The B7/CD28 costimulatory family in autoimmunity

Tissue-specific expression of B7x protects from CD4 T cell-mediated autoimmunity

B7x, an inhibitory member of the B7/CD28 superfamily, is highly expressed in a broad range of nonhematopoietic organs, suggesting a role in maintaining peripheral tolerance. As endogenous B7x protein is expressed in pancreatic islets, we investigated whether the molecule inhibits diabetogenic responses. Transfer of disease-inducing BDC2.5 T cells into B7x-deficient mice resulted in a more aggressive form of diabetes than in wild-type animals. This exacerbation of disease correlated with higher frequencies of islet-infiltrating Th1 and Th17 cells. Conversely, local B7x overexpression inhibited the development of autoimmunity, as crossing diabetes-susceptible BDC2.5/B6(g7) mice to animals overexpressing B7x in pancreatic islets abrogated disease induction. This protection was caused by the inhibition of IFN-γ production by CD4 T cells and not to a skewing or expansion of Th2 or regulatory T cells. The suppressive function of B7x was also supported by observations from another autoimmune model, experimental autoimmune encephalomyelitis, in which B7x-deficient mice developed exacerbated disease in comparison with wild-type animals. Analysis of central nervous system-infiltrating immune cells revealed that the loss of endogenous B7x resulted in expanded Th1 and Th17 responses. Data from these two autoimmune models provide evidence that B7x expression in the periphery acts as an immune checkpoint to prevent tissue-specific autoimmunity.

The expression and distribution of immunomodulatory proteins B7-H1, B7-DC, B7-H3, and B7-H4 in rheumatoid synovium

CD28/B7 signals have been shown to have the capacity to regulate T cell activation and participate in regulating the development of rheumatoid arthritis (RA). However, the expression and anatomical distribution of some members of the B7 superfamily including B7-H1, B7-DC, B7-H3 and B7-H4 in RA synovium is still unclear. We analyzed the expression of these molecules in synovial tissues from RA patients. Immunohistochemistry showed that all of these molecules were observed in synovium. On the cellular level, all of them were found on cell membrane and in cytoplasma. The expression of B7-DC and B7-H3 was major on capillaries, synovicytes and infiltrated inflammatory cells in the lining layer, while B7-H1 and B7-H4 were detected in some inflammatory cells residing in the sublining and lining layer. Fluorescent dual staining indicated that all these molecules were principally associated with CD31(+) endothelial cells and CD68(+) macrophages. In addition, B7-H1 and B7-H3 were also observed on CD3(+) T cells (including CD4(+) and CD8(+) T cells). Interestingly, B7-H1/B7-H4, B7-H3/B7-DC were co-expressed on the same cells. The characteristic expression and distribution of these molecules in synovium indicated that they probably have different effects during the progress of RA, and a clear understanding of their functional roles may further elucidate the pathogenesis of this disease.

Aberrant production of soluble co-stimulatory molecules CTLA-4 and CD28 in patients with chronic hepatitis B

Co-stimulation signals are critical for anti-viral immunity. Here we investigated whether there is altered expression and the clinical significance of soluble co-stimulatory molecules in patients with chronic HBV infection. Serum concentrations and ex vivo production of soluble CTLA-4, CD28, CD80 and CD86 were analyzed by enzyme-linked immunosorbent assay. Serum sCTLA-4 and sCD28 concentrations in all chronic HBV patients were significantly higher than concentrations in healthy control subjects. Serum sCTLA-4 and sCD28 correlated significantly with alanine aminotransferase in all chronic HBV patients. Upon mitogen stimulation of peripheral blood mononuclear cells, the percentage increases in ex vivo production of sCD28 and sCD80 and the percentage decrease in sCTLA-4 release were all significantly lower in chronic HBV patients than those in healthy subjects. The aberrant production of soluble co-stimulatory molecules should reflect the dysregulation of T cell activation and is related to the pathogenesis and severity of chronic HBV infection.

T cells from Programmed Death-1 deficient mice respond poorly to Mycobacterium tuberculosis infection

BACKGROUND

Programmed Death-1 (PD-1; CD279) receptor molecule is widely believed to be a negative regulator predominantly expressed by exhausted/activated mouse T cells. Upon interaction with its ligands, PD-L1 and PD-L2, PD-1 inhibits activation of T cells and cytokine production, which has been documented in various viral and fungal infections as well as in vitro studies. Therefore, inhibition of T cell responses by PD-1 resulted in disease resistance in a variety of mouse infection models studied heretofore.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we report that PD-1 deficient (PD-1(-/-)) mice infected with Mycobacterium tuberculosis (M. tb) H37Rv by the aerosol route have increased susceptibility as compared with their wild type littermates. Surprisingly, M. tb antigen-specific T cell proliferation was dramatically reduced in PD-1 deficient animals compared with wild-type littermates, and this was due to increased numbers of regulatory T cells (Tregs) and recruitment of mesenchymal stem cells. Furthermore, PD-1(-/-) mice exhibited decreases in the autophagy-induced LC3-B marker protein in macrophages.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that PD-1 does not play an inhibitory role during M. tb infection and instead promotes mycobacterial clearance in mice.

Vstm3 is a member of the CD28 family and an important modulator of T-cell function

Members of the CD28 family play important roles in regulating T-cell functions and share a common gene structure profile. We have identified VSTM3 as a protein whose gene structure matches that of the other CD28 family members. This protein (also known as TIGIT and WUCAM) has been previously shown to affect immune responses and is expressed on NK cells, activated and memory T cells, and Tregs. The nectin-family proteins CD155 and CD112 serve as counter-structures for VSTM3, and CD155 and CD112 also bind to the activating receptor CD226 on T cells and NK cells. Hence, this group of interacting proteins forms a network of molecules similar to the well-characterized CD28-CTLA-4-CD80-CD86 network. In the same way that soluble CTLA-4 can be used to block T-cell responses, we show that soluble Vstm3 attenuates T-cell responses in vitro and in vivo. Moreover, animals deficient in Vstm3 are more sensitive to autoimmune challenges indicating that this new member of the CD28 family is an important regulator of T-cell responses.

