T cell-specific ablation of Fas leads to Fas ligand-mediated lymphocyte depletion and inflammatory pulmonary fibrosis

Distinct type 1 immune networks underlie the severity of restrictive lung disease after COVID-19

The variable origins of persistent breathlessness after coronavirus disease 2019 (COVID-19) have hindered efforts to decipher the immunopathology of lung sequelae. Here we analyzed hundreds of cellular and molecular features in the context of discrete pulmonary phenotypes to define the systemic immune landscape of post-COVID lung disease. Cluster analysis of lung physiology measures highlighted two phenotypes of restrictive lung disease that differed according to their impaired diffusion and severity of fibrosis. Machine learning revealed marked CCR5+CD95+CD8+ T cell perturbations in milder lung disease but attenuated T cell responses hallmarked by elevated CXCL13 in more severe disease. Distinct sets of cells, mediators and autoantibodies distinguished each restrictive phenotype and differed from those of patients without substantial lung involvement. These differences were reflected in divergent T cell-based type 1 networks according to the severity of lung disease. Our findings, which provide an immunological basis for active lung injury versus advanced disease after COVID-19, might offer new targets for treatment.

Distinct Type 1 Immune Networks Underlie the Severity of Restrictive Lung Disease after COVID-19

The variable etiology of persistent breathlessness after COVID-19 have confounded efforts to decipher the immunopathology of lung sequelae. Here, we analyzed hundreds of cellular and molecular features in the context of discrete pulmonary phenotypes to define the systemic immune landscape of post-COVID lung disease. Cluster analysis of lung physiology measures highlighted two phenotypes of restrictive lung disease that differed by their impaired diffusion and severity of fibrosis. Machine learning revealed marked CCR5+CD95+ CD8+ T-cell perturbations in mild-to-moderate lung disease, but attenuated T-cell responses hallmarked by elevated CXCL13 in more severe disease. Distinct sets of cells, mediators, and autoantibodies distinguished each restrictive phenotype, and differed from those of patients without significant lung involvement. These differences were reflected in divergent T-cell-based type 1 networks according to severity of lung disease. Our findings, which provide an immunological basis for active lung injury versus advanced disease after COVID-19, might offer new targets for treatment.

Fas ligand intracellular signaling: does PSTPIP mediate T cell death?

Fas and Fas ligand (FasL)-induced cell death is critical for the appropriate regulation of immune responses, especially those mediated by T cells. In this letter, several studies are discussed that reinforce the importance of FasL intracellular signaling for CD4 + T cell death, which might involve PSTPIP phosphatase and/or MAPKs.

Possible Mechanisms of Lymphopenia in Severe Tuberculosis

Tuberculosis (TB) is a chronic infectious disease caused by Mycobacterium tuberculosis (M. tuberculosis). In lymphopenia, T cells are typically characterized by progressive loss and a decrease in their count results. Lymphopenia can hinder immune responses and lead to systemic immunosuppression, which is strongly associated with mortality. Lymphopenia is a significant immunological abnormality in the majority of patients with severe and advanced TB, and its severity is linked to disease outcomes. However, the underlying mechanism remains unclear. Currently, the research on the pathogenesis of lymphopenia during M. tuberculosis infection mainly focuses on how it affects lymphocyte production, survival, or tissue redistribution. This includes impairing hematopoiesis, inhibiting T-cell proliferation, and inducing lymphocyte apoptosis. In this study, we have compiled the latest research on the possible mechanisms that may cause lymphopenia during M. tuberculosis infection. Lymphopenia may have serious consequences in severe TB patients. Additionally, we discuss in detail potential intervention strategies to prevent lymphopenia, which could help understand TB immunopathogenesis and achieve the goal of preventing and treating severe TB.

Potential biomarkers for diagnosis and disease evaluation of idiopathic pulmonary fibrosis

ABSTRACT

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive lung disease characterized by progressive lung fibrogenesis and histological features of usual interstitial pneumonia. IPF has a poor prognosis and presents a spectrum of disease courses ranging from slow evolving disease to rapid deterioration; thus, a differential diagnosis remains challenging. Several biomarkers have been identified to achieve a differential diagnosis; however, comprehensive reviews are lacking. This review summarizes over 100 biomarkers which can be divided into six categories according to their functions: differentially expressed biomarkers in the IPF compared to healthy controls; biomarkers distinguishing IPF from other types of interstitial lung disease; biomarkers differentiating acute exacerbation of IPF from stable disease; biomarkers predicting disease progression; biomarkers related to disease severity; and biomarkers related to treatment. Specimen used for the diagnosis of IPF included serum, bronchoalveolar lavage fluid, lung tissue, and sputum. IPF-specific biomarkers are of great clinical value for the differential diagnosis of IPF. Currently, the physiological measurements used to evaluate the occurrence of acute exacerbation, disease progression, and disease severity have limitations. Combining physiological measurements with biomarkers may increase the accuracy and sensitivity of diagnosis and disease evaluation of IPF. Most biomarkers described in this review are not routinely used in clinical practice. Future large-scale multicenter studies are required to design and validate suitable biomarker panels that have diagnostic utility for IPF.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Role of Mesenchymal Stem Cells and Extracellular Vesicles in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial fibrotic disease that leads to disability and death within 5 years of diagnosis. Pulmonary fibrosis is a disease with a multifactorial etiology. The concept of aberrant regeneration of the pulmonary epithelium reveals the pathogenesis of IPF, according to which repeated damage and death of alveolar epithelial cells is the main mechanism leading to the development of progressive IPF. Cell death provokes the migration, proliferation and activation of fibroblasts, which overproduce extracellular matrix, resulting in fibrotic deformity of the lung tissue. Mesenchymal stem cells (MSCs) and extracellular vesicles (EVs) are promising therapies for pulmonary fibrosis. MSCs, and EVs derived from MSCs, modulate the activity of immune cells, inhibit the expression of profibrotic genes, reduce collagen deposition and promote the repair of damaged lung tissue. This review considers the molecular mechanisms of the development of IPF and the multifaceted role of MSCs in the therapy of IPF. Currently, EVs-MSCs are regarded as a promising cell-free therapy tool, so in this review we discuss the results available to date of the use of EVs-MSCs for lung tissue repair.

