Homeostatic expansion of T cells during immune insufficiency generates autoimmunity

NFKBIL1 confers resistance to experimental autoimmune arthritis through the regulation of dendritic cell functions

We and others have reported that human NF-κB inhibitor-like-1 (NFKBIL1) was a putative susceptible gene for autoimmune diseases such as rheumatoid arthritis (RA). However, its precise role in the pathogenesis of RA is still largely unknown. In this study, we generated transgenic mice expressing human NFKBIL1 (NFKBIL1-Tg) and examined whether NFKBIL1 plays some role(s) in the development of autoimmune arthritis. In both a collagen-induced arthritis model and a collagen antibody-induced arthritis model, NFKBIL1-Tg mice showed resistance to arthritis compared to control mice, indicating that the gene product of NFKBIL1 was involved in the control of thusly induced arthritis. Total spleen cells of NFKBIL1-Tg mouse showed decreased proliferation to mitogenic stimuli, consistent with its resistance to arthritis. Unexpectedly, purified T cells of NFKBIL1-Tg mouse showed increased proliferation and cytokine production. This apparent discrepancy was accounted for by the impaired functions of antigen-presenting cells of NFKBIL1-Tg mouse; both T/B cell-depleted spleen cells and bone marrow-derived dendritic cells of the Tg mouse induced less prominent proliferation and IL-2 production of T cells. Furthermore, dendritic cells (DCs) derived from NFKBIL1-Tg mouse showed lower expression of co-stimulatory molecules and decreased production of inflammatory cytokines when they were activated by lipopolysaccharide. Taken together, these results indicated that NFKBIL1 affected the pathogenesis of RA at least in part through the regulation of DC functions.

Autoreactive cytotoxic T lymphocytes acquire higher expression of cytotoxic effector markers in the islets of NOD mice after priming in pancreatic lymph nodes

Cytotoxic T lymphocytes (CTLs) that cause type 1 diabetes are activated in draining lymph nodes and become concentrated as fully active CTLs in inflamed pancreatic islets. It is unclear whether CTL function is driven by signals received in the lymph node or also in the inflamed tissue. We studied whether the development of cytotoxicity requires further activation in islets. Autoreactive CTLs found in the islets of diabetes-prone NOD mice had acquired much higher expression of the cytotoxic effector markers granzyme B, interferon γ, and CD107a than had those in the pancreatic lymph node (PLN). Increased expression seemed to result from stimulation in the islet itself. T cells held up from migrating from the PLN by administration of the sphingosine-1-phosphate agonist FTY720 did not increase expression of cytotoxic molecules in the PLN. Stimulation did not require antigen presentation or cytokine secretion by the target β cells because it was not affected by the absence of class I major histocompatibility complex expression or by the overexpression of suppressor of cytokine signaling-1. Activation of CD40-expressing cells stimulated increased CTL function and β-cell destruction, suggesting that signals derived from CD40-expressing cells promote the acquisition of cytotoxicity in the islet environment. These data provide in vivo evidence that stimulation of cytotoxic effector molecule expression occurs in inflamed islets and is independent of β cells.

Secondary autoimmune diseases occurring after HSCT for an autoimmune disease: a retrospective study of the EBMT Autoimmune Disease Working Party

To specify the incidence and risk factors for secondary autoimmune diseases (ADs) after HSCT for a primary AD, we retrospectively analyzed AD patients treated by HSCT reported to EBMT from 1995 to 2009 with at least 1 secondary AD (cases) and those without (controls). After autologous HSCT, 29 of 347 patients developed at least 1 secondary AD within 21.9 (0.6-49) months and after allogeneic HSCT, 3 of 16 patients. The observed secondary ADs included: autoimmune hemolytic anemia (n = 3), acquired hemophilia (n = 3), autoimmune thrombocytopenia (n = 3), antiphospholipid syndrome (n = 2), thyroiditis (n = 12), blocking thyroid-stimulating hormone receptor antibody (n = 1), Graves disease (n = 2), myasthenia gravis (n = 1), rheumatoid arthritis (n = 2), sarcoidosis (n = 2), vasculitis (n = 1), psoriasis (n = 1), and psoriatic arthritis (n = 1). After autologous HSCT for primary AD, the cumulative incidence of secondary AD was 9.8% ± 2% at 5 years. Lupus erythematosus as primary AD, and antithymocyte globulin use plus CD34(+) graft selection were important risk factors for secondary AD by multivariate analysis. With a median follow-up of 6.2 (0.54-11) years after autologous HSCT, 26 of 29 patients with secondary AD were alive, 2 died during their secondary AD (antiphospholipid syndrome, hemophilia), and 1 death was HSCT-related. This European multicenter study underlines the need for careful management and follow-up for secondary AD after HSCT.

Reduced IL-2 expression in NOD mice leads to a temporal increase in CD62Llo FoxP3+ CD4+ T cells with limited suppressor activity

IL-2 plays a critical role in the induction and maintenance of FoxP3-expressing regulatory T cells (FoxP3(+) Tregs). Reduced expression of IL-2 is linked to T-cell-mediated autoimmune diseases such as type 1 diabetes (T1D), in which an imbalance between FoxP3(+) Tregs and pathogenic T effectors exists. We investigated the contribution of IL-2 to dysregulation of FoxP3(+) Tregs by comparing wildtype NOD mice with animals congenic for a C57BL/6-derived disease-resistant Il2 allele and in which T-cell secretion of IL-2 is increased (NOD.B6Idd3). Although NOD mice exhibited a progressive decline in the frequency of CD62L(hi) FoxP3(+) Tregs due to an increase in CD62L(lo) FoxP3(+) Tregs, CD62L(hi) FoxP3(+) Tregs were maintained in the pancreatic lymph nodes and islets of NOD.B6Idd3 mice. Notably, the frequency of proliferating CD62L(hi) FoxP3(+) Tregs was elevated in the islets of NOD.B6Idd3 versus NOD mice. Increasing levels of IL-2 in vivo also resulted in larger numbers of CD62L(hi) FoxP3(+) Tregs in NOD mice. These results demonstrate that IL-2 influences the suppressor activity of the FoxP3(+) Tregs pool by regulating the balance between CD62L(lo) and CD62L(hi) FoxP3(+) Tregs. In NOD mice, reduced IL-2 expression leads to an increase in nonsuppressive CD62L(lo) FoxP3(+) Tregs, which in turn correlates with a pool of CD62L(hi) FoxP3(+) Tregs with limited proliferation.

