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

Increased specific T cell cytokine responses in patients with active pulmonary tuberculosis from Central Africa

An understanding of T cell responses that are crucial for control of Mycobacterium tuberculosis (MTB) has major implications for the development of immune-based interventions. We studied the frequency of purified protein derivative (PPD)-specific CD3) cells expressing interleukin-2 (IL)-2, gamma interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and IL-10 in HIV-negative pulmonary tuberculosis patients (TB, n=30) as well as in healthy individuals (controls, n=21) from Central Africa. Increased frequencies of PPD-stimulated CD3+ cells expressing IL-2, IFN-gamma, and TNF-alpha in TB were seen when compared with frequencies of controls. The presence of type 1 cytokine biased responses in TB patients was supported by a shift in the distribution pattern of cytokine expression from exclusively IL-2 or TNF-alpha expression seen in controls towards an increased frequency of IFN-gamma/IL-2 or IFN-gamma/TNF-alpha co-expression in TB. Higher levels of PPD-induced IFN-gamma in the supernatants from TB patients than from controls were found, which correlated with its intracellular expression. PPD was a weak inducer of IL-10 in T cells and insufficient in promoting cytokine production in TCRgammadelta+CD3+ cells. Non-specific stimulation with PMA and ionomycin revealed increased frequencies of CD4+ cells expressing IFN-gamma in controls, while expression of IL-2, IL-4, IL-10, IL-13, and TNF-alpha was not different. Non-specific cytokine responses of TCRgammadelta+CD3+ cells were similar in all groups. Pulmonary TB in Central Africa is associated with enhanced expression and secretion of specifically induced cytokines that are frequently implicated in host defense against MTB.

Apoptosis in tissue inflammation and allergic disease

Genetic predisposition and environmental instructions tune thresholds for the activation, effector functions and lifespan of T cells, other inflammatory cells and resident tissue cells. Defects in apoptosis and peripheral tolerance in T cells define different allergic phenotypes. In individuals with atopic allergic disease, activated allergen-specific T cells expressing high levels of IFN-gamma predominantly undergo apoptosis in the circulation, skewing the immune response to surviving T helper type 2 (Th2) cells. In affected tissues, these cells switch on effector cytokines and induce the activation and apoptosis of epithelial cells. In individuals with non-atopic monoallergic disease, by contrast, a disturbed balance towards allergen-specific Th2 cells instead of T regulatory type 1 (Tr1) cells characterizes the T cell response.

Induction of tolerance using Fas ligand: a double-edged immunomodulator

Apoptosis mediated by Fas ligand (FasL) interaction with Fas receptor plays a pivotal regulatory role in immune homeostasis, immune privilege, and self-tolerance. FasL, therefore, has been extensively exploited as an immunomodulatory agent to induce tolerance to both autoimmune and foreign antigens with conflicting results. Difficulties associated with the use of FasL as a tolerogenic factor may arise from (1) its complex posttranslational regulation, (2) the opposing functions of different forms of FasL, (3) different modes of expression, systemic versus localized and transient versus continuous, (4) the level and duration of expression, (5) the sensitivity of target tissues to Fas/FasL-mediated apoptosis and the efficiency of antigen presentation in these tissues, and (6) the types and levels of cytokines, chemokines, and metalloproteinases in the extracellular milieu of the target tissues. Thus, the effective use of FasL as an immunomodulator to achieve durable antigen-specific immune tolerance requires careful consideration of all of these parameters and the design of treatment regimens that maximize tolerogenic efficacy, while minimizing the non-tolerogenic and toxic functions of this molecule. This review summarizes the current status of FasL as a tolerogenic agent, problems associated with its use as an immunomodulator, and new strategies to improve its therapeutic potential.

Committed memory effector type 2 cytotoxic T (Tc2) cells are ineffective in protective anti-tumor immunity

Cytotoxic CD8+ T cells (Tc) are a major effector cell population in protection against tumor growth and classified into Tc1 or Tc2 based on their cytokine-secreting profiles. However, their relative tumor protective roles remain undefined. In the present study, CD8+ memory T cells were obtained from mice given with CT26-IL 12 and tumor-specific Tc1 and Tc2 cells were induced by in vitro primary stimulation (1 degrees). In vivo anti-tumor immunity and in vitro cytotoxicity of 1 degrees Tc2 memory effector cells were highly protective comparably to 1 degrees Tc1, but they secreted high level of IFNgamma as well as IL 4 and IL 5. Moreover, memory cells obtained again from tumor-protected mice by either 1 degrees Tc1 or Tc2 transfer showed indistinguishable, Tc1-like, cytokine profiles. These results strongly suggest that 1 degrees Tc2 cells are insufficiently polarized. Tc2 memory effector cells were therefore examined for their transitional anti-tumor activity during consecutive stimulation until Th2 commitment. Secondary stimulation (2 degrees) markedly reduced secretion of IFNgamma (by 94%) and in vivo tumor protection (by 83%). Tertiary (3 degrees) and further stimulation completely abrogated both of tumor protective activity and IFNgamma secretion of Tc2 cells. This progressive loss of activity following repeated stimulation was accompanied by a reduction of in vitro cytotoxicity to CT26 tumor cells. In addition, when 1 degrees Tc2 cells were trans-differentiated to Tc1 during secondary stimulation, 2 of 6 cultures recovered tumor protective activity concomitantly with IFNgamma secretion, indicating that repeated stimulation does not deteriorate tumor protective activity of 2 degrees Tc2 cells. Collectively, these data demonstrate that highly committed Tc2 cells are ineffective in tumor protection.

Dual functions of murine gammadelta cells in inflammation and autoimmunity in coxsackievirus B3-induced myocarditis: role of Vgamma1+ and Vgamma4+ cells

Coxsackieviruses are a cause of clinical myocarditis. Both virus replication and host defense mechanisms, including virus-induced autoimmunity, mediate heart injury and cardiac dysfunction. Vgamma4+ cells kill infected cardiocytes and virus-specific CD4+ Th2 cells through Fas-dependent apoptosis and CD1d. The CD4+ Th1 response is necessary for activation of the autoimmune CD8+ T cells, which kill uninfected cardiocytes through perforin-dependent mechanisms.

An A > G polymorphism at position -670 in the Fas (TNFRSF6) gene in pregnant women with pre-eclampsia and intrauterine growth restriction

Fas-mediated apoptosis of maternal lymphocytes during pregnancy has been postulated to prevent the development of pre-eclampsia. A single adenine (A) to guanine (G) polymorphism at position -670 in the Fas gene (TNFRSF6) results in decreased Fas synthesis. The association between this polymorphism and pre-eclampsia in Hungarian women was investigated. In a case-control study, buccal swabs from 38 pregnant women with pre-eclampsia and 89 normotensive controls were analysed for the TNFRSF6-670 polymorphism. Investigators were blinded to clinical outcomes. Maternal homozygosity for the TNFRSF6-670*A occurred in 33 (37.1%) normotensive pregnant women as compared to only 5 (16.1%) of 31 pre-eclamptic pregnant women who delivered at < 37 weeks gestation (P = 0.04). The carriage rate of the TNFRSF6-670*G variant was also higher among these patients (59.7%) than among normotensive controls (42.1%; P = 0.01). There was no relation between the polymorphism and the pre-eclampsia diagnosed at > or = 37 weeks. Among pre-eclamptic patients with an intrauterine growth restriction (IUGR) neonate, eight (57.2%) were TNFRSF6-670*G homozygous as opposed to 3 (17.6%) of 17 pre-eclamptics who did not have IUGR (P = 0.03) and 19 (21.3%) normotensive controls (P = 0.008). Carriage of the TNFRSF6-670 polymorphism in the neonate was not associated with pre-eclampsia or IUGR. Maternal possession of the TNFRSF6-670*G increases the risk for pre-eclampsia and pre-eclampsia-associated IUGR in women who deliver at < 37 weeks.

