Ultraviolet B irradiation modulates susceptibility to tumour necrosis factor-alpha-induced apoptosis via induction of death receptors in murine fibroblasts.

Ultraviolet B (UVB) irradiation causes cell death by apoptosis in murine fibroblast cells. Tumor necrosis factor-alpha (TNF-alpha) is also a well known inducer of apoptosis, although the physiological significance of this activity is poorly understood. We investigated the effects of pretreatment with UVB (312 nm) on TNF-alpha-induced apoptosis in murine fibroblast cells. UVB enhanced susceptibility to cell death by TNF-alpha in a dose-dependent manner. UVB but not TNF-alpha induced the expression of TNF receptor type-1 (TNFR-1) and type-2 (TNFR-2) in a dose-dependent manner. Expression of Fas (CD95) and Fas-ligand (Fas-L), and significant DNA fragmentation were observed in the cells that died. These results suggest that UVB irradiation modulates susceptibility to TNF-alpha-induced apoptosis through the induction of TNFRs, Fas, and Fas-L in murine fibroblasts.     

UV-B诱导的酵母凋亡现象及调节机制的作用

研究UV-B诱导的酵母凋亡现象及调节机制的作用。通过高密度细胞培养, UV-B能够抑制酵母细胞生长和诱导细胞凋亡。然而, 将UV-B已照射96 h活酵母细胞重新进行UV-B照射时发现, 培养12 d照射过细胞的存活率仍有10% (P<0.05), 而未照射细胞已经基本死亡。同时, 经0.01 mol/L和0.1 mol/L H2O2处理, UV-B照射24 h活细胞的存活率分别是对照的3.0倍和5.2倍; 而经30 min和60 min 55°C热处理, UV-B照射24 h活细胞的存活率分别是对照的3.5倍和9.0倍。     

Possible role of acylphosphatase,Bcl-2 and Fas/Fas-L system in the early changes of cardiac remodeling induced by volume overload

To identify early adaptive processes of cardiac remodeling (CR) in response to volume overload, we investigated the molecular events that may link intracellular Ca(2+) homeostasis alterations and cardiomyocyte apoptosis. In swine heart subjected to aorto-cava shunt for 6, 12, 24, 48 and 96 h sarcoplasmic reticulum (SR) Ca(2+) pump activity was reduced until 48 h (-30%), but a recovery of control values was found at 96 h. The decrease in SR Ca(2+)-ATPase (SERCA2a) expression at 48 h, was more marked (-60%) and not relieved by a subsequent recovery, while phospholamban (PLB) concentration and phosphorylation were unchanged at all the considered times. Conversely, acylphosphatase activity and expression significantly increased from 48 to 96 h (+40%). Bcl-2 expression increased significantly from 6 to 24 h, but at 48 h, returned to control values. At 48 h, microscopic observations showed that overloaded myocardium underwent substantial damage and apoptotic cell death in concomitance with an enhanced Fas/Fas-L expression. At 96 h, apoptosis appeared attenuated, while Fas/Fas-L expression was still higher than control values and cardiomyocyte hypertrophy became to develop. These data suggest that in our experimental model, acylphosphatase could be involved in the recovery of SERCA2a activity, while cardiomyocyte apoptosis might be triggered by a decline in Bcl-2 expression and a concomitant activation of Fas.     

ULTRAVIOLET B IRRADIATION MODULATES SUSCEPTIBILITY TO TUMOUR NECROSIS FACTOR-α-INDUCED APOPTOSIS VIA INDUCTION OF DEATH RECEPTORS IN MURINE FIBROBLASTS

Ultraviolet B (UVB) irradiation causes cell death by apoptosis in murine fibroblast cells. Tumor necrosis factor-α (TNF-α) is also a well known inducer of apoptosis, although the physiological significance of this activity is poorly understood. We investigated the effects of pretreatment with UVB (312 nm) on TNF-α-induced apoptosis in murine fibroblast cells. UVB enhanced susceptibility to cell death by TNF-α in a dose-dependent manner. UVB but not TNF-α induced the expression of TNF receptor type-1 (TNFR-1) and type-2 (TNFR-2) in a dose-dependent manner. Expression of Fas (CD95) and Fas-ligand (Fas-L), and significant DNA fragmentation were observed in the cells that died. These results suggest that UVB irradiation modulates susceptibility to TNF-α-induced apoptosis through the induction of TNFRs, Fas, and Fas-L in murine fibroblasts.     