Thymus-specific serine protease controls autoreactive CD4 T cell development and autoimmune diabetes in mice

Type 1 diabetes is a chronic autoimmune disease in which genetic predispositions affect the immune system, leading to a loss of T cell tolerance to β cells and consequent T cell-mediated destruction of insulin-producing islet cells. Genetic studies have suggested that PRSS16 is linked to a diabetes susceptibility locus of the extended HLA class I region in humans. PRSS16 encodes what we believe to be a novel protease, thymus-specific serine protease (TSSP), which shows predominant expression in thymic epithelial cells and is suspected to have a restricted role in the class II presentation pathway. Consistently, Tssp is necessary for the intrathymic selection of few class II-restricted T cell receptor specificities in B6 mice. To directly assess the role of Tssp in autoimmune diabetes, we generated Tssp-deficient (Tssp°) NOD mice. While remaining immunocompetent, Tssp° NOD mice were protected from diabetes and severe insulitis. Diabetes resistance of Tssp° NOD mice was a property of the CD4 T cell compartment that is acquired during thymic selection and correlated with an impaired selection of CD4 T cells specific for islet antigens. Hence, in the NOD mouse, Tssp is a critical regulator of diabetes development through the selection of the autoreactive CD4 T cell repertoire.

Programmed death-1 is required for systemic self-tolerance in newly generated T cells during the establishment of immune homeostasis

Lymphopenia driven T cell activation is associated with autoimmunity. That lymphopenia does not always lead to autoimmunity suggests that control mechanisms may exist. We assessed the importance of the co-inhibitory receptor programmed death-1 (PD-1) in the control of lymphopenia-driven autoimmunity in newly generated T cells vs. established peripheral T cells and in thymic selection. PD-1 was not required for negative selection in the thymus or for maintenance of self tolerance following transfer of established PD-1⁻/⁻ peripheral T cells to a lymphopenic host. In contrast, PD-1 was essential for systemic self tolerance in newly generated T cells under lymphopenic conditions, as PD-1⁻/⁻ recent thymic emigrants (RTE), generated after transfer of PD-1⁻/⁻ hematopoietic stem cell (HSC) precursors or thymocytes into lymphopenic adult Rag⁻/⁻ recipients, induced a rapidly lethal multi-organ inflammatory disease. Disease could be blocked by using lymph node deficient recipients, indicating that lymphopenia driven PD-1⁻/⁻ T cell activation required access to sufficient lymph node stroma. These data suggested that PD-1⁻/⁻ mice themselves might be substantially protected from autoimmunity because their T cell repertoire is first generated early in life, a period naturally deficient in lymph node stroma. Consistent with this idea, neonatal Rag⁻/⁻ recipients of PD-1⁻/⁻ HSC were resistant to disease. Thus, a critical role of PD-1 resides in the control of RTE in lymphopenia. The data suggest that PD-1 and a paucity of lymphoid stroma cooperate to control autoimmunity in newly generated T cells. Clinical therapies for autoimmune disease employing lymphoablation and hematopoietic stem cell transplantation will need to take into account functional polymorphisms in the PD-1 pathway, if the treatment is to ameliorate rather than exacerbate autoimmunity.

Exposure to IL-15 and IL-21 enables autoreactive CD8 T cells to respond to weak antigens and cause disease in a mouse model of autoimmune diabetes

Autoreactive CD8(+) T lymphocytes play a key role in the pathogenesis of several autoimmune diseases. It is not yet well understood how autoreactive CD8(+) T cells, which express TCRs with low reactivity toward self-Ags, gain the ability to respond to autoantigens to cause disease. Previously, we have shown that prior stimulation of CD8(+) T cells with synergistic combinations of cytokines produced by the innate immune response, such as IL-21 and IL-15, induces Ag-independent proliferation. Such "cytokine-primed" CD8 T cells displayed increased responsiveness to limiting quantities of the cognate Ag. In this paper, we report that prior stimulation with IL-15 and IL-21 also enables CD8(+) T cells to respond to weakly agonistic TCR ligands, resulting in proliferation, cytokine secretion, and cytolytic activity. Using a transgenic mouse model of autoimmune diabetes, we show that cytokine-primed autoreactive CD8(+) T cells induce disease following stimulation by weak TCR ligands, but their diabetogenic potential is dependent on continuous availability of IL-15 in vivo. These findings suggest that inflammatory cytokines could facilitate the triggering of autoreactive CD8(+) T cells by weak autoantigens, and this mechanism may have important implications for autoimmune diseases associated with microbial infections and chronic inflammation.

IL-18 is required for self-reactive T cell expansion in NOD mice

IL-18 has a well-established role in pro-inflammatory responses in the islets in type 1 diabetes. Here, we identify a distinctive role for IL-18 in expanding pathogenic T cells in the periphery of NOD mice. Well in advance of disease onset, the periphery of IL-18-deficient mice exhibits reduced T cell turnover, an increased prevalence of naïve and quiescent T cells, emergence of fewer effector T cells, and disease protection. Islet-reactive T cells fail to become activated in the lymphoid organs of mice lacking IL-18 and their rapid expansion is inhibited. IL-18 secretion by antigen presenting cells increases with advancing disease and is required for expression of its receptor on T cells. Our results demonstrate that induction of the IL-18 receptor reflects a critical stage of autoreactive T cell activation and expansion on the pathway toward effector T cell differentiation. This study therefore assigns a novel role to IL-18 for expanding the pool of islet-destructive T cells during pre-diabetes. This report highlights a new basic mechanism in type 1 diabetes pathogenesis and suggests that targeting the IL-18 pathway should be explored as a potential treatment strategy.

Cell-to-cell interactions and signals involved in the reconstitution of peripheral CD8 T(CM) and T(EM) cell pools

We here describe novel aspects of CD8⁺ and CD4⁺ T cell subset interactions that may be clinically relevant and provide new tools for regulating the reconstitution of the peripheral CD8⁺ T cell pools in immune-deficient states. We show that the reconstitution capacity of transferred isolated naïve CD8⁺ T cells and their differentiation of effector functions is limited, but both dramatically increase upon the co-transfer of CD4⁺ T cells. This helper effect is complex and determined by multiple factors. It was directly correlated to the number of helper cells, required the continuous presence of the CD4⁺ T cells, dependent on host antigen-presenting cells (APCs) expressing CD40 and on the formation of CD4/CD8/APC cell clusters. By comparing the recovery of (CD44⁺CD62L^high) T_CM and (CD44⁺CD62L^low) T_EM CD8⁺ T cells, we found that the accumulation of T_CM and T_EM subsets is differentially regulated. T_CM-cell accumulation depended mainly on type I interferons, interleukin (IL)-6, and IL-15, but was independent of CD4⁺ T-cell help. In contrast, T_EM-cell expansion was mainly determined by CD4⁺ T-cell help and dependent on the expression of IL-2Rβ by CD8 cells, on IL-2 produced by CD4⁺ T-cells, on IL-15 and to a minor extent on IL-6.

Targeting interleukin-21 in inflammatory diseases

INTRODUCTION

IL-21, a new member of the type 1 cytokine superfamily, is produced by various subsets of CD4(+) T cells and binds to a composite receptor that consists of a specific receptor, termed IL-21 receptor and the common γ-chain subunit. Initially considered to be a critical regulator of T and B cell function, IL-21 is now known to regulate the activity of many other cell types, including both immune and non-immune cells.