Cellular FLIP (long isoform) overexpression in T cells drives Th2 effector responses and promotes immunoregulation in experimental autoimmune encephalomyelitis

Cellular FLIP (c-FLIP) is an endogenous inhibitor of death receptor-induced apoptosis through the caspase 8 pathway. It is an NF-kappaB-inducible protein thought to promote the survival of T cells upon activation, and its down-regulation has been implicated in activation-induced cell death. We have generated transgenic mice overexpressing human c-FLIP long form (c-FLIP(L)) specifically in T cells using the CD2 promoter (TgFLIP(L)). TgFLIP(L) mice exhibit increased IgG1 production upon stimulation by a T cell-dependent Ag and a markedly enhanced contact hypersensitivity response to allergen. In addition to showing augmented Th2-type responses, TgFLIP(L) mice are resistant to the development of myelin oligodendrocyte glycoprotein 35-55 peptide-induced experimental autoimmune encephalomyelitis, a Th1-driven autoimmune disease. In vitro analyses revealed that T cells of TgFLIP(L) mice proliferate normally, but produce higher levels of IL-2 and show preferential maturation of Th2 cytokine-producing cells in response to antigenic stimulation. After adoptive transfer, these (Th2) cells protected wild-type recipient mice from experimental autoimmune encephalomyelitis induction. Our results show that the constitutive overexpression of c-FLIP(L) in T cells is sufficient to drive Th2 polarization of effector T cell responses and indicate that it might function as a key regulator of Th cell differentiation.

A single nucleotide A>G polymorphism at position -670 in the Fas gene promoter: relationship to preterm premature rupture of fetal membranes in multifetal pregnancies

OBJECTIVE

The relationship between a polymorphism at position -670 in the Fas gene (TNFRSF6) and preterm premature rupture of membranes (PPROM) in multifetal pregnancies was examined.

METHODS

Buccal swabs from 119 mother-infant sets were analyzed for an adenine (A) to guanine (G) substitution at position -670 in the TNFRSF6 promoter. Pregnancy outcome data were subsequently obtained. Analysis was by Fisher exact test.

RESULTS

Maternal allele G homozygosity (TNFRSF6*G) was observed in 42.4% of 33 PPROM pregnancies as opposed to 19.5% of 77 with no spontaneous preterm birth (P = .01). Similarly, TNFRSF6*G homozygosity was present in 37.5% of 32 first-born neonates from PPROM pregnancies as opposed to 18.7% of 75 uncomplicated pregnancies (P = .04). PPROM occurred in 8 of 14 (57.1%) pregnancies in which mother and all neonates were TNFRSF6*G homozygotes as opposed to 25 of 105 (23.8%) cases in which uniform TNFRSF6*G homozygosity was not observed (P = .02).

CONCLUSIONS

A genetic variant in the Fas gene is associated with an increased rate of PPROM in multifetal pregnancies.

Disease-stage variance in functional CD4(+) T-cell responses against novel pan-human leukocyte antigen-D region presented human papillomavirus-16 E7 epitopes

Given the anticipated clinical importance of helper and regulatory CD4(+) T cells reactive against human papillomavirus-16 E7 in the cervical carcinoma setting, we performed this study to identify novel E7-derived T helper (Th) epitopes and to characterize functional anti-E7 Th responses in normal donors and patients with cervical intraepithelial neoplasia I-III or cervical cancer. Candidate pan-HLA-DR (D region) binding peptides were identified and synthesized based on results obtained using a predictive computer algorithm, then applied in short-term in vitro T-cell sensitization assays. Using IFN-gamma/IL-5 (interleukin 5) enzyme-linked immunospot assays as readouts for Th1-type and Th2-type CD4(+) T-cell responses, respectively, we identified three E7-derived T helper epitopes (E7(1-12), E7(48-62), and E7(62-75)), two of which are novel. Normal donor CD4(+) T cells failed to react against these E7 peptides, whereas patients with premalignant cervical intraepithelial neoplasia I-III lesions displayed preferential Th1-type responses against all three E7 epitopes. Th1-type responses were still observed to the E7(48-62) but not to the E7(1-12) and E7(62-75) peptides in cancer patients, where these latter two epitopes evoked Th2-type responses. Notably all responders to the E7(1-12) and E7(62-75) peptides expressed the HLA-DR4 or -DR15 alleles, whereas all responders to the E7(48-62) peptide failed to express the HLA-DR4 allele. Our results are consistent with a model in which cervical cancer progression is linked to an undesirable Th1- to Th2-type shift in functional CD4(+) T cell responses to two novel E7-derived epitopes. These peptides may prove important in vaccines to promote and maintain protective Th1-type antihuman papillomavirus immunity and in the immune monitoring of treated patients harboring HPV-16(+) malignancies.

CD4+ CCR5+ and CD4+ CCR3+ lymphocyte subset and monocyte apoptosis in patients with acute visceral leishmaniasis

The potential involvement of apoptosis in the pathogenesis of visceral leishmaniasis (VL) was examined by studying spontaneous and Leishmania antigen (LAg)-induced apoptosis using cryopreserved peripheral blood mononuclear cells (PBMC) of Sicilian patients with VL. Results indicate that monocytes and T lymphocytes from acute VL patients show a significantly higher level of apoptosis compared with that observed in healed subjects. The percentage of apoptotic cells was higher in monocytes than in T lymphocytes. T cells involved in programmed cell death (PCD) were mainly of the CD4(+) phenotype. In particular, the T helper 1-type (Th1) subset, as evaluated by chemokine receptor-5 (CCR5) expression, is involved in this process. Cell death in Th1-type uses a CD95-mediated mechanism. Furthermore, Th1-type CCR5(+) cells are prone to cell suicide in an autocrine or paracrine way, as attested by enhanced expression of CD95L in acute VL patients. The reduction in Th1-type cells by apoptosis was confirmed by the decrease in interferon-gamma secretion. In conclusion, apoptosis of monocytes, CD4(+) and CD4(+) CCR5(+) T cells could be involved in the failure of cell mediated immunity that is responsible for severe immune-depression in VL.

The development of effector and memory T cells in cutaneous leishmaniasis: the implications for vaccine development

Leishmania major infections induce the development of a CD4(+) T-helper 1 (Th1) response that not only controls the primary infection but also results in life-long immunity to reinfection. How that immunity is maintained is unknown, although because of the existence of infection-induced immunity, there has been an assumption that the development of a vaccine against leishmaniasis would be relatively easy. This has turned out not to be the case. One problem has been the finding that a large part of the immunity induced by a primary infection depends upon the presence of persistent parasites. Nevertheless, there are ample situations where immunologic memory persists without the continued presence of antigen, providing the prospect that a non-live vaccine for leishmaniasis can be developed. To do so will require an understanding of the events involved in the development of an effective protective T-cell response and, more importantly, an understanding of how to maintain that response. Here, we review work from our laboratory, describing how Th1 cells develop in L. major-infected mice, the nature of the memory T cells that provide protection to reinfection, and how that information may be utilized in the development of vaccines.