Highly specialized role of Forkhead box O transcription factors in the immune system

Recent studies have highlighted a fundamental role for Forkhead box O (Foxo) transcription factors in immune system homeostasis. Initial reports designed to dissect function of individual Foxo isoforms in the immune system were based on in vitro overexpression systems, and these experiments suggested that Foxo1 and Foxo3 are important for growth factor withdrawal-induced cell death. Moreover, Foxo factors importantly regulate basic cell cycle progression, and so the implication was that these factors may control lymphocyte homeostasis, including a critical function in the termination and resolution of an immune response. Most recently, cell-type-specific loss mutants for the different Foxo isoforms have revealed unexpected and highly specialized functions in the control of multiple cell types in the immune system, but they have yet to reveal a role in cell death or proliferation. This review will focus on the recent advances made in the understanding of the many ways that Foxo factors regulate the immune system, including a discussion of how the specialized versus redundant functions of Foxo transcription factors impact immune system homeostasis.

Critical role of transcription factor PU.1 in the expression of CD80 and CD86 on dendritic cells

In this study, we investigated the role of a transcription factor, PU.1, in the regulation of CD80 and CD86 expression in dendritic cells (DCs). A chromatin immunoprecipitation assay revealed that PU.1 is constitutively bound to the CD80 and CD86 promoters in bone marrow-derived DCs. In addition, co-expression of PU.1 resulted in the transactivation of the CD80 and CD86 promoters in a reporter assay. The binding of PU.1 to cis-enhancing regions was confirmed by electromobility gel-shift assay. As expected, inhibition of PU.1 expression by short interfering RNA (siRNA) in bone marrow-derived DCs resulted in marked down-regulation of CD80 and CD86 expression. Moreover, overexpression of PU.1 in murine bone marrow-derived lineage-negative cells induced the expression of CD80 and CD86 in the absence of monocyte/DC-related growth factors and/or cytokines. Based on these results, we conclude that PU.1 is a critical factor for the expression of CD80 and CD86. We also found that subcutaneous injection of PU.1 siRNA or topical application of a cream-emulsified PU.1 siRNA efficiently inhibited murine contact hypersensitivity. Our results suggest that PU.1 is a potential target for the treatment of immune-related diseases.

Emergence of chronic Lyme arthritis: putting the breaks on CD28 costimulation

Lyme disease is a debilitating infection that is caused upon a bite of Borrelia burgdorferi (Bb)-infected ticks. One of the most prominent clinical manifestations is the development of chronic Lyme arthritis. Months after Bb infection, approximately 60% of untreated Lyme patients experience intermittent arthritic attacks that may last for years. The use of the CD28(-/-) mouse in Bb infection has helped to shed light into the mechanisms that govern this inflammatory process, which seems to be tightly regulated. In this current review, the effect of immunoregulation, as well as CD28 deficiency in the development of chronic Lyme arthritis is discussed.

Down-regulation of Z39Ig on macrophages by IFN-gamma in patients with chronic HBV infection

Co-inhibitory signals from the B7 superfamily have been demonstrated to induce T cell dysfunction in chronic HBV infection (CHB). However, the expression and function of Z39Ig, a new inhibitor of the B7 superfamily, is still unclear in CHB. Here immunohistochemical staining showed that Z39Ig was restricted to macrophages and that its level was decreased significantly in CHB patients compared to healthy controls. Moreover, reduced Z39Ig expression was positively correlated with plasma HBV load but was inversely related to serum alanine aminotransaminase levels. Further, Z39Ig mRNA had a negative relation to IFN-gamma in vivo, and IFN-gamma also down-regulated Z39Ig expression on monocyte-derived macrophages (MDMs) in a time- and dose-dependent manner in vitro. Interestingly, Z39Ig expression on MDMs was restored when IFN-gamma neutralizing antibodies were added to the T cell/MDM co-culture system, indicating that the IFN-gamma derived from activated-T cells may contribute to the reduction of Z39Ig in the CHB environment. Our results suggest that T cells can opposite T cell hyporesponsiveness through dampening Z39Ig inhibitory signals from macrophages and thus maintain their anti-viral function in CHB. Therefore, decreasing Z39Ig signals from macrophages could contribute to CHB clinical therapy.

TNFRI is a positive T-cell costimulatory molecule important for the timing of cytokine responses

Tumor necrosis factor (TNF)- and TNF receptor I (TNFRI)-deficient mice are resistant to initiation and show delayed resolution of disease in paradigms of autoimmune disease, but the contribution of TNF/TNFRI signaling to T-cell activation and effector responses has not been determined. In this study, we investigated the role of TNFRI in T-cell receptor (TCR)-mediated T-cell activation in vitro and in vivo using CD3(+)-enriched primary T cells and mice deficient in TNFRI. Following TCR engagement, TNFRI knockout (KO) T cells showed significantly delayed proliferation, cell division, upregulation of interleukin 2 (IL-2) and IL-2 receptor alpha chain (CD25) mRNA and cell-surface expression of CD25 compared with wild-type (WT) cells. Thus, WT and TNFRI KO cells showed equivalent proliferation peaks at 48 and 72 h, respectively. TNFRI KO mice also developed a defective primary T-cell response to ovalbumin and an acute contact hypersensitivity response to oxazolone (4-ethoxymethylene-2-phenyl-2-oxazolin-5-one). However, TNFRI KO splenocytes that were stimulated by TCR engagement in vitro for 96 h produced significantly higher intracellular levels of interferon-gamma (IFN-gamma), IL-2 and TNF-alpha, but not IL-17, compared with WT cells, in correlation with their relatively higher proliferation rate at this time point. Further, TCR-stimulated CD3(+)-enriched TNFRI KO T cells showed similarly higher production and secretion of IFN-gamma and IL-2 compared with WT, suggesting that TNFRI-mediated cytokine regulation might involve a T-cell autonomous effect. Our results show a novel role for TNFRI as a positive T-cell costimulatory molecule that is important for timely T-cell activation and effector cytokine production and the development of primary immune responses in mice.

