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.

sFasL-The Key to a Riddle: Immune Responses in Aging Lung and Disease

By dint of the aging population and further deepened with the Covid-19 pandemic, lung disease has turned out to be a major cause of worldwide morbidity and mortality. The condition is exacerbated when the immune system further attacks the healthy, rather than the diseased, tissue within the lung. Governed by unremittingly proliferating mesenchymal cells and increased collagen deposition, if inflammation persists, as frequently occurs in aging lungs, the tissue develops tumors and/or turns into scars (fibrosis), with limited regenerative capacity and organ failure. Fas ligand (FasL, a ligand of the Fas cell death receptor) is a key factor in the regulation of these processes. FasL is primarily found in two forms: full length (membrane, or mFasL) and cleaved (soluble, or sFasL). We and others found that T-cells expressing the mFasL retain autoimmune surveillance that controls mesenchymal, as well as tumor cell accumulation following an inflammatory response. However, mesenchymal cells from fibrotic lungs, tumor cells, or cells from immune-privileged sites, resist FasL⁺ T-cell-induced cell death. The mechanisms involved are a counterattack of immune cells by FasL, by releasing a soluble form of FasL that competes with the membrane version, and inhibits their cell death, promoting cell survival. This review focuses on understanding the previously unrecognized role of FasL, and in particular its soluble form, sFasL, in the serum of aged subjects, and its association with the evolution of lung disease, paving the way to new methods of diagnosis and treatment.

MiR-7e-5p downregulation promotes transformation of low-grade follicular lymphoma to aggressive lymphoma by modulating an immunosuppressive stroma through the upregulation of FasL in M1 macrophages

BACKGROUND

In follicular lymphoma (FL), histologic transformation to high-grade FL and diffuse large B-cell lymphoma (DLBCL) is a critical adverse step in disease progression. Activation of the oncogene c-MYC and tumor microenvironment remodeling account for FL progression. A panel of microRNA (miRNA) was downregulated in transformed FL (tFL).

METHODS

Differentially expressed miRNAs were systematically compared in 11 lymph nodes from patients at different stages of disease. Expression of miR-7e-5p was analyzed in 46 B-cell lymphomas, including 30 FL tissues and 16 DLBCL tissues. In FL cells, transcriptional regulation of the oncogene c-MYC on its target miR-7e-5p was revealed by Chromatin Immunoprecipitation (ChIP) assay. Exosome, carrying differentially expressed miR-7e-5p was isolated and visualized by transmission electron microscope and fluorescence tracing. The effect of miR-7e-5p on recipient macrophage was determined by target gene quantification, flow cytometry, and TUNEL method in a cocultured system with miR-7e-5p-mimics or inhibitors treatment. Expression of miR-7e-5p targets, macrophage proportions, and clinical parameters were included for correlation analysis.

RESULTS

We determined that downregulation of miR-7e-5p, driven by c-MYC overexpression, was associated with poorer prognosis in FL patients. The decreased expression of miR-7e-5p in lymphoma cells led to a reduced exosomal transfer to surrounding macrophages. As a result, the target gene of miR-7e-5p, Fas ligand (FasL), was upregulated and activated the caspase signaling, which led to the apoptosis of M1 macrophages in tumor stroma. Finally, in transformed FL tissues, overexpression of FasL and activation of caspase proteins was detected in tumor stromal macrophages. Downregulation of miR-7e-5p was associated with poorer clinical outcomes.

CONCLUSION

Downregulation of exosomal miR-7e-5p induces stromal M1 macrophage apoptosis, which leads to immunosurveillance and transformation of FL.

Fas Ligand (FasL) in Association with Tumor-Infiltrating Lymphocytes (TILs) in Early Stage Cervical Cancer

OBJECTIVE

To date, little is known about the roles of FasL and TILs in cervical cancer. This study aims to determine the correlation between FasL expression and TILs presence in cervical cancer.

METHODS

In this study, we analysed the FasL and TIL presence in 32 squamous cell carcinoma or adenocarcinoma that were obtained from early stage (≤ IIA2) cervical cancer patients using immunohistochemistry. The level of FasL and TIL was assessed qualitatively, and then quantified with the H-Score system.

RESULTS

Most of the patients were between 30 to 50 years old (59,4%), and had never taken pap smear examination before (96,9%). Based on the Pearson analysis of FasL and TIL presence, we found that FasL was inversely correlated with CD45 or TIL number when the level of FasL is above 140 and the CD45 is below 160. Based on Chi-Square test of FasL and TIL classification, there was a nine-fold odds ratio (OR) of lower TILs classification in high expression of FasL classification (OR 9, p=0.01).

CONCLUSION

An inverse correlation between FasL expression and TILs level, that might indicate FasL-induced TILs apoptosis in tumor tissue, was observed. The strong inverse correlation between FasL and TILs presence showed some insight about the interactions between cancer cells and its surroundings inside of the cervical cancer tissue. This might also be further developed to tailor a prognostic marker that can predict the outcome of therapy in patients, not only in cervical cancer, but generally in all cancer.

Killing Effects of IFN R-/- Mouse NK Cells Activated by HN Protein of NDV on Mouse Hepatoma Cells and Possible Mechanism with Syk and NF-κB

The objective of this article is to evaluate whether the tumoricidal activity of mouse IFN R-/- nature killer (NK) cells is induced by Newcastle disease virus hemagglutinin-neuraminidase (NDV-HN) stimulation, and to investigate what is the mechanism of the HN-stimulated NK cells to kill mouse hepatoma cell line in vitro. The mouse IFN R-/- NK cells were stimulated for 16 hr with 500 ng/mL NDV-HN in 1640 medium. Quantify the cytotoxic activities of NK cells against mouse hepatoma cells (Hepa1-6) by flow cytometry. Granzymes B (GrB) and Fas/FasL concentrations in the supernatants of IFN R-/- NK cells medium were determined by specific ELISA assay. The expression of cell surface GrB and Fas was determined by Western blot. NDV-HN stimulation enhanced tumoricidal activity of IFN R-/- NK cells toward Hepa1-6 in vitro. Treating with anti-HN neutralizing mAb induced significant decline in the cytotoxicity of IFN R-/- NK cells toward Hepa1-6 cell line (P < 0.05). After treating with anti-HN protein (1 μL/mL), Syk-specific inhibitor Herbimycin A(250 ng/mL) and NF-κB inhibitor PDTC (500 ng/mL) downregulated the tumoricidal activity of HN-stimulated IFN R-/- NK cells (P < 0.05). Moreover, significant suppressions in the production of GrB and Fas/FasL were observed in HN-stimulated IFN R-/- NK cells (P < 0.05). Thus, we concluded that killer activation receptors pathway is involved in the IFN-γ-independent GrB and Fas/FasL expression of NDV-HN-stimulated IFN R-/- NK cells, and these are activated by Syk and NF-κB. Anat Rec, 302:1718-1725, 2019. © 2019 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association for Anatomy.

Bcells and their regulatory functions during Tuberculosis: Latency and active disease

Tuberculosis (TB) is a global epidemic with devastating consequences. Emerging evidence suggests that B-cells have the ability to modulate the immune response and understanding these roles during Mycobacterium tuberculosis (M.tb) infection can help to find new strategies to treat TB. The immune system of individuals with pulmonary TB form granulomas in the lung which controls the infection by inhibiting the M.tb growth and acts as a physical barrier. Thereafter, surviving M.tb become dormant and in most cases the host's immunity prevents TB reactivation. B-cells execute several immunological functions and are regarded as protective regulators of immune responses by antibody and cytokine production, as well as presenting antigen. Some of these B-cells, or regulatory B-cells, have been shown to express death-inducing ligands, such as Fas ligand (FasL). This expression and binding to the Fas receptor leads to apoptosis, a major immune regulation mechanism, in addition to the ability to induce T-cell tolerance. Here, I discuss the relevance of B-cells, in particular their non-humoral functions by addressing their regulatory properties during M.tb infection.