Fas/FasL Signaling Regulates CD8 Expression During Exposure to Self-Antigens

Activation of self-reactive CD8+ T cells induces a peripheral tolerance mechanism that involves loss of CD8 expression. Because genetic deficiency of Fas and Fasl causes the accumulation of double-negative (DN; CD3+ TCR-αβ+ CD4- CD8-) T cells that have been proposed to derive from CD8+ cells, we decided to explore the role of Fas and FasL in self-antigen-induced CD8 downregulation. To this end, we quantified Fas and FasL induction by different stimuli and analyzed the effects of Fas/FasL deficiency during a protective immune response and after exposure to self-antigens. Our data describes how Fas and FasL upregulation differs depending on the setting of CD8 T cell activation and demonstrates that Fas/FasL signaling maintains CD8 expression during repetitive antigen stimulation and following self-antigen encounter. Together, our results reveal an unexpected role of Fas/FasL signaling and offer a new insight into the role of these molecules in the regulation of immune tolerance.

CD8 T cell-Derived Perforin and TNF-α Are Crucial Mediators of Neuronal Destruction in Experimental Autoimmune Enteric Ganglionitis

In neuron-specific ovalbumin-transgenic CKTAC mice, antigen-specific OT-I CD8 T cells home to the enteric nervous system, where they attack and destroy neurons of the myenteric and submucosal plexus. Clinically, experimental autoimmune enteric ganglionitis (EAEG) manifests with gastrointestinal dysmotility and rapidly progresses to lethal ileus. Although interferon-γ has been identified as capable of damaging neurons in EAEG, the role of perforin, Fas/FasL, and tumor necrosis factor-α (TNF-α) in this disease is still a matter of debate. Thus, CKTAC mice were adoptively transferred with either perforin^-/- or wild-type OT-I CD8 T cells. In addition, CKTAC mice that had received wild-type OT-I CD8 T cells were treated by either anti-TNF-α or anti-FasL. Furthermore, wild-type OT-I CD8 T cells were adoptively transferred into CKTAC mice with neuron-specific deletion of Fas. Although neither inactivation of enteric neuronal Fas nor anti-FasL treatment improved the disease, the absence of perforin from OT-I CD8 T cells and anti-TNF-α treatment significantly ameliorated EAEG and prevented lethal ileus by rescue of enteric neurons. Thus, these experiments identify perforin and TNF-α as important in the pathogenesis of EAEG.

Compromised counterselection by FAS creates an aggressive subtype of germinal center lymphoma

Fas is highly expressed on germinal center (GC) B cells, and mutations of FAS have been reported in diffuse large B cell lymphoma (DLBCL). Although GC-derived DLBCL has better overall outcomes than other DLBCL types, some cases are refractory, and the molecular basis for this is often unknown. We show that Fas is a strong cell-intrinsic regulator of GC B cells that promotes cell death in the light zone, likely via T follicular helper (Tfh) cell-derived Fas ligand. In the absence of Fas, GCs were more clonally diverse due to an accumulation of cells that did not demonstrably bind antigen. FAS alterations occurred most commonly in GC-derived DLBCL, were associated with inferior outcomes and an enrichment of Tfh cells, and co-occurred with deficiency in HVEM and PD-L1 that regulate the Tfh-B cell interaction. This work shows that Fas is critically required for GC homeostasis and suggests that loss of Tfh-mediated counterselection in the GC contributes to lethality in GC-derived lymphoma.

Examination of Fas-Induced Apoptosis of Murine Thymocytes in Thymic Tissue Slices Reveals That Fas Is Dispensable for Negative Selection

The death receptor Fas can induce cell death through the extrinsic pathway of apoptosis in a variety of cells, including developing thymocytes. Although Fas-induced cell death has been researched and modeled extensively, most of the studies have been done in vitro because of the lethality of Fas triggering in vivo. Thus, little is known about the time line of this type of cell death in vivo, specifically, how does the presence of macrophages and pro-survival cytokines affect apoptosis progression. In addition, although the sequence and timing of events during intrinsic pathway activation in thymocytes in situ have been described, no corresponding data for the extrinsic pathway are available. To address this gap in our knowledge, we established a novel system to study Fas-induced thymocyte cell death using tissue explants. We found that within 1 h of Fas ligation, caspase 3 was activated, within 2 h phosphatidylserine was externalized to serve as an "eat-me" signal, and at the same time, we observed signs of cell loss, likely due to efferocytosis. Both caspase 3 activation and phosphatidylserine exposure were critical for cell loss. Although Fas ligand (FasL) was delivered simultaneously to all cells, we observed significant variation in the entry into the cell death pathway. This model also allowed us to revisit the role of Fas in negative selection, and we ruled out an essential part for it in the deletion of autoreactive thymocytes. Our work provides a timeline for the apoptosis-associated events following Fas triggering in situ and confirms the lack of involvement of Fas in the negative selection of thymocytes.

Bcl-3 inhibits lupus-like phenotypes in BL6/lpr mice

Bcl-3 is an atypical member of the IκB family that modulates NF-κB activity in nuclei. lpr mice carry the lpr mutation in Fas, resulting in functional loss of this death receptor; they serve as models for lupus erythematosus and autoimmune lymphoproliferation syndrome (ALPS). To explore the biologic roles of Bcl-3 in this disease model, we generated BL6/lpr mice lacking Bcl-3. Unlike lpr mice on an MRL background, BL6/lpr mice present with very mild lupus- or ALPS-like phenotypes. Bcl-3 KO BL6/lpr mice, however, developed severe splenomegaly, dramatically increased numbers of double negative T cells - a hallmark of human lupus, ALPS, and MRL/lpr mice - and exhibited inflammation in multiple organs, despite low levels of autoantibodies, similar to those in BL6/lpr mice. Loss of Bcl-3 specifically in T cells exacerbated select lupus-like phenotypes, specifically organ infiltration. Mechanistically, elevated levels of Tnfα in Bcl-3 KO BL6/lpr mice may promote lupus-like phenotypes, since loss of Tnfα in these mice reversed the pathology due to loss of Bcl-3. Contrary to the inhibitory functions of Bcl-3 revealed here, this regulator has also been shown to promote inflammation in different settings. Our findings highlight the profound, yet highly context-dependent roles of Bcl-3 in the development of inflammation-associated pathology.

