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CD40, a TNF-R-related cell surface receptor, is shown here to be expressed by glioma cells in vitro and in vivo. Glioma cell lines expressing low levels of CD40 at the cell surface resist cytotoxic effects of CD40L. CD40 gene transfer sensitizes glioma cells to CD40L. Inhibition of protein synthesis potentiates cell death which involves CD40 clustering and caspases 8 and 3 processing. CD40-transfected LN-18 cells acquire resistance to CD95L. In contrast, subtoxic concentrations of CD40L strongly sensitize these cells for TNF-alpha-induced apoptosis. Bispecific CD40xCD95 antibodies specifically kill glioma cells, disclosing the property of endogenous CD40 to facilitate death signalling.

Human plasmacytoid dendritic cells (DC) (PDC, CD123+) and myeloid DC (MDC, CD11c+) may be able to discriminate between distinct classes of microbial molecules based on a different pattern of Toll-like receptor (TLR) expression. TLR1-TLR9 were examined in purified PDC and MDC. TLR9, which is critically involved in the recognition of CpG motifs in mice, was present in PDC but not in MDC. TLR4, which is required for the response to LPS, was selectively expressed on MDC. Consistent with TLR expression, PDC were susceptible to stimulation by CpG oligodeoxynucleotide (ODN) but not by LPS, while MDC responded to LPS but not to CpG ODN. In PDC, CpG ODN supported survival, activation (CD80, CD86, CD40, MHC class II), chemokine production (IL-8, IP-10) and maturation (CD83). CD40 ligand (CD40L) and CpG ODN synergized to activate PDC and to stimulate the production of IFN-alpha and IL-12 including bioactive IL-12 p70. Previous incubation of PDC with IL-3 decreased the amount of CpG-induced IFN-alpha and shifted the cytokine response in favor of IL-12. CpG ODN-activated PDC showed an increased ability to stimulate proliferation of naive allogeneic CD4 T cells, butTh1 polarization of developing T cells required simultaneous activation of PDC by CD40 ligation and CpG ODN. CpG ODN-stimulated PDC expressed CCR7, which mediates homing to lymph nodes. In conclusion, our studies reveal that IL-12 p70 production by PDC is under strict control of two signals, an adequate exogenous microbial stimulus such as CpG ODN, and CD40L provided endogenously by activated T cells. Thus, CpG ODN acts as an enhancer of T cell help, while T cell-controlled restriction to foreign antigens is maintained.

The monocytic cell line U937 is a frequently used model in studies on the cytotoxic effect of tumour necrosis factor (TNF). Two sublines of this cell line, termed U937(G) and U937(M), revealing different patterns of response to this cytokine, have been identified. The U937(G) cells, similarly to the cells obtained from ATCC, were resistant to the cytotoxic action of TNF in the absence of the protein-synthesis blocker cycloheximide (CHX). The U937(M) cells, however, were sensitive to the cytotoxic action of TNF both in the presence and absence of cycloheximide. Genetic analysis of the U937 sublines confirmed their common origin. The described U937 sublines may be useful models for analysis of the mechanisms of response to TNF. Additionally, our observation underscores the variability of the U937 cell line, which is described by most authors as a TNF-sensitive line.

CD40, a member of the TNF receptor family, has been characterized as an important T-B cell interaction molecule. In B cells it co-stimulates isotype switching, proliferation, adhesion and is involved in cell death regulation. In addition to B cells, CD40 expression was found on transformed cells and carcinomas. However, little is known about its functions in these cell types. Recent studies show that CD40 mediates the production of pro-inflammatory cytokines in non-hematopoietic cells, inhibits proliferation or induces cell death. In some cell types the apoptotic program triggered by CD40 is only executed when protein synthesis is blocked, suggesting the existence of constitutively expressed resistance proteins. Here we demonstrate that CD40, similar to the 55-kDa TNF receptor (p55TNFR), has a dual role in the regulation of apoptosis in such cells. In the fibroblast cell line SV80 both CD40 and the p55TNFR trigger apoptosis when protein synthesis is blocked with cycloheximide (CHX). Simultaneous activation of both receptors results in markedly enhanced cell death. However, CD40 activation more than 4 h prior to a challenge with TNF/CHX paradoxically conferred resistance to TNF-induced cell death. Protection correlated with NF-kappaB induction and up-regulation of the anti-apoptotic zinc finger protein A20. Overexpression of A20 in turn rendered SV80 cells resistant to TNF cytotoxicity. In conclusion, our data provide evidence that CD40 may regulate cell death in non-hematopoietic cells in a dual fashion: the decision upon apoptosis or survival of a CD40-activated cell seems to depend on its ability to up-regulate resistance factors.

