Absence Of Fas Research Articles

Skin biomarkers predict the development of food allergy in early life

BackgroundFood allergy (FA) often occurs in early childhood with and without atopic dermatitis (AD). FA can be severe and even fatal. For primary prevention, it is important to find early biomarkers to predict the future onset of FA before any clinical manifestations. ObjectiveTo find early predictors of future onset of FA in the stratum corneum (SC). MethodsSkin tape strips (STS) were collected from the forearm of newborns (n=129) at the age of 2 months before any signs of clinical FA or AD. Children were clinically monitored until they reached 2 years of age to confirm the presence or absence of FA and AD. STS were subjected to lipidomic analyses by the LC-MS/MS and cytokine determination by Meso Scale Discovery U-Plex assay. ResultsOverall, 9/129 (7.0%) infants developed FA alone, and 9/129 (7.0%) infants developed FA concomitantly with AD (ADFA). In the SC of future FA and ADFA children, absolute amounts of unsaturated (N24:1)(C18S)Ceramide and (N26:1)(C18S)Ceramide and their relative percentages within the molecular group were increased in comparison to healthy children with p-values between <0.01 and p<0.05, ANOVA. Future AD children had normal levels of these molecules. Interleukin (IL)-33 was upregulated in future FA but not AD infants, whereas thymic stromal lymphopoietin (TSLP) was upregulated in AD but not FA. Logistic regression analysis revealed strong FA predicting power for the combination of dysregulated lipids and cytokines, with an odds ratio reaching 101.4 (95% CI 5.4 – 1910.6). ConclusionNon-invasive STS analysis at 2 months of age can identify infants at risk of future FA.

A novel role of Fas in delaying cellular senescence

Fas-mediated apoptosis is a major player of many physiological and pathological cellular processes. Fas-regulated immune regulation exhibits either the beneficial or the harmful effects which is associated with the onset or development of immune disorders. Alterations in apoptosis may contribute to age-associated changes. However, the role of apoptosis in the ageing process remains ambiguous. Here we demonstrated Fas signaling-mediated premature senescence in young mouse embryonic fibroblast (MEF) cells. Activated Fas signaling by agonist Jo-2 resulted in declined senescence in young and aged MEFs. Premature senescence induced the early activation of senescence markers, including the increase in the percentage of SA-β-galactosidase (SA-β-gal) cells, the induction of p53 phosphorylation, and the enhanced expression of p16 and p21 protein and elevated IL-6 pro-inflammatory cytokine in the absence of Fas. The elevated production of reactive oxygen species (ROS) in Fas-deficient MEFs was associated with dysfunctional mitochondria. Further, we determined that the known ROS scavenger NAC (N-acetyl-l-cysteine) could reverse the process of premature senescence in absence of Fas. Therefore, this study signifies a novel role of Fas in the control of cellular senescence.

Effects of microalgal diet on growth, survival and fatty acid composition of larvae rock oyster Striostrea prismatica (Gray, 1825)

The biochemical nature and composition of fatty acids (FA's) in microalgae influence the nutritional quality and efficiency of this food source in bivalve larviculture. This research analyses the effect FA's content of Chaetoceros gracilis and Tisochrysis lutea on the FA's composition, growth and survival of Striostrea prismatica larvae. We analysed the FA's profiles of the microalgae, and the tissue of the larvae during a S. prismatica larviculture at day 1 (“D” larvae), day 8 (umbonate larvae) and day 22 (pediveliger) post fertilization (PF). Larvae growth and survival were evaluated during two phases: phase I from day 1 to day 8 PF and phase II from day 9 to day 22 PF. In phase I, we recorded a daily growth rate of 4.76 μm.day−1, while in phase II we recorded increases of 13.24 μm.day−1. In phase I, survival was 36.6%, and decreased further to 9.3% at the end of phase II. The sharp decrease in survival and low growth during phase I could possibly be explained by a specific nutritional deficiency of the microalgae diet (absence of FA's 15:0, 20:4n-3, 20:4n-6 and 22:5n- 3), especially if we consider the starting FA's profile of the “D” larvae. The larvae showed a high nutritional requirement for palmitic, stearic and oleic FA's and long-chain PUFA's, especially 20:5n-3 and 22:6n-3. The absence of these FA's in the diet and their presence in the larval profile suggest that S. prismatica could have the ability to synthesize these FA's; however, more research is needed to corroborate this hypothesis.