FAS and FASL variations in outcomes of tobacco- and alcohol-related head and neck squamous cell carcinoma patients

Radiotherapy and cisplatin lead to cell killing in head and neck squamous cell carcinoma patients, but adverse events and response to treatment are not the same in patients with similar clinicopathological aspects. The aim of this prospective study was to evaluate the roles of TP53 c.215G > C, FAS c.-671A > G, FAS c.-1378G > A, FASL c.-844 C > T, CASP3 c.-1191A > G, and CASP3 c.-182-247G > T single nucleotide variants in toxicity, response rate, and survival of cisplatin chemoradiation-treated head and neck squamous cell carcinoma patients. Genomic DNA was analyzed by polymerase chain reaction for genotyping. Differences between groups of patients were analyzed by chi-square test or Fisher's exact test, multiple logistic regression analysis, and Cox hazards model. One hundred nine patients with head and neck squamous cell carcinoma were enrolled in study. All patients were smokers and/or alcoholics. Patients with FAS c.-671GG genotype, FAS c.-671AG or GG genotype, and FASL c.-844CC genotype had 5.52 (95% confidence interval (CI): 1.42-21.43), 4.03 (95% CI: 1.51-10.79), and 5.77 (95% CI: 1.23-27.04) more chances of presenting chemoradiation-related anemia of grades 2-4, lymphopenia of grade 3 or 4, and ototoxicity of all grades, respectively, than those with the remaining genotypes. FAS c.-671GG genotype was also seen as an independent predictor of shorter event-free survival (hazard ratio (HR): 2.05; P = 0.007) and overall survival (HR: 1.83; P = 0.02) in our head and neck squamous cell carcinoma patients. These findings present, for the first time, preliminary evidence that inherited abnormalities in apoptosis pathway, related to FAS c.-671A > G and FASL c.-844 C > T single nucleotide variants, can alter toxicity and survival of tobacco- and alcohol-related head and neck squamous cell carcinoma patients homogeneously treated with cisplatin chemoradiation.

T Cells in Fibrosis and Fibrotic Diseases

Fibrosis is the extensive deposition of fibrous connective tissue, and it is characterized by the accumulation of collagen and other extracellular matrix (ECM) components. Fibrosis is essential for wound healing and tissue repair in response to a variety of triggers, which include infection, inflammation, autoimmune disorder, degenerative disease, tumor, and injury. Fibrotic remodeling in various diseases, such as liver cirrhosis, pulmonary fibrosis, renal interstitial fibrosis, myocardial infarction, systemic sclerosis (SSc), and graft-versus-host disease (GVHD), can impair organ function, causing high morbidity and mortality. Both innate and adaptive immunity are involved in fibrogenesis. Although the roles of macrophages in fibrogenesis have been studied for many years, the underlying mechanisms concerning the manner in which T cells regulate fibrosis are not completely understood. The T cell receptor (TCR) engages the antigen and shapes the repertoire of antigen-specific T cells. Based on the divergent expression of surface molecules and cell functions, T cells are subdivided into natural killer T (NKT) cells, γδ T cells, CD8⁺ cytotoxic T lymphocytes (CTL), regulatory T (Treg) cells, T follicular regulatory (Tfr) cells, and T helper cells, including Th1, Th2, Th9, Th17, Th22, and T follicular helper (Tfh) cells. In this review, we summarize the pro-fibrotic or anti-fibrotic roles and distinct mechanisms of different T cell subsets. On reviewing the literature, we conclude that the T cell regulations are commonly disease-specific and tissue-specific. Finally, we provide perspectives on microbiota, viral infection, and metabolism, and discuss the current advancements of technologies for identifying novel targets and developing immunotherapies for intervention in fibrosis and fibrotic diseases.

RIPK1 and death receptor signaling drive biliary damage and early liver tumorigenesis in mice with chronic hepatobiliary injury

Hepatocyte apoptosis is intrinsically linked to chronic liver disease and hepatocarcinogenesis. Conversely, necroptosis of hepatocytes and other liver cell types and its relevance for liver disease is debated. Using liver parenchymal cell (LPC)-specific TGF-beta-activated kinase 1 (TAK1)-deficient (TAK1^LPC-KO) mice, which exhibit spontaneous hepatocellular and biliary damage, hepatitis, and early hepatocarcinogenesis, we have investigated the contribution of apoptosis and necroptosis in hepatocyte and cholangiocyte death and their impact on liver disease progression. Here, we provide in vivo evidence showing that TAK1-deficient cholangiocytes undergo spontaneous necroptosis induced primarily by TNFR1 and dependent on RIPK1 kinase activity, RIPK3, and NEMO. In contrast, TAK1-deficient hepatocytes die by FADD-dependent apoptosis, which is not significantly inhibited by LPC-specific RIPK1 deficiency, inhibition of RIPK1 kinase activity, RIPK3 deficiency or combined LPC-specific deletion of TNFR1, TRAILR, and Fas. Accordingly, normal mouse cholangiocytes can undergo necroptosis, while primary hepatocytes are resistant to it and die exclusively by apoptosis upon treatment with cell death-inducing stimuli in vitro, likely due to the differential expression of RIPK3. Interestingly, the genetic modifications that conferred protection from biliary damage also prevented the spontaneous lethality that was often observed in TAK1^LPC-KO mice. In the presence of chronic hepatocyte apoptosis, preventing biliary damage delayed but did not avert hepatocarcinogenesis. On the contrary, inhibition of hepatocyte apoptosis fully prevented liver tumorigenesis even in mice with extensive biliary damage. Altogether, our results suggest that using RIPK1 kinase activity inhibitors could be therapeutically useful for cholestatic liver disease patients.

Programmed Cell Death in Immune Defense: Knowledge and Presumptions

Cell-culture studies are our main source of knowledge of the various forms of programmed cell death. Yet genetic perturbations of death-protein function in animal models are almost the only source of our knowledge of the physiological roles of these programs. Shortcomings in the state of knowledge acquired by these two experimental approaches are exemplified in this Perspective by reference to research on the contribution of apoptosis to lymphocyte development, a subject on which there is already much knowledge, and on the role of necroptosis in inflammation, about which information is just beginning to emerge. To address these shortcomings, there is need to find ways to verify the notions obtained through the current experimental approaches by directly monitoring death programs within specific cells in vivo.

Navigating the Fas lane to improved cellular therapy for cancer

Genetically engineered T cells have shown promising activity in the treatment of cancer. However, these cells are also potentially susceptible to immune-suppressive pathways in the tumor microenvironment that may limit their efficacy. In this issue of the JCI, Yamamoto et al. describe a new cellular engineering approach to prevent Fas-mediated inhibition of T cell function, which may be exploited to improve cellular therapy for cancer.

T cells genetically engineered to overcome death signaling enhance adoptive cancer immunotherapy

Across clinical trials, T cell expansion and persistence following adoptive cell transfer (ACT) have correlated with superior patient outcomes. Herein, we undertook a pan-cancer analysis to identify actionable ligand-receptor pairs capable of compromising T cell durability following ACT. We discovered that FASLG, the gene encoding the apoptosis-inducing ligand FasL, is overexpressed within the majority of human tumor microenvironments (TMEs). Further, we uncovered that Fas, the receptor for FasL, is highly expressed on patient-derived T cells used for clinical ACT. We hypothesized that a cognate Fas-FasL interaction within the TME might limit both T cell persistence and antitumor efficacy. We discovered that genetic engineering of Fas variants impaired in the ability to bind FADD functioned as dominant negative receptors (DNRs), preventing FasL-induced apoptosis in Fas-competent T cells. T cells coengineered with a Fas DNR and either a T cell receptor or chimeric antigen receptor exhibited enhanced persistence following ACT, resulting in superior antitumor efficacy against established solid and hematologic cancers. Despite increased longevity, Fas DNR-engineered T cells did not undergo aberrant expansion or mediate autoimmunity. Thus, T cell-intrinsic disruption of Fas signaling through genetic engineering represents a potentially universal strategy to enhance ACT efficacy across a broad range of human malignancies.