AREAS COVERED

In this review, we discuss the biological features of IL-21 and summarize recent advances in the pathogenic role of IL-21 in chronic inflammatory diseases. Moreover, we discuss why IL-21 blockers can have a place in the therapeutic armamentarium for patients with immune-mediated diseases and the potential risks of such treatments.

EXPERT OPINION

Data emerging from studies in human and experimental models of autoimmunity suggest that IL-21 is critically involved in the initiation and/or progression of inflammatory reactions where self-reactive immune cells or antibodies cause damage in tissue. Thus, theoretically, targeting IL-21 could help attenuate the activation of inflammatory pathways and facilitate the resolution of tissue damaging immune responses. However, one should also take into consideration some potential risks that could derive from the blockade of IL-21.

Interleukin-21 is critically required in autoimmune and allogeneic responses to islet tissue in murine models

OBJECTIVE

Type 1 diabetes is an incurable chronic autoimmune disease. Although transplantation of pancreatic islets may serve as a surrogate source of insulin, recipients are subjected to a life of immunosuppression. Interleukin (IL)-21 is necessary for type 1 diabetes in NOD mice. We examined the efficacy of an IL-21-targeted therapy on prevention of diabetes in NOD mice, in combination with syngeneic islet transplantation. In addition, we assessed the role of IL-21 responsiveness in islet allograft rejection in mouse animal models.

RESEARCH DESIGN AND METHODS

NOD mice were treated with IL-21R/Fc, an IL-21-neutralizing chimeric protein. This procedure was combined with syngeneic islet transplantation to treat diabetic NOD mice. Survival of allogeneic islet grafts in IL-21R-deficient mice was also assessed.

RESULTS

Evidence is provided that IL-21 is continually required by the autoimmune infiltrate, such that insulitis was reduced and reversed and diabetes inhibited by neutralization of IL-21 at a late preclinical stage. Recovery from autoimmune diabetes was achieved by combining neutralization of IL-21 with islet transplantation. Furthermore, IL-21-responsiveness by CD8+ T-cells was sufficient to mediate islet allograft rejection.

CONCLUSIONS

Neutralization of IL-21 in NOD mice can inhibit diabetes, and when paired with islet transplantation, this therapeutic approach restored normoglycemia. The influence of IL-21 on a graft-mounted immune response was robust, since the absence of IL-21 signaling prevented islet allograft rejection. These findings suggest that therapeutic manipulation of IL-21 may serve as a suitable treatment for patients with type 1 diabetes.

Recurrence of autoimmunity in pancreas transplant patients: research update

Type 1 diabetes is an autoimmune disorder leading to loss of pancreatic β-cells and insulin secretion, followed by insulin dependence. Islet and whole pancreas transplantation restore insulin secretion. Pancreas transplantation is often performed together with a kidney transplant in patients with end-stage renal disease. With improved immunosuppression, immunological failures of whole pancreas grafts have become less frequent and are usually categorized as chronic rejection. However, growing evidence indicates that chronic islet autoimmunity may eventually lead to recurrent diabetes, despite immunosuppression to prevent rejection. Thus, islet autoimmunity should be included in the diagnostic work-up of graft failure and ideally should be routinely assessed pretransplant and on follow-up in Type 1 diabetes recipients of pancreas and islet cell transplants. There is a need to develop new treatment regimens that can control autoimmunity, as this may not be effectively suppressed by conventional immunosuppression.

The incidence of type-1 diabetes in NOD mice is modulated by restricted flora not germ-free conditions

In the NOD mouse, the incidence of type-1 diabetes is thought to be influenced by the degree of cleanliness of the mouse colony. Studies collectively demonstrate that exposure to bacterial antigen or infection in the neonatal period prevents diabetes [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], supporting the notion that immunostimulation can benefit the maturation of the postnatal immune system [11]. A widely accepted extrapolation from this data has been the notion that NOD mice maintained under germ-free conditions have an increased incidence of diabetes. However, evidence supporting this influential concept is surprisingly limited [12]. In this study, we demonstrate that the incidence of diabetes in female NOD mice remained unchanged under germ-free conditions. By contrast, a spontaneous monoculture with a gram-positive aerobic spore-forming rod delayed the onset and reduced the incidence of diabetes. These findings challenge the view that germ-free NOD mice have increased diabetes incidence and demonstrate that modulation of intestinal microbiota can prevent the development of type-1 diabetes.

Elevated mitochondrial superoxide disrupts normal T cell development, impairing adaptive immune responses to an influenza challenge

Reactive oxygen species (ROS) are critical in a broad spectrum of cellular processes including signaling, tumor progression, and innate immunity. The essential nature of ROS signaling in the immune systems of Drosophila and zebrafish has been demonstrated; however, the role of ROS, if any, in mammalian adaptive immune system development and function remains unknown. This work provides the first clear demonstration that thymus-specific elevation of mitochondrial superoxide (O(2)(•-)) disrupts normal T cell development and impairs the function of the mammalian adaptive immune system. To assess the effect of elevated mitochondrial superoxide in the developing thymus, we used a T-cell-specific knockout of manganese superoxide dismutase (i.e., SOD2) and have thus established a murine model to examine the role of mitochondrial superoxide in T cell development. Conditional loss of SOD2 led to increased superoxide, apoptosis, and developmental defects in the T cell population, resulting in immunodeficiency and susceptibility to the influenza A virus H1N1. This phenotype was rescued with mitochondrially targeted superoxide-scavenging drugs. These findings demonstrate that loss of regulated levels of mitochondrial superoxide lead to aberrant T cell development and function, and further suggest that manipulations of mitochondrial superoxide levels may significantly alter clinical outcomes resulting from viral infection.

Local microbleeding facilitates IL-6- and IL-17-dependent arthritis in the absence of tissue antigen recognition by activated T cells

Local microbleeding induces the accumulation of Th17 cells and the development of IL-17– and IL-6–dependent arthritis in the absence of cognate antigen recognition by CD4⁺ T cells.

Cognate antigen recognition by CD4⁺ T cells is thought to contribute to the tissue specificity of various autoimmune diseases, particularly those associated with class II MHC alleles. However, we show that localized class II MHC–dependent arthritis in F759 mice depends on local events that result in the accumulation of activated CD4⁺ T cells in the absence of cognate antigen recognition. In this model, transfer of in vitro polarized Th17 cells combined with the induction of experimental microbleeding resulted in CCL20 production, the accumulation of T cells in the joints, and local production of IL-6. Disease induction required IL-17A production by transferred T cells, IL-6 and CCL20 expression, and STAT3 signaling in type I collagen–expressing cells. Our data suggest a model in which the development of autoimmune disease in F759 mice depends on four events: CD4⁺ T cell activation regardless of antigen specificity, local events that induce T cell accumulation, enhanced sensitivity to T cell–derived cytokines in the tissue, and activation of IL-6 signaling in the tissue. This model provides a possible explanation for why tissue-specific antigens recognized by activated CD4⁺ T cells have not been identified in many autoimmune diseases, especially those associated with class II MHC molecules.

