Increases in circulating and lymphoid tissue interleukin-10 in autoimmune lymphoproliferative syndrome are associated with disease expression

Combined germline and somatic human FADD mutations cause autoimmune lymphoproliferative syndrome

BACKGROUND

The autoimmune lymphoproliferative syndrome (ALPS) is a noninfectious and nonmalignant lymphoproliferative disease frequently associated with autoimmune cytopenia resulting from defective FAS signaling. We previously described germline monoallelic FAS (TNFRSF6) haploinsufficient mutations associated with somatic events, such as loss of heterozygosity on the second allele of FAS, as a cause of ALPS-FAS. These somatic events were identified by sequencing FAS in DNA from double-negative (DN) T cells, the pathognomonic T-cell subset in ALPS, in which the somatic events accumulated.

OBJECTIVE

We sought to identify whether a somatic event affecting the FAS-associated death domain (FADD) gene could be related to the disease onset in 4 unrelated patients with ALPS carrying a germline monoallelic mutation of the FADD protein inherited from a healthy parent.

METHODS

We sequenced FADD and performed array-based comparative genomic hybridization using DNA from sorted CD4+ or DN T cells.

RESULTS

We found homozygous FADD mutations in the DN T cells from all 4 patients, which resulted from uniparental disomy. FADD deficiency caused by germline heterozygous FADD mutations associated with a somatic loss of heterozygosity was a phenocopy of ALPS-FAS without the more complex symptoms reported in patients with germline biallelic FADD mutations.

CONCLUSIONS

The association of germline and somatic events affecting the FADD gene is a new genetic cause of ALPS.

Autoimmune lymphoproliferative syndrome: A disorder of immune dysregulation

Autoimmune Lymphoproliferative Syndrome (ALPS) is an autoimmune disease that has been reported in over 2200 patients. It is a rare, genetic disease where pathogenic variants occur in the extrinsic pathway of apoptosis. Various mutations in different genes, such as FAS, FASL, and CASP10, can result in ALPS. Most commonly, pathogenic variants occur in the FAS receptor. This malfunctioning pathway allows for the abnormal accumulation of lymphocytes, namely CD3 + TCRαβ+CD4 - CD8- (double negative (DN) T) cells, which are a hallmark of the disease. This disease usually presents in childhood with lymphadenopathy and splenomegaly as a result of lymphoproliferation. Over time, these patients may develop cytopenias or lymphomas because of irregularities in the immune system. Current treatments include glucocorticoids, mycophenolate mofetil, sirolimus, immunoglobulin G, and rituximab. These medications serve to manage the symptoms and there are no standardized recommendations for the management of ALPS. The only curative therapy is a bone marrow transplant, but this is rarely done because of the complications. This review serves to broaden the understanding of ALPS by discussing the mechanism of immune dysregulation, how the symptoms manifest, and the mechanisms of treatment. Additionally, we discuss the epidemiology, comorbidities, and medications relating to ALPS patients across the United States using data from Cosmos.

mTOR inhibition attenuates cTfh cell dysregulation and chronic T-cell activation in multilineage immune cytopenias

mTOR inhibitors such as sirolimus are increasingly used in the management of multilineage immune cytopenia (m-IC) in children. Although sirolimus is effective in improving IC, it is unclear how sirolimus affects the broader immune dysregulation associated with m-IC. We profiled T- and B-cell subsets longitudinally and measured cytokines and chemokines before and after sirolimus treatment. Eleven of the 12 patients with m-IC who tolerated sirolimus were followed for a median duration of 17 months. All patients had an improvement in IC, and sirolimus therapy did not result in significant decreases in T-, B- and NK-cell numbers. However, the expansion and activation of circulating T follicular helper and the Th1 bias noted before the initiation of sirolimus were significantly decreased. Features of chronic T-cell activation and exhaustion within effector memory compartments of CD4+ and CD8+ T cells decreased with sirolimus therapy. Corresponding to these changes, plasma levels of CXCL9 and CXCL10 also decreased. Interestingly, no significant improvement in the proportion of class-switched memory B cells or frequencies of CD4+ naive T cells were noted. Longer follow-up and additional studies are needed to validate these findings and evaluate the effect of sirolimus on B-cell maturation.

The genetic landscape of the FAS pathway deficiencies

Dysfunction of the FAS-FASLG pathway causes a lymphoproliferative disorder with autoimmunity called Autoimmune lymphoproliferative syndrome (ALPS) mainly caused by FAS mutations. The goal of this review is to describe the genetic bases of the autoimmune lymphoproliferative syndrome and to underline their genetic complexity with the contribution of both germline and somatic events accounting for the variable clinical penetrance of the FAS mutations. Starting from the cohort of patients studied in the French cohort (>165 cases), we also reviewed the literature cases in order to depict a full description of the mutations affecting the FAS-FASLG pathway involved in the outcome of this rare non-malignant and non-infectious pediatric lymphoproliferative disease. We also discussed the variable clinical penetrance associated with mutations affecting the extracellular domain of the protein. Such non-penetrant germline mutations are frequently associated with an additional somatic event impacting the second allele of FAS. Moreover, the uncomplete clinical penetrance associated with mutations affecting the intracellular domain of FAS, in patient lacking additional FAS somatic event, suggested a potential digenic inheritance with a FAS mutation accompanied by a genetic modifier possibly impacting another player of the lymphocytes homeostasis (affecting the survival, activation or apoptosis of the peripheral leukocytes).

Immunologic evaluation and genetic defects of apoptosis in patients with autoimmune lymphoproliferative syndrome (ALPS)

Apoptosis plays an important role in controlling the adaptive immune response and general homeostasis of the immune cells, and impaired apoptosis in the immune system results in autoimmunity and immune dysregulation. In the last 25 years, inherited human diseases of the Fas-FasL pathway have been recognized. Autoimmune lymphoproliferative syndrome (ALPS) is an inborn error of immunity, characterized clinically by nonmalignant and noninfectious lymphoproliferation, autoimmunity, and increased risk of lymphoma due to a defect in lymphocyte apoptosis. The laboratory hallmarks of ALPS are an elevated percentage of T-cell receptor αβ double negative T cells (DNTs), elevated levels of vitamin B12, soluble FasL, IL-10, IL-18 and IgG, and defective in vitro Fas-mediated apoptosis. In order of frequency, the genetic defects associated with ALPS are germinal and somatic ALPS-FAS, ALPS-FASLG, ALPS-CASP10, ALPS-FADD, and ALPS-CASP8. Partial disease penetrance and severity suggest the combination of germline and somatic FAS mutations as well as other risk factor genes. In this report, we summarize human defects of apoptosis leading to ALPS and defects that are known as ALPS-like syndromes that can be clinically similar to, but are genetically distinct from, ALPS. An efficient genetic and immunological diagnostic approach to patients suspected of having ALPS or ALPS-like syndromes is essential because this enables the establishment of specific therapeutic strategies for improving the prognosis and quality of life of patients.