Fas/FasL-mediated apoptosis in perinatal murine lungs

Postcanalicular lung development is characterized by a time-specific increase in alveolar epithelial type II cell apoptosis. We have previously demonstrated that, in fetal rabbits, developmental type II cell apoptosis coincides with transient upregulation of the cell death regulator Fas ligand (FasL). The aims of this study were 1) to determine the spatiotemporal patterns of pulmonary apoptosis and Fas/FasL gene expression in the murine model [embryonic day 17 (E17) through postnatal day 5 (P5)], and 2) to investigate the functional involvement of the Fas/FasL system by determining the effect of Fas activation and inhibition on perinatal pulmonary apoptosis. The apoptotic activity of alveolar epithelial type II cells, determined by combined TUNEL labeling and anti-surfactant protein B immunohistochemistry, showed a dramatic increase during the perinatal transition (type II cell apoptotic index <0.1% at E17, 1.5% at P1-P3, and 0.3% at P5). This timing of enhanced type II cell apoptosis coincided with a robust 14-fold increase in Fas mRNA and protein levels and a threefold increase in FasL protein levels; both Fas and FasL immunolocalized to type II and bronchial epithelial cells. In vitro and in vivo exposure of fetal and postnatal murine type II cells to anti-Fas antibody induced a fourfold increase in apoptotic activity that was prevented by administration of a broad-spectrum caspase inhibitor; the pulmonary apoptotic activity of Fas-deficient lpr mice remained unchanged. Conversely, administration of a caspase inhibitor to newborn mice (P1) resulted in marked diminution of pulmonary apoptotic activity. These combined findings strongly implicate the Fas/FasL system as a critical regulator of perinatal type II cell apoptosis. The developmental time dependence of apoptosis-related events in the murine model should facilitate investigations of the regulation of perinatal pulmonary apoptotic gene expression.     

Effect of overexpression of human Cu/Zn-SOD on activation-induced lymphocyte proliferation and apoptosis

The process of lymphocyte proliferation and apoptosis is known to be linked to oxidative stress. In the present study, we have used a new transgenic mouse model to investigate the effect of human Cu/Zn superoxide dismutase (Cu/Zn-SOD) overexpression on activation-induced lymphocytes proliferation and apoptosis. Cu/Zn-SOD activity was 3.5-fold higher in the spleen of the transgenic mice overexpressing Cu/Zn-SOD (Tg-Cu/Zn-SOD) compared to the wild-type littermates. Proliferative response of lymphocytes to lipopolysaccharide (LPS), Concanavalin A (Con A), and anti-CD3 was measured by [3H]-thymidine incorporation. Activation-induced apoptosis was determined by incubating the T cells with anti-CD3 (primary stimulus) for 72 h, followed by restimulation with Con A (secondary stimulus) for various times. Apoptosis was assessed by measuring DNA fragmentation using a spectrofluorimetric assay and monitoring the expression of the specific apoptotic markers (Fas/CD95 receptor and Fas/CD95 ligand (Fas-L) using flow cytometry. There was no significant difference in proliferative response of lymphocytes to LPS, Con A, or anti-CD3 in transgenic mice overexpressing human Cu/Zn superoxide dismutase (Tg-Cu/Zn-SOD) compared to wild-type littermates. In addition, no significant difference was observed in lymphocyte populations and subsets between Tg-Cu/Zn-SOD mice and wild-type littermates. However, splenic T cells from Tg-Cu/Zn-SOD mice exhibited a significantly (p <.05) higher level of activation-induced DNA fragmentation than T cells from wild-type littermates. The increase in DNA fragmentation was paralleled with an increase in the proportion of T cells expressing Fas and Fas-L molecules. The possible consequences of Cu/Zn-SOD overproduction on activation-induced apoptosis are discussed.     

Cathepsin D及Fas ligand在苦参碱诱导急性T淋巴母细胞白血病JM细胞株凋亡中的表达研究

为了检测苦参碱诱导JM细胞发生凋亡过程中Cathepsin D、Fas-L的表达情况,应用光镜及电镜观察加药及未加药组细胞形态学变化。免疫细胞化学染色观察Cathepsin D在细胞内的表达及定位。半定量PCR检测Cathepsin D mRNA在转录水平的变化并用Western Blot检测Cathepsin D、Fas-L蛋白表达。结果显示0．6mg/ml倒加药组细胞培养72h,出现凋亡形态学改变。免疫细胞化学染色Cathepsin D阳性信号主要位于呈凋亡形态学改变的胞浆和胞核内。其阳性细胞率在处理组明显高于对照组,处理组Cathepsin D的mRNA转录上调。处理组前体Cathepsin D(52kD)的条带亮度较对照组强,而切割后产物(32kD)亮度较对照组弱;Fas-L在处理组表达上调。提示：苦参碱诱导JM细胞的凋亡伴随Cathepsin D及Fas-L的表达改变。     