T lymphocytes apoptosis and mitochondrial membrane potential in Down's syndrome

The increased susceptibility to infection, malignancies, and autoimmune disease, suggest that immunodeficiency is an integral part of Down's syndrome (DS). Little is known about the mitochondrial damage and tendency to apoptosis in peripheral T lymphocyte cells in DS. We studied 30 children with DS and 30 normal children, 15 of each group having no evidence of acute infection and 15 with acute infection. Potential apoptosis and membrane mitochondrial potential (MMP) were measured by flow cytometry. T lymphocytes in peripheral blood from DS patients do not display an increased tendency to undergo apoptosis, although a significant loss of MMP was found.

Specific elimination of effector memory CD4+ T cells due to enhanced Fas signaling complex formation and association with lipid raft microdomains

Elimination of autoreactive CD4(+) T cells through the death receptor Fas/CD95 is an important mechanism of immunological self-tolerance. Fas deficiency results in systemic autoimmunity, yet does not affect the kinetics of T-cell responses to acute antigen exposure or infection. Here we show that Fas and TCR-induced apoptosis are largely restricted to CD4(+) T cells with an effector memory phenotype (effector memory T cells (T(EM))), whereas central memory and activated naïve CD4(+) T cells are relatively resistant to both. Sensitivity of T(EM) to Fas-induced apoptosis depends on enrichment of Fas in lipid raft microdomains, and is linked to more efficient formation of the Fas death-inducing signaling complex. These results explain how Fas can cull T cells reactive against self-antigens without affecting acute immune responses. This work also identifies Fas-induced apoptosis as a possible immunotherapeutic strategy to eliminate T(EM) linked to the pathogenesis of a number of autoimmune diseases.

Transplantation of mouse HSCs genetically modified to express a CD4-restricted TCR results in long-term immunity that destroys tumors and initiates spontaneous autoimmunity

The development of effective cancer immunotherapies has been consistently hampered by several factors, including an inability to instigate long-term effective functional antitumor immunity. This is particularly true for immunotherapies that focus on the adoptive transfer of activated or genetically modified mature CD8+ T cells. In this study, we sought to alter and enhance long-term host immunity by genetically modifying, then transplanting, mouse HSCs. We first cloned a previously identified tumor-reactive HLA-DR4-restricted CD4+ TCR specific for the melanocyte differentiation antigen tyrosinase-related protein 1 (Tyrp1), then constructed both a high-expression lentivirus vector and a TCR-transgenic mouse expressing the genes encoding this TCR. Using these tools, we demonstrated that both mouse and human HSCs established durable, high-efficiency TCR gene transfer following long-term transplantation into lethally irradiated mice transgenic for HLA-DR4. Recipients of genetically modified mouse HSCs developed spontaneous autoimmune vitiligo that was associated with the presence of a Th1-polarized memory effector CD4+ T cell population that expressed the Tyrp1-specific TCR. Most importantly, large numbers of CD4+ T cells expressing the Tyrp1-specific TCR were detected in secondary HLA-DR4-transgenic transplant recipients, and these mice were able to destroy subcutaneously administered melanoma cells without the aid of vaccination, immune modulation, or cytokine administration. These results demonstrate the creation of what we believe to be a novel translational model of durable lentiviral gene transfer that results in long-term effective immunity.

Aberrant ROCK activation promotes the development of type I diabetes in NOD mice

Aberrant production of IL-21 by T cells is critical for the development of type 1 diabetes (T1D) in NOD mice. The pathogenic effects of IL-21 are partly due to its ability to promote the generation of T(H)-17 cells. Interferon Regulatory Factor (IRF4) is a crucial regulator of IL-17 and IL-21 production. We recently found that the serine-threonine kinase ROCK2 phosphorylates IRF4 and regulates its ability to control IL-17 and IL-21 production. Here we show that NOD T cells aberrantly activate ROCK2. We furthermore demonstrate that ROCK inhibition corrects the abnormal IRF4 function in NOD T cells and diminishes their production of IL-17 and IL-21. Importantly, administration of a ROCK inhibitor to NOD mice protects against diabetes development. These studies thus support the idea that ROCK2 is inappropriately activated in NOD T cells and that ROCK kinases could represent important therapeutic targets for the treatment of T1D.

Recent thymic emigrants are biased against the T-helper type 1 and toward the T-helper type 2 effector lineage

After intrathymic development, T cells exit the thymus and join the peripheral T-cell pool. Such recent thymic emigrants (RTEs) undergo both phenotypic and functional maturation during the first 3 weeks they reside in the periphery. Using a well-controlled in vitro polarization scheme, we now show that CD4(+) RTEs are defective in T-helper (Th) type 0 (Th0), Th1, Th17, and regulatory T-cell lineage commitment, with dampened cytokine production and transcription factor expression. In contrast, CD4(+) RTES are biased toward the Th2 lineage both in vitro and in vivo, with more robust interleukin-4, interleukin-5, and interleukin-13 production than their mature naive counterparts. Coculture experiments demonstrate that mature naive T cells influence neighboring RTEs in their Th responses. In adoptive hosts, CD4(+) RTEs drive production of the Th2-associated antibody isotype immunoglobulin G1 and mediate airway inflammatory disease. This bias in RTEs likely results from dampened negative regulation of the Th2 lineage by diminished levels of T-bet, a key Th1 transcription factor. CD4(+) RTEs thus represent a transitional population with a distinct interpretation of, and response to, immunologic cues. These characteristics may be beneficial during the postthymic maturation period by leading to the avoidance of inappropriate immune responses, particularly in lymphopenic neonates and adults.

NFAT5 regulates T lymphocyte homeostasis and CD24-dependent T cell expansion under pathologic hypernatremia

Immune cells rely on the transcription factor NFAT5 to adapt to hypertonic stress. The hypertonicity-dependent role of NFAT5 in T cells in vivo remains unclear because mouse models of NFAT5 deficiency have produced substantially different T cell phenotypes. In this study, we analyzed the T cell compartment in NFAT5-null and T cell-specific NFAT5 knockout mice. We found that NFAT5-null mice had constitutive, pronounced hypernatremia and suffered a severe immunodeficiency, with T cell lymphopenia, altered CD8 naive/memory homeostasis, and inability to reject allogeneic tumors. By contrast, T cell-specific NFAT5 knockout mice had normal plasma tonicity, rejected allogeneic tumors, and exhibited only a mild, low-penetrance memory bias in CD8 cells. Notably, when T cells from these mice were cultured ex vivo in hypernatremic media, they exhibited features found in NFAT5-null mice, with pronounced naive/memory imbalance and impaired homeostatic survival in response to IL-7, as well as a severe inhibition of their mitogen-induced proliferation. By analyzing surface receptors whose expression might be affected in NFAT5-deficient cells, we identified CD24 as a novel NFAT5 target induced by hypertonicity both in vitro and in vivo, and required to sustain T cell expansion under osmostress. NFAT5 bound to the Cd24 promoter in response to hypertonicity facilitated the local derepression of chromatin and enhanced the expression of CD24 mRNA and protein. Altogether, our results indicate that the systemic hypernatremia of NFAT5-null mice is a major contributor to their immunodeficiency, and highlight the role of NFAT5 and CD24 in the homeostasis of T cells under osmostress in vivo.

