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Biomedical subjects

D Spriggs

Publications and source records attributed to D Spriggs.

At least 55 records · Page 3Linked to original sources
PubMed1994

Phase I trial of 3-hour infusion of paclitaxel with or without granulocyte colony-stimulating factor in patients with advanced cancer.

PURPOSE: We conducted a phase I trial of a 3-hour infusion of Taxol (paclitaxel; Bristol-Myers Squibb Co, Princeton, NJ) to identify the maximum-tolerated dose of Taxol as a 3-hour infusion with and without granulocyte colony-stimulating factor (G-CSF) support. MATERIALS AND METHODS: Thirty-five patients with advanced, untreatable malignancies were treated with a 3-hour infusion of Taxol once every 3 weeks. Groups of three patients were entered at escalating dose levels of Taxol in a traditional phase I design in each of two parallel arms: arm A, without G-CSF, and arm B, with G-CSF. Patients assigned to the G-CSF arm received G-CSF 5 micrograms/kg/d subcutaneously starting on day 2 for 9 to 14 days. All patients were pretreated with dexamethasone, diphenhydramine, and ranitidine, and were monitored continuously for cardiac arrhythmias during the first treatment. RESULTS: Dose-limiting myelosuppression with Taxol without G-CSF was observed at the 250-mg/m2 dose level. The dose-limiting toxicity for Taxol with G-CSF was peripheral neuropathy at the 300-mg/m2 dose level. One of 35 patients (2.8%) had a grade 3 anaphylactic reaction at 250 mg/m2. No clinically significant cardiac arrhythmias were documented. Twenty-seven of 111 courses (24%) were associated with grade 3 arthralgias or myalgias requiring narcotics for pain control. Taxol plasma concentrations declined in a triexponential fashion, with a final elimination half-life of 10 to 12 hours. The peak Taxol plasma concentrations and total area under the curve (AUC) increased with increasing doses of Taxol, although this increase appeared to be somewhat nonlinear. CONCLUSION: The maximum dose of Taxol recommended for phase II and III studies, when administered as a 3-hour infusion alone and with G-CSF support, is 210 mg/m2 and 250 mg/m2, respectively. No increased incidence of hypersensitivity reactions or other side effects were observed, with the possible exception of arthralgias and myalgias. If ongoing trials demonstrate that a 3-hour infusion is as efficacious as a 24-hour infusion, we conclude that with proper monitoring and premedication, high-dose Taxol can be safely administered in the outpatient setting.

Aged↗
PubMed1994

A phase I trial of 3-hour infusions of paclitaxel (Taxol) with or without granulocyte colony-stimulating factor.

Paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ), a novel antitubulin agent derived from the bark of the Pacific yew tree, may be one of the most active single agents in our chemotherapy armamentarium. Concern over acute hypersensitivity reactions has resulted in an administration schedule consisting of a 24-hour infusion. We conducted a phase I trial of a 3-hour infusion of paclitaxel to determine whether a 3-hour infusion could be administered with relative safety, and to identify the maximal tolerated dose with and without granulocyte colony-stimulating factor (G-CSF) support. Thirty-five patients with advanced, untreatable malignancies received a 3-hour infusion of paclitaxel once every 3 weeks. Groups of three patients were entered at escalating dose levels in a traditional phase I design consisting of two parallel arms: arm A (without G-CSF) and arm B (with G-CSF). Dose levels of paclitaxel ranged from 210 mg/m2 to 300 mg/m2. Patients assigned to the G-CSF arm received 5 micrograms/kg/d subcutaneously starting on day 2. All patients were pretreated with dexamethasone, diphenhydramine, and ranitidine, and were monitored continuously for cardiac arrhythmias during the first treatment. The dose-limiting toxicity for paclitaxel without G-CSF was myelosuppression at the 250 mg/m2 dose level and with G-CSF was peripheral neuropathy at the 300 mg/m2 dose level. The mean absolute neutrophil count at the 250 mg/m2 dose level when administered with and without G-CSF support was 4,500/microL and 840/microL, respectively. Neuropathy appeared to be dose related and somewhat cumulative. One patient who previously received cisplatin developed a severe grade III peripheral neuropathy at the 300 mg/m2 dose level, which left her unable to use her hands and wheelchair bound; the peripheral neuropathy slowly resolved to a grade I level. Twenty-seven of III courses (24%) were associated with grade III arthralgias or myalgias, requiring narcotics for pain control. Prednisone was empirically started in 10 patients and found to be helpful in the control of these symptoms. One of 35 (2.9%) patients had a grade III anaphylactic reaction. No clinically significant cardiac arrhythmias were observed. Two previously treated patients (one with breast cancer and one with ovarian cancer) had a partial response. The maximum tolerated dose of paclitaxel administered as a 3-hour infusion was 210 mg/m2 without G-CSF and 250 mg/m2 with G-CSF.(ABSTRACT TRUNCATED AT 400 WORDS)

