A critical role for B7/CD28 costimulation in experimental autoimmune encephalomyelitis: a comparative study using costimulatory molecule-deficient mice and monoclonal antibody blockade

Modulating co-stimulation

The modulation of co-stimulatory pathways represents a novel therapeutic strategy to regulate autoimmune diseases. Auto-reactive CD4+ T cells play a critical role in initiating the immune response leading to inflammation and autoimmune diseases. Blocking co-stimulatory signals prevents T-cell activation, thus diminishing autoimmune responses and possibly preventing the progression of autoimmune disease. Blockade of several co-stimulatory pathways has been investigated in animal models and has led to clinical trials testing specific blocking agents in humans. In this review we will describe the role of co-stimulatory pathways, primarily the CD28-B7 pathway, in autoimmune diseases, and we will present in vivo and in vitro studies supporting the efficacy of co-stimulation blockade in animal models of autoimmune disease. Finally, we will discuss the clinical therapeutic efficacy of blocking monoclonal antibodies in preventing or reducing auto-antigen driven T-cell activation in humans with particular attention to the CD28/B7 pathway. Inhibiting co-stimulatory molecule interactions by using monoclonal antibodies seems to be an original approach to regulate autoimmune diseases in humans.

Constitutive expression of B7-1 on B cells uncovers autoimmunity toward the B cell compartment in the nonobese diabetic mouse

The NOD mouse is an invaluable model for the study of autoimmune diabetes. Furthermore, although less appreciated, NOD mice are susceptible to other autoimmune diseases that can be differentially manifested by altering the balance of T cell costimulatory pathways. In this study, we show that constitutively expressing B7-1 on B cells (NOD-B7-1B-transgenic mice) resulted in reduced insulitis and completely protected NOD mice from developing diabetes. Furthermore, B7-1 expression led to a dramatic reduction of the B cell compartment due to a selective deletion of follicular B cells in the spleen, whereas marginal zone B cells were largely unaffected. B cell depletion was dependent on B cell specificity, mediated by CD8(+) T cells, and occurred exclusively in the autoimmune-prone NOD background. Our results suggest that B cell deletion was a consequence of the specific activation of autoreactive T cells directed at peripheral self Ags presented by maturing B cells that expressed B7-1 costimulatory molecules. This study underscores the importance of B7 costimulatory molecules in controlling the amplitude and target of autoimmunity in genetically prone individuals and has important implications in the use of costimulatory pathway antagonists in the treatment of human autoimmune diseases.

A two-signal model for T cell trafficking

T-cell-receptor triggering and the delivery of co-stimulation are essential events leading to T cell expansion, differentiation and effector function. The influence that such signals exert on T cell migration during and following priming has been highlighted by recent reports. Moreover, induction of peripheral tolerance might act in part by affecting T cell migration. Here, we propose that the integration of co-stimulatory signals, which regulate the ability of primed T cells to access nonlymphoid tissue, and cognate recognition of the endothelium, which determines the selective recruitment of specific T cells, contribute to the anatomy of T cell-mediated immunity and tolerance. The implications for therapeutic strategies manipulating these signals are discussed.

Experimental autoimmune encephalomyelitis in the mouse

This unit details the materials and methods required for both active induction and adoptive transfer of experimental autoimmune encephalomyelitis (EAE) in the SJL mouse strain using intact proteins or peptides from the two major myelin proteins: proteolipid protein (PLP) and myelin basic protein (MBP). Detailed materials and methods required for the purification of both PLP and MBP are also described. Modifications of the specified protocols may be necessary for efficient induction of active or adoptive EAE in other mouse strains.

Janus faces of microglia in multiple sclerosis

Multiple sclerosis (MS) is the most common cause of neurological disability in young adults. The disease is characterized by inflammatory reactions, demyelination and axonal loss in the brain, spinal cord and optic nerves. Microglia seem to play an important role in the inflammatory processes in MS, since they are found in actively demyelinating lesions. Their role in the differentiation of T cells could led to the expansion of inflammation and tissue destruction. However, microglia are also involved in the termination of an inflammatory response and produce protective factors. To be able to therapeutically manipulate microglia, their exact function in the onset and development of MS needs to be clarified. This review provides an overview of the functions of the most important microglia-associated molecules in MS, being CD40, B7-1 and B7-2, interferon-gamma, tumor necrosis factor-alpha, chemokines, prostanoids, and nitric oxide.

Physiologic and aberrant regulation of memory T-cell trafficking by the costimulatory molecule CD28

Productive T-cell immunity requires both the activation and the migration of specific T cells to the antigenic tissue. The costimulatory molecule CD28 plays an essential role in the initiation of T-cell–mediated immunity. We investigated the possibility that CD28 may also regulate migration of primed T cells to target tissue. In vitro, CD28-mediated signals enhanced T-cell transendothelial migration, integrin clustering, and integrin-mediated migration. In vivo, T cells bearing a mutation in the CD28 cytoplasmic domain, which abrogates PI3K activation, displayed normal clonal expansion but defective localization to antigenic sites following antigenic rechallenge. Importantly, antibody-mediated CD28 stimulation led to unregulated memory T-cell migration to extra-lymphoid tissue, which occurred independently of T-cell receptor (TCR)–derived signals and homing-receptor expression. Finally, we provide evidence that CD28- and CTLA-4–mediated signals exert opposite effects on T-cell trafficking in vivo. These findings highlight a novel physiologic function of CD28 that has crucial implications for the therapeutic manipulation of this and other costimulatory molecules.

Costimulatory molecules as immunotherapeutic targets in systemic lupus erythematosus

T cells undergo full and productive activation when they traffic to lymph nodes where they encounter dendritic cells displaying foreign antigen in the context of MHC molecules on their surface. Recognition of these antigen-MHC complexes by the T cell's receptor for antigen, or T cell receptor, provides the first of two obligate signals needed to drive cell proliferation. The second antigen-independent signal is provided by the costimulatory receptor, CD28, as it engages its ligand on the antigen-presenting cells. Failure of the T cell to receive this second signal after antigen recognition leaves the T cell in a state of anergy. Understanding the role of T cell costimulatory receptors in T cell activation has led to the development of novel approaches for regulating immune responses in subjects with cancer or autoimmune disease by experimentally triggering or blocking costimulatory receptor signaling. In this review, we will discuss, first, several costimulatory pathways known to participate or regulate the progression of autoimmune disease, and, second, how manipulation of T cell costimulation and/or costimulation blockade has been used to treat systemic lupus erythematosus.

CD62L is required for the priming of encephalitogenic T cells but does not play a major role in the effector phase of experimental autoimmune encephalomyelitis

CD62L (l-selectin, mel 14) regulates naïve T cell homing into lymph nodes and the migration of leucocytes to sites of inflammation. The requirement of CD62L in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, has been demonstrated previously. However, it remains controversial as to whether CD62L is required for the induction or the effector phase of EAE. It is also unclear whether other non-T effector cells need CD62L to enter the central nervous system (CNS) parenchyma and exert their damaging effects on myelin. We report that mice with a targeted mutation of CD62L are resistant to Myelin oligodendrocyte glycoprotein peptide-induced EAE. CD62L-deficient mice had no peptide-specific T cell responses in the draining lymph nodes and had lower levels of peptide-specific T cell responses in spleens at a later time point. Adoptive transfer studies showed that CD62L-deficient mice were fully susceptible to adoptive transfer EAE induced by either wildtype or CD62L-deficient T cells. Moreover, CD62L-deficient, F4/80(+) macrophages can be efficiently recruited into the CNS parenchyma. These data suggest that CD62L is required for the induction of encephalitogenic T cells during EAE development, but is not required by T and non-T effector cells to attack the CNS parenchyma.