Critical role for IL-21 in both primary and memory anti-viral CD8+ T-cell responses

While it is well established that CD8(+) T cells generated in the absence of CD4(+) T cells mediate defective recall responses, the mechanism by which CD4(+) T cells confer help in the generation of CD8(+) T-cell responses remains poorly understood. To determine whether CD4(+) T-cell-derived IL-21 is an important regulator of CD8(+) T-cell responses in help-dependent and -independent viral infections, we examined these responses in the IL-21Rα(-/-) mouse model. We show that IL-21 has a role in primary CD8(+) T-cell responses and in recall CD8(+) T-cell responses in help-dependent viral infections. This effect is due to a direct action of IL-21 in enhancing the proliferation of virus-specific CD8(+) T cells and reducing their TRAIL expression. These findings indicate that IL-21 is an important mediator of CD4(+) T-cell help to CD8(+) T cells.

Apoptosis regulators Fas and Bim synergistically control T-lymphocyte homeostatic proliferation

The size of the peripheral T-lymphocyte compartment is governed by complex homeostatic mechanisms that balance T-cell proliferation and death. Proliferation and survival signals are mediated in part by recurrent self-peptide/MHC-TCR interactions and signaling by the common γ chain-containing cytokine receptors, including those for IL-7 and IL-15. We have previously shown that the death receptor Fas (CD95/APO-1) regulates apoptosis in response to repeated TCR stimulation, whereas the Bcl-2 homology domain 3-only protein Bim mediates cytokine withdrawal-induced apoptosis. We therefore reasoned that these two molecules might cooperate in the regulation of homeostatic proliferation. In this study, we observe that the combined loss of Fas and Bim synergistically enhances the accumulation of T cells in lymphopenic host mice, and this is particularly pronounced for the unusual CD4(-) CD8(-) TCRαβ(+) T cells that are characteristic of Fas-deficient (Fas(lpr/lpr) ) mice. Our findings demonstrate that these CD4(-) CD8(-) TCRαβ(+) T cells arise from homeostatic proliferation of CD8(+) T cells. These studies also underscore the profound rate of baseline T-cell proliferation that likely occurs in wild-type mice even in the absence of foreign antigen, and the consequent need for its coordinated regulation by multiple death-signaling pathways.

Mammalian target of rapamycin activation underlies HSC defects in autoimmune disease and inflammation in mice

The mammalian target of rapamycin (mTOR) is a signaling molecule that senses environmental cues, such as nutrient status and oxygen supply, to regulate cell growth, proliferation, and other functions. Unchecked, sustained mTOR activity results in defects in HSC function. Inflammatory conditions, such as autoimmune disease, are often associated with defective hematopoiesis. Here, we investigated whether hyperactivation of mTOR in HSCs contributes to hematopoietic defects in autoimmunity and inflammation. We found that in mice deficient in Foxp3 (scurfy mice), a model of autoimmunity, the development of autoimmune disease correlated with progressive bone marrow loss and impaired regenerative capacity of HSCs in competitive bone marrow transplantation. Similarly, LPS-mediated inflammation in C57BL/6 mice led to massive bone marrow cell death and impaired HSC function. Importantly, treatment with rapamycin in both models corrected bone marrow hypocellularity and partially restored hematopoietic activity. In cultured mouse bone marrow cells, treatment with either of the inflammatory cytokines IL-6 or TNF-α was sufficient to activate mTOR, while preventing mTOR activation in vivo required simultaneous inhibition of CCL2, IL-6, and TNF-α. These data strongly suggest that mTOR activation in HSCs by inflammatory cytokines underlies defective hematopoiesis in autoimmune disease and inflammation.

T cells expressing two different T cell receptors form a heterogeneous population containing autoreactive clones

During T cell development both alleles of the T cell receptor (TCR) alpha locus are rearranged. As a result, a sizeable proportion of T cells can express two distinct TCRs, but the functional significance of this phenomenon remains controversial. Studies on transgenic mice with two TCRs have focused on the risk of immunopathology that such cells may pose, while some have suggested that most dual-specific T cells are nonfunctional or even protective. We tracked the fate and TCR repertoire of single- and dual-specific T cells within a normal polyclonal population undergoing lymphopenia-induced proliferation, a setting which has been shown to cause immunopathology and autoimmunity. After the expansion the repertoire of dual-specific T cells had become highly biased, with both prominent clonal expansions and the complete disappearance of other clones. Our results suggest that the normal repertoire of dual-specific T cells contains both nonfunctional cells and a small, 5% fraction of clones which display a much higher than average affinity to antigens normally tolerated as harmless. This heterogeneity may also help in reconciling some of the earlier, conflicting results.

Immune aging and rheumatoid arthritis

Immunologic models of rheumatoid arthritis (RA) have to take into account that the disease occurs at an age when immunocompetence is declining and in a host whose immune system shows evidence of accelerated immune aging. By several immune aging biomarkers, the immune system in patients with RA is prematurely aged by more than 20 years. One major pathogenetic mechanism is a defect in telomere maintenance and DNA repair that causes accelerated cell death. These findings in RA are reminiscent of murine autoimmunity models, in which lymphopenia was identified as a major risk factor for autoimmunity. Progress in the understanding of how accelerated immune aging is pathogenetically involved in RA may allow development of new therapeutic approaches that go beyond the use of anti-inflammatory agents and eventually could open new avenues for preventive intervention.

Single cell analysis of complex thymus stromal cell populations: rapid thymic epithelia preparation characterizes radiation injury

Thymic epithelial cells (TECs) and dendritic cells are essential for the maintenance of thymopoiesis. Because these stromal elements define the progenitor niche, provide critical survival signals and growth factors, and direct positive and negative selection, detailed study of these populations is necessary to understand important elements for thymic renewal after cytotoxic injury. Study of TEC is currently hindered by lengthy enzymatic separation techniques with decreased viability. We present a new rapid separation technique that yields consistent viable TEC numbers in a quarter of the prior preparation time. Using this new procedure, we identify changes in stroma populations following total body irradiation (TBI). By flow cytometry, we show that TBI significantly depletes UEA+ medullary TEC, while sparing Ly51+ CD45- cells. Further characterization of the Ly51+ subset reveals enrichment of fibroblasts (CD45- Ly51+ MHCII-), while cortical TECs (CD45- Ly51+ MHCII+) were markedly reduced. Dendritic cells (CD11lc+ CD45+) were also decreased following TBI. These data suggest that cytotoxic preparative regimens may impair thymic renewal by reducing critical populations of cortical and medullary TEC, and that such thymic damage can be assessed by this new rapid separation technique, thereby providing a means of assessing optimal conditioning pretransplantfor enhancing thymic-dependent immune reconstitution posttranspiant.

