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Biomedical subjects

C Baglioni

Publications and source records attributed to C Baglioni.

At least 55 records · Page 3Linked to original sources
PubMed1988

Tumor necrosis factor receptors and cytocidal activity are down-regulated by activators of protein kinase C.

Human HeLa cells and murine L(S) cells are highly sensitive to the cytocidal activity of tumor necrosis factor (TNF) when simultaneously treated with the inhibitor of protein synthesis cycloheximide. This cytocidal activity of TNF was inhibited up to 90% in both cell lines after a 15-60-min pretreatment with 3-10 ng/ml of phorbol 12-myristate 13-acetate (PMA). This inhibition was long lasting for HeLa cells but transient for L(S) cells. The protection afforded by PMA was most effective when the cells were pretreated with this phorbol ester, but it decreased when PMA was added together with TNF or after TNF addition. This finding suggested that PMA interfered with one of the early steps in the mechanism of action of TNF. A pretreatment with the calcium ionophore A23187 also reduced the cytocidal activity of TNF in both HeLa and L(S) cells to about the same extent. Treatment of these cells with either PMA or A23187 significantly decreased the binding of 125I-TNF to cell surface receptors. This decrease paralleled the time course and dose-response of the inhibition of cytocidal activity. In addition, treatment of HeLa cells with 1-oleyl-2-acetyl-glycerol (OAG) also induced a rapid loss of TNF binding capacity. Since OAG, PMA, and A23187 are all activators of protein kinase C (Ca2+/phospholipid-dependent enzyme), these results suggest that this kinase is involved in modulation of TNF sensitivity. Furthermore, depletion or inhibition of protein kinase C antagonized PMA-induced effects on TNF cytotoxicity and binding to receptors. Internalization of bound TNF was not significantly affected by PMA treatment, and Scatchard analysis of binding data indicated that PMA decreased TNF receptor binding affinity rather than the number of TNF-binding sites. These findings suggest that protein kinase C may have a physiological role in mediating TNF sensitivity.

Animals↗
PubMed1988

Tumor necrosis factor stimulates proliferation of human osteosarcoma cells and accumulation of c-myc messenger RNA.

The objective of this study was to establish whether human recombinant tumor necrosis factor (TNF) can significantly stimulate the proliferation of some tumor cells. Treatment with TNF had little or no effect on the growth of human tumor cells and murine NIH/3T3 cells cultured in medium with high serum concentration. Two tumor lines, SK-MEL-109 melanoma and HOS osteosarcoma cells, were adapted to grow in medium supplemented with 0.5% serum. The growth of these SK-MEL-109 cells was inhibited by TNF, but that of the HOS cells was greatly stimulated by TNF in a dose-dependent way. Treatment with 10 ng/ml of TNF resulted in a two-fold increase in the rate of cell division. This effect of TNF was also shown by measuring DNA and protein synthesis. The continuous presence of TNF was not required for its mitogenic activity on HOS cells cultured with 0.5% serum, since treatment for only one day with TNF resulted in prolonged growth stimulation. The failure of TNF to promote division of cells cultured in medium with 10% serum may possibly be explained by the presence of saturating amounts of growth factors in serum. Interferons abolished the mitogenic activity of TNF on HOS cells. Furthermore, TNF did not show synergism with insulin or epidermal growth factor in stimulating growth of these cells. The level of c-myc mRNA was increased five-fold after 30 minutes of treatment with TNF. This shows that TNF is a growth factor for HOS cells and that it induces accumulation of c-myc mRNA.

Animals↗
PubMed1987

Tumor necrosis factor/cachectin stimulates peritoneal macrophages, polymorphonuclear neutrophils, and vascular endothelial cells to synthesize and release platelet-activating factor.

Murine tumor necrosis factor (mTNF) stimulates production of platelet-activating factor (PAF) by cultured rat peritoneal macrophages in amounts comparable to those formed during treatment with the calcium ionophore A23187 or phagocytosis of zymosan. The cell-associated PAF that was released into the medium was identical to synthetic PAF, as determined with physicochemical, chromatographic, and enzymatic assays. Furthermore, de novo synthesis of PAF by macrophages was demonstrated by the incorporation of radioactive precursors such as [3H]acetyl-coenzyme A or [3H]2-lyso-PAF. Macrophages incubated with mTNF for 4 h synthesized PAF only during the first h of treatment. At this time, the amount of cell-associated PAF was approximately equal to that released into the medium. The cell-associated PAF decreased afterwards, whereas that in the medium did not correspondingly increase, suggesting that some PAF was being degraded. The response of rat macrophages to different doses of mTNF and human TNF (hTNF) was examined. Maximal synthesis of PAF was obtained with 10 ng/ml of mTNF and 50 ng/ml of hTNF. This finding may be explained by a lower affinity of hTNF for TNF receptors of rat cells. The hTNF stimulated production of PAF by human vascular endothelial cells cultured from the umbilical cord vein. The time course of PAF synthesis was slower than that observed with macrophages, with maximal production between 4 and 6 h of treatment. Optimal synthesis of PAF was obtained with 10 ng/ml of hTNF. Only 20-30% of the PAF synthesized by endothelial cells was released into the medium, even after several hours of incubation. Synthesis of PAF in response to TNF was also detected in rat polymorphonuclear neutrophils, but not in human tumor cells and dermal fibroblasts. Therefore, production of PAF is a specialized response that is transient in macrophages continuously treated with TNF, and that appears to be controlled by unidentified regulatory mechanisms.

Animals↗
PubMed1987

The active form of tumor necrosis factor is a trimer.