Drug Hypersensitivity↗
PubMed1993

Evidence of an absorption phase after short intravenous suramin infusions.

Suramin was given as an intravenous infusion to 16 cancer patients in a phase I trial. Individual pharmacokinetic parameters were calculated from a test dose given 1 week prior to the administration of a full-dose (350-700 mg/m2) regimen of 1-h loading and maintenance infusions. A distribution phase of 3.8 h was found. Plasma suramin concentrations were noted to increase following cessation of the intravenous test infusion in eight subjects. A model is proposed in which high-capacity, low-affinity binding of suramin to a shallow compartment adjacent to the intravascular space occurs rapidly during infusion, followed by absorption back into the measured blood pool with binding to plasma albumin. Despite the observable presence of this postinfusion peak shortly after the cessation of the brief suramin infusion, the pharmacokinetics of suramin were best characterized by a traditional two-compartment model. The dose-adjusted area under the concentration-time curve (AUC) increased with dose, supporting a hypothesis of sustained absorption of suramin to vascular endothelium but also raising the possibility of dose-dependent clearance.

Absorption↗
PubMed1993

Phase I trial of mitoxantrone and granulocyte-macrophage colony-stimulating factor (GM-CSF) in patients with advanced solid malignancies.

PURPOSE: To determine the maximally tolerated dose (MTD) and pharmacokinetics of high-dose mitoxantrone and document the toxicities and side effects of mitoxantrone when administered with GM-CSF. PATIENTS AND METHODS: Twenty-three patients with advanced solid tumors were entered into a phase I and pharmacokinetic study. Mitoxantrone was administered at doses of 12, 21, 28, 32, 37, and 48 mg/m2 on day 1; GM-CSF (5 micrograms/kg once or twice daily) was administered on days 2 to 14. Therapy was repeated every 3 weeks. Dose escalation continued in sets of three patients until the dose limiting toxicity (DLT) was observed. The DLT was based on hematologic, non-hematologic, and cardiac toxicity, and delay of therapy by more than 1 week due to toxicity. Plasma samples were assayed for mitoxantrone concentrations using high performance liquid chromatography (HPLC). RESULTS: Twelve patients required either mitoxantrone dose reductions or delays. DLT of neutropenia was observed at a mitoxantrone dose of 48 mg/m2/day. Therefore, we conclude the MTD was 37 mg/m2/day. Myelosuppression appeared to be cumulative. Two patients were withdrawn from the study due to a drop in left ventricular ejection fraction (LVEF). Two of 23 patients experienced a partial response. The mean area under the curve (AUC) and peak mitoxantrone levels increased linearly with dose; triexponential elimination of mitoxantrone was observed. No statistically significant correlation was observed between either peak mitoxantrone level or AUC and duration of absolute neutrophil count (ANC) < 500/mm3. CONCLUSION: The use of GM-CSF allows administration of mitoxantrone at a dose greater than three times that given in standard therapy; treatment is well tolerated. Further studies are needed to determine whether mitoxantrone has cumulative cardiac or hematologic toxicity.

Adult↗
PubMed1991

Tumor necrosis factor expression by human ovarian carcinoma in vivo.

Tumor necrosis factor (TNF) is a cytokine produced by monocytes and other cells with selective cytolytic activity against some but not all tumor cells. Cellular resistance to the cytolytic effects of TNF has been reported to be associated with autocrine production of TNF by the target cells. The purpose of this study was to determine whether or not human tumors produce tumor necrosis factor in vivo. Ovarian carcinoma tissue from 25 patients with ovarian carcinoma was examined for the presence of TNF. Four of 5 ascites fluid specimens and tissue sections of 16 of 20 patients were positive for TNF by immunoperoxidase staining. The source of the immunoreactive protein was further examined by in situ hybridization studies. TNF mRNA was detectable in each of the ascites specimens and 7 of 16 tissue sections that were positive by immunoperoxidase staining. These findings suggest that TNF is produced by some human tumors in vivo and that the association between TNF production and resistance to TNF antitumor action may be clinically relevant.

