Unequal death in T helper cell (Th)1 and Th2 effectors: Th1, but not Th2, effectors undergo rapid Fas/FasL-mediated apoptosis

Cytokines and effector T cell subsets causing autoimmune CNS disease

Although experimental autoimmune encephalomyelitis (EAE) is limited in its potency to reproduce the entirety of clinical and histopathologic features of multiple sclerosis (MS), this model has been successfully used to prove that MS like autoimmunity in the CNS is orchestrated by autoantigen specific T cells. EAE was also very useful to refute the idea that IFN-γ producing T helper type 1 (Th1) cells were the sole players within the pathogenic T cell response. Rather, "new" T cell lineages such as IL-17 producing Th17 cells or IL-9 producing Th9 cells have been first discovered in the context of EAE. Here, we will summarize new concepts of early and late T cell plasticity and the cytokine network that shapes T helper cell responses and lesion development in CNS specific autoimmunity.

Sublingual immunotherapy in asthma does not influence lymphocyte sensitivity to Fas stimulation

BACKGROUND

The resistance of T lymphocytes to Fas-mediated apoptosis is an important feature of atopic asthma. The only effective causative treatment of atopic diseases is immunotherapy. Clinical efficacy of sublingual immunotherapy (SLIT) has been already proven, but there is still limited number of studies on its influence on lymphocytes function.

OBJECTIVES

The aim of the study was to evaluate whether SLIT could restore the sensitivity of asthmatic T cells to undergo Fas-mediated apoptosis.

MATERIAL AND METHODS

Peripheral blood was collected from 12 patients aged 8 ±2 years suffering from atopic asthma and undergoing sublingual specific immunotherapy. To evaluate sensitivity to Fas-mediated apoptosis, the blood was transmitted to sterile tubes and mixed with purified monoclonal antibody anti-CD95. After incubation, leukocytes were stained with Annexin V, propidium iodide, and monoclonal antibody against CD2 conjugated with phycoerythrin-cyanin 5.1, and then analyzed with flow cytometry. The procedure was repeated for each patient after 12 months of SLIT. -

RESULTS

Stimulation with anti-CD95 of T lymphocytes from patients with atopic asthma before treatment increased the number of early apoptotic cells (from 19.5 ±16.7% before stimulation to 26.6 ±16.7% Annexin V positive cells after stimulation). After one year of SLIT anti-CD95 still caused an increase of the early apoptotic cells ratio in the lymphocyte population (from 12.4 ±7.4% before stimulation to 24.7 ±15.4% Annexin V positive T cells after CD95 stimulation). Although an increasing trend could be observed, differences between the analyzed groups were not statistically significant.

CONCLUSIONS

A year of SLIT does not change the sensitivity of T lymphocytes from peripheral blood of children suffering from atopic asthma to Fas-mediated apoptosis.

Persistence of effector memory Th1 cells is regulated by Hopx

Th1 cells are prominent in inflamed tissue, survive conventional immunosuppression, and are believed to play a pivotal role in driving chronic inflammation. Here, we identify homeobox only protein (Hopx) as a critical and selective regulator of the survival of Th1 effector/memory cells, both in vitro and in vivo. Expression of Hopx is induced by T-bet and increases upon repeated antigenic restimulation of Th1 cells. Accordingly, the expression of Hopx is low in peripheral, naïve Th cells, but highly up-regulated in terminally differentiated effector/memory Th1 cells of healthy human donors. In murine Th1 cells, Hopx regulates the expression of genes involved in regulation of apoptosis and survival and makes them refractory to Fas-induced apoptosis. In vivo, adoptively transferred Hopx-deficient murine Th1 cells do not persist. Consequently, they cannot induce chronic inflammation in murine models of transfer-induced colitis and arthritis, demonstrating a key role of Hopx for Th1-mediated immunopathology.

T lymphocyte apoptosis in asthma

The paper describes the possible role of apoptosis of T lymphocytes in asthma pathogenesis. The authors focused on resistance against Fas-mediated programed cell death and the role of Bcl-2 protein in impaired programed cell death process. The reports from the literature regarding the imbalance of Th1 and Th2, caused by impaired apoptosis of T cells, in asthma pathogenesis are reviewed.

Lymphocytes sensitivity to Fas stimulation in healthy and asthmatic children

The T cell hypothesis of asthma is based on the concept that the disease is driven and maintained by the persistence of a specialized subset of chronically activated T memory cells sensitized against an array of allergenic, occupational or viral antigens. Overreaction of CD4+ T cells in the peripheral blood and airway tissues is an invariant feature of asthma; therefore a potent mechanism for augmenting the number of activated T cells in this disease would be the resistance to the normally programmed pathway for cell death. The aim of the study was to evaluate the presence of apoptotic markers on peripheral blood lymphocytes from healthy and asthmatic children before and after stimulation with antiCD95 antibodies. The blood was collected from 21 children with atopic asthma suffering from allergic rhinitis because of house dust mite and/or grass pollen allergens and 8 healthy children matched for their age and sex. Blood was mixed with purified monoclonal antibody antiCD95 (Beckman Coulter), incubated for 24 hours and than stained with Annexin V andPI (Becton Dickinson). Prepared suspensions were analyzed with Cytomics FC 500 (Beckman Coulter) flow cytometer. Annexin V(+)/PI(-) cells were characterized as early apoptotic, Annexin V(+)/PI(+) as late apoptotic and Annexin V(-)/PI(+) as dead. In unstimulated sample from asthmatic children 21.09+/-11.20% cells were characterized as Annexin V positive/PI negative. After stimulation with antiCD95 Annexin V positive/PI negative cells constituted 18.72+/-9.42% of cells, p=0.1. In unstimulated sample from healthy children 11.69+/-6.70% cells were characterized as Annexin V positive/PI negative. In the sample stimulated with antiCD95 16.54+/-2.98% of cells were Annexin V positive/PI negative, p=0.02. There were no differences between results of late apoptotic and necrotic lymphocytes from healthy and asthmatic children. Performed research indicates that lymphocytes from asthmatic children are resistant to Fas mediated apoptosis.

