Shedding of tumor necrosis factor receptors by activated human neutrophils

The influence of growth hormone on tumour necrosis factor and neutrophil leukocyte function in sepsis

The aim of this study was to assess the influence of growth hormone (GH) in sepsis on the immune system represented by the circulating TNF-levels and the neutrophil leukocytes phagocytic capacity and respiratory burst, 22 piglets were randomized to 3 groups; pretreatment with GH (16 i.u.) before sepsis (n = 8), non-treated septic controls (n = 8), and non-septic controls (n = 6). Sepsis was induced by a standardized infusion of live E. coli. TNF was measured by a cytotoxic bioassay, while neutrophil function tests were carried out by flowcytometric assays. In brief, phagocytosis was evaluated by the neutrophils' ability to ingest FITC-labelled (fluorescein isothiocyanate) E. coli and intracellular release of oxygen metabolites was detected by the oxidation of 2',7'-dichlorofluorescin (DCFH) to the fluorescent 2',7'-dichlorofluorescein (DCF). Our data show a suppression of phagocytosis in the GH-treated group before sepsis; however, when challenged with Gram-negative bacteria, the phagocytic capacity was similar to that of the non-treated animals. The serum levels of TNF in the non-treated septic control group were twice the levels of those in the GH-treated group, 65.7 pg/ml (septic controls) vs 32.8 pg/ml (GH). Pretreatment with a single dose of GH few hours prior to sepsis does not seem to entail any further imbalance of the neutrophil function in sepsis. Lowering of the circulating TNF-levels is a presumptive favourable effect of GH in sepsis.

Tumor necrosis factor alpha and its receptors in relapsing-remitting multiple sclerosis

In the attempt to further characterize the extent and timing of tumor necrosis factor (TNF)alpha-system activation during multiple sclerosis (MS), we performed a cross-sectional and a longitudinal study in a total of 73 relapsing-remitting MS patients. We assessed serum levels of soluble TNFalpha, soluble TNFalpha receptor 1 (R1) and soluble TNFalpha receptor 2 (R2) in 65 relapsing-remitting MS patients in different phases of disease. TNFalpha, R1 and R2 serum levels measured in MS patients did not differ from those measured in healthy individuals and did not correlate with (a) clinical relapses, (b) presence of gadolinium-enhancing brain-magnetic resonance imaging (MRI) lesions, and (c) bioactivity of TNFalpha. We also measured in 8 additional relapsing-remitting MS patients peripheral blood mononuclear cells (PBMC) mRNA levels of TNFalpha, R1 and R2 every 15 days for one year. In 4 of these patients we also measured levels of soluble TNFalpha, R1 and R2 every 15 days for 5 months across a clinical exacerbation. PBMC TNFalpha, R1 and R2 mRNA levels and serum levels of soluble R1 and R2, but not TNFalpha, fluctuated concordantly (P<0.05) and peaked a mean of 6 weeks before clinical and MRI evidence of disease activity. Moreover, we found a significant positive correlation between cumulative TNFalpha and R2 mRNA levels (measured during the follow-up period in the 8 MS patients studied serially) and the number of clinical attacks recorded in these patients during the study. Our data show that serum levels of soluble TNFalpha, R1, and R2 in MS patients do not differ from those of healthy individuals. However, although within normal values, the transcription and production rate of all these molecules fluctuate concordantly in the peripheral blood during the course of the disease (with the exception of soluble TNFalpha) and their maximal elevation significantly precedes the occurrence of clinical exacerbations. It is not clear whether soluble TNFalpha escapes recognition by commonly used assays or is simply not released in its soluble form in MS patients. In any case, measurement of TNFalpha mRNA levels and R1 and R2 mRNA and protein levels appears to be a better indicator of disease fluctuations during the course of MS than assessments of soluble TNFalpha protein.

Reed-Sternberg cells and the TNF family of receptors/ligands

Treatment of cancer with means other than chemo- and radiation therapy becomes more and more important. Through the better understanding of tumor biology approaches towards the cure of cancer interfering with the pathophysiological mechanisms of malignancy can be considered. Hodgkin's disease is a good example for the role of the immune system in cancer. The Reed-Sternberg (RS) cells, malignant cells of Hodgkin's disease (HD), are surrounded by tumor infiltrating lymphocytes (TILs) and still evade immunesurveillance. In this respect the importance of the superfamily of tumor necrosis factor (TNF) receptors and ligands is becoming more and more clear. Ligand-receptor interaction either leads to death or survival signals. Many of these receptors and ligands are expressed by the RS cells and the surrounding lymphocytes. Their expression and function in HD are discussed and future directions for possible therapeutical investigations are proposed.

Serum levels of soluble tumor-necrosis-factor receptors in patients with benign and malignant HPV-associated anogenital lesions

The levels of type-I and type-II soluble TNF-alpha receptors (sTNF-Rs) were evaluated in sera from patients with various human-papillomavirus-(HPV)-associated benign and malignant anogenital lesions using specific enzyme-linked immunobiological assays. In patients with benign HPV6/11-associated condylomata acuminata, the levels of sTNF-RI were significantly increased, while sTNF-RII were in normal range. Both types of sTNF-Rs were in normal range in patients with benign HPV16-associated grade-I/II and grade-III cervical intra-epithelial neoplasia. However, their levels were significantly increased in patients with HPV16/18-associated squamous cervical cancer and anogenital Bowen's carcinoma. Sera from patients with condylomata acuminata and anogenital carcinomas displayed significantly increased TNF-alpha-inhibitory activity, as revealed by L929 cell-cytotoxicity assay. Increased serum TNF-alpha-inhibitory activity correlated with higher levels of sTNF-Rs. Furthermore, this inhibitory activity could be specifically abrogated by htr9 and utr1 monoclonal antibodies recognizing TNF-RI and TNF-RII respectively. Our results strongly suggest that serum sTNF-Rs may protect tumor cells from cytotoxic/cytostatic effects of locally released TNF-alpha, and that elevated levels of circulating sTNF-Rs may facilitate the growth of HPV-associated anogenital lesions.

Pharmacokinetic studies with recombinant cytokines. Scientific issues and practical considerations

Advances in molecular biology and recombinant DNA technology have led to the development of cytokines as therapeutic agents for a variety of disease states. The pharmacokinetic analysis of cytokines involves the understanding of analytical methods capable of detecting these agents in biological fluids and recognition of several factors which may have an impact on the cytokine concentration-time curves. Enzyme-linked immunosorbent assays (ELISA) have become the most common method of detection and commercial kits are available for a wide variety of cytokines. Monoclonal antibody products are sensitive, have minimal cross-reactivity and are relatively inexpensive when compared with high performance liquid chromatography (HPLC). However, the primary limitation of these assays is their inability to measure biologically active protein. Conversely, bioassays do measure a biological event (i.e. proliferation or cytotoxicity) but are generally not used for cytokine analysis because of their high cost, long assay completion time, lack of specificity, poor sensitivity and influence of environmental conditions on the outcome. The pharmacokinetic profile of recombinant cytokines is influenced by a number of variables: endogenous production, circulating soluble receptors and cell-associated receptors, immunocompetence and antibody production against the cytokine all may influence the disposition of the agent. Thus, pharmacokinetic modelling of cytokines may involve complex models capable of characterising these nonlinear processes and resulting effects. The route of administration is an important variable since cytokines administered by subcutaneous injection may be partially metabolised by proteases present in the subcutaneous tissue. Other methods to simplify cytokine delivery are being actively investigated and include formulations for inhalation, topical and oral administration. A variety of cytokines (including interferon-alpha, interleukin-6 and tumour necrosis factor) are capable of inhibiting cytochrome P450 hepatic enzymes and, therefore, possess the potential to cause drug-cytokine interactions. Inhibition has been demonstrated in several in vitro systems and animal models, although clinical data are currently limited. An increased understanding of the many factors which can alter the analysis and pharmacokinetics of cytokines is essential to the design of optimal dosage regimens.

Affinity and kinetics of the interaction between soluble trimeric OX40 ligand, a member of the tumor necrosis factor superfamily, and its receptor OX40 on activated T cells

OX40 ligand (OX40L) and OX40 are members of the tumor necrosis factor and tumor necrosis factor receptor superfamilies, respectively. OX40L is expressed on activated B and T cells and endothelial cell lines, whereas OX40 is expressed on activated T cells. A construct for mouse OX40L was expressed as a soluble protein with domains 3 and 4 of rat CD4 as a tag (sCD4-OX40L). It formed a homotrimer as assessed by chemical cross-linking and gel filtration chromatography. Radiolabeled sCD4-OX40L bound to activated mouse T cells with a high affinity (KD = 0.2-0.4 nM) and dissociated slowly (koff = 4 x 10(-5) s-1). The affinity and kinetics of the OX40L/OX40 interactions were studied using the BIAcoreTM biosensor, which measures macromolecular interactions in real time. The extracellular part of the OX40 antigen was expressed as a soluble monomeric protein and immobilized on the BIAcore sensor chip. sCD4-OX40L bound the OX40 with a high affinity (KD = 3.8 nM), although this was lower than that determined on the surface of activated T cells (KD = 0.2-0.4 nM), where there is likely to be less restriction in mobility of the receptor. In the reverse orientation, sOX40 bound to immobilized sCD4-OX40L with a stoichiometry of 3.1 receptors to one ligand, with low affinity (KD = 190 nM) and had a relatively fast dissociation rate constant (koff = 2 x 10(-2) s-1). Thus if the OX40 receptor is cleaved by proteolysis, it will release any bound ligand and is unlikely to block re-binding of ligand to cell surface OX40 because of the low monomeric affinity.