T-cell tolerance or function is determined by combinatorial costimulatory signals

Activated in immune responses, T lymphocytes differentiate into effector cells with potent immune function. CD28 is the most prominent costimulatory receptor for T-cell activation. However, absence of CD28 costimulation did not completely impair effector function of CD4 or CD8 T cells. Moreover, increasing number of costimulatory molecules are recently found on antigen-presenting cells to regulate T-cell activation. To understand the molecular mechanisms that determine T-cell function or tolerance, we have collectively examined the roles of positive and negative costimulatory molecules. Antigen-specific naïve CD4 and CD8 T cells, only when activated in the absence of both CD28 and ICOS pathways, were completely impaired in effector function. These tolerant T cells not only were anergic with profound defects in TcR signal transduction but also completely lacked expression of effector-specific transcription factors. T-cell tolerance induction in this system requires the action by negative costimulatory molecules; T-cell proliferation and function was partially restored by inhibiting PD-1, B7-H3 or B7S1. This work demonstrates that T-cell function or tolerance is controlled by costimulatory signals.

CD28-dependent differentiation into the effector/memory phenotype is essential for induction of arthritis in interleukin-1 receptor antagonist-deficient mice

OBJECTIVE

Interleukin-1 receptor antagonist (IL-1Ra)-deficient mice on a BALB/c background spontaneously develop a chronic inflammatory polyarthropathy closely resembling that of rheumatoid arthritis in humans. To elucidate the role of CD28 costimulatory signals in the development of this disease, we studied IL-1Ra/CD28-double-deficient mice.

METHODS

We crossed IL-1Ra-deficient mice with CD28-deficient mice and observed the incidence and severity of arthritis. To investigate functions of IL-1Ra/CD28-double-deficient T cells, cells were stimulated with CD3 monoclonal antibody or allogeneic antigen-presenting cells (APCs) and their proliferative responses and levels of cytokine production were measured.

RESULTS

Disease severity was lower in IL-1Ra/CD28-double-deficient mice than in mice that were deficient only in IL-1Ra, although incidence of arthritis was not affected by the presence or absence of CD28. When pathogenic IL-1Ra-KO T cells were transferred into nude mice, severe arthritis developed. Even though T cells from double-deficient mice showed the same diminished proliferative capacity as was seen in T cells from CD28-single-deficient animals, nude mice into which double-deficient T cells were transferred never developed arthritis.

CONCLUSION

These findings indicate that IL-1Ra/CD28-double-deficient T cells can be activated by IL-1Ra-deficient activated APCs, resulting in induction of arthritis; however, these T cells did not induce the disease under normal conditions, because they did not differentiate into effector/memory phenotype.

CD28-mediated costimulation impacts on the differentiation of DC vaccination-induced T cell responses

Costimulatory signals such as the ones elicited by CD28/B7 receptor ligation are essential for efficient T cell activation but their role in anti-tumour immune responses remains controversial. In the present study we compared the efficacy of DC vaccination-induced melanoma specific T cell responses to control the development of subcutaneous tumours and pulmonary metastases in CD28-deficient mice. Lack of CD28-mediated costimulatory signals accelerated tumour development in both model systems and also the load of pulmonary metastases was strongly increased by the end of the observation period. To scrutinize whether lack of CD28 signalling influences priming, homing or effector function of Trp-2(180-188)/K(b)-reactive T cells we investigated the characteristics of circulating and tumour infiltrating T cells. No difference in the frequency of Trp-2(180-188)/K(b)-reactive CD8+ T cells could be demonstrated among the cellular infiltrate of subcutaneous tumours after DC vaccination between both genotypes. However, the number of IFN-gamma-producing Trp-2-reactive cells was substantially lower in CD28-deficient mice and also their cytotoxicity was reduced. This suggests that CD28-mediated costimulatory signals are essential for differentiation of functional tumour-specific CD8+ T-effector cells despite having no impact on the homing of primed CD8+ T cells.

Mycobacterium tuberculosis in the adjuvant modulates the balance of Th immune response to self-antigen of the CNS without influencing a “core” repertoire of specific T cells

In the present study, we use modified CDR3 beta-chain spectratyping (immunoscope) to dissect the effect of Mycobacterium tuberculosis (MT)-derived proteins on individual PLP139-151-specific cells in the SJL mouse strain. In this model, the immunoscope technique allows the characterization of a public TCR that involves rearrangement of Vbeta10 and Jbeta1.1 and a semi-private TCR characterized by rearrangement of Vbeta4 and Jbeta1.6. Both rearrangements are specific for PLP139-151 and sequences of the CDR3 region of the two beta-chains show a conserved motif for the public rearrangement and related but more variable sequences for the semi-private rearrangement. MT-derived proteins promote increase of IFN-gamma-secreting cells. However, we observe that the presence and amount of MT used during immunization have no effect on the frequency of usage, polarization and in vivo expansion of cells carrying the studied rearrangements. Rather, the strong Th1-promoting effect of adjuvant is possibly due to recruitment toward Th1 of a wider spectrum of TCR repertoires. Therefore, instead of having a comprehensive effect on the entire repertoire, MT modulates the immune response by affecting a subset of antigen-specific T cells whose polarization can be adapted to the environment. This step establishes the final balance between Th1 and Th2 and may be essential for the enhancement or protection of disease.

Distinct effects of CD86-mediated costimulation on resting versus activated human CD4+ T cells

CD80 and CD86 are important in the initiation of T cell immunity. Although their costimulatory function has long been appreciated, it remains unclear whether the biological significance of the two B7 isoforms resides in their different patterns and kinetics of expression or whether differences exist in their function. We have addressed this issue using HLA-DR1 transfectants co-expressing CD80, CD86, or both molecules as stimulators for naïve, memory, and activated human CD4+ T cells. Both CD80 and CD86 efficiently costimulated alloresponses by unseparated peripheral blood CD4+ T cells; however, CD86 was substantially inferior in costimulating alloresponses by separated memory T cells, and completely incompetent in costimulating three human T cell clones. Furthermore, CD80/CD86 double transfectants stimulated lower responses by the clones than cells expressing CD80 alone. That CD86 was actively inhibitory rather than merely neutral was evidenced by the increase in response to the double CD80/CD86 APC when anti-CD86 antibody was added. Furthermore, addition of anti-CTLA-4 Fab to cultures of HLA-DR1 transfectants co-expressing CD86, fully restored the proliferative response. These results indicate that CD80 and CD86 mediate distinct signals in previously activated T cells, and demonstrate that CTLA-4 ligation may dominate the outcome of CD86-mediated costimulation of activated CD4+ T cells.

Prophylactic administration of abatacept prevents disease and bone destruction in a rat model of collagen-induced arthritis

Abatacept is the first in a new class of agents that selectively modulates T-cell activation by attenuating CD28-mediated co-stimulation. This study examined the effects of abatacept on disease development in a rat model of collagen-induced arthritis (CIA). The rats were treated with either abatacept (1mg/kg) or control IgG beginning at the time of induction of CIA. By day 16, significant paw swelling was observed in IgG-treated control animals that continued to increase, reaching a plateau on day 21. Prophylactic treatment with abatacept completely abrogated paw swelling throughout the study. Histopathology demonstrated a significant reduction in inflammation, cartilage destruction, bone resorption and pannus formation. Abatacept treatment resulted in 90% inhibition of circulating collagen-specific antibodies and decreased the serum expression of many cytokines and chemokines that were upregulated in diseased animals. Immunohistochemical analysis of the ankle joints demonstrated that interleukin-6 production was reduced in the tissues and the numbers of osteoclasts present in the joints were also decreased. Ankle microcomputer tomography (micro-CT) analyses dramatically demonstrated the protective effects of abatacept on bone destruction in these animals. Data presented here demonstrate that prophylactic administration of abatacept significantly inhibits the onset and progression of disease in a rat CIA model, with reductions in inflammation, inflammatory mediators, and bone and joint destruction.

CD80 and CD86 costimulatory molecules regulate crescentic glomerulonephritis by different mechanisms

BACKGROUND

CD80 and CD86 costimulatory molecules have been shown to affect the induction of Th1-mediated crescentic antiglomerular basement membrane (GBM) antibody-initiated glomerulonephritis (GN). The aim of the current studies was to define the mechanisms by which CD80 and CD86 regulate the development of this disease.

METHODS

Anti-GBM GN was induced in CD80-/-, CD86-/-, and CD80/86-/- mice, as well as in C57BL/6 controls. Renal injury and immune responses were assessed after 21 days. To examine whether costimulation by OX40-ligand compensates for the absence of CD80 and CD86 in inducing GN, OX40-ligand was blocked in wild-type and CD80/86-/- mice.