B7-1/2, but not PD-L1/2 molecules, are required on IL-10-treated tolerogenic DC and DC-derived exosomes for in vivo function

Costimulatory molecules, such as B7-1/2 and PD-L1/2 play an important role in the function of APC. The regulation of the surface levels of costimulatory molecules is one mechanism by which APC maintain the balance between tolerance and immunity. We examined the contributions of B7-1/2 and PD-L1/2 to the function of IL-10-treated, immunosuppressive DC as well as therapeutic exosomes derived from these DC. IL-10 treatment of DC significantly downregulated surface expression of MHC II, B7-1, B7-2, and decreased levels of MHC I and PD-L2. IL-10 treatment of DC resulted in a modified costimulatory profile of DC-secreted exosomes with a reduction in B7-1, PD-L1 and PD-L2. We further demonstrate that absence of B7-1 or B7-2 on donor DC results in a loss of ability of IL-10-treated DC and their exosomes to suppress the delayed-type hypersensitivity response, whereas IL-10-treated DC deficient in PD-L1/2 as well as their secreted exosomes retained the ability to suppress delayed-type hypersensitivity responses. We conclude that B7-1 and B7-2, but not PD-L1 and PD-L2, on IL-10-treated DC and DC-derived exosomes play a critical role in immunosuppressive functions of both DC and exosomes.

Dynamic equilibrium of B7-1 dimers and monomers differentially affects immunological synapse formation and T cell activation in response to TCR/CD28 stimulation

Under steady-state conditions, B7-1 is present as a mixed population of noncovalent dimers and monomers on the cell surface. In this study, we examined the physiological significance of this unique dimer-monomer equilibrium state of B7-1. We demonstrate that altering B7-1 to create a uniformly covalent dimeric state results in enhanced CD28-mediated formation of T cell-APC conjugates. The enhanced T cell-APC conjugate formation correlates with persistent concentration of signaling molecules PKC- and lck at the immunological synapse. In contrast, T cell acquisition of B7-1 from APCs, an event that occurs as a consequence of CD28 engagement with B7-1/B7-2 and is thought to play a role in the dissociation of T cell-APC conjugates, is highly reduced when B7-1 is present in the covalently dimeric state. The ability of covalently dimeric and wild type B7-1 to costimulate Ag-specific T cell proliferation was also assessed. In contrast to the enhanced ability of dimeric B7-1 to support conjugate formation and early parameters of T cell signaling, sensitivity to competitive inhibition by soluble CTLA-4-Ig indicated that the covalent dimeric form of B7-1 is less efficient in costimulating T cell proliferation. These findings suggest a novel model in which optimal T cell costimulatory function of B7-1 requires high-avidity CD28 engagement by dimeric B7-1, followed by dissociation of these noncovalent B7-1 dimers, facilitating downregulation of CD28 and internalization of B7-1. These events regulate signaling through TCR/CD28 to maximize T cell activation to proliferation.

Understanding dendritic cell biology and its role in immunological disorders through proteomic profiling

Dendritic cells (DC) have always been present on the bright spot of immune research. They have been extensively studied for the last 35 years, and much is known about their different phenotypes, stimulatory capacity, and role in the immune system. During the last 15 years, great attention has been given to studies on global gene and protein expression profiles during the differentiation and maturation processes of these cells. It is well understood that studying the proteome, together with information on the role of protein post-translational modifications (PTM), will reveal the real dynamics of a living cell. The rapid increase of proteomic studies during the last decade describing the differentiation and maturation process in DCs, as well as modifications brought by the use of different compounds that either increase or decrease their immunogenicity, reflects the importance of understanding the molecular processes behind the functional properties of these cells. In the present review, we will give an overview of proteomic studies focusing on DCs. Thereby we will concentrate on the importance of these studies in understanding DC behavior from a molecular point of view and how these findings have aided in understanding the differences in functional properties of these cells.

Potential role of decoy B7-H4 in the pathogenesis of rheumatoid arthritis: a mouse model informed by clinical data

BACKGROUND

A pathogenic hallmark of rheumatoid arthritis (RA) is persistent inflammatory responses in target tissues and organs. Immune responses mediated by T cells and autoantibodies are known to play pivotal roles. A possible interpretation for this observation is a loss of negative regulation of autoimmune responses. Here we sought to investigate whether B7-H4, a cell surface inhibitory molecule of the B7-CD28 signaling pathway, may play a role in the pathogenesis of RA.

METHODS AND FINDINGS

In a cross-sectional study of a clinical convenience sample using monoclonal antibodies against human B7-H4 molecules, we detected high levels of the soluble form of B7-H4 (sH4) in the sera of 65% of patients with RA (n = 68) versus only 13% of healthy donors (n = 24). Elevated sH4 was associated with an increased disease severity score (DAS28) in a cross-sectional analysis. In a mouse model of RA, transgenic expression of sH4 or genetic deletion of B7-H4 accelerated the progression of collagen-induced arthritis, accompanied by enhanced T and B cell-mediated autoimmune responses as well as increased activity of neutrophils. Expression in vivo of an agonist, a B7-H4-immunoglobulin Fc fusion protein, profoundly suppressed disease progression in the mouse model.

CONCLUSIONS

Our findings in mice indicate that sH4 acts as a decoy molecule to block the inhibitory functions of cell-surface B7-H4, leading to exacerbation of collagen-induced arthritis. If the preliminary correlation between sH4 levels and disease activity in patients with RA can be confirmed to reflect a similar mechanism, these findings suggest a novel target for treatment approaches. Please see later in the article for the Editors' Summary.

The development and function of regulatory T cells

Regulatory T cells (Tregs) are a critical subset of T cells that mediate peripheral tolerance. There are two types of Tregs: natural Tregs, which develop in the thymus, and induced Tregs, which are derived from naive CD4(+) T cells in the periphery. Tregs utilize a variety of mechanisms to suppress the immune response. While Tregs are critical for the peripheral maintenance of potential autoreactive T cells, they can also be detrimental by preventing effective anti-tumor responses and sterilizing immunity against pathogens. In this review, we will discuss the development of natural and induced Tregs as well as the role of Tregs in a variety of disease settings and the mechanisms they utilize for suppression.