The human blastocyst regulates endometrial epithelial apoptosis in embryonic adhesion

The implanting blastocyst must appose and adhere to the endometrial epithelium and, subsequently, invade it. Locally regulated uterine epithelial apoptosis induced by the embryo is a crucial step of the epithelial invasion in rodents. To address the physiological relevance of this process in humans, we investigated the effect of single human blastocysts on the regulation of apoptosis in cultured human endometrial epithelial cells (hEEC) in both apposition and adhesion phases of implantation. Here, we report a co-ordinated embryonic regulation of hEEC apoptosis. In the apposition phase, the presence of a blastocyst rescues hEEC from the apoptotic pathway. However, when the human blastocyst adheres to the hEEC monolayer, it induces a paracrine apoptotic reaction. Fas ligand (Fas-L) was present at the embryonic trophoectoderm. Fas was localized at the apical cell surface of hEEC, and flow cytometry revealed that 60% of hEEC express Fas. Neutralizing adhesion assays revealed that the Fas/Fas-L death system may be an important mechanism to cross the epithelial barrier, which is crucial for embryonic adhesion, and the manipulation of this system could have potential clinical implications as an interceptive mechanism.     

Matrix attachment regulates Fas-induced apoptosis in endothelial cells: a role for c-flip and implications for anoikis

Survival of endothelial cells is critical for cellular processes such as angiogenesis. Cell attachment to extracellular matrix inhibits apoptosis in endothelial cells both in vitro and in vivo, but the molecular mechanisms underlying matrix-induced survival signals or detachment-induced apoptotic signals are unknown. We demonstrate here that matrix attachment is an efficient regulator of Fas-mediated apoptosis in endothelial cells. Thus, matrix attachment protects cells from Fas-induced apoptosis, whereas matrix detachment results in susceptibility to Fas-mediated cell death. Matrix attachment modulates Fas-mediated apoptosis at two different levels: by regulating the expression level of Fas, and by regulating the expression level of c-Flip, an endogenous antagonist of caspase-8. The extracellular signal-regulated kinase (Erk) cascade functions as a survival pathway in adherent cells by regulating c-Flip expression. We further show that detachment-induced cell death, or anoikis, itself results from activation of the Fas pathway by its ligand, Fas-L. Fas-L/Fas interaction, Fas-FADD complex formation, and caspase-8 activation precede the bulk of anoikis in endothelial cells, and inhibition of any of these events blocks anoikis. These studies identify matrix attachment as a survival factor against death receptor-mediated apoptosis and provide a molecular mechanism for anoikis and previously observed Fas resistance in endothelial cells.     

Apoptosis induced by adenovirus-mediated p14ARF expression in U2OS osteosarcoma cells is associated with increased Fas expression

The INK4A/ARF locus on chromosome 9 is a tumor suppressor gene frequently mutated in human cancers. In order to study the effects of p14ARF expression in tumor cells, we constructed a recombinant adenovirus containing p14ARF cDNA (Adp14ARF). Adp14ARF infection of U2OS osteosarcoma cells which has wild type p53 and mutant p14ARF revealed high levels of p14 (ARF) expression within 24h. In addition, Adp14ARF-mediated expressing of p14 (ARF) was associated with increased levels of p53, p21, and mdm2 protein. Growth inhibition assays following Adp14ARF infection demonstrated that the growth of U2OS cells was inhibited relative to infection with control virus. Furthermore, TUNEL analysis as well as PARP cleavage assays demonstrated that Adp14ARF infection was associated with increased apoptosis in U2OS cell line and that it was associated with Adp14ARF induced overexpression of Fas and Fas-L. Addition of Fas-L neutralizing antibody NOK-1 decreased Adp14-mediated cell death, indicating that p14 (ARF) induction of the Fas pathway is associated with increased apoptosis. The finding that Adp14ARF infection did not induce Fas expression in U2OS/E6 and MCF/E6 cells suggests that wild type p53 expression may be necessary for Adp14ARF-mediated induction of Fas. The observation that overexpression of p53 by Adp53 infection in MCF-7 does not induce increased Fas protein levels nor apoptotic cell death suggests that p53 overexpression is required but not sufficient enough for apoptosis. These studies suggest there are other mechanisms other than induction of p53 in ARF-mediated apoptosis and gene therapy using Adp14ARF may be a promising treatment option for human cancers containing wild type p53 and mutant or deleted p14 expression.     