Flow Cytometry for Diagnosis of Primary Immune Deficiencies-A Tertiary Center Experience From North India

Flow cytometry has emerged as a useful technology that has facilitated our understanding of the human immune system. Primary immune deficiency disorders (PIDDs) are a heterogeneous group of inherited disorders affecting the immune system. More than 350 genes causing various PIDDs have been identified. While the initial suspicion and recognition of PIDDs is clinical, laboratory tools such as flow cytometry and genetic sequencing are essential for confirmation and categorization. Genetic sequencing, however, are prohibitively expensive and not readily available in resource constrained settings. Flow cytometry remains a simple, yet powerful, tool for multi-parametric analysis of cells. While it is confirmatory of diagnosis in certain conditions, in others it helps in narrowing the list of putative genes to be analyzed. The utility of flow cytometry in diagnosis of PIDDs can be divided into four major categories: (a) Enumeration of lymphocyte subsets in peripheral blood. (b) Detection of intracellular signaling molecules, transcription factors, and cytokines. (c) Functional assessment of adaptive and innate immune cells (e.g., T cell function in severe combined immune deficiency and natural killer cell function in familial hemophagocytic lymphohistiocytosis). (d) Evaluation of normal biological processes (e.g., class switching in B cells by B cell immunophenotyping). This review focuses on use of flow cytometry in disease-specific diagnosis of PIDDs in the context of a developing country.

Regulation of Cathepsin E gene expression by the transcription factor Kaiso in MRL/lpr mice derived CD4+ T cells

Global DNA hypomethylation in CD4+ cells in systemic lupus erythematosus (SLE) was suggested to play a key role in the pathogenesis. To identify new methylation-sensitive genes, we integrated genome-wide DNA methylation and mRNA profiling data in CD4+ cells of MRL/lpr (MRL) and C57BL6/J (B6) mice. We identified Cathepsin E (Ctse), in which 13 methyl-CpGs within 583 bp region of intron 1 were hypomethylated, and Ctse mRNA upregulated in MRL compared with B6 mice. One of methyl-CpGs, mCGCG was 93.3 ± 2.05% methylated in B6 mice, while 80.0 ± 6.2% methylated and mutated to CGGG in MRL mice. Kaiso is known to bind to mCGCG and we hypothesized that it represses expression of Ctse in B6 mice. The binding of Kaiso to mCGCG site in B6 mice was reduced in MRL mice revealed by ChIP-PCR. EL4 cells treated with 5-azaC and/or Trichostatin A showed the suppression of binding of Kaiso to mCGCG motif by ChIP-PCR and the overexpression of Ctse was demonstrated by qPCR. Ctse gene silencing by siRNA in EL4 cells resulted in reduction of IL-10 secretion. The hypomethylation of mCGCG motif, reduced recruitment of Kaiso, and increased expression of Ctse and Il-10 in CD4+ cells may be involved in the pathogenesis of SLE.

The Role of Efferocytosis in Autoimmune Diseases

Apoptosis happens continuously for millions of cells along with the active removal of apoptotic debris in order to maintain tissue homeostasis. In this respect, efferocytosis, i.e., the process of dead cell clearance, is orchestrated through cell exposure of a set of "find me," "eat me," and "tolerate me" signals facilitating the engulfment of dying cells through phagocytosis by macrophages and dendritic cells. The clearance of dead cells via phagocytes is of utmost importance to maintain the immune system tolerance to self-antigens. Accordingly, this biological activity prevents the release of autoantigens by dead cells, thus potentially suppressing the undesirable autoreactivity of immune cells and the appearance of inflammatory autoimmune disorders as systemic lupus erythematous and rheumatoid arthritis. In the present study, the apoptosis pathways and their immune regulation were reviewed. Moreover, efferocytosis process and its impairment in association with some autoimmune diseases were discussed.

IL-10 Paradoxically Promotes Autoimmune Neuropathy through S1PR1-Dependent CD4+ T Cell Migration

Chronic inflammatory demyelinating polyneuropathy (CIDP) is a debilitating condition caused by autoimmune demyelination of peripheral nerves. CIDP is associated with increased IL-10, a cytokine with well-described anti-inflammatory effects. However, the role of IL-10 in CIDP is unclear. In this study, we demonstrate that IL-10 paradoxically exacerbates autoimmunity against peripheral nerves. In IL-10-deficient mice, protection from neuropathy was associated with an accrual of highly activated CD4+ T cells in draining lymph nodes and absence of infiltrating immune cells in peripheral nerves. Accumulated CD4+ T cells in draining lymph nodes of IL-10-deficient mice expressed lower sphingosine-1-phosphate receptor 1 (S1pr1), a protein important in lymphocyte egress. Additionally, IL-10 stimulation in vitro induced S1pr1 expression in lymph node cells in a STAT3-dependent manner. Together, these results delineate a novel mechanism in which IL-10-induced STAT3 increases S1pr1 expression and CD4+ T cell migration to accelerate T cell-mediated destruction of peripheral nerves.

Downregulated regulatory T cell function is associated with increased peptic ulcer in Helicobacter pylori-infection

BACKGROUND

Helicobacter pylori (H. pylori) chronically colonizes gastric/duodenal mucosa and induces gastroduodenal disease such as gastritis and peptic ulcer and induces vigorous innate and specific immune responses; however, the infection is not removed, a state of chronic active gastritis persists for life if untreated. The objective of this study was to determine the number of regulatory T cells (Tregs) in gastric mucosa of patients with gastritis and peptic ulcer and determined the relationship between main virulence factor of H. pylori and Tregs.

METHODS AND MATERIALS

A total of 89 patients with gastritis, 63 patients with peptic ulcer and 40 healthy, H. pylori-negative subjects were enrolled in this study. Expression of CD4 and Foxp3 was determined by immunohistochemistry. Antrum biopsy was obtained for detection of H. pylori, bacterial virulence factors and histopathological assessments. TGF-β1, IL-10 and FOXP3 expressions were determined by real-time polymerase chain reaction (qPCR).

RESULTS

The numbers of CD4⁺ and Foxp3⁺ T cells as well as the expression of IL-10, TGF-β1, FOXP3, INF-γ and IL-17A in infected patients were significantly higher than the ones in uninfected patients. Also, the number of CD4⁺ T cells was independent on the vacuolating cytotoxin A (vacA) and outer inflammatory protein A (oipA), but it was positively correlated with cytotoxin-associated gene A (cagA). Instead, the number of Foxp3⁺ T cells was dependent on the vacA and oipA, but it was independent on cagA. The number of Foxp3⁺ T cells and the expression of IL-10, TGF-β1 and FOXP3 in infected patients with gastritis were significantly higher than the ones in infected patients with peptic ulcer. Moreover, the number of CD4⁺ T cells and the expression of IL-17A and INF-γ was the lowest in the gastritis patients, however, increased progressively in the peptic ulcer patients. Additionally, the numbers of CD4⁺ and Foxp3⁺ T cells as well as the expression of IL-10, TGF-β1, FOXP3 and INF-γ were positively correlated with the degree of H. pylori density and chronic inflammation.