B and T lymphocyte attenuator suppresses IL-21 production from follicular Th cells and subsequent humoral immune responses

We recently showed that mice lacking B and T lymphocyte attenuator (BTLA), a third inhibitory coreceptor expressed on B cells and T cells, exhibit an increased Ag-specific IgG response and gradually develop hyper-gamma-globulinemia and autoantibody production. Recent studies revealed that follicular Th (Tfh) cells, which are non-Th1, non-Th2 effector T cells that express CXCR5 and provide help for B cells to produce Ig, also express BTLA. However, the role of BTLA in Tfh cell function remains unknown. In this study, we examined the regulatory role of BTLA in the development and function of Tfh cells. We found that CXCR5(+) Tfh cells expressed higher levels of BTLA than did CXCR5(-) conventional CD4(+) T cells. We also found that adoptive transfer of BTLA(-/-) CD4(+) T cells, stimulated under Tfh cell-inducing conditions (Tfh-like cells), to wild-type (WT) mice induced more Ag-specific IgG2a and IgG2b production compared with that of WT Tfh-like cells. By contrast, another adoptive-transfer experiment using BTLA(-/-) mice as recipients showed that the expression of BTLA on B cells was not involved in the regulation of Tfh-like cell-mediated Ag-specific IgG responses. Moreover, the development of IL-21-producing CXCR5(+) Tfh-like cells was significantly increased in BTLA(-/-) CD4(+) T cells compared with WT CD4(+) T cells. Furthermore, Tfh-like cell-mediated IgG responses were abolished when IL-21R(-/-) mice were used as recipients. These results suggest that BTLA signaling suppresses IL-21 production from Tfh cells and subsequent Tfh cell-mediated IgG responses.

Th1-driven immune reconstitution disease in Mycobacterium avium-infected mice

Following antiretroviral therapy, a significant proportion of HIV(+) patients with mycobacterial coinfections develop a paradoxical, poorly understood inflammatory disease termed immune reconstitution inflammatory syndrome (IRIS). Here, we show that Mycobacterium avium-infected T cell-deficient mice injected with CD4 T cells also develop an immune reconstitution disease (IRD) manifesting as weight loss, impaired lung function, and rapid mortality. This form of IRD requires Ag recognition and interferonγ production by the donor CD4 T cells and correlates with marked alterations in blood and tissue CD11b(+) myeloid cells. Interestingly, disease is associated with impaired, rather than augmented, T-cell expansion and function and is not strictly dependent on lymphopenia-induced T-cell proliferation. Instead, our findings suggest that mycobacterial-associated IRIS results from a heightened sensitivity of infected lymphopenic hosts to the detrimental effects of Ag-driven CD4 T-cell responses.

Immunosuppressive therapy exacerbates autoimmunity in NOD mice and diminishes the protective activity of regulatory T cells

Mounting evidence indicates that immunosuppressive therapy and autologous bone marrow transplantation are relatively inefficient approaches to treat autoimmune diabetes. In this study we assessed the impact of immunosuppression on inflammatory insulitis in NOD mice, and the effect of radiation on immunomodulation mediated by adoptive transfer of various cell subsets. Sublethal radiation of NOD females at the age of 14 weeks (onset of hyperglycemia) delayed the onset of hyperglycemia, however two thirds of the mice became diabetic. Adoptive transfer of splenocytes into irradiated NON and NOD mice precipitated disease onset despite increased contents of CD25(+)FoxP3(+) T cells in the pancreas and regional lymphatics. Similar phenotypic changes were observed when CD25(+) T cells were infused after radiation, which also delayed disease onset without affecting its incidence. Importantly, irradiation increased the susceptibility to diabetes in NOD and NON mice (71-84%) as compared to immunomodulation with splenocytes and CD25(+) T cells in naïve recipients (44-50%). Although irradiation had significant and durable influence on pancreatic infiltrates and the fractions of functional CD25(+)FoxP3(+) Treg cells were elevated by adoptive cell transfer, this approach conferred no protection from disease progression. Irradiation was ineffective both in debulking of pathogenic clones and in restoring immune homeostasis, and the consequent homeostatic expansion evolves as an unfavorable factor in attempts to restore self-tolerance and might even provoke uncontrolled proliferation of pathogenic clones. The obstacles imposed by immunosuppression on abrogation of autoimmune insulitis require replacement of non-specific immunosuppressive therapy by selective immunomodulation that does not cause lymphopenia.

Patient-derived granulocyte/macrophage colony-stimulating factor autoantibodies reproduce pulmonary alveolar proteinosis in nonhuman primates

RATIONALE

Granulocyte/macrophage colony-stimulating factor (GM-CSF) autoantibodies (GMAb) are strongly associated with idiopathic pulmonary alveolar proteinosis (PAP) and are believed to be important in its pathogenesis. However, levels of GMAb do not correlate with disease severity and GMAb are also present at low levels in healthy individuals.

OBJECTIVES

Our primary objective was to determine whether human GMAb would reproduce PAP in healthy primates. A secondary objective was to determine the concentration of GMAb resulting in loss of GM-CSF signaling in vivo (i.e., critical threshold).

METHODS

Nonhuman primates (Macaca fascicularis) were injected with highly purified, PAP patient-derived GMAb in dose-ranging (2.2-50 mg) single and multiple administration studies, and after blocking antihuman immunoglobulin immune responses, in chronic administration studies maintaining serum levels greater than 40 microg/ml for up to 11 months.

MEASUREMENTS AND MAIN RESULTS

GMAb blocked GM-CSF signaling causing (1) a milky-appearing bronchoalveolar lavage fluid containing increased surfactant lipids and proteins; (2) enlarged, foamy, surfactant-filled alveolar macrophages with reduced PU.1 and PPARgamma mRNA, and reduced tumor necrosis factor-alpha secretion; (3) pulmonary leukocytosis; (4) increased serum surfactant protein-D; and (5) impaired neutrophil functions. GM-CSF signaling varied inversely with GMAb concentration below a critical threshold of 5 microg/ml, which was similar in lungs and blood and to the value observed in patients with PAP.

CONCLUSIONS

GMAb reproduced the molecular, cellular, and histopathologic features of PAP in healthy primates, demonstrating that GMAb directly cause PAP. These results have implications for therapy of PAP and help define the therapeutic window for potential use of GMAb to treat other disorders.