Ascites↗
PubMed1990

Effects of dexamethasone on induction of monocytic differentiation in human U-937 cells by dimethylsulfoxide.

The present studies demonstrate that dimethylsulfoxide (DMSO) treatment of human U-937 myelomonocytic leukemia cells is associated with induction of monocytic differentiation. The DMSO-induced U-937 monocytic phenotype was associated with 1) growth inhibition, 2) loss of clonogenic survival, 3) increases in alpha-naphthyl acetate esterase (NSE) staining, and 4) increases in cell surface expression of the monocyte marker Mac-1. DMSO treatment of U-937 cells was also associated with down-regulation of c-myc and c-myb gene expression as well as with increases in tumor necrosis factor (TNF) mRNA levels. The results further demonstrate that induction of U-937 monocytic differentiation by DMSO is accompanied by increases in phospholipase A2 activity. Moreover, this stimulation of phospholipase A2 was sensitive to dexamethasone. We therefore studied the effects of dexamethasone on DMSO-induced differentiation of U-937 cells. Although dexamethasone had no effect on growth inhibition or loss of clonogenic survival by DMSO, this glucocorticoid blocked increases in NSE staining and cell surface Mac-1 expression. Dexamethasone also had no effect on the down-regulation of c-myc and c-myb expression but blocked the reappearance of c-myb transcripts after 6 hr of DMSO treatment. Finally, dexamethasone inhibited DMSO-induced increases in TNF gene expression. Taken together, the results demonstrate that dexamethasone inhibits multiple characteristics, including the stimulation of phospholipase A2 activity, associated with DMSO-induced monocytic differentiation of U-937 cells.

Antigens, Differentiation↗
PubMed1989

Binding properties of monoclonal antibodies against human fragment D-dimer of cross-linked fibrin to human plasma clots in an in vivo model in rabbits.

Two (MA-15C5 and MA-8D3) out of approximately 500 monoclonal antibodies, obtained by fusion of P3X63-Ag8-6.5.3 myeloma cells with spleen cells of mice immunized with purified fragment D-dimer from human fibrin, demonstrated a more than 1,000-fold higher affinity for fragment D-dimer than for native fibrinogen. MA-15C5 was directed against a neoantigenic determinant only expressed in fragment D-dimer. MA-8D3 reacted equally well with fragment D-dimer of crosslinked fibrin and with fragment D of non-crosslinked fibrin but not with fragment D of fibrinogen. Both monoclonal antibodies did not crossreact with rabbit fibrin and its degradation products. The binding of 125I-labeled Fab fragments to human plasma clots, introduced and aged for 1 hr in the jugular vein of heparinized rabbits was studied. Following injection of an equimolar mixture of Fab fragments derived from MA-15C5 and MA-8D3, the clot to blood ratios of radioactivity increased from 3.2 +/- 1.2 (mean +/- SD) at 4 hr to 7.2 +/- 1.4 at 17 hr. The binding of Fab fragments of MA-15C5 and MA-8D3 was independent of the age (1 to 72 hrs) of the clot and of heparin anticoagulation and was only slightly decreased (by 20%) in the presence of circulating human fibrinogen (90 mg/kg body weight) and of human cross-linked fibrin degradation products at a plasma concentration of 10 micrograms/ml. The binding of Fab fragments of MA-15C5 and MA-8D3 to occlusive human plasma clots in the femoral artery of rabbits was comparable to that of the non-occlusive human plasma clots in the jugular vein.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1989

Sequence-specific inhibition of DNA strand elongation by incorporation of 9-beta-D-arabinofuranosyladenine.