High endothelial venules of the lymph nodes express Fas ligand.

Fas (CD95, APO-1) is widely expressed on lymphatic cells, and by interacting with its natural ligand (Fas-L), Fas induces apoptosis through a complex caspase cascade. In this study we sought to survey Fas-L expression in vascular and sinusoidal structures of human reactive lymph nodes. Immunohistochemical Fas-L expression was present in all paracortical high endothelial venules (HEVs), in cells lining the marginal sinus wall, and in a few lymphocytes, but only occasionally in non-HEV vascular endothelium. In the paracortical zone over 60% of all vessels and all paracortical HEVs showed Fas-L expression, whereas in the medullary zone less than 10% of the blood vessels were stained with Fas-L. Normal vessels outside lymph nodes mostly showed no Fas-L expression. We show that in human reactive lymph nodes Fas-L expression is predominantly present in HEVs. Because the circulating lymphocytes gain entry to nodal parenchyma by transendothelial migration through HEVs, the suggested physiological importance of Fas-L expression in these vessels lies in the regulation of lymphocyte access to lymph node parenchyma by possibly inducing Fas/Fas-L mediated apoptosis of activated Fas-expressing lymphoid cells. The Fas-L expressing cells in the marginal sinus might have a similar function for cells accessing the node in afferent lymph.     

Apoptosis-induced by TRAIL AND TNF-alpha in human multiple myeloma cells is not blocked by BCL-2

TRAIL, the ligand for the newly discovered DR-4 and DR-5 receptor is a member of the tumour necrosis factor (TNF) family of death signal tranduction proteins with a mechanism of cell death, similar to the Fas and Fas ligand (Fas-L) system. Here, we provide first time evidence that TRAIL and TNF-alpha are potent inducers of apoptosis in multiple myeloma (MM) cell lines and freshly isolated myeloma cells. TRAIL effectively induced extensive apoptosis in 8226 and ARP-1 MM cells in a time- and dose-dependent manner reaching 80% within 48 h of treatment with a dose of 160 ng/ml. Bcl-2 transfected 8226 and ARP-1 cells were equally sensitive to apoptosis by TRAIL. Apoptosis with TNFalpha, reached >60% within 48 h of treatment with a dose of 160 ng/ml. In addition to MM cell lines, freshly isolated, flow-sorted myeloma cells from 8 different MM patients expressing variable levels of bcl-2 were equally sensitive to both TRAIL and TNF-alpha. We have previously shown that anti-Fas-induced apoptosis is not blocked by endogenous or ectopic bcl-2 in MM cell lines. Here we extend our observation with Fas to include TNF-alpha and TRAIL to the apoptotic signals that are not be blocked by bcl-2, in MM cells.     

Promotion of neutrophil apoptosis by TNF-alpha

We examined the ability of TNF-alpha to modulate human neutrophil apoptosis. Neutrophils cultured with TNF-alpha alone undergo a low but significant increase in the number of apoptotic cells. More interestingly, when neutrophils were pretreated with TNF-alpha for 1-2 min at 37 degrees C and then were exposed to a variety of agents such as immobilized IgG, IgG-coated erythrocytes, complement-treated erythrocytes, zymosan, PMA, zymosan-activated serum, fMLP, Escherichia coli, and GM-CSF for 3 h at 37 degrees C, a marked stimulation of apoptosis was observed. Similar results were obtained in neutrophils pretreated with TNF-alpha for 30 min, 1 h, 3 h, and 18 h. Dose-dependent studies showed that TNF-alpha enhances neutrophil apoptosis at concentrations ranging from 1 to 100 ng/ml. In contrast to the observations made in neutrophils pretreated with TNF-alpha, there was no stimulation of apoptosis when TNF-alpha was added to neutrophils previously activated by conventional agonists. Experiments performed to establish the mechanism through which TNF-alpha promotes neutrophil apoptosis showed that neither reactive oxygen intermediates nor the Fas/Fas ligand system appear to be involved. Our results suggest that TNF-alpha plays a critical role in the control of neutrophil survival by virtue of its ability to induce an apoptotic death program which could be triggered by a variety of conventional agonists.     