Cytotoxicity of Human Hepatic Intrasinusoidal CD56bright Natural Killer Cells against Hepatocellular Carcinoma Cells

Hepatic intrasinusoidal (HI) natural killer (NK) cells from liver perfusate have unique features that are similar to those of liver-resident NK cells. Previously, we have reported that HI CD56^bright NK cells effectively degranulate against SNU398 hepatocellular carcinoma (HCC) cells. Thus, the aim of this study was to further investigate the phenotype and function of HI NK cells. We found that HI CD56^bright NK cells degranulated much less to Huh7 cells. HI CD56^bright NK cells expressed NKG2D, NKp46, TNF-related apoptosis-inducing ligand (TRAIL), and FAS ligand (FASL) at higher levels than CD56^dim cells. SNU398 cells expressed more NKG2D ligands and FAS and less PD-L1 than Huh7 cells. Blockade of NKG2D, TRAIL, and FASL significantly reduced the cytotoxicity of HI NK cells against SNU398 cells, but blockade of PD-L1 did not lead to any significant change. However, HI NK cells produced IFN-γ well in response to Huh7 cells. In conclusion, the cytotoxicity of HI CD56^bright NK cells was attributed to the expression of NKG2D, TRAIL, and FASL. The results suggest the possible use of HI NK cells for cancer immunotherapy and prescreening of HCC cells to help identify the most effective NK cell therapy recipients.

Endogenous IL-10 maintains immune tolerance but IL-10 gene transfer exacerbates autoimmune cholangitis

The immunomodulatory effect of IL-10 as an immunosuppressive and anti-inflammatory cytokine is well known. Taking advantage of our established mouse model of autoimmune cholangitis using 2-octynoic acid conjugated ovalbumin (2-OA-OVA) induction, we compared liver pathology, immune cell populations and antimitochondrial antibodies between IL-10 knockout and wild type mice immunized with 2-OA-OVA. At 10 weeks post immunization, portal inflammation and fibrosis were more severe in 2-OA-OVA immunized IL-10 knockout mice than in wild type mice. This was accompanied by significant higher levels of collagen I and III expression, T, NK and NKT subsets in liver and IgG anti-mitochondrial autoantibodies (AMAs) compared to 2-OA-OVA immunized wild type mice, suggesting that endogenous IL-10 is necessary for the maintenance of immune tolerance in primary biliary cholangitis (PBC). Further, we investigated whether administration of exogenous IL-10 could prevent PBC by administration of IL-10 expressing recombinant adeno-associated virus (AAV-IL-10) either 3 days before or 3 weeks after the establishment of liver pathology. Interestingly, administration of AAV-IL-10 resulted in increased liver inflammation and fibrosis, accompanied by increases in IFN-γ in liver CD4⁺ T cell, granzyme B, FasL, and CD107a in liver CD8⁺ T and NKT cells, and granzyme B and FasL in liver NK cells of AAV-IL-10 administered mice compared with control mice. Furthermore, administration of AAV-IL-10 significantly increased levels of proinflammatory cytokines and chemokines (IFN-γ, TNF-α, CXCL9 and CXCL10) and collagen I and III production in naïve mice, together with increase in immune cell infiltration and collagen deposition in the liver, suggesting a role of IL-10 in fibrosis. In conclusion, our data demonstrate that endogenous IL-10 is critical in the maintenance of immune tolerance but exogenous administration of IL-10 exacerbates liver inflammation and fibrosis. Furthermore, the distinctive presence of inflammatory immune cell populations and collagen expression in AAV-IL-10 treated naïve mice cautions against the clinical use of exogenous IL-10 in patients with autoimmune cholangitis.

FasL and the NKG2D receptor are required for the secretion of the Tag7/PGRP-S-Hsp70 complex by the cytotoxic CD8+ lymphocytes

Tag7 (PGRP-S or PGLYRP1), while possessing an antimicrobial activity, also exhibits an antitumor effect when in complex with the major heat shock protein Hsp70. The cytotoxic Tag7-Hsp70 complex is secreted by lymphocytes after interaction with the HLA-negative tumors. Previously, we have shown that IL-2 induces formation of the CD4⁺ and CD8⁺ cytotoxic subpopulations of human lymphocytes, which kill tumor cells through the FasL-Fas interaction. Here, we show that only the CD8⁺ T cells are able to secrete the Tag7-Hsp70 complex. For its secretion the same proteins on the surface of the lymphocytes and target cells, which are involved in the contact lysis, are necessary as well. The interaction of Fas receptor with FasL leads to an activation of the Tag7-Hsp70 complex in the lymphocyte membrane fraction, and here FasL acts as a receptor that induces intracellular signaling in lymphocytes. An interaction of the MicA stress ligand with the NKG2D receptor is necessary for the release of this cytotoxic complex. It is possible, that CD8⁺ T lymphocytes interacting with a target cell can both carry out the contact killing of these cells and to secrete the cytotoxic factor. © 2016 IUBMB Life, 69(1):30-36, 2017.

Interferon Gamma and Contact-dependent Cytotoxicity Are Each Rate Limiting for Natural Killer Cell-Mediated Antibody-dependent Chronic Rejection

Natural killer (NK) cells are key components of the innate immune system. In murine cardiac transplant models, donor-specific antibodies (DSA), in concert with NK cells, are sufficient to inflict chronic allograft vasculopathy independently of T and B cells. In this study, we aimed to determine the effector mechanism(s) required by NK cells to trigger chronic allograft vasculopathy during antibody-mediated rejection. Specifically, we tested the relative contribution of the proinflammatory cytokine interferon gamma (IFN-γ) versus the contact-dependent cytotoxic mediators of perforin and the CD95/CD95L (Fas/Fas ligand [FasL]) pathway for triggering these lesions. C3H/HeJ cardiac allografts were transplanted into immune-deficient C57BL/6 rag-/- γc-/- recipients, who also received monoclonal anti-major histocompatibility complex (MHC) class I DSA. The combination of DSA and wild-type NK cell transfer triggered aggressive chronic allograft vasculopathy. However, transfer of IFN-γ-deficient NK cells or host IFN-γ neutralization led to amelioration of these lesions. Use of either perforin-deficient NK cells or CD95 (Fas)-deficient donors alone did not alter development of vasculopathy, but simultaneous disruption of NK cell-derived perforin and allograft Fas expression resulted in prevention of these abnormalities. Therefore, both NK cell IFN-γ production and contact-dependent cytotoxic activity are rate-limiting effector pathways that contribute to this form of antibody-induced chronic allograft vasculopathy.

Dendritic Cells Regulate Extrafollicular Autoreactive B Cells via T Cells Expressing Fas and Fas Ligand

The extrafollicular (EF) plasmablast response to self-antigens that contain Toll-like receptor (TLR) ligands is prominent in murine lupus models and some bacterial infections, but the inhibitors and activators involved have not been fully delineated. Here, we used two conventional dendritic cell (cDC) depletion systems to investigate the role of cDCs on a classical TLR-dependent autoreactive EF response elicited in rheumatoid-factor B cells by DNA-containing immune complexes. Contrary to our hypothesis, cDC depletion amplified rather than dampened the EF response in Fas-intact but not Fas-deficient mice. Further, we demonstrated that cDC-dependent regulation requires Fas and Fas ligand (FasL) expression by T cells, but not Fas expression by B cells. Thus, cDCs activate FasL-expressing T cells that regulate Fas-expressing extrafollicular helper T (Tefh) cells. These studies reveal a regulatory role for cDCs in B cell plasmablast responses and provide a mechanistic explanation for the excess autoantibody production observed in Fas deficiency.

Immunohistochemical Expression of Apoptotic Markers in Drug-Induced Erythema Multiforme, Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are considered to be severity variants of the same disease, which is almost always associated with drug intake. In contrast, erythema multiforme (EM) is a disorder regarded as only rarely caused by drugs. Keratinocyte apoptosis has been shown to play an important part in the pathogenesis of SJS and TEN, whilst its role in EM remains controversial. To determine the expression of apoptosis-associated molecules Fas, Fas ligand (FasL), Bcl-2 and Bax in the above disorders, an immunohistochemical analysis was performed. We studied both lesional skin from thirty patients having drug-induced EM and 5 cases classified within the SJS/TEN spectrum and normal skin samples. We found a keratinocyte overexpression of Fas antigen, an important molecule mediating apoptosis, not only in SJS and TEN but also in EM. Another noteworthy finding was the strong expression of Bcl-2, a protein known as blocking apoptosis, along the basal layer and in the dermal infiltrate both in SJS/TEN and in EM. Taken together, these findings suggest that Fas-dependent keratinocyte apoptosis may play a part in the pathogenesis of both SJS/TEN and EM. Fas-mediated cell death may be partially suppressed by the Bcl-2 protein.