The TNF-ligand and receptor superfamilies: controllers of immunity and the Trojan horses of autoimmune disease?

This review is concerned with the tumour necrosis factor receptor and ligand superfamilies, with particular reference to their roles in the immunopathogenesis of Systemic Lupus Erythematosus (SLE). The tumour necrosis factor receptor and ligand superfamilies are well characterized as the molecular controllers of the immune system, acting as 'judges', 'juries', and, where necessary, 'executioners' to determine the fate of immune cells during development, proliferation and differentiation. However, these molecules exert extreme immunopathological effects when unregulated, or dysfunctional. The importance of these molecules in the pathogenesis of autoimmunity is now apparent, and has been considered in detail. Finally, specific consideration has been given to their clinical significance and potential diagnostic and therapeutic applications.

The role of receptors for tumour necrosis factor-alpha in the induction of human polymorphonuclear neutrophil chemiluminescence

Tumour necrosis factor-alpha (TNF-alpha) is a potent mediator of inflammation, which exerts profound effects on polymorphonuclear neutrophils (PMN). TNF-alpha binds to distinct cell surface receptors termed p55 and p75, expressed in approximately equal amounts on the PMN surface. We have studied the effects of TNF-alpha on the priming of F-Met-Leu-Phe (FMLP)-stimulated oxidative metabolism of PMN, using a luminol-enhanced chemiluminescence assay, and have examined the relative roles of PMN receptors for TNF-alpha in priming this oxidative metabolism, using antibodies with p55 and p75 receptor-specific agonistic and antagonistic activities. We have obtained the following results: (1) Antibody Htr-9 with agonistic activity at the p55 receptor mimicked the effect of TNF-alpha; however, a combination of Htr-9 and TNF-alpha did not results in any further increase in chemiluminescence relative to the response observed with TNF-alpha alone. The p75 agonistic antibody MR2-1 actually decreased basal and FMLP-enhanced chemiluminescence. Additionally, MR2-1 substantially inhibited the effects of both TNF-alpha itself and of the p55 agonist Htr-9. (2) Addition of antibodies with antagonistic activities at the p55 (antibody TBP-2) and p75 (antibody Utr-1) receptors resulted in a marked inhibition of the PMN response to TNF-alpha. A combination of both Utr-1 and TBP-2 was most effective at inhibiting the action of TNF. We have confirmed previously published observations that TNF-alpha alone effectively stimulates the oxidative metabolism of PMN in vitro, and that pre-incubation of PMN with TNF-alpha enhances subsequent generation of oxidative metabolites in response to FMLP. We conclude that both p55 and p75 receptors play a critical role in mediating the activation of PMN by TNF-alpha.

Effects of clozapine on plasma cytokine and soluble cytokine receptor levels

The antipsychotic drug clozapine frequently induces fever during the first weeks of administration. In addition, it has been shown that clozapine increases plasma soluble interleukin-2 receptor (sIL-2r) levels as early as 1 week after treatment is started. These findings suggest that clozapine has immunomodulatory effects. To investigate this issue in more detail, we assessed the time course of rectal temperature, blood cell counts, and cytokine and soluble cytokine receptor plasma levels during 6 weeks of clozapine treatment in 27 schizophrenic patients. Clozapine increased the plasma levels of tumor necrosis factor-alpha (TNF-alpha), soluble TNF receptors p55 and p75, and sIL-2r. These increases were independent of prior or concurrent medication and did also occur in patients who did not experience clozapine-induced fever. However, increases in TNF-alpha and sIL-2r levels were more pronounced in patients with clozapine-induced fever who showed in addition increased plasma IL-6 levels and granulocyte counts. Plasma IL-1 receptor antagonist levels and monocyte and lymphocyte counts were not affected by clozapine treatment. It is concluded that clozapine has consistent in vivo immunomodulatory effects. The results presented suggest that clozapine-induced fever is mediated by pyrogenic cytokines.

Influence of pentoxifylline on cytokine levels and inflammatory parameters in septic shock

OBJECTIVE

To evaluate the influence of pentoxifylline (PTX), a phosphodiesterase inhibitor, on cytokines and inflammatory proteins in patients suffering from septic shock.

DESIGN

Prospective study comparing a therapy group to a matched control group.

SETTING

Medical intensive care unit at a university hospital.

PATIENTS

Twenty four patients fulfilling the criteria of septic shock were included in this study. Twelve patients received PTX (therapy group) and 12 patients matched for diagnosis, age and gender served as the control group.

INTERVENTIONS

Pentoxifylline at 1 mg/kg per hour over 24 h in the therapy group.

MEASUREMENTS AND RESULTS

Cytokine levels [tumor necrosis factor-alpha (TNF)], soluble TNF receptor [TNF-R], and interleukin-6 [IL-6] and inflammatory proteins [C-reactive protein, alpha-1-antitrypsin (AAT), fibronectin, and haptoglobin], as well as hemodynamic parameters and the APACHE III score were evaluated before initiation of therapy and 24 h-later. After 24 h, TNF levels were significantly lower in the therapy group (p = 0.013), while IL-6 levels were significantly higher in the therapy group (p = 0.030). Within the 24 h TNF declined significantly in the therapy group (p = 0.006), while IL-6 showed a significant increase (p = 0.043). AAT and the APACHE III score tended to differ significantly after 24 h between the groups [AAT levels higher in the therapy group (p = 0.05), APACHE III score lower (p = 0.05)]. In the therapy group, the systemic vascular resistance index was significantly higher after 24 h (p = 0.0026) whereas the cardiac index declined (p = 0.035).

CONCLUSIONS

PTX does influence TNF levels in septic shock patients. Nevertheless, inhibiting a single mediator in severe septic shock cannot stop the inflammatory overreaction.

Decreased interleukin-10 production by neonatal monocytes and T cells: relationship to decreased production and expression of tumor necrosis factor-alpha and its receptors

The production of IL-10 by human neonatal blood mononuclear leukocytes (BML) stimulated with lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha), antibodies to CD3, or phorbol 12-myristate 13-acetate (PMA) was measured. The production of IL-10 by neonatal BML cultured with LPS or TNF-alpha was approximately 20 and approximately 15%, respectively, of adult BML. The combination of human recombinant TNF-alpha and LPS failed to augment IL-10 production in neonatal BML. The decreased production of IL-10 by neonatal leukocytes was not due to an autocrine feedback mechanism because only low concentrations of IL-10 were found in newborn sera. A connection with TNF-alpha could not be ruled out, because TNF-alpha production by LPS-stimulated newborn BML and the expression of TNF-alpha receptors on newborn monocytes were reduced. Mean +/- SD of concentrations of IL-10 in supernatants from adult and neonatal BML after stimulation with antibodies to human CD3 for 48 or 72 h were 914 +/- 386 and 178 +/- 176 pg/mL, respectively (p < 0.0001). In experiments with enriched populations of neonatal T cells, the addition of PMA failed to augment IL-10 production. This suggested that newborn T cells may be in a different state of activation than adult T cells Thus, IL-10 production in neonatal monocytes and T cells is reduced and this study suggests that the reduction may be secondary in part to regulatory processes involving TNF-alpha and its receptors.

Alterations in TNF-alpha signal transduction in resistant human papillary thyroid carcinoma cells

Tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) inhibit the growth of the human papillary thyroid carcinoma (PTC) cell line, NP. Exposure of NP cells to TNF-alpha resulted in the development of several PTC cell lines (R30, R45, and R60) with graded loss to the TNF-alpha-induced antiproliferation, termed resistance. In contrast, the NP cells and the resistant cells were equally sensitive to the antiproliferative action of interferon-gamma. Utilizing TNF-alpha receptor-specific agonist monoclonal antibodies, we demonstrated that the TNF-alpha receptor p55 mediated the antiproliferative action of TNF-alpha, while the p75 receptor did not affect cell proliferation in the NP cell line. The resistant PTC cell lines, however, showed a graded loss of p55 receptor-mediated antiproliferation and a concomitant activation of a p75 receptor-mediated growth stimulation. Shedding of TNF receptors is an important mechanism of TNF-alpha receptor metabolism. The p55 receptor mediated the TNF-alpha-induced up-regulation of the shedding of the p75 TNF-alpha receptor. The p75 receptor mediated the TNF-alpha-induced down-regulation of the shedding of the p55 receptor. However, the shedding of the p75 receptor was decreased and the shedding of the p55 receptor was increased in the resistant R60 cell line compared with the NP cell line, in the presence and absence of TNF-alpha. In contrast, IFN-gamma increased shedding of both p55 and p75 TNF-alpha receptors in NP and R60 cell lines with equal potency. Furthermore, the resistant PTC cell lines have increased basal manganous superoxide dismutase (MnSOD) expression and blunted induction of MnSOD mRNA upon short-term. TNF-alpha treatment (less than 2 h of treatment). The results indicate that a decrease in signal transduction via the p55 TNF-alpha receptor and concomitant increase in signal transduction via the p75 TNF-alpha receptor are involved in the development of PTC cell resistance.