Regulation of CD4+ T-cell contraction during pathogen challenge

Signals orchestrating productive CD4+ T-cell responses are well documented; however, the regulation of contraction of CD4+ T-cell effector populations following the resolution of primary immune responses is not well understood. While distinct mechanisms of T-cell death have been defined, the relative importance of discrete death pathways during the termination of immune responses in vivo remains unclear. Here, we review the current understanding of cell-intrinsic and -extrinsic variables that regulate contraction of CD4+ T-cell effector populations through multiple pathways that operate both initially during T-cell priming and later during the effector phase. We discuss the relative importance of antigen-dependent and -independent mechanisms of CD4+ T-cell contraction during in vivo responses, with a special emphasis on influenza virus infection. In this model, we highlight the roles of greater differentiation and presence in the lung of CD4+ effector T cells, as well as their polarization to particular T-helper subsets, in maximizing contraction. We also discuss the role of autocrine interleukin-2 in limiting the extent of contraction, and we point out that these same factors regulate contraction during secondary CD4+ T-cell responses.

Comparison of sensitivity of Th1, Th2, and Th17 cells to Fas-mediated apoptosis

Following activation through the TCR, CD4+ T cells can differentiate into three major subsets: Th1, Th2, and Th17 cells. IL-17-secreting Th17 cells play an important role in the pathogenesis of several autoimmune diseases and in immune responses to pathogens, but little is known about the regulation of apoptosis in Th17 cells. In this study, the sensitivity of in vitro-polarized Th1, Th2, and Th17 cells to Fas-mediated apoptosis was compared directly by different methods. The order of sensitivity of T cell subsets to Fas-mediated apoptosis is: Th1 > Th17 > Th2. The greater sensitivity of Th17 cells to Fas-mediated apoptosis compared with Th2 cells correlated with their higher expression of FasL and comparable expression of the antiapoptotic molecule FLIP. The decreased sensitivity of Th17 compared with Th1 cells correlated with the higher expression of FLIP by Th17 cells. Transgenic overexpression of FLIP in T cells protected all three subsets from Fas-mediated apoptosis. These findings provide new knowledge for understanding how survival of different subsets of T cells is regulated.

Pathogens and immunologic memory in asthma: what have we learned?

Animal models and clinical studies of asthma have generated important insights into the first effector phase leading to the development of allergic airway disease and bronchial hyper-reactivity. In contrast, mechanisms related to asthma chronicity or persistence are less well understood. The CD4(+) T-helper 2 lymphocytes are known initiators of the inflammatory response associated with asthma. There is now increasing evidence that memory T-cells, sensitized against allergenic, occupational or viral antigens, are also involved in the persistence of asthma. Additionally, the role of pathogens in asthma has been linked to both the initial susceptibility to and flares of this disease. This review will discuss the potential links between infection and asthma, the role of the memory T-cells in asthma, and the potential mechanisms by which these factors interact to lead to the development and/or persistence of asthma.

Immunotherapy of autoimmune diabetes by nasal administration of tandem glutamic acid decarboxylase 65 peptides

Mucosally induced tolerance is an attractive strategy for immunotherapy of autoimmune diseases. Treatment of nonobese diabetic (NOD) mice with a mixture of autoantigen peptides is better geared toward slowing the progression of late stage type 1 diabetes (T1D) than treatment with any of the peptides alone. In this study, we constructed a fusion protein CTB-GADIII. It contains cholera toxin B subunit (CTB) and three tandem peptides derived from glutamic acid decarboxylase 65 (GAD65), p217-236, p524-538 and p290-306. The purified renatured pentamer fusion protein was effective in inhibiting the development of diabetes in NOD mice when the mice were nasally immunized three times (8w, 10w and 12w). Prevention of diabetes was associated with special humoral immune tolerance against tandem peptides GADIII. These data indicate that using CTB as a vaccine carrier, tandem GAD65 peptides can prevent T1D in NOD mice at the late stage of disease.

CD44 regulates survival and memory development in Th1 cells

Optimal immunity to microorganisms depends upon the regulated death of clonally expanded effector cells and the survival of a cohort of cells that become memory cells. After activation of naive T cells, CD44, a widely expressed receptor for extracellular matrix components, is upregulated. High expression of CD44 remains on memory cells and despite its wide usage as a "memory marker," its function is unknown. Here we report that CD44 was essential for the generation of memory T helper 1 (Th1) cells by promoting effector cell survival. This dependency was not found in Th2, Th17, or CD8(+) T cells despite similar expression of CD44 and the absence of splice variants in all subsets. CD44 limited Fas-mediated death in Th1 cells and its ligation engaged the phosphoinositide 3-kinase-Akt kinase signaling pathway that regulates cell survival. The difference in CD44-regulated apoptosis resistance in T cell subpopulations has important implications in a broad spectrum of diseases.

Activation-induced T helper cell death contributes to Th1/Th2 polarization following murine Schistosoma japonicum infection

In chronic infectious diseases, such as schistosomiasis, pathogen growth and immunopathology are affected by the induction of a proper balanced Th1/Th2 response to the pathogen and by antigen-triggered activation-induced T cell death. Here, by using S. japonicum infection or schistosome antigens-immunized mouse model, or antigens in vitro stimulation, we report that during the early stage of S. japonicum infection, nonegg antigens trigger Th2 cell apoptosis via the granzyme B signal pathway, contributing to Th1 polarization, which is thought to be associated with worm clearance and severe schistosomiasis. Meanwhile, after the adult worms lay their eggs, the egg antigens trigger Th1 cell apoptosis via the caspase pathway, contributing to Th2 polarization, which is associated with mild pathology and enhanced survival of both worms and their hosts. Thus, our study suggests that S. japonicum antigen-induced Th1 and Th2 cell apoptosis involves the Th1/Th2 shift and favorites both hosts and parasites.

Short-term stress enhances cellular immunity and increases early resistance to squamous cell carcinoma

In contrast to chronic/long-term stress that suppresses/dysregulates immune function, an acute/short-term fight-or-flight stress response experienced during immune activation can enhance innate and adaptive immunity. Moderate ultraviolet-B (UV) exposure provides a non-invasive system for studying the naturalistic emergence, progression and regression of squamous cell carcinoma (SCC). Because SCC is an immunoresponsive cancer, we hypothesized that short-term stress experienced before UV exposure would enhance protective immunity and increase resistance to SCC. Control and short-term stress groups were treated identically except that the short-term stress group was restrained (2.5h) before each of nine UV-exposure sessions (minimum erythemal dose, 3-times/week) during weeks 4-6 of the 10-week UV exposure protocol. Tumors were measured weekly, and tissue collected at weeks 7, 20, and 32. Chemokine and cytokine gene expression was quantified by real-time PCR, and CD4+ and CD8+ T cells by flow cytometry and immunohistochemistry. Compared to controls, the short-term stress group showed greater cutaneous T-cell attracting chemokine (CTACK)/CCL27, RANTES, IL-12, and IFN-gamma gene expression at weeks 7, 20, and 32, higher skin infiltrating T cell numbers (weeks 7 and 20), lower tumor incidence (weeks 11-20) and fewer tumors (weeks 11-26). These results suggest that activation of short-term stress physiology increased chemokine expression and T cell trafficking and/or function during/following UV exposure, and enhanced Type 1 cytokine-driven cell-mediated immunity that is crucial for resistance to SCC. Therefore, the physiological fight-or-flight stress response and its adjuvant-like immuno-enhancing effects, may provide a novel and important mechanism for enhancing immune system mediated tumor-detection/elimination that merits further investigation.