The B cell surface molecule CD40 may be activated either by its ligand CD40L or by anti-CD40 antibodies. In this study, five new anti-CD40 monoclonal antibodies (MAb) were characterized. Bioactivity of the MAb was assessed using a receptor hybrid consisting of the extracellular domain of CD40 and the intracellular domain of the p55 TNF receptor as a model for CD40 activation. Two agonistic MAb were able to enhance the activation of this CD40 hybrid CD40L. These MAb bound to an epitope that was not located within the CD40L-binding region indicating that activation of CD40 occurs epitope-independent. A second pair of ligand mimetic anti-CD40 MAb which appeared to bind to the CD40L binding site decreased CD40L bioactivity. With regard to ligand mimetic effects binding of the CD40L epitope was not of advantage. Combining anti-CD40 MAb with different epitope specificities or cross linking anti-CD40 MAB with secondary antibodies enhanced ligand mimetic effects. These data clearly show that ligand or antibody-mediated receptor aggregation is the major mechanism by which CD40 is activated. Furthermore, our data support that an aggregate of activated receptors is favorable in regard to CD40 activation.

CD40 is known as an important T-B cell interaction molecule which rescues B lymphocytes from undergoing apoptosis. Like other receptors of the tumor necrosis factor (TNF) receptor gene family, CD40 is expressed on cells of different tissue origins including some transformed cells. In contrast to its well-studied effects on B cells, the biological functions of CD40 in non-immune cells remain largely unknown. Here we show that CD40 ligation induces apoptotic cell death in transformed cells of mesenchymal and epithelial origin. This CD40-mediated cell death seems to use a preformed signaling pathway since it occurs even when protein synthesis is blocked. Notably, the CD40 cytoplasmic domain shares a structural homology with the recently defined "death domains" of the 55-kD TNF receptor (p55TNFR) and Fas. Despite these structural similarities, differences are seen in the way phorbol myristate acetate, interleukin 1, TNF, and various metabolic inhibitors influence the cellular responsiveness to CD40, p55TNFR, and Fas-mediated killing. Our study indicates that CD40 induces cell death by a distinct mechanism.

The receptor for lipopolysaccharide LPS (CD14) exists in a membrane-associated (mCD14) and a soluble form (sCD14). Previous studies indicate that monocytes produce sCD14 by limited proteolysis of the membrane-bound receptor. In this study we demonstrate that human monocytes also produce sCD14 by a protease-independent mechanism. To investigate the molecular nature of this second pathway we studied sCD14 formation in the monocytic cell line Mono Mac 6 (MM6) and in CD14 transfectants. Both MM6 and the CD14 transfectants constitutively produce sCD14 by a protease-independent mechanism. Structural analysis of sCD14 produced by the CD14 transfectants reconfirmed the presence of the COOH terminus predicted from the cDNA. Since glycosylphosphatidylinositol anchor attachment is associated with the removal of a hydrophobic C-terminal signal peptide, our finding demonstrates that the transfectants secrete sCD14 which escaped this posttranslational modification. Identical results obtained for sCD14 derived from peritoneal dialysis fluid of a patient with kidney dysfunction show the in vivo relevance of this pathway for sCD14 production.