Phorbol ester-induced shedding of intercellular adhesion molecule-1 (ICAM-1) on erythroleukemic K 562 cells

The effect of phorbol 12-myristate 13-acetate (PMA) on the expression and shedding of intercellular adhesion molecule-1 (ICAM-1) was investigated on the hematopoietic cell lines K 562 and U 937 using flow cytometry, fluorescence microscopy and ELISA technique. At low concentration of 1 nM, PMA stimulated the expression of ICAM-1 on the cell surface about 4-fold within 24 h, whereas a short-term treatment with 100 nM PMA led to the shedding of 35% of ICAM-1 from the surface of K 562 cells. The release of surface ICAM-1 was found on single cells by fluorescence microscopy to be a uniform process proceeding within 15 min. The shedding of ICAM-1 correlated with elevated levels of sICAM-1 in the supernatants of cultured cells. Also on K 562 cells stimulated by TNF-alpha, a PMA-induced release of ICAM-1 was observed in addition to the known spontaneous shedding. In contrast to the results with K 562 cells, no PMA-induced shedding of ICAM-1 was found on U 937 cells. This indicates a cell-specific process for K 562 cells. The PMA-mediated release of ICAM-1 from K 562 cells suggests that the shedding process does not only occur in parallel to the surface expression of ICAM-1, but may be controlled by particular mechanisms of down-regulation.

Tumor necrosis factor priming of peripheral blood neutrophils from rheumatoid arthritis patients

Recently it was shown that tumor necrosis factor-alpha (TNF) receptors on neutrophils may be down-regulated after stimulation with proinflammatory mediators. Since in rheumatoid arthritis neutrophils are likely to encounter these mediators in the circulation, we tested the hypothesis that rheumatoid arthritis neutrophil TNF receptors are down-regulated. Peripheral blood neutrophils from patients with rheumatoid arthritis and healthy subjects were compared with respect to their TNF binding activity and ability to be primed by TNF. There were no differences between rheumatoid arthritis and control neutrophils in receptor-mediated TNF binding, superoxide release in response to agonist, and TNF priming of this respiratory burst or in the ability to degrade cartilage in vitro and TNF priming for increased cartilage damage. It is evident that rheumatoid arthritis blood neutrophils retain the ability to bind TNF and can be primed by TNF for increased oxygen radical production and augmented cartilage damage. These findings further implicate the role of neutrophils in the pathogenesis of arthritis.

Progressive growth of human papillomavirus type 16-transformed keratinocytes is associated with an increased release of soluble tumour necrosis factor (TNF) receptor

Analysis of conditioned media generated by weakly and highly tumorigenic SKv-1 keratinocyte lines harbouring integrated human papillomavirus type 16 (HPV16) DNA sequences revealed a factor inhibiting TNF-alpha and TNF-beta cytotoxic activity. This inhibitory activity was specifically blocked by htr-9 monoclonal antibody (MAb) recognising 55/60 kDa type I TNF receptor suggesting that it is related to a soluble form of this particular receptor (sTNF-RI). The presence of sTNF-RI was confirmed by Western blot analysis of SKv-1 cell-conditioned medium showing a band of 31.5 kDa as well as by the specific enzyme-linked immunobiological assay (ELIBA). Release of sTNF-RI was a result of shedding because Northern blot analysis showed that SKv-1 cells expressed a full-length TNF-RI mRNA, and radioimmunoprecipitation of TNF-RI from [32S]cysteine-labelled cell extracts demonstrated the presence of normal 55 kDa molecule. Evaluation by ELIBA showed that highly tumorigenic SKv-12 cells released significantly more sTNF-RI than their weakly tumorigenic SKv-11 parental cells. Furthermore, human recombinant as well as SKv cell-derived sTNF-RI stimulated proliferation of weakly tumorigenic SKv-11 cells. This suggests that a progressive growth of some neoplastic cells may be, at least partially, a result of an increased spontaneous release of sTNF-RI that enables the cells to escape from local TNF-alpha-mediated growth inhibition.

Chemokines: a superfamily of chemotactic cytokines

Chemokines are a bipartite family of chemotactic proteins that bear the structural hallmark of four cysteine residues, the first two of which are in tandem. The spectrum of action of chemokines encompasses a large number of leukocyte populations, including monocytes, granulocytes, lymphocytes, NK and dendritic cells. Although the spectrum of action of chemokines largely overlaps, clear differences are still present. Chemokines play an important role in the recruitment of leukocytes at the site of inflammation, allergic reaction and tumors. Available information on receptor usage by MCP-1 and related chemokines and signal transduction pathways is reviewed. The better understanding of signaling mechanisms will provide a new basis for the development of therapeutic strategies.

Biological significance of serum soluble tumor necrosis factor receptor I in hepatoma patients

AIM: In order to elucidate the biological significance of soluble tumor necrosis factor receptor (sTNF-R) in hepatomas, we observed the differential profiles of serum sTNF-R levels in 83 hepatoma patients and 61 healthy controls.

METHODS: The serum levels of soluble sTNF-R were measured with sandwich enzyme immunoassay.

RESULTS: The mean serum sTNF-R levels were significantly higher in the hepatoma patients than in the controls (2.69 ± 0.79 μg/L vs 0.93 ± 0.29 μg/L, P < 0.001). The increment correlated well with the stage of the disease, i.e. the serum levels of soluble sTNF-RI in the patients with stages III-IV were greater than in those with stages I-II (2.97 ± 0.43 μg/L vs 1.74 ± 0.41 μg/L, P < 0.001). Additionally, we found that increased sTNF-R level correlated positively with serum alkaline phosphatase (r = 0.59), white cell count (r = 0.43) and serum globulin (r = 0.32), and correlated negatively with serum albumin (r = -0.71). Among the hepatoma patients, the frequency of increased serum sTNF-RI level (89.16%) greatly exceeded that of serum AFP (54.22%). Moreover, comparison of 25 patients before and after chemotherapy indicated that patients with a rise in sTNF-R over the therapy course had decreased clinical response (3.39 ± 0.43 μg/L vs 2.67 ± 0.34 μg/L, P < 0.001).

CONCLUSION: In patients with hepatoma, serum soluble sTNF-R levels correlate well with disease stage and response to chemotherapy. It is reasonable to postulate that this determination can serve as an aid for the detection of these cancers, for follow-up studies, and for assessments of prognosis.

Paradoxical effects of a synthetic metalloproteinase inhibitor that blocks both p55 and p75 TNF receptor shedding and TNF alpha processing in RA synovial membrane cell cultures

We have previously hypothesized that the pro-inflammatory cytokine TNF alpha has a pivotal role in the pathogenesis of rheumatoid arthritis (RA). It mediates its effects by cross-linking surface p55 TNF receptors (TNF-R), which can be proteolytically cleaved to yield soluble fragments. Upon binding TNF alpha soluble TNF-R (sTNF-R) can inhibit its function. We investigated the enzymatic nature of the proteases involved in TNF-R cleavage, and found that this process is blocked by a synthetic inhibitor of matrix metallo-proteinase activity (MMP), BB-2275. Inhibition of TNF-R cleavage was observed in a number of different cell types, as detected by retention of surface bound TNF receptor and by less sTNF-R released into the cell supernatant. The augmentation of surface TNF-R expression was of biological relevance as TNF alpha-mediated necrosis of human KYM.1D4 rhabdosarcoma cells was enhanced approximately 15-fold in the presence of BB-2275. The addition of BB-2275 to rheumatoid synovial membrane cell cultures totally inhibited MMP activity and also significantly reduced the levels of soluble TNF alpha (P < 0.006), p55 sTNF-R (P < 0.006), and p75 sTNF-R (P < 0.004). Paradoxically, despite the reduction in soluble TNF alpha levels, the production of IL-1 beta, IL-6, and IL-8, cytokines whose production was previously demonstrated to be inhibited by the addition of neutralizing anti-TNF alpha antibody were not down-regulated by BB-2275. These results raise the interesting possibility that a close relationship exits between the enzyme(s) which process membrane-bound TNF alpha, and those involved in surface TNF-R cleavage. Furthermore our observations suggest that hydroxamate inhibitors of MMP activity which block TNF alpha secretion and TNF-R cleavage may not modulate down-stream effects of TNA alpha, and as such suggest that the precise specificity of these compounds will be highly relevant to their clinical efficacy in inflammatory diseases.