Bortezomib Improves Adoptive T-cell Therapy by Sensitizing Cancer Cells to FasL Cytotoxicity

Cancer immunotherapy shows great promise but many patients fail to show objective responses, including in cancers that can respond well, such as melanoma and renal adenocarcinoma. The proteasome inhibitor bortezomib sensitizes solid tumors to apoptosis in response to TNF-family death ligands. Because T cells provide multiple death ligands at the tumor site, we investigated the effects of bortezomib on T-cell responses in immunotherapy models involving low-avidity antigens. Bortezomib did not affect lymphocyte or tissue-resident CD11c(+)CD8(+) dendritic cell counts in tumor-bearing mice, did not inhibit dendritic cell expression of costimulatory molecules, and did not decrease MHC class I/II-associated antigen presentation to cognate T cells. Rather, bortezomib activated NF-κB p65 in CD8(+) T cells, stabilizing expression of T-cell receptor CD3ζ and IL2 receptor-α, while maintaining IFNγ secretion to improve FasL-mediated tumor lysis. Notably, bortezomib increased tumor cell surface expression of Fas in mice as well as human melanoma tissue from a responsive patient. In renal tumor-bearing immunodeficient Rag2(-/-) mice, bortezomib treatment after adoptive T-cell immunotherapy reduced lung metastases and enhanced host survival. Our findings highlight the potential of proteasome inhibitors to enhance antitumor T-cell function in the context of cancer immunotherapy.

Plasmacytoid dendritic cells promote HIV-1-induced group 3 innate lymphoid cell depletion

Group 3 innate lymphoid cells (ILC3s) have demonstrated roles in promoting antibacterial immunity, maintaining epithelial barrier function, and supporting tissue repair. ILC3 alterations are associated with chronic inflammation and inflammatory disease; however, the characteristics and relevant regulatory mechanisms of this cell population in HIV-1 infection are poorly understood due in part to a lack of a robust model. Here, we determined that functional human ILC3s develop in lymphoid organs of humanized mice and that persistent HIV-1 infection in this model depletes ILC3s, as observed in chronic HIV-1-infected patients. In HIV-1-infected mice, effective antiretroviral therapy reversed the loss of ILC3s. HIV-1-dependent reduction of ILC3s required plasmacytoid dendritic cells (pDCs), IFN-I, and the CD95/FasL pathway, as targeted depletion or blockade of these prevented HIV-1-induced ILC3 depletion in vivo and in vitro, respectively. Finally, we determined that HIV-1 infection induces CD95 expression on ILC3s via a pDC- and IFN-I-dependent mechanism that sensitizes ILC3s to undergo CD95/FasL-mediated apoptosis. We conclude that chronic HIV-1 infection depletes ILC3s through pDC activation, induction of IFN-I, and CD95-mediated apoptosis.

Characterization and activity of Fas ligand producing CD5⁺ B cells

B lymphocytes make several contributions to immune regulation including production of antibodies with regulatory properties, release of immune suppressive cytokines, and expression of death-inducing ligands. A role for Fas ligand (FasL)-expressing "killer" B cells in regulating T helper cell survival and chronic inflammation has been demonstrated in animal models of schistosome worm infection, asthma, and autoimmune arthritis. Interestingly, a population of CD5(+) B cells found in the spleen and lungs of naïve mice constitutively expresses FasL and has potent killer function against T helper cells that is antigen-specific and FasL-dependent. Killer B cells therefore represent a novel target for immune modulation in many disease settings. Our laboratory has recently published methods of characterizing FasL(+) B cells and inducing their proliferation in vitro. This chapter will describe detailed methods of identifying and expanding killer B cells from mice, detecting FasL expression in B cells, and performing functional killing assays against antigen-specific TH cells.

Ectopic expression of Fas Ligand on cardiomyocytes renders cardiac allografts resistant to CD4(+) T-cell mediated rejection

Fas Ligand limits inflammatory injury and permits allograft survival by inducing apoptosis of Fas-bearing lymphocytes. Previous studies have shown that the CD4(+) T-cell is both sufficient and required for murine cardiac allograft rejection. Here, utilizing a transgenic mouse that over-expresses Fas Ligand specifically on cardiomyocytes as heart donors, we sought to determine if Fas Ligand on graft parenchymal cells could resist CD4(+) T-cell mediated rejection. When transplanted into fully immunocompetent BALB/c recipients Fas Ligand transgenic hearts were acutely rejected. However, when transplanted into CD4(+) T-cell reconstituted BALB/c-rag(-/-) recipients, Fas Ligand hearts demonstrated long-term survival. These results indicate that Fas Ligand over-expression on cardiomyocytes can indeed resist CD4(+) T-cell mediated cardiac rejection and suggests contact dependence between Fas Ligand expressing graft parenchymal cells and the effector CD4(+) T-cells.

Coordinated histone H3 methylation and acetylation regulate physiologic and pathologic fas ligand gene expression in human CD4+ T cells

Activation-induced Fas ligand (FasL) mRNA expression in CD4+ T cells is mainly controlled at transcriptional initiation. To elucidate the epigenetic mechanisms regulating physiologic and pathologic FasL transcription, TCR stimulation-responsive promoter histone modifications in normal and alcohol-exposed primary human CD4+ T cells were examined. TCR stimulation of normal and alcohol-exposed cells led to discernible changes in promoter histone H3 lysine trimethylation, as documented by an increase in the levels of transcriptionally permissive histone 3 lysine 4 trimethylation and a concomitant decrease in the repressive histone 3 lysine 9 trimethylation. Moreover, acetylation of histone 3 lysine 9 (H3K9), a critical feature of the active promoter state that is opposed by histone 3 lysine 9 trimethylation, was significantly increased and was essentially mediated by the p300-histone acetyltransferase. Notably, the degree of these coordinated histone modifications and subsequent recruitment of transcription factors and RNA polymerase II were significantly enhanced in alcohol-exposed CD4+ T cells and were commensurate with the pathologic increase in the levels of FasL mRNA. The clinical relevance of these findings is further supported by CD4+ T cells obtained from individuals with a history of heavy alcohol consumption, which demonstrate significantly greater p300-dependent H3K9 acetylation and FasL expression. Overall, these data show that, in human CD4+ T cells, TCR stimulation induces a distinct promoter histone profile involving a coordinated cross-talk between histone 3 lysine 4 and H3K9 methylation and acetylation that dictates the transcriptional activation of FasL under physiologic, as well as pathologic, conditions of alcohol exposure.

Negative regulation by PD-L1 during drug-specific priming of IL-22-secreting T cells and the influence of PD-1 on effector T cell function

Activation of PD-1 on T cells is thought to inhibit Ag-specific T cell priming and regulate T cell differentiation. Thus, we sought to measure the drug-specific activation of naive T cells after perturbation of PD-L1/2/PD-1 binding and investigate whether PD-1 signaling influences the differentiation of T cells. Priming of naive CD4(+) and CD8(+) T cells against drug Ags was found to be more effective when PD-L1 signaling was blocked. Upon restimulation, T cells proliferated more vigorously and secreted increased levels of IFN-γ, IL-13, and IL-22 but not IL-17. Naive T cells expressed low levels of PD-1; however, a transient increase in PD-1 expression was observed during drug-specific T cell priming. Next, drug-specific responses from in vitro primed T cell clones and clones from hypersensitive patients were measured and correlated with PD-1 expression. All clones were found to secrete IFN-γ, IL-5, and IL-13. More detailed analysis revealed two different cytokine signatures. Clones secreted either FasL/IL-22 or granzyme B. The FasL/IL-22-secreting clones expressed the skin-homing receptors CCR4, CCR10, and CLA and migrated in response to CCL17/CCL27. PD-1 was stably expressed at different levels on clones; however, PD-1 expression did not correlate with the strength of the Ag-specific proliferative response or the secretion of cytokines/cytolytic molecules. This study shows that PD-L1/PD-1 binding negatively regulates the priming of drug-specific T cells. ELISPOT analysis uncovered an Ag-specific FasL/IL-22-secreting T cell subset with skin-homing properties.

Phenotypic and functional characterization of cytotoxic T lymphocytes by flow cytometry

Cytotoxic T lymphocytes (CTLs) are important constituents of the adaptive immune system. Development of CTLs are particularly important for bacterial and viral infections, in addition to tumor surveillance. Measuring T cell immune function is important in evaluating host defense, allergy, autoimmunity, transplant rejection, and tumor immunity. In these recent years it has become possible to measure multiple effector functions in a single cell such as cytokine, transcription factors, and cytolytic function. In addition these parameters can be evaluated in conjunction with cellular proliferation. In this chapter we detail these cellular based assays and the methods used to characterize and quantify both phenotype and function of CTL.