T Cell Immunity Induced by Live, Necrotic, and Apoptotic Tumor Cells

The rules that govern the engagement of antitumor immunity are not yet fully understood. Ags expressed by tumor cells are prone to induce T cell tolerance unless the innate immune system is activated. It is unclear to what extent tumors engage this second signal link by the innate immune system. Apoptotic and necrotic (tumor) cells are readily recognized and phagocytosed by the cells of the innate immune system. It is unknown how this affects the tumor's immunogenicity. Using a murine melanoma (B16m) and lymphoma (L5178Y-R) model, we studied the clonal sizes and cytokine signatures of the T cells induced by these tumors in syngeneic mice when injected as live, apoptotic, and necrotic cells. Both live tumors induced a type 2 CD4 cell response characterized by the prevalent production of IL-2, IL-4, and IL-5 over IFN-gamma. Live, apoptotic, and necrotic cells induced CD4 (but no CD8) T cells of comparable frequencies and cytokine profiles. Therefore, live tumors engaged the second signal link, and apoptotic or necrotic tumor cell death did not change the magnitude or quality of the antitumor response. A subclone of L5178Y-R, L5178Y-S cells, were found to induce a high-frequency type 1 response by CD4 and CD8 cells that conveyed immune protection. The data suggest that the immunogenicity of tumors, and their characteristics to induce type 1 or type 2, CD4 or CD8 cell immunity is not primarily governed by signals associated with apoptotic or necrotic cell death, but is an intrinsic feature of the tumor itself.

Regulation of activation-induced Fas (CD95/Apo-1) ligand expression in T cells by the cyclin B1/Cdk1 complex

Fas (CD95/Apo-1) ligand-mediated apoptosis has been recognized as an important mechanism of cell-mediated cytotoxicity and maintenance of immune homeostasis. Chronically activated T cells undergo activation-induced cell death (AICD), which depends on simultaneous Fas and Fas ligand expression. Previous reports have suggested that AICD might be linked to cell cycle progression of T cells and therefore to the expression of cell cycle-related molecules. In particular, cyclin B1 has been implicated in the induction of AICD in T cells. In this study, we have investigated the role of cyclin B1 in AICD and the expression of effector molecules involved in this form of cell death. Our results show that inhibition of cyclin B1 blocks AICD in T cells through specific inhibition of Fas ligand expression but not Fas-induced apoptosis. This effect of cyclin B1 appears to be mediated through the cyclin B1/cyclin-dependent kinase 1 (Cdk1/Cdc2) complex because overexpression of cyclin B1 enhances FasL promoter activity, whereas a dominant-negative version of Cdk1 blocks Fas ligand promoter induction. We provide further evidence that cyclin B1/Cdk1 regulates FasL transcription through the regulation of NFkappaB activation because dominant-negative Cdk1 inhibits activation-induced NFkappaB reporter and Rel A-induced FasL promoter activity. In conclusion, our data support a link between cell cycle progression, activation-induced Fas ligand expression, and apoptosis in T cells.

Adjuvant costimulation during secondary antigen challenge directs qualitative aspects of oral tolerance induction, particularly during the neonatal period

In this report we demonstrate that although passive feeding of specific Ag to mice as neonates or adults can induce oral tolerance in both the cellular and humoral arms of the immune response, quantitative and, in particular, qualitative aspects of the tolerance process are determined by the nature of the inflammatory costimuli provided at the time of secondary Ag challenge. Moreover, this dependency upon nonspecific costimulation is more profound in Ag-fed neonates than in their adult counterparts. Thus, administration of Ag in the Th1-selective adjuvant CFA to prefed animals resulted in significant inhibition of IgG2a, IL-2, and IFN-gamma responses, whereas IL-5 responses were increased. In contrast, rechallenge with Ag in the Th2-selective adjuvant aluminum hydroxide resulted in significant inhibition of IgG1, IgE, IL-2, and IL-5 responses, whereas IFN-gamma responses were increased. Additionally, although soluble Ag challenge of prefed adults revealed marginal tolerogenic effects, the same challenge protocol in animals prefed as neonates elicited enhanced Th2-dependent IgG1 production. These results suggest that inflammatory stimulation at the time of Ag challenge is obligatory to trigger oral tolerance mechanisms, particularly in animals fed as neonates and also that the type of adjuvant used at the time of challenge selects for the type of Th cell population to be inhibited.

TH1/TH2 paradigm in pregnancy: paradigm lost? Cytokines in pregnancy/early abortion: reexamining the TH1/TH2 paradigm

In this paper, we briefly survey the history of concepts in reproductive immunology from antibody-mediated tolerance to the "fetal allograft" to the current concept of an embryo "bathing in a sea of cytokines". We then review the paradigm that "allopregnancy is a Th2 phenomenon" and some of the evidence gained in animals and humans supporting it. We continue by discussing the light it sheds on immunologically caused recurrent abortion, and the present status of the concepts. We next show the limits of the Th1/Th2 paradigm by reviewing the role of "inflammatory" cytokines in implantation (as first seen with leukemia inhibitory factor). We go on to discuss recent data showing that interferon-gamma is not solely a "bad guy", e.g. abortifacient as the paradigm would predict, but is needed at low doses for the vascular development and transformation of uterine spiral arteries required for implantation and successful pregnancy. We conclude by discussing the emerging role of NK and IL-12, IL-15, IL-18 tripods and other cytokines in local angiogenesis and tissue remodelling, a series of new data bringing us well beyond the Th1/Th2 paradigm in pregnancy which, in this context, appears now obsolete and an oversimplification, although it has indeed been useful at first. Rather, step-specific events have to be considered and a key role is seen in local tissue remodelling, in which immune cytokines play an important role while not always being secreted by immune cells.

Dietary n-3 polyunsaturated fatty acids promote activation-induced cell death in Th1-polarized murine CD4+ T-cells

Dietary n-3 PUFAs have been shown to attenuate T-cell-mediated inflammation. To investigate whether dietary n-3 PUFAs promote activation-induced cell death (AICD) in CD4+ T-cells induced in vitro to a polarized T-helper1 (Th1) phenotype, C57BL/6 mice were fed diets containing either 5% corn oil (CO; n-6 PUFA control) or 4% fish oil (FO) plus 1% CO (n-3 PUFA) for 2 weeks. Splenic CD4+ T-cells were cultured with alpha-interleukin-4 (alphaIL-4), IL-12, and IL-2 for 2 days and then with recombinant (r) IL-12 and rIL-2 for 3 days in the presence of diet-matched homologous mouse serum (HMS) to prevent loss of cell membrane fatty acids, or with fetal bovine serum. After polarization, Th1 cells were reactivated and analyzed for interferon-gamma and IL-4 by intracellular cytokine staining and for apoptosis by Annexin V/propidium iodide. Dietary FO enhanced Th1 polarization by 49% (P = 0.0001) and AICD by 24% (P = 0.0001) only in cells cultured in the presence of HMS. FO enhancement of Th1 polarization and AICD after culture was associated with the maintenance of eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) in plasma membrane lipid rafts. In conclusion, n-3 PUFAs enhance the polarization and deletion of proinflammatory Th1 cells, possibly as a result of alterations in membrane microdomain fatty acid composition.