Proteolytic inactivation of the leukocyte C5a receptor by proteinases derived from Porphyromonas gingivalis

The anaerobic bacterium Porphyromonas gingivalis has been implicated as a primary causative agent in adult periodontitis. Several proteinases are produced by this bacterium, and it is suggested that they contribute to virulence and to local tissue injury resulting from infection by P. gingivalis. Cysteine proteinases with specificities to cleave either Arg-X or Lys-X peptide bonds (i.e., gingipains) have been characterized as predominant enzymes associated with vesicles shed from the surface of this bacterium. It has recently been demonstrated that these proteinases are capable of degrading the blood complement component C5, resulting in the generation of biologically active C5a. By using an affinity-purified rabbit antibody raised against residues 9 to 29 of the C5a receptor (C5aR; CD88), we demonstrate that noncysteinyl proteinases associated with vesicles obtained from P. gingivalis cleave the C5aR on human neutrophils. Proteolytic attack of the C5aR by enzymes from the P. gingivalis vesicles was inhibited by TPCK (tolylsullonyl phenylalanyl chloromethyl ketone), PMSF (phenylmethylsulfonyl fluoride), and dichloroisocoumarin, suggesting that serine proteinases are primarily responsible for this degradative activity. The purified vesicle proteinase Lys-gingipain but not Arg-gingipain also cleaved the N-terminal region of the C5aR on the human neutrophils. Lys-gingipain activity was essentially resistant to these inhibitors but was inhibited by TLCK (Nalpha-p-tosyl-L-lysine chloromethyl ketone) and iodoacetamide. A synthetic peptide that mimics the N-terminal region of C5aR (residues 9 to 29; PDYGHY DDKDTLDLNTPVDKT) was readily cleaved by chymotrypsin but not by trypsin, despite the presence of two potential trypsin (i.e., lysyl-X) cleavage sites. The specific sites of cleavage in the C5aR 9-29 peptide were determined by mass spectroscopy for both chymotrypsin and Lys-gingipain digests. This analysis demonstrated that the C5aR peptide is susceptible to cleavage at both potential Lys-gingipain sites (i.e., between residues 17 and 18 [K-D] and 28 and 29 [K-T]) and at two chymotrypsin sites (between residues 14 and 15 [Y-D] and 20 and 21 [L-D]), respectively. These studies suggest that P. gingivalis contains at least two enzymes capable of cleaving the C5aR, Lys-gingipain and a second nontryptic serine proteinase that is distinct from either Arg- or Lys-gingipain.

Soluble TNF alpha receptors are increased in chronic renal insufficiency and hemodialysis and inhibit neutrophil priming by TNF alpha

The oxidative burst of neutrophils from azotemic patients is refractory to priming by tumor necrosis factor-alpha (TNF alpha). Soluble TNF alpha binding protiens (sTNFR) accumulate in the plasma of azotemic patients. To test the hypothesis that these increased sTNFR concentrations inhibit TNF alpha priming of oxidative burst activity, we measured plasma sTNFR concentrations in nondialyzed azotemic patients, hemodialysis patients, and normal subjects, and determined TNF alpha priming of fMet-Leu-Phe-stimulated superoxide production in neutrophils incubated in plasma with differing levels of sT-NFR. These sTNFR concentrations increased significantly as creatinine clearance decreased and were significantly greater in hemodialysis patients than could be accounted for by loss of renal function alone. TNF alpha primed superoxide production by normal neutrophils in normal plasma, but this effect was significantly reduced in plasma with increased concentrations of sTNFR. Neutrophils from azotemic and hemodialysis patients were refractory to priming by TNF alpha in autologous plasma, and incubation in normal plasma only partially corrected this defect. We conclude that sTNFR accumulate as a result of the loss of renal function and hemodialysis and inhibit TNF alpha priming of neutrophils in azotemic and hemodialysis patients, but that these cells also have an intrinsic functional defect.

Granulocyte colony-stimulating factor immunomodulation in the rat cardiac transplantation model

Granulocyte colony-stimulating factor (G-CSF) administration decreases tumor necrosis factor(TNF) release, an important mechanism in allograft rejection. to study G-CSF's possible antirejection effects, 30 Lewis rats underwent heart transplantation using Brown-Norway donors and were assigned varying dosages of recombinant human G-CSF (0, 20, 100, 250 and 500 microgram/kg/day) for 14 days following the operation. Recipients receiving 250 microgram/kg/day experienced an improvement in graft survival (12.3+/-4 days vs. 7.0+/-0.6 days, P>0.05, Breslow). In a separate cohort, G-CSF-treated recipients (250 microgram/kg/day x 14) killed at 2,4,and 6 days after transplantation revealed improved serial allograft biopsy grading scores versus untreated controls (P<0.001 stratified Wilcoxon). Significant reduction in serum TNF levels was noted in the G-CSF-treated animals (P<0.025, analysis of variance). These data describe a moderate antirejection effect of G-CSF administration. Inhibition of circulating TNF in the G-CSF-treated recipients may describe a marker or possible mechanism of this antirejection effect.

Shedding of the lymphocyte L-selectin adhesion molecule is inhibited by a hydroxamic acid-based protease inhibitor. Identification with an L-selectin-alkaline phosphatase reporter

Expression of the L-selectin adhesion molecule can be rapidly down-modulated by regulated proteolysis at a membrane-proximal site. The L-selectin secretase has remained undefined, and the secretase activity is resistant to a broad panel of common protease inhibitors. We have developed an L-selectin-alkaline phosphatase reporter, consisting of the ectodomain of human placental alkaline phosphatase fused to the membrane-proximal cleavage, transmembrane, and cytoplasmic domains of L-selectin, to aid in the screening for L-selectin secretase inhibitors. A hydroxamic acid-based metalloprotease inhibitor, KD-IX-73-4, inhibited release of the L-selectin-alkaline phosphatase reporter in a dose-dependent manner. The hydroxamic acid-based peptide was also found to inhibit wild type L-selectin down-regulation from the surfaces of phorbol myristate acetate-activated peripheral blood lymphocytes and phytohemagglutinin-stimulated lymphoblasts. Analysis of the proteolytic cleavage fragments of L-selectin confirmed that KD-IX-73-4 inhibited L-selectin proteolysis. Lymphocyte L-selectin was not down-regulated when co-cultured with formylmethionylleucylphenylalanine-stimulated neutrophils, suggesting that the putative secretase acts in cis with the membrane-bound L-selectin. These results suggest that the L-selectin secretase activity may involve a cell surface, zinc-dependent metalloprotease, although L-selectin shedding is not affected by EDTA and may be related to the recently described activity involved in processing of membrane-bound TNF-alpha.

Correlation between Acute Physiology and Chronic Health Evaluation (APACHE) III score and immunological parameters in critically ill patients with sepsis

A relationship between physiological parameters of severe sepsis and immunological function has not been established. In ten severely ill patients with sepsis physiological risk was assessed by the Acute Physiology and Chronic Health Evaluation (APACHE) III score, while one component of immunological function was evaluated using peripheral blood mononuclear cell (PBMC) cytokine production after stimulation with lipopolysaccharide (LPS) in vitro. Five of the ten patients died. Mean (s.e.m.) APACHE III scores at admission were not significantly different between survivors and non-survivors (82(13) versus 95(13)) but after 72 h they were lower in survivors (51(13) versus 111(15), P < 0.05). Downregulation of cytokine production by PBMC on LPS stimulation was a transient event in survivors. Survivors had a three-fold increase in tumour necrosis factor alpha bioactivity within 72 h, but there was no increase in non-survivors. A similar pattern was demonstrated for interleukin (IL) 1 beta (P < 0.05 between survivors and non-survivors) and IL-6 (P = 0.06) immunoactivity. Physiological as well as immunological parameters in critically ill patients with sepsis independently predicted hospital survival (r2 = 0.2). These data demonstrate a relationship between the pattern of cytokine production in vitro and survival.