Normalization of tumor microenvironment by neem leaf glycoprotein potentiates effector T cell functions and therapeutically intervenes in the growth of mouse sarcoma

We have observed restriction of the murine sarcoma growth by therapeutic intervention of neem leaf glycoprotein (NLGP). In order to evaluate the mechanism of tumor growth restriction, here, we have analyzed tumor microenvironment (TME) from sarcoma bearing mice with NLGP therapy (NLGP-TME, in comparison to PBS-TME). Analysis of cytokine milieu within TME revealed IL-10, TGFβ, IL-6 rich type 2 characters was switched to type 1 microenvironment with dominance of IFNγ secretion within NLGP-TME. Proportion of CD8(+) T cells was increased within NLGP-TME and these T cells were protected from TME-induced anergy by NLGP, as indicated by higher expression of pNFAT and inhibit related downstream signaling. Moreover, low expression of FasR(+) cells within CD8(+) T cell population denotes prevention from activation induced cell death. Using CFSE as a probe, better migration of T cells was noted within TME from NLGP treated mice than PBS cohort. CD8(+) T cells isolated from NLGP-TME exhibited greater cytotoxicity to sarcoma cells in vitro and these cells show higher expression of cytotoxicity related molecules, perforin and granzyme B. Adoptive transfer of NLGP-TME exposed T cells, but not PBS-TME exposed cells in mice, is able to significantly inhibit the growth of sarcoma in vivo. Such tumor growth inhibition by NLGP-TME exposed T cells was not observed when mice were depleted for CD8(+) T cells. Accumulated evidences strongly suggest NLGP mediated normalization of TME allows T cells to perform optimally to inhibit the tumor growth.

CD4+ CD25+ Foxp3+ IFNγ+ CD178+ human induced Treg (iTreg) contribute to suppression of alloresponses by apoptosis of responder cells

Induced Treg with the phenotype CD4(+)CD25(+)Foxp3(+)IFNγ(+) were shown to be associated with good long-term graft outcome in renal transplant recipients and inhibition of allogeneic T-cell responses in vitro. In the present study, we investigated whether apoptosis and Fas/FasL-dependent pathways contribute to the inhibition of T-cell activation. Early apoptosis and necrosis rates as well as co-expression of immunostimulatory and immunosuppressive proteins in/on CD4(+)CD25(+)Foxp3(+), CD4(+)IFNγ(+)Foxp3(+) and CD4(+)CD25(+)IFNγ(+) PBL were analyzed using cells from healthy controls and four-color flow cytometry, PMA/Ionomycin-stimulated PBL, and MLC. Sixteen hours PMA/Ionomycin stimulation induced iTreg subsets with the phenotype CD4(+)CD25(+)Foxp3(+), CD4(+)IFNγ(+)Foxp3(+) and CD4(+)CD25(+)IFNγ(+) co-expressing CD95, CD152, CD178, CD279, Granzyme A, Granzyme B, Perforin, IL-10, and TGFβ(1). CD178(+) iTreg increased within 3h after PMA/Ionomycin stimulation in parallel to early apoptotic Annexin(+)/PI(-) PBL, suggesting CD178-mediated apoptosis of responder cells by CD4(+)CD25(+)Foxp3(+)IFNγ(+)CD178(+) iTreg. CD4(+)CD25(+)IFNγ(+) and CD4(+)CD25(+)CD178(+) PBL separated from primary cell cultures and added to autologous PMA/Ionomycin stimulated secondary cell cultures induced apoptosis immediately. Early apoptosis was not antigen-specific as shown in secondary MLC with separated CD4(+)CD25(+)IFNγ(+) and CD4(+)CD25(+)CD178(+) PBL and third-party cells as stimulator. CD4(+)CD25(+)Foxp3(+)IFNγ(+)CD178(+) iTreg differentiate after cell stimulation and induce antigen-unspecific apoptosis of activated CD95(+) responder/effector cells in vitro that might contribute to iTreg-mediated inhibition of T-cell activation.

Activation of CD11b+ Kupffer cells/macrophages as a common cause for exacerbation of TNF/Fas-ligand-dependent hepatitis in hypercholesterolemic mice

We have reported that the mouse hepatic injury induced by either α-galactosylceramide (α-GalCer) or bacterial DNA motifs (CpG-ODN) is mediated by the TNF/NKT cell/Fas-ligand (FasL) pathway. In addition, F4/80(+) Kupffer cells can be subclassified into CD68(+) subset with a phagocytosing capacity and CD11b(+) subset with a TNF-producing capacity. CD11b(+) subset increase if mice are fed high-fat and cholesterol diet (HFCD). The present study examined how a HFCD affects the function of NKT cells and F4/80(+) CD11b(+) subset and these hepatitis models. After the C57BL/6 mice received a HFCD, high-cholesterol diet (HCD), high-fat diet (HFD) and control diet (CD) for four weeks, the HFCD mice increased surface CD1d and intracellular TLR-9 expression by the CD11b(+) population compared to CD mice. Hepatic injury induced either by α-GalCer or CpG-ODN was more severe in HCD and HFCD mice compared to CD mice, which was in proportion to the serum TNF levels. In addition, liver cholesterol levels but not serum cholesterol levels nor liver triglyceride levels were involved in the aggravation of hepatitis. The FasL expression of NKT cells induced by both reagents was upregulated in HFCD mice. Furthermore, the liver mononuclear cells and purified F4/80(+) CD11b(+) subset from HFCD mice stimulated with either reagent in vitro produced a larger amount of TNF than did those from CD mice. Intracellular TNF production in F4/80(+) CD11b(+) cells was confirmed. The increased number of F4/80(+) CD11b(+) Kupffer cells/macrophages by HFCD and their enhanced TNF production thus play a pivotal role in TNF/NKT cell/FasL dependent hepatic injury.

Distinct different sensitivity of Treg and Th17 cells to Fas-mediated apoptosis signaling in patients with acute coronary syndrome

OBJECTIVE

An imbalance in CD4(+)CD25(+) regulatory T (Treg) cells and Th17 cells has been found to correlate to occurrence of acute coronary syndrome [ACS, including unstable angina (UA) and acute myocardial infarction (AMI)]. However, the mechanisms of Th17/Treg imbalance in ACS patients are still unclear. The purpose of this study is to investigate the possibility of differences in sensitivity of Th17 and Tregs to Fas-mediated apoptosis which could lead to Th17/Treg imbalance in ACS patients.

METHODS

We examined the apoptosis of Th17 and Treg cells, apoptosis-related Fas/Fas ligand(FasL) pathway, and inflammatory markers in patients with AMI, UA, stable angina (SA) and controls by Flow cytometry and ELISA. Then we analysed the correlation of inflammatory markers and sFasL to Treg apoptosis, and the effect of anti-FasL antibody on Treg apoptois in vitro.

RESULTS

Our study demonstrated that apoptotic Tregs, Fas and FasL expression, Caspase-3 activity of Tregs were significantly higher in ACS patients than those in NCA and SA patients (all P < 0.05). The percentage of apoptotic Tregs is positively correlated with the levels of inflammatory markers and sFasL. In vitro incubation of peripheral blood mononuclear cells from ACS patients with anti-FasL antibody resulted in a markedly reduction of apoptotic Treg cells. However, there were no significant differences in apoptotic Th17 cells and in Fas and FasL expression for Th17 cells between the four groups (all P >0.05).

CONCLUSIONS

Tregs, but not Th17 cells, become apoptotic through Fas/FasL pathway, which contributed to reduction of Tregs leading to an imbalance between Th17 and Treg cells. This could be the mechanism underlying Th17/Treg imbalance and occurrence of ACS.

Critical role of the death receptor pathway in the antitumoral effects induced by hispanolone derivatives

Labdane diterpenoids have a broad spectrum of biological activities including antibacterial, antiviral and anti-inflammatory properties. However, little is known about their possible role in the apoptotic cell death machinery. Here, we report that hispanolone derivatives, a group of labdane diterpenoids, induce apoptosis in different tumor cell lines by activating caspase-8 with subsequent participation of mitochondrial signaling. Activation of caspase-8 by hispanolone derivatives was followed by a decrease in mitochondrial membrane potential, the release of apoptotic factors from mitochondria to the cytosol, and activation of caspases-9 and 3. Hispanolone derivatives also led to a time-dependent cleavage of Bid. Inhibition of caspase-8 abrogated these processes, suggesting that the death receptor pathway has a critical role in the apoptotic events induced by hispanolone derivatives. In addition, silencing death receptors with small interfering RNA s or pretreating cells with neutralizing antibodies to Fas ligand, tumor necrosis factor receptor 1 (TNF-R1), and TNF-α receptor 2 (TRAIL) inhibited diterpenoid-induced apoptosis, revealing it to be dependent on these death receptors. Interestingly, hispanolone derivatives had no effect on non-tumor cells. Consistently, in vivo bioluminescence imaging corroborates this antineoplasic effect, as hispanolone derivatives significantly decrease cancer growth in tumor xenograft assays. These data demostrate the antitumoral effects of hispanolone derivatives and provide relevant preclinical validation for the use of these compounds as potent therapeutic agents in cancer treatment.