Translational mini-review series on Th17 cells: CD4 T helper cells: functional plasticity and differential sensitivity to regulatory T cell-mediated regulation

CD4(+) T cells display considerable flexibility in their effector functions, allowing them to tackle most effectively the range of pathogenic infections with which we are challenged. The classical T helper (Th) 1 and Th2 subsets have been joined recently by the Th17 lineage. If not controlled, the potent effector functions (chiefly cytokine production) of which these different cells are capable can lead to (sometimes fatal) autoimmune and allergic inflammation. The primary cell population tasked with providing this control appears to be CD4(+) regulatory T (T(reg)) cells expressing the forkhead box P3 (FoxP3) transcription factor. Here we consider the comparative capacity of FoxP3(+) T(regs) to influence the polarization, expansion and effector function of Th1, Th2 and Th17 cells in vitro and in vivo as well as in relation to human disease. This remains a particularly challenging series of interactions to understand, especially given our evolving understanding of T(reg) and T effector interrelationships, as well as recent insights into functional plasticity that cast doubt upon the wisdom of a strict categorization of T effector cells based on cytokine production.

Abundant c-Fas-associated death domain-like interleukin-1-converting enzyme inhibitory protein expression determines resistance of T helper 17 cells to activation-induced cell death

Activation-induced cell death (AICD) plays an important role in peripheral T-cell tolerance. AICD in CD4 T helper (Th) cells, including Th1 and Th2 effectors, has been extensively studied. Recently, interleukin-17-producing CD4(+) T cells (Th17 cells) have been identified as a unique Th subset, but their susceptibility to AICD and the underlying molecular mechanisms have not been defined. In this study, we found that Th17 cells were significantly less susceptible to AICD than Th1 cells, and Th17 cell resistance to AICD is due to the high levels of c-Fas-associated death domain-like interleukin-1-converting enzyme inhibitory protein preventing Fas-mediated apoptosis. The resistance of Th17 cells to AICD reveals a novel mechanism to explain the high pathogenicity of Th17 cells in autoimmune diseases, and may also provide a rationale to generate tumor-specific Th17 cells for adoptive immunotherapy.

[CCR4, HTLV-1 infection, and ATL oncogenesis]

Adult T-cell leukemia (ATL) is a malignancy of mature CD4+ T cells that is etiologically associated with the infection of human T-cell leukemia virus type 1 (HTLV-1), an exogenous human retrovirus. Previously, we have shown that leukemic cells of most ATL patients express CCR4, a chemokine receptor known to be selectively expressed by T cell subsets such as Th2 cells, skin-homing memory/effector T cells, and regulatory T cells. Therefore, the expression of CCR4 suggests that ATL cells are mostly derived from one of these T cell subsets. We have also shown that Tax, the HTLV-1-encoded potent transcriptional activator, strongly induces the expression of CCL22, a CCR4 ligand, which promotes the cell-dependent transmission of HTLV-1 from HTLV-1-infected T cells to CCR4+ target T cells by inducing close cell-to-cell interactions. We have also shown that ATL cells aberrantly express the AP-1 family member Fra-2 which, by forming the heterodimer with JunD, potently induces the expression of not only CCR4 but also the genes such as c-Myb, MDM2 and Bcl-6, the well-known proto-oncogenes. Thus, Fra-2 is a novel oncogene of ATL, and CCR4 may be regarded as a useful tumor marker of ATL.

A new function of the Fas-FasL pathway in macrophage activation

Upon infection with the protozoan parasite Leishmania major, susceptible BALB/c mice develop unhealing lesions associated with the maturation of CD4(+)Th2 cells secreting IL-4. In contrast, resistant C57BL/6 mice heal their lesions, because of expansion and secretion of IFN-gamma of CD4(+) Th1 cells. The Fas-FasL pathway, although not involved in Th cell differentiation, was reported to be necessary for complete resolution of lesions. We investigate here the role of IFN-gamma and IL-4 on Fas-FasL nonapoptotic signaling events leading to the modulation of macrophage activation. We show that addition of FasL and IFN-gamma to BMMø led to their increased activation, as reflected by enhanced secretion of TNF, IL-6, NO, and the induction of their microbicidal activity, resulting in the killing of intracellular L. major. In contrast, the presence of IL-4 decreased the synergy of IFN-gamma/FasL significantly on macrophage activation and the killing of intracellular L. major. These results show that FasL synergizes with IFN-gamma to activate macrophages and that the tight regulation by IFN-gamma and/or IL-4 of the nonapoptotic signaling events triggered by the Fas-FasL pathway affects significantly the activation of macrophages to a microbicidal state and may thus contribute to the pathogenesis of L. major infection.

Fas mediates cardiac allograft acceptance in mice with impaired T-cell-intrinsic NF-kappaB signaling

The transcription factor NF-kappaB is critical for T-cell activation and survival. We have shown that mice expressing a T-cell-restricted NF-kappaB superrepressor (IkappaBalphaDeltaN-Tg) permanently accept heart but not skin allografts. Overexpression of the prosurvival factor Bcl-x(L) in T cells restored heart rejection, suggesting that graft acceptance in IkappaBalphaDeltaN-Tg mice was attributable to deletion of alloreactive T cells.In vitro, the increased death of IkappaBalphaDeltaN-Tg T cells upon TCR stimulation when compared with wildtype T cells was mostly because of Fas/FasL interaction. Similarly, Fas played a key role in cardiac allograft acceptance by IkappaBalphaDeltaN-Tg mice as both genetic and antibody-mediated inhibition of Fas-signaling restored cardiac allograft rejection. Rejection correlated with graft infiltration by T cells and splenic production of IFN-gamma upon allostimulation. These results indicate that T-cell inhibition of NF-kappaB results in cardiac allograft acceptance because of increased susceptibility to Fas-mediated cell death.

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.