Altered effector CD4+ T cell function in IL-21R-/- CD4+ T cell-mediated graft-versus-host disease

We previously showed that transplantation with IL-21R gene-deficient splenocytes resulted in less severe graft-versus-host disease (GVHD) than was observed with wild type splenocytes. In this study, we sought to find mechanism(s) explaining this observation. Recipients of donor CD4(+) T cells lacking IL-21R exhibited diminished GVHD symptoms, with reduced inflammatory cell infiltration into the liver and intestine, leading to prolonged survival. After transplantation, CD4(+) T cell numbers in the spleen were reduced, and MLR and cytokine production by CD4(+) T cells were impaired. These results suggest that IL-21 might promote GVHD through enhanced production of effector CD4(+) T cells. Moreover, we found that CD25 depletion altered neither the impaired MLR in vitro nor the ameliorated GVHD symptoms in vivo. Thus, the attenuated GVHD might be caused by an impairment of effector T cell differentiation itself, rather than by an increase in regulatory T cells and suppression of effector T cells.

Spontaneous autoimmune dacryoadenitis in aged CD25KO mice

To investigate time-related immunopathological changes in the lacrimal glands (LGs) of CD25KO mice, we examined LGs of C57BL/6 (wild-type) and CD25KO mice at 8, 12, and 16 weeks of age. T cell infiltration was quantified by flow cytometry, and gland function by tear peroxidase activity and epidermal growth factor mRNA expression. T helper (Th)-1, -2 and -17-associated cytokine expression was evaluated by real-time PCR. Epithelial apoptosis was assessed by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay and activated caspase-3 staining. Eight-week-old CD25KO mice demonstrated significantly increased numbers of CD4 and CD8 T cells infiltrating the LGs. This peaked at 12 weeks of age. No peroxidase secretion was detected, and epidermal growth factor mRNA expression was barely detected in CD25KO mice. Ductal epithelial apoptosis was noted in CD25KO mice. Young CD25KO LGs had higher Th-17- (interleukin [IL]-23R, transforming growth factor-beta1, IL-17A, CC chemokine attractant ligand-20) and Th-1-associated cytokine transcripts (interferon-gamma, T-bet, IL-12, IL-2, IL-18) than young wild-type LGs. There was also a significant time-related decrease in IL-17A and CC chemokine attractant ligand-20 in CD25KO LGs. Taken together, autoimmune LG infiltration with loss of LG function was observed in CD25KO mice as early as 8 weeks of age. Time-related switch from Th-17 to Th-1 inflammation was noted in CD25KO mice.

CD122+CD8+ Treg suppress vaccine-induced antitumor immune responses in lymphodepleted mice

Lymphodeleption prior to adoptive transfer of tumor-specific T cells greatly improves the clinical efficacy of adoptive T-cell therapy for patients with advanced melanoma, and increases the therapeutic efficacy of cancer vaccines in animal models. Lymphodepletion reduces competition between lymphocytes, and thus creates "space" for enhanced expansion and survival of tumor-specific T cells. Within the lymphodepleted host, Ag-specific T cells still need to compete with other lymphocytes that undergo lymphopenia-driven proliferation. Herein, we describe the relative capacity of naïve T cells, Treg, and NK cells to undergo lymphopenia-driven proliferation. We found that the major population that underwent lymphopenia-driven proliferation was the CD122+ memory-like T-cell population (CD122+CD8+ Treg), and these cells competed with Ag-driven proliferation of melanoma-specific T cells. Removal of CD122+CD8+ Treg resulted in a greater expansion of tumor-specific T cells and tumor infiltration of functional effector/memory T cells. Our results demonstrate the lymphopenia-driven proliferation of CD122+CD8+ Treg in reconstituted lymphodepleted mice limited the antitumor efficacy of DC vaccination in conjunction with adoptive transfer of tumor-specific T cells.

Microbiota innate stimulation is a prerequisite for T cell spontaneous proliferation and induction of experimental colitis

Little is known about how the microbiota regulates T cell proliferation and whether spontaneous T cell proliferation is involved in the pathogenesis of inflammatory bowel disease. In this study, we show that stimulation of innate pathways by microbiota-derived ligands and antigen-specific T cell stimulation are both required for intestinal inflammation. Microbiota-derived ligands promoted spontaneous T cell proliferation by activating dendritic cells (DCs) to produce IL-6 via Myd88, as shown by the spontaneous proliferation of T cells adoptively transferred into specific pathogen-free (SPF) RAG-/- mice, but not in germfree RAG-/- mice. Reconstitution of germfree RAG-/- mice with cecal bacterial lysate-pulsed DCs, but not with IL-6-/- or Myd88-/- DCs, restored spontaneous T cell proliferation. CBir1 TCR transgenic (CBir1 Tg) T cells, which are specific for an immunodominant microbiota antigen, induced colitis in SPF RAG-/- mice. Blocking the spontaneous proliferation of CBir1 Tg T cells by co-transferring bulk OT II CD4+ T cells abrogated colitis development. Although transferred OT II T cells underwent spontaneous proliferation in RAG-/- mice, the recipients failed to develop colitis because of the lack of cognate antigen in the intestinal lumen. Collectively, our data demonstrate that induction of colitis requires both spontaneous proliferation of T cells driven by microbiota-derived innate signals and antigen-specific T cell proliferation.

Regulation of cytokine-driven functional differentiation of CD8 T cells by suppressor of cytokine signaling 1 controls autoimmunity and preserves their proliferative capacity toward foreign antigens

We have previously shown that naive CD8 T cells exposed to IL-7 or IL-15 in the presence of IL-21 undergo Ag-independent proliferation with concomitant increase in TCR sensitivity. In this study, we examined whether CD8 T cells that accumulate in suppressor of cytokine signaling 1 (SOCS1)-deficient mice because of increased IL-15 signaling in vivo would respond to an autoantigen expressed at a very low level using a mouse model of autoimmune diabetes. In this model, P14 TCR transgenic CD8 T cells (P14 cells) adoptively transferred to rat insulin promoter-glycoprotein (RIP-GP) mice, which express the cognate Ag in the islets, do not induce diabetes unless the donor cells are stimulated by exogenous Ag. Surprisingly, SOCS1-deficient P14 cells, which expanded robustly following IL-15 stimulation, proliferated poorly in response to Ag and failed to cause diabetes in RIP-GP mice. SOCS1-deficient CD8 T cells expressing a polyclonal TCR repertoire also showed defective expansion following in vivo Ag stimulation. Notwithstanding the Ag-specific proliferation defect, SOCS1-null P14 cells produced IFN-gamma and displayed potent cytolytic activity upon Ag stimulation, suggesting that SOCS1-null CD8 T cells underwent cytokine-driven functional differentiation that selectively compromised their proliferative response to Ag but not to cytokines. Cytokine-driven homeostatic expansion in lymphopenic RIP-GP mice allowed SOCS1-null, but not wild-type, P14 cells to exert their pathogenic potential even without Ag stimulation. These findings suggest that by attenuating cytokine-driven proliferation and functional differentiation, SOCS1 not only controls the pathogenicity of autoreactive cells but also preserves the ability of CD8 T cells to proliferate in response to Ags.