Increased synapse formation obtained by T cell epitopes containing a CxxC motif in flanking residues convert CD4+ T cells into cytolytic effectors

The nature of MHC class II-binding epitopes not only determines the specificity of T cell responses, but may also alter effector cell functions. Cytolytic CD4+ T cells have been observed primarily in anti-viral responses, but very little is known about the conditions under which they can be elicited. Their potential as regulators of immune responses, however, deserves investigations. We describe here that inclusion of a thiol-disulfide oxidoreductase motif within flanking residues of class II-restricted epitopes results, both in vitro and in vivo, in elicitation of antigen-specific cytolytic CD4+ T cells through increased synapse formation. We show that both naïve and polarized CD4+ T cells, including Th17 cells, can be converted by cognate recognition of such modified epitopes. Cytolytic CD4+ T cells induce apoptosis on APCs by Fas-FasL interaction. These findings potentially open the way towards a novel form of antigen-specific immunosuppression.

Recovered patients with Stevens-Johson syndrome and toxic epidermal necrolysis maintain long-lived IFN-γ and sFasL memory response

There is evidence that drug-specific T cells are involved in inducing keratinocyte apoptosis in acute stage of Steven-Johson syndrome (SJS) and Toxic epidermal necrolysis (TEN). However, there are few studies that have attempted to examine T cell memory responses over time. We sought to determine the duration of IFN-γ and sFasL memory response to causal drugs in patients with SJS and TEN after remission. Eight patients with previous SJS and TEN were enrolled. Memory T cells were measured by 10-day cultured IFN-γ enzyme-linked immunosorbent spot-forming cell (ELISpot) assay. Effector T-cell responses were measured by ex vivo IFN-γ ELISpot assay and sFasL ELISA. The sFasL-mediated toxicities of drug-stimulated PBMC supernatants against keratinocyte line were further investigated by MTT proliferation assay and Annexin-V staining. We observed significant cultured and ex vivo IFN-γ ELISpot responses against causal drugs in all 8 patients. In addition, the sFasL levels were specifically increased in the supernatant of PBMCs cultured with causal drugs from 6 of 8 patients. Drug-stimulated PBMC supernatants were cytotoxic against keratinocyte line, which was inhibited by anti-FasL mAb in a dose-dependent manner. Our findings confirmed that drug-specific IFN-γ and sFasL memory response against causal drugs could be sustained over several years and further suggest that patients should avoid causal drug re-exposure after the recovery of TEN and SJS.

Regulating the suppressors: apoptosis and inflammation govern the survival of tumor-induced myeloid-derived suppressor cells (MDSC)

Immune suppressive myeloid-derived suppressor cells (MDSC) are present in most cancer patients where they inhibit innate anti-tumor immunity and are a significant obstacle to cancer immunotherapy. Inflammation is a known inducer of Gr1(+)CD11b(+) MDSC; however, the factors/conditions that regulate MDSC survival and half-life have not been identified. We have used mass spectrometry (MS) and proteomic analysis to identify proteins and pathways that regulate MDSC survival. This analysis revealed high expression of caspase family proteins and the Fas-FasL, p38 MAPK, and TGFβ pathways, suggesting that Fas-FasL apoptosis regulates MDSC survival. Flow cytometry, confocal microscopy, and western blot analyses confirmed the MS findings and demonstrated that Fas(+) MDSC are susceptible to Fas-mediated killing in vitro. In vivo studies with FasL-deficient and Fas-deficient mice demonstrated that Fas-FasL interactions are essential for MDSC apoptosis and for rejection of established metastatic disease and survival and that FasL(+) T cells are the effector population mediating MDSC apoptosis. MS findings validated by biological experiments demonstrated that inflammation increases MDSC levels by protecting MDSC from Fas-mediated apoptosis, possibly by activating p38 MAPK. These results demonstrate that MDSC half-life in vivo is regulated by FasL(+) T cells and that inflammation increases MDSC levels by conferring resistance to Fas-mediated apoptosis and identifies T cells as the relevant effector cells causing MDSC apoptosis in vivo. This newly recognized mechanism for regulating MDSC levels identifies potential new targets for decreasing MDSC in cancer patients.

Activation-induced cell death of memory CD8+ T cells from pleural effusion of lung cancer patients is mediated by the type II Fas-induced apoptotic pathway

Lung cancer is the second most common form of cancer and the leading cause of cancer death worldwide. Pleural effusions, containing high numbers of mononuclear and tumor cells, are frequent in patients with advanced stages of lung cancer. We reported that in pleural effusions from primary lung cancer, the CD8+ T cell subpopulation, and particularly the terminally differentiated subset, is reduced compared to that of non-malignant effusions. We analyzed the participation of activation-induced cell death (AICD) and extrinsic pathways (type I or II) as mechanisms for the decrease in pleural effusion CD8+ T cell subpopulation. Pleural effusion or peripheral blood CD4+ and CD8+ T cells, from lung cancer patients, were stimulated with anti-CD3 antibody and analyzed for (a) apoptosis by annexin-V-binding and TUNEL assay, (b) transcript levels of Fas ligand (FasL) and TRAIL by real-time RT-PCR, (c) expression of FasL and TRAIL, measured as integrated mean fluorescence intensities (iMFI) by flow cytometry, (d) expression of Bcl-2 and BIM molecules, measured as MFI, and (e) apoptosis inhibition using caspase-8 and -9 inhibitors. Pleural effusion CD8+ T cells, but not CD4+ T cells, from cancer patients underwent AICD. Blocking FasL/Fas pathway protected from AICD. Upregulation of FasL and TRAIL expressions was found in pleural effusion CD8+ T cells, which also showed a subset of Bcl-2 low cells. In memory CD8+ T cells, AICD depended on both extrinsic and intrinsic apoptotic pathways. Hence, in the pleural space of lung cancer patients, AICD might compromise the antitumor function of CD8+ T cells.

The ROS scavenger, NAC, regulates hepatic Vα14iNKT cells signaling during Fas mAb-dependent fulminant liver failure

Uncontrolled systemic activation of the immune system is an early initiating event that leads to development of acute fulminant liver failure (FLF) in mice after treatment with agonistic Fas mAb. In this study, we demonstrate that treatment of mice with N-acetylcysteine (NAC), an ROS scavenger and glutathione (GSH) precursor, almost completely abolished Fas mAb-induced FLF through suppression of Vα14iNKT cell activation, IFN-γ signaling, apoptosis and nitrotyrosine formation in liver. In addition, enrichment of the liver with GSH due to Vα14iNKT cells deficiency, induced an anti-inflammatory response in the liver of Jα18(-/-) mice that inhibited apoptosis, nitrotyrosine formation, IFN-γ signaling and effector functions. In summary, we propose a novel and previously unrecognized pro-inflammatory and pro-apoptotic role for endogenous ROS in stimulating Th1 signaling in Vα14iNKT cells to promote the development of FLF. Therefore, our study provides critical new insights into how NAC, a ROS scavenger, regulates Th1 signaling in intrahepatic Vα14iNKT cells to impact inflammatory and pathological responses.

Underlying mechanisms of cAMP- and glucocorticoid-mediated inhibition of FasL expression in activation-induced cell death

Glucocorticoids (GCs) and cAMP-dependent signaling pathways exert diverse and relevant immune regulatory functions, including a tight control of T cell death and homeostasis. Both of these signaling molecules inhibit TCR-induced cell death and FasL expression, but the underlying mechanisms are still poorly understood. Therefore, to address this question, we performed a comprehensive screening of signaling pathways downstream of the TCR, in order to define which of them are targets of cAMP- and GC-mediated inhibition. We found that cAMP inhibited NF-κB and ERK pathways through a PKA-dependent mechanism, while Dexamethasone blocked TCR-induced NF-κB signaling. Although GCs and cAMP inhibited the induction of endogenous FasL mRNA expression triggered by TCR activation, they potentiated TCR-mediated induction of FasL promoter activity in transient transfection assays. However, when the same FasL promoter was stably transfected, the facilitatory effect of GCs and cAMP became inhibitory, thus resembling the effects on endogenous FasL mRNA expression. Hence, the endogenous chromatinization status known to occur in integrated or genomic vs. episomic DNA might be critical for proper regulation of FasL expression by cAMP and GCs. Our results suggest that the chromatinization status of the FasL promoter may function as a molecular switch, controlling cAMP and GC responsiveness and explaining why these agents inhibit FasL expression in T cells but induce FasL in other cell types.