Induction of IL-10 in rat peritoneal macrophages and dendritic cells by glatiramer acetate

Glatiramer acetate (GLAT) is a mixture of basic polypeptides that have been shown to suppress experimental autoimmune encephalomyelitis (EAE). As Copaxone, GLAT is approved for the treatment of relapsing-remitting multiple sclerosis (MS). Different immunomechanisms have been suggested to contribute to the beneficial effects of GLAT which rely on blockade of MHC class II molecules or cross-recognition with myelin basic protein (MBP). Because GLAT could also inhibit experimental autoimmunity not related to myelin proteins, we searched for additional, less-restricted immunomodulatory actions of GLAT. Using freshly isolated resident peritoneal macrophages from naive Lewis rats, it is shown that GLAT profoundly modulates cytokine secretion of the cells. In unseparated macrophages (MPhi) and MPhi of low density, GLAT enhanced constitutive and LPS-induced production of interleukin 10 (IL-10) while LPS-induced synthesis of tumor necrosis factor-alpha (TNF-alpha) was dose-dependently suppressed by GLAT. Although both basic proteins GLAT and MBP facilitated adherence of MPhi, MBP had opposite effects on cytokine production suggesting unique properties of GLAT. In contrast to MPhi, peritoneal mast cells produced only little amounts of cytokines. The inductive effect of GLAT on IL-10 production by antigen-presenting cells was also observed in bone marrow-derived rat dendritic cells (DCs) which, unlike MPhi, were not suppressed in their production of TNF-alpha. Induction of IL-10 in different antigen-presenting cells is a new immunomodulatory mechanism of GLAT. In part, it goes along with the inhibition of TNF-alpha and may be a common basis for the known beneficial effects of GLAT on various cellular autoimmune responses including MS.

Death receptor signaling and autoimmunity

In recent years, it has become clear that self-nonself discrimination by the immune system is driven not so much by the specificities of the antigen receptors themselves, but by ligand-receptor systems that sense the presence of foreign pathogens (toll-like receptors) and those that regulate the balance between cellular proliferation and programmed cell death (tumor necrosis factor [TNF] family ligands and receptors). Interestingly, these two receptor families share a number of common signaling pathways, mediated by the cytoplasmic proteins containing death domains and TRAF domains, which trigger the complementary processes of programmed cell death and inflammation. Both humans and mice with genetic defects in the TNF-receptor family member Fas accumulate abnormal lymphocytes and develop systemic autoimmunity. These findings highlighted the importance of this TNF-receptor family member in the homeostasis of the immune system. In particular, the Fas receptor has been shown to be important in immunoreceptor-mediated apoptosis of activated T and B lymphocytes. Six members of the TNF-receptor superfamily share a common signaling domain with Fas, termed the death domain, that directly links these receptors to the apoptotic machinery of the cell, and, collectively, these receptors have been designated as "death receptors."We are currently investigating a number of important unresolved issues in this field, including: (1). how susceptibility to apoptosis through death receptors is regulated, (2). how Fas and related death receptors function in the maintenance of self-tolerance and homeostasis in the major cell types of the immune system, and (3). recently described nonapoptotic lymphocyte activation signals that use components of death receptor signaling.

Homing to nonlymphoid tissues is not necessary for effector Th1 cell differentiation

The differentiation of naive T cells into effector Th1 cells is a complex process that may proceed in two steps, commitment and development. Initial TCR engagement and IFN-gamma signaling instruct the T cells to commit to the Th1 lineage, while subsequent IL-12 and potentially TCR signaling induces final differentiation into irreversible, Th1 effector cells. In agreement with a multistep process of Th1 cell differentiation, effector Th1 cell generation requires repeated TCR and cytokine signaling, thus raising the possibility that commitment and differentiation processes may occur in two distinct anatomical sites, the lymphoid organ and the site of infection, respectively. We tested this possibility using a model of skin sensitization that permits a direct analysis of Ag-specific T cells both within lymphoid organs and at the site of sensitization. We show in this study that Ag presentation in the skin does not induce further differentiation of skin-infiltrating T cells that are highly divided and fully differentiated effector cells. Thus, effector Th1 cell differentiation is completed within lymphoid organs. In addition, we examined the heterogeneity of CD4 T cell responses in vivo through the analysis of the expression, by activated T cells, of different selectins, including P-selectin ligand and CD62L known to define separable effector populations. We delineated, in lymph nodes, at least five distinct subpopulations of activated CD4 T cells with different phenotypes and recirculation properties. Collectively, these results show that the lymphoid environment orchestrates T cell activation to generate a repertoire of effector T cells with a diversity of effector functions.

CD152 (CTLA-4) determines the unequal resistance of Th1 and Th2 cells against activation-induced cell death by a mechanism requiring PI3 kinase function

Survival of antigen-experienced T cells is essential for the generation of adaptive immune responses. Here, we show that the genetic and antibody-mediated inactivation of CD152 (cytotoxic T lymphocyte antigen 4) in T helper (Th) effector cells reduced the frequency of nonapoptotic cells in a completely Fas/Fas ligand (FasL)–dependent manner. CD152 cross-linking together with stimulation of CD3 and CD28 on activated Th2 cells prevented activation-induced cell death (AICD) as a result of reduced Fas and FasL expression. Apoptosis protection conferred by CD152 correlated with the up-regulation of Bcl-2 and was mediated by phosphatidylinositol 3 kinase, which prevented FasL expression through the inhibitory phosphorylation of Forkhead transcription factor FKHRL1. We show that signals induced by CD152 act directly on activated T lymphocytes and, due to its differential surface expression on activated Th1 and Th2 cells, induce resistance to AICD mainly in Th2 cells.

The generation of T cell memory: a review describing the molecular and cellular events following OX40 (CD134) engagement

OX40 (CD134), a membrane-bound member of the tumor necrosis factor-receptor superfamily, is expressed primarily on activated CD4(+) T cells. Following engagement on the cell surface, OX40 delivers a costimulatory signal that leads to potent, proinflammatory effects. Engagement of OX40 during antigen (Ag)-specific stimulation of T cells leads to increased production of memory T cells, increased migration of Ag-specific T cells, enhanced cytokine production by effector T cells, and the ability to break peripheral T cell tolerance in vivo. Therefore, OX40 engagement in vivo could have important ramifications for the enhancement of vaccine strategies and inhibition of unwanted inflammation. This review summarizes the molecular and cellular events that occur following OX40 engagement during Ag-specific T cell activation.

Antigen dose, type of antigen-presenting cell and time of differentiation contribute to the T helper 1/T helper 2 polarization of naive T cells

Antigenic encounter by T cells induces immunological synapse formation and T-cell activation. Using different concentrations of toxic shock syndrome toxin-1 (TSST-1) as stimulus, we examined the capacities of dendritic cells (DC) and macrophages (Mphi) to prime syngeneic naive T cells. DCs were, under all experimental settings, more efficient than Mphi at clustering T cells. Translocation of the T-cell receptor (TCR) to the contact area was found to be induced by DCs, as well as by Mphi, in an antigen-dependent manner, although Mphi were less efficient at inducing TCR translocation. Capping of protein kinase C theta (PKCtheta) was also antigen dependent but induced exclusively by DCs. Likewise, DCs were found to be more potent inducers of interleukin-2 (IL-2) production and proliferation of naive T cells than Mphi. After 3 days of culture, DCs presenting 100 ng/ml TSST-1 induced interferon-gamma (IFN-gamma)-secreting cells, whereas Mphi did not. After 7 days of culture, DCs presenting 0.1 ng/ml TSST-1, and Mphi presenting high (as well as low) doses of TSST-1, induced IL-4-producing cells. We therefore provide evidence to show that antigen dose, type of antigen-presenting cell and time of differentiation can contribute to T-cell differentiation.