RESULTS

Crescentic GN and glomerular accumulation of CD4+ T cells and macrophages were attenuated in CD80-/- mice, correlating with significantly enhanced apoptosis and decreased proliferation of spleen CD4+ T cells. GN was exacerbated in CD86-/- mice, which was associated with attenuated IL-4 and enhanced IFN-gamma levels. In contrast, CD80/86-/- mice developed crescentic GN similar to that in controls. Inhibition of OX40-ligand exacerbated GN in wild-type mice by enhancing IFN-gamma production, and attenuated disease in CD80/86-/- mice by reducing glomerular CD4+ T-cell and macrophage accumulation.

CONCLUSION

CD80 is pathogenic in crescentic GN by enhancing survival and proliferation of CD4+ T cells, whereas CD86 is protective by enhancing Th2 and attenuating Th1 responses. Furthermore, in the presence of CD80 and CD86, OX40-ligand attenuates, whereas in their absence it enhances GN, suggesting that, in the absence of CD80 and CD86, the OX40/OX40-ligand pathway is an alternative costimulatory pathway in inducing crescentic GN.

Block and tackle: CTLA4Ig takes on lupus

Blockade of antigen nonspecific costimulatory signals is a promising approach for the treatment of autoimmune diseases including systemic lupus erythematosus (SLE). CTLA4Ig, an antagonist of the CD28/B7 costimulatory interaction, effectively prevents SLE onset in several murine models and, when used in combination with cyclophosphamide, can induce remission of active SLE nephritis. In this review we describe the known mechanisms of action of CTLA4Ig both in normal immunity and in autoimmune disease models and address issues about its activity that still need to be resolved. We discuss the preclinical use of CTLA4Ig in murine SLE models and the rationale for a clinical trial in SLE patients.

Multivalent recombinant proteins for probing functions of leucocyte surface proteins such as the CD200 receptor

CD200 (OX2) is a membrane glycoprotein that interacts with a structurally related receptor (CD200R) involved in the regulation of macrophage function. The interaction is of low affinity (K(D) approximately 1 microm) but can be detected using CD200 displayed in a multivalent form on beads or with dimeric fusion proteins consisting of the extracellular region of CD200 and immunoglobulin Fc regions. We prepared putative pentamers and trimers of mouse CD200 with sequences from cartilage oligomeric matrix protein (COMP) and surfactant protein D (SP-D), respectively. The COMP protein gave high-avidity binding and was a valuable tool for showing the interaction whilst the SP-D protein gave weak binding. In vivo experiments showed that an agonistic CD200R monoclonal antibody caused some amelioration in a model of experimental autoimmune encephalomyelitis but the COMP protein was cleared rapidly and had minimal effect. Pentameric constructs also allowed detection of the rat CD48/CD2 interaction, which is of much lower affinity (K(D) approximately 70 microm). These reagents may have an advantage over Fc-bearing hybrid molecules for probing cell surface proteins without side-effects due to the Fc regions. The CD200-COMP gave strong signals in protein microarrays, suggesting that such reagents may be valuable in high throughput detection of weak interactions.

The NOD mouse: a model of immune dysregulation

Autoimmunity is a complex process that likely results from the summation of multiple defective tolerance mechanisms. The NOD mouse strain is an excellent model of autoimmune disease and an important tool for dissecting tolerance mechanisms. The strength of this mouse strain is that it develops spontaneous autoimmune diabetes, which shares many similarities to autoimmune or type 1a diabetes (T1D) in human subjects, including the presence of pancreas-specific autoantibodies, autoreactive CD4+ and CD8+ T cells, and genetic linkage to disease syntenic to that found in humans. During the past ten years, investigators have used a wide variety of tools to study these mice, including immunological reagents and transgenic and knockout strains; these tools have tremendously enhanced the study of the fundamental disease mechanisms. In addition, investigators have recently developed a number of therapeutic interventions in this animal model that have now been translated into human therapies. In this review, we summarize many of the important features of disease development and progression in the NOD strain, emphasizing the role of central and peripheral tolerance mechanisms that affect diabetes in these mice. The information gained from this highly relevant model of human disease will lead to potential therapies that may alter the development of the disease and its progression in patients with T1D.

Glomerular expression of CD80 and CD86 is required for leukocyte accumulation and injury in crescentic glomerulonephritis

The participation of renal expression of CD80 and CD86 in the immunopathogenesis of crescentic Th1-mediated anti-glomerular basement membrane (anti-GBM) glomerulonephritis (GN) has not been assessed. Immunohistochemical staining demonstrated prominent upregulation of both molecules in glomeruli of mice with anti-GBM GN, suggesting a potential role for the local expression of CD80 and CD86 in nephritogenic effector T cell responses. For testing this hypothesis, control or inhibitory anti-CD80 and/or anti-CD86 mAb were administered to mice during the effector phase of the disease but after the establishment of a systemic immune response. Anti-CD80 or anti-CD86 mAb treatment had no effect on the development of GN or infiltration of leukocytes into glomeruli; however, administration of anti-CD80/86 mAb attenuated glomerular accumulation of CD4+ T cells and macrophages, crescent formation, and proteinuria, correlating with reduced antigen-specific skin delayed-type hypersensitivity. Attenuated glomerular infiltration of leukocytes in mice that were treated with anti-CD80/86 mAb was associated with decreased intraglomerular expression of adhesion molecules P-selectin and intercellular adhesion molecule-1, as well as attenuated renal mRNA levels of proinflammatory cytokines IFN-gamma and migration inhibitory factor, without reducing chemokine and chemokine receptor expression in the kidney or intraglomerular apoptosis and proliferation. The systemic Th1/Th2 balance (assessed by splenocyte production of IFN-gamma and IL-4 and circulating levels of IgG1 and IgG2a) was not affected by the inhibition of CD80 and CD86. These studies show that CD80 and CD86 are expressed in glomeruli of mice with crescentic anti-GBM GN, in which they play a critical role in facilitating accumulation of Th1 effectors and macrophages, thus exacerbating renal injury.

The evolving clinical profile of abatacept (CTLA4-Ig): a novel co-stimulatory modulator for the treatment of rheumatoid arthritis

Abatacept (CTLA4–Ig) is a novel fusion protein designed to modulate the T cell co-stimulatory signal mediated through the CD28–CD80/86 pathway. Clinical trials have provided preliminary evidence of the efficacy of this compound in the treatment of rheumatoid arthritis. This review describes the molecular and biologic bases for the use of abatacept in rheumatoid arthritis and summarizes the current clinical data on its safety and effectiveness in this disease.

Monocyte-derived HLA-G acts as a strong inhibitor of autologous CD4 T cell activation and is upregulated by interferon-β in vitro and in vivo: rationale for the therapy of multiple sclerosis

Peripheral antigen presenting cells (APCs) contribute to the maintenance of immune tolerance and are considered to play a critical role in promoting the (re)activation of autoreactive T cells in multiple sclerosis (MS). Interferon-beta (IFN-beta) is the principle immune-modulatory agent used in the treatment of MS, but its mechanism of action remains elusive. HLA-G is a non-classical MHC molecule (MHC class Ib) attributed chiefly immune-regulatory functions. We here investigated the role of monocyte-derived HLA-G in the immune-regulatory processes of MS and its implications for current immune-modulatory therapies. Monocytes constitutively express cell surface HLA-G1 and soluble HLA-G5. Comparison of monocytic HLA-G expression between patients with relapsing-remitting MS (n=17) and healthy donors (n=20) revealed significantly lower levels of HLA-G1 protein in MS patients. However, both groups showed a significant upregulation of HLA-G in response to IFN-beta in vitro. Serial measurements of HLA-G mRNA levels in MS patients before and during IFN-beta therapy corroborated the relevance of these results in vivo: 1 month after initiation of IFN-beta1b therapy (n=9), HLA-G1 and HLA-G5 were significantly increased compared to baseline levels and remained elevated during treatment for 6 months (n=3). Importantly, functional experiments demonstrated that monocyte-derived HLA-G inhibits both Th1 (IFN-gamma, IL-2) and Th2 (IL-10) cytokine production by antigen-stimulated autologous CD4 T cells. Soluble HLA-G added to antigen-specific T cell lines (TCLs) has similar effects on the release of cytokines and reduces T cell proliferation. Although both IFN-beta and IFN-gamma strongly enhance HLA-G1 and HLA-G5 expression by monocytes in vitro, IFN-beta leads to a stronger relative upregulation of HLA-G compared to classical MHC class I molecules than stimulation with IFN-gamma. Taken together, monocyte-derived HLA-G mediates the inhibition of autologous CD4 T cell activation and might be involved in immune-regulatory pathways in the pathogenesis of MS. We conclude that some desirable immune-modulatory effects of INF-beta might be accomplished via the upregulation of the immune-tolerogenic molecule HLA-G.