The B cell activation molecule CD40 and the p55 tumor necrosis factor receptor (p55TNFR) belong to the same family of structurally conserved proteins. We constructed a chimeric receptor consisting of the CD40 extracellular and transmembrane domains and the p55TNFR intracellular domain. This receptor hybrid retained the biological activity and the ligand specificity of the respective wild-type receptor domains. Thus it exerted a marked cytotoxic effect in three different transfected cell lines after activation not only with anti-CD40 antibody but also with CD40 ligand (CD40L) in soluble and membrane-bound forms. Using hybrid-transfected baby hamster kidney cells we demonstrated that herpesvirus saimiri-transformed human CD4+ T lymphocytes constitutively express bioactive CD40 ligand on their surface. The hybrid receptor-based assay was highly specific for CD40 activating reagents and more sensitive than an assay measuring CD40-mediated B cell rescue from apoptosis. Hence CD40/p55TNFR transfectants may be useful for dissecting CD40L-mediated events in T-B cell interactions, and also to detect a defective CD40L molecule in putative hyper-IgM syndrome patients.

Objective. To determine the value of measurement of serum soluble tumor necrosis factor receptor (sTNFR), compared with established parameters such as anti–double-stranded DNA, in monitoring systemic lupus erythematosus (SLE) disease activity, and to determine whether serum sTNFR are bioactive and can effectively inhibit TNF bioactivity. Methods. Fifty-three consecutive ambulatory or hospitalized SLE patients and 140 consecutive healthy subjects were enrolled in a prospective cohort study. Serum levels of sTNFR were measured by a unique 2-sided capture enzyme-linked immunosorbent assay using mouse monoclonal antibodies and rabbit antisera against the sTNFR. Results. The mean ± SD concentrations of both the p55 (type I) and p75 (type II) soluble receptors were significantly higher in a group of 46 SLE patients than in controls: 1.89 ± 0.89 ng/ml versus 0.77 ± 0.19 ng/ml and 7.25 ± 3.89 ng/ml versus 3.02 ± 0.57 ng/ml, respectively (P < 0.0001 for both). The incidence and the extent of the increase among the healthy subjects and these patients (as well as in 7 additional patients on whom sequential studies were performed) correlated with disease activity more than did the occurrence of serum anti-DNA antibodies (correlation coefficients with disease activity 0.81 and 0.85 for p55 and p75 sTNFR, respectively, and 0.51 for anti-DNA antibodies). The increase in sTNFR levels seems to reflect, largely, enhanced formation, and only to a minor extent, reduced clearance due to impairment of renal function. Sera of the SLE patients had a marked inhibitory effect on the in vitro cytocidal activity of TNF, and this was shown to result entirely from their higher sTNFR receptor concentration. Conclusion. An increase in serum levels of sTNFR may become a useful marker for SLE activity since it shows a stronger correlation than do any other laboratory or clinical parameters employed presently in the daily clinical setting. At the concentrations attained in the serum of SLE patients, sTNFR effectively inhibit the bioactivity of TNF and may thus be a significant determinant of the intensity of the manifestations of SLE.

TNF family members and their receptors contribute to increased gene expression for inflammatory processes and intracellular cascades leading to programmed cell death, both via activation of NF-kappaB. TNF receptor (TNFR)-associated factors (TRAFs) are cytoplasmic adaptor proteins binding to various receptors of the TNFR family. In an attempt to delineate the role of individual TRAFs, we compared NF-kappaB activation by CD40(wt) and CD40 mutants with different TRAF recruitment patterns. Recognized only recently, NF-kappaB signaling occurs at least via two different pathways. Each pathway results in nuclear translocation of two different Reldimers, the canonical p50/RelA and the noncanonical p52/RelB. Here, we show that via TRAF6, CD40 mediates only the activation of the canonical NF-kappaB pathway. Via TRAF2/5, CD40 activates both the canonical and the noncanonical NF-kappaB pathways. We observed that TRAF3 specifically blocked the NF-kappaB activation via TRAF2/5. This inhibitory effect of TRAF3 depends on the presence of an intact zinc finger domain. Paradoxically, suppression of TRAF2/5-mediated NF-kappaB activation by TRAF3 resulted in enhanced transcriptional activity of TRAF6-mediated canonical NF-kappaB emanating from CD40. We also observed that 12 TNFR family members (p75TNFR, LTbetaR, RANK, HVEM, CD40, CD30, CD27, 4-1BB, GITR, BCMA, OX40, and TACI) are each capable of activating the alternative NF-kappaB pathway and conclude that TRAF3 serves as a negative regulator of this pathway for all tested receptors.