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

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

Abstract PO-22: Compromised counterselection by FAS creates a lethal subtype of germinal center lymphoma

Abstract Fas is highly expressed on germinal center (GC) B cells, and mutations of FAS have been reported in diffuse large B-cell lymphoma (DLBCL); however, the function of Fas in the GC remains controversial. Although GC-derived DLBCL has better overall outcomes to therapy than other DLBCL types, some cases are refractory and the molecular basis for this is often unknown. We show that Fas is a strong cell-intrinsic regulator of GC B cells that promotes B-cell death in the light zone likely via T follicular helper (Tfh) cell-derived Fas ligand. In the absence of Fas, GCs were more clonally diverse due to an accumulation of cells that did not demonstrably bind antigen. We found that FAS alterations occurred most commonly in the GC-derived genetic subtype of DLBCL, EZB. FAS alterations in EZB were associated with inferior outcomes and an enrichment of Tfh cells. Alterations in FAS co-occurred with deficiency in HVEM and PD-1 ligands that regulate the Tfh-B cell interaction and were associated with increased diversity of B-cell receptor variable genes across samples. This work shows that Fas is critically required for GC homeostasis and suggests that loss of Tfh-mediated counterselection in the GC contributes to lethality in a distinct subtype of GC-derived lymphoma. Citation Format: Raud Razzaghi, Shreya Agarwal, Nikita Kotlov, Olga Plotnikova, Krystle Nomie, Da Wei Huang, George W. Wright, Moyi Li, Katsuyoshi Takata, Chen Yao, John J. O'Shea, James D. Phelan, Stefania Pittaluga, David W. Scott, Jagan R. Muppidi. Compromised counterselection by FAS creates a lethal subtype of germinal center lymphoma [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-22.

Fibroadenoma in adolescent females after living donor liver transplantation.

Breast FA is the most common breast tumor diagnosed in young women. Female renal transplant recipients on CsA have an increased risk of developing FA. However, reports of FA after LDLT have not been described. Our objectives were to determine the incidence of FA, analyze risk factors for FA, and evaluate treatment strategies in adolescent females after LDLT. A total of 18 female patients aged 10-19years who underwent LDLT and survived at least one year after transplantation were enrolled in our study. The incidence of FA was 11.1%. To determine pre- or post-transplant conditions that are associated with FA after transplantation, the patients were divided into two groups according to the presence or absence of FA: FA group (n=2) and non-FA group (n=16). There were no differences in mean age at LDLT, mean age at breast evaluation, and mean duration between transplantation and breast evaluation between the two groups. However, there was a difference in the immunosuppressive regimen between the two groups. The FA group was maintained on CsA, whereas the non-FA group was maintained on tacrolimus. CsA might be implicated in FA development in adolescent females after LDLT.

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

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

Food-related aggression in shelter dogs: A comparison of behavior identified by a behavior evaluation in the shelter and owner reports after adoption