CONCLUSION

Tregs are positively associated with vacA alleles and oipA status of H. pylori and histological grade but negatively associated with peptic ulcer disease.

The molecular signature of murine T cell homeostatic proliferation reveals both inflammatory and immune inhibition patterns

T lymphocyte homeostatic proliferation, driven by the engagement of T cell antigen receptor with self-peptide/major histocompatibility complexes, and signaling through the common γ-chain-containing cytokine receptors, is critical for the maintenance of the T cell compartment and is regulated by the Fas death receptor (Fas, CD95). In the absence of Fas, Fas-deficient lymphoproliferation spontaneous mutation (lpr) mice accumulate homeostatically expanded T cells. The functional consequences of sequential rounds of homeostatic expansion are not well defined. We thus examined the gene expression profiles of murine wild-type and Fas-deficient lpr CD8⁺ T cell subsets that have undergone different amounts of homeostatic proliferation as defined by their level of CD44 expression, and the CD4^-CD8^-TCRαβ⁺ T cell subset that results from extensive homeostatic expansion of CD8⁺ T cells. Our studies show that recurrent T cell homeostatic proliferation results in global gene expression changes, including the progressive upregulation of both cytolytic proteins such as Fas-Ligand and granzyme B as well as inhibitory proteins such as programmed cell death protein 1 (PD-1) and lymphocyte activating 3 (Lag3). These findings provide an explanation for how augmented T cell homeostatic expansion could lead to the frequently observed clinical paradox of simultaneous autoinflammatory and immunodeficiency syndromes and provide further insight into the regulatory programs that control chronically stimulated T cells.

Autoimmune Lymphoproliferative Syndrome: A Rare Cause of Disappearing HDL Syndrome

The term disappearing HDL syndrome refers to development of severe high density lipoprotein cholesterol (HDL-C) deficiency in noncritically ill patients with previously normal HDL-C and triglyceride levels. Autoimmune lymphoproliferative syndrome (ALPS) is a disorder of the immune system due to an inability to regulate lymphocyte homeostasis resulting in lymphadenopathy and hepatosplenomegaly. We describe a 17-year-old boy who was evaluated in the lipid clinic for history of undetectable or low HDL-C and low density lipoprotein cholesterol (LDL-C) levels. Past medical history was significant for ALPS IA diagnosed at 10 years of age when he presented with bilateral cervical adenopathy. He was known to have a missense mutation in one allele of the FAS protein extracellular domain consistent with ALPS type 1A. HDL-C and LDL-C levels had been undetectable on multiple occasions, though lipids had not been measured prior to the diagnosis of ALPS. He had been receiving sirolimus for immunosuppression. The HDL-C and LDL-C levels correlated with disease activity and improved to normal levels during times when the activity of ALPS was controlled. This case highlights the importance of considering ALPS as a cause of low HDL-C and LDL-C levels in a child with evidence of lymphoproliferation.

IL-10/Janus kinase/signal transducer and activator of transcription 3 signaling dysregulates Bim expression in autoimmune lymphoproliferative syndrome

BACKGROUND

Autoimmune lymphoproliferative syndrome (ALPS) is a human disorder of T cell homeostasis caused by mutations that impair FAS-mediated apoptosis. A defining characteristic of ALPS is the expansion of double negative T cells (DNTC). Relatively little is known about how defective FAS-driven cell death and the Bcl-2 apoptotic pathway intersect in ALPS patients.

OBJECTIVE

We studied changes in Bcl-2 family member expression in ALPS to determine whether the Bcl-2 pathway might provide a therapeutic target.

METHODS

We used flow cytometry to analyze the expression of pro- and anti-apoptotic Bcl-2 family members in T cells from 12 ALPS patients and determined the in vitro sensitivity of ALPS DNTC to the pro-apoptotic BH3 mimetic, ABT-737.

RESULTS

The pro-apoptotic molecule, Bim, was significantly elevated in DNTC. Although no general pattern of individual anti-apoptotic Bcl-2 family members emerged, increased expression of Bim was always accompanied by increased expression of at least 1 anti-apoptotic Bcl-2 family member. Strikingly, Bim levels in DNTC correlated significantly with serum IL-10 in ALPS patients, and IL-10 was sufficient to mildly induce Bim in normal and ALPS T cells via a Janus kinase/signal transducer and activator of transcription 3-dependent mechanism. Finally, ABT-737 preferentially killed ALPS DNTC in vitro.

CONCLUSION

Combined, these data show that an IL-10/Janus kinase/signal transducer and activator of transcription 3 pathway drives Bim expression in ALPS DNTC, which renders them sensitive to BH3 mimetics, uncovering a potentially novel therapeutic approach to ALPS.

Abnormally differentiated CD4+ or CD8+ T cells with phenotypic and genetic features of double negative T cells in human Fas deficiency

Lack of KLRG1 and T-bet expression is a unique feature of DNT and subsets of single positive T cells in ALPS patients. Genetic, phenotypic, and transcriptional evidence indicates that DNT in ALPS patients derive from both CD4+ and CD8+ T cells.

Causes and consequences of the autoimmune lymphoproliferative syndrome

Autoimmune lymphoproliferative syndrome (ALPS) is the first autoimmune hematological disease whose genetic basis has been defined. It is a disorder of apoptosis in which the inability of lymphocytes to die leads to lymphadenopathy, hypersplenism, and autoimmune cytopenias of childhood onset. More than 200 ALPS patients have been studied over the last 15 years and followed by our colleagues and ourselves at the Clinical Center of the National Institutes of Health. Based upon this experience we have determined that patients with germline mutations of the intracellular domain of Fas protein, the most frequent single genetic cause of ALPS, have a significantly increased risk of developing Hodgkin and non-Hodgkin lymphoma (NHL), underscoring the critical role played by cell surface receptor-mediated apoptosis in eliminating redundant proliferating lymphocytes with autoreactive and oncogenic potential. The major determinants of morbidity and mortality in ALPS are the severity of the autoimmune disease, hypersplenism, asplenia-related sepsis, and the risk of lymphoma, which in itself requires long-term surveillance. Though most episodes of cytopenias respond to courses of conventional immunomodulatory agents, some ALPS patients, especially those with massive splenomegaly and hypersplenism, may require splenectomy and/or ongoing immunosuppressive treatment. Thus, ALPS highlights the importance of cell death pathways in health and disease.

Nodular regenerative hyperplasia in common variable immunodeficiency

PURPOSE

Patients with Common Variable Immunodeficiency (CVID) are subject to the development of a liver disease syndrome known as nodular regenerative hyperplasia (NRH). The purpose of this study was to define the characteristics and course of this complication of CVID.