The T-cell population of a patient with persistent polyclonal B-cell lymphocytosis (PPBL) presenting with an intermittent Epstein-Barr virus (EBV)-associated disease was studied. Unstimulated T-cells did not express CD40 ligand (CD40L), whereas activation with IL-2 led to expression of this costimulatory molecule. CD40L expression was inhibited upon incubation with the supernatant of an EBV-positive B-cell line (SM) which had been grown spontaneously from the patient's peripheral blood cells. The supernatant of SM cells effectively inhibited cytotoxic T-cells. Elevated levels of IL-10, TNF-alpha and soluble CD40 were found in the supernatant of SM cells. Additionally, enhanced levels of LMP-1 protein were detected.

The finding that the two tumor necrosis factor receptors (TNFR) exist in soluble form in various body fluids not only has substantiated the paradigm of naturally existing soluble cytokine receptors but also has represented a milestone on the road to the biochemical and biological characterization of the two TNFRs. This chapter gives a simple, basic protocol for the purification of the two soluble TNFRs. The protocols found here may be easily adapted for the purification of various other soluble cytokine receptors. The purified proteins may be used in biological experiments or for the generation of specific research tools such as polyclonal or monoclonal antibodies.

The finding that the two tumor necrosis factor receptors (TNFR) exist in soluble form in various body fluids not only has substantiated the paradigm of naturally existing soluble cytokine receptors but also has represented a milestone on the road to the biochemical and biological characterization of the two TNFRs. This chapter gives a simple, basic protocol for the purification of the two soluble TNFRs. The protocols found here may be easily adapted for the purification of various other soluble cytokine receptors. The purified proteins may be used in biological experiments or for the generation of specific research tools such as polyclonal or monoclonal antibodies.

The adenovirus (Ad) early transcription unit E3 encodes immunosubversive functions. The E3 transmembrane proteins 10.4 and 14.5 form a complex that down-regulates the epidermal growth factor receptor and apoptosis receptors from the cell surface by diverting them to endosomes/lysosomes for degradation. The latter process protects infected cells from ligand-induced apoptosis. The mechanism by which 10.4-14.5 mediate re-routing remains elusive. We examined the role of putative YXXΦ and dileucine (LL) transport motifs within Ad2 10.4-14.5 for target protein modulation. By generating stable E3 transfectants expressing 10.4-14.5 proteins with alanine substitutions in these motifs, we show that 3 of the 5 motifs are essential for functional activity. Whereas tyrosine 74 in 14.5 appears to be important for efficient 10.4-14.5 interaction, the 122YXXΦ motif in 14.5 and the dileucine motif Leu 87-Leu88 in 10.4 constitute genuine transport motifs: disruption of either motif abolished binding to the cellular adaptor proteins AP-1 and AP-2, as shown by surface plasmon resonance spectroscopy, and caused missorting, dramatically altering cell surface appearance and the intracellular location of viral proteins. Fluorescence-activated cell sorter analysis and immunofluorescence data provide evidence that Tyr122 in 14.5 is essential for rapid endocytosis of the 10.4-14.5 complex, whereas the 10.4LL motif acts down-stream and protects 10.4-14.5 from extensive degradation by rerouting it into a recycling pathway. Infection of primary cells with adenoviruses carrying the relevant point mutations confirmed the crucial role of these transport motifs for down-regulation of Fas, TRAIL-R1, TRAIL-R2, and epidermal growth factor receptor. Thus, two distinct transport motifs present in two proteins synergize for efficient target removal and immune evasion.