Targeting lymphocyte activation through the lymphotoxin and LIGHT pathways

SUMMARY

Cytokines mediate key communication pathways essential for regulation of immune responses. Full activation of antigen-responding lymphocytes requires cooperating signals from the tumor necrosis factor (TNF)-related cytokines and their specific receptors. LIGHT, a lymphotoxin-beta (LTbeta)-related TNF family member, modulates T-cell activation through two receptors, the herpesvirus entry mediator (HVEM) and indirectly through the LT-beta receptor. An unexpected finding revealed a non-canonical binding site on HVEM for the immunoglobulin superfamily member, B and T lymphocyte attenuator (BTLA), and an inhibitory signaling protein suppressing T-cell activation. Thus, HVEM can act as a molecular switch between proinflammatory and inhibitory signaling. The non-canonical HVEM-BTLA pathway also acts to counter LTbetaR signaling that promotes the proliferation of antigen-presenting dendritic cells (DCs) within lymphoid tissue microenvironments. These results indicate LTbeta receptor and HVEM-BTLA pathways form an integrated signaling circuit. Targeting these cytokine pathways with specific antagonists (antibody or decoy receptor) can alter lymphocyte differentiation and activation. Alternately, agonists directed at their cell surface receptors can restore homeostasis and potentially reset immune and inflammatory processes, which may be useful in treating autoimmune and infectious diseases and cancer.

Impaired CD4 and CD8 effector function and decreased memory T cell populations in ICOS-deficient patients

Interaction of ICOS with its ligand is essential for germinal center formation, T cell immune responses, and development of autoimmune diseases. Human ICOS deficiency has been identified worldwide in nine patients with identical ICOS mutations. In vitro studies of the patients to date have shown only mild T cell defect. In this study, we report an in-depth analysis of T cell function in two siblings with novel ICOS deficiency. The brother displayed mild skin infections and impaired Ig class switching, whereas the sister had more severe symptoms, including immunodeficiency, rheumatoid arthritis, inflammatory bowel disease, interstitial pneumonitis, and psoriasis. Despite normal CD3/CD28-induced proliferation and IL-2 production in vitro, peripheral blood T cells in both patients showed a decreased percentage of CD4 central and effector memory T cells and impaired production of Th1, Th2, and Th17 cytokines upon CD3/CD28 costimulation or PMA/ionophore stimulation. The defective polarization into effector cells was associated with impaired induction of T-bet, GATA3, MAF, and retinoic acid-related orphan nuclear hormone receptor (RORC). Reduced CTLA-4(+)CD45RO(+)FoxP3(+) regulatory T cells and diminished induction of inhibitory cell surface molecules, including CTLA-4, were also observed in the patients. T cell defect was not restricted to CD4 T cells because reduced memory T cells and impaired IFN-gamma production were also noted in CD8 T cells. Further analysis of the patients demonstrated increased induction of receptor activator of NF-kappaB ligand (RANKL), lack of IFN-gamma response, and loss of Itch expression upon activation in the female patient, who had autoimmunity. Our study suggests that extensive T cell dysfunction, decreased memory T cell compartment, and imbalance between effector and regulatory cells in ICOS-deficient patients may underlie their immunodeficiency and/or autoimmunity.

B7 costimulation is critical for host control of chronic Mycobacterium tuberculosis infection

Although much is understood regarding the role of B7/CD28 family of costimulatory molecules in regulating host resistance in the context of several pathogens, analogous information with Mycobacterium tuberculosis is lacking. To address the requirements of B7-mediated costimulation in host resistance against tuberculosis, mice deficient in both B7.1 and B7.2 (B7DKO) were aerosol infected with M. tuberculosis Erdman and disease progression was monitored. We report herein that B7DKO mice are initially able to contain the bacterial load in the lung, but exhibit enhanced susceptibility during chronic infection. Despite the early control of bacterial replication, B7DKO mice essentially start off with compromised Th1 immunity and slower granulomatous response in the lung, characterized by markedly reduced lymphocytic infiltration. As the infection progresses from acute phase to the chronic phase, the nascent granulomas in the B7DKO lungs never fully achieve the architecture of granulomas developing in wild-type mice. Instead, lesions spread progressively to involve much of the lung in the B7DKO mice, ultimately leading to necrosis. Thus, early control of M. tuberculosis growth in the lung can occur in the absence of B7 costimulation and is less dependent on Th1 immunity and formation of a granulomatous structure. However, B7 costimulation is critical for long-term containment of infection within lung granulomas. These findings suggest that the use of costimulation-based immunomodulators may have significant repercussions on the induction of host protective immunity against tuberculosis.

Targeted knock-in mice expressing mutations of CD28 reveal an essential pathway for costimulation

Despite extensive study, the role of phosphatidylinositol 3-kinase (PI3-kinase) activation in CD28 function has been highly contentious. To definitively address this question, we generated knock-in mice expressing mutations in two critical domains of the cytoplasmic tail of CD28. Mutation of the proximal tyrosine motif interrupted PI3-kinase binding and prevented CD28-dependent phosphorylation of protein kinase B (PKB)/Akt; however, there was no detectable effect on interleukin-2 (IL-2) secretion, expression of Bcl-X(L), or on T-cell function in vivo. Furthermore, we demonstrate that signaling initiated by the C-terminal proline motif is directly responsible for tyrosine phosphorylation of phosphoinosotide-dependent kinase 1, protein kinase C theta, and glycogen synthase kinase 3beta, as well as contributing to threonine phosphorylation of PKB. T cells mutated in this domain were profoundly impaired in IL-2 secretion, and the mice had marked impairment of humoral responses as well as less severe disease manifestations in experimental allergic encephalomyelitis. These data demonstrate that the distal proline motif initiates a critical nonredundant signaling pathway, whereas direct activation of PI3-kinase by the proximal tyrosine motif of CD28 is not required for normal T-cell function.