METHODS

CVID patients were evaluated by retrospective and prospective clinical course review. Liver biopsy specimens were evaluated for evidence of NRH and studied via RT-PCR for cytokine analysis.

RESULTS

NRH in our CVID patient population occurred in approximately 5 % of the 261 patients in our total CVID study group, initially presenting in most cases with an elevated alkaline phosphatase level. While in some patients the disease remained static, in a larger proportion a more severe disease developed characterized by portal hypertension, the latter leading to hypersplenism with neutropenia and thrombocytopenia and, in some cases, to ascites. In addition, a substantial proportion of patients either developed or presented initially with an autoimmune hepatitis-like (AIH-like) liver disease that resulted in severe liver dysfunction and, in most cases to death due to infections. The liver histologic findings in these AIH-like patients were characterized by underlying NRH pattern with superimposed interface hepatitis, lymphocytic infiltration and fibrosis. Immunologic studies of biopsies of NRH patients demonstrated the presence of infiltrating T cells producing IFN-γ, suggesting that the NRH is due to an autoimmune process.

CONCLUSION

Overall, these studies provide evidence that NRH may not be benign but, can be a severe and potentially fatal disease complication of CVID that merits close monitoring and intervention.

Fas-independent T-cell apoptosis by dendritic cells controls autoimmune arthritis in MRL/lpr mice

Background

Although autoimmunity in MRL/lpr mice occurs due to a defect in Fas-mediated cell death of T cells, the role of Fas-independent apoptosis in pathogenesis has rarely been investigated. We have recently reported that receptor activator of nuclear factor (NF)-κB ligand (RANKL)-activated dendritic cells (DCs) play a key role in the pathogenesis of rheumatoid arthritis (RA) in MRL/lpr mice. We here attempted to establish a new therapeutic strategy with RANKL-activated DCs in RA by controlling apoptosis of peripheral T cells. Repeated transfer of RANKL-activated DCs into MRL/lpr mice was tested to determine whether this had a therapeutic effect on autoimmunity.

Methods and Finding

Cellular and molecular mechanisms of Fas-independent apoptosis of T cells induced by the DCs were investigated by in vitro and in vivo analyses. We demonstrated that repeated transfers of RANKL-activated DCs into MRL/lpr mice resulted in therapeutic effects on RA lesions and lymphoproliferation due to declines of CD4⁺ T, B, and CD4⁻CD8⁻ double negative (DN) T cells. We also found that the Fas-independent T-cell apoptosis was induced by a direct interaction between tumor necrosis factor (TNF)-related apoptosis-inducing ligand-receptor 2 (TRAIL-R2) on T cells and TRAIL on Fas-deficient DCs in MRL/lpr mice.

Conclusion

These results strongly suggest that a novel Fas-independent apoptosis pathway in T cells maintains peripheral tolerance and thus controls autoimmunity in MRL/lpr mice.

Autoimmune lymphoproliferative syndrome caused by a homozygous null FAS ligand (FASLG) mutation

BACKGROUND

Autoimmune lymphoproliferative syndrome (ALPS) is characterized by chronic nonmalignant lymphoproliferation, accumulation of double-negative T cells, hypergammaglobulinemia G and A, and autoimmune cytopenia.

OBJECTIVES

Although mostly associated with FAS mutations, different genetic defects leading to impaired apoptosis have been described in patients with ALPS, including the FAS ligand gene (FASLG) in rare cases. Here we report on the first case of complete FAS ligand deficiency caused by a homozygous null mutant.

METHODS

Double-negative T-cell counts and plasma IL-10 and FAS ligand concentrations were determined as ALPS markers. The FASLG gene was sequenced, and its expression was analyzed by means of Western blotting. FAS ligand function was assessed based on reactivation-induced cell death.

RESULTS

We describe a patient born to consanguineous parents who presented with a severe form of ALPS caused by FASLG deficiency. Although the clinical presentation was compatible with a homozygous FAS mutation, FAS-induced apoptosis was normal, and plasma FAS ligand levels were not detectable. This patient carries a homozygous, germline, single-base-pair deletion in FASLG exon 1, leading to a premature stop codon (F87fs x95) and a complete defect in FASLG expression. The healthy parents were each heterozygous for the mutation, confirming its recessive trait.

CONCLUSION

FAS ligand deficiency should be screened in patients presenting with ALPS features but lacking the usual markers, including plasma soluble FAS ligand and an in vitro apoptotic defect. An activation-induced cell death test could help in discrimination.

Regulation of immune responses by histone deacetylase inhibitors

Both genetic and epigenetic factors are important regulators of the immune system. There is an increasing body of evidence attesting to epigenetic modifications that influence the development of distinct innate and adaptive immune response cells. Chromatin remodelling via acetylation, methylation, phosphorylation, and ubiquitination of histone proteins as well as DNA, methylation is epigenetic mechanisms by which immune gene expression can be controlled. In this paper, we will discuss the role of epigenetics in the regulation of host immunity, with particular emphasis on histone deacetylase inhibitors. In particular, the role of HDAC inhibitors as a new class of immunomodulatory therapeutics will also be reviewed.

Monogenic autoimmunity

Monogenic autoimmune syndromes provide a rare yet powerful glimpse into the fundamental mechanisms of immunologic tolerance. Such syndromes reveal not only the contribution of an individual breakpoint in tolerance but also patterns in the pathogenesis of autoimmunity. Disturbances in innate immunity, a system built for ubiquitous sensing of danger signals, tend to generate systemic autoimmunity. For example, defects in the clearance of self-antigens and chronic stimulation of type 1 interferons lead to the systemic autoimmunity seen in C1q deficiency, SPENCDI, and AGS. In contrast, disturbances of adaptive immunity, which is built for antigen specificity, tend to produce organ-specific autoimmunity. Thus, the loss of lymphocyte homeostasis, whether through defects in apoptosis, suppression, or negative selection, leads to organ-specific autoimmunity in ALPS, IPEX, and APS1. We discuss the unique mechanisms of disease in these prominent syndromes as well as how they contribute to the spectrum of organ-specific or systemic autoimmunity. The continued study of rare variants in autoimmune disease will inform future investigations and treatments directed at rare and common autoimmune diseases alike.