Requirement for CD28 May Not Be Absolute for Collagen-Induced Arthritis: Study with HLA-DQ8 Transgenic Mice

CD28 is required to achieve optimal T cell activation to an Ag. To determine the role CD28 costimulation plays in collagen-induced arthritis, we have generated DQ8 transgenic, CD28-deficient mice. DQ8 mice deficient for CD28 had comparable numbers of CD4 and CD8 T cells as DQ8.CD28(+/+) mice. DQ8.CD28(-/-) mice develop collagen-induced arthritis with delayed onset and less severity than DQ8.CD28(+/+) mice. T cells from DQ8.CD28(-/-) mice did not respond to type II collagen efficiently in vitro, although the response to DQ8-restricted peptides was similar to that in the parent mice. There was no functional defect in T cells as observed by proliferation with Con A. Cytokine analysis from in vitro study showed the production of high levels of the inflammatory cytokine, IFN-gamma, in response to type II collagen. We observed an increase in CD4(+)CD28(-)NKG2D(+) cells after immunization, suggesting an important role for cells bearing this receptor in the disease process. CD28(-/-) mice also have an increased number of DX5(+) cells compared with CD28(+/+) mice, which can lead to the production of high levels of IFN-gamma. DQ8.CD28(-/-) mice had an increased number of cells bearing other costimulatory markers. Cells from DQ8.CD28(-/-) mice exhibited a lower proliferation rate and were resistant to activation-induced cell death compared with DQ8.CD28(+/+) mice. This study supports the idea that CD28 plays a crucial role in the regulation of arthritis. However, in the absence of CD28 signaling, other costimulatory molecules can lead to the development of disease, thus indicating that the requirement for CD28 may not be absolute in the development of arthritis.

Genetic Interactions in Eae2 Control Collagen-Induced Arthritis and the CD4+/CD8+ T Cell Ratio

The Eae2 locus on mouse chromosome 15 controls the development of experimental autoimmune encephalomyelitis (EAE); however, in this study we show that it also controls collagen-induced arthritis (CIA). To find the smallest disease-controlling locus/loci within Eae2, we have studied development of CIA in 676 mice from a partially advanced intercross. Eae2 congenic mice were bred with mice congenic for the Eae3/Cia5 locus on chromosome 3, previously shown to interact with Eae2. To create a large number of genetic recombinations within the congenic fragments, the offspring were intercrossed, and the eight subsequent generations were analyzed for CIA. We found that Eae2 consists of four Cia subloci (Cia26, Cia30, Cia31, and Cia32), of which two interacted with each other, conferring severe CIA. Genes within the other two loci independently interacted with genes in Eae3/Cia5. Investigation of the CD4/CD8 T cell ratio in mice from the partially advanced intercross shows that this trait is linked to one of the Eae2 subloci through interactions with Eae3/Cia5. Furthermore, the expression of CD86 on stimulated macrophages is linked to Eae2.

B7.2 on activated and phagocytic microglia in the facial axotomy model: regulation by interleukin-1 receptor type 1, tumor necrosis factor receptors 1 and 2 and endotoxin

Co-stimulatory factors are involved in different forms of brain pathology and play an important role in the activation of T-cells. In the current study, we explored the regulation of B7.2, a prominent member of the B7 family of costimulatory factors, in the facial motor nucleus (FMN) following facial axotomy and systemic application of lipopolysaccharide (LPS, endotoxin) using light and electron immunohistochemistry and cytokine-receptor-deficient mice. Facial axotomy led to a gradual increase of B7.2 immunoreactivity (IR) on microglial cell surface; similar effects were also observed following application of LPS, but both effects were not additive, suggesting overlapping or saturated signaling pathways. Some B7.2-IR was already present on activated microglia surrounding injured neurons at days 1-4 after injury, but became particularly intense during neuronal cell death, peaking at day 14. Previous studies revealed that these late microglial changes are accompanied by a strong increase in the expression of proinflammatory cytokines such as interleukin-1 beta (IL1beta) tumor necrosis factor-alpha (TNFalpha) and interferon gamma (IFNgamma) [J. Neurosci. 18 (1998a) 5804]. Here, deletion of the receptors for these cytokines-IL1R1, TNFR1 or TNFR2, but not IFNgammaR1-caused a strong and significant reduction in B7.2-IR in reactive microglial cells, compared with their wild type (WT) controls on the same genetic strain background, with a 31% decrease in IL1R1-/- , 39% in TNFR1-/- and 49% in TNFR2-/- mice. These data underscore the significance of IL1beta, TNFalpha and LPS, and their receptors, as potent inflammatory signals that regulate the cellular response in the injured brain as well as the interaction with the rapidly recruited immune system. The broad susceptibility of B7.2 regulation to a wide range of different inflammatory signals also points to its role as a sensor of molecular pathology, and a factor that plays an important accessory role in allowing and shaping the microglia/T-cell interaction in the injured central nervous system.

B7-1 and B7-2 selectively recruit CTLA-4 and CD28 to the immunological synapse

The reported affinity differences between CD28 and CTLA-4 binding to B7-1 and B7-2 may serve to selectively regulate CD28 and CTLA-4 function by differentially recruiting and/or stabilizing these molecules at the immunological synapse. Here we show that ligand binding is important for the accumulation of both CD28 and CTLA-4 at the synapse. While CD28 is recruited to the synapse in the absence of B7-1 and B7-2 binding, it is not effectively stabilized there, as its localization can be disrupted by CTLA-4. In the case of CTLA-4, ligand binding is critical for its concentration at the synapse. We also demonstrate that the affinity and avidity differences in ligand binding translate into selective recruitment of CD28 or CTLA-4 to the immunological synapse--B7-1 is the major ligand mediating CTLA-4 localization, while B7-2 is the main ligand for CD28 concentration at the synapse.

Interferon-beta enhances monocyte and dendritic cell expression of B7-H1 (PD-L1), a strong inhibitor of autologous T-cell activation: relevance for the immune modulatory effect in multiple sclerosis

Antigen-presenting cells (APC) are considered to play a critical role in promoting the (re)activation of potentially autoreactive T cells in multiple sclerosis (MS), an inflammatory demyelinating disorder of the central nervous system (CNS). B7-H1 (PD-L1) is a novel member of the B7 family proteins which exert costimulatory and immune regulatory functions. Here we characterize the expression and functional activity of B7-H1 expressed on monocytes and dendritic cells (DC) of healthy donors and MS patients. B7-H1 is constitutively expressed on monocytes and differentially matured DC, but not on B cells. IFN-beta, the principle immune modulatory agent used for the treatment of MS, strongly enhances B7-H1 expression on monocytes and semi-matured DC, but not B cells, in vitro. Importantly, B7-H1 expressed on APC strongly inhibits autologous CD4 T-cell activation. Neutralization of B7-H1 on monocytes or differentially matured monocyte-derived DC markedly increases the secretion of the pro-inflammatory cytokines, IFN-gamma and IL-2, T-cell proliferation, and the expression of T-cell activation markers. B7-H1 exhibits strong inhibitory effects when expressed on monocytes, immature or semi-mature DC, but less so when expressed on fully matured DC. B7-H1-dependent immune inhibition is in part mediated by CD4/CD25+ regulatory T cells. There is no difference in the baseline expression levels of monocytic B7-H1 between untreated MS patients and healthy donors. However, both groups show a significant concentration-dependent up-regulation of B7-H1 mRNA and protein in response to IFN-beta in vitro. Serial measurements of B7-H1 mRNA in MS patients before and 6 months after initiation of IFN-beta therapy corroborated the relevance of these results in vivo: Nine of nine patients showed a significant increase in B7-H1 mRNA levels after 6 months of IFN-beta therapy (median 1.04 vs. 8.78; p<0.05, two-sided t-test). Accordingly, protein expression of B7-H1 on monocytes was up-regulated after 24 h of IFN-beta application. In summary, B7-H1 expressed on APC acts as a strong inhibitor of autologous CD4 T-cell activation and may thus contribute to the maintenance of peripheral immune tolerance. IFN-beta up-regulates B7-H1 in vitro and in MS patients in vivo and might represent a novel mechanism how IFN-beta acts as a negative modulator on APC T-cell interactions in the periphery.

