these questions.

Use of a high-affinity peptide that aborts MHC-restricted cytotoxic T lymphocyte activity against multiple viruses in vitro and virus-induced immunopathologic disease in vivo

Binding of a specific peptide(s) from a viral protein to major histocompatibility complex (MHC) class I molecules is a critical step in the activation of CD8(+) cytotoxic T lymphocytes (CTLs). Once activated, CTLs can cause lethal disease in an infected host, for example, by killing virus-containing ependymal and ventricular cells in the central nervous system or viral protein-expressing beta cells in the pancreatic islets of Langerhans. Here we describe the usage of a designed (not natural) high-affinity peptide to compete with viral peptide(s)-MHC binding. This peptide blocks virus-induced CTL-mediated disease both in the CNS and in the pancreatic islets in vivo. Further, the blocking peptide aborts MHC-restricted killing of target cells by CTLs generated to three separate viruses: lymphocytic choriomeningitis virus, influenza virus, and simian virus 40.

From genome to aetiology in a multifactorial disease, type 1 diabetes

The common autoimmune disease type 1 diabetes provides a paradigm for the genetic analysis of multifactorial disease. Disease occurrence is attributable to the interaction with the environment of alleles at many loci interspersed throughout the genome. Their mapping and identification is difficult because the disease-associated alleles occur almost as commonly in patients as in healthy individuals; even the highest-risk genotypes bestow only modest risks of disease. The identification of common quantitative trait loci (QTL) in autoimmune disease and in other common disorders, therefore, requires a very close marriage of genetics and biology. Two QTLs have been identified in human type 1 diabetes: the major histocompatibility complex HLA class II loci and a promoter polymorphism of the insulin gene. The evidence for their primary roles in disease aetiology demonstrates the necessity of combined studies of genetics and biology. Their functions and interaction underpin an emerging picture of the basic causes of the disease and direct analyses towards other candidate genes and pathways. The genetic tools used for QTL identification include transgenesis and gene knockouts, whole genome scanning for linkage, mouse congenic strains, linkage disequilibrium mapping, and the establishment of ancestral haplotypes among disease-associated chromosomes.

Degree of TCR Internalization and Ca2+ Flux Correlates with Thymocyte Selection

Recent evidence suggests that TCR down-regulation directly reflects the number of TCRs that have engaged MHC/peptide ligand complexes. Here, we examined the influence of defined peptides on thymic selection based on their ability to induce differential TCR internalization. Our results demonstrate that there is a direct correlation: peptides that induce strong TCR down-regulation are most efficient at mediating negative selection, whereas peptides that induce suboptimal TCR internalization are more efficient at triggering positive selection. As a consequence of suboptimal TCR internalization, a proportion of TCR complexes that remain on the cell surface may be able to relay continual signals required for survival and differentiation. In addition, we show that the magnitude of Ca2+ influx set by these peptides reflects the hierarchy of TCR down-regulation and correlates with positive vs negative selection of transgenic thymocytes. Together, our data suggest that T cell selection is mediated by differing intensities of the same TCR-mediated signal, rather than by distinct signals.