FAS/FAS-L dependent killing of activated human monocytes and macrophages by CD4+CD25- responder T cells, but not CD4+CD25+ regulatory T cells

Conclusive resolution of an immune response is critical for the prevention of autoimmunity and chronic inflammation. We report that following co-culture with autologous CD4+CD25- responder T cells, human CD14+ monocytes and monocyte-derived macrophages become activated but also significantly more prone to apoptosis than monocytes/macrophages cultured alone. In contrast, in the presence of CD4+CD25+ regulatory T cells (Tregs), monocytes and macrophages survive whilst adopting an anti-inflammatory phenotype. The induction of monocyte death requires responder T cell activation and cell-contact between responder T cells and monocytes. We demonstrate a critical role for FAS/FAS-L ligation in responder T cell-induced monocyte killing since responder T cells, but not Tregs, upregulate FAS-ligand (FAS-L) mRNA, and induce FAS expression on monocytes. Furthermore, responder T cell-induced monocyte apoptosis is blocked by neutralising FAS/FAS-L interaction, and is not observed when monocytes from an autoimmune lymphoproliferative syndrome (ALPS) patient with complete FAS-deficiency are used as target cells. Finally, we show that responder T cell-induced killing of monocytes is impaired in patients with active rheumatoid arthritis (RA). Our data suggest that resolution of inflammation in the course of a healthy immune response is aided by the unperturbed killing of monocytes with inflammatory potential by responder T cells and the induction of longer-lived, Treg-induced, anti-inflammatory monocytes.

Onset of autoimmune lymphoproliferative syndrome (ALPS) in humans as a consequence of genetic defect accumulation

Autoimmune diseases develop in approximately 5% of humans. They can arise when self-tolerance checkpoints of the immune system are bypassed as a consequence of inherited mutations of key genes involved in lymphocyte activation, survival, or death. For example, autoimmune lymphoproliferative syndrome (ALPS) results from defects in self-tolerance checkpoints as a consequence of mutations in the death receptor-encoding gene TNF receptor superfamily, member 6 (TNFRSF6; also known as FAS). However, some mutation carriers remain asymptomatic throughout life. We have now demonstrated in 7 ALPS patients that the disease develops as a consequence of an inherited TNFRSF6 heterozygous mutation combined with a somatic genetic event in the second TNFRSF6 allele. Analysis of the patients' CD4(-)CD8(-) (double negative) T cells--accumulation of which is a hallmark of ALPS--revealed that in these cells, 3 patients had somatic mutations in their second TNFRSF6 allele, while 4 patients had loss of heterozygosity by telomeric uniparental disomy of chromosome 10. This observation provides the molecular bases of a nonmalignant autoimmune disease development in humans and may shed light on the mechanism underlying the occurrence of other autoimmune diseases.

Cell type specificity and host genetic polymorphisms influence antibody-dependent enhancement of dengue virus infection

Antibody-dependent enhancement (ADE) is implicated in severe, usually secondary, dengue virus (DV) infections. Preexisting heterotypic antibodies, via their Fc-gamma receptor (FcγR) interactions, may increase disease severity through enhanced target cell infection. Greater numbers of infected target cells may contribute to higher viremia and excess cytokine levels often observed in severe disease. Monocytes, macrophages, and immature and mature dendritic cells (DC) are considered major cellular targets of DV. Apheresis of multiple donors allowed isolation of autologous primary myeloid target cell types for head-to-head comparison of infection rates, viral output, and cytokine production under direct infection (without antibody) or ADE conditions (with antibody). All studied cell types except immature DC supported ADE. All cells undergoing ADE secreted proinflammatory cytokines (interleukin-6 [IL-6] and tumor necrosis factor alpha [TNF-α]) at enhancement titers, but distinct cell-type-specific patterns were observed for other relevant proteins (alpha/beta interferon [IFN-α/β] and IL-10). Macrophages produced type I interferons (IFN-α/β) that were modulated by ADE. Mature DC mainly secreted IFN-β. Interestingly, only monocytes secreted IL-10, and only upon antibody-enhanced infection. While ADE infection rates were remarkably consistent in monocytes (10 to 15%) across donors, IL-10 protein levels varied according to previously described regulatory single nucleotide polymorphisms (SNPs) in the IL-10 promoter region. The homozygous GCC haplotype was associated with high-level IL-10 secretion, while the ACC and ATA haplotypes produced intermediate and low levels of IL-10, respectively. Our data suggest that ADE effects are cell type specific, are influenced by host genetics, and, depending on relative infection rates, may further contribute to the complexity of DV pathogenesis.

Clinical and immunological overlap between autoimmune lymphoproliferative syndrome and common variable immunodeficiency

Autoimmune lymphoproliferative syndrome (ALPS) is mainly caused by defects in the CD95 pathway. Raised CD3+TCRαβ+CD4-CD8- double negative T cells and impaired T cell apoptosis are hallmarks of the disease. In contrast, the B cell compartment has been less well studied. We found an altered distribution of B cell subsets with raised transitional B cells and reduced marginal zone B cells, switched memory B cells and plasma blasts in most of 22 analyzed ALPS patients. Moreover, 5 out of 66 ALPS patients presented with low IgG and susceptibility to infection revealing a significant overlap between ALPS and common variable immunodeficiency (CVID). In patients presenting with lymphoproliferation, cytopenia, hypogammaglobulinemia and impaired B cell differentiation, serum biomarkers were helpful in addition to apoptosis tests for the identification of ALPS patients. Our observations may indicate a role for apoptosis defects in some diseases currently classified as CVID.

Role of tissue inhibitor of metalloproteinases-1 in the development of autoimmune lymphoproliferation

BACKGROUND

Inherited defects decreasing function of the Fas death receptor cause autoimmune lymphoproliferative syndrome and its variant Dianzani's autoimmune lymphoproliferative disease. Analysis of the lymphocyte transcriptome from a patient with this latter condition detected striking over-expression of osteopontin and tissue inhibitor of metalloproteinases-1. Since previous work on osteopontin had detected increased serum levels in these patients, associated with variations of its gene, the aim of this work was to extend the analysis to tissue inhibitor of metalloproteinases-1.

DESIGN AND METHODS

Tissue inhibitor of metalloproteinases-1 levels were evaluated in sera and culture supernatants from patients and controls by enzyme-linked immunosorbent assay. Activation- and Fas-induced cell death were induced, in vitro, using anti-CD3 and anti-Fas antibodies, respectively.

RESULTS

Tissue inhibitor of metalloproteinases-1 levels were higher in sera from 32 patients (11 with autoimmune lymphoproliferative syndrome and 21 with Dianzani's autoimmune lymphoproliferative disease) than in 50 healthy controls (P<0.0001), unassociated with variations of the tissue inhibitor of metalloproteinases-1 gene. Both groups of patients also had increased serum levels of osteopontin. In vitro experiments showed that osteopontin increased tissue inhibitor of metalloproteinases-1 secretion by peripheral blood monocytes. Moreover, tissue inhibitor of metalloproteinases-1 significantly inhibited both Fas- and activation-induced cell death of lymphocytes.

CONCLUSIONS

These data suggest that high osteopontin levels may support high tissue inhibitor of metalloproteinases-1 levels in autoimmune lymphoproliferative syndrome and Dianzani's autoimmune lymphoproliferative disease, and hence worsen the apoptotic defect in these diseases.