Increased expression of soluble inducible costimulator ligand (ICOSL) in patients with systemic lupus erythematosus

To investigate the level of costimulating molecules in systemic lupus erythematosus (SLE), we assessed the plasma concentrations of soluble forms of costimulatory molecules such as programmed death-1 (PD-1), B7-H1 (also called PD-L1 or CD274) and inducible costimulator ligand (ICOSL) in patients with SLE. Plasma concentrations of soluble PD-1, B7-H1 and ICOSL were measured by ELISA using plasma samples from 57 SLE patients with or without the active disease, 21 rheumatoid arthritis (RA) patients and 35 healthy subjects. We also evaluated surface ICOSL expression on B cells using flow cytometry to gain a better understanding of ICOSL expression. To compare the level of ICOSL mRNA expression, reverse transcriptase-polymerase chain reaction (RT-PCR) was performed using total RNA from peripheral blood mononuclear cells (PBMCs) isolated from eight healthy subjects and 11 patients with SLE. The concentration of plasma ICOSL was significantly higher in patients with SLE compared with healthy subjects ( P = 0.005). Plasma ICOSL concentrations in patients with active SLE were also significantly higher than those of either patients with inactive SLE or patients with RA ( P = 0.001, P = 0.015, respectively). Plasma ICOSL concentrations in patients with SLE correlated modestly with the SLE disease activity index score ( r = 0.298, P = 0.024). We also found a significant inverse correlation between the soluble ICOSL expression and the surface ICOSL expression on B cells ( r = −0.690, P = 0.001). However, ICOSL mRNA levels of patients with SLE were comparable with those of the control subjects. There was also no significant difference in plasma B7-H1 concentrations between groups, and plasma PD-1 was not detectable in any of the groups. The plasma concentration of soluble ICOSL might be correlated to the disease severity of lupus. The increased levels of ICOSL in active lupus suggest that this pathway is involved in the pathogenesis of SLE. The mechanism and physiological role of soluble ICOSL in the pathogenesis of SLE, however, remains to be investigated.

Transcription factor Foxo3 controls the magnitude of T cell immune responses by modulating the function of dendritic cells

Foxo transcription factors regulate cell cycle progression, survival, and DNA repair pathways. Here, we demonstrate that a deficiency in Foxo3 resulted in increased expansion of T cell populations after viral infection. This exaggerated expansion was not T cell intrinsic. Rather, it was caused by the enhanced capacity of Foxo3-deficient dendritic cells to sustain T cell viability by producing increased amounts of interleukin 6 (IL-6). CTLA-4-mediated stimulation of dendritic cells induced nuclear localization of Foxo3, which in turn inhibited IL-6 and tumor necrosis factor production. Thus, Foxo3 acts to constrain dendritic cell production of key inflammatory cytokines and control T cell survival.

Murine dendritic cell antigen-presenting cell function is not altered by burn injury

Severe injury disrupts normal immune regulation causing a transient hyperinflammatory reaction and suppressed adaptive immune function. This report addresses the potential contribution of dendritic cells (DC) to changes in adaptive immune function after injury by specifically measuring injury-induced changes in splenic DC numbers and subsets, cell-surface markers, TLR responses, and APC function. Using a mouse burn injury model, we found that injury did not markedly alter the relative percentage of lymphoid, myeloid, or plasmacytoid DC in the spleens of burn-injured mice. Moreover, we did not observe a significant reduction in cell-surface expression of several major costimulatory molecules, CD40, CD80, CD86, programmed death 1 ligand, ICOS ligand, and B7-H3, on DC. Instead, we observed increased cell-surface expression of CD86 at 1 day after injury with no significant changes in costimulatory molecule expression at 7 days after injury, suggesting that burn injury causes an early activation of DC. In addition, injury did not suppress DC reactivity to TLR2, TLR4, or TLR9 agonists. Most important, DC prepared from injured mice were able to present peptide antigen to naive OTII TCR transgenic CD4+ T cells as efficiently and effectively as DC from sham-injured mice. We also found that CD4 T cells stimulated with antigen presented by DC from sham or burn mice showed similar levels of IL-2, IFN-gamma, IL-10, and IL-13 production. Taken together, these findings support the conclusion that DC do not acquire a suppressive phenotype following severe injury in mice.

Abatacept, a novel CD80/86-CD28 T cell co-stimulation modulator, in the treatment of rheumatoid arthritis

Rheumatoid arthritis is a chronic systemic inflammatory disease with major articular manifestations. While its aetiology still remains to be resolved, our understanding on the pathogenesis of rheumatoid arthritis has become clearer during two decades enlightening the role of adaptative immunity in the development of the symptoms and signs as well as in the progression of the pathological articular changes taking place in inadequately controlled disease. T lymphocytes are considered to be an important cell type in the pathogenesis of rheumatoid arthritis through production of proinflammatory cytokines, promotion of formation of ectopic lymphoid structures and neovascularization in synovial tissue, promotion autoantibody production by B cells, and activation of synoviocytes and osteoclasts. Abatacept, a CTLA4-Ig fusion protein, represents a new therapeutic approach in rheumatoid arthritis. Abatacept attenuates T cell activation as it regulates the activation of T cells by inhibiting the CD80/86:CD28 co-stimulatory pathway that is required for the proper T cell activation. This MiniReview gives an overview on the mechanism of action of abatacept and summarizes the published clinical data on abatacept in the treatment of rheumatoid arthritis.

Dendritic cells in renal biopsies of patients with ANCA-associated vasculitis

BACKGROUND

Dendritic cells (DCs) maintain immune tolerance and are able to initiate immune responses. Their involvement in ANCA-associated vasculitis (AAV) is unknown. In this study, the participation of DC subsets is investigated in renal biopsies of AAV patients.

METHOD

A total of 25 patients with biopsy-proven AAV and five healthy controls (HC) with normal renal histology were included. Renal biopsies were stained for mature (CD208), immature (CD209), plasmacytoid (CD303) and Langerhans (CD1a) DC subsets. Furthermore, T-cells were stained using a T-cell marker (CD3). The interstitial cellular infiltrate was graded semi-quantitatively from 0+ (= absence of cells) to 3+ (= numerous cells). Within the glomeruli, an absolute count was performed for positive cells.