IL-7 promotes the transition of CD4 effectors to persistent memory cells

After transfer to adoptive hosts, in vitro–generated CD4 effectors can become long-lived memory cells, but the factors regulating this transition are unknown. We find that low doses of interleukin (IL) 7 enhance survival of effectors in vitro without driving their division. When in vitro–generated effectors are transferred to normal intact adoptive hosts, they survive and rapidly become small resting cells with a memory phenotype. CD4 effectors generated from wild-type versus IL-7 receptor^−/− mice were transferred to adoptive hosts, including intact mice and those deficient in IL-7. In each case, the response to IL-7 was critical for good recovery of donor cells after 5–7 d. Recovery was also IL-7–dependent in Class II hosts where division was minimal. Blocking antibodies to IL-7 dramatically decreased short-term recovery of transferred effectors in vivo without affecting their division. These data indicate that IL-7 plays a critical role in promoting memory CD4 T cell generation by providing survival signals, which allow effectors to successfully become resting memory cells.

Hepatitis B immunisation induces higher antibody and memory Th2 responses in new-borns than in adults

New-borns raise limited antibody responses to most T cell-dependent antigens but little is known about neonatal T lymphocyte responses to vaccines. In this study, we compared the immune response induced by the hepatitis B vaccine in new-borns and nai;ve adults. Infants produced markedly higher serum anti-hepatitis B surface (HBs) antibody titres than adults. This was not associated with greater HBs Ag-specific Th2 cytokine responses but with lower primary IFN-gamma responses. At 1 year, the infant memory response to HBs Ag was characterised by higher Th2 responses than those of adults. We conclude that neonatal antibody and T cell responses to hepatitis B vaccine differ from those induced in adults.

The threshold pattern of calcineurin-dependent gene expression is altered by loss of the endogenous inhibitor calcipressin

Calcineurin links calcium signaling to transcriptional responses in the immune, nervous and cardiovascular systems. To determine the function of the calcipressins, a family of putative calcineurin inhibitors, we assessed the calcineurin-dependent process of T cell activation in mice engineered to lack the gene encoding calcipressin 1 (Csp1). Csp1 regulated calcineurin in vivo, and genes triggered in an immune response had unique transactivation thresholds for T cell receptor stimulation. In the absence of Csp1, the apparent transactivation thresholds for all these genes were shifted because of enhanced calcineurin activity. This unbridled calcineurin activity drove Fas ligand expression, which normally requires high T cell receptor stimulation and results in the premature death of T helper type 1 cells. Thus, calcipressins modulate the pattern of calcineurin-dependent transcription, and may influence calcineurin activity beyond calcium to integrate a broad array of signals into the cellular response.

Both the Fas ligand and inducible nitric oxide synthase are needed for control of parasite replication within lesions in mice infected with Leishmania major whereas the contribution of tumor necrosis factor is minimal

Following infection with the protozoan parasite Leishmania major, C57BL/6 mice develop a small lesion that heals spontaneously. Resistance to infection is associated with the development of CD4(+) Th1 cells producing gamma interferon (IFN-gamma) and tumor necrosis factor (TNF), which synergize in activating macrophages to their microbicidal state. We show here that C57BL/6 mice lacking both TNF and Fas ligand (FasL) (gld TNF(-/-) mice) infected with L. major neither resolved their lesions nor controlled Leishmania replication despite the development of a strong Th1 response. Comparable inducible nitric oxide synthase (iNOS) activities were detected in lesions of TNF(-/-), gld TNF(-/-), and gld mice, but only gld and gld TNF(-/-) mice failed to control parasite replication. Parasite numbers were high in gld mice and even more elevated in gld TNF(-/-) mice, suggesting that, in addition to iNOS, the Fas/FasL pathway is required for successful control of parasite replication and that TNF contributes only a small part to this process. Furthermore, FasL was shown to synergize with IFN-gamma for the induction of leishmanicidal activity within macrophages infected with L. major in vitro. Interestingly, TNF(-/-) mice maintained large lesion size throughout infection, despite being able to largely control parasite numbers. Thus, IFN-gamma, FasL, and iNOS appear to be essential for the complete control of parasite replication, while the contribution of TNF is more important in controlling inflammation at the site of parasite inoculation.

Similarities and differences in CD4+ and CD8+ effector and memory T cell generation

Naive CD4+ and CD8+ T cells undergo unique developmental programs after activation, resulting in the generation of effector and long-lived memory T cells. Recent evidence indicates that both cell-intrinsic and cell-extrinsic factors regulate memory T cell differentiation. This review compares and contrasts how naive CD4+ and CD8+ T cells make the transition to effector and/or memory cells and discusses the implications of these findings for vaccine development.

T cell-intrinsic requirement for NF-kappa B induction in postdifferentiation IFN-gamma production and clonal expansion in a Th1 response

NF-kappaB/Rel transcription factors are linked to innate immune responses and APC activation. Whether and how the induction of NF-kappaB signaling in normal CD4(+) T cells regulates effector function are not well-understood. The liberation of NF-kappaB dimers from inhibitors of kappaB (IkappaBs) constitutes a central checkpoint for physiologic regulation of most forms of NF-kappaB. To investigate the role of NF-kappaB induction in effector T cell responses, we targeted inhibition of the NF-kappaB/Rel pathway specifically to T cells. The Th1 response in vivo is dramatically weakened when T cells defective in their NF-kappaB induction (referred to as IkappaBalpha(DeltaN) transgenic cells) are activated by a normal APC population. Analyses in vivo, and IL-12-supplemented T cell cultures in vitro, reveal that the mechanism underlying this T cell-intrinsic requirement for NF-kappaB involves activation of the IFN-gamma gene in addition to clonal expansion efficiency. The role of NF-kappaB in IFN-gamma gene expression includes a modest decrease in Stat4 activation, T box expressed in T cell levels, and differentiation efficiency along with a more prominent postdifferentiation step. Further, induced expression of Bcl-3, a trans-activating IkappaB-like protein, is decreased in T cells as a consequence of NF-kappaB inhibition. Together, these findings indicate that NF-kappaB induction in T cells regulates efficient clonal expansion, Th1 differentiation, and IFN-gamma production by Th1 lymphocytes at a control point downstream from differentiation.

A liver tolerates a portal antigen by generating CD11c+ cells, which select Fas ligand+ Th2 cells via apoptosis

Administration of an antigen (Ag) per oral route leads to apoptosis of Ag-specific CD4(+) T cells and to development of Th2 cells expressing Fas ligand (FasL) in the liver. We determined whether presentation of an ingested Ag in the liver alone was enough to select these FasL(+)Th2 cells and explored how this selection was achieved in the liver. Ovalbumin (OVA) administered orally was colocalized with class II(+) cells in the periportal and parenchymal area of the liver. On coculture with naive OVA-specific CD4(+) T cells, hepatic CD11c(+) cells from mice fed OVA generated Ag-specific Th2 cells. This was achieved by apoptosis of CD4(+) T cells, decrease of interleukin 12 (IL-12) secretion, and increase of IL-18 secretion by the CD11c(+) cells. Addition of IL-12 to this coculture prevented apoptosis of the CD4(+) T cells, which was associated with up-modulation of IL-2 receptor beta chain expression. Administration of IL-12 to mice fed OVA prevented apoptosis of OVA-specific CD4(+) T cells in the liver. Moreover, adoptive transfer of hepatic CD11c(+) cells from mice fed OVA together with OVA-specific CD4(+) T cells led to development of Th2 cells as well as apoptosis of the transferred CD4(+) T cells in the lymph nodes of the recipient mice on immunization with OVA. In conclusion, presentation of an ingested Ag by hepatic CD11c(+) cells selects Th2 cells resistant to apoptosis in the liver, which is mediated in part by down-regulation of IL-12 secretion by the former cells.