Cryptococcal polysaccharides induce L-selectin shedding and tumor necrosis factor receptor loss from the surface of human neutrophils

High titers of cryptococcal polysaccharides in the serum and spinal fluid and the lack of cellular infiltrates in the infected tissues are hallmarks of disseminated cryptococcosis. Cryptococcal polysaccharides given intravenously to mice inhibit the influx of leukocytes into sites injected with inflammatory mediators. The purpose of this investigation was to determine if cryptococcal polysaccharides, i.e., glucuronoxylomannan (GXM), galactoxylomannan, and mannoprotein, affect expression of molecules on the surface of neutrophils that are important in extravasation. GXM in the absence of serum was shown to induce human neurophils to shed L-selectin, a molecule needed in the first step of neutrophil movement into tissues. In the presence of serum, GXM caused a further shedding of L-selectin. Shedding of L-selectin was evident by reduced amounts of L-selectin on the neutrophils treated with GXM and by increased levels of soluble L-selectin in the GXM-treated neutrophil supernatants. GXM also stimulated neutrophils to have reduced expression of TNF receptor. In contrast, GXM-treated neutrophils showed increased levels of CD15 and CD11b, and unchanged CD16 expression. In the absence of serum, galactoxylomannan and mannoprotein did not affect L-selectin, TNF receptor, CD15, CD11b, or CD16 on neutrophils but did induce loss of L-selectin in the presence of serum. Our results indicate that cryptococcal polysaccharides, especially GXM, can cause shedding of L-selectin from the surface of neutrophils, and this may prevent neutrophils from attaching to the endothelial cell surfaces. Blockage of this early step in cell migration from the vessels into tissues may be responsible in part for reduced cellular infiltration into infected tissues of individuals with disseminated cryptococcosis.

Modulation of superantigen-induced T-cell deletion by antibody anti-Pgp-1 (CD44)

We examined the effects of anti-Pgp-1 (CD44) antibody on the in vitro deletion of murine CD4 and CD8 single positive T cells induced by Staphylococcal enterotoxin B (SEB). Soluble anti-Pgp-1 antibody enhanced the apoptosis and decreased the proliferation of SEB-responding T cells. In contrast, cross-linked anti-Pgp-1 antibody provided costimulatory signals for the T-cell activation induced by anti-CD3 antibody. Hyaluronic acid (HA), a ligand of Pgp-1, did not affect proliferation and deletion induced by SEB, whereas it mimicked the effects of the cross-linked antibody in anti-CD3-driven proliferation. T-cell Pgp-1 surface expression after 48 hr incubation with SEB was unchanged as compared to unstimulated cells. However, when the memory T cells were established, some V beta 8+ (SEB-specific) T cells Pgp-1low became Pgp-1high, displaying a bimodal character. Moreover, the Pgp-1 increased expression correlated with an increase of Pgp-1 soluble form in the supernatant. These findings suggested that signals following the triggering of the Pgp-1 molecule are important in controlling T-cell survival.

Flow cytometric analysis of cytokine receptors on human Langerhans' cells. Changes observed after short-term culture

It is well established that granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-1 and tumour necrosis factor-alpha (TNF-alpha) are involved in Langerhans' cell (LC) development and dendritic cell traffic. However, little is known about the pattern of cytokine receptors on human LC and their modulation during different stages of maturation. The expression of cytokine receptors was studied by flow cytometry on both freshly isolated LC (fLC) and 72-hr cultured LC (cLC). Epidermal cell suspensions enriched in LC were obtained after skin trypsinization and Ficoll-Hypaque gradient. LC were identified by their CD1a positivity. Although the majority of fLC were positive for the alpha chain of GM-CSF receptor (GM-CSFR), the beta chain of GM-CSFR was detected only on 15% of CD1a+ cells. fLC were also positive for IL-1 receptor (IL-1R) type 1, IL-1R type 2, 75,000 molecular weight TNF receptor (TNFR) and interferon-gamma receptor (IFN-gamma R). IL-6R and its transducing signal gp130 were present in a subset of fLC. Granulocyte colony-stimulating factor receptor (G-CSFR), macrophage colony-stimulating factor receptor (M-CSFR), the alpha and beta chain of IL-2R, IL-4R, IL-7R, IL-8R and 55,000 molecular weight TNFR were not detected on fLC. After culture, LC up-regulated the expression of both the alpha and beta chains of GM-CSFR, IL-1R type 2, alpha and beta chains of IL-2R, IL-6R and gp130. In contrast, IL-1R type 1 and 75,000 molecular weight TNFR were down-modulated and the expression of IFN-gamma R was not affected by culture. These results suggest that LC undergo changes in the cytokine receptor repertory during in vitro maturation.

Route of nutritional supply influences local, systemic, and remote organ responses to intraperitoneal bacterial challenge

OBJECTIVE

The authors' aim was to investigate whether antecedent nutritional routes influence immune responses after surgical insult.

SUMMARY BACKGROUND DATA

Total parenteral nutrition (TPN) may influence host responses to infection. To the best of the authors' knowledge, however, no study has focused on the mechanisms underlying the influence of nutritional route on local, systemic, and remote organ (lung) responses after surgical insult.

METHODS

Sixty-eight rats were divided into TPN and total enteral nutrition (TEN) groups. The two groups received identical nutrients for 7 days and were then challenged intraperitoneally with 3 x 10(8) Escherichia coli. In the first experiment, the rats were observed for survival. In the second experiment, the rats were killed before (0 hours) challenge or 2 or 6 hours after challenge. Peritoneal exudative cells (PEC) and bronchoalveolar cells (BALC) were harvested and cultured in vitro. Colony-forming units of bacteria in the peritoneal lavage fluid (PLF) were determined. Tumor necrosis factor (TNF), interleukin-1 alpha (IL-1 alpha), interferon-gamma (IFN-gamma) levels in serum, PLF, bronchoalveolar lavage fluid (BALF), and cell culture supernatants were measured.

RESULTS

The 48-hour survival rate was higher in TEN than in TPN rats. Local immunity was depressed in the TPN group. Bacterial colony counts in PLF were significantly higher in the TPN group than in the TEN group after challenge. The number of PECs was significantly lower, and at 2 hours, local cytokine (TNF and IL-1 alpha) responses were diminished in the TPN group compared with the TEN group at 2 hours. The number of PECs showed a significant positive correlation with levels of local cytokines in the TEN group but not in the TPN group. Elevation of local IFN-gamma was significant from 0 to 6 hours in the TEN group but not in the TPN group. In vitro production of TNF by PEC was impaired in the TPN rats before challenge. Remote organ (lung) responses were suppressed in the TPN group. The number of BALCs and the TNF levels in BALF declined significantly between 0 and 2 hours in the TEN group but not in the TPN group. Interferon-gamma levels in BALF were higher in the TEN group than in the TPN group at 2 hours. Systemic cytokine responses were disturbed in the TPN group. Production of systemic TNF was greater, but the IFN-gamma response was diminished in the TPN group compared with the TEN group after intraperitoneal bacterial challenge.

CONCLUSION

Local, systemic, and remote organ (lung) immune responses to intraperitoneal bacterial challenge are suppressed in TPN-treated animals, leading to poor survival after challenge. Enteral nutrition before surgical insult may enhance host immune responses after the insult as compared to parenteral nutrition.

Release of anti-inflammatory mediators after mechanical trauma correlates with severity of injury and clinical outcome

Excessive synthesis of proinflammatory cytokines [tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 beta] after trauma has been correlated with poor outcome. Recently, naturally occurring inhibitors of TNF-alpha and IL-1 beta have been characterized such as soluble TNF receptors (sTNFRs) and IL-1 receptor antagonist (IL-1ra). The present study was undertaken to determine whether injury results in a rise of circulating sTNFRs and IL-1ra. If so, whether plasma levels of these anti-inflammatory mediators correlate with severity of injury and clinical outcome of these patients. Injured patients (n = 213) showed significantly increased sTNFR and IL-1ra plasma levels throughout the observation period of 14 days, compared with healthy volunteers (n = 127). Patients with severe injury (Injury Severity Score > 16 points) revealed higher levels (p < 0.05) of sTNFRs and IL-1ra than patients with minor trauma (Injury Severity Score < or = 16 points). Patients who died from injury demonstrated increased (p < 0.05) sTNFR p55 and IL-1ra plasma levels, compared with survivors. Thus, anti-inflammatory mechanisms are activated after trauma dependent on severity of injury. Because increased plasma levels of anti-inflammatory reacting proteins portended poorly for patient survival, these mediators may contribute to prediction of outcome after severe injury.

Effect of cell cycle on the regulation of the cell surface and secreted forms of type I and type II human tumor necrosis factor receptors

The cell cycle has been shown to regulate the biological effects of human tumor necrosis factor (TNF), but to what extent that regulation is due to the modulation of TNF receptors is not clear. In the present report we investigated the effect of the cell cycle on the expression of surface and soluble TNF receptors in human histiocytic lymphoma U-937. Exposure to hydroxyurea, thymidine, etoposide, bisbensimide, and demecolcine lead to accumulation of cells primarily in G1/S, S, S/G2/M, G2/M, and M stages of the cell cycle, respectively. While no significant change in TNF receptors occurred in cells arrested in G1/S or S/G2 stages, about a 50% decrease was observed in cells at M phase of the cycle. Scatchard analysis showed a reduction in receptor number rather than affinity. In contrast, cells arrested at S phase (thymidine) showed an 80% increase in receptor number. The decrease in the TNF receptors was not due to changes in cell size or protein synthesis. The increase in receptors, however, correlated with an increase in total protein synthesis (to 3.8-fold of the control levels). A proportional change was observed in the p60 and p80 forms of the TNF receptors. A decrease in the surface receptors in cells arrested in M phase correlated with an increase in the amount of soluble receptors. The cellular response to TNF increased to 8- and 2-fold in cells arrested in G1 and S phase, respectively; but cells at G2/M phase showed about 6-fold decrease in response. In conclusion, our results demonstrate that the cell cycle plays an important role in regulation of cell-surface and soluble TNF receptors and also in the modulation of cellular response.