缺氧环境下大鼠骨髓间充质干细胞凋亡相关蛋白和mRNA的表达

目的探讨大鼠骨髓间充质干细胞（MSCs）在缺氧环境下凋亡相关蛋白和mRNA的表达。方法将接种的P3细胞置于94％N2、1％O2和5％CO2缺氧箱中37℃孵育,分别于0．5h、1h、2h、4h、6h、8h和12h取出分别应用Annexin V／PI双染法进行流式细胞仪（FCM）分析MSCs凋亡率（Apoptotic Rate,AR）,并同步用免疫细胞化学、western blotting和Rt-PCR等方法检测Bax／Bcl-2,Fas／FasL和Caspase-3蛋白和mRNA的表达。结果1．缺氧前,免疫细胞化学法未检测到Bcl-2、Bax、Fas、FasL和Caspase-3蛋白表达,缺氧0．5h后均可较强表达;2．各缺氧时间点Bcl-2、Bax、Fas、FasL、Caspase-3蛋白和mRNA表达较缺氧前均显著性增高（P均〈0．05）;随缺氧时间延伸,Bcl-2蛋白和mRNA表达不显著增加（P〉0．05）,而Bax、Fas、FasL、Caspase-3蛋白和mRNA表达均显著增加（P均〈0．05）,但缺氧6-12h时间点之间表达均没有统计学意义（P均〉0．05）;3．AR和Bcl-2／Bax蛋白（r1=0．417,P=0．043）及mRNA（r2=-0．435,P=0．040）呈显著负相关,而和Fas（r1=0．639,P=0．025;r2=0．711,P=0．018）、Fas-L（r1=0．581,P=0．022;r2=0．605,P=0．037）、Caspase-3（r1=0．704,P=O．014;r2=0．657,P=0．026）蛋白及mRNA均呈显著正相关。结论在缺氧促进MSCs凋亡的过程中,Bcl-2蛋白和mRNA可能起着保护作用,而Bax、Fas-L、Fas、Caspase-3蛋白和mRNA可能在MsCs凋亡的进程中起着促进作用。     

Oxidative stress induces the expression of Fas and Fas ligand and apoptosis in murine intestinal epithelial cells

Intestinal epithelial cell function is compromised by local immune and inflammatory responses. In this study, we examined the possibility that intestinal epithelial cell injury occurs in the presence of activated inflammatory cells, such as neutrophils and macrophages, via production of reactive oxygen species (ROS). Following exposure to 50–150 μM H₂O₂, levels of mRNA and protein for Fas and, to a lesser degree, Fas-L were increased and intestinal epithelial cells underwent apoptosis. Treatment of H₂O₂-exposed cells with agonistic anti-Fas antibody, but not isotype control antibody, significantly enhanced apoptosis. Apoptosis was associated with the activation of caspase 8, while Z-IETD, an inhibitor of caspase 8, blocked apoptosis of H₂O₂-exposed intestinal epithelial cells. Thus, ROS induced Fas and Fas-L expression in association with intestinal epithelial cell apoptosis. These data support the hypothesis that, following exposure to oxidative stress, enterocytes are primed for cell death via Fas-mediated pathways.     

UV-B Irradiated Cell Lines Execute Programmed Cell Death in Various Forms

We investigated changes typical for apoptosis in various cell lines after UV-B irradiation. Using established methods for detection of apoptosis we demonstrate changes of cellular morphology, phosphatidylserine (PS) exposure, ollgonucleosomal DNA fragmentation and generation of hypochrome nuclei. To isolated high-molecular-weight (hmwt) DNA fragments we engaged a new method avoiding pulse field gel electrophoresis. Most UV-B irradiated cell lines showed oligonucleosomal DNA fragmentation, hypochrome nuclei, morphological changes, annexin-V binding and positive TUNEL reaction. However, no oligonucleosomal DNA fragmentation could be detected in Raji and HaCaT cells. Whereas HaCaT cells displayed all other changes typical for apoptosis, Raji cells were TUNEL negative, formed low amounts of hmwt DNA and showed an 'atypically' low hypochrome shift. Nevertheless, UV-B irradiated Raji cells excluded propidium iodide (PI), bound annexin-V and stopped proliferation. This suggests that Raji cells underwent growth arrest with exposure of PS being the only feature of apoptosis. However, in the presence of phagocytes expressing the phosphatidylserine receptor these cells would share the removal pathway with apoptotic cells. Since UV-B induced programmed cell death differs in dependence of cells under investigation, the failure to detect oligonucleosomal DNA fragmentation or chromatin condensation is not suitable to exclude programmed (apoptotic?) cell death.     