In order to assess the relationship between food-related aggression in the shelter as identified by a standardized canine behavior evaluation and owner-reported food-related aggression after adoption, this retrospective cohort study followed 97 dogs adopted from a shelter and their adoptive owners. The Match-Up II Shelter Dog Rehoming Program, a standardized canine behavior evaluation that was administered to all the dogs in the study prior to adoption, was used to classify dogs as either food aggressive (FA+) or not food aggressive (FA−). Adoptive owners were subsequently surveyed to assess the dogs’ behavior after adoption, the owners’ perception of food-related aggression, and their satisfaction with the dog as a pet. Twenty (20.6%) dogs evaluated were deemed FA+ in the shelter, and slightly more than half (11/20; 55%) of them were later reported by adopters as exhibiting FA+ behavior in the home after adoption, whereas out of the 77 dogs that were deemed to be FA− in the shelter, 17 (22%) were reported to be FA+ by adopters; conversely, the majority (60/77; 78%) of dogs identified as FA− in the shelter were reported by adopters as not having exhibited FA+ behavior in the home (P=0.004). Most adopters, including those whose dogs were reported FA+ in the home, did not consider FA+ behavior to be a challenge to keeping the dog as a pet. In conclusion, in this sample of shelter dogs, the observation of FA+ behavior during a standardized dog behavior evaluation was associated with FA+ behavior in the home following adoption, however, an almost equal number of dogs observed to be FA+ on the behavior evaluation did not show food aggression after adoption. Failure to observe FA+ behavior on the shelter test was associated with the absence of FA+ behavior after adoption. The detection of FA+ via a behavior evaluation should be interpreted with caution, since a positive finding in the shelter evaluation does not consistently indicate that the behavior will occur in the home nor that a dog is unsuitable for adoption.

Mesodermal Development From Reprogrammed Fanconi Anemia Cells Is Affected by ALDH2 Enzymatic Activity

Abstract 648 IntroductionFanconi anemia (FA) is a genome instability disorder with clinical characteristics including progressive bone marrow failure (BMF), developmental abnormalities, and increased occurrence of leukemia and cancer. To date 15 genes have been implicated in FA, and their products form a common DNA repair network often referred to as “FA pathway”. Following DNA damage or replication stress, the FA pathway is activated, leading to the monoubiquitination of FANCD2 and FANCI proteins (the ID complex). The monoubiquitinated ID complex is loaded on damaged chromatin with subnuclear foci formation, and mediates homologous recombination.Since cells derived from FA patients are hypersensitive to treatments that induce DNA interstrand cross-links (ICLs), the FA pathway has been considered to function in ICL repair. However, it still remains unclear what type of endogenous DNA damage is repaired through the FA pathway and is the cause of phenotypes in FA patients. Recent studies have suggested that cells deficient in the FA pathway are also sensitive to formaldehyde and acetaldehyde. Aldehydes may create DNA adducts including ICLs or protein DNA crosslinking. These results raise a possibility that the FA pathway prevents BMF by mitigating genotoxicity due to endogenous aldehydes.It has been known that ALDH2 deficiency resulting from Glu487Lys substitution (A allele) is prevalent in East Asian populations. While the Glu487 form (G allele) is proficient in aldehyde catabolism, even the GA heterozygote displayed strongly reduced catalysis because ALDH2 is a tetrameric enzyme and the variant form can suppress the activity in a dominant negative manner. Therefore some Japanese FA patients are expected to be deficient in ALDH2, providing an opportunity to test role of ALDH2 and aldehyde metabolism in human FA patients. Results and discussionIn FA fetus, p53/p21 axis has already activated in fetal liver (Ceccaldi, Cell stem cell, 2012), indicating the possibility that hematopoietic defects in FA patients originates from an earlier developmental stage. Since human hematopoietic system originates from embryonic mesoderm, we set out to estimate the role of ALDH2 and FANCA pathway during early embryogenesis. For this, we reprogrammed somatic cells from a patient with ALDH2 GA genotype and observed their in vitro mesodermal differentiation. We first introduced reprogramming factors into fibroblasts by episomal vectors, and obtained colonies which are morphologically compatible with human induced pluripotent stem cells (iPSCs). These iPSC-like cells (designated as FA-iPLCs) showed close similarity to conventional ES/iPSCs regarding marker gene expressions and differentiation ability into three germ layers. We obtained gene-complemented FA-iPLCs (designated as cFA-iPLCs) for control study.To evaluate the impact of ALDH2 activity on iPSC- or iPLC-derived mesodermal differentiation, we next adapted the previously reported serum-free monolayer culture system. Both FA- and cFA-iPLCs showed similar differentiation manners with conventional embryonic stem cells and iPSCs, and percentages of KDR+ mesodermal progenitors including KDR+CD34+ common hemoangiogenic progenitors were comparable. Notably, ALDH2 agonist Alda1 did increase only FA-iPLC-derived mesodermal progenitors but not cFA-iPLCs. These data supported the hypothesis that mesodermal development towards hematopoietic cells in human can be affected by ALDH2 activity in the absence of FA pathway.To confirm the hypothesis, next we set out to assess whether the variation in ALDH2 affects symptoms in Japanese FA patients. Strikingly, we found that progression of BMF was strongly accelerated in heterozygous carrier of the variant A allele compared to homozygous GG patients. Furthermore we looked at occurrence of leukemia and/or myelodysplasia and the somatic developments. Interestingly, these were not significantly difference between patients with each variation of ALDH2, indicating the possibility that aldehydes affect only in early hematopoietic development, not other mesodermal tissues.Overall, our results from FA-iPLCs and clinical study indicate that the variation in ALDH2 affects the occurrence of bone marrow failure in FA patients, and that hematopoietic defect in FA patients is caused by aldehydes in early mesodermal developmental stage. Disclosures:No relevant conflicts of interest to declare.