Differences in APOBEC3G expression in CD4+ T helper lymphocyte subtypes modulate HIV-1 infectivity

The cytidine deaminases APOBEC3G and APOBEC3F exert anti–HIV-1 activity that is countered by the HIV-1 vif protein. Based on potential transcription factor binding sites in their putative promoters, we hypothesized that expression of APOBEC3G and APOBEC3F would vary with T helper lymphocyte differentiation. Naive CD4+ T lymphocytes were differentiated to T helper type 1 (Th1) and 2 (Th2) effector cells by expression of transcription factors Tbet and GATA3, respectively, as well as by cytokine polarization. APOBEC3G and APOBEC3F RNA levels, and APOBEC3G protein levels, were higher in Th1 than in Th2 cells. T cell receptor stimulation further increased APOBEC3G and APOBEC3F expression in Tbet- and control-transduced, but not in GATA3-transduced, cells. Neutralizing anti–interferon-γ antibodies reduced both basal and T cell receptor-stimulated APOBEC3G and APOBEC3F expression in Tbet- and control-transduced cells. HIV-1 produced from Th1 cells had more virion APOBEC3G, and decreased infectivity, compared to virions produced from Th2 cells. These differences between Th1- and Th2-produced virions were greater for viruses lacking functional vif, but also seen with vif-positive viruses. Over-expression of APOBEC3G in Th2 cells decreased the infectivity of virions produced from Th2 cells, and reduction of APOBEC3G in Th1 cells increased infectivity of virions produced from Th1 cells, consistent with a causal role for APOBEC3G in the infectivity difference. These results indicate that APOBEC3G and APOBEC3F levels vary physiologically during CD4+ T lymphocyte differentiation, that interferon-γ contributes to this modulation, and that this physiological regulation can cause changes in infectivity of progeny virions, even in the presence of HIV-1 vif.

Some host cell proteins can hinder, or restrict, the life cycle of HIV-1. APOBEC3G and APOBEC3F are cellular enzymes that decrease HIV-1's ability to replicate in a subsequent target cell if they are present in the virus particle. As a countermeasure, HIV-1 virion infectivity factor (vif) induces degradation of APOBEC3G and APOBEC3F, thereby preventing them from getting into the budding virus. Although vif-defective viruses cannot evade the antiviral effect of APOBEC3G, such viruses are very rarely present in HIV-1-infected humans. It is not yet known whether physiological variation in APOBEC3G and APOBEC3F expression in CD4+ T lymphocytes is substantial enough to reduce vif-positive HIV-1 infectivity. In this study, we found that T helper type 1 (Th1) cells, a subtype of CD4+ lymphocytes, expressed greater amounts of APOBEC3G and APOBEC3F than T helper type 2 (Th2) cells. This difference led to a difference in infectivity of HIV-1 produced from the two cell types, whether vif was expressed or not. These results demonstrate that physiological regulation of APOBEC3G does restrict vif-positive HIV-1, as well as vif-negative HIV-1. In addition, this study reveals biological factors regulating expression of these proteins that may be exploitable for new therapeutic or preventive strategies against HIV-1.

Human circulating CD4+CD25highFoxp3+ regulatory T cells kill autologous CD8+ but not CD4+ responder cells by Fas-mediated apoptosis

Mechanisms utilized by human regulatory T cells (Treg) for elimination of effector cells may vary. We investigated the possibility that the mechanism of Treg suppression depends on Fas/FasL-mediated apoptosis of responder cells (RC). CD4(+)CD25(high)Foxp3(+) Treg and autologous CD4(+)CD25(-) and CD8(+)CD25(-) subsets of RC were isolated from blood of 25 cancer patients and 15 normal controls and cocultured in the presence of OKT3 and IL-2 (150 or 1000 IU/ml). Suppression of RC proliferation was measured in CFSE assays. RC and Treg apoptosis was monitored by 7-aminoactinomycin D staining in flow-based cytotoxicity assays. Treg from all subjects expressed CD95(+), but only Treg from cancer patients expressed CD95L. These Treg, when activated via TCR plus IL-2, up-regulated CD95 and CD95L expression (p < 0.001) and suppressed CD8(+) RC proliferation (p < 0.001) by inducing Fas-mediated apoptosis. However, Treg cocultured with CD4(+) RC suppressed proliferation independently of Fas/FasL. In cocultures, Treg were found to be resistant to apoptosis in the presence of 1000 IU/ml IL-2, but at lower IL-2 concentrations (150 IU/ml) they became susceptible to RC-induced death. Thus, Treg and RC can reciprocally regulate Treg survival, depending on IL-2 concentrations present in cocultures. This divergent IL-2-dependent resistance or sensitivity of Treg and RC to apoptosis is amplified in patients with cancer.

The BH3-only protein Bik/Blk/Nbk inhibits nuclear translocation of activated ERK1/2 to mediate IFNgamma-induced cell death

IFNγ induces cell death in epithelial cells, but the mediator for this death pathway has not been identified. In this study, we find that expression of Bik/Blk/Nbk is increased in human airway epithelial cells (AECs [HAECs]) in response to IFNγ. Expression of Bik but not mutant BikL61G induces and loss of Bik suppresses IFNγ-induced cell death in HAECs. IFNγ treatment and Bik expression increase cathepsin B and D messenger RNA levels and reduce levels of phospho–extracellular regulated kinase 1/2 (ERK1/2) in the nuclei of bik^+/+ compared with bik^−/− murine AECs. Bik but not BikL61G interacts with and suppresses nuclear translocation of phospho-ERK1/2, and suppression of ERK1/2 activation inhibits IFNγ- and Bik-induced cell death. Furthermore, after prolonged exposure to allergen, hyperplastic epithelial cells persist longer, and nuclear phospho-ERK is more prevalent in airways of IFNγ^−/− or bik^−/− compared with wild-type mice. These results demonstrate that IFNγ requires Bik to suppress nuclear localization of phospho-ERK1/2 to channel cell death in AECs.

Regulation of autoimmune inflammation by pro-inflammatory cytokines

The pro-inflammatory cytokines play a critical role in the initiation and propagation of autoimmune arthritis and many other disorders resulting from a dysregulated self-directed immune response. These cytokines influence the interplay among the cellular, immunological and biochemical mediators of inflammation at multiple levels. Regulation of the pro-inflammatory activity of these cytokines is generally perceived to be mediated by the anti-inflammatory and immunosuppressive cytokines such as IL-4, IL-10, or TGF-beta. However, increasing evidence is accumulating in support of the regulatory attributes of the pro-inflammatory cytokines themselves, in studies conducted in animal models of diabetes, multiple sclerosis, uveitis, and lupus. The results of our recent studies have shown that the pro-inflammatory cytokines, TNF-alpha and IFN-gamma, can suppress arthritic inflammation in rats, and also contribute to resistance against arthritis. These results are of paramount significance not only in fully understanding the pathogenesis of autoimmune arthritis, but also in anticipating the full ramifications of the in vivo neutralization of the pro-inflammatory cytokines, including that for therapeutic purposes.