Development of disseminated histiocytic sarcoma in a patient with autoimmune lymphoproliferative syndrome and associated Rosai-Dorfman disease

Patients with autoimmune lymphoproliferative syndrome (ALPS) have defective lymphocyte apoptosis with increased risk for lymphoid malignancies. Herein, we report a patient with ALPS who developed histiocytic sarcoma in a background of sinus histiocytosis and massive lymphadenopathy or Rosai- Dorfman disease. This patient had documented ALPS type Ia with a germline missense mutation in exon 9 of the TNFRSF6 gene (973 A>T, D244V) encoding Fas (CD95/Apo-1). He presented at 10 months with hepatosplenomegaly and autoimmune hemolytic anemia and was diagnosed with ALPS. At the age of 6 (1/2) years, he developed classic Hodgkin lymphoma which was treated using standard chemotherapy. Two years later, a biopsy of a positron emission tomography-positive axillary node showed features of ALPS and focal involvement by sinus histiocytosis and massive lymphadenopathy. Thereafter, the patient continued to have continued lymphadenopathy and progressive splenomegaly, leading to exploratory surgery at the age of 13 years for suspicion of lymphoma. Para-abdominal nodes revealed sheets of malignant- looking histiocytes with increased mitotic activity and areas of necrosis, indicative of histiocytic sarcoma. Spleen and lymph nodes also showed involvement by Rosai-Dorfman disease. Both components had an identical phenotype of S-100+/CD68+/ CD163+. The occurrence of malignancies involving 2 separate hematopoietic lineages in ALPS has not been reported earlier. Given the central role of defective Fas signaling in ALPS, histiocytes may be yet another lineage at risk for neoplastic transformation secondary to a block in apoptosis.

Somatic FAS mutations are common in patients with genetically undefined autoimmune lymphoproliferative syndrome

Autoimmune lymphoproliferative syndrome (ALPS) is characterized by childhood onset of lymphadenopathy, hepatosplenomegaly, autoimmune cytopenias, elevated numbers of double-negative T (DNT) cells, and increased risk of lymphoma. Most cases of ALPS are associated with germline mutations of the FAS gene (type Ia), whereas some cases have been noted to have a somatic mutation of FAS primarily in their DNT cells. We sought to determine the proportion of patients with somatic FAS mutations among a group of our ALPS patients with no detectable germline mutation and to further characterize them. We found more than one-third (12 of 31) of the patients tested had somatic FAS mutations, primarily involving the intracellular domain of FAS resulting in loss of normal FAS signaling. Similar to ALPS type Ia patients, the somatic ALPS patients had increased DNT cell numbers and elevated levels of serum vitamin B(12), interleukin-10, and sFAS-L. These data support testing for somatic FAS mutations in DNT cells from ALPS patients with no detectable germline mutation and a similar clinical and laboratory phenotype to that of ALPS type Ia. These findings also highlight the potential role for somatic mutations in the pathogenesis of nonmalignant and/or autoimmune hematologic conditions in adults and children.

The autoimmune lymphoproliferative syndrome: A rare disorder providing clues about normal tolerance

The autoimmune lymphoproliferative syndrome (ALPS) is characterized by chronic, non-malignant lymphoproliferation, autoimmunity often manifesting as multilineage cytopenias, and an increased risk of lymphoma. While considered a rare disease, there are currently over 250 patients with ALPS being followed at the National Institutes of Health in Bethesda, Maryland. Most of these patients have a mutation in the gene for the TNF receptor-family member Fas (CD 95, Apo-1), and about one-third have an unknown defect or mutations affecting function of other signaling proteins involved in the apoptotic pathway. While ALPS is one of the few autoimmune diseases with a known genetic defect, there remain unanswered questions regarding how a defect in apoptosis results in the observed phenotype. In addition to shedding light on the pathophysiology of this rare and fascinating condition, studying ALPS may improve our understanding of normal tolerance and more common, sporadic autoimmune disorders.

Autoimmune Lymphoproliferative Syndrome

The autoimmune lymphoproliferative syndrome (ALPS) is a rare disease. ALPS is an inherited condition that affects both sexes. ALPS is not cancer, it is not infectious, and its incidence has not yet been estimated. ALPS generally does not lead to death and most individuals with ALPS are able to live normal lives. ALPS is a disorder associated with abnormal lymphocyte apoptosis, lymphoproliferation, and autoimmunity. Serologic testing is critical in the evaluation of these individuals. Lymphoproliferation in ALPS patients is generally benign, but they are at increased risk for the development of Hodgkin's and non-Hodgkin's lymphoma. It is characterized by massive lymphoadenopathy, splenomegaly, autoimmunity including episodes of immune hemolityc anemia, thrombocytopenia, and neutropenia. ALPS patients have lymphocytosis and a number of lymphocyte abnormalities, including the marked expansion of T lymphocytes that express alpha/beta T-cell receptors, but neither CD4 nor CD8 surface markers (TCR alpha/beta+; CD4-; CD8- cells).

Development of Lymphoma in Autoimmune Lymphoproliferative Syndrome (ALPS) and its Relationship to Fas Gene Mutations

Autoimmune Lymphoproliferative Syndrome (ALPS) is generally the result of a mutation in genes associated with apoptosis, like Fas, Fas ligand, Casp 8 and Casp 10. As a result, the normal homeostasis of T- and B-lymphocytes is disturbed and a proliferation of polyclonal T lymphocytes occurs. This leads to hepatosplenomegaly and lymphadenopathy and in most patients also to autoimmune phenomena like anemia and thrombocytopenia. The proliferating T cells are TCRalphabeta and/or TCRgammadelta positive but lack both CD4 and CD8. Hence they are termed double negative (DN) T cells. In addition, there is an increase of CD5 positive B cells. Individuals with germline mutations in the Fas gene have a high risk to develop non Hodgkin lymphomas (x 14) as well as Hodgkin lymphomas (x 51), in particular NLP Hodgkin lymphoma. Somatic mutations of Fas are frequently acquired during the normal germinal center reaction. Non Hodgkin lymphomas carry somatic mutations of the Fas gene in 11% and of the Casp 10 gene in 14.5% of the patients. In Hodgkin lymphomas, Fas mutations can be demonstrated in Reed-Sternberg cells in 10-20% of the patients. These data implicate a role for Fas-mediated apoptosis in preventing lymphomas. Inherited defects in receptor-mediated lymphocyte apoptosis represent a risk factor for lymphomas and somatic mutations of these genes may also play a role in the development and/or progression of lymphomas.

Valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, diminishes lymphoproliferation in the Fas -deficient MRL/lpr(-/-) murine model of autoimmune lymphoproliferative syndrome (ALPS)

OBJECTIVE

Autoimmune lymphoproliferative syndrome (ALPS) is a disorder of apoptosis, often presenting in childhood. Similarly, MRL/lpr(-/-) mice homozygous for Fas mutations develop an ALPS-like disease with autoimmunity, lymphadenopathy, splenomegaly, and expansion of double-negative T cells. Currently, there are no proven therapies with adequate safety margins for sustained abolition of the lymphoproliferation associated with ALPS. We sought to test the ability of valproic acid (VPA), a histone deacetylase inhibitor, to induce apoptosis and inhibit lymphoproliferation.