CD28 costimulation is required for the expression of T-cell-dependent cell-mediated immunity against blood-stage Plasmodium chabaudi malaria parasites

Mice suppress the parasitemia of acute blood-stage Plasmodium chabaudi malaria by an antibody- or T-cell-dependent cell-mediated mechanism of immunity (AMI and CMI, respectively) or by both mechanisms. To determine whether CD28 costimulation is required for expression of these polar immune responses, we first compared the time courses of P. chabaudi malaria in CD28-deficient (CD28(-/-)) and CD28-intact (CD28(+/+)) mice. Acute infections in both knockout (KO) and control mice followed similar time courses, with the period of descending parasitemia being prolonged approximately 2 weeks in KO mice followed by intermittent low-grade chronic parasitemia. Infected CD28(-/-) mice produced primarily the immunoglobulin M antibody, which upon passive transfer provided partial protection against P. chabaudi challenge, suggesting that the elimination of blood-stage parasites by CD28(-/-) mice was achieved by AMI. To determine whether CD28(-/-) costimulation is required for the expression of CMI against the parasite, we compared the time courses of parasitemia in B-cell-deficient double-KO (J(H)(-/-) x CD28(-/-)) mice and control (J(H)(-/-) x CD28(+/+)) mice. Whereas control mice suppressed parasitemia to subpatent levels within approximately 2 weeks postinoculation, double-KO mice developed high levels of parasitemia of long-lasting duration. Although not required for the suppression of acute P. chabaudi parasitemia by AMI, CD28 costimulation is essential for the elimination of blood-stage parasites by CMI.

Immunosuppression of rat myasthenia gravis by oral administration of a syngeneic acetylcholine receptor fragment

A syngeneic rat recombinant fragment of the extracellular domain of the acetylcholine receptor (AChR) alpha-subunit (Ralpha1-205), administered orally, suppresses ongoing experimental autoimmune myasthenia gravis (EAMG) in rats. The underlying mechanism is a shift from Th1 to Th2 regulation as evidenced by downregulated mRNA expression levels of IFN-gamma and TNF-alpha, upregulated IL-10, changes in anti-AChR IgG isotypes and diminished Th1 signaling via CD28/CTLA-4:B7. Unlike the xenogeneic fragment, the syngeneic Ralpha1-205 does not induce elevation in TGF-beta and elicitation of autoregulatory cells. The ability to suppress EAMG by a non-immunogenic syngeneic fragment of AChR is encouraging and may in the future be applied for the treatment of myasthenia gravis in humans.

B7-2 (CD86) Controls the Priming of Autoreactive CD4 T Cell Response against Pancreatic Islets

The B7-1/2-CD28 system provides the critical signal for the generation of an efficient T cell response. We investigated the role played by B7-2 in influencing pathogenic autoimmunity from islet-reactive CD4 T cells in B7-2 knockout (KO) NOD mice which are protected from type 1 diabetes. B7-2 deficiency caused a profound diminishment in the generation of spontaneously activated CD4 T cells and islet-specific CD4 T cell expansion. B7-2 does not impact the effector phase of the autoimmune response as adoptive transfer of islet Ag-specific BDC2.5 splenocytes stimulated in vitro could easily induce disease in B7-2KO mice. CD4 T cells showed some hallmarks of hyporesponsiveness because TCR/CD28-mediated stimulation led to defective activation and failure to induce disease in NODscid recipients. Furthermore, CD4 T cells exhibited enhanced death in the absence of B7-2. Interestingly, we found that B7-2 is required to achieve normal levels of CD4+CD25+CD62L+ T regulatory cells because a significant reduction of these T regulatory cells was observed in the thymus but not in the peripheral compartments of B7-2KO mice. In addition, our adoptive transfer experiments did not reveal either pathogenic or regulatory potential associated with the B7-2KO splenocytes. Finally, we found that the lack of B7-2 did not induce a compensatory increase in the B7-1 signal on APC in the PLN compartment. Taken together these results clearly indicate that B7-2 plays a critical role in priming islet-reactive CD4 T cells, suggesting a simplified, two-cell model for the impact of this costimulatory molecule in autoimmunity against islets.

K+ channel expression during B cell differentiation: implications for immunomodulation and autoimmunity

Using whole-cell patch-clamp, fluorescence microscopy and flow cytometry, we demonstrate a switch in potassium channel expression during differentiation of human B cells from naive to memory cells. Naive and IgD(+)CD27(+) memory B cells express small numbers of the voltage-gated Kv1.3 and the Ca(2+)-activated intermediate-conductance IKCa1 channel when quiescent, and increase IKCa1 expression 45-fold upon activation with no change in Kv1.3 levels. In contrast, quiescent class-switched memory B cells express high levels of Kv1.3 ( approximately 2000 channels/cell) and maintain their Kv1.3(high) expression after activation. Consistent with their channel phenotypes, proliferation of naive and IgD(+)CD27(+) memory B cells is suppressed by the specific IKCa1 inhibitor TRAM-34 but not by the potent Kv1.3 blocker Stichodactyla helianthus toxin, whereas the proliferation of class-switched memory B cells is suppressed by Stichodactyla helianthus toxin but not TRAM-34. These changes parallel those reported for T cells. Therefore, specific Kv1.3 and IKCa1 inhibitors may have use in therapeutic manipulation of selective lymphocyte subsets in immunological disorders.

The Diabetes Susceptibility Locus Idd5.1 on Mouse Chromosome 1 Regulates ICOS Expression and Modulates Murine Experimental Autoimmune Encephalomyelitis

Linkage analysis and congenic mapping in NOD mice have identified a susceptibility locus for type 1 diabetes, Idd5.1 on mouse chromosome 1, which includes the Ctla4 and Icos genes. Besides type 1 diabetes, numerous autoimmune diseases have been mapped to a syntenic region on human chromosome 2q33. In this study we determined how the costimulatory molecules encoded by these genes contribute to the immunopathogenesis of experimental autoimmune encephalomyelitis (EAE). When we compared levels of expression of costimulatory molecules on T cells, we found higher ICOS and lower full-length CTLA-4 expression on activated NOD T cells compared with C57BL/6 (B6) and C57BL/10 (B10) T cells. Using NOD.B10 Idd5 congenic strains, we determined that a 2.1-Mb region controls the observed expression differences of ICOS. Although Idd5.1 congenic mice are resistant to diabetes, we found them more susceptible to myelin oligodendrocyte glycoprotein 35-55-induced EAE compared with NOD mice. Our data demonstrate that higher ICOS expression correlates with more IL-10 production by NOD-derived T cells, and this may be responsible for the less severe EAE in NOD mice compared with Idd5.1 congenic mice. Paradoxically, alleles at the Idd5.1 locus have opposite effects on two autoimmune diseases, diabetes and EAE. This may reflect differential roles for costimulatory pathways in inducing autoimmune responses depending upon the origin (tissue) of the target Ag.