The oncogenic latent membrane protein 1 (LMP1) of the Epstein-Barr virus recruits tumor necrosis factor-receptor (TNFR)-associated factors (TRAFs), the TNFR-associated death domain protein (TRADD) and JAK3 to induce intracellular signaling pathways. LMP1 serves as the prototype of a TRADD-binding receptor that transforms cells but does not induce apoptosis. Here we show that TRAF6 critically mediates LMP1 signaling to p38 mitogen-activated protein kinase (MAPK) via a MAPK kinase 6-dependent pathway. In addition, NF-kappaB but not c-Jun N-terminal kinase 1 (JNK1) induction by LMP1 involves TRAF6. The PxQxT motif of the LMP1 C-terminal activator region 1 (CTAR1) and tyrosine 384 of CTAR2 together are essential for full p38 MAPK activation and for TRAF6 recruitment to the LMP1 signaling complex. Dominant-negative TRADD blocks p38 MAPK activation by LMP1. The data suggest that entry of TRAF6 into the LMP1 complex is mediated by TRADD and TRAF2. In TRAF6-knockout fibroblasts, significant induction of p38 MAPK by LMP1 is dependent on the ectopic expression of TRAF6. We describe a novel role of TRAF6 as an essential signaling mediator of a transforming oncogene, downstream of TRADD and TRAF2.

SUMMARYCD40 and its ligand CD40L are key players in T cell–B cell interaction and T cell–antigen-presenting cell (APC) interaction. Inhibition of CD40–CD40L interaction leads to severe humoral and cellular immunodeficiency. In this study we examined the presence of soluble CD40 (sCD40) in the serum of haemodialysis (HD) patients, CAPD patients, chronic renal failure (CRF) patients and healthy donors in order to evaluate the possible involvement of CD40 in uraemic immunodeficiency. Soluble CD40 was detected in the serum of healthy donors (n = 41) with a mean of 0.14 ± 0.12 ng/ml and in the urine of healthy donors with a mean of 1.80 ± 0.74 ng/ml. Soluble CD40 was highly elevated in all patients with impaired renal function. HD patients (n = 22) had up to 100-fold elevated sCD40 levels with a mean concentration of 8.32 ± 4.11 ng/ml, whereas CAPD patients (n = 10) had considerably lower levels of sCD40 with a mean of 3.58 ± 2.40 ng/ml. A strong correlation between sCD40 and serum creatinine levels was noted in CRF patients (n = 66). The highly elevated levels of sCD40 may point to the involvement of CD40 and its ligand CD40L in the clinical manifestation of uraemic immunodeficiency.

Several members of the tumour necrosis factor receptor (TNF-R) superfamily can induce cell death. For TNF-R1, Fas/APO-1, DR3, DR6, TRAIL-R1 and TRAIL-R2, a conserved 'death domain' in the intracellular region couples these receptors to activation of caspases. However, it is not yet known how TNF receptor family members lacking a death domain, such as TNF-R2, CD40, LT-betaR, CD27 or CD30, execute their death-inducing capability. Here we demonstrate in different cellular systems that cytotoxic effects induced by TNF-R2, CD40 and CD30 are mediated by endogenous production of TNF and autotropic or paratropic activation of TNF-R1. In addition, stimulation of TNF-R2 and CD40 synergistically enhances TNF-R1-induced cytotoxicity. These findings describe a novel pro-apoptotic mechanism induced by some members of the TNF-R family.

Tumor necrosis factor (TNF) and lymphotoxin alpha (LT alpha) are closely related cytokines which bind with nearly identical affinities to the same pair of cell surface receptors, p55 and p75TNFR. Therefore it is assumed that TNF and LT alpha are redundant cytokines. This study, however, demonstrates that TNF and LT alpha differ significantly with regard to their mitogenic and cytotoxic potentials. LT alpha's superior mitogenic effect could be explained by its formation of a more stable trimer. In contrast to the TNF trimer, which disintegrated under physiological conditions into biologically inactive monomers, the LT alpha trimer remained stable for several days. Accordingly, LT alpha more effectively induced fibroblast growth which demands long-term presence of the cytokine. TNF's superior cytotoxicity, which requires only short-term impact of the cytokine, could be attributed to a distinct interaction with the human p55TNFR. This was demonstrated in NIH 3T3 cells transfected with the human p55TNFR, where cytotoxicity is mediated exclusively by the transfected receptor. Although the p55ATNFR had virtually identical affinities for TNF and LT alpha, as defined by Scatchard analysis, it nevertheless discriminated between binding of each cytokine and showed a 200-fold enhanced cytotoxicity mediated by TNF.