Tumor necrosis factor alpha and interleukin-1 alpha stimulate late shedding of p75 TNF receptors but not p55 TNF receptors from human monocytes

Soluble receptors for TNF (sTNF-R) are present at elevated concentrations in the synovial fluid of patients with rheumatoid arthritis. They are presumably released by cells of the synovial membrane, including the monocyte-derived synovial macrophages. Cytokines from the synovium, including IL-1 and TNF-alpha, may stimulate release. We therefore examined the release of sTNF-R from monocytes exposed to IL-1 and TNF-alpha. Elutriator-purified human blood monocytes spontaneously released both the p75 and the p55 sTNF-R (1011 +/- 199 and 177 +/- 20 pg/10(6) cells, respectively, mean +/- SEM) during 48 h of in vitro culture. TNF-alpha and IL-1 alpha induced time- and concentration-dependent increases in the release of sTNF-R75 from monocytes, but neither had a measurable effect on the release of sTNF-R55. The release of sTNF-R75 was inhibited by cycloheximide. Neither lymphocytes nor polymorphonuclear leukocytes (PMN) released measurable sTNF-R spontaneously or in response to stimulation with IL-1 alpha, but TNF-alpha stimulated the release of small amounts of sTNF-R75 by PMN. The timing, cycloheximide sensitivity, and selectivity of stimulated release of TNF-R75 by monocytes are consistent with previous observations on other cell types of late (8-20 h) increased synthesis and turnover of cell surface TNF-R75, but not TNF-R55, after stimulation with TNF-alpha or IL-1. These observations help to explain why elevated levels of sTNF-R in synovial fluid coexist with enhanced expression of cell surface TNF-R on synovial macrophages in rheumatoid arthritis.

Metalloproteases and serineproteases are involved in the cleavage of the two tumour necrosis factor (TNF) receptors to soluble forms in the myeloid cell lines U-937 and THP-1

The proteolytic processing of the two TNF receptors (TNF-R55 and TNF-R75) into soluble forms was investigated in the myeloid cell lines U-937 and THP-1. Phorbol myristate acetate (PMA) rapidly stimulated release of soluble forms of both TNF-receptors. Incubations were made with PMA and protease inhibitors directed against different target protease groups. The serineprotease inhibitors TPCK and dichloroisocoumarin and the metalloprotease inhibitor 1,10-phenanthroline reduced PMA-induced release of both soluble receptor forms with about 60-70%. Furthermore, 1,10-phenanthroline also reduced PMA-induced down-regulation of TNF-receptors in both cell lines as judged by TNF-binding to cells. Reduced down-regulation and TNF-receptor shedding by 1,10-phenanthroline was reversed by Zn2+, indicating involvement of a Zn(2+)-dependent metalloprotease. Thus, both serine proteases and metalloproteases are involved in the processing of TNF-receptors.

Inhibition by bacterial lipopolysaccharide of spontaneous and TNF-alpha-induced human neutrophil apoptosis in vitro

In the previous paper (Takeda et al, Int. Immunol., 5, 691-694, 1993), we demonstrated that tumor necrosis factor-alpha (TNF-alpha) promptly accelerates apoptosis of human neutrophils in vitro. In order to determine the role of neutrophil apoptosis in defending against bacterial infection, we studied the effect of bacterial lipopolysaccharide (LPS) on this process. LPS inhibited spontaneous and TNF-alpha-induced human neutrophil apoptosis in vitro, as determined by 1) light and electron microscopy, 2) flow cytometry, and 3) agarose gel electrophoresis of DNA. Low concentrations of cycloheximide, a protein synthesis inhibitor, which alone did not affect neutrophil apoptosis, were able to reduce spontaneous apoptosis inhibition by LPS, suggesting the involvement of newly synthesized protein in this phenomenon.

Nutrition support affects the distribution and organ uptake of cachectin/tumor necrosis factor in rats

BACKGROUND

We have previously observed a potentiation of the metabolic response to cachectin/tumor necrosis factor (TNF) by total parenteral nutrition (TPN) but not in anorexic orally fed animals. We hypothesized that nutritional status might affect TNF clearance kinetics.

METHODS

We compared the clearance of a bolus of labeled TNF in TPN-fed animals given sufficient nutrients to grow called weight-gaining rats (WGR) with those given 50% of the WGR called weight-losing rats (WLR) and with orally fed rats (OFR). Data were analyzed using a two-compartment open system model and by linear systems analysis.

RESULTS

The data from both types of analysis indicator that although metabolic clearance was similar, WGR had a slower fractional TNF clearance rate (FCR) as well as a larger volume of distribution than WLR or OFR. Further analysis showed that an increased proportion of the total mass of TNF resided in a plasma-associated compartment in WGR compared with WLR and OFR. In addition, WGR had reduced uptake of labeled TNF by the kidney.

CONCLUSION

The data suggest that nutrition support influences either the distribution of TNF or the FCR, resulting in a greater retention in the plasma-associated compartment with intact absolute removal rates. This study has important implications concerning the type of nutrition support provided to the critically ill patient because our data suggest that clinical states with increased circulating TNF levels may be adversely affected by currently available nutritional practices.

Mediators and vascular effects in response to endotoxin

Recent experimental findings indicate that endotoxin (i.e. lipopolysaccharide) interacts with specific membrane receptors localized to mononuclear phagocytic cells and neutrophils. Binding of endotoxin to these cells, together with endotoxin-induced activation of host vascular endothelium, initiates a series of signal transduction events that culminate in release of numerous biochemical mediators. The latter include cytokines, platelet-activating factor, thromboxane A2, prostaglandins, leukotrienes, nitric oxide, proteases, toxic O2 radicals, and vasoactive amines. These mediators orchestrate complex biological interactions and amplification signals that lead to cardiopulmonary dysfunction and multi-organ failure within 4-6 h of experimental infusion of endotoxin into animals. The pathophysiological changes include decreased cardiac output, systemic hypotension, decreased blood flow and O2 delivery to tissues, intense pulmonary vasoconstriction and hypertension, bronchoconstriction, increased permeability, pulmonary oedema, ventilation-to-perfusion inequalities, hypoxaemia, and haemoconcentration. Metabolic alterations include increased blood lactate and pyruvate, metabolic acidosis, hyperkalaemia and hypoglycaemia. Potential therapeutic modalities for treatment of endotoxaemia/septic shock include specific antagonists directed against lipopolysaccharide, cytokine, and platelet-activating factor receptors, monoclonal antibodies directed against cytokines and lipid A/core polysaccharides of endotoxin, antiproteases, and agents that block release of toxic O2 and arachidonic acid metabolites.

Structural requirements regulate endoproteolytic release of the L-selectin (CD62L) adhesion receptor from the cell surface of leukocytes

L-selectin mediates leukocyte rolling on vascular endothelium at sites of inflammation and lymphocyte migration to peripheral lymph nodes. L-selectin is rapidly shed from the cell surface after leukocyte activation by a proteolytic mechanism that cleaves the receptor in a membrane proximal extracellular region. This process may allow rapid leukocyte detachment from the endothelial surface before entry into tissues. In this study, the structural requirements for regulation of human L-selectin endoproteolytic release were examined through analysis of chimeric selectin molecules and mutant L-selectin receptors. The use of chimeric selectins and a cytoplasmic tail truncation mutant demonstrated that the extracellular membrane-proximal 15-amino acid region of L-selectin is required for endoproteolytic release. The introduction of alanine-scanning mutations within this membrane-proximal region did not prevent endoproteolytic release, indicating that a specific amino acid motif was not an absolute requirement for cleavage. Furthermore, alterations within the putative primary cleavage site (K283-S284) resulted in either constitutive endoproteolytic release of the receptor or inhibition of cell activation-induced shedding to variable extents. The length of the membrane-proximal region was also critical since truncations of this region completely abolished endoproteolytic release. Thus, release of L-selectin is likely to be regulated by the generation of an appropriate tertiary conformation within the membrane-proximal region of the receptor which allows recognition by a membrane-bound endoprotease with relaxed sequence specificity that cleaves the receptor at a specific distance from the plasma membrane. These observations suggest a generalized protein-processing pathway involved in the endoproteolytic release of specific transmembrane proteins which harbor widely differing primary sequences at or neighboring their cleavage sites.