Monoclonal antibody therapy in experimental allergic encephalomyelitis and multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is a T-cell-mediated demyelinating disease of the central nervous system that has been used as an animal model for multiple sclerosis (MS). Based on the exciting results in EAE, a number of novel immunotherapies employing biotechnological products, rather than conventional immunosuppressants, are being developed for the treatment of MS. In this review, we delineate the rationale for monoclonal antibody (MAb) therapy in EAE and MS and summarize the various levels at which immune intervention was performed. For each approach, we discuss the role of MAbs at the level of lymphocyte and cytokine networks, chemokines, and adhesion molecules or their receptors.

Immune regulation by novel costimulatory molecules

CD4 helper T (Th)-cells and the cytokines that they produce play essential regulatory roles in immune and autoimmune responses. Th activation and differentiation is regulated by costimulatory receptors. CD28 and CTLA-4 are important in maintaining the threshold of T-cell activation. ICOS and PD-1 are novel costimulatory receptors expressed on activated T-cells. B7-H3 recognizes a putative costimulatory receptor on activated T-cells. Here we summarize the latest developments in the novel costimulatory molecules and their roles in regulating Th activation, differentiation, and function.

The role of ICOS and other costimulatory molecules in allergy and asthma

Activation and differentiation of T cells play a critical role in the pathogenesis of allergies and asthma. Upon encounter with specific antigen, naïve T helper precursor (ThP) cells become activated, an event that is regulated not only by engagement of the T cell receptor (TCR) with peptide presented in the context of MHC class II molecules, but also by a number of costimulatory signals. CD28 engagement by B7-1 and B7-2 on resting ThP cells provides a critical signal for initial cell cycle progression, interleukin-2 production and clonal expansion. However, in recent years, other related members of the immunoglobulin (Ig) family, such as inducible costimulatory molecules (ICOS) and the TNF receptor family members which include OX40, have also been demonstrated to play an important role in providing unique and complementary signals that regulate the outcome of immune responses. These positive costimulatory signals are counterbalanced by signals that dampen down immune responses and include CTLA-4, PD-1 and the recently described Ig superfamily members BTLA and TIM-3. This review discusses the role of these costimulatory signals and their potential involvement in the pathogenesis of asthma and allergic responses.

Role of costimulatory pathways in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis

Multiple sclerosis is an immune-mediated disorder of the central nervous system. T lymphocytes are thought to play a central role in the initiation and potentially in the propagation of this disease. Two signals are required for T-cell activation. The first signal consists of the interaction of the T-cell receptor with antigen presented by the MHC molecule on antigen-presenting cells. The second signal requires engagement of costimulatory receptors on T cells with their ligands on antigen-presenting cells. Several costimulatory pathways have been shown to play an important role in T-lymphocyte activation. Here we will review the current literature on the contribution of the B7-1/2-CD28/CTLA-4, inducible costimulatory molecule-B7h, programmed death pathway 1-programmed death pathway ligand 1/ligand 2, CD40-CD154, OX40-OX40 ligand, and CD137-CD137 ligand pathways to the pathogenesis of multiple sclerosis and their potential roles as therapeutic targets.

CD80, but not CD86 were up-regulated on the spleen-derived dendritic cells from OVA-sensitized and challenged BALB/c mice

Allergen-specific CD4+ T-helper (Th) 2 cells are involved in the induction and effector phase of allergic asthma. It is well established that T cells activation requires interaction of T cell receptor (TCR) and MHC-peptide complex, as well as costimulatory signal delivered by antigen presenting cells (APCs). There is increasing evidence that CD80 (B7.1) and CD86 (B7.2), as the most important costimulatory molecules, are involved in the allergic immune responses. In the present study, we investigated the CD80 and CD86 expression of spleen-derived dendritic cells (DCs) in a murine model of allergic asthma. We first established a murine model of ovalbumin (OVA)-allergic asthma that showed unique histological characteristic of allergic inflammation in the lung, high serum OVA-specific IgE level, high numbers of eosinophils in the bronchoalveolar lavage (BAL) and high production of Type 2 cytokines in the splenic T cells. In this model, we found that CD80 were significantly upregulated on the spleen-derived DCs from OVA-sensitized and challenged mice compared with that from PBS-treated or non-treated mice, while CD86 is not different among three groups. Furthermore, we demonstrated that Th2 immune responses were elicited by these DCs with high expression of CD80, even to nai;ve T cells from non-treated mice. Our results suggest that DCs in the spleen of allergic mice, via upregulation of CD80 might play a pivotal role in the maintenance and amplification of allergic immune response, namely Th2 immune response.

Regulatory functions of CD8+CD28- T cells in an autoimmune disease model

CD8+ T cell depletion renders CD28-deficient mice susceptible to experimental autoimmune encephalomyelitis (EAE). In addition, CD8-/-CD28-/- double-knockout mice are susceptible to EAE. These findings suggest a role for CD8+ T cells in the resistance of CD28-deficient mice to disease. Adoptive transfer of CD8+CD28- T cells into CD8-/- mice results in significant suppression of disease, while CD8+CD28+ T cells demonstrate no similar effect on the clinical course of EAE in the same recipients. In vitro, CD8+CD28- but not CD8+CD28+ T cells suppress IFN-gamma production of myelin oligodendrocyte glycoprotein-specific CD4+ T cells. This suppression requires cell-to-cell contact and is dependent on the presence of APCs. APCs cocultured with CD8+CD28- T cells become less efficient in inducing a T cell-dependent immune response. Such interaction prevents upregulation of costimulatory molecules by APCs, hence decreasing the delivery of these signals to CD4+ T cells. These are the first data establishing that regulatory CD8+CD28- T cells occur in normal mice and play a critical role in disease resistance in CD28-/- animals.

Break of neonatal Th1 tolerance and exacerbation of experimental allergic encephalomyelitis by interference with B7 costimulation

Ig-PLP1 is an Ig chimera expressing proteolipid protein-1 (PLP1) peptide corresponding to aa residues 139-151 of PLP. Newborn mice given Ig-PLP1 in saline on the day of birth and challenged 7 wk later with PLP1 peptide in CFA develop an organ-specific neonatal immunity that confers resistance against experimental allergic encephalomyelitis. The T cell responses in these animals comprise Th2 cells in the lymph node and anergic Th1 lymphocytes in the spleen. Intriguingly, the anergic splenic T cells, although nonproliferative and unable to produce IFN-gamma or IL-4, secrete significant amounts of IL-2. In this work, studies were performed to determine whether costimulation through B7 molecules plays any role in the unusual form of splenic Th1 anergy. The results show that engagement of either B7.1 or B7.2 with anti-B7 Abs during induction of EAE in adult mice that were neonatally tolerized with Ig-PLP1 restores and exacerbates disease severity. At the cellular level, the anergic splenic T cells regain the ability to proliferate and produce IFN-gamma when stimulated with Ag in the presence of either anti-B7.1 or anti-B7.2 Ab. However, such restoration was abolished when both B7.1 and B7.2 molecules were engaged simultaneously, indicating that costimulation is necessary for reactivation. Surprisingly, both anti-B7.1 and anti-B7.2 Abs triggered splenic dendritic cells to produce IL-12, a key cytokine required for restoration of the anergic T cells. Thus, recovery from neonatally induced T cell anergy requires B7 molecules to serve double functions, namely, costimulation and induction of cytokine production by APCs.

Critical role of the programmed death-1 (PD-1) pathway in regulation of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is mediated by autoantigen-specific T cells dependent on critical costimulatory signals for their full activation and regulation. We report that the programmed death-1 (PD-1) costimulatory pathway plays a critical role in regulating peripheral tolerance in murine EAE and appears to be a major contributor to the resistance of disease induction in CD28-deficient mice. After immunization with myelin oligodendrocyte glycoprotein (MOG) there was a progressive increase in expression of PD-1 and its ligand PD-L1 but not PD-L2 within the central nervous system (CNS) of mice with EAE, peaking after 3 wk. In both wild-type (WT) and CD28-deficient mice, PD-1 blockade resulted in accelerated and more severe disease with increased CNS lymphocyte infiltration. Worsening of disease after PD-1 blockade was associated with a heightened autoimmune response to MOG, manifested by increased frequency of interferon gamma-producing T cells, increased delayed-type hypersensitivity responses, and higher serum levels of anti-MOG antibody. In vivo blockade of PD-1 resulted in increased antigen-specific T cell expansion, activation, and cytokine production. Interestingly, PD-L2 but not PD-L1 blockade in WT animals also resulted in disease augmentation. Our data are the first demonstration that the PD-1 pathway plays a critical role in regulating EAE.