Pancreatic islets engineered with SA-FasL protein establish robust localized tolerance by inducing regulatory T cells in mice

Allogeneic islet transplantation is an important therapeutic approach for the treatment of type 1 diabetes. Clinical application of this approach, however, is severely curtailed by allograft rejection primarily initiated by pathogenic effector T cells regardless of chronic use of immunosuppression. Given the role of Fas-mediated signaling in regulating effector T cell responses, we tested if pancreatic islets can be engineered ex vivo to display on their surface an apoptotic form of Fas ligand protein chimeric with streptavidin (SA-FasL) and whether such engineered islets induce tolerance in allogeneic hosts. Islets were modified with biotin following efficient engineering with SA-FasL protein that persisted on the surface of islets for >1 wk in vitro. SA-FasL-engineered islet grafts established euglycemia in chemically diabetic syngeneic mice indefinitely, demonstrating functionality and lack of acute toxicity. Most importantly, the transplantation of SA-FasL-engineered BALB/c islet grafts in conjunction with a short course of rapamycin treatment resulted in robust localized tolerance in 100% of C57BL/6 recipients. Tolerance was initiated and maintained by CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells, as their depletion early during tolerance induction or late after established tolerance resulted in prompt graft rejection. Furthermore, Treg cells sorted from graft-draining lymph nodes, but not spleen, of long-term graft recipients prevented the rejection of unmodified allogeneic islets in an adoptive transfer model, further confirming the Treg role in established tolerance. Engineering islets ex vivo in a rapid and efficient manner to display on their surface immunomodulatory proteins represents a novel, safe, and clinically applicable approach with important implications for the treatment of type 1 diabetes.

Destruction of lymphoid organ architecture and hepatitis caused by CD4+ T cells

Immune responses have the important function of host defense and protection against pathogens. However, the immune response also causes inflammation and host tissue injury, termed immunopathology. For example, hepatitis B and C virus infection in humans cause immunopathological sequel with destruction of liver cells by the host's own immune response. Similarly, after infection with lymphocytic choriomeningitis virus (LCMV) in mice, the adaptive immune response causes liver cell damage, choriomeningitis and destruction of lymphoid organ architecture. The immunopathological sequel during LCMV infection has been attributed to cytotoxic CD8(+) T cells. However, we now show that during LCMV infection CD4(+) T cells selectively induced the destruction of splenic marginal zone and caused liver cell damage with elevated serum alanin-transferase (ALT) levels. The destruction of the splenic marginal zone by CD4(+) T cells included the reduction of marginal zone B cells, marginal zone macrophages and marginal zone metallophilic macrophages. Functionally, this resulted in an impaired production of neutralizing antibodies against LCMV. Furthermore, CD4(+) T cells reduced B cells with an IgM(high)IgD(low) phenotype (transitional stage 1 and 2, marginal zone B cells), whereas other B cell subtypes such as follicular type 1 and 2 and germinal center/memory B cells were not affected. Adoptive transfer of CD4(+) T cells lacking different important effector cytokines and cytolytic pathways such as IFNγ, TNFα, perforin and Fas-FasL interaction did reveal that these cytolytic pathways are redundant in the induction of immunopathological sequel in spleen. In conclusion, our results define an important role of CD4(+) T cells in the induction of immunopathology in liver and spleen. This includes the CD4(+) T cell mediated destruction of the splenic marginal zone with consecutively impaired protective neutralizing antibody responses.

Killer artificial antigen-presenting cells deplete alloantigen-specific T cells in a murine model of alloskin transplantation

FasL-expressing killer antigen-presenting cells (KAPCs) have the ability to delete antigen-specific T cells and, therefore, could potentially be used for the treatment of allograft rejection and autoimmunity; however, their cellular nature markedly limits their clinical use. Novel bead-based killer artificial antigen-presenting cells (KaAPCs), which are generated by coupling major histocompatibility complex (MHC) class I antigens together with the apoptosis-inducing anti-Fas monoclonal antibody (mAb) onto magnetic beads, have recently attracted more attention. KaAPCs have a number of advantages over KAPCs and are able to deplete specific T cells in cocultures. However, it remains unknown whether bead-based KaAPCs can also induce apoptosis of alloreactive or autoreactive T cells and, consequently, generate hyporesponsiveness in vivo. In this study, H-2K(b)/peptide monomers and anti-Fas mAb have been covalently coupled to latex beads and administered intravenously into BALB/c mice (H-2K(d)) that had previously been grafted with skin squares from C57BL/6 mice (H-2K(b)). Alloskin graft survival was prolonged for 6 days. A 60% decrease of H-2K(b) antigen-alloreactive T cells was demonstrated by several measures 2 days after each injection of KaAPCs, but intact immune function, including antitumor activity, was maintained. These data provide the first in vivo evidence that bead-based KaAPCs can selectively deplete antigen-specific T cells without the loss of overall immune responsiveness and, therefore, highlight the therapeutic potential of this novel strategy for the treatment of allograft rejection and autoimmune disorders.

IRF8 regulates acid ceramidase expression to mediate apoptosis and suppresses myelogeneous leukemia

IFN regulatory factor 8 (IRF8) is a key transcription factor for myeloid cell differentiation and its expression is frequently lost in hematopoietic cells of human myeloid leukemia patients. IRF8-deficient mice exhibit uncontrolled clonal expansion of undifferentiated myeloid cells that can progress to a fatal blast crisis, thereby resembling human chronic myelogeneous leukemia (CML). Therefore, IRF8 is a myeloid leukemia suppressor. Whereas the understanding of IRF8 function in CML has recently improved, the molecular mechanisms underlying IRF8 function in CML are still largely unknown. In this study, we identified acid ceramidase (A-CDase) as a general transcription target of IRF8. We demonstrated that IRF8 expression is regulated by IRF8 promoter DNA methylation in myeloid leukemia cells. Restoration of IRF8 expression repressed A-CDase expression, resulting in C16 ceramide accumulation and increased sensitivity of CML cells to FasL-induced apoptosis. In myeloid cells derived from IRF8-deficient mice, A-CDase protein level was dramatically increased. Furthermore, we demonstrated that IRF8 directly binds to the A-CDase promoter. At the functional level, inhibition of A-CDase activity, silencing A-CDase expression, or application of exogenous C16 ceramide sensitized CML cells to FasL-induced apoptosis, whereas overexpression of A-CDase decreased CML cells' sensitivity to FasL-induced apoptosis. Consequently, restoration of IRF8 expression suppressed CML development in vivo at least partially through a Fas-dependent mechanism. In summary, our findings determine the mechanism of IRF8 downregulation in CML cells and they determine a primary pathway of resistance to Fas-mediated apoptosis and disease progression.

Lymphocytes with T-cell-like properties express the Fas ligand in the Japanese flounder Paralichthys olivaceus

In this study, we aimed to identify the leukocyte population that expresses Fas ligand (FasL) in the Japanese flounder (Paralichthys olivaceus). The transcriptional activity of FasL was examined for the first time in the fish leukocytes. Transcription of the FasL gene in flounder leukocytes was significantly increased by phytohemagglutinin (PHA) treatment. All the leukocyte populations we tested possessed binding activity for PHA, but this was especially high in the lymphocyte population. However, the lymphocytes consisted of two subsets showing heterogeneity with respect to PHA binding, with the high-binding subset being surface IgM-negative. We also found that only the lymphocyte population showed a significant increase in the expression of the FasL gene after stimulation with PHA. In addition, only the lymphocyte subset showing high binding to PHA showed conspicuous expression of the FasL gene. This subset also had a CD3γ/δ+, CD8α+ and IgM heavy-chain (-) phenotype. These results suggested that lymphocytes with T-cell-like properties are FasL-expressing cells in the Japanese flounder.

Early markers for protective mechanisms during rush venom immunotherapy

BACKGROUND

Allergen-specific venom immunotherapy (VIT) represents the only rational-based option to treat allergic sensitizations against bee and wasp venom. So far, there is not much knowledge about early induction of protective and tolerogenic pathways during VIT.

OBJECTIVES

To identify the earliest markers for protective mechanisms against allergic reactions in the peripheral blood during the build-up phase of VIT.

METHODS

PBMC and monocytes were isolated, and serum samples were taken before and during a five day build-up phase from 65 hymenoptera venom allergic patients. Expression level of tolerogenic markers was analyzed on mRNA and protein level. Serum levels of different soluble tolerogenic factors were measured.