MATERIALS AND METHODS

Human peripheral blood mononuclear cells from patients with ALPS and normal controls were tested in vitro to determine the efficacy of VPA at inducing cell death. VPA was used in vivo to control lymphoproliferation in MRL/lpr(-/-) mice, a model for ALPS.

RESULTS

VPA induced cell death in vitro, and was partially inhibited by the pan caspase inhibitor, Z-VAD-FMK. MRL/lpr(-/-) mice treated with VPA for 8 weeks showed significant reductions in spleen and lymph node weights and cellularity compared to controls. A concomitant decrease in double-negative T cells was observed in the spleen, lymph nodes, and peripheral blood. Serum levels of VPA peaked 1 hour after injection, and a 2.5-fold increase in histone acetylation was observed in the spleen at 4 hours after injection.

CONCLUSION

Based on our data, VPA is effective at reducing lymphoproliferation in mice, and is currently being studied in a clinical trial as a lympholytic agent in patients with ALPS.

FAS-L, IL-10, and double-negative CD4- CD8- TCR alpha/beta+ T cells are reliable markers of autoimmune lymphoproliferative syndrome (ALPS) associated with FAS loss of function

Autoimmune lymphoproliferative syndrome (ALPS) is characterized by splenomegaly, lymphadenopathy, hypergammaglobulinemia, accumulation of double-negative TCRalphabeta(+) CD4(-)CD8(-) T cells (DNT cells), and autoimmunity. Previously, DNT cell detection and a functional defect of T cells in a FAS-induced apoptosis test in vitro had been used for ALPS diagnosis. However, a functional defect can also be detected in mutation-positive relatives (MPRs) who remain free of any ALPS-related disease. In contrast, lymphocytes from patients carrying a somatic mutation of FAS exhibit normal sensitivity to FAS-induced apoptosis in vitro. We assessed the soluble FAS-L concentration in the plasma of ALPS patients carrying FAS mutations. Overall, we showed that determination of the FAS-L represents, together with the IL-10 concentration and the DNT cell percentage, a reliable tool for the diagnosis of ALPS.

Genetic defects of apoptosis and primary immunodeficiency

Programmed cell death is important for maintaining lymphocyte homeostasis. Several human-inherited diseases with impaired apoptosis have been identified at the genetic level: autoimmune lymphoproliferative syndrome, caspase-8 deficiency state, and X-linked lymphoproliferative syndrome. These diseases feature excess lymphocyte accumulation, autoimmunity, or immunodeficiency. Elucidating their molecular pathogenesis has also provided new insights into the signaling mechanisms regulating apoptosis and lymphocyte activation.

Human TCR alpha/beta+ CD4-CD8- double-negative T cells in patients with autoimmune lymphoproliferative syndrome express restricted Vbeta TCR diversity and are clonally related to CD8+ T cells

The peripheral expansion of alpha/beta+-CD4-CD8- double negative (DN) T cells in patients with autoimmune lymphoproliferative syndrome (ALPS) is a consistent feature of this disease, and part of the diagnostic criteria of ALPS. The origin of these cells remains undetermined. They could derive from mature T cells that have lost coreceptor expression, or represent a special minor cell lineage. To investigate relationship of DN and single positive (SP) T cells in ALPS, we used Immunoscope technology to analyze the TCRVbeta repertoire diversity of sorted DN and SP T cells, and we performed CDR3 sequence analyses of matching clonotypes. We show that DN T cells express all the Vbeta gene families that are used by their SP counterparts, though they dominantly use some Vbeta genes. Analysis of CDR3 length distribution revealed a diverse polyclonal TCR repertoire for sorted CD4+ T cells, whereas both DN and CD8+ T cells showed a skewed TCR repertoire with oligoclonal expansions throughout most of the Vbeta families. CDR3 sequencing of matching clonotypes revealed a significant sharing of CDR3 sequences from selected Vbeta-Jbeta transcripts between DN and CD8+ T cells. Altogether, these data strongly argue for a CD8 origin of DN T cells in ALPS.

The autoimmune lymphoproliferative syndrome: an experiment of nature involving lymphocyte apoptosis

Autoimmune lymphproliferative syndrome (ALPS) is a human disorder that has been characterized in the past two decades at both a functional and a genetic level. The underlying basis for this disorder is a defect in lymphocyte apoptosis that alters immune homeostasis resulting in an expansion of a normally rare circulating lymphocyte, the alpha beta double negative T cell. The abnormality in Fas mediated apoptosis underlying ALPS serves as a risk factor for autoimmunity involving blood cells and the development of lymphoma. There remain patients with a diagnosis of ALPS but without a defined genetic defect and current investigations are focusing on fully characterizing this patient subgroup.

Autoimmune lymphoproliferative syndrome (ALPS) caused by Fas (CD95) mutation mimicking sarcoidosis

Autoimmune lymphoproliferative syndrome (ALPS) is an inherited disorder associated with defects in apoptosis, characterized by childhood onset of lymphadenopathy, splenomegaly, hyperimmunoglobulinemia, and autoimmune disease. ALPS is most frequently associated with a mutation in the cell death receptor Fas (CD95). Very rarely a mutation in caspase 10 is present. An increase of CD4/CD8 double negative T cells in the peripheral blood and lymph nodes is a feature characteristic of ALPS. Additionally, histiocytic proliferations resembling sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease) were reported recently in patients with ALPS. In the rare cases with a caspase 10 mutation an accumulation of dendritic cells in lymphoid organs was noted. We describe a different, sarcoidosislike, histiocytic infiltration of lymph nodes that persisted for years in a girl, that was initially supposed to suffer from sarcoidosis, but was eventually diagnosed as ALPS, associated with a missense mutation in the intracellular death domain of Fas. This sarcoidosislike histologic picture extends the spectrum of histiocytic lymph node alterations observed in ALPS and alerts of a potential diagnostic pitfall.

Pyrimethamine treatment does not ameliorate lymphoproliferation or autoimmune disease in MRL/lpr-/- mice or in patients with autoimmune lymphoproliferative syndrome

Autoimmune lymphoproliferative syndrome (ALPS) is an inherited disorder of lymphocyte apoptosis leading to childhood onset of marked lymphadenopathy, hepatosplenomegaly, autoimmune cytopenias, and increased risk of lymphoma. Most cases are associated with heterozygous mutations in the gene encoding Fas protein. Prolonged use of immunosuppressive drugs that do ameliorate its autoimmune complications fail to consistently lessen lymphoproliferation in ALPS. A case series had described children with ALPS, whose spleens (SPL) and lymph nodes decreased in size when treated weekly with pyrimethamine and sulfadoxine; parallel in vitro studies showed only pyrimethamine to promote apoptosis. On the basis of that experience, we undertook additional in vitro lymphocyte apoptosis assays, and measured SPL weights, lymphocyte numbers, and immunophenotypes in Fas-deficient MRL/lpr-/- mice to gain further insights into the utility of combined pyrimethamine/sulfadoxine or pyrimethamine alone. Moreover, seven children with ALPS enrolled in a study of escalating dose of pyrimethamine alone given twice weekly for 12 weeks to determine if their lymphadenopathy and/or splenomegaly would diminish, as assessed by standardized computerized tomography. Neither pyrimethamine alone or with sulfadoxine in the MRL/lpr-/- mice, nor pyrimethamine alone in ALPS patients proved efficacious. We conclude that these drugs do not warrant further use empirically or as part of clinical trials in ALPS Type Ia as a lympholytic agent.