Role of the CTLA4 pathway in hyporesponsiveness induced by intratracheal delivery of alloantigen

BACKGROUND

The authors previously reported that intratracheal delivery (ITD) of donor alloantigen induced donor-specific hyporesponsiveness to C57BL/10 cardiac allografts in CBA recipients and that blockade of the B7 pathways abrogated that hyporesponsiveness. In this study, the authors used a CD28-deficient model to evaluate which signal, either through CD28 or cytotoxic T-lymphocyte-associated antigen (CTLA4), is involved in the induction of hyporesponsiveness.

METHODS

Seven days before transplantation of hearts from C3H/HeJ (H2k) mice into C57BL/6 (H2b) or CD28-deficient (C57BL/6 background) mice, the transplant recipients were given ITD of donor splenocytes (1 x 10(7)), alone or in combination with human CTLA4-immunoglobulin (Ig) (200 microg).

RESULTS

ITD of C3H splenocytes induced donor-specific hyporesponsiveness to C3H cardiac grafts in C57BL/6 recipients (graft median survival time [MST], 40 days). Administration of CTLA4-Ig concurrently with ITD abrogated the prolonged allograft survival (MST, 12 days). Interestingly, ITD of C3H splenocytes induced prolonged survival of C3H allografts in CD28-deficient recipients (MST, 55 days). Furthermore, administration of CTLA4-Ig combined with ITD of C3H splenocytes abrogated the prolonged survival of C3H allografts in CD28-deficient recipients (MST, 7 days), whereas recipients given isotype-control antibody in combination with ITD of splenocytes had prolonged survival of C3H allografts (MST, 58 days).

CONCLUSIONS

Taken together, the authors' findings indicate that a signal through CTLA4, rather than through CD28, plays an important role in the induction of hyporesponsiveness by ITD of alloantigen in this model.

Suppression of experimental autoimmune encephalomyelitis by selective blockade of encephalitogenic T-cell infiltration of the central nervous system

Multiple sclerosis (MS) is a devastating neuroinflammatory disorder of the central nervous system (CNS) in which T cells that are reactive with major components of myelin sheaths have a central role. The receptor for advanced glycation end products (RAGE) is present on T cells, mononuclear phagocytes and endothelium. Its pro-inflammatory ligands, S100-calgranulins, are upregulated in MS and in the related rodent model, experimental autoimmune encephalomyelitis (EAE). Blockade of RAGE suppressed EAE when disease was induced by myelin basic protein (MBP) peptide or encephalitogenic T cells, or when EAE occurred spontaneously in T-cell receptor (TCR)-transgenic mice devoid of endogenous TCR-alpha and TCR-beta chains. Inhibition of RAGE markedly decreased infiltration of the CNS by immune and inflammatory cells. Transgenic mice with targeted overexpression of dominant-negative RAGE in CD4+ T cells were resistant to MBP-induced EAE. These data reinforce the importance of RAGE-ligand interactions in modulating properties of CD4+ T cells that infiltrate the CNS.

NOD congenic mice genetically protected from autoimmune diabetes remain resistant to transplantation tolerance induction

The loss of self-tolerance leading to autoimmune type 1 diabetes in the NOD mouse model involves at least 19 genetic loci. In addition to their genetic defects in self-tolerance, NOD mice resist peripheral transplantation tolerance induced by costimulation blockade using donor-specific transfusion and anti-CD154 antibody. Hypothesizing that these two abnormalities might be related, we investigated whether they could be uncoupled through a genetic approach. Diabetes-resistant NOD and C57BL/6 stocks congenic for various reciprocally introduced Idd loci were assessed for their ability to be tolerized. Surprisingly, in NOD congenic mice that are almost completely protected from diabetes, costimulation blockade failed to prolong skin allograft survival. In reciprocal C57BL/6 congenic mice with NOD-derived Idd loci, skin allograft survival was readily prolonged by costimulation blockade. These data indicate that single or multiple combinations of evaluated Idd loci that dramatically reduce diabetes frequency do not correct resistance to peripheral transplantation tolerance induced by costimulation blockade. We suggest that mechanisms controlling autoimmunity and transplantation tolerance in NOD mice are not completely overlapping and are potentially distinct, or that the genetic threshold for normalizing the transplantation tolerance defect is higher than that for preventing autoimmune diabetes.

Broadening of epitope recognition during immune rejection of ErbB-2-positive tumor prevents growth of ErbB-2-negative tumor

Tumor heterogeneity is a limiting factor in Ag-specific vaccination. Ag-negative variants may arise after tumor cells bearing the immunizing Ags are destroyed. In situ priming to tumor-associated epitopes distinct from and not cross-reactive with the immunizing Ags may be crucial to the ultimate success of cancer vaccination. Immunization of BALB/c mice with DNA encoding wild-type human ErbB-2 (Her-2/neu, E2) or cytoplasmic ErbB-2 (cytE2), activated primarily CD4 or CD8 T cells, respectively, and both vaccines protected against ErbB-2-positive D2F2/E2 tumors. In > or =50% of protected mice, a second challenge of ErbB-2-negative D2F2 tumor cells was rejected. Recognition of non-ErbB-2, tumor-associated Ags was demonstrated by immune cell proliferation upon stimulation with irradiated D2F2 cells. This broadening of epitope recognition was abolished if CD4 T cells were depleted before D2F2/E2 tumor challenge, demonstrating their critical role in Ag priming. Similarly, mice that rejected D2F2/cytE2 tumor cells, which express only MHC I epitopes of ErbB-2, were not protected from a second challenge with D2F2 cells. Depletion of CD8 T cells abolished protection against D2F2, indicating the activation of D2F2-specific CTL. Therefore, long term protection may be achieved by immunization with dominant Ag(s), followed by a general enhancement of CD4 T cell activity to promote priming to multiple tumor-associated Ags.

Expression of B7 molecules in the eye during experimental autoimmune anterior uveitis (EAAU)

PURPOSE

We have reported that CTLA4-Fc, a fusion protein that binds B7, prevents the induction of EAAU and reduces the severity of disease in Lewis rats. Since B7.1 and B7.2 have distinctive roles in other autoimmune diseases, we investigated their roles in the development of EAAU.

METHODS

Lewis rats were immunized with melanin associated antigen (MAA). Eyes were collected at different stages of EAAU and the expression of B7 on iris and ciliary body (ICB) cell suspensions determined by flow cytometry analysis. The incidence of EAAU after treatment with anti B7, and the requirement of B7.1 and B7.2 for proliferation and cytokine production of lymphoid cells to MAA were also studied.

RESULTS

B7.2 is up-regulated in resident ICB cells or bone-marrow derived cells which have infiltrated the ICB by day 10 and remains elevated during the acute phase of disease. B7.1 is expressed later during the acute phase. Both B7.1 and B7.2 are down-regulated during remission, with low levels of B7.2 and no detectable B7.1. The incidence of EAAU was reduced by anti-B7.2 treatment and completely inhibited by a combination of both B7.1 and B7.2 antibodies. Neither anti-B7.1 nor anti-B7.2 alone affected proliferation or cytokine production. However, administration of both anti-B7.1 and B7.2 completely inhibited proliferation as well as IL-2 and TNF-alpha production.

CONCLUSIONS

B7.1 and B7.2 are expressed in the eye at different times during EAAU. Both B7 molecules are required for the induction of EAAU, although they probably have different roles.