Chondrocyte IGF-1 receptor expression and responsiveness to IGF-1 stimulation in mouse articular cartilage during various phases of experimentally induced arthritis

OBJECTIVE

To examine the distribution of insulin like growth factor-1 (IGF-1) receptors and the biological response to IGF-1 stimulation in articular cartilage of normal mouse knee joints and arthritic joints taken at various stages of experimentally induced arthritis.

METHODS

In situ IGF-1 receptor expression and responsiveness to IGF-1 stimulation were examined in murine articular cartilage at different phases in two models of experimentally induced arthritis. IGF-1 receptor expression was visualised in joint sections with the use of anti-IGF-1 receptor antibodies and quantified by confocal laser scanning microscopy. Chondrocyte proteoglycan (PG) synthesis was measured by incorporation of 35S-sulphate.

RESULTS

In control cartilage, the majority of IGF-1 receptors were found on chondrocytes localised in the middle and deeper zones of the cartilage, whereas receptor expression in surface zone chondrocytes was very low. During culture of normal articular cartilage, IGF-1 was able to maintain chondrocyte PG synthesis at the in vivo level. Concurrently with the development of arthritis, cartilage lost its capacity to react to IGF-1, but IGF-1 stimulation recovered when the inflammatory response waned. Shortly after induction of arthritis, IGF-1 receptor expression initially declined, but it had returned to normal levels by day 1 and remained increased thereafter.

CONCLUSION

The distribution of IGF-1 receptor expression in the different zones of normal articular cartilage reflects IGF-1 stimulation and metabolic activity of chondrocytes in these layers. This correlation is disturbed in arthritic cartilage, suggesting inadequate or overruled signalling.

Mutational analysis of the membrane-proximal cleavage site of L-selectin: relaxed sequence specificity surrounding the cleavage site

L-selectin expression is regulated in part by membrane-proximal cleavage from the cell surface of leukocytes and L-selectin-transfected cells. The downregulation of L-selectin from the surface of neutrophils is speculated to be a process involved in the adhesion cascade leading to neutrophil recruitment to sites of inflammation. We previously reported that L-selectin is cleaved between Lys321 and Ser322 in a region that links the second short consensus repeat (SCR) and the transmembrane domain. We demonstrate that replacing this cleavage domain of L-selectin with the corresponding region of E-selectin prevents L-selectin shedding, as judged by inhibiting the generation of the 68-kD soluble and 6-kD transmembrane cleavage products of L-selectin. Unexpectedly, we found that point mutations of the cleavage site, as well as mutations of multiple conserved amino acids within the cleavage domain, do not significantly affect L-selectin shedding. However, short deletions of four or five amino acids in the L-selectin cleavage domain inhibit L-selectin downregulation. Mutations that appeared to inhibit L-selectin shedding resulted in higher levels of cell surface expression, consistent with a lack of apparent proteolysis from the cell membrane. One deletion mutant, I327 delta N332, retains the native cleavage site yet inhibits L-selectin proteolysis as well. Restoring the amino acids deleted between I327 and N332 with five alanine residues restores L-selectin proteolysis. Thus, the proteolytic processing of L-selectin appears to have a relaxed sequence specificity at the cleavage site, and it may depend on the physical length or other secondary structural characteristics of the cleavage domain.

TNF inhibitors are produced spontaneously by rheumatoid and osteoarthritic synovial joint cell cultures: evidence of feedback control of TNF action

We have proposed the hypothesis that tumour necrosis factor alpha (TNF-alpha) has a pivotal role in the pathogenesis of rheumatoid arthritis, based on in vitro observations that in RA synovial joint cell cultures removal of TNF-alpha, inhibited other potentially pathogenic cytokines such as the equally proinflammatory cytokine interleukin 1 (IL-1) and the macrophage activating factor, GM-CSF. Here we describe that in both rheumatoid (RA) and osteoarthritic (OA) synovial cultures there is a homeostatic mechanism to regulate the activities of TNF-alpha. This concept is based on several observations. First in these synovial joint cell cultures the substantial discrepancy between the levels of bioactive and immunoreactive TNF-alpha indicates the presence of an inhibitor. Second, TNF binding proteins are produced spontaneously, which are the soluble variants of surface p75 and p55 TNF receptor. The amount of soluble TNF receptors (sTNF-R) produced varied between cultures; p75 sTNF-R was more abundant than p55 sTNF-R (as detected by ELISA), and both were produced at higher levels by RA synovial joint cells in culture, compared to OA cultures. These TNF binding proteins act as endogenous inhibitors of TNF-alpha, since blocking their activity in synovial joint cell culture supernatants with MoAb to p55 and p75 sTNF-R enhanced their cytotoxic activity in the TNF bioassay. The regulation of production of these sTNF-R in synovial joint cell cultures is important as the balance between TNF-alpha and sTNF-R production may determine the outcome of the inflammatory process.

Neutrophil expression of tumour necrosis factor receptors (TNF-R) and of activation markers (CD11b, CD43, CD63) in rheumatoid arthritis

In vitro analysis of polymorphonuclear neutrophils (PMN) has allowed various stages of cell activation to be distinguished, characterized by the expression level of specific membrane markers and of functional receptors. Among those, TNF-alpha receptors (TNF-R) are modulated by various PMN activators, a mechanism which may be important to control cell responses to TNF in inflammatory reactions such as rheumatoid arthritis (RA). PMN, isolated from the blood of 36 RA patients and from the synovial fluid of 23 of them, were analysed for membrane expression of the two TNF-R (p55 and p75). Soluble p55 and p75 (sTNF-R) and TNF concentrations were measured in the plasma and synovial fluid by specific ELISA assays. Our results show that PMN from the blood of RA patients bear a normal number of TNF-R, with a normal p55/p75 ratio, compared with PMN from normal controls. Soluble TNF-R levels were similar in patients and normal plasma. In spite of high endogenous TNF concentration, patients' circulating PMN were not activated, as shown by a CD11b/CD18 expression similar to that of control resting cells. In contrast with blood neutrophils, PMN from RA patients' synovial fluids had an activated phenotype, characterized by increased expression of CD11b, decreased expression of leukosialin, CD43, and the appearance on the plasma membrane of an azurophil granule protein, CD63. High levels of soluble TNF-R were measured in RA synovial fluids. Nevertheless, membrane TNF-R levels and p55 and p75 proportions were similar to those of PMN from normal blood. These results suggest the existence of regulatory mechanisms which maintain a stable neutrophil expression of TNF-R as well as a balance between both types of receptors in inflammatory situations where neutrophils are strongly activated.

Chemoattractants induce rapid release of the interleukin 1 type II decoy receptor in human polymorphonuclear cells

Molecules representative of different classes of chemotactic agents, including formyl-Met-Leu-Phe (FMLP), C5a, leukotriene B4, platelet-activating factor, and interleukin (IL)-8, caused a rapid reduction in the IL-1 binding capacity by human polymorphonuclear leukocytes (PMN), a cell type expressing predominantly the IL-1 type II decoy receptor (IL-1 decoy RII). N-t-Boc-Met-Leu-Phe, an antagonist for the FMLP receptor, inhibited the loss of IL-1 binding capacity induced by FMLP. Monocyte chemotactic protein 1, a chemokine related to IL-8 but inactive on PMN, had no effect on IL-1 binding in this cell type. FMLP was selected for further detailed analysis of chemoattractant-induced loss of IL-1 binding by PMN. The action of FMLP was rapid, reaching 50% of its maximum (80%) at 30 s, the earliest measurable time point, and plateauing between 10 and 30 min. Dose-response analysis revealed that maximal reduction of IL-1 binding was reached at FMLP concentrations that were also optimal for chemotaxis (50% effective dose = 5 x 10(-9) M). The loss of IL-1 binding capacity caused by FMLP was determined by a reduction in receptor number with no change in their affinity. The effect of FMLP on IL-1 receptor (IL-1R) was selective in that the PMN surface structures IL-8R, CD16, CD18, and major histocompatibility complex class I antigens were unaffected under these conditions. Loss of surface IL-1R was not due to an augumented rate of internalization. FMLP caused rapid release of a 45-kD IL-1-binding molecule identified as the IL-1 decoy RII. After FMLP-induced release, PMN reexpressed newly synthesized receptors, reaching basal levels by 4 h. FMLP-induced release of the IL-1 decoy RII did not impair the responsiveness of PMN to IL-1 in terms of promotion of survival and cytokine production. FMLP-induced release of the IL-1 decoy RII was unaffected by protein synthesis inhibitors, was blocked by certain protease inhibitors, and was mimicked by agents (the Ca++ ionophore A23187 and phorbol myristate acetate) that recapitulate elements in the signal transduction pathway of chemoattractant receptors. The time frame and concentration range of chemoattractant-induced rapid release of the IL-1 decoy RII are consistent with the view that IL-1 decoy RII release is an early event in the multistep process of leukocyte recruitment.(ABSTRACT TRUNCATED AT 400 WORDS)