Regulation of CD95/APO-1/Fas-induced apoptosis by protein phosphatases

Triggering the CD95/APO-1/Fas receptor by CD95-L induces the assembly of the death-inducing signaling complex (DISC), which permits initiator caspases activation and progression of a signaling cascade that culminates in cellular apoptosis. Despite the CD95 receptor does not exhibit any kinase activity by itself, phosphorylation/dephosphorylation events seem important to regulate many aspects of CD95-mediated apoptosis. Here, we try to highlight particularly the importance of protein phosphatases in the modulation of the CD95 system.

Increased activation-induced cell death of high IFN-gamma-producing T(H)1 cells as a mechanism of T(H)2 predominance in atopic diseases

BACKGROUND

A dysregulated and T(H)2-biased immune response appears to be a key pathogenetic factor in atopic diseases. Increased activation and massive infiltration of T cells in the dermis without any evidence for the expansion of their numbers in peripheral blood characterize atopic dermatitis.

OBJECTIVE

To investigate differences and mechanisms of T(H)1 and T(H)2 cell activation-induced cell death (AICD) in atopic disease.

METHODS

Naive (CD4(+)CD45(+)RA) and memory (CD4(+)CD45(+)RO) T cells were isolated from healthy and atopic individuals. T(H)1 and T(H)2 subsets were in vitro differentiated. High IFN-gamma-producing T cells and CXCR3(+) T cells were purified, and AICD of isolated cells was determined in addition to expression of apoptosis receptors and caspase activation.

RESULTS

T(H)1 cells, particularly their high IFN-gamma-producing fraction, and CXCR3(+) T cells showed significantly increased apoptosis in atopic individuals. During their in vitro differentiation, both T(H)1 and T(H)2 cells of atopic individuals showed increased apoptosis compared with the healthy control group, with a significantly high apoptosis in T(H)1 cells. Increased expression of Fas, Fas-ligand, tumor necrosis factor receptor-II, and caspase activation was detected on T(H)1 cells that underwent apoptosis. Neutralization experiments demonstrated a dominant role of IFN-gamma and Fas-Fas-ligand interaction-mediated suicide in T(H)1 cell AICD.

CONCLUSION

Predominant T(H)2 profile in atopic diseases might be a result of the increased tendency to activation and apoptosis of high IFN-gamma-producing T(H)1 cells.

Apoptosis signaling pathways and lymphocyte homeostasis

It has been almost three decades since the term "apoptosis" was first coined to describe a unique form of cell death that involves orderly, gene-dependent cell disintegration. It is now well accepted that apoptosis is an essential life process for metazoan animals and is critical for the formation and function of tissues and organs. In the adult mammalian body, apoptosis is especially important for proper functioning of the immune system. In recent years, along with the rapid advancement of molecular and cellular biology, great progress has been made in understanding the mechanisms leading to apoptosis. It is generally accepted that there are two major pathways of apoptotic cell death induction: extrinsic signaling through death receptors that leads to the formation of the death-inducing signaling complex (DISC), and intrinsic signaling mainly through mitochondria which leads to the formation of the apoptosome. Formation of the DISC or apoptosome, respectively, activates initiator and common effector caspases that execute the apoptosis process. In the immune system, both pathways operate; however, it is not known whether they are sufficient to maintain lymphocyte homeostasis. Recently, new apoptotic mechanisms including caspase-independent pathways and granzyme-initiated pathways have been shown to exist in lymphocytes. This review will summarize our understanding of the mechanisms that control the homeostasis of various lymphocyte populations.

Expression of transgenic FLIP on thyroid epithelial cells inhibits induction and promotes resolution of granulomatous experimental autoimmune thyroiditis in CBA/J mice

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced by transfer of thyroglobulin-primed in vitro activated splenocytes. Thyroid lesions reach maximal severity 20 d later, and inflammation resolves or progresses to fibrosis by d 60, depending on the extent of thyroid damage at d 20. Depletion of CD8+ T cells inhibits G-EAT resolution. We showed that expression of Fas-associated death domain-like IL-1beta-converting enzyme inhibitory protein (FLIP) transgene (Tg) on thyroid epithelial cells (TECs) of DBA/1 mice had no effect on G-EAT induction but promoted earlier resolution of G-EAT. However, when CBA/J wild-type donor cells were transferred to transgenic CBA/J mice expressing FLIP on TECs, they developed less severe G-EAT than FLIP Tg- littermates. Both strains expressed similar levels of the FLIP Tg, but endogenous FLIP was up-regulated to a greater extent on infiltrating T cells during G-EAT development in DBA/1 compared with CBA/J mice. After transient depletion of CD8+ T cells, FLIP Tg+ and Tg- CBA/J recipients both developed severe G-EAT at d 20. Thyroid lesions in CD8-depleted Tg+ recipients were resolving by d 60, whereas lesions in Tg- littermates did not resolve, and most were fibrotic. FLIP Tg+ recipients had increased apoptosis of CD3+ T cells compared with Tg- recipients. The results indicate that transgenic FLIP expressed on TECs in CBA/J mice promotes G-EAT resolution, but induction of G-EAT is inhibited unless CD8+ T cells are transiently depleted.

Long-term exposure to superantigen induces p27Kip1 and Bcl-2 expression in effector memory CD4+ T cells

The long-term exposure of mice to superantigen SEA using a mini-osmotic pump (SEA pump) induced a long-lasting expansion of Vbeta3+ CD4+ T cells with T helper (Th) 2 cell-type properties. Removal of the SEA pump 10 days after pump implantation did not significantly alter the level of Vbeta3+ CD4+ T cell expansion/maintenance. Furthermore, CFSE-labeled CD4+ T cells failed to divide when transferred to post-implantation day 15 mice. Thus, CD4+ T cells appeared to survive for at least 30 days in the absence of a sufficient amount of antigen to trigger cell division. STAT6 deficient mice, in which Th2 cell development is largely impaired, also exhibited a protracted cell expansion, similar to that observed in normal mice, suggesting that the Th2 cell property is dispensable for the maintenance of Vbeta3+ CD4+ T cell expansion. The expanded CD4+ T cells on post-implantation day 26 were arrested in the G0/G1 phase of the cell cycle and showed a lower level of cell division upon restimulation. The Cdk inhibitor p27(Kip1) was highly expressed, and Cdk2 was downregulated. Moreover, the CD4+ T cells were resistant to in vitro apoptosis induction in parallel with their level of Bcl-2 expression. Collectively, the Vbeta3+ CD4+ T cells appeared to develop into long-lived memory T cells with cell cycle arrest upon long-term exposure to SEA.