Differential Expression of Fas in Moderate/Severe and Mild Persistent Allergic Rhinitis and Its Correlation With Pathological Parameters

BACKGROUND AND AIMS

The roles of Fas in immune system are multifaceted, and the interaction between Fas receptor and Fas ligand is essential for maintaining the immune tolerance. We aimed to assess the level of the expression of Fas receptor on nasal inferior turbinate mucosa in patients with mild persistent allergic rhinitis (M PAR) and moderate to severe (M/S) PAR and determined the relationship between disease severity and production of Fas.

METHODS

A total of 70 patients with M/S PAR, 70 patients with M PAR, and 70 healthy individuals were enrolled in this study. We obtained biopsies of nasal inferior turbinate mucosa from the participants. The expression of Fas mRNA was evaluated by real-time polymerase chain reaction. The presence and location of Fas were determined by immunohistochemistry. The number of eosinophils per field, blood eosinophils, total serum IgE levels, and specific serum IgE levels were measured. Clinical manifestations of patients were assessed by Total Nasal Syndrome Score (TNSS).

RESULTS

The expression of Fas in patients with M/S PAR was decreased significantly compared to the control group and patients with M PAR. Local mucosal expression of Fas was correlated with specific IgE, nasal eosinophil count, and TNSS.

CONCLUSION

According to the results of this study, there might be a relationship between the expression of Fas receptor on nasal turbinate mucosa and the severity of persistent allergic rhinitis.

The TNF Family of Ligands and Receptors: Communication Modules in the Immune System and Beyond

The tumor necrosis factor (TNF) and TNF receptor (TNFR) superfamilies (TNFSF/TNFRSF) include 19 ligands and 29 receptors that play important roles in the modulation of cellular functions. The communication pathways mediated by TNFSF/TNFRSF are essential for numerous developmental, homeostatic, and stimulus-responsive processes in vivo. TNFSF/TNFRSF members regulate cellular differentiation, survival, and programmed death, but their most critical functions pertain to the immune system. Both innate and adaptive immune cells are controlled by TNFSF/TNFRSF members in a manner that is crucial for the coordination of various mechanisms driving either co-stimulation or co-inhibition of the immune response. Dysregulation of these same signaling pathways has been implicated in inflammatory and autoimmune diseases, highlighting the importance of their tight regulation. Investigation of the control of TNFSF/TNFRSF activities has led to the development of therapeutics with the potential to reduce chronic inflammation or promote anti-tumor immunity. The study of TNFSF/TNFRSF proteins has exploded over the last 30 yr, but there remains a need to better understand the fundamental mechanisms underlying the molecular pathways they mediate to design more effective anti-inflammatory and anti-cancer therapies.

Immune Tolerance and Rejection in Organ Transplantation

In this chapter, we describe the history of transplantation, the multiple cell types, and mechanisms that are involved in rejection and tolerance of a transplanted organ, as well as summarize the common and promising new therapeutics used in transplant patients.

Fas Promotes T Helper 17 Cell Differentiation and Inhibits T Helper 1 Cell Development by Binding and Sequestering Transcription Factor STAT1

The death receptor Fas removes activated lymphocytes through apoptosis. Previous transcriptional profiling predicted that Fas positively regulates interleukin-17 (IL-17)-producing T helper 17 (Th17) cells. Here, we demonstrate that Fas promoted the generation and stability of Th17 cells and prevented their differentiation into Th1 cells. Mice with T-cell- and Th17-cell-specific deletion of Fas were protected from induced autoimmunity, and Th17 cell differentiation and stability were impaired. Fas-deficient Th17 cells instead developed a Th1-cell-like transcriptional profile, which a new algorithm predicted to depend on STAT1. Experimentally, Fas indeed bound and sequestered STAT1, and Fas deficiency enhanced IL-6-induced STAT1 activation and nuclear translocation, whereas deficiency of STAT1 reversed the transcriptional changes induced by Fas deficiency. Thus, our computational and experimental approach identified Fas as a regulator of the Th17-to-Th1 cell balance by controlling the availability of opposing STAT1 and STAT3 to have a direct impact on autoimmunity.

CNS Macrophages Control Neurovascular Development via CD95L

The development of neurons and vessels shares striking anatomical and molecular features, and it is presumably orchestrated by an overlapping repertoire of extracellular signals. CNS macrophages have been implicated in various developmental functions, including the morphogenesis of neurons and vessels. However, whether CNS macrophages can coordinately influence neurovascular development and the identity of the signals involved therein is unclear. Here, we demonstrate that activity of the cell surface receptor CD95 regulates neuronal and vascular morphogenesis in the post-natal brain and retina. Furthermore, we identify CNS macrophages as the main source of CD95L, and macrophage-specific deletion thereof reduces both neurovascular complexity and synaptic activity in the brain. CD95L-induced neuronal and vascular growth is mediated through src-family kinase (SFK) and PI3K signaling. Together, our study highlights a coordinated neurovascular development instructed by CNS macrophage-derived CD95L, and it underlines the importance of macrophages for the establishment of the neurovascular network during CNS development.

Inactivation of TRPM7 kinase in mice results in enlarged spleens, reduced T-cell proliferation and diminished store-operated calcium entry

T lymphocytes enlarge (blast) and proliferate in response to antigens in a multistep program that involves obligatory cytosolic calcium elevations. Store-operated calcium entry (SOCE) pathway is the primary source of Ca²⁺ in these cells. Here, we describe a novel modulator of blastogenesis, proliferation and SOCE: the TRPM7 channel kinase. TRPM7 kinase-dead (KD) K1646R knock-in mice exhibited splenomegaly and impaired blastogenic responses elicited by PMA/ionomycin or anti-CD3/CD28 antibodies. Splenic T-cell proliferation in vitro was weaker in the mutant compared to wildtype littermates. TRPM7 current magnitudes in WT and KD mouse T cells were, however, similar. We tested the dependence of T-cell proliferation on external Ca²⁺ and Mg²⁺ concentrations. At a fixed [Mg²⁺_o] of ~0.4 mM, Ca²⁺_o stimulated proliferation with a steep concentration dependence and vice versa, at a fixed [Ca²⁺_o] of ~0.4 mM, Mg²⁺_o positively regulated proliferation but with a shallower dependence. Proliferation was significantly lower in KD mouse than in wildtype at all Ca²⁺ and Mg²⁺ concentrations. Ca²⁺ elevations elicited by anti-CD3 antibody were diminished in KD mutant T cells and SOCE measured in activated KD splenocytes was reduced. These results demonstrate that a functional TRPM7 kinase supports robust SOCE, blastogenesis and proliferation, whereas its inactivation suppresses these cellular events.