RESULTS

CD208+ and CD209+ cells were found within patients' glomeruli but not in HC (1 +/- 0.3 versus 0.08 +/- 0.1 cells/glom; 2 +/- 0.3 versus 0.1 +/- 0.07 cells/glom). An average of 0.3 +/- 0.1 cell/glom expressed CD3 in patients while few cells were found in HC (0.1 +/- 0.7 cell/glom). Focal interstitial cellular infiltrates were observed in patients' biopsies but not in HC. Interstitial infiltration with CD3+ and CD209+ cells was assessed at an average of 1+, but some glomeruli and tubuli were surrounded by CD3+ and CD209+ cells forming clusters. Serial sections revealed that CD209+ cells were present in CD3+ rich areas.

CONCLUSION

Both mature and immature glomerular DCs are found in renal biopsies of patients with AAV. Immature DCs cluster with T-cells in interstitial infiltrates in these biopsies. Since DCs form aggregates in T-cell areas, we hypothesize that these cells interact with each other and are involved in lymphoid neogenesis.

Semaphorin 6D regulates the late phase of CD4+ T cell primary immune responses

The semaphorin and plexin family of ligand and receptor proteins provides important axon guidance cues required for development. Recent studies have expanded the role of semaphorins and plexins in the regulation of cardiac, circulatory and immune system function. Within the immune system, semaphorins and plexins regulate cell-cell interactions through a complex network of receptor and ligand pairs. Immune cells at different stages of development often express multiple semaphorins and plexins, leading to multivariate interactions, involving more than one ligand and receptor within each functional group. Because of this complexity, the significance of semaphorin and plexin regulation on individual immune cell types has yet to be fully appreciated. In this work, we examined the regulation of T cells by semaphorin 6D. Both in vitro and in vivo T cell stimulation enhanced semaphorin 6D expression. However, semaphorin 6D was only expressed by a majority of T cells during the late phases of activation. Consequently, the targeted disruption of semaphorin 6D receptor-ligand interactions inhibited T cell proliferation at late but not early phases of activation. This proliferation defect was associated with reduced linker of activated T cells protein phosphorylation, which may reflect semaphorin 6D regulation of c-Abl kinase activity. Semaphorin 6D disruption also inhibited expression of CD127, which is required during the multiphase antigen-presenting cell and T cell interactions leading to selection of long-lived lymphocytes. This work reveals a role for semaphorin 6D as a regulator of the late phase of primary immune responses.

Distinct functions of autoreactive memory and effector CD4+ T cells in experimental autoimmune encephalomyelitis

The persistence of human autoimmune diseases is thought to be mediated predominantly by memory T cells. We investigated the phenotype and migration of memory versus effector T cells in vivo in experimental autoimmune encephalomyelitis (EAE). We found that memory CD4(+) T cells up-regulated the activation marker CD44 as well as CXCR3 and ICOS, proliferated more and produced more interferon-gamma and less interleukin-17 compared to effector T cells. Moreover, adoptive transfer of memory T cells into T cell receptor (TCR)alphabeta(-/-) recipients induced more severe disease than did effector CD4(+) T cells with marked central nervous system inflammation and axonal damage. The uniqueness of disease mediated by memory T cells was confirmed by the differential susceptibility to immunomodulatory therapies in vivo. CD28-B7 T cell costimulatory signal blockade by CTLA4Ig suppressed effector cell-mediated EAE but had minimal effects on disease induced by memory cells. In contrast, ICOS-B7h blockade exacerbated effector T cell-induced EAE but protected from disease induced by memory T cells. However, blockade of the OX40 (CD134) costimulatory pathway ameliorated disease mediated by both memory and effector T cells. Our data extend the understanding of the pathogenicity of autoreactive memory T cells and have important implications for the development of novel therapies for human autoimmune diseases.

Revival of CD8+ Treg-mediated suppression

Despite their first recognition almost 40 years ago, CD8(+) 'suppressor' T cells remain poorly characterized. Recent studies of these lymphocytes, now popularly referred to as regulatory CD8(+) T cells (CD8(+) Tregs), have helped clarify their important role in the regulation of autoimmune disease. Here, we review progress related to the identification, phenotype and function of CD8(+) Tregs. We also focus on a newly described subset, CD8alphaalpha(+)TCRalphabeta(+) Tregs, which in mice recognize a T-cell receptor-derived peptide in the context of the class Ib major histocompatibility complex molecule Qa-1. These Tregs target only activated T cells and complement the suppression provided by CD4(+)Foxp3(+) Tregs. Investigations leading to the detailed identification, expansion, maintenance and function of CD8alphaalpha(+) Tregs should result in new therapeutic strategies for human inflammatory diseases.

Cigarette smoke exposure impairs dendritic cell maturation and T cell proliferation in thoracic lymph nodes of mice

Respiratory tract dendritic cells (DCs) are juxtaposed to directly sample inhaled environmental particles. Processing and presentation of these airborne Ags could result in either the development of immunity or tolerance. The purpose of this study was to determine the consequences of cigarette smoke exposure on DC function in mice. We demonstrate that while cigarette smoke exposure decreased the number of DCs in the lungs, Ag-induced DC migration to the regional thoracic lymph nodes was unaffected. However, cigarette smoking suppressed DC maturation within the lymph nodes as demonstrated by reduced cell surface expression of MHC class II and the costimulatory molecules CD80 and CD86. Consequently, DCs from cigarette smoke-exposed animals had a diminished capacity to induce IL-2 production by T cells that was associated with diminished Ag-specific T cell proliferation in vivo. Smoke-induced defects in DC function leading to impaired CD4(+) T cell function could inhibit tumor surveillance and predispose patients with chronic obstructive pulmonary disease to infections and exacerbations.

B7-H4 reverse signaling induces the apoptosis of EBV-transformed B cells through Fas ligand up-regulation

B7-H4 has an inhibitory effect on immune responses via the down-regulation of T cell-mediated immunity, but how the engagement of B7-H4 molecules by counter molecules affects the signaling mechanism of the B7-H4-expressing cells is poorly defined. In this study, we found that B7-H4 expression was enhanced on B cells infected with Epstein-Barr virus (EBV) and that triggering of these molecules induced apoptosis of EBV-transformed B cells. Engagement of B7-H4 initially increased intracellular level of ROS, which then induced the expression of FasL. Engagement of B7-H4 subsequently provoked Fas-mediated and caspase-dependent apoptosis in association with cytochrome c and AIF, and EndoG was released from the mitochondria on EBV-transformed B cells. These results suggest that B7-H4 may be a potential therapeutic target for EBV involved malignancy diseases.