Vesicles Released by Activated T Cells Induce Both Fas-Mediated RIP-Dependent Apoptotic and Fas-Independent Nonapoptotic Cell Deaths

Activated T cells secrete Fas ligand (FasL)-containing vesicles (secreted vesicles) that induce death of target cells. We provide evidence that secreted vesicles from culture supernatants (Csup) of various origins are able to generate both Fas-dependent apoptotic and Fas-independent, nonapoptotic cell death. In the absence of Fas, the nonapoptotic, Fas-independent pathway could still induce cell death. In contrast to RIP-independent classical Fas-induced cell death triggered by cross-linked or membrane-bound FasL, CSup-derived stimuli-induced apoptosis exhibited unique molecular and enzymatic characteristics. It could be partially inhibited by blocking cathepsin D enzyme activity and required the presence of RIP. Whereas stimulation with CSup, derived from both FasL-overexpressing Jurkat cells and PBMC, could induce cell death, the requirements for Fas-associated death domain protein and caspase-9 were different between the two systems. Our study highlights an important distinction between cell contact-mediated and secreted vesicle-generated activation-induced cell death and also demonstrates that the type of the secreted vesicles can also modify the cell death route. We propose that besides cell-to-cell interaction-mediated Fas triggering, stimuli induced by secreted vesicles can mediate important additional cell death signals regulating activation-induced cell death under physiological conditions.

Fitness-Associated Sexual Reproduction in a Filamentous Fungus

Sex is a long-standing evolutionary enigma. Although the majority of eukaryotes reproduce sexually at least sometimes [1-3], the evolution of sex from an asexual ancestor has been difficult to explain because it requires sexually reproducing lineages to overcome the manifold costs of sex, including the destruction of favorable gene combinations created by selection [4, 5]. Conditions for the evolution of sex are much broader if individuals can reproduce either sexually or asexually (i.e., facultative sex) and allocate disproportionately more resources to sex when their fitness is low (fitness-associated-sex or FAS [6-10]). Although facultatively sexual organisms have been shown to engage in more sex when stressed [11], direct evidence for FAS is lacking. We provide evidence using 53 genotypes of the filamentous fungus Aspergillus nidulans in a reciprocal transplant experiment across three environments. Different genotypes achieved highest fitness in different environments and genotypes invested relatively more in sex in environments in which their fitness was lower, showing that allocation to sexual reproduction is a function of how well-adapted a genotype is to its environment. FAS in A. nidulans is unlikely to have evolved as a strategy to resist or avoid stress because asexual spores are more dispersive and equally resistant [12, 13].