Excessive interferon-α signaling in autoimmunity alters glycosphingolipid processing in B cells

Excessive interferon-α (IFN-α) production by innate immune cells is a hallmark of autoimmune diseases. What other cell type secretes IFN-α and how IFN-α affects immune cell metabolism and homeostasis in autoimmunity are largely unclear. Here, we report that autoimmune B cells, arising from two different B cell-specific genetic lesions in mice, secrete IFN-α. In addition, IFN-α, found in abundance in autoimmunity, elicited profound changes in the B cell lipidome, increasing their expression of glycosphingolipids (GSLs) and leading to their CD1d-mediated depletion of iNKT cells in vitro and in vivo. IFN-α receptor blockade could reverse the loss of iNKT cells. Excessive stimulation of B cells with IFN-α altered the expression of enzymes that catalyze critical steps in GSL processing, increasing the expressions of glucosylceramide synthase (GCS) and globotrihexosylceramide synthase (Gb3S) but decreasing that of α-galactosidase A (α-galA). Inhibiting GCS or restoring α-galA expression prevented iNKT depletion by IFN-α-activated B cells. Taken together, our work indicated that excessive IFN-α perturbs GSL metabolism in B cells which in turn adversely affects iNKT homeostasis.

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.

Rare phenotypes in the understanding of autoimmunity

The study of rare phenotypes has a long history in the description of autoimmune disorders. First Mendelian syndromes of idiopathic tissue destruction were defined more than 100 years ago and were later revealed to result from immune-mediated reactivity against self. In the past two decades, continuous advances in sequencing technology and particularly the advent of next-generation sequencing have allowed to define the genetic basis of an ever-growing number of Mendelian forms of autoimmunity. This has provided unique insight into the molecular pathways that govern immunological homeostasis and that are indispensable for the prevention of self-reactive immune-mediated tissue damage and 'horror autotoxicus'. Here we will discuss selected examples of past and recent investigations into rare phenotypes of autoimmunity that have delineated pathways critical for central and peripheral control of the adaptive immune system. We will outline the implications of these findings for rare and common forms of autoimmunity and will discuss the benefits and potential pitfalls of the integration of next-generation sequencing into algorithms for clinical diagnostics. Because of the concise nature of this review, we will focus on syndromes caused by defects in the control of adaptive immunity as innate immune-mediated autoinflammatory disorders have been covered in excellent recent reviews on Mendelian and polygenic forms of autoimmunity.

Impact of loss of NF-κB1, NF-κB2 or c-REL on SLE-like autoimmune disease and lymphadenopathy in Fas(lpr/lpr) mutant mice

Defects in apoptosis can cause autoimmune disease. Loss-of-function mutations in the 'death receptor' FAS impair the deletion of autoreactive lymphocytes in the periphery, leading to progressive lymphadenopathy and systemic lupus erythematosus-like autoimmune disease in mice (Fas(lpr/lpr) (mice homozygous for the lymphoproliferation inducing spontaneous mutation)) and humans. The REL/nuclear factor-κB (NF-κB) transcription factors regulate a broad range of immune effector functions and are also implicated in various autoimmune diseases. We generated compound mutant mice to investigate the individual functions of the NF-κB family members NF-κB1, NF-κB2 and c-REL in the various autoimmune pathologies of Fas(lpr/lpr) mutant mice. We show that loss of each of these transcription factors resulted in amelioration of many classical features of autoimmune disease, including hypergammaglobulinaemia, anti-nuclear autoantibodies and autoantibodies against tissue-specific antigens. Remarkably, only c-REL deficiency substantially reduced immune complex-mediated glomerulonephritis and extended the lifespan of Fas(lpr/lpr) mice. Interestingly, compared with the Fas(lpr/lpr) animals, Fas(lpr/lpr)nfkb2(-/-) mice presented with a dramatic acceleration and augmentation of lymphadenopathy that was accompanied by severe lung pathology due to extensive lymphocytic infiltration. The Fas(lpr/lpr)nfkb1(-/-) mice exhibited the combined pathologies caused by defects in FAS-mediated apoptosis and premature ageing due to loss of NF-κB1. These findings demonstrate that different NF-κB family members exert distinct roles in the development of the diverse autoimmune and lymphoproliferative pathologies that arise in Fas(lpr/lpr) mice, and suggest that pharmacological targeting of c-REL should be considered as a strategy for therapeutic intervention in autoimmune diseases.

Free fatty acids shift insulin-induced hepatocyte proliferation towards CD95-dependent apoptosis

Insulin is known to induce hepatocyte swelling, which triggers via integrins and c-Src kinase an activation of the epidermal growth factor receptor (EGFR) and subsequent cell proliferation (1). Free fatty acids (FFAs) are known to induce lipoapoptosis in liver cells in a c-Jun-NH2-terminal kinase (JNK)-dependent, but death receptor-independent way (2). As non-alcoholic steatohepatitis (NASH) is associated with hyperinsulinemia and increased FFA-blood levels, the interplay between insulin and FFA was studied with regard to hepatocyte proliferation and apoptosis in isolated rat and mouse hepatocytes. Saturated long chain FFAs induced apoptosis and JNK activation in primary rat hepatocytes, but did not activate the CD95 (Fas, APO-1) system, whereas insulin triggered EGFR activation and hepatocyte proliferation. Coadministration of insulin and FFAs, however, abolished hepatocyte proliferation and triggered CD95-dependent apoptosis due to a JNK-dependent association of the activated EGFR with CD95, subsequent CD95 tyrosine phosphorylation and formation of the death-inducing signaling complex (DISC). JNK inhibition restored the proliferative insulin effect in presence of FFAs and prevented EGFR/CD95 association, CD95 tyrosine phosphorylation and DISC formation. Likewise, in presence of FFAs insulin increased apoptosis in hepatocytes from wild type but not from Alb-Cre-FAS(fl/fl) mice, which lack functional CD95. It is concluded that FFAs can shift insulin-induced hepatocyte proliferation toward hepatocyte apoptosis by triggering a JNK signal, which allows activated EGFR to associate with CD95 and to trigger CD95-dependent apoptosis. Such phenomena may contribute to the pathogenesis of NASH.