Pigment Epithelial-derived Factor (PEDF)-triggered Lung Cancer Cell Apoptosis Relies on p53 Protein-driven Fas Ligand (Fas-L) Up-regulation and Fas Protein Cell Surface Translocation

Pigment epithelium-derived factor (PEDF), a potent antiangiogenesis agent, has recently attracted attention for targeting tumor cells in several types of tumors. However, less is known about the apoptosis-inducing effect of PEDF on human lung cancer cells and the underlying molecular events. Here we report that PEDF has a growth-suppressive and proapoptotic effect on lung cancer xenografts. Accordingly, in vitro, PEDF apparently induced apoptosis in A549 and Calu-3 cells, predominantly via the Fas-L/Fas death signaling pathway. Interestingly, A549 and Calu-3 cells are insensitive to the Fas-L/Fas apoptosis pathway because of the low level of cell surface Fas. Our results revealed that, in addition to the enhancement of Fas-L expression, PEDF increased the sensitivity of A549 and Calu-3 cells to Fas-L-mediated apoptosis by triggering the translocation of Fas protein to the plasma membrane in a p53- and FAP-1-dependent manner. Similarly, the up-regulation of Fas-L by PEDF was also mediated by p53. Furthermore, peroxisome proliferator-activated receptor γ was determined to be the upstream regulator of p53. Together, these findings uncover a novel mechanism of tumor cell apoptosis induced by PEDF and provide a potential therapeutic strategy for tumors that are insensitive to Fas-L/Fas-dependent apoptosis because of a low level of cell surface Fas.     

APOPTOSIS-INDUCED BY TRAIL AND TNF-α IN HUMAN MULTIPLE MYELOMA CELLS IS NOT BLOCKED BY BCL-2

TRAIL, the ligand for the newly discovered DR-4 and DR-5 receptor is a member of the tumour necrosis factor (TNF) family of death signal tranduction proteins with a mechanism of cell death, similar to the Fas and Fas ligand (Fas-L) system. Here, we provide first time evidence that TRAIL and TNF-α are potent inducers of apoptosis in multiple myeloma (MM) cell lines and freshly isolated myeloma cells. TRAIL effectively induced extensive apoptosis in 8226 and ARP-1 MM cells in a time- and dose-dependent manner reaching 80% within 48 h of treatment with a dose of 160 ng/ml. Bcl-2 transfected 8226 and ARP-1 cells were equally sensitive to apoptosis by TRAIL. Apoptosis with TNFα, reached >60% within 48 h of treatment with a dose of 160 ng/ml. In addition to MM cell lines, freshly isolated, flow-sorted myeloma cells from 8 different MM patients expressing variable levels of bcl-2 were equally sensitive to both TRAIL and TNF-α. We have previously shown that anti-Fas-induced apoptosis is not blocked by endogenous or ectopic bcl-2 in MM cell lines. Here we extend our observation with Fas to include TNF-α and TRAIL to the apoptotic signals that are not be blocked by bcl-2, in MM cells.     

Increased apoptosis in lamina propria B cells during polymicrobial sepsis is FasL but not endotoxin mediated

Recent studies from our laboratory demonstrated that mucosal lymphoid tissue such as Peyer's patch cells and lamina propria (LP) B lymphocytes from mice shows evidence of increased apoptosis after sepsis that is associated with localized inflammation/activation. The mechanism for this is poorly understood. Endotoxin as well as Fas/Fas ligand (FasL) have been shown to augment lymphocyte apoptosis; however, their contribution to the increase of apoptosis in LP B-cells during sepsis is not known. To study this, sepsis was induced by cecal ligation and puncture (CLP) in endotoxin-tolerant C3H/HeJ or FasL-deficient C3H/HeJ-FasL(gld) (FasL(-)) mice and LP lymphocytes were isolated 24 h later. Phenotypic, apoptotic, and functional indexes were assessed. The number of LP B cells decreased markedly in C3H/HeJ mice but not in FasL-deficient animals at 24 h after CLP. This was associated with comparable alteration in apoptosis and Fas antigen expression in the B cells of these mice. Septic LP lymphocytes also showed increased IgA production, which was absent in the FasL-deficient CLP mice. Furthermore, Fas ligand deficiency appeared to improve survival of septic challenge. These data suggest that the increase in B cell apoptosis in septic animals is partially due to a Fas/FasL-mediated process but not endotoxin.