Roles of cytokines in the pathogenesis and therapy of type 1 diabetes

Type 1 diabetes (T1D) results from autoimmune destruction of the insulin-producing beta-cells in the pancreatic islets of Langerhans by autoreactive T helper 1 (Th1) cells characterized by their cytokine secretory products, interleukin-2 (IL-2) and interferon gamma (IFNgamma). Th1-type cytokines (IL-2 and IFNgamma) correlate with T1D, whereas Th2 (IL-4 and IL-10), Th3 (transforming growth factor beta [TGFbeta]), and T regulatory cell-type cytokines (IL-10 and TGFbeta) correlate with protection from T1D. Paradoxically, however, administrations of Th1-type cytokines (IL-2 and IFNgamma) and immunotherapies that induce Th1-type cytokine responses actually prevent T1D, at least in animal models. Therefore, immunotherapies that inhibit IL-2 production/action will block Th1 cell/cytokine-driven effector mechanisms of pancreatic islet beta-cell destruction; however, anti-IL-2 therapy will not allow immune tolerance to be established. In contrast, immunotherapies that increase IL-2 production/action may correct an immunodeficiency in IL-2 production that appears to underlie the autoimmunity of T1D, thereby restoring immune tolerance to islet beta-cells and prevention of T1D.

c-Maf interacts with c-Myb to down-regulate Bcl-2 expression and increase apoptosis in peripheral CD4 cells

The transcription factor c-Maf is critical for IL-4 production and the development of Th2 cells, which promote humoral immunity and protect against extracellular parasites. Yet, little else is known of c-Maf function in CD4 cells. Here, we identify a novel role for c-Maf in regulating susceptibility to apoptosis. Overexpression of c-Maf results in increased susceptibility of CD4 cells to apoptosis induced by multiple stimuli, including growth factor withdrawal, dexamethasone, irradiation, and TCR engagement. This effect is independent of Fas or p53; however, Bcl-2 expression is reduced in c-Maf Tg CD4 cells. Immunoprecipitation and Western blot analyses demonstrate that c-Maf-c-Myb complex formation is enhanced among T cells from c-Maf Tg mice compared to non-Tg littermates following TCR engagement. Unlike non-Tg T cells, c-Myb binding to the Bcl-2 promoter is not detectable in c-Maf Tg T cells by chromatin immunoprecipitation. In reporter assays, Bcl-2 promoter activity is reduced by c-Maf in a dose-dependent manner. Furthermore, transgene-mediated Bcl-2 expression corrects the apoptosis defect observed among c-Maf Tg CD4 cells. These data suggest that c-Maf can interact with c-Myb to reduce Bcl-2 expression, thereby limiting CD4 cell survival following TCR engagement.

Pathophysiology of acute graft-versus-host disease: recent advances

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative therapy for many malignant and nonmalignant hematologic diseases. Donor T cells from the allografts are critical for the success of this effective therapy. Unfortunately these T cells not only recognize and attack the disease cells/tissues but also the other normal tissues of the recipient as "foreign" or "nonself" and cause severe, immune-mediated toxicity, graft-versus-host disease (GVHD). Several insights into the complex pathophysiology of GVHD have been gained from recent experimental observations, which show that acute GVHD is a consequence of interactions between both the donor and the host innate and adaptive immune systems. These insights have identified a role for a variety of cytokines, chemokines, novel T-cell subsets (naĩve, memory, regulatory, and NKT cells) and for non-T cells of both the donor and the host (antigen presenting cells, delta T cells, B cells, and NK cells) in modulating the induction, severity, and maintenance of acute GVHD. This review will focus on the immunobiology of experimental acute GVHD with an emphasis on the recent observations.

Heligmosomoides polygyrus: Decreased apoptosis in fast responder FVB mice during infection

Primary infection with Heligmosomoides polygyrus in some strains of mice is chronic although fast responder mouse strains eliminate the parasite in a short period of time. The reason for the differences is unknown. In this study apoptosis, proliferation, IL-2 and IL-6 production of mesenteric lymph node (MLN) and spleen cells in vitro from fast (FVB) and slow (C57Bl/6) responder mice were compared during H. polygyrus infection. FVB cells showed decreased apoptosis, more proliferation and more cytokine production than cells from C57Bl/6 mice during infection. At the beginning of infection in C57Bl/6 mice the apoptosis of CD4(+) but not CD8(+) cells significantly increased in MLN and spleen cell cultures. Apoptosis, when the first immune signal is given by infective larvae, might play an important role in the modulation of the response in slow responder mice.

FasL expression in hepatic antigen-presenting cells and phagocytosis of apoptotic T cells by FasL+ Kupffer cells are indicators of rejection activity in human liver allografts

Fas-Fas ligand (FasL) interaction and apoptosis are important in the mechanism of allograft rejection. However, the interaction between donor and recipient cells, specifically focusing on antigen-presenting cells (APCs), under various conditions is poorly understood in human liver allografts. FasL expression on APCs, its association with apoptosis, and the origin of apoptotic lymphocytes in human liver allografts were assessed by immunohistochemistry and in situ hybridization. We found increased expression of FasL on Kupffer cells (KCs) and endothelium in acute cellular rejection (n = 20) and to lesser extent in chronic rejection (n = 6) and septic cholangitis (n = 5) compared with stable grafts and normal controls. In addition, the graft specificity of infiltrating T cells was confirmed by polymerase chain reaction examination of T-cell receptor-gamma loci. T-cell apoptosis occurred at a higher rate in acute cellular rejection than in chronic rejection or septic cholangitis. The number of apoptotic bodies derived from recipient lymphocytes correlated with the severity of rejection and was reversed by treatment. FasL(+) KCs phagocytosed CD4(+) interferon-gamma(+) T cells, rather than CD4(+) interleukin-4(+) T cells, suggesting a role of KCs in regulating CD4(+) T-cell subset differentiation. In conclusion, our data suggest that FasL expression on APCs and phagocytosis of apoptotic T cells by FasL(+) KCs are indicators of rejection activity in human liver allografts.