Fas regulates neutrophil lifespan during viral and bacterial infection

The regulation of neutrophil lifespan is critical for a circumscribed immune response. Neutrophils are sensitive to Fas/CD95 death receptor signaling in vitro, but it is unknown if Fas regulates neutrophil lifespan in vivo. We hypothesized that FasL-expressing CD8(+) T cells, which kill antigen-stimulated T cells during chronic viral infection, can also induce neutrophil death in tissues during infection. With the use of LysM-Cre Fas(fl/fl) mice, which lack Fas expression in macrophages and neutrophils, we show that Fas regulates neutrophil lifespan during lymphocytic choriomeningitis virus (LCMV) infection in the lung, peripheral blood, and spleen. Fas also contributed to the regulation of neutrophil numbers in the colon of Citrobacter rodentium-infected mice. To examine the effects of infection on Fas activation in neutrophils, we primed neutrophils with TLR ligands or IL-18, resulting in ablation of Fas death receptor signaling. These data provide the first in vivo genetic evidence that neutrophil lifespan is controlled by death receptor signaling and provide a mechanism to account for neutrophil resistance to Fas stimulation during infection.

Lymphoid hyperplasia and lymphoma in KSHV K1 transgenic mice

Growing evidence supports the involvement of human herpervirus 8, Kaposi's sarcoma associated herpesvirus (KSHV), in the pathology of primary effusion lymphoma, multicentric Castleman's disease, and Kaposi's sarcoma, but the exact mechanism of KSHV contribution to the oncogenic process remains elusive. We studied transgenic mice expressing the ORF K1 of KSHV, whose position in the KSHV genome corresponds to known lymphoproliferative genes of other herpesviruses. K1 protein was previously shown to contain a constitutively active ITAM domain, involved in activation of Akt and pro-survival signaling, and to inhibit Fas-mediated apoptosis by interfering with binding of FasL. All this pointed to a possible role of K1 in the pathogenesis of KSHV-associated cancers. K1 transgenic mice (80-90%) developed lymphoid hyperplasia and splenomegaly at 8 and 10 months of age, 25% had confirmed diagnosis of lymphoma, and 50% developed abdominal and/or hepatic tumors by 18 months of age. Histological examination showed loss of splenic architecture and increased cellularity. Lymph nodes showed disrupted architecture with effaced follicles and other pathological changes, including signs of angiofollicular lymphoid hyperplasia. One of the livers showed signs of angiosarcoma. In summary, our histology results revealed pathological changes in K1 transgenic mice similar to lymphoma, Castleman's disease, and angiosarcoma, suggesting that K1 may contribute to the development of KSHV-associated cancers.

Aberrant presentation of self-lipids by autoimmune B cells depletes peripheral iNKT cells

Invariant natural killer T (iNKT) cells provide cognate help via CD1d to lipid antigen-presenting B cells for antibody production, but whether B cells reciprocally regulate iNKT cells remains largely unexplored. Here, we found peripheral, but not thymic, iNKT cells to be numerically reduced in autoimmune mice lacking Fas specifically in B cells. The residual iNKT cells were antigenically overstimulated, had altered cytokine production, and manifested enhanced proliferation and apoptosis. B cell-specific ablation of CD1d ameliorated these iNKT defects, suggesting that inappropriate presentation of CD1d-restricted self-lipids by autoimmune B cell-depleted peripheral iNKT cells. CD1d(+) autoimmune B cells have reduced α-galactosidase A expression and, as revealed by lipidomic profiling, altered lipidome with aberrant accumulation of certain self-lipids and reduction of others. These findings unveil a critical link between autoimmunity, B cell lipidome, and the maintenance of peripheral iNKT cells and highlight an essential homeostatic function of B cells beyond antibody production.

Death receptor-independent FADD signalling triggers hepatitis and hepatocellular carcinoma in mice with liver parenchymal cell-specific NEMO knockout

Hepatocellular carcinoma (HCC) usually develops in the context of chronic hepatitis triggered by viruses or toxic substances causing hepatocyte death, inflammation and compensatory proliferation of liver cells. Death receptors of the TNFR superfamily regulate cell death and inflammation and are implicated in liver disease and cancer. Liver parenchymal cell-specific ablation of NEMO/IKKγ, a subunit of the IκB kinase (IKK) complex that is essential for the activation of canonical NF-κB signalling, sensitized hepatocytes to apoptosis and caused the spontaneous development of chronic hepatitis and HCC in mice. Here we show that hepatitis and HCC development in NEMO(LPC-KO) mice is triggered by death receptor-independent FADD-mediated hepatocyte apoptosis. TNF deficiency in all cells or conditional LPC-specific ablation of TNFR1, Fas or TRAIL-R did not prevent hepatocyte apoptosis, hepatitis and HCC development in NEMO(LPC-KO) mice. To address potential functional redundancies between death receptors we generated and analysed NEMO(LPC-KO) mice with combined LPC-specific deficiency of TNFR1, Fas and TRAIL-R and found that also simultaneous lack of all three death receptors did not prevent hepatocyte apoptosis, chronic hepatitis and HCC development. However, LPC-specific combined deficiency in TNFR1, Fas and TRAIL-R protected the NEMO-deficient liver from LPS-induced liver failure, showing that different mechanisms trigger spontaneous and LPS-induced hepatocyte apoptosis in NEMO(LPC-KO) mice. In addition, NK cell depletion did not prevent liver damage and hepatitis. Moreover, NEMO(LPC-KO) mice crossed into a RAG-1-deficient genetic background-developed hepatitis and HCC. Collectively, these results show that the spontaneous development of hepatocyte apoptosis, chronic hepatitis and HCC in NEMO(LPC-KO) mice occurs independently of death receptor signalling, NK cells and B and T lymphocytes, arguing against an immunological trigger as the critical stimulus driving hepatocarcinogenesis in this model.

Differential impact of CD27 and 4-1BB costimulation on effector and memory CD8 T cell generation following peptide immunization

The factors that determine differentiation of naive CD8 T cells into memory cells are not well understood. A greater understanding of how memory cells are generated will inform of ways to improve vaccination strategies. In this study, we analyzed the CD8 T cell response elicited by two experimental vaccines comprising a peptide/protein Ag and an agonist that delivers a costimulatory signal via CD27 or 4-1BB. Both agonists increased expansion of Ag-specific CD8 T cells compared with Ag alone. However, their capacity to stimulate differentiation into effector and memory cells differed. CD27 agonists promoted increased expression of perforin and the generation of short-lived memory cells, whereas stimulation with 4-1BB agonists favored generation of stable memory. The memory-promoting effects of 4-1BB were independent of CD4 T cells and were the result of programing within the first 2 d of priming. Consistent with this conclusion, CD27 and 4-1BB-stimulated CD8 T cells expressed disparate amounts of IL-2, IFN-γ, CD25, CD71, and Gp49b as early as 3 d after in vivo activation. In addition, memory CD8 T cells, generated through priming with CD27 agonists, proliferated more extensively than did 4-1BB-generated memory cells, but these cells failed to persist. These data demonstrate a previously unanticipated link between the rates of homeostatic proliferation and memory cell attrition. Our study highlights a role for these receptors in skewing CD8 T cell differentiation into effector and memory cells and provides an approach to optimize vaccines that elicit CD8 T cell responses.