Clinical and histologic response to single-dose treatment of moderate to severe psoriasis with an anti-CD80 monoclonal antibody

Pathologic T-cell activation is implicated in psoriasis progression. CD80, a costimulatory molecule involved in T-cell activation, likely plays a key role. IDEC-114, an IgG(1) anti-CD80 antibody, was evaluated for safety, pharmacokinetics, and preliminary clinical activity in this open-label, single-dose, dose-escalating study in patients with moderate to severe chronic plaque psoriasis. Twenty-four patients received IDEC-114 (0.05 mg/kg, 0.25 mg/kg, 1 mg/kg, 5 mg/kg, 10 mg/kg, or 15 mg/kg). Psoriasis Area and Severity Index, Physician's Global Psoriasis Assessment, and Psoriasis Severity Scale scores improved in the highest-dose groups. Average plaque thickness and plaque CD3+ and CD8+ T-cell counts decreased in the 10 mg/kg dose group. Adverse events were primarily mild, transient, constitutional symptoms; the most common related events were mild asthenia (29% of patients), chills (25%), and headache (21%). The serum half-life of IDEC-114 was approximately 13 days. A single dose of IDEC-114 appears to be safe and well tolerated and has promising clinical activity in psoriasis.

The Th2-response in mercuric chloride-induced autoimmunity requires continuing costimulation via CD28

Mercuric chloride (HgCl2)-induced autoimmunity in Brown Norway (BN) rats is a highly polarized polyclonal Th2-driven autoimmune response with increased IgE production, lymphoproliferation, vasculitis and proteinuria. The increase in serum IgE concentration is clearly measurable by day 4 after the first HgCl2 injection and peaks between days 15 and 20. Treatment with CD80 and CD86 antibodies prior to administration of HgCl2 completely suppresses the autoimmune process. To determine whether interruption of CD28 signalling after initial stimulation of the Th2-response would be suppressive, antibody treatment was delayed. BN rats were given 5 doses of HgCl2 subcutaneously on alternate days. CD80 and CD86 antibodies, or an isotype control, were given daily for 3 days and then on alternate days until day 12 commencing either on the day of the first HgCl2 injection (day 0) or on days 4 or 8. Treatment from day 0 reduced serum IgE concentrations to below baseline (median 9.34 microg/ml on day 0 versus 4.6 microg/ml, on day 5, P = 0.03) suggesting that ongoing costimulation via CD28 is required to maintain basal serum IgE production. Delaying treatment until day 4 or day 8 after the first HgCl2 injection resulted in significant inhibition of IgE secretion, lymphoproliferation, and vasculitis, although less markedly than when treatment was commenced on day 0. These data indicate that CD28-mediated costimulation is not only required for the initiation of the Th2-response but is required for maintenance of a maximal response, making this an attractive therapeutic target for antibody-mediated autoimmune diseases.

Differential effect of CD28 versus B7 blockade on direct pathway of allorecognition and self-restricted responses

Immunosuppression with B7 antagonists might have 2 opposite effects: reducing T-cell costimulation through CD28 but also preventing CTLA-4 from transmitting its negative regulatory signal. We therefore hypothesized that a selective blockade of CD28 might be qualitatively different from blocking B7. It was previously reported that CD28 modulation prolongs allograft survival in the rat and reverses induction of experimental autoimmune encephalomyelitis in mice. However, whether CD28 or B7 blockade results in similar immunosuppression on alloimmune and self-restricted responses to soluble antigens has not yet been investigated. Here, we addressed this issue in vitro with antagonist anti-CD28 Fab fragments and in vivo using the modulating anti-rat JJ319 monoclonal antibody. As in the inhibition of B7 with CTLA4 immunoglobulin, anti-CD28 Fab fragments inhibited allogenic T-cell proliferation in mixed cultures. In vivo modulation of CD28 blocked the expansion of alloreactive T cells and promoted their apoptosis. In contrast, selective blockade of CD28 did not modify T-cell proliferative responses and antibody production to soluble antigens, whereas blocking B7 with CTLA4 immunoglobulin did. Our data show that blocking CD28, while leaving CTLA4-B7 interactions undisturbed, inhibits alloreactive CD4+ T-cell expansion but does not modify the response to nominal antigens presented in the context of a self-major histocompatibility complex. That B7 engagement is needed for self-restricted responses whereas engagement of CD28 is not essential adds to the suggestion that another unidentified ligand of B7 might deliver a costimulatory signal in the absence of CD28.

CD40/CD40L interaction is essential for the induction of EAE in the absence of CD28-mediated co-stimulation

CD28 provides a co-stimulatory signal critical for optimal T cell activation. We and others have shown that the B7/CD28 co-stimulatory pathway is a major regulatory pathway for the control of immune responses. Experimentally induced models of autoimmunity have been shown to be prevented or reduced in intensity in mice deficient for CD28. Here, we show that EAE and accompanying neuroantigen-specific immune responses are drastically reduced in the absence of CD28. However, we go on to show that EAE can be induced in CD28-deficient mice following two immunizations. After re-immunization, CD28-deficient mice develop severe EAE with myelin-specific responses equal to those of wildtype controls, and extensive demyelination in the spinal cord. Treatment of CD28-deficient mice with anti-CD40L at the time of immunization significantly reduced DTH responses and prevented the development of EAE following two immunizations, indicating a critical role for CD40/CD40L signaling in the absence of CD28. Taken together, our results indicate that CD28-mediated co-stimulation does not regulate immunological anergy. Instead, CD28 appears to adjust the threshold for activation and expansion of autoreactive cells.

CD28 costimulation and parasite dose combine to influence the susceptibility of BALB/c mice to infection with Leishmania major

Infection with Leishmania major in BALB/c mice is accompanied by the development of a nonprotective Th2-type response. It has previously been shown that disease progression, and the activation of a Th2-type response, can occur in the absence of CD28 costimulation following the inoculation of high numbers of L. major promastigotes. In this study, we show that in the absence of CD28-B7 interactions, BALB/c mice can spontaneously resolve their infections following the inoculation of low numbers of parasites. BALB/c CD28+/+ and CD28-/-mice were inoculated with 250, 500, and 750 metacyclic parasites. The CD28-/- mice controlled their lesions, whereas the wild-type (WT) mice developed progressive nonhealing infections. Resistance to infection was associated with reduced numbers of parasites in the CD28-/- mice compared with the WT mice. Infection of the CD28-/- mice resulted in the activation of a Th1-type response as evidenced by increased levels of mRNA for IFN-gamma and reduced levels of message for IL-4 and IL-10 in draining lymph nodes compared with those in WT mice. Healing of infected CD28-/- mice could also be ablated with anti-CD4 Ab treatment or treatment with anti-IFN-gamma Ab. In addition, healed CD28-/- mice were resistant to a challenge infection with L. major. These results suggest that CD28 costimulation influences the in vivo activation of a Th2-type response in a manner that is dependent on the size of the parasite inoculum.

Differential expression of costimulatory molecules B7-1 and B7-2 on microglial cells induced by Th1 and Th2 cells in organotypic brain tissue

Autoreactive T-cells are involved in demyelination, neurodegeneration, and the recruitment of peripheral macrophages and nonspecific activated T-cells in autoimmune diseases such as multiple sclerosis (MS). The ligation of costimulatory B7 molecules on microglia with CD28/CTLA-4 on T-cells is thought to be crucial to the onset and course of MS and its rodent model experimental autoimmune encephalomyelitis (EAE). It is currently unclear as to how far the nature of infiltrating T-cells has an impact on the expression of the B7 molecules on microglia, the resident antigen-presenting cells (APCs) of the brain. We studied the expression of B7-1 and B7-2 on microglia after encounter with preactivated Th1 and Th2 cells from transgenic mice whose T-cells express a receptor (TCR) either specific to myelin basic protein (MBP) or ovalbumin (OVA) using murine organotypic entorhinal-hippocampal slice cultures (OEHSC). Our main finding was that Th1 cells downregulate the constitutive expression of B7-2 and induce B7-1 expression while Th2 cells do not induce this B7-1 upregulation. The main difference between MBP- and OVA-specific cells was seen in experiments were Th1 cells had direct contact to APCs but not to brain tissue. In contrast to MBP-specific Th1 cells, OVA-specific Th1 cells required the addition of antigen to upregulate B7-1 and downregulate B7-2. When the cells were allowed to have contact to brain tissue, no difference was seen in the pattern of B7 regulation between OVA- and MBP-specific T-cells. Our data suggest that T-cells are able to modulate B7 expression on microglial cells in the brain independent of antigen presentation through TCR/MHC-II ligation but presumably by soluble mediators.