9-beta-D-Arabinofuranosyladenine (ara-A) is an inhibitor of DNA replication with antitumor and antiviral activity. The molecular basis for this inhibitory effect has remained unclear. The present work has examined the effects of 9-beta-D-arabinofuranosyladenine-triphosphate on DNA polymerase-beta. These studies were performed on different M13 phage DNA templates. The findings demonstrate that 9-beta-D-arabinofuranosyladenine is incorporated into the elongating DNA strand by DNA polymerase-beta. The findings also demonstrate that the incorporated 9-beta-D-arabinofuranosyladenine residue acts as a relative chain terminator. Furthermore, the relative chain-terminating effects of this agent are sequence specific and reversed by competition with deoxyadenosine-triphosphate for incorporation into the DNA strand. These findings are in concert with hydrogen bonding differences of the incorporated arabinosyl moiety which alters reactivity of the chain terminus and thereby inhibits elongation. These findings are also in agreement with recent studies of 1-beta-D-arabinofuranosylcytosine and provide insights into the sequence specific effects of these agents.

Base Sequence↗
PubMed1989

Absence of potentiation with murine antiplatelet GPIIb/IIIa antibody of thrombolysis with recombinant tissue-type plasminogen activator (rt-PA) in a canine venous thrombosis model.

F(ab')2 fragments of a murine monoclonal anti-platelet GPIIb/IIIa antibody (7E3) are a potent platelet aggregation inhibitor, which in a canine coronary artery thrombosis model accelerate lysis with recombinant tissue-type plasminogen activator (rt-PA) and prevent reocclusion (7). In the present study, we have investigated the potential value of platelet aggregation inhibition as adjunctive therapy to lysis of venous thrombi, by measuring the thrombolytic potency of 7E3-F(ab')2 and rt-PA used alone or in combination, in dogs with a 125I-fibrin labeled femoral vein thrombus. The dose-response of thrombolysis with rt-PA infused over 4 hours was linear: doses of 0.075 mg/kg, 0.15 mg/kg and 0.3 mg/kg produced 37 +/- 3, 57 +/- 11 and 83 +/- 4% lysis respectively, against a background value of 20 +/- 2%. With F(ab')2 fragments of 7E3 given as a bolus of 1.2 mg/kg, which saturated 70% of the platelet GPIIb/IIIa receptors and prolonged the bleeding to more than 30 min, lysis was not significantly increased over background. Combination of 0.3 or 0.6 mg/kg of 7E3-F(ab')2 with either 0.03 or 0.06 mg/kg of rt-PA did not produce more lysis than obtained with a comparable dose of rt-PA alone. No significant changes in plasma fibrinogen or alpha 2-antiplasmin were observed with either agent alone or with the combination. It is concluded that extensive inhibition of platelet aggregation does not potentiate the thrombolytic effect of rt-PA in this venous thrombosis model.

Animals↗
PubMed1989

Role of arachidonic acid metabolism in transcriptional induction of tumor necrosis factor gene expression by phorbol ester.

The treatment of human HL-60 promyelocytic leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with induction of tumor necrosis factor (TNF) transcript. The study reported here has examined TPA-induced signaling mechanisms responsible for the regulation of TNF gene expression in these cells. Run-on assays demonstrated that TPA increases TNF mRNA levels by transcriptional activation of this gene. The induction of TNF transcripts by TPA was inhibited by the isoquinolinesulfonamide derivative H7 but not by HA1004, suggesting that this effect of TPA is mediated by activation of protein kinase C. TPA treatment also resulted in increased arachidonic acid release. Moreover, inhibitors of phospholipase A2 blocked both the increase in arachidonic acid release and the induction of TNF transcripts. These findings suggest that TPA induces TNF gene expression through the formation of arachidonic acid metabolites. Although indomethacin had no detectable effect on this induction of TNF transcripts, ketoconazole, an inhibitor of 5-lipoxygenase, blocked TPA-induced increases in TNF mRNA levels. Moreover, TNF mRNA levels were increased by the 5-lipoxygenase metabolite leukotriene B4. In contrast, the cyclooxygenase metabolite prostaglandin E2 inhibited the induction of TNF transcripts by TPA. Taken together, these results suggest that TPA induces TNF gene expression through the arachidonic acid cascade and that the level of TNF transcripts is regulated by metabolites of the pathway, leukotriene B4 and prostaglandin E2.

Arachidonic Acid↗
PubMed1989

Effects of botulinum toxin type D on secretion of tumor necrosis factor from human monocytes.