Fc gamma receptor IIIb enhances Fc gamma receptor IIa function in an oxidant-dependent and allele-sensitive manner

Two classes of receptors for IgG, Fc gamma RIIa and Fc gamma RIIIb, both of which exist in two allelic forms, are expressed on human neutrophils. Neutrophils from normal donors, homozygous for the different allelic phenotypes of Fc gamma RIIIb, have significantly different levels of Fc gamma receptor-mediated phagocytosis of IgG-opsonized erythrocytes (EA). However, the observation that Fc gamma RIIIb mediates phagocytosis of specific mAb-targeted erythrocytes poorly suggests that this receptor may influence EA internalization by Fc gamma RIIa in an allele-sensitive fashion. Donors homozygous for the NA1 allele of Fc gamma RIIIb showed greater activation of Fc gamma RIIa after Fc gamma RIIIb cross-linking than donors homozygous for the NA2 allele of Fc gamma RIIIb. This increase in receptor-specific internalization reflects both an increase in ligand binding by Fc gamma RIIa and an increase in internalization efficiency of targets bound. Activation of Fc gamma RIIa by Fc gamma RIIIb is transferable by supernatants from activated cells and is blocked by inhibitors of reactive oxygen species and the H2O2-myeloperoxidase-chloride system and by serine protease inhibitors. Thus, cross-linking of Fc gamma RIIIb, which leads to neutrophil degranulation and the generation of reactive oxygen intermediates, in turn alters Fc gamma RIIa avidity and efficiency. These oxidant-mediated changes in Fc gamma RIIa function provide a novel mechanism for receptors to collaborate in both an autocrine and paracrine fashion. The allele sensitivity of these effects suggests that Fc gamma receptor polymorphisms may be inherited disease susceptibility factors in host defense against infection and in the development of autoimmunity.

Activation of protein kinase C enhances the phosphorylation of the type B interleukin-8 receptor and stimulates its degradation in non-hematopoietic cells

We have previously characterized the stably transfected, clonally selected human placental cell line, 3ASubE P-3, which overexpresses the type B interleukin-8 receptor (IL-8RB) and responds to the chemokine melanoma growth stimulatory activity (MGSA) with enhanced phosphorylation of this receptor. In work described here, we demonstrate that the MGSA-enhanced phosphorylation of this receptor is mediated via a process involving pertussis toxin-sensitive G proteins. Furthermore, treatment of the 3ASubE P-3 cells with either 12-O-tetradecanoylphorbol 13-acetate (TPA) or 1,2-dioctanoyl-sn-glycerol (diC8), two different activators of protein kinase C (PKC), results in a concentration-dependent increase in the phosphorylation of the IL-8RB. Inhibition of PKC, by treatment with staurosporin (50 nM for 2 h), or down-regulation of PKC, by prolonged treatment with TPA (400 nM for 40 h) suppresses the TPA-enhanced receptor phosphorylation, but has no effect on the MGSA-enhanced receptor phosphorylation. These data suggest that the isoforms of PKC that are sensitive to these manipulations may not play a role in mediating the MGSA-enhanced phosphorylation of the IL-8RB. TPA treatment also results in a time-dependent decrease in 125I-MGSA binding to the 3ASubE P-3 cells. A 30-min treatment with 400 nM TPA results in approximately a 50% decrease in binding, whereas a 2-h treatment essentially eliminates specific binding of 125I-MGSA to these cells. The TPA-induced decrease in 125I-MGSA binding is accompanied by enhanced degradation of the IL-8RB, as indicated by Western blot analysis and pulse-chase experiments, suggesting a potential role for PKC as a negative regulator of the IL-8RB. MGSA treatment (50 nM for 2 h) also stimulates receptor degradation in the 3ASubE P-3 cells, indicating that this receptor is down-regulated in response to prolonged exposure to its ligand. In similar studies conducted on the promonocytic cell line, U937, MGSA treatment of the U937 cells resulted in receptor phosphorylation, whereas PKC activation failed to significantly modulate the phosphorylation state of the IL-8RB. Treatment of the U937 cells with MGSA, TPA, or diC8 resulted in a loss of receptor protein present in these cell types. These data imply that MGSA signaling through the IL-8RB is similar in both the non-hematopoietic and hematopoietic cell types, whereas activation of PKC by TPA or diC8 elicits different responses in these two distinct cell types.

Strategies for blocking the systemic effects of cytokines in the sepsis syndrome

OBJECTIVES

To review and evaluate animal and human data regarding strategies to intervene in the pathogenesis of the sepsis syndrome by specifically blocking the action of single cytokines.

DATA SOURCES

The English language medical literature was reviewed, including reports of human clinical trials, animal experiments, and in vitro studies elucidating cellular and molecular interactions.

STUDY SELECTION

Emphasis was placed on controlled experimental studies that elucidated the effectiveness of antibodies, soluble receptors, and receptor antagonists in intervening in the pathogenesis of the sepsis reaction.

DATA EXTRACTION

This review focuses on data that directly involve the induction and regulation of protein mediators of sepsis, especially tumor necrosis factor-alpha, interleukin-1 beta, interleukin-6, and interleukin-8.

DATA SYNTHESIS

Information concerning the potential of cytokine blockers in modulating the sepsis reaction is presented in a logical, clinically oriented fashion. The purpose is to emphasize the potential role of these agents by focusing on the actual existing data.

CONCLUSIONS

The pathophysiology of the sepsis reaction appears to involve the sequential release of cytokines. Interventions designed to specifically block the biological effects of single cytokines appear to have a role in the management of sepsis syndrome, but well-designed, prospective, randomized, placebo-controlled clinical trials in well-defined clinical populations are necessary to define this role. These trials require the cooperation of clinical and basic scientists.

Tumor necrosis factor receptors in patients with chronic hepatitis B virus infection

BACKGROUND/AIMS

Patients with chronic hepatitis B infection have elevated plasma tumor necrosis factor (TNF) alpha levels. Two TNF-alpha receptors have been identified, each responsible for distinct TNF-alpha activities. The aim of this study was to evaluate the biological function of the elevated TNF-alpha in chronic hepatitis B virus infection by examining the two TNF signaling pathways in the evolution of hepatitis B-related liver injury.

METHODS

The hepatic expression of the two TNF receptors and the corresponding serum levels of the soluble forms of both TNF receptors were determined and correlated with hepatic inflammation and virus replication in 98 chronic hepatitis B surface antigen carriers. Forty hepatitis B e antigen-positive patients were also studied prospectively, while on interferon alfa treatment, to examine the TNF receptor response during viral clearance.

RESULTS

In chronic hepatitis B virus infection, the hepatic expression and serum levels of TNF receptors, in particular 75-kilodalton TNF receptor subtype (TNF-R p75), are significantly enhanced in association with hepatic inflammation and hepatocytolysis but not with hepatitis B virus replication. During interferon alfa treatment, a significant increase of soluble TNF-R p75 always precedes the hepatitis B e antigen antibody against hepatitis B e antigen seroconversion in responders to treatment.

CONCLUSIONS

In chronic active hepatitis B infection, there is an up-regulation of the TNF receptor system, preferentially the TNF-R p75 signaling pathway, which suggests that the TNF-alpha/TNF receptor system has an important role in the pathogenesis of liver damage and viral clearance.

Soluble tumour necrosis factor receptors, tumour necrosis factor and interleukin-6 in serum in granulocytopenic patients with fever

Serum levels of TNF, IL-6 and soluble TNF receptors p55 and p75 (sTNFR-p55 and sTNFR-p75) were examined in 14 patients with acute myeloid leukaemia during 43 courses of chemotherapy. The patients experienced 30 episodes of fever which occurred during granulocytopenia (defined as granulocyte counts < 0.2 x 10(9)/l) and six fever episodes when granulocyte counts were > 1.0 x 10(9)/l. Febrile episodes were classified as microbiologically defined infection, clinically defined infection, and unexplained fever. Levels of bioactive IL-6 and immunoreactive TNF increased in response to fever during granulocytopenia, whereas bioactive TNF was not detected in any sample in this study. During granulocytopenia, both sTNFR rose significantly in microbiologically defined infection (P < 0.01 for sTNFR-p55 and P < 0.05 for sTNFR-p75), but not in the other two categories. The ratio of sTNFR-p55 to sTNFR-p75 was higher during febrile periods in granulocytopenia than in a non-granulocytopenic situation with granulocyte counts > 1.0 x 10(9)/l (P < 0.01). We conclude that granulocytopenia affects release of the two sTNFR differently during febrile periods, and that release of sTNFR-p75 in response to fever is reduced during granulocytopenia, suggesting a role for the granulocytes in systemic release of sTNFR-p75.