Quantitative analysis of T cell homeostatic proliferation

T cell homeostatic proliferation occurs on transfer of T cells into lymphopenic recipients; transferred cells undergo several rounds of division in the absence of specific antigen stimulation. For a quantitative analysis of this phenomenon, we applied a mathematical method to describe proliferating T cells to match peak distributions from actual CFSE dilution data. For in vitro stimulation of T cells with anti-CD3/anti-CD28, our simulation confirmed a high proportion of cells entering cell cycle with a low proportion undergoing apoptosis. When applied to homeostatic proliferation, it described striking differences in CD4 and CD8 T cell proliferation rates, and accurately predicted that successive divisions were accompanied by higher rates of apoptosis, limiting the accumulation of proliferating cells. Thus, the presence of multiple CFSE dilution peaks cannot be considered equivalent to lymphocyte expansion. Finally, genetic effects were identified that may help explain links between homeostatic proliferation and autoimmunity.

Limited costimulatory molecule expression on renal tubular epithelial cells impairs T cell activation

BACKGROUND/AIMS

MHC molecules are upregulated on renal proximal tubular epithelial cells (TEC) under inflammatory conditions. This allows TEC to act as 'non-professional' antigen-presenting cells (APC). The aim of this study was to compare the costimulatory molecule expression pattern and the T cell activation capacity between renal TEC and professional APC, e.g. bone marrow-derived dendritic cells (BM-DC).

METHODS

Flow cytometry analysis was used to study the costimulatory molecule surface expression on TEC or BM-DC. Ovalbumin-specific CD4 and CD8 T cell activation induced by TEC or BM-DC was compared, in terms of T cell proliferation, cytokine production and CTL activity.

RESULTS

TEC did not constitutively express significant amounts of costimulatory molecules. Stimulation of TEC with IFN-beta or IFN-gamma, but not other tested cytokines, enhanced the expression of PD-L1, ICOS-L and CD40. Compared to BM-DC, TEC only induced suboptimal T cell activation. Blockade of PD-L1 on both APC strongly increased T cell activity. Furthermore, high PD-L1-expressing TEC were more resistant to the cytolysis by CTL.

CONCLUSION

The low costimulatory molecule expression may explain the suboptimal T cell activation by TEC. The IFN-upregulated negative costimulatory molecule PD-L1 on TEC may play a protective role to limit tissue injury during renal parenchymal immune responses.

Oxidative stress causes bone loss in estrogen-deficient mice through enhanced bone marrow dendritic cell activation

Increased production of tumor necrosis factor alpha (TNF) in the bone marrow (BM) in response to both oxidative stress and T cell activation contributes to the bone loss induced by estrogen deficiency, but it is presently unknown whether oxidative stress causes bone loss through T cells. Here we show that ovariectomy causes an accumulation in the BM of reactive oxygen species, which leads to increased production of TNF by activated T cells through up-regulation of the costimulatory molecule CD80 on dendritic cells. Accordingly, bone loss is prevented by treatment of ovariectomized mice with either antioxidants or CTLA4-Ig, an inhibitor of the CD80/CD28 pathway. In summary, reactive oxygen species accumulation in the BM is an upstream consequence of ovariectomy that leads to bone loss by activating T cells through enhanced activity of BM dendritic cells, and these findings suggest that the CD80/CD28 pathway may represent a therapeutic target for postmenopausal bone loss.

ICOS gene haplotypes correlate with IL10 secretion and multiple sclerosis evolution

Human ICOS is a T cell costimulatory molecule supporting IL10 secretion. A pilot study investigating variations of the ICOS gene 3'UTR detected 8 polymorphisms forming three haplotypes (A, B, C). Haplotype-A and -C displayed the highest difference. Activated T cells from healthy AA homozygotes expressed significantly less ICOS and secreted more IL10 than AC heterozygotes, whereas AB heterozygotes displayed intermediate levels. Analysis of 441 multiple sclerosis patients and 793 controls showed that frequency of AA homozygosity was significantly lower in MS patients with relapsing-remitting onset (N=416) than in controls (OR=0.70). Moreover, AA patients with relapsing-remitting onset had lower relapse rate and multiple sclerosis severity score than non-AA patients.

T cells and B cells in lupus nephritis

T and B lymphocytes play diverse roles at multiple stages in the development and progression of lupus nephritis. Disruption of T- and B-cell regulatory functions by environmental and genetic influences permits pathogenic effectors to emerge in disease. New insights into the biology of these multifunctional cells offer novel targets for intervention in lupus nephritis and systemic autoimmunity.

Limited peripheral T cell anergy predisposes to retinal autoimmunity

Autoimmune uveoretinitis accounts for at least 10% of worldwide blindness, yet it is unclear why tolerance to retinal Ags is so fragile and, particularly, to what extent this might be due to defects in peripheral tolerance. To address this issue, we generated double-transgenic mice expressing hen egg lysozyme, under the retinal interphotoreceptor retinoid-binding promoter, and a hen egg lysozyme-specific CD4(+) TCR transgene. In this manner, we have tracked autoreactive CD4(+) T cells from their development in the thymus to their involvement in uveoretinitis and compared tolerogenic mechanisms induced in a variety of organs to the same self-Ag. Our findings show that central tolerance to retinal and pancreatic Ags is qualitatively similar and equally dependent on the transcriptional regulator protein AIRE. However, the lack of Ag presentation in the eye-draining lymph nodes results in a failure to induce high levels of T cell anergy. Under these circumstances, despite considerable central deletion, low levels of retinal-specific autoreactive CD4(+) T cells can induce severe autoimmune disease. The relative lack of anergy induction by retinal Ags, in contrast to the same Ag in other organs, helps to explain the unique susceptibility of the eye to spontaneous and experimentally induced autoimmune disease.