Botulinum toxins are potent neurotoxins which block the release of neurotransmitters. The effects of these toxins on hematopoietic cells, however, are unknown. Monocytes secrete a variety of polypeptide growth factors, including tumor necrosis factor (TNF). In the study reported here, the effects of botulinum toxin type D on the secretion of TNF from human monocytes were examined. The results demonstrate that botulinum toxin type D inhibits the release of TNF from monocytes activated by lipopolysaccharide (LPS) but not by 12-O-tetradecanoylphorbol-13-acetate. Botulinum toxin type D had no detectable effect on intracellular TNF levels in LPS-treated monocytes, indicating that the effects of this toxin involve the secretory process. This inhibitory effect of botulinum toxin type D on TNF secretion from LPS-treated monocytes was partially reversed by treatment with 12-O-tetradecanoylphorbol-13-acetate or introduction of guanosine 5'-[gamma-thio]triphosphate into these cells. The results demonstrate that TNF secretion is regulated by at least two distinct guanine nucleotide-binding proteins, one responsible for the activation of phospholipase C and another which acts as a substrate for botulinum toxin type D. ADP-ribosylation of monocyte membranes by botulinum toxin type D demonstrated the presence of three substrates with Mrs of 45,000, 21,000, and 17,000. While the role of these substrates in exocytosis is unknown, the results suggest that the Mr 21,000 substrate is involved in a process other than TNF secretion.

Binding Sites↗
PubMed1989

Detection of tumor necrosis factor gene expression at a cellular level in human acute myeloid leukemias.

Tumor necrosis factor (TNF) is a Mr 17,000 cytokine produced by macrophages. We have recently demonstrated that TNF is also produced by transformed human epithelial cells. The present studies have examined TNF expression in human myeloid leukemic cells. We have monitored TNF expression at a cellular level using alkaline phosphatase detection of a biotinylated TNF cDNA probe in situ. Using this approach, TNF transcripts were detectable in HL-60 cells induced along the monocytic lineage by phorbol ester but not in uninduced cells. The specific detection of TNF RNA at a cellular level was supported by the absence of histochemical staining in RNase-treated cells and when using biotinylated pBR322 plasmid without insert. These studies were extended to preparations of purified acute myeloblastic leukemia cells. The results demonstrate that TNF is expressed in myeloblasts in eight of nine patients with AML. In each preparation of myeloblasts with detectable TNF RNA, transcripts were present at 89-98% of the cells. The identification of TNF RNA in situ was also associated with the detection of TNF protein in leukemic blasts by indirect immunofluorescence. Moreover, the detection of TNF protein in these preparations of myeloblasts was confirmed by immunoblotting. However, using this approach to examine AML cells before and after purification indicated that TNF expression is induced as a result of the enrichment procedures. Thus, certain populations of purified myeloid leukemic cells are capable of expressing TNF at both the RNA and protein levels.

Cell Line↗
PubMed1988

Effect of tumor necrosis factor on GTP binding and GTPase activity in HL-60 and L929 cells.

Tumor necrosis factor (TNF) is a monokine that induces pleiotropic events in both transformed and normal cells. These effects are initiated by the binding of TNF to high affinity cell surface receptors. The post-receptor events and signaling mechanisms induced by TNF, however, have remained unknown. The present studies demonstrate the presence of a single class of high affinity receptors on membranes prepared from HL-60 promyelocytic leukemic cells. The interaction of TNF with these membrane receptors was associated with a 3.8-fold increase in specific binding of the GTP analogue, GTP gamma S. Scatchard analysis of GTP gamma S binding data demonstrated that TNF stimulates GTP binding by increasing the affinity of available sites. The TNF-induced stimulation of GTP binding was also associated with an increase in GTPase activity. Moreover, the increase in GTPase activity induced by TNF was sensitive to pertussis toxin. The results also demonstrate that TNF similarly increased GTP binding and pertussis toxin-sensitive GTPase activity in membranes from mouse L929 fibroblasts, thus indicating that these effects are not limited to hematopoietic cells. Analysis of HL-60 membranes after treatment with pertussis toxin in the presence of [32P]NAD revealed three substrates with relative molecular masses of approximately Mr 41,000, 40,000, and 30,000. In contrast, L929 cell membranes had only two detectable pertussis toxin substrates of approximately Mr 41,000 and 40,000. Although the Mr 41,000 pertussis toxin substrate represents the guanine nucleotide-binding inhibitory protein Gi, the identities of the Mr 40,000 and Mr 30,000 substrates remain unclear. In any event, inhibition of the TNF-induced increase in GTPase activity and ADP-ribosylation of Gi by pertussis toxin suggested that TNF might act by increasing GTPase activity of the Gi protein. However, the results further indicate that TNF has no detectable effect on basal or prostaglandin E2-stimulated cAMP levels in HL-60 cells. Taken together, these findings indicate that a pertussis toxin-sensitive GTP-binding protein other than Gi, and possibly the Mr 40,000 substrate, is involved in the action of TNF. Finally, the demonstration that pertussis toxin inhibited TNF-induced cytotoxicity in L929 cells supports the presence of a GTP-binding protein which couples TNF-induced signaling to a biologic effect.