Erratum to: Trans Fatty Acid‐Induced NF‐κB Activation Does Not Induce Insulin Resistance in Cultured Murine Skeletal Muscle Cells

In error, an incorrect version of Fig. 2a was published. They-axis of Fig. 2a was erroneously labeled, whereas the description in the text contained the correct data. The correct version of Fig. 2a is displayed below. These changes do not impact the interpretation of the data. NF-κB transcriptional activity and insulin sensitivity in skeletal muscle cells after incubation with geometric and positional C18:1 or C18:2 isomers. C2C12 myoblasts stably transfected with the 6κB-TK-luciferase construct were differentiated for 5 days and incubated with 400 μmol/l of the indicated FAs for 24 h (a). Lysates were prepared for assessment of luciferase activity. Values were corrected for protein content and expressed as fold-induction over control. Alternatively, 5 days differentiated L6-GLUT4myc myotubes were incubated with and without the indicated fatty acids (200 μmol/l, 16 h). Nuclear extracts were prepared and assessed for RelA DNA binding activity to a consensus NF-κB oligonucleotide by EMSA (b). Relative DNA binding activity was determined by phosphor-imager analysis and expressed as fold induction. Furthermore, 2-deoxyglucose uptake (c) and GLUT4 translocation (d) were measured after stimulation with 25 nmol/l insulin for 15 min in 5 days differentiated L6-GLUT4myc myotubes. Data are expressed as percentage of insulin-stimulated glucose uptake or GLUT4 translocation in absence of FA. Basal and insulin-stimulated conditions are represented by the white and black bars, respectively. *p < 0.05 versus control. #p < 0.05 versus insulin-stimulated control. Data shown are representative examples of three independent experiments

Deletion of Fas in the pancreatic β-cells leads to enhanced insulin secretion

Fas/Fas ligand belongs to the tumor necrosis factor superfamily of receptors/ligands and is best known for its role in apoptosis. However, recent evidence supports its role in other cellular responses, including proliferation and survival. Although Fas has been implicated as an essential mediator of beta-cell death in the pathogenesis of type 1 diabetes, the essential role of Fas specifically in pancreatic beta-cells has been found to be controversial. Moreover, the role of Fas on beta-cell homeostasis and function is not clear. The objective of this study is to determine the role of Fas specifically in beta-cells under both physiological and diabetes models. Mice with Fas deletion specifically in the beta-cells were generated using the Cre-loxP system. Cre-mediated Fas deletion was under the control of the rat insulin promoter. Absence of Fas in beta-cells leads to complete protection against FasL-induced cell death. However, Fas is not essential in determining beta-cell mass or susceptibility to streptozotocin- or HFD-induced diabetes. Importantly, Fas deletion in beta-cells leads to increased p65 expression, enhanced glucose tolerance, and glucose-stimulated insulin secretion, with increased exocytosis as manifested by increased changes in membrane capacitance and increased expression of Syntaxin1A, VAMP2, and munc18a. Together, our study shows that Fas in the beta-cells indeed plays an essential role in the canonical death receptor-mediated apoptosis but is not essential in regulating beta-cell mass or diabetes development. However, beta-cell Fas is critical in the regulation of glucose homeostasis through regulation of the exocytosis machinery.

The BH3-Only Protein Bid Does Not Mediate Death-Receptor-Induced Liver Injury in Obstructive Cholestasis