Resveratrol and curcumin suppress immune response through CD28/CTLA-4 and CD80 co-stimulatory pathway

The role of resveratrol and curcumin is well documented in cancer, inflammation, diabetes and various other diseases. However, their immunosuppressive action on T cells, B cells and macrophages is not well documented. In the present study, we have ascertained the effect of resveratrol and curcumin on T and B cells and macrophages. The most striking findings were that both resveratrol and curcumin suppressed the activity of T and B cells and macrophages, as evidenced by significant inhibition in proliferation, antibody production and lymphokine secretion. Interestingly, curcumin imparted immunosuppression by mainly down-regulating the expression of CD28 and CD80 and up-regulating CTLA-4. Resveratrol also functioned by decreasing the expression of CD28 and CD80, as well as by augmenting the production of interleukin (IL)-10.

Suppression of immune responses in collagen-induced arthritis by a rationally designed CD80-binding peptide agent

OBJECTIVE

The CD80/CD86-CD28/CD152 costimulatory pathways transmit signals for CD4+ T cell activation and suppression and are critically involved in the pathogenesis of rheumatoid arthritis (RA). A significant number of CD4+ T cells and macrophages in the rheumatoid synovium express elevated levels of CD80, increasing the potential for costimulation in trans of naive T cells. To determine the effect of blockade of this costimulatory axis in RA, we designed novel CD80-binding peptides and evaluated their therapeutic potential in collagen-induced arthritis (CIA), an animal model of RA.

METHODS

The conserved MYPPPY motif of CD152 adopts a polyproline type II (PPII) helical conformation in the CD80-CD152 complex. The pairing preferences of the critical residues at the CD80-CD152 interface and their propensity to form PPII helices were integrated to design peptides with optimum PPII helical content that selectively block CD80-receptor interactions. The clinical efficacy was tested in DBA/1LacJ mice that were administered the CD80 blocking agents, called CD80-binding competitive antagonist peptides (CD80-CAPs), at the time of immunization with bovine type II collagen or 3 weeks after immunization.

RESULTS

A single administration of select CD80-CAPs significantly reduced the clinical, radiologic, and histologic disease severity in CIA. Importantly, administration of CD80-CAPs during activated immune response significantly suppressed disease development by reducing mononuclear cell infiltration in the joints and mediating peripheral deletion of activated CD4+ T cells.

CONCLUSION

A rationally designed CD80-binding peptide both prevents and suppresses CIA, suggesting a potential application in RA. Apoptosis of activated CD4+ T cells following in vivo blockade suggests that the effects of CD80-CAPs may be long-lasting.

Genetics of autoimmune diseases--disorders of immune homeostasis

In the past few years, our extensive knowledge of the mammalian immune system and our increasing ability to understand the genetic causes of complex human disease have opened a window onto the pathways that lead to autoimmune disorders. In addition to the well-established role of genetic variation that affects the major histocompatibility complex, a number of rare and common variants that affect a range of immunological pathways are now known to have important influences on the phenotypic diversity that is seen among autoimmune diseases. Recent studies have also highlighted a previously unanticipated interplay between the innate and adaptive immune system, providing a new direction for research in this field.

Microarray analysis of gene expression in peripheral blood mononuclear cells from dioxin-exposed human subjects

Tetrachlorodibenzo-p-dioxin (TCDD) is classified as a human carcinogen and exerts toxic effects on the skin (chloracne). Effects on reproductive, immunological, and endocrine systems have also been observed in animal models. TCDD acts through the aryl hydrocarbon receptor (AhR) pathway influencing largely unknown gene networks. An industrial accident in Seveso, Italy in 1976 exposed thousands of people to substantial quantities of TCDD. Twenty years after the exposure, this study examines global gene expression in the mononuclear cells of 26 Seveso female never smokers, with similar age, alcohol consumption, use of medications, and background plasma levels of 22 dioxin congeners unrelated to the Seveso accident. Plasma dioxin levels were still elevated in the exposed subjects. We performed analyses in two different comparison groups. The first included high-exposed study subjects compared with individuals with background TCDD levels (average plasma levels 99.4 and 6.7ppt, respectively); the second compared subjects who developed chloracne after the accident, and those who did not develop this disease. Overall, we observed a modest alteration of gene expression based on dioxin levels or on chloracne status. In the comparison between high levels and background levels of TCDD, four histone genes were up-regulated and modified expression of HIST1H3H was confirmed by real-time PCR. In the comparison between chloracne case-control subjects, five hemoglobin genes were up-regulated. Pathway analysis revealed two major networks for each comparison, involving cell proliferation, apoptosis, immunological and hematological disease, and other pathways. Further examination of the role of these genes in dioxin induced-toxicity is warranted.

Role of CEACAM1 as a Regulator of T Cells

A major immunological attribute of inflammatory bowel disease (IBD) is the presence of unrestrained activation of T cells that produce a variety of inflammatory cytokines and other mediators. Gaining an understanding of T cell regulation is therefore of major importance to IBD. Carcinoembryonic antigen-related cell adhesion molecule 1 CEACAM1) is a novel protein that has been recently recognized as being expressed by immune cells and T lymphocytes, in particular; this protein appears to function as a coinhibitory receptor after T cell activation. Ligation of CEACAM1 on T cells induces a signal cascade that leads inhibition of T cell cytokine production and IBD. CEACAM1 is thus a novel potential therapeutic target in the treatment of IBD.

Dendritic cells in a mature age

A common view supposes that dendritic cells (DCs) exist in two basic functional states: immature DCs induce tolerance to self, whereas mature DCs induce immunity to foreign antigens. However, the term 'mature' is often used not only functionally to designate immunogenic DCs but also as a phenotypic description of DCs expressing high levels of MHC, adhesion and co-stimulatory molecules. The recent realization that DCs can express such markers under non-immunogenic conditions raises the question of whether the two connotations of the term 'mature' should continue to be used interchangeably. Here, I discuss the origins of the maturation model and how terminology is evolving to better accommodate our current understanding of the function of DCs.