Rapid default transition of CD4 T cell effectors to functional memory cells

The majority of highly activated CD4 T cell effectors die after antigen clearance, but a small number revert to a resting state, becoming memory cells with unique functional attributes. It is currently unclear when after antigen clearance effectors return to rest and acquire important memory properties. We follow well-defined cohorts of CD4 T cells through the effector-to-memory transition by analyzing phenotype, important functional properties, and gene expression profiles. We find that the transition from effector to memory is rapid in that effectors rested for only 3 d closely resemble canonical memory cells rested for 60 d or longer in the absence of antigen. This is true for both Th1 and Th2 lineages, and occurs whether CD4 T cell effectors rest in vivo or in vitro, suggesting a default pathway. We find that the effector–memory transition at the level of gene expression occurs in two stages: a rapid loss of expression of a myriad of effector-associated genes, and a more gradual gain of expression of a cohort of genes uniquely associated with memory cells rested for extended periods.

Half-truths and selective memory: Interferon gamma, CD4(+) T cells and protective memory against tuberculosis

Efforts to develop a new, more effective vaccine for tuberculosis have been hampered by a lack of understanding of what constitutes a protective memory immune response. While interferon gamma production by CD4(+) T cells after vaccination is commonly used as a surrogate of protective memory immunity, its use in this regard appears to have little predictive value. We argue that this is due to the different requirements for interferon gamma-mediated protection in the primary response versus the memory recall response. In this review, we present evidence that suggests memory CD4(+) T cells can protect against tuberculosis in the absence of interferon gamma, and discuss potential mechanisms that may be involved such as IL-17 and regulatory T cells. A comprehensive understanding of the requirements for protective memory immunity to tuberculosis is essential for the development of an effective vaccine.

Tumors Hamper the Immunogenic Competence of CD4+T Cell-Directed Dendritic Cell Vaccination

Dendritic cells loaded with tumor-derived peptides induce protective CTL responses and are under evaluation in clinical trails. We report in this study that prophylactic administration of dendritic cells loaded with a MHC class II-restricted peptide derived from a model tumor Ag (Leishmania receptor for activated C kinase (LACK)) confers protection against LACK-expressing TS/A tumors, whereas therapeutic vaccination fails to cure tumor-bearing mice. Although CD4+ T cell-directed dendritic cell vaccination primed effector-like (CD44(high)CD62L(low), IL-2(+), IFN-gamma(+)) and central memory-like lymphocytes (CD44(high)CD62L(high), only IL-2(+)) in tumor-free mice, this was not the case in tumor-bearing animals in which both priming and persistence of CD4+ T cell memory were suppressed. Suppression was specific for the tumor-associated Ag LACK, and did not depend on CD25+ T cells. Because T cell help is needed for protective immunity, we speculate that the ability of tumors to limit vaccine-induced CD4+ T cell memory could provide a partial explanation for the limited efficacy of current strategies.

Decoding caspase signaling in host immunity to the protozoan Trypanosoma cruzi

Caspases, a family of cysteinyl-aspartate-specific proteases, induce apoptosis but are also involved in signal transduction in live cells. Caspase activation and apoptosis in T lymphocytes occur following infection with parasites and might affect immune responses. Rapid progress has occurred in the development and testing of caspase inhibitors and other apoptosis blockers, which are potentially useful for treating diseases associated with the pathogenic effects of apoptosis. Pharmacological approaches and the use of genetically modified hosts can be combined in research strategies to understand how apoptosis and caspase signaling affect the immune system.

A chimeric TCR-β chain confers increased susceptibility to EAE

Autoreactive myelin-specific CD4(+) T cells play an important role in CNS demyelination observed in MS and EAE. Consequently, it is important to understand the mechanisms of T cell receptor signalling leading to the activation of autoreactive T cells. We have previously generated a chimeric T cell receptor beta-chain (betaIII) displaying increased antigen sensitivity by exchanging most of the transmembrane and the intracellular domain of the TCR-beta chain with the corresponding TCR-gamma sequence. To investigate the effect of this "super-signalling" TCR in an autoimmune setting, we generated MOG(35-55) specific TCR transgenic mice expressing either the wild-type or the chimeric betaIII TCR-beta chain. We found that naïve transgenic T cells expressing the chimeric betaIII chain proliferated more extensively than wild-type cells in response to MOG(35-55)in vitro. Likewise, betaIII T cells skewed into a TH1 phenotype maintained the proliferative advantage over wild-type TH1 T cells at low antigen concentration. However, when skewed into a TH2 phenotype, there was no difference in proliferation between wild-type and betaIII T cells. Blocking of Fas-mediated cell death evenly affected wild-type and betaIII TH1 T cells and resulted in increased proliferation of both subsets, suggesting that betaIII T cells did not show defective Fas-FasL signalling. Finally, we found that betaIII TCR transgenic mice are more susceptible to EAE than wild-type TCR transgenic mice. We conclude that the change in the transmembrane domain of the TCR-beta chain affects TH1 T cells and the susceptibility to EAE, but does not affect TH2 cells. Investigating the molecular interaction within the TCR complex will help us to identify signalling pathways that can be manipulated to stop the progression of MS.

Differential glycosylation of TH1, TH2 and TH-17 effector cells selectively regulates susceptibility to cell death

Regulated glycosylation controls T cell processes, including activation, differentiation and homing by creating or masking ligands for endogenous lectins. Here we show that stimuli promoting T helper type 1 (TH1), TH2 or interleukin 17-producing T helper (TH-17) differentiation can differentially regulate the glycosylation pattern of T helper cells and modulate their susceptibility to galectin-1, a glycan-binding protein with anti-inflammatory activity. Although TH1- and TH-17-differentiated cells expressed the repertoire of cell surface glycans critical for galectin-1-induced cell death, TH2 cells were protected from galectin-1 through differential sialylation of cell surface glycoproteins. Consistent with those findings, galectin-1-deficient mice developed greater TH1 and TH-17 responses and enhanced susceptibility to autoimmune neuroinflammation. Our findings identify a molecular link among differential glycosylation of T helper cells, susceptibility to cell death and termination of the inflammatory response.