The accumulation of bile acids during obstructive cholestasis causes liver injury and fibrosis, which is at least partly mediated by the death receptors Tumor necrosis factor-related apoptosis-inducing ligand, Tumor necrosis factor-alpha, and Fas. The BH3-interacting domain death agonist Bid is a critical mediator of death receptor-induced apoptosis in hepatocytes. Our aim for this study was, therefore, to elucidate whether Bid also mediates death receptor-induced liver injury in obstructive cholestasis. Overall, survival and various aspects of liver injury were analyzed in wild-type and Bid(-/-) mice after bile duct ligation (BDL), a commonly used model to study obstructive cholestasis in mice. Liver injury was examined at 3, 7, and 14 days after BDL. Loss of Bid did not affect the number of bile infarcts, serum aspartate aminotransferase values, or animal survival. Processing of procaspase-3 and procaspase-9, and caspase-3 enzyme activities, were not detectable in either group, and Bid(-/-) mice displayed the same pattern of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling positive hepatocytes as wild-type controls following BDL. In contrast to Fas-receptor deficient lpr mice, hepatic fibrosis and the inflammatory response was not affected by loss of Bid. Together, these data suggest that Bid is not a downstream target of death receptors in obstructive cholestasis and does not significantly contribute to bile acid induced liver injury and fibrosis.

Fas expression in primary breast cancer is related to neoplastic infiltration of perilymphatic fat

Various studies have revealed that both Fas and its ligand play an important role in cancer biology. The aim of our study was to determine if there is a relationship between the expression of Fas or Fas-ligand in breast cancer and the presence of malignant cells in perilymphatic fat. Tumor samples from 147 consecutive breast cancer patients, aged 35-81 (median, 59), were subjected to analysis. The expressions of Fas and Fas-ligand were determined immunohistochemically. The expression of Fas, but not Fas-ligand, was significantly less frequent in breast cancer patients in whom malignant cells infiltrated through the perilymphatic fat (p=0.042). The infiltration of paranodal fatty tissue occurred more often in cases of ductal carcinomas (p=0.008), larger primary tumors (pT>or=2, p=0.030) and regional lymph node involvement (pN>or=1, p=0.021). Univariate analysis revealed that perilymphatic fat infiltration shortened overall survivals in breast cancer patients (p=0.05), similarly to postmenopausal status (p=0.034), age >60 years (p=0.05) and regional lymph node involvement (p=0.05). None of the aforementioned factors, however, was revealed as an independent predictor of survival in multivariate analysis. The study showed that lack of Fas in primary breast cancer is associated with perilymphatic fat infiltration. Consequently, both the absence of Fas in the primary tumor and the occurrence of neoplatic cells in paranodal fatty tissue should be considered in the prognosis, complementing existing conventional factors.

Caspase-8 and c-FLIPL Associate in Lipid Rafts with NF-κB Adaptors during T Cell Activation

Humans and mice lacking functional caspase-8 in T cells manifest a profound immunodeficiency syndrome due to defective T cell antigen receptor (TCR)-induced NF-kappaB signaling and proliferation. It is unknown how caspase-8 is activated following T cell stimulation, and what is the caspase-8 substrate(s) that is necessary to initiate T cell cycling. We observe that following TCR ligation, a small portion of total cellular caspase-8 and c-FLIP(L) rapidly migrate to lipid rafts where they associate in an active caspase complex. Activation of caspase-8 in lipid rafts is followed by rapid cleavage of c-FLIP(L) at a known caspase-8 cleavage site. The active caspase.c-FLIP complex forms in the absence of Fas (CD95/APO1) and associates with the NF-kappaB signaling molecules RIP1, TRAF2, and TRAF6, as well as upstream NF-kappaB regulators PKC theta, CARMA1, Bcl-10, and MALT1, which connect to the TCR. The lack of caspase-8 results in the absence of MALT1 and Bcl-10 in the active caspase complex. Consistent with this observation, inhibition of caspase activity attenuates NF-kappaB activation. The current findings define a link among TCR, caspases, and the NF-kappaB pathway that occurs in a sequestered lipid raft environment in T cells.