Memory and effector T cells modulate subsequently primed immune responses to unrelated antigens

Memory and effector T cells modulate subsequently primed T cell responses to the same antigen. However, little is known about the impact of pre-existing memory and effector T cell immunity on subsequently primed immune responses to unrelated antigens. Here, we show that an antigen-primed first wave of Th1 and Th2 immunity enhanced or inhibited the subsequently primed T cell immunity to an unrelated antigen, depending on whether the second antigen was administered in the same or opposite type of adjuvant. The regulatory effects of the first wave of T cell immunity on the subsequent T cell responses to an unrelated antigen attenuated over time. Notably, following challenge with the second antigen, there was a mutual cross-regulation between the first and second wave of humoral responses to unrelated antigens. Thus, immunization with one antigen not only primes immune responses to that antigen, but also influences subsequently primed immune responses to unrelated antigens.

Hepatitis C virus infection: when silence is deception

Hepatitis C virus (HCV) uses complex and unique mechanisms to prevent, evade or subvert innate and adaptive immune responses and to establish persistent infection and chronic hepatitis. Recently developed experimental systems have significantly facilitated the analysis of HCV replication, virus-host interaction and pathogenesis of chronic hepatitis and have provided new insights into the mechanisms of HCV clearance and persistence.

TID1, a mammalian homologue of the drosophila tumor suppressor lethal(2) tumorous imaginal discs, regulates activation-induced cell death in Th2 cells

We previously described two human DnaJ proteins, hTid-1L and hTid-1S, which are derived from alternative splicing of the TID1 gene, the human homologue of the Drosophila tumor suppressor lethal(2) tumorous imaginal discs, and showed that hTid-1L promoted while hTid-1S antagonized apoptosis. There are two subsets of helper T cells, Th1 and Th2, of which Th2 cells are significantly less prone to apoptosis induced by stimulation through the T-cell receptor. This apoptotic process is known as activation-induced cell death (AICD). The molecular basis for the differential susceptibility of Th1 and Th2 cells to AICD is not known. Here we show that the antiapoptotic variant, Tid-1S, is selectively induced in murine Th2 cells following activation. Expression of a dominant-negative mutant of hTid-1S in a Th2 cell line strikingly enhanced activation of caspase 3 in response to CD3 stimulation, and caused the cells to become sensitive to AICD. Hence, the accumulation of Tid-1S in Th2 cells following activation represents a novel mechanism that may contribute to the induction of apoptosis resistance during the activation of Th2 cells.

Differential susceptibility to staphylococcal superantigen (SsAg)-induced apoptosis of CD4+ T cells from atopic dermatitis patients and healthy subjects: the inhibitory effect of IL-4 on SsAg-induced apoptosis

This study had two aims: 1) to determine whether there are differences between atopic dermatitis (AD) patients and healthy subjects in staphylococcal superantigen (SsAg)-induced CD4(+) T cell activation, cytokine production, chemokine receptor expression, and apoptosis; and 2) to investigate the effect of IL-4 on SsAg-induced apoptosis. By using immunofluorescence and annexin V staining, we analyzed PBMC with or without staphylococcal enterotoxin B (SEB) stimulation in the presence or absence of rIL-4 or anti-IL-4-neutralizing Abs in 15 healthy subjects and 27 AD patients. We found that SEB preferentially induced production of Th1 cytokine in SEB-reactive (TCRVbeta3(+) or Vbeta12(+) or Vbeta17(+)) CD4(+) T cells from healthy subjects and Th2 cytokine in those from AD patients. SEB induced up-regulation of CXCR3(+) cells in SEB-reactive CD4(+) T cells from healthy subjects and CCR4(+) cells in those from AD patients. SEB-reactive CD4(+) T cells from AD patients were more resistant to SEB-induced apoptosis than those from healthy subjects. There was no significant difference between AD and healthy subjects in SEB-induced activation of CD4(+) T cells. CXCR3(+) CD4(+) T cells were more susceptible to SEB-induced apoptosis than CCR4(+) CD4(+) T cells in healthy subjects. Exogenously added IL-4 inhibited SEB-induced apoptosis of SEB-reactive CD4(+) and CXCR3(+) CD4(+) T cells but not of CCR4(+) CD4(+) T cells in healthy subjects. Inhibition of endogenous IL-4 increased SEB-induced apoptosis of SEB-reactive CD4(+) T cells from AD patients. These results might provide new clues to the mechanism that SsAgs contribute to the persistence and exacerbation of allergic skin inflammation in AD.

Role of Fas/Fas ligand-mediated apoptosis in murine contact hypersensitivity

Apoptosis plays an important role in immune responses, but little is known about its involvement in contact hypersensitivity (CH). In this study, we have investigated the role of Fas/Fas ligand (FasL)-mediated apoptosis in the pathogenesis of CH. Mice were sensitized by one topical application of 100 microl of 3% oxazolone to shaved skin of the abdomen. Six days later, CH was provoked by challenging both sides of sensitized mouse right ear with 15 microl of 1% oxazolone. Using a DNA ladder assay, we found that apoptosis was induced in the skin of oxazolone-sensitized mice 24-96 h after allergen challenge. Annexin V-fluorescein isothiocyanate (FITC)-propidium iodide (PI) apoptosis flow cytometric assay showed that early apoptotic CD4(+) T cells (annexin V-FITC(+)PI(-)), but not late apoptotic CD4(+) T cells (annexin V-FITC(+)PI(+)), increased in the inflamed skin of mice with CH. Moreover, the expressions of mRNAs for T helper (Th2) cytokine (interleukin (IL)-4), Th1 cytokine (interferon (IFN)-gamma) and proapoptotic molecules (Bax, Fas, FasL and IL-1beta-converting enzyme (ICE)/caspase-1) were significantly elevated in the oxazolone-sensitized mouse skin 6-72 h after allergen challenge. Dramatic increase in IL-10 mRNA was only observed in the sensitized mouse skin 6 and 12 h after allergen challenge. Furthermore, CH was significantly inhibited with decreased apoptosis and early apoptotic CD4(+) T cells in inflamed skin in Fas mutant lpr/lpr mice compared to wild-type mice, whereas there were no significant differences in IL-4, IFN-gamma, IL-10, Bax and ICE mRNAs in the inflamed skin of CH between lpr/lpr and wild-type mice. Our results thus suggest that Fas/FasL pathway partially contributes to apoptosis in murine CH and that Fas/FasL-mediated apoptosis plays a partial role in the development of CH. The contribution of Fas/FasL-mediated apoptosis to CH appears independent of Th1 and Th2 cytokines.