RESULTS

We observed significantly enhanced tryptophan degradation, elevated ILT4 expression of monocytes as well as IL-10 production of CD3(+) T cells only a few hours after the first injection on day 1, followed by increased IL-10 serum levels, monocyte apoptosis and elevated intracellular cAMP levels of monocytes on day 3 combined with a higher ILT3 protein expression and IL-10 secretion of monocytes on day 5.

CONCLUSION

From these data, we conclude that tryptophan depletion, ILT3/4-mediated inhibition, higher IL-10 production as well as intracellular cAMP might contribute to early induction of protective mechanisms against allergic reactions during the build-up phase of VIT.

[Allograft tolerance induced by FasL chimeric protein decorated donor splenocytes]

OBJECTIVE

To investigate the feasibility of strategy of allograft tolerance induction by injection of FasL-decorated donor splenocytes.

METHODS

Chimeric FasL with core streptavidin (SA-FasL) was efficiently displayed on the surface of splenocytes by the technology of ProtEx™. Heterotopic heart transplant procedures were performed from donor WF rats to recipient ACI rats, F344 rats were used as third-party. Intraperitoneal injection of ACI rats with "decorated" WF splenocytes was used as the approach to induce tolerance in this study. According to different therapeutic strategies, three groups were set up: SA-FasL group (n = 23), SA group (n = 20) and naive splenocytes only group (n = 8). No treatment group was regarded as control (n = 10). Adoptive transfer was underwent with injection of splenocytes from tolerant recipients into naive ACI followed by heart transplant procedures. Mixed lymphocyte reaction (MLR) and third party transplantation were performed to detect allogenic tolerance.

RESULTS

The injection of ACI rats with WF rat splenocytes displaying SA-FasL on their surface resulted in tolerance to donor, but not F344 third-party cardiac allografts. There were 70% cardiac allografts in SA-FasL group achieved long term survival, and it was significantly higher than the rats in other groups (P < 0.05). Adoptive transfer of splenocytes from long-term graft recipients into naive unmanipulated ACI rats resulted in indefinite survival of secondary WF grafts. Donor specific tolerance was identified by MLR and third-party transplant.

CONCLUSION

The direct display of SA-FasL on the cell membrane in a rapid and efficient manner provides a practical and clinically applicable means of immunomodulation for tolerance induction with considerable therapeutic potential for transplantation.

The role of apoptosis proteins and complement components in the etiopathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus is a prototypical autoimmune disease characterized by the deregulation of T and B cells, tissue infiltration by mononuclear cells, tissue damage and the production of autoantibodies. There is a consensus that accelerated apoptosis of circulating lymphocytes and/or impaired clearance of apoptotic bodies may increase the amount of nuclear antigens presented to T lymphocytes. This process is accompanied by autoimmune responses that can lead to the development of lupus. The dysfunction of apoptosis may be a direct consequence of alterations in proteins/genes such as Fas, Bcl-2 and C1q. Increased expression of Fas antigen could intensify the exposure of hidden antigens. The overexpression of Bcl-2 protein might inhibit the removal of auto-reactive cells, and the lack of C1q could impair the clearance of self-antigens. The complete knowledge of the role of apoptosis components in the etiopathogenesis of lupus could lead to the development of new therapies targeting the apoptotic threshold, which could result in a more specific and effective disease response compared to global immunosuppression. This review summarizes the role of each component of the apoptotic process in the pathogenesis of lupus.

Temporal association of large granular lymphocytosis, neutropenia, proviral load, and FasL mRNA in cats with acute feline immunodeficiency virus infection

During acute feline immunodeficiency virus-C(PGammar) (FIV-C-PG) infection, we observed that cats develop large granular lymphocyte (LGL) lymphocytosis concurrent with a marked neutropenia that is temporally associated with the rise and fall of FIV-C-PG proviral loads. LGLs, generally considered to be analogous to natural killer (NK) cells, can also be highly cytolytic CD8/CD57 T cells. Neutropenia has been reported during acute human immunodeficiency virus (HIV-1) infection, but there is a paucity of information describing the pathogenesis of this condition. During HIV-1 infection, LGLs have been shown to be both CD16(+) NK cells and CD8(+)/CD57(+) T cells, but an association with neutropenia has not been described. However, neutropenia with concurrent LGL lymphocytosis has been demonstrated in both LGL leukemia and common variable immunodeficiency syndrome in people, and in both syndromes, an increase in soluble Fas ligand (FasL) has been associated with neutrophil apoptosis leading to neutropenia. Flow cytometric analysis demonstrated increases in CD56 and CD8 peripheral blood cell surface expression during acute FIV-C-PG infection. Expression of FasL mRNA was increased at the same time points as these peripheral hematologic abnormalities, and also decreased as FIV-C-PG proviral load reached set point. We describe an interesting temporal association between innate immune responses and viral load during acute FIV-C-PG infection, which has similarities to HIV-1 infection and other immune dyscrasias of people, and which may contribute to the neutropenia and LGL lymphocytosis during FIV-C-PG infection.

A novel Fas ligand in mollusk abalone: molecular characterization, immune responses and biological activity of the recombinant protein

Fas ligand is a member of the TNF superfamily that plays an important role by inducing apoptosis and homeostasis of immune responses. The gene encoding Fas ligand was isolated from a disk abalone (Haliotis discus discus) cDNA library, denoted as the AbFas ligand. It contains an 1832bp transcript with a 945bp open reading frame, encoding 315 amino acids. The AbFas ligand showed characteristic transmembrane and TNF family signature domains. The deduced amino acid comparison showed that the AbFas ligand exhibits 22.0, 16.1 and 14.5% identities to human Fas ligand, TNF-alpha, and lymphotoxin (LT-alpha), respectively. Phylogenetic analysis indicates that the AbFas ligand belongs to the invertebrate TNF family and it is closely related to vertebrate Fas ligand counterparts. Quantitative real-time PCR analysis results showed that the AbFas ligand transcripts were constitutively expressed in abalone hemocytes, gills, mantle, muscle, digestive tract and digestive gland in a tissue-specific manner. By immune stimulation, AbFas ligand mRNA was significantly (p<0.05) up-regulated after infection with a mixture of bacteria (Vibrio alginolyticus, Vibrio parahemolyticus, and Listeria monocytogenes), viral haemorrhagic septicaemia virus (VHSV), and lipopolysaccharide (LPS) in abalone gills. The recombinant AbFas ligand was over-expressed in Escherichia coli (E. coli) and purified using a pMAL protein fusion system. This recombinant AbFas ligand showed its biological activity by inducing both superoxide anion (O(2-) and H(2)O(2) in human THP-1 cells in concentration-dependant manner. Correlating the AbFas ligand transcriptional up-regulation against bacteria, virus and LPS with the biological activity of its recombinant protein, we could suggest that the abalone Fas ligand may control microbial infection by inducing O(2-), H(2)O(2) and other ROS.

Treatment with anti-FasL antibody preserves memory lymphocytes and virus-specific cellular immunity in macaques challenged with simian immunodeficiency virus

Immune deficiency viruses such as SIV in macaques or HIV-1 in human beings have evolved mechanisms to defeat host immunity that also impact the efficacy of vaccines. A key factor for vaccine protection is whether immune responses elicited by prior immunization remain at levels sufficient to limit disease progression once a host is exposed to the pathogen. One potential mechanism for escaping pre-existing immunity is to trigger death among antigen-activated cells. We tested whether FasL/CD178 is involved in destroying preexisting immunity. Rhesus macaques were immunized with recombinant vesicular stomatitis virus vaccine expressing SIV Gag to elicit cellular immune responses, then treated with antibody that neutralizes FasL and challenged with intravenous SIVmac251. Compared with animals injected with control antibody, anti-FasL-treated macaques had superior preservation of central memory CD4(+) and CD8(+) cells and decreased regulatory T cells in the blood. The CD4(+) and CD8(+) lymphocytes from treated animals responded better to SIV Gag compared with controls, evidenced by higher cell-mediated immune responses to viral antigens for at least 17 weeks after SIV challenge. Anti-FasL treatment during the initial stages of acute SIV infection preserved the T-cell compartment and sustained cell-mediated immunity to SIV.

Enrichment and analysis of secretory lysosomes from lymphocyte populations

BACKGROUND

In specialized cells, such as mast cells, macrophages, T lymphocytes and Natural Killer cells in the immune system and for instance melanocytes in the skin, secretory lysosomes (SL) have evolved as bifunctional organelles that combine degradative and secretory properties. Mutations in lysosomal storage, transport or sorting molecules are associated with severe immunodeficiencies, autoimmunity and (partial) albinism. In order to analyze the function and content of secretory lysosomes in different cell populations, an efficient enrichment of these organelles is mandatory.