Caspase-8 acts as a molecular rheostat to limit RIPK1- and MyD88-mediated dendritic cell activation

Caspase-8, an executioner enzyme in the death receptor pathway, was shown to initiate apoptosis and suppress necroptosis. In this study, we identify a novel, cell death-independent role for caspase-8 in dendritic cells (DCs): DC-specific expression of caspase-8 prevents the onset of systemic autoimmunity. Failure to express caspase-8 has no effect on the lifespan of DCs but instead leads to an enhanced intrinsic activation and, subsequently, more mature and autoreactive lymphocytes. Uncontrolled TLR activation in a RIPK1-dependent manner is responsible for the enhanced functionality of caspase-8-deficient DCs, because deletion of the TLR-signaling mediator, MyD88, ameliorates systemic autoimmunity induced by caspase-8 deficiency. Taken together, these data demonstrate that caspase-8 functions in a cell type-specific manner and acts uniquely in DCs to maintain tolerance.

DICE: A novel tumor surveillance mechanism-a new therapy for cancer?

The conventional view of CD95 (Fas/APO-1) is that it is a dedicated apoptosis-inducing receptor with important functions in immune cell homeostasis and in viral and tumor defense. There is an emerging recognition, however, that CD95 also has multiple non-apoptotic activities. In the context of cancer, CD95 was shown to have tumor-promoting activities, and the concept of this new function of CD95 in cancer is gaining traction. Recently, we showed that not only is CD95 a growth promoter for cancer cells, but, paradoxically, when either CD95 or CD95 ligand (CD95L) is removed, that virtually all cancer cells die through a process we have named DICE (death induced by CD95R/L elimination). In this perspective, I outline a hypothesis regarding the physiological function of DICE, and why it may be possible to use induction of DICE to treat many, if not most, cancers.

Increased IL-17 and IL-21 producing TCRαβ+CD4−CD8− T cells in Chinese systemic lupus erythematosus patients

Background: Increased numbers of TCRαβ+CD4−CD8− T cells in the peripheral blood of systemic lupus erythematosus (SLE) patients in the United States and United Kingdom have been reported. However, the proportions of TCRαβ+CD4−CD8− T cells and their involvement in the pathogenesis of SLE in Chinese populations are yet to be determined. Methods: A total of 120 SLE patients, 38 rheumatoid arthritis (RA) patients and 43 normal control subjects were examined. The proportion of TCRαβ+CD4−CD8− T cells in the peripheral blood, Fas expression on these cells, and intracellular cytokine levels in these cells were assessed using flow cytometry. Plasma cytokine concentrations were measured using enzyme-linked immunosorbent assay. Results: The percentages of TCRαβ+CD4−CD8− T cells were increased in Chinese SLE patients, particularly in active SLE patients, correlated with decreased Fas expression on these cells. IL-17 and IL-21 levels in the blood and in TCRαβ+CD4−CD8− T cells from SLE patients were increased. Moreover, a positive correlation was evident between IL-17- and IL-21-producing TCRαβ+CD4−CD8− T cells. Conclusions: Increased TCRαβ+CD4−CD8− T cells expressing inflammatory cytokines, such as IL-17 and IL-21, may be implicated in the pathogenesis of SLE in patients. Appropriate IL-17- and/or IL-21 blockage may be utilized as a novel immunotherapeutic strategy for SLE patients.

CD95 in cancer: tool or target?

The role of CD95 (Fas/Apo1) in cancer has been a matter of debate for over 30 years. First discovered as an apoptosis-inducing molecule, CD95 soon emerged as a potential anticancer therapy. Yet accumulating evidence indicates a profound role for CD95 in alternative nonapoptotic signaling pathways that increase tumorigenesis. This fact challenges the initial clinical idea of using CD95 as a 'tumor killer' while setting the stage for clinical studies targeting the nonapoptotic signaling branch of CD95. This review summarizes the findings surrounding manipulation of the CD95 pathway for cancer therapy, considering how one receptor can both promote and prevent cell growth.

Somatic mutagenesis in autoimmunity

Our laboratory investigates systemic autoimmune disease in the context of mouse models of systemic lupus erythematosus (SLE). SLE is associated with high titers of serum autoantibodies of the IgG class that are predominantly directed against nuclear antigens, with pathological manifestations that are considered by many to be characteristic of an immune-complex mediated disease. In this review, we focus on the known and potential roles of somatic mutagenesis in SLE. We will argue that anti-nuclear antibodies (ANA) arise predominantly from nonautoreactive B cells that are transformed into autoreactive cells by the process of somatic hypermutation (SHM), which is normally associated with affinity maturation during the germinal center reaction. We will also discuss the role of SHM in creating antigenic peptides in the V region of the B cell receptor (BCR) and its potential to open an avenue of unregulated T cell help to autoreactive B cells. Finally, we will end this review with new experimental evidence suggesting that spontaneous somatic mutagenesis of genes that regulate B cell survival and activation is a rate-limiting causative factor in the development of ANA.

Cleavage of TRPM7 releases the kinase domain from the ion channel and regulates its participation in Fas-induced apoptosis

Transient receptor potential melastatin-like 7 (TRPM7) is a channel protein that also contains a regulatory serine-threonine kinase domain. Here, we find that Trpm7-/- T cells are deficient in Fas-receptor-induced apoptosis and that TRPM7 channel activity participates in the apoptotic process and is regulated by caspase-dependent cleavage. This function of TRPM7 is dependent on its function as a channel, but not as a kinase. TRPM7 is cleaved by caspases at D1510, disassociating the carboxy-terminal kinase domain from the pore without disrupting the phosphotransferase activity of the released kinase but substantially increasing TRPM7 ion channel activity. Furthermore, we show that TRPM7 regulates endocytic compartmentalization of the Fas receptor after receptor stimulation, an important process for apoptotic signaling through Fas receptors. These findings raise the possibility that other members of the TRP channel superfamily are also regulated by caspase-mediated cleavage, with wide-ranging implications for cell death and differentiation.

p38α protein negatively regulates T helper type 2 responses by orchestrating multiple T cell receptor-associated signals