Helper CD4+ T cells for IgE response to a dietary antigen develop in the liver

BACKGROUND

Although T-cell responses to food antigens are normally inhibited either by deletion, active suppression, or both of antigen-specific T cells, T helper cells for IgE response to a food antigen still develop by unknown mechanisms in a genetically susceptible host.

OBJECTIVE

We determined the site at which those IgE helper T cells develop.

METHODS

We administered ovalbumin (OVA) orally to DO11.10 mice and studied CD4+ T cells in Peyer's patches, the spleen, and the liver. Helper activity for IgE response was assessed by adoptively transferring those CD4+ T cells to naive BALB/c mice, followed by systemic immunization with OVA.

RESULTS

OVA-specific CD4+ T cells were deleted by cell death in the liver and Peyer's patches of DO11.10 mice fed OVA. OVA-specific CD4+ T cells that survived apoptosis in the liver expressed Fas ligand and secreted IL-4, IL-10, and transforming growth factor beta(1). CD4+ T cells producing IFN-gamma were deleted in the liver by repeated feeding of OVA. On transfer of CD4+ T cells to naive mice and systemic immunization with OVA, a marked increase in OVA-specific IgE response developed only in the mice that received hepatic CD4+ T cells from OVA-fed mice, the effect of which was not observed in the recipients of hepatic CD4+ T cells deficient in IL-4. In addition, significant suppression of delayed-type hypersensitivity and IgG(1)/IgG(2a) responses to OVA was observed in the recipients of hepatic CD4+ T cells, and this suppression required Fas/Fas ligand interaction.

CONCLUSION

Together, these results suggested that a food antigen might negatively select helper T cells for IgE response to the antigen by preferential deletion of T(H)1 cells in the liver.

Activation-induced cell death in T cells

A properly functioning immune system is dependent on programmed cell death at virtually every stage of lymphocyte development and activity. This review addresses the phenomenon of activation-induced cell death (AICD) in T lymphocytes, in which activation through the T-cell receptor results in apoptosis. AICD can occur in a cell-autonomous manner and is influenced by the nature of the initial T-cell activation events. It plays essential roles in both central and peripheral deletion events involved in tolerance and homeostasis, although it is likely that different forms of AICD proceed via different mechanisms. For example, while AICD in peripheral T cells is often caused by the induction of expression of the death ligand, Fas ligand (CD95 ligand, FasL), it does not appear to be involved in AICD in thymocytes. This and other mechanisms of AICD are discussed. One emerging model that may complement other forms of AICD involves the inducible expression of FasL by nonlymphoid tissues in response to activated T lymphocytes. Induction of nonlymphoid FasL in this manner may serve as a sensing mechanism for immune cell infiltration, which contributes to peripheral deletion.

T helper (Th) 2 predominance in atopic diseases is due to preferential apoptosis of circulating memory/effector Th1 cells

T cells constitute a large population of cellular infiltrate in atopic/allergic inflammation and a dysregulated, Th2-biased peripheral immune response appears to be an important pathogenetic factor. In atopic dermatitis, circulating cutaneous lymphocyte-associated antigen-bearing (CLA+) CD45RO+ T cells with skin-specific homing property represent an activated memory/effector T cell subset. They express high levels of Fas and Fas ligand and undergo activation-induced apoptosis. The freshly purified CLA+ CD45RO+ T cells of atopic individuals display distinct features of in vivo-triggered apoptosis such as pro-caspase degradation and active caspase-8 formation. In particular, the Th1 compartment of activated memory/effector T cells selectively undergoes activation-induced cell death, skewing the immune response toward surviving Th2 cells in atopic dermatitis patients. The apoptosis of circulating memory/effector T cells was confined to atopic individuals whereas non-atopic patients such as psoriasis, intrinsic-type asthma, contact dermatitis, intrinsic type of atopic dermatitis, bee venom allergic patients, and healthy controls showed no evidence for enhanced T cell apoptosis in vivo. These results define a novel mechanism for peripheral Th2 response in atopic diseases.

CD4+ cell memory: the enigma of Th1 cells

Despite a wealth of information pertaining to functional and phenotypic attributes of memory CD4(+) cells, the mechanisms that underlie the generation and persistence of memory in this subset are largely unknown. Recent work suggests that the development of memory might be differently regulated in T-helper-1 and T-helper-2 cells, owing to differences in their susceptibility to cell death. These studies support a new paradigm, in which memory T cells are heterogeneous in terms of their stage of maturation and function as well as mechanisms of homeostatic control.

Defect in activation-induced cell death in non-obese diabetic (NOD) T lymphocytes

Activation-induced cell death (AICD) represents a major means of peripheral tolerance induction, eliminating effector cells. NOD mice, a widely used model for autoimmune diabetes, are characterized by high levels of circulating T lymphocytes and by resistance to several apoptosis-inducing signals. The aim of this study was to analyse AICD in peripheral NOD T lymphocytes. First, we demonstrated in an in vitro AICD model that NOD T lymphocytes are more resistant to AICD (64+/-2%) compared to non-autoimmune C57BL/6 T lymphocytes (73+/-2%), but also diabetes-resistant NOR T lymphocytes (76+/-3%, P<0.05). Moreover, both CD4(+)and CD8(+)subsets were affected. Analysis of the cellular and molecular pathways revealed lower caspase 8 levels, a central caspase proximally involved in the AICD-pathway (fluorescence of 258+/-47 in NOD vs. 441+/-16 in NOR and 414+/-61 in C57BL/6 T lymphocytes, P<0.05). Gene expression analysis using real-time RT-PCR additionally revealed low expression of Fas and FasL, the death receptor system activating caspase 8 and contributing to AICD. Additionally, low IL-2 levels, together with high TGFbeta and Bclx-L levels, confirm the presence of a NOD-specific AICD-resistance profile. In conclusion, we present cellular and molecular evidence for disturbed AICD mechanisms in NOD T lymphocytes. This resistance in AICD may contribute to defective tolerance induction to autoantigens in NOD mice.

Hepatic allograft-derived Kupffer cells regulate T cell response in rats

In liver transplantation, the development of tolerance is associated with an increased rate of apoptosis of T lymphocytes in the portal inflammatory infiltrate and the presence of an intragraft Th2-like T cell population. Underlying mechanisms are poorly understood. Kupffer cells (KC), which reside in the hepatic sinosoids, can directly interact with circulating T lymphocytes and thus are uniquely positioned to play a role in immunomodulation. In this study, the immunoregulatory effects of KC were investigated. We show that KC can significantly suppress T cell proliferation in mixed leukocyte reaction (MLR). Furthermore, KC express functional Fas ligand (FasL) and can induce apoptosis of Fas+ cells. This process can be blocked by addition of neutralizing anti-FasL antibody. Moreover, using an allogeneic liver transplant model we have determined that 1. KC recovered from chronically accepted hepatic allografts have increased FasL messenger RNA (mRNA) and protein expression and a greater ability to induce apoptosis of alloreactive T cells compared with KC recovered from an acute rejection model; 2. KC not only induce apoptosis of T cells, but also regulate cytokine production and Th2/Th3-like cytokine (interleukin [IL]-10 / transforming growth factor [TGF]-beta) mRNA expression in allogeneic MLR in vitro; and 3. administration of KC derived from chronically accepted liver allografts significantly prolongs the survival of hepatic allografts in an acute rejection model in an alloantigen-specific manner. In conclusion, these data implicate the possible role of KC-mediated regulation of T cell response in the induction of immune tolerance in liver allografts.