RESULTS

Based on a combination of differential and density gradient centrifugation steps, we provide a protocol to enrich intact SL from expanded hematopoietic cells, here T lymphocytes and Natural Killer cells. Individual fractions were initially characterized by Western blotting using antibodies against an array of marker proteins for intracellular compartments. As indicated by the presence of LAMP-3 (CD63) and FasL (CD178), we obtained a selective enrichment of SL in one of the resulting organelle fractions. The robustness and reproducibility of the applied separation protocol was examined by a high-resolution proteome analysis of individual SL preparations of different donors by 2D difference gel electrophoresis (2D-DIGE).

CONCLUSION

The provided protocol is readily applicable to enrich and isolate intact secretory vesicles from individual cell populations. It can be used to compare SL of normal and transformed cell lines or primary cell populations from healthy donors and patients with lysosomal storage or transport diseases, or from corresponding mutant mice. A subsequent proteome analysis allows the characterization of molecules involved in lysosomal maturation and cytotoxic effector function at high-resolution.

IL-2 and antigen dose differentially regulate perforin- and FasL-mediated cytolytic activity in antigen specific CD4+ T cells

CD4 T cell effectors can promote survival against lethal influenza virus via perforin mediated cytolytic mechanisms; however, our understanding of how naïve CD4 cells differentiate into class II restricted killers remains obscure. To address this, TCR Tg CD4 cells were activated in vitro and examined for their ability to lyse target cells. We found that cytokine polarized CD4 T cell effectors displayed cytolytic activity with the hierarchy Th0>Th1>Th2. Further, IL-4 inhibited the generation of cytotoxic CD4 cells. LPS stimulated B cells and bone marrow derived dendritic cells (BMDC) both induced potent cytolytic activity; however, IL-6, TGF-beta, IL-10, IL-12 or TNF-alpha were not required for inducing cytolytic activity in CD4 effectors. Antigen dose had a marked effect on cytotoxicity: low concentrations of peptide induced more potent cytolytic activity than relatively high concentrations. At low peptide concentration, exogenous IL-2 was necessary to drive granzyme B (GrB) expression and perforin mediated lysis. Thus, low antigen dose and early activation signals via IL-2 direct the CD4 T cell response toward effectors with perforin mediated cytolytic potential. These data have implications for the design of vaccines that may induce cytolytic CD4 cells in vivo and improve cell-mediated immunity to viral and bacterial infections.

Killer B lymphocytes: the evidence and the potential

Immune regulation plays a critical role in controlling potentially dangerous inflammation and maintaining health. The Fas ligand/Fas receptor axis has been studied extensively as a mechanism of killing T cells and other cells during infections, autoimmunity, and cancer. FasL expression has been primarily attributed to activated T cells and NK cells. Evidence has emerged that B lymphocytes can express FasL and other death-inducing ligands, and can mediate cell death under many circumstances. Among B cell subsets, the expression of both Fas ligand and IL-10 is highest on the CD5(+) B cell population, suggesting that CD5(+) B cells may have a specialized regulatory function. The relevance of killer B cells to normal immune regulation, disease pathogenesis, and inflammation is discussed.

FasL expression and reverse signalling

FasL plays a central role in the induction of apoptosis within the immune system. It mediates activation-induced cell death (AICD) of T lymphocytes and contributes to the cytotoxic effector function of T and NK cells. Moreover, FasL is discussed as direct effector molecule for the establishment of immune privilege and tumour survival. Besides its death-promoting activity, FasL has been implicated in reverse signalling and might thus also play a role in T cell development and selection and the modulation of T cell activation. Considering these diverse functions, the overall FasL expression has to be tightly controlled to avoid unwanted damage. Based on an activation-associated transcriptional control, several post-transcriptional processes ensure a safe storage, a rapid mobilisation, a target-directed activity and a subsequent inactivation. Over the past years, the identification and characterisation of FasL-interacting proteins provided novel insight into the mechanisms of FasL transport, processing and reverse signalling, which might be exemplary also for the other members of the TNF family.

Many checkpoints on the road to cell death: regulation of Fas-FasL interactions and Fas signaling in peripheral immune responses

Interactions between the TNF-family receptor Fas (CD95) and Fas Ligand (FasL, CD178) can efficiently induce apoptosis and are critical for the maintenance of immunological self-tolerance. FasL is kept under strict control by transcriptional and posttranslational regulation. Surface FasL can be cleaved by metalloproteases, resulting in shed extracellular domains, and FasL can also traffic to secretory lysosomes. Each form of FasL has distinct biological functions. Fas is more ubiquitously expressed, but its apoptosis-inducing function is regulated by a number of mechanisms including submembrane localization, efficiency of receptor signaling complex assembly and activation, and bcl-2 family members in some circumstances. When apoptosis is not induced, Fas-FasL interactions can also trigger a number of activating and proinflammatory signals. Harnessing the apoptosis-inducing potential of Fas for therapy of cancer and autoimmune disease has been actively pursued, and despite a number of unexpected side-effects that result from manipulating Fas-FasL interactions, this remains a worthy goal.

Clinical-grade ex vivo-expanded human natural killer cells up-regulate activating receptors and death receptor ligands and have enhanced cytolytic activity against tumor cells

BACKGROUND AIMS

Cancer immunotherapy involving natural killer (NK) cell infusions and administration of therapeutic agents modulating the susceptibility of tumors to NK-cell lysis has been proposed recently. We provide a method for expanding highly cytotoxic clinical-grade NK cells in vitro for adoptive transfer following bortezomib treatment in patients with advanced malignancies.

METHODS

NK cells were expanded with irradiated Epstein-Barr virus-transformed lymphoblastoid cells. Expanded cells were evaluated for their phenotype, cytotoxicity, cytokine secretion, dependence on interleukin (IL)-2 and ability to retain function after cryopreservation.

RESULTS

A pure population of clinical-grade NK cells expanded 490+/-260-fold over 21 days. Expanded NK cells had increased TRAIL, FasL and NKG2D expression and significantly higher cytotoxicity against bortezomib-treated tumors compared with resting NK cells. Expanded NK cells, co-cultured with K562 and renal cell carcinoma tumor targets, secreted significantly higher levels of soluble Fas ligand 6; fgjhd IFN-gamma, GM-CSF, TNF-alpha, MIP-1alpha and MIP-1beta compared with resting NK cells. Secretion of the above cytokines and NK-cell cytolytic function were IL-2 dose dependent. Cryopreservation of expanded NK cells reduced expression of NKG2D and TRAIL and NK-cell cytotoxicity, although this effect could be reversed by exposure of NK cells to IL-2.

CONCLUSIONS

We describe a method for large-scale expansion of NK cells with increased expression of activating receptors and death receptor ligands resulting in superior cytotoxicity against tumor cells. This ex vivo NK-cell expansion technique is currently being utilized in a clinical trial evaluating the anti-tumor activity of adoptively infused NK cells in combination with bortezomib.

The role of apoptotic proteins in patients with systemic lupus erythematosis

Lymphocytes and granulocytes from healthy donors and SLE patients were used to investigate the role of Fas/FasL system in the pathogenesis of systemic lupus erythematosus (SLE). Determination of lymphocyte subpopulations was carried out by flowcytometry. Fas and FasL expression in lymphocytes and granulocytes were measured by immunofluorescence. Apoptotic cells were measured by TUNEL assay. sFas in the plasma was measured by ELISA. Thirty five normal blood donors and 45 SLE patients were selected for this study. This study was carried out between 2005 and 2007. The number of peripheral leukocytes undergoing apoptosis in SLE patients was greater than those of healthy donors. The degree of DNA damage in lymphocytes and granulocytes of SLE patients was much higher than those of healthy donors (P < 0.05 & P < 0.5, respectively). Additionally, a positive relationship was seen between the level of apoptotic lymphocytes'and the dosage of prednisolone used for treatment of SLE (r = 0.6). The level of Fas and FasL expression on different lymphocyte subpopulations increased depending on the activity of the disease (P < 0.5 & P < 0.05, respectively). There was an inverse correlation between the sFas and the stage of disease. Finally, we have demonstrated a relationship between the titre of autoantibodies and the degree of DNA damage in lymphocytes and granulocytes (r = 0.7 & r = 0.6, respectively). In conclusion, Fas and FasL are likely to play an important role in the pathogenesis of SLE. The real value may be used as a predictor for the activity of disease as well.