Mitogen-activated protein kinase p38α is a critical regulator of certain inflammatory diseases. However, its role in T helper type 2 (Th2) responses and allergic inflammation remains unknown. Here we show an increase in the production of interleukin-4 (IL-4) in p38α(-/-) CD4(+) T cells in response to antigen stimulation. p38α-deficient naïve CD4(+) T cells preferentially differentiate into Th2 cells through increased endogenous production of IL-4. Consistent with those results, we also observed decreased expression of p38α during T helper cell differentiation. Furthermore, deficiency of p38α alters the balance in the expression of NFATc1 and NFATc2 under steady-state conditions and enhances the expression and nuclear translocation of NFATc1 in CD4(+) T cells upon antigen stimulation. Knockdown of NFATc1 significantly inhibits Th2 differentiation in p38α(-/-) T cells but not in p38α(+/-) T cells. p38α deficiency also inhibits the activation of Akt but enhances the activation of ERK in response to T cell receptor engagement without impacting IL-2/Stat5 signaling. In a model of ovalbumin-induced acute allergic airway inflammation, mice with induced deletion of p38α show elevated serum ovalbumin-specific IgE level, increased infiltration of eosinophils, and higher concentrations of Th2 cytokines including IL-4 and IL-5 in the bronchoalveolar lavage fluid relative to control mice. Taken together, p38α regulates multiple T cell receptor-associated signals and negatively influences Th2 differentiation and allergic inflammation.

The Fas/CD95 Receptor Regulates the Death of Autoreactive B Cells and the Selection of Antigen-Specific B Cells

Cell death receptors have crucial roles in the regulation of immune responses. Here we review recent in vivo data confirming that the Fas death receptor (TNFSR6) on B cells is important for the regulation of autoimmunity since the impairment of only Fas function on B cells results in uncontrolled autoantibody production and autoimmunity. Fas plays a role in the elimination of the non-specific and autoreactive B cells in germinal center, while during the selection of antigen-specific B cells different escape signals ensure the resistance to Fas-mediated apoptosis. Antigen-specific survival such as BCR or MHCII signal or coreceptors (CD19) cooperating with BCR inhibits the formation of death inducing signaling complex. Antigen-specific survival can be reinforced by antigen-independent signals of IL-4 or CD40 overproducing the anti-apoptotic members of the Bcl-2 family proteins.

Molecular and cellular mechanisms of pulmonary fibrosis

Pulmonary fibrosis is a chronic lung disease characterized by excessive accumulation of extracellular matrix (ECM) and remodeling of the lung architecture. Idiopathic pulmonary fibrosis is considered the most common and severe form of the disease, with a median survival of approximately three years and no proven effective therapy. Despite the fact that effective treatments are absent and the precise mechanisms that drive fibrosis in most patients remain incompletely understood, an extensive body of scientific literature regarding pulmonary fibrosis has accumulated over the past 35 years. In this review, we discuss three broad areas which have been explored that may be responsible for the combination of altered lung fibroblasts, loss of alveolar epithelial cells, and excessive accumulation of ECM: inflammation and immune mechanisms, oxidative stress and oxidative signaling, and procoagulant mechanisms. We discuss each of these processes separately to facilitate clarity, but certainly significant interplay will occur amongst these pathways in patients with this disease.

Requirement of myeloid cell-specific Fas expression for prevention of systemic autoimmunity in mice

OBJECTIVE

The death receptor Fas is a critical mediator of the extrinsic apoptotic pathway, and its role in mediating lymphoproliferation has been extensively examined. The present study was undertaken to investigate the impact of myeloid cell-specific loss of Fas.

METHODS

Mice with Fas flanked by loxP sites (Fas(flox/flox) ) were crossed with mice expressing Cre under control of the murine lysozyme M gene promoter (Cre(LysM) ), which functions in mature lysozyme-expressing cells of the myelomonocytic lineage. The genotype for Cre(LysM) Fas(flox/flox) mice was verified by polymerase chain reaction and flow cytometric analysis. Flow cytometric analysis was also used to characterize myeloid, dendritic, and lymphoid cell distribution and activation in bone marrow, blood, and spleen. Luminex-based assays and enzyme-linked immunosorbent assays were used to measure serum cytokine/chemokine and immunoglobulin levels. Renal damage or dysfunction was examined by immunohistochemical and immunofluorescence analysis.

RESULTS

Cre(LysM) Fas(flox/flox) mice exhibited a systemic lupus erythematosus (SLE)-like disease that included leukocytosis, splenomegaly, hypergammaglobulinemia, antinuclear autoantibody and proinflammatory cytokine production, and glomerulonephritis. Loss of Fas in myeloid cells increased levels of both Gr-1(low) and Gr-1(intermediate) blood monocytes and splenic macrophages and, in a paracrine manner, incited activation of conventional dendritic cells and lymphocytes in Cre(LysM) Fas(flox/flox) mice.

CONCLUSION

Taken together, these results suggest that loss of Fas in myeloid cells is sufficient to induce inflammatory phenotypes in mice, reminiscent of an SLE-like disease. Thus, Fas in myeloid cells may be considered a suppressor of systemic autoimmunity.

Cytokine-like factor 1 gene expression is enriched in idiopathic pulmonary fibrosis and drives the accumulation of CD4+ T cells in murine lungs: evidence for an antifibrotic role in bleomycin injury

Idiopathic pulmonary fibrosis (IPF) is a progressive and typically fatal lung disease. To gain insight into the pathogenesis of IPF, we reanalyzed our previously published gene expression data profiling IPF lungs. Cytokine receptor-like factor 1 (CRLF1) was among the most highly up-regulated genes in IPF lungs, compared with normal controls. The protein product (CLF-1) and its partner, cardiotrophin-like cytokine (CLC), function as members of the interleukin 6 (IL-6) family of cytokines. Because of earlier work implicating IL-6 family members in IPF pathogenesis, we tested whether CLF-1 expression contributes to inflammation in experimental pulmonary fibrosis. In IPF, we detected CLF-1 expression in both type II alveolar epithelial cells and macrophages. We found that the receptor for CLF-1/CLC signaling, ciliary neurotrophic factor receptor (CNTFR), was expressed only in type II alveolar epithelial cells. Administration of CLF-1/CLC to both uninjured and bleomycin-injured mice led to the pulmonary accumulation of CD4(+) T cells. We also found that CLF-1/CLC administration increased inflammation but decreased pulmonary fibrosis. CLF-1/CLC leads to significantly enriched expression of T-cell-derived chemokines and cytokines, including the antifibrotic cytokine interferon-γ. We propose that, in IPF, CLF-1 is a selective stimulus of type II alveolar epithelial cells and may potentially drive an antifibrotic response by augmenting both T-helper-1-driven and T-regulatory-cell-driven inflammatory responses in the lung.

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.