Adjuvant treatment suppresses IL-17 production by T cell-independent myeloid sources in nonobese diabetic mice

Recent studies have shown that Th17 cells, as a distinct lineage from Th1 and Th2 subsets, play an obligatory role in the pathogenesis of autoimmune diseases. It is well known that immunotherapy with Complete Freund's adjuvant (CFA) is effective in preventing from the onset of autoimmune diabetes in nonobese diabetic (NOD) mice. In the present study, we investigated whether CFA treatment restrained Th17 development and down-regulated Th17-related cytokine production in NOD mice. Th17-related cytokines (i.e. IL-17A, IL-17F, IL-21, IL-22, IL-23, IL-6, TGF-beta) production in splenocytes was decreased dramatically on day 18 following CFA immunization. This effect was also observed at 10 and 20 week after adjuvant treatment. Injection of IL-17 into CFA-treated diabetes-free mice led to occurrence of overt diabetes, indicating that therapeutic effects of adjuvant treatment may be partially due to suppressing Th17 commitment. Interestingly, the main producer of IL-17 resided in a population of myeloid cells, which negatively expressed makers of neutrophil or macrophages. IL-23 stimulation did not alter the distribution of IL-17 in myeloid cells. Furthermore, this pattern of IL-17 expression was also present in Balb/c and C57BL/6 strains. These findings may have important implications for understanding of mechanisms underlying adjuvant treatment on autoimmune diseases.

CD4+CD25+ regulatory T cells in autoimmune arthritis

CD4(+)CD25(+) regulatory T (Treg) cells can play a critical role in the prevention of autoimmunity, as evidenced by the cataclysmic autoimmune disease that develops in mice and humans lacking the key transcription factor forkhead box protein 3 (Foxp3). At present, however, how and whether Treg cells participate in the development of rheumatoid arthritis (RA), which has both systemic manifestations and a joint-targeted pathology that characterizes the disease, remains unclear. In this review, we describe work that has been carried out aimed at determining the role of Treg cells in disease development in RA patients and in mouse models of inflammatory arthritis. We also describe studies in a new model of spontaneous autoimmune arthritis (TS1 x HACII mice), in which disease is caused by CD4(+) T cells recognizing a neo-self-antigen expressed by systemically distributed antigen-presenting cells. We show that TS1 x HACII mice develop arthritis despite the presence of CD4(+)CD25(+)Foxp3(+) Treg cells that recognize this target autoantigen, and we outline steps in the development of arthritis at which Treg cells might potentially act, or fail to act, in the development of inflammatory arthritis.

Secondary immunologic consequences in chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

Clinical evidence suggests that patients with Chromosome 22q11.2 deletion (Ch22q11.2D) have an increased prevalence of atopic and autoimmune disease and this has been without explanation. We hypothesized that the increase in atopy was due to homeostatic proliferation of T cells leading to a Th2 skew. We performed intracellular cytokine staining to define Th1/Th2 phenotypes in toddlers (early homeostatic proliferation) and adults (post homeostatic proliferation) with this syndrome. To attempt to understand the predisposition to autoimmunity we performed immunophenotyping analyses to define Th17 cells and B cell subsets. Adult Ch22q11.2D patients had a higher percentage of IL-4+CD4+ T cells than controls. Th17 cells were no different in patients and controls. In addition, adult Ch22q11.2D syndrome patients had significantly lower switched memory B cells, suggesting a dysregulated B cell compartment. These studies demonstrate that the decrement in T cell production has secondary consequences in the immune system, which could mold the patients' clinical picture.

NK cells delay allograft rejection in lymphopenic hosts by downregulating the homeostatic proliferation of CD8+ T cells

T cells present in lymphopenic environments undergo spontaneous (homeostatic) proliferation resulting in expansion of the memory T cell pool. Homeostatically generated memory T cells protect the host against infection but can cause autoimmunity and allograft rejection. Therefore, understanding the mechanisms that regulate homeostatic T cell proliferation is germane to clinical settings in which lymphodepletion is used. In this study, we asked whether NK cells, which regulate immune responses in lymphocyte-replete hosts, also regulate homeostatic T cell proliferation under lymphopenic conditions. We found that T cells transferred into genetically lymphocyte-deficient RAG-/- mice proliferate faster and generate more CD8+ memory T cells if NK cells were absent. CD8+ T cells that underwent homeostatic proliferation in the presence of NK cells generated mostly effector memory (CD44highCD62Llow) lymphocytes, whereas those that divided in the absence of NK cells were skewed toward central memory (CD44highCD62Lhigh). The latter originated predominantly from proliferation of the "natural" central memory CD8+ T cell pool. Regulation of homeostatic proliferation by NK cells occurred independent of perforin but was reversed by excess IL-15. Importantly, NK depletion enhanced CD8+ T cell recovery in T cell-depleted wild-type mice and accelerated rejection of skin allografts, indicating that regulation of homeostatic proliferation by NK cells is not restricted to genetically lymphocyte-deficient animals. These results demonstrate that NK cells downregulate homeostatic CD8+ T cell proliferation in lymphopenic environments by competing for IL-15. Concomitant NK and T cell depletion may be undesirable in transplant recipients because of enhanced expansion of memory CD8+ T cells that increase the risk of rejection.

Systemic autoimmunity and defective Fas ligand secretion in the absence of the Wiskott-Aldrich syndrome protein

Autoimmunity is a surprisingly common complication of primary immunodeficiencies, yet the molecular mechanisms underlying this clinical observation are not well understood. One widely known example is provided by Wiskott-Aldrich syndrome (WAS), an X-linked primary immunodeficiency disorder caused by mutations in the gene encoding the WAS protein (WASp) with a high incidence of autoimmunity in affected patients. WASp deficiency affects T-cell antigen receptor (TCR) signaling and T-cell cytokine production, but its role in TCR-induced apoptosis, one of the mechanisms of peripheral immunologic tolerance, has not been investigated. We find that WASp-deficient mice produce autoantibodies and develop proliferative glomerulonephritis with immune complex deposition as they age. We also find that CD4(+) T lymphocytes from WASp-deficient mice undergo reduced apoptosis after restimulation through the TCR. While Fas-induced cell death is normal, WASp deficiency affects TCR-induced secretion of Fas ligand (FasL) and other components of secretory granules by CD4(+) T cells. These results describe a novel role of WASp in regulating TCR-induced apoptosis and FasL secretion and suggest that WASp-deficient mice provide a good model for the study of autoimmune manifestations of WAS and the development of more specific therapies for these complications.