Sensitizing antigen-specific CD8+ T cells for accelerated suicide causes immune incompetence

Death receptor-mediated activation-induced apoptosis of antigen-specific T cells is a major mechanism of peripheral tolerance induction and immune homeostasis. Failure to undergo activation-induced cell death (AICD) is an important underlying cause of many autoimmune diseases. Thus, enhancing the T cell's own suicide mechanism may provide an efficient therapy for the treatment of autoimmune diseases. Bisindolylmaleimide VIII (Bis VIII), a PKC inhibitor, can sensitize T cells for death receptor-induced apoptosis and thus can inhibit the development of T cell-mediated autoimmune disease in vivo. In this study, we have analyzed the functional consequences of accelerated suicide for a protective CD8+ T cell-mediated immune response. Our data indicate that CD8+ T cells are sensitized by Bis VIII to AICD, both in vitro and in vivo. The sensitizing effect of Bis VIII appears to be mediated by specific downmodulation of the antiapoptotic molecule cellular FLICE-like inhibitory protein (cFLIP(L)). Importantly, Bis VIII administration during an acute lymphocytic choriomeningitis virus (LCMV) infection causes the depletion of virus-specific CD8+ T cells and subsequently impaired cytotoxicity and virus clearance. We conclude that resistance to death receptor-induced apoptosis is crucial for the efficient induction of a protective immune response, and that Bis VIII-based immunotherapies have to be applied under well-controlled conditions to avoid the induction of immune incompetence and the inability to respond to pathogen infection.

Immune response and protection elicited by DNA immunisation against Taenia cysticercosis

The study evaluated DNA vaccination in Taenia solium cysticercosis prevention by using cDNA of an antigen (cC1) from T. solium metacestode. pcDNA3-cC1 DNA vaccine was constructed by inserting the cDNA into the eukaryotic expression plasmid pcDNA3. Positive expression of the pcDNA3-cC1 product was confirmed by its transfection into COS7 cell and enzyme-linked immunoabsorbent assay using serum of pigs infected with T. solium metacestode. Immunisation of BALB/c mice with three injections of pcDNA3-cC1 induced antigen-specific immune responses of the Th1 phenotype. Inoculation of new-born pigs induced protection against challenge with T. solium by 73.3% reduction of the metacestode number. Antibodies elicited by DNA immunisation with pcDNA3-cC1 specifically reacted with native cC1 protein, which was mainly restricted to the cyst wall of T. solium metacestode. Positive apoptosis signals were also detected in the cyst wall cells of metacestode slices from pigs immunised with pcDNA3-cC1 by TUNEL staining method. Those suggested that apoptosis played a role in protecting pigs immunised with pcDNA3-cC1 nucleic acid vaccine from pathogen challenge.

The effect on the proliferation and apoptosis of alloreactive T cells of cell dose in a murine MHC-mismatched hematopoietic cell transplantation model

Activation-induced cell death (AICD) of lymphocytes is an apoptotic pathway involved in the control of T-cell homeostasis. The magnitude of graft-vs.-host disease (GVHD) following allogeneic hematopoietic cell transplantation may be attenuated by the enhancement of AICD. The aim of the present study was to clarify the effect of T cell dose upon the fate (proliferation or apoptosis) of individual activated T cells in a murine GVHD model. To this end, we investigated the kinetics of the proliferation and apoptosis of donor T cells in recipient spleens in the early stage of a fully major histocompatibility complex (MHC)-mismatched murine transplantation model from C57BL/6 (H-2(b)) to lethally-irradiated (8.5 Gy) BALB/c (H-2(d)) mice. To track the behavior of alloreactive lymphocytes in vivo, we used the fluorescent cytoplasmic dye carboxyfluorescein diacetate succinimidyl ester in combination with flow cytometry. Engraftment of donor T cells to recipient spleens was almost completed within 24 h after transfer. After that, at higher doses of transferred cells, the donor T cells actively divided for up to 72 h resulting in a 30-fold increase in cell number at the maximum cell dose (2.0 x 10(7)). As the transferred cell dose decreased, the proliferation of T cells tended to be suppressed. At cell doses of 0.5 x 10(7) or less, the proliferation of T cells was profoundly suppressed, ultimately resulting in little proliferation of donor T cells observed from 24 to 72 h at the minimum cell dose (0.1 x 10(7)). The frequency of Annexin-V-positive cells was found to increase gradually as the transferred cell dose decreased. Thus, an increase in apoptotic events appeared to play an important role in the suppression of the proliferation of T cells at lower splenocyte doses. Further analyses revealed that Fas ligand (FasL)-positive T cells were observed exclusively among T cells that divided at least 5 times, and that all of them were positive for Annexin-V, indicating that they were in the process of apoptosis. Together with our finding that the frequency of apoptosis increased with the progression of cell division, these findings strongly suggest that AICD occurred through the Fas/FasL system and that AICD increased as the dose of donor T cells participating in the allogeneic response decreased. When relatively small numbers of T cells are confronted with an excess of antigen, they disappear. This process is called clonal exhaustion-deletion. Our results support the idea that AICD is involved in the process of clonal exhaustion-deletion. Relevant to the clinical aspects of hematopoietic cell transplantation, our findings indicate that AICD may be associated with tolerance induction in T-cell-depleted transplantation from HLA-mismatched donors, in which T cells contaminating marrow grafts do not need to be completely removed for achieving tolerance between donors and recipients. Furthermore, our results indicate that a small change in the quantitative balance between antigens and T cells responding to them leads to a large difference in the fate of T cells activated in response to MHC-incompatible antigens. Thus, the size of the T cell dose is one of the important considerations in tolerance induction, GVHD and rejection.

Display of Fas ligand protein on cardiac vasculature as a novel means of regulating allograft rejection

BACKGROUND

Fas ligand (FasL) is a potent death-inducing molecule with important functions in immune homeostasis and tolerance to self-antigens. The complex biological activities of FasL and its inefficient expression using conventional gene transfer approaches limit its use for immunomodulation to prevent allograft rejection. We have recently generated a chimeric FasL with core streptavidin (SA-FasL) with potent apoptotic activity and designed a novel approach to display it on the surface of several cell types via biotinylation. We herein tested whether SA-FasL can also be displayed on vascular endothelial cells in the heart and examined its effect on graft survival after transplantation into syngeneic and allogeneic hosts.

METHODS AND RESULTS

SA-FasL was efficiently displayed on the vasculature of BALB/c hearts with a half-life of 9 days in vivo. Transplantation of hearts displaying SA-FasL into syngeneic hosts resulted in indefinite graft survival without detectable toxicity to the grafts and hosts. In contrast, transplantation of allogeneic C57BL/10 hearts displaying SA-FasL into BALB/c recipients resulted in graft rejection, but in a delayed fashion as compared with control hearts (mean survival time=17.4+/-5 versus 9.6+/-1 days). Allograft survival was further extended to 21+/-2.6 and 24+/-3 days (P<0.05) by intravenous treatment of graft recipients with 1 dose of SA-FasL-decorated donor splenocytes on days 2 and 6 after transplantation, respectively.

CONCLUSIONS

This study shows for the first time that exogenous proteins can be displayed on the endothelium of solid organs for therapeutic purposes. This approach provides a convenient and rapid means of displaying exogenous proteins on the surface of cells, tissues, and solid organs, with broad research and therapeutic implications.