ABSTRACT
In contrast to very immature dendritic cells (DC), mature DC are largely resistant to death by CD95 (CD95/APO-1) ligation. Investigation of other potential death-inducing ligands showed that mature DC were instead highly susceptible to apoptosis induced by cross-linking of MHC class II. Thus, increasing DC maturity correlates with increased resistance to CD95 killing, but an increased susceptibility to class II-mediated killing. Anti-I-A/I-E monoclonal antibodies (mAb) induced rapid (<2 h) apoptotic cell death in mature epidermal, spleen and bone marrow-derived DC, as determined by annexin/propidium iodide staining, morphological changes, decreased diploidy and loss in mitochondrial membrane potential. Although full class II-mediated killing required DC cytoskeletal motion, divalent cations and phosphatase activity, neither caspase activation, respiration, RNA or protein synthesis, NO production, nor CD95:CD95L interactions were required. Strikingly, DC pretreated by CD40 mAb cross-linking, but not by lipopolysaccharide or TNF-alpha, were completely resistant to class II-mediated killing. CD40-mediated protection was reduced in the presence of the SB202190 inhibitor of the mitogen-activated protein kinase p38 pathway, but appeared to be independent of p42/44 extracellular signal-related kinase or NF-KB activation. Our findings show that in addition to its role as an activator of antigen-presenting cell function, CD40 provides an important counter-signal against class II-induced apoptosis. Thus, these data point to an important role of the T cell in regulating DC survival.
Subject(s)
Apoptosis , CD40 Antigens/physiology , Dendritic Cells/physiology , Histocompatibility Antigens Class II/physiology , Animals , CD40 Ligand , Cell Survival , Membrane Glycoproteins/physiology , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Signal Transduction , fas Receptor/analysisABSTRACT
Dendritic cells (DCs) disappear from lymph nodes 1 to 2 days after antigen presentation, presumably by apoptosis. To evaluate the role of death ligands in elimination of DCs, we analyzed the sensitivity of human DCs to CD95 ligand (CD95L) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). We found mature DCs to be resistant to killing via CD95L or TRAIL, whereas only immature DCs were partially sensitive. However, all DC populations expressed CD95, TRAIL-R2, and TRAIL-R3 at comparable levels, suggesting that sensitivity to death ligand-induced DC apoptosis is not regulated at the receptor level. Interestingly, mature DCs highly expressed the caspase 8 inhibitory protein cFLIP, whereas only low levels were detected in immature DCs. Thus, death ligand sensitivity proved to be dependent on DC maturation and inversely correlated with expression levels of cFLIP. Induction of apoptosis by TRAIL or CD95L does not seem to play a role in the elimination of mature DCs, but instead might serve to regulate immature DC populations.
Subject(s)
Apoptosis , Dendritic Cells/physiology , Membrane Glycoproteins/pharmacology , Tumor Necrosis Factor-alpha/pharmacology , fas Receptor/pharmacology , Antigens, CD , Apoptosis Regulatory Proteins , Caspase 8 , Caspase 9 , Caspases/metabolism , Cells, Cultured , Dendritic Cells/chemistry , Dinoprostone/pharmacology , Drug Resistance , Granulocyte-Macrophage Colony-Stimulating Factor/pharmacology , Humans , Immunoglobulins/analysis , Interleukin-1/pharmacology , Interleukin-4/pharmacology , Interleukin-6/pharmacology , Membrane Glycoproteins/analysis , TNF-Related Apoptosis-Inducing Ligand , Tumor Necrosis Factor-alpha/analysis , fas Receptor/analysis , CD83 AntigenABSTRACT
Disappearance of antigen presenting cells (APC) from the lymph node occurs following antigen specific interactions with T cells. We have investigated the regulation of CD95 (Apo-1/Fas) induced apoptosis during murine dendritic cell (DC) development. Consistent with the moderate levels of CD95 surface expression and low, or absent, MHC class II expression, immature DC in bone marrow cultures were highly sensitive to CD95 induced apoptosis, but insensitive to class II mediated apoptosis. In contrast, mature splenic, epidermal and bone marrow derived DC were fully resistant to CD95 induced cell death, but sensitive to class II induced apoptosis. Although caspase 3 and 8 activation was detected in immature DC undergoing CD95L-induced apoptosis, the pan-caspase inhibitor zVAD-fmk did not inhibit the early events of CD95-induced mitochondrial depolarisation or phosphatidyl serine exposure and only partially inhibited the killing of immature DC. In contrast, zVAD-fmk was completely effective in preventing CD95L mediated death of murine thymocytes. Collectively, these data do not support a major role of CD95: CD95L ligation in apoptosis of mature DC, but rather emphasise the existence of distinct pathways for the elimination of DC at different stages of maturation.
Subject(s)
Apoptosis/immunology , Dendritic Cells/cytology , Dendritic Cells/immunology , Histocompatibility Antigens Class II/metabolism , fas Receptor/metabolism , Amino Acid Chloromethyl Ketones/pharmacology , Animals , Apoptosis/drug effects , Bone Marrow Cells/cytology , Bone Marrow Cells/immunology , Bone Marrow Cells/metabolism , Caspases/metabolism , Cell Differentiation/immunology , Cross-Linking Reagents/metabolism , Cysteine Proteinase Inhibitors/pharmacology , Dendritic Cells/metabolism , Histocompatibility Antigens Class II/analysis , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Mitochondria/metabolism , fas Receptor/analysisABSTRACT
Two outbreaks of haemorrhagic fever caused by a Marburg-like virus occurred in the Sudan and Zaire from August to November 1976. The inital epidemiological investigations and emergency control measures were carried out by Sudanese and Zairian health personnel and several of them unfortunately died in the course of their duties. In view of the unusual gravity of the outbreaks and the unknown nature of the agent, assistance was provided by a WHO team in the Sudan and a multinational team in Zaire. A consultation arranged by WHO was held at the London School of Hygiene and Tropical Medicine in January 1977 to review the experience acquired during these outbreaks and to make recommendations which, to a large extent, may be applicable to other outbreaks of suspected viral haemorrhagic fever. Because it is felt that this information would be of value to many health administrations, large abstracts of the report of this consultation are given here.