The Death Receptor Fas (CD95/APO-1) Mediates the Deletion of T Lymphocytes Undergoing Homeostatic Proliferation

Murine T cells adoptively transferred into syngeneic lymphopenic recipients undergo proliferation. Despite continued cell division, this lymphopenia-induced or homeostatic proliferation of a limited number of transferred T cells does not fill the T cell compartment. The continued expansion of the transferred T cells, even after stable T cell numbers have been reached, suggests that active cell death prevents further increase in T cell number. In this study, we show that wild-type T cells undergoing homeostatic proliferation are sensitive to Fas-mediated cell death. In the absence of Fas, T cells accumulate to significantly higher levels after transfer into lymphopenic recipients. Fas is, thus, a principal regulator of the expansion of peripheral T cells in response to self-peptide/MHC during T cell homeostasis. As Fas-deficient lpr mice manifest no significant abnormalities in thymic negative selection or in foreign Ag-induced peripheral T cell deletion, their lymphadenopathy may result from unrestrained homeostatic proliferation.

Constitutive activation of the aryl hydrocarbon receptor in T-lineage cells induces thymus involution independently of the Fas/Fas ligand signaling pathway

Thymus involution is one of the most prominent consequences of exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The characteristic features of TCDD-induced thymic changes include reductions in the number of the thymocytes and in the ratio of CD4 to CD8 T cells in the thymus. While these changes have been shown to be caused by activation of a transcription factor, the aryl hydrocarbon receptor (AhR), the down-stream biological events that induce the thymic changes have not been determined. In the present study, we examined the involvement of Fas/Fas ligand (FasL)-dependent apoptosis, a likely mechanism suggested by previous studies, in the thymocyte loss by AhR activation of thymocytes. We recently generated transgenic (Tg) mice expressing a constitutively active AhR (CA-AhR) mutant specifically in T-lineage cells. These Tg mice reproduced the thymus involution caused by TCDD at relatively high doses. In this study, we crossed the T-cell-specific CA-AhR Tg mice with Faslpr mice, which have the homozygous defective fas (lpr) gene, or with FasLgld mice, which have the homozygous mutated fas ligand (gld) gene, to generate mice that are defective in Fas/FasL signaling and express the CA-AhR in T lineage cells. Faslpr and FasLgld CA-AhR Tg mice showed the same extent of thymocyte reduction as Faswt and FasLwt CA-AhR Tg mice. The ratio of CD4 to CD8 T cells in thymocytes was also not affected by the absence of Fas or FasL in the CA-AhR Tg mice. These results show that strong activation of the AhR in thymocytes induces thymus involution independently of Fas/FasL signaling.

The bile acid glycochenodeoxycholate induces p53-independent trail receptor 2/DR5 expression and apoptosis in the absence of Fas: Hajime Higuchi, Steven F Bronk, Yasuhiro Takikawa, Nathan W Werneburg, Gregory J Gores, Mayo Clinic, Rochester, MN

The bile acid glycochenodeoxycholate induces p53-independent trail receptor 2/DR5 expression and apoptosis in the absence of Fas: Hajime Higuchi, Steven F Bronk, Yasuhiro Takikawa, Nathan W Werneburg, Gregory J Gores, Mayo Clinic, Rochester, MN

Fas-mediated inhibition of CD4+ T cell priming results in dominance of type 1 CD8+ T cells in the immune response to the contact sensitizer trinitrophenyl.

One of the unusual properties of chemically reactive haptens is their capacity to simultaneously generate immunogenic determinants for hapten-specific CD8(+) and CD4(+) T cells. Surprisingly, however, a clear dominance of CD8(+) effector T cells is observed in murine contact hypersensitivity to various haptens and upon T cell priming with hapten-modified APCs in vitro. In this study we show that trinitrophenyl-specific CD8(+) T cells actively prevent CD4(+) T cell priming in vitro. This process requires cell-cell contact and is dependent on the expression of Fas on the CD4(+) T cells. Our results reveal an important Fas-dependent mechanism for the regulation of hapten-specific CD4(+) T cell responses by CD8(+) T cells, which causes the dominance of CD8(+) effector T cells and the active suppression of a CD4(+) T cell response. Moreover, our demonstration of reduced contact hypersensitivity to trinitrophenyl in the absence of Fas, but not of perforin and/or granzymes A and B, underlines the important role of Fas as a pathogenetic factor for contact hypersensitivity.