Adenosine Diphosphate Ribose↗
PubMed1988

Effects of 1-beta-D-arabinofuranosylcytosine incorporation on elongation of specific DNA sequences by DNA polymerase beta.

1-beta-D-Arabinofuranosylcytosine (ara-C) is an effective antileukemic agent which acts as an inhibitor of DNA synthesis. The precise mechanism responsible for this inhibitory effect, however, remains unclear. The present work has examined the effects of the triphosphate derivative, ara-CTP, on purified DNA polymerase beta. These studies were performed on M13 phage DNA templates of defined sequence. The results demonstrate that ara-C is incorporated into DNA by DNA polymerase beta. The results also demonstrate that the incorporated ara-C residue acts as a relative chain terminator. Moreover, the relative chain terminating effects of ara-C are sequence specific. In this regard, DNA strand elongation was progressively slowed at sequences of two, three, and four contiguous sites for cytosine incorporation. We also demonstrate that the inhibitory effects of ara-C are reversed by competition with deoxycytidine-triphosphate for incorporation into the DNA strand. Taken together, these findings are consistent with structural differences of the incorporated arabinosyl moiety which alter reactivity of the 3'-terminus and thereby inhibit chain elongation. These findings also provide new insights regarding the inhibitory effects of ara-C on elongation of specific DNA sequences.

Arabinofuranosylcytosine Triphosphate↗
PubMed1987

Detection of 1-beta-D-arabinofuranosylcytosine incorporation into DNA in vivo.

The incorporation of (1-beta-d-arabinofuranosylcytosine (ara-C) into the DNA of leukemic cells is highly correlated with cytotoxicity in vitro. However, the measurement of ara-C incorporation into leukemic cell DNA in vivo during ara-C therapy has been limited by the lack of a suitably sensitive method. A quantitative assay procedure has therefore been developed to determine incorporation of unlabeled ara-C into DNA. This method involves DNA isolation from patient myeloblasts, enzymatic digestion of the DNA, high pressure liquid chromatography separation of the nucleosides, and determination of ara-C in the eluate fractions by radioimmunoassay. Using this approach, incorporation of unlabeled ara-C into DNA of HL-60 cells is log linear over concentrations of 1 to 100 microM ara-C. Furthermore, the extent of ara-C incorporation into DNA as determined by this method correlates significantly with measurements of [3H]ara-C (DNA) formation under similar conditions. This approach has also been applied to clinical samples. Myeloblasts from 6 patients receiving high-dose continuous-infusion ara-C therapy incorporated 0.00-0.36 pmol ara-C/microgram DNA during 24 h of therapy. These findings thus suggest that this method can be used to monitor the in vivo incorporation of ara-C into leukemic cell DNA.

Adult↗
PubMed1987

Expression of tumor necrosis factor receptors on human monocytes and internalization of receptor bound ligand.

Tumor necrosis factor (TNF) is a polypeptide produced by monocytes and macrophages. Although TNF receptors have been identified on a variety of cell types, previous studies have not determined whether these receptors also exist on monocytes. In the present work, highly purified recombinant TNF was labeled with 125I. The 125I-labeled TNF bound specifically to receptors on human monocytes and monocyte membrane preparations. A curvilinear Scatchard plot indicated the presence of TNF-binding sites with two different affinities. The results also indicate that receptor-bound TNF is rapidly internalized by monocytes and then degraded intracellularly. These findings are in concert with recent studies demonstrating that TNF immunomodulates monocyte function by an autocrine mechanism.

Binding Sites↗