Relative importance of T-cell subsets in monocytotropic ehrlichiosis: a novel effector mechanism involved in Ehrlichia-induced immunopathology in murine ehrlichiosis

Infection with gram-negative monocytotropic Ehrlichia strains results in a fatal toxic shock-like syndrome characterized by a decreased number of Ehrlichia-specific CD4(+) Th1 cells, the expansion of tumor necrosis factor alpha (TNF-alpha)-producing CD8(+) T cells, and the systemic overproduction of interleukin-10 (IL-10) and TNF-alpha. Here, we investigated the role of CD4(+) and CD8(+) T cells in immunity to Ehrlichia and the pathogenesis of fatal ehrlichiosis caused by infection with low- and high-dose (10(3) and 10(5) bacterial genomes/mouse, respectively) ehrlichial inocula. The CD4(+) T-cell-deficient mice showed exacerbated susceptibility to a lethal high- or low-dose infection and harbored higher bacterial numbers than did wild-type (WT) mice. Interestingly, the CD8(+) T-cell-deficient mice were resistant to a low dose but succumbed to a high dose of Ehrlichia. The absence of CD8(+) T cells abrogated TNF-alpha and IL-10 production, reduced tissue injury and bacterial burden, restored splenic CD4(+) T-cell numbers, and increased the frequency of Ehrlichia-specific CD4(+) Th1 cells in comparison to infected WT mice. Although fatal disease is perforin independent, our data suggested that perforin played a critical role in controlling bacterial burden and mediating liver injury. Similar to WT mice, mortality of infected perforin-deficient mice was associated with CD4(+) T-cell apoptosis and a high serum concentration of IL-10. Depletion of IL-10 restored the number of CD4(+) and CD8(+) T cells in infected WT mice. Our data demonstrate a novel mechanism of immunopathology in which CD8(+) T cells mediate Ehrlichia-induced toxic shock, which is associated with IL-10 overproduction and CD4(+) T-cell apoptosis.

Instruction of naive CD4+ T-cell fate to T-bet expression and T helper 1 development: roles of T-cell receptor-mediated signals

Using T-cell receptor (TCR) transgenic mice, we demonstrate that TCR stimulation of naive CD4(+) T cells induces transient T-bet expression, interleukin (IL)-12 receptor beta2 up-regulation, and GATA-3 down-regulation, which leads to T helper (Th)1 differentiation even when the cells are stimulated with peptide-loaded I-A(b)-transfected Chinese hamster ovary cells in the absence of interferon-gamma (IFN-gamma) and IL-12. Sustained IFN-gamma and IL-12 stimulation augments naive T-cell differentiation into Th1 cells. Intriguingly, a significant Th1 response is observed even when T-bet(-/-) naive CD4(+) T cells are stimulated through TCR in the absence of IFN-gamma or IL-12. Stimulation of naive CD4(+) T cells in the absence of IFN-gamma or IL-12 with altered peptide ligand, whose avidity to the TCR is lower than that of original peptide, fails to up-regulate transient T-bet expression, sustains GATA-3 expression, and induces differentiation into Th2 cells. These results support the notion that direct interaction between TCR and peptide-loaded antigen-presenting cells, even in the absence of T-bet expression and costimulatory signals, primarily determine the fate of naive CD4(+) T cells to Th1 cells.

Murine FLIP transgene expressed on thyroid epithelial cells promotes resolution of granulomatous experimental autoimmune thyroiditis in DBA/1 mice

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced by mouse thyroglobulin-sensitized splenocytes activated in vitro with mouse thyroglobulin and interleukin-12. In wild-type (WT) DBA/1 recipients of WT donor splenocytes, thyroid lesions reach maximal severity at day 20, with ongoing inflammation and extensive fibrosis at day 60. Our previous studies indicated the site of expression of FLIP and Fas ligand [thyroid epithelial cells (TECs) versus inflammatory cells] differed in mice when lesions would resolve or progress to fibrosis. To test the hypothesis that expression of FLIP by TECs would promote earlier G-EAT resolution in DBA/1 mice, transgenic (Tg) DBA/1 mice expressing FLIP on TECs were generated. In FLIP Tg(+) and Tg(-) littermate recipients of WT donor splenocytes, G-EAT severity was comparable at day 20, but fibrosis was decreased, and many lesions resolved by day 60 in Tg(+) but not Tg(-) recipients. FLIP and Fas ligand were primarily expressed by TECs in Tg(+) recipients and by inflammatory cells in Tg(-) recipients at day 60. Apoptosis of inflammatory cells was greater, and expression of proinflammatory cytokines was decreased in thyroids of Tg(+) compared with Tg(-) recipients. These results are consistent with the hypothesis that transgenic expression of FLIP on thyroid epithelial cells promotes earlier resolution of granulomatous experimental autoimmune thyroiditis.

Glial progenitor-based repair of demyelinating neurological diseases

Demyelinating diseases of the brain and spinal cord affect more than one-quarter million of Americans, with numbers reaching more than two million across the world. These patients experience not only the vascular, traumatic, and inflammatory demyelinations of adulthood but the congenital and childhood dysmyelinating syndromes of the pediatric leukodystrophies. Several disease-modifying strategies have been developed that slow disease progression, especially in the inflammatory demyelinations and in multiple sclerosis in particular. Yet, currently available disease modifiers typically influence the immune system and are neither intended to nor competent to reverse the structural neurologic damage attending acquired demyelination. Fortunately, however, the disorders of myelin lend themselves well to attempts at structural repair, because central oligodendrocytes are the primary, and often sole, victims of the underlying disease process. Given the relative availability and homogeneity of human oligodendrocyte progenitor cells, the disorders of myelin formation and maintenance may be especially compelling targets for cell-based neurologic therapy.

Autophagy is induced in CD4+ T cells and important for the growth factor-withdrawal cell death

Autophagy is a tightly regulated catabolic mechanism that degrades proteins and organelles. Autophagy mediates programmed cell death under certain conditions. To determine the role of autophagy in T cells, we examined, in mouse CD4+ T cells, conditions under which autophagy is induced and alterations of the cell fate when autophagy is blocked. We have found that resting naive CD4+ T cells do not contain detectable autophagosomes. Autophagy can be observed in activated CD4+ T cells upon TCR stimulation, cytokine culturing, and prolonged serum starvation. Induction of autophagy in T cells requires JNK and the class III PI3K. Autophagy is inhibited by caspases and mammalian target of rapamycin in T cells. Interestingly, more Th2 cells than Th1 cells undergo autophagy. Th2 cells become more resistant to growth factor-withdrawal cell death when autophagy is blocked using either chemical inhibitors 3-methyladenine, or by RNA interference knockdown of beclin 1 and Atg7. Therefore, autophagy is an important mechanism that controls homeostasis of CD4+ T cells.

Cross-talk between apoptosis and cytokines in the regulation of parasitic infection

Parasitic diseases have worldwide medical and economical impact. Host T lymphocytes and the cytokines they produce determine the outcome of parasitic infections. Programmed cell death by apoptosis is induced in the course of parasitic infections, and affects cytokine production by removing activated effector T and B cells. In addition, engulfment of apoptotic cells promotes the secretion of cytokines that regulate intracellular replication of protozoan parasites. In this review, we discuss how the cross-talk between apoptosis and cytokines regulates parasitic infection.