The chromosomal translocation t(7;12) was described recently in MLL negative acute myeloid leukemias of infancy associated with a very poor clinical outcome. The rearrangement involves the genes HLXB9 (7q36) and ETV6 (12p13) with a fusion transcript of exon1/HLXB9 and exon3/ETV6. An alternative in frame splicing variant of exon1/HLXB9 to exon2/ETV6 is also detectable. Leukemic bone marrow samples of 42 infants, diagnosed in Germany with AML, were screened for the fusion transcript HLXB9/ETV6 with RT-PCR. Inclusion criteria were diagnosis of AML, age Conclusion: The HLXB9/ETV6 fusion transcript can be found in 17% of infants with MLL-negative AML in a German cohort. HLXB9/ETV6 positive leukemias show no increased expression on HOXA9 and MEIS1, but coexpression of T-cell markers and inhibition of the non-canonical NF-kappaB pathway on protein level. HLXB9/ETV6 did not induce malignant transformation in murine hematopoietic precursor cells.

Affinity chromatography of crude human urinary proteins on either human rIL-6, human rIFN-gamma, or anti-IFN-gamma-R mAb yielded the two respective soluble receptors in significant quantities. A single sequence of 30 amino acid residues was obtained by NH2-terminal microsequencing of the protein peak purified in tandem by affinity chromatography on an IL-6 column and reversed-phase HPLC. This sequence was identical to the predicted NH2-terminal sequence of IL-6-R as previously reported. Analysis of the eluted proteins from both IFN-gamma and anti-IFN-gamma-R columns by inhibition of solid phase RIA, ELISA, SDS-PAGE, and Western blotting proved the existence of soluble IFN-gamma-R in normal urine. Our finding, together with the already known presence of urinary TNF binding proteins and a soluble IL-2-R both in plasma and in urine, indicates that release of soluble cytokine receptors into body fluids is a general phenomenon that occurs under normal physiological conditions.

A severe congenital deficiency of protein C was diagnosed in a 10-month-old girl who had been suffering from skin necrosis since the age of 7 months. The patient was treated initially with fresh frozen plasma, 10 ml per kg body weight, every 24 h. Following treatment, the mean plasma level of protein C was 0.1 U/ml after 30 min and less than 0.02 U/ml after 24 h. The child was then treated with a concentrate of human protein C and S, 100 U protein C per kg body weight, given every 48 h for a period of 9 months. The mean plasma level of protein C was 0.93 U/ml 30 min after administration of the concentrate and 0.13 and 0.08 U/ml after 24 and 48 h, respectively. The mean post-transfusional in vivo recovery of protein C was 44% and the half life was 8.3 h. The mean plasma level of 'free' protein S increased from 1.1 to 2.2 U/ml after administration of the concentrate. There was no increase in 'bound' protein S. The in vivo recovery of 'free' protein S was 49% and the half life was about 17 h. Since the start of this replacement therapy using a human protein C and S concentrate, the patient has not developed any thromboembolic complications. These results indicate the therapeutic value of human protein C and S concentrate in the treatment of severe protein C deficiency.

Affinity chromatography of crude human urinary proteins on either human rIL-6, human rIFN-gamma, or anti-IFN-gamma-R mAb yielded the two respective soluble receptors in significant quantities. A single sequence of 30 amino acid residues was obtained by NH2-terminal microsequencing of the protein peak purified in tandem by affinity chromatography on an IL-6 column and reversed-phase HPLC. This sequence was identical to the predicted NH2-terminal sequence of IL-6-R as previously reported. Analysis of the eluted proteins from both IFN-gamma and anti-IFN-gamma-R columns by inhibition of solid phase RIA, ELISA, SDS-PAGE, and Western blotting proved the existence of soluble IFN-gamma-R in normal urine. Our finding, together with the already known presence of urinary TNF binding proteins and a soluble IL-2-R both in plasma and in urine, indicates that release of soluble cytokine receptors into body fluids is a general phenomenon that occurs under normal physiological conditions.