Perforin-dependent apoptosis functionally compensates Fas deficiency in activation-induced cell death of human T lymphocytes

Activation-induced cell death (AICD) is involved in peripheral tolerance by controlling the expansion of repeatedly stimulated T cells via an apoptotic Fas (CD95; APO-1)-dependent pathway. The TNFRSF-6 gene encoding Fas is mutated in children suffering from autoimmune lymphoproliferative syndrome (ALPS), which is characterized by lymphoproliferation and autoimmunity. We examined AICD in Fas-deficient T cells from ALPS patients. We showed that primary activated Fas-deficient T cells die by apoptosis after repeated T cell antigen receptor (TCR) stimulation despite resistance to Fas-mediated cell death. This Fas-independent AICD was found to be mediated through a cytotoxic granules-dependent pathway. Cytotoxic granules-mediated AICD was also detected in normal T lymphocytes though to a lesser extent. As expected, the cytotoxic granules-dependent AICD was abolished in T cells from Rab27a- or perforin-deficient patients who exhibited defective granules-dependent cytotoxicity. Supporting an in vivo relevance of the cytotoxic granules-dependent AICD in ALPS patients, we detected an increased number of circulating T lymphocytes expressing granzymes A and B. Altogether, these data indicated that the cytotoxic granules-dependent cell death in ALPS may compensate for Fas deficiency in T lymphocytes. Furthermore, they identified a novel AICD pathway as a unique alternative to Fas apoptosis in human peripheral T lymphocytes.

Dominant inhibition of Fas ligand-mediated apoptosis due to a heterozygous mutation associated with autoimmune lymphoproliferative syndrome (ALPS) Type Ib

Background:

Autoimmune lymphoproliferative syndrome (ALPS) is a disorder of lymphocyte homeostasis and immunological tolerance due primarily to genetic defects in Fas (CD95/APO-1; TNFRSF6), a cell surface receptor that regulates apoptosis and its signaling apparatus.

Methods:

Fas ligand gene mutations from ALPS patients were identified through cDNA and genomic DNA sequencing. Molecular and biochemical assessment of these mutant Fas ligand proteins were carried out by expressing the mutant FasL cDNA in mammalian cells and analysis its effects on Fas-mediated programmed cell death.

Results:

We found an ALPS patient that harbored a heterozygous A530G mutation in the FasL gene that replaced Arg with Gly at position 156 in the protein's extracellular Fas-binding region. This produced a dominant-interfering FasL protein that bound to the wild-type FasL protein and prevented it from effectively inducing apoptosis.

Conclusion:

Our data explain how a naturally occurring heterozygous human FasL mutation can dominantly interfere with normal FasL apoptotic function and lead to an ALPS phenotype, designated Type Ib.

Eosinophilia is associated with a higher mortality rate among patients with autoimmune lymphoproliferative syndrome

Autoimmune lymphoproliferative syndrome (ALPS) is a disorder associated with heritable defects in lymphocyte apoptosis that result in chronic nonmalignant lymphadenopathy, splenomegaly, and autoimmunity. To examine the prevalence, mechanisms, and potential implications of eosinophilia in ALPS, we reviewed data retrospectively from 187 consecutive ALPS patients and their family members studied at the National Institutes of Health. ALPS patients with eosinophilia were compared with ALPS patients without eosinophilia with respect to their clinical and immunologic phenotype. Potential mechanisms for the eosinophilia, including abnormal Fas-mediated eosinophil apoptosis, increased production of eosinophilopoietic cytokines, and presence of anti-eosinophilic autoantibodies were also explored in a small number of patients from whom samples were available. Analysis of data from 68 ALPS patients and 119 of their relatives identified a distinct subgroup of patients with prominent and persisting eosinophilia that proved to be associated with increased numbers of peripheral blood leukocytes (PBL) of multiple lineages and a trend towards increased serum IgE levels. Eosinophilic ALPS patients also had a significantly higher risk of death due to infectious complications. Although the specific etiology of the eosinophilia in these patients remains uncertain, it does not appear to be associated with an altered serum cytokine profile, increased survival responsiveness of eosinophils to IL-5, defective Fas-mediated eosinophil apoptosis, or anti-eosinophil antibodies. Eosinophilia defines a distinct subgroup of ALPS patients with increased serum IgE levels, increased numbers of PBL of multiple lineages, and higher mortality from infectious complications.

Arsenic trioxide: a promising novel therapeutic agent for lymphoproliferative and autoimmune syndromes in MRL/lpr mice

MRL/lpr mice develop a human lupuslike syndrome and, as in autoimmune lymphoproliferative syndrome (ALPS), massive lymphoproliferation due to inactivation of Fas-mediated apoptosis. Presently, no effective therapy exists for ALPS, and long term, therapies for lupus are hazardous. We show herein that arsenic trioxide (As2O3) is able to achieve quasi-total regression of antibody- and cell-mediated manifestations in MRL/lpr mice. As2O3 activated caspases and eliminated the activated T lymphocytes responsible for lymphoproliferation and skin, lung, and kidney lesions, leading to significantly prolonged survival rates. This treatment also markedly reduced anti-DNA autoantibody, rheumatoid factor, IL-18, IFN-γ, nitric oxide metabolite, TNF-α, Fas ligand, and IL-10 levels and immune-complex deposits in glomeruli. As2O3 restored cellular reduced glutathione levels, thereby limiting the toxic effect of nitric oxide, which is overproduced in MRL/lpr mice. Furthermore, As2O3 protected young animals against developing the syndrome and induced almost total disease disappearance in older affected mice, thereby demonstrating that it is a novel promising therapeutic agent for autoimmune diseases.

Genetic disorders of programmed cell death in the immune system

Human genetics offers new possibilities for understanding physiological regulatory mechanisms and disorders of the immune system. Genetic abnormalities of lymphocyte cell death programs have provided insights into mechanisms of receptor biology and principles of immune homeostasis and tolerance. Thus far, there are two major diseases of programmed cell death associated with inherited human mutations: the autoimmune lymphoproliferative syndrome and the caspase-eight deficiency state. We describe the details of their molecular pathogenesis and discuss how these diseases illustrate important concepts in immune regulation and genetics.