Natural human and recombinant human and murine tumor necrosis factors (TNF) were fractionated by gel filtration chromatography on Sephadex G-75. The active form of TNF was identified by its inhibitory activity in receptor binding assays with HeLa cells and was eluted as a protein of Mr approximately 55,000. Radioiodinated human and murine TNF were fractionated by gel filtration into a major peak of Mr approximately 55,000, corresponding to a trimer, and a minor peak of Mr approximately 17,000, corresponding to a monomer. Binding assays showed that the timer was at least 8-fold more active than the monomer. The human TNF partially dissociated into monomers upon addition of the nonionic detergent Triton X-100. Isolated monomers showed low binding affinity (KD = 70 nM) and reduced cytotoxicity, whereas trimers showed high binding affinity (KD = 90 pM) and cytotoxicity. When 125I-TNF was bound to cells, no release of monomer was detectable, suggesting that the trimer could directly bind to cellular receptors without dissociating into subunits. Further evidence for such binding was obtained by cross-linking 125I-TNF trimers with bis[2-(succinimidooxycarbonyloxy)ethyl]sulfone. These trimers were bound to HeLa cells, could be dissociated from cellular receptors, and elicited a cytotoxic response. These results show that trimers, whether native or cross-linked, bind to receptors and are the biologically active form of TNF.

Animals↗
PubMed1987

Cytostatic and cytotoxic activity of tumor necrosis factor on human cancer cells.

The cytostatic and cytotoxic activity of human recombinant tumor necrosis factor (rTNF) was assayed on different tumor cell lines. Human BT-20 breast and ME-180 cervix cancer cells were growth-inhibited by rTNF, whereas two other cell lines were not significantly inhibited. However, when protein synthesis was inhibited by cycloheximide, rTNF was cytotoxic for these cells but not for BT-20 cells. This finding suggested that different mechanisms are responsible for the cytostatic and cytotoxic activity of rTNF. The sensitivity of different cell lines to rTNF could not be correlated with a high number or affinity of rTNF receptors. Occupancy of only a few receptors was sufficient for rTNA cytotoxicity, but an increase in receptor number after treatment with interferon-gamma, or a decrease after pretreatment with cycloheximide, correspondingly enhanced or depressed the cytotoxicity of rTNF. It seemed possible that some cells could be protected from this effect of rTNF by synthesizing "protective" proteins. While searching for such proteins, we observed that rTNF induced the synthesis of two polypeptides in SK-MEL-109 melanoma cells, but not in other cancer cells. Actinomycin D added with rTNF abolished synthesis of these polypeptides, suggesting that rTNF induced transcription of the corresponding mRNAs. Surprisingly, rTNF stimulated growth of SK-MEL-109 cells cultured in medium with low serum.

Breast Neoplasms↗
PubMed1987

Induction of class I major histocompatibility complex antigens in human teratocarcinoma cells by interferon without induction of differentiation, growth inhibition, or resistance to viral infection.

The behavior of human teratocarcinoma cells, and especially their stem cells (embryonal carcinoma cells), may provide insights into the properties of human early embryonic cells. We report here that human recombinant gamma-interferon (IFN-gamma) induced the expression of major histocompatibility complex Class I (HLA-A, B, C) antigens and beta 2-microglobulin in the two human embryonal carcinoma cell lines, 2102Ep cl.4D3 and NTERA-2 cl.D1, and in the yolk sac carcinoma cell line, 1411H; human recombinant IFN-alpha and IFN-beta were less effective inducers of these cell surface molecules. No induction was observed in the gestational choriocarcinoma cell line, JAR. Neither IFN-alpha, IFN-beta, nor IFN-gamma caused growth inhibition, expression of major histocompatibility complex Class II (HLA-DR) antigens, resistance to viral (vesicular stomatitis virus) infection, or expression of 2',5'-oligo(A)synthetase in any of the cells. Also, IFN-gamma neither induced differentiation of NTERA-2 cl.D1 cells, which are pluripotent human stem cells, nor influenced their differentiation induced by retinoic acid. However, developmental regulation of responsiveness to IFN was evident, since IFN-gamma induced higher levels of surface expression of HLA-A, B, C and beta 2-microglobulin in the retinoic acid-induced differentiated NTERA-2 cl.D1 cells than in the undifferentiated parental cells. Also, 2',5'-oligo(A)synthetase was inducible in the NTERA-2 cl.D1 differentiated cells by IFN-alpha and -beta, although not by IFN-gamma, and slight resistance to vesicular stomatitis virus infection was evident in aged cultures of differentiated cells exposed to IFN-alpha. The effect of recombinant mouse IFN-gamma on major histocompatibility complex expression by several murine teratocarcinoma cells was also examined: H-2 Class I (H-2Db), but not class II (I-Ab), antigens were induced in the parietal yolk sac carcinoma lines, PYS and F9Ac cl.9; in cultures of PCC3/A/1 containing both embryonal carcinoma (EC) and differentiated cells; and in cultures of the EC cells, PCC4azaR and PCC4AO, without evidence of differentiation. No induction was observed in the murine EC cell lines, F9 or FA (H-2Kk). Our results indicate that human EC cells, like murine EC cells, exhibit only a partial response to the interferons, and that the extent of this response is developmentally regulated.

Antigens, Surface↗
PubMed1987

Cytocidal activity of tumour necrosis factor: protection by protease inhibitors.

The mechanism of the cytostatic and cytocidal activities of TNF was studied in human tumour cells. BT-20 breast and ME-180 cervical cancer cells were significantly growth-inhibited by TNF, but other cells were not. When protein synthesis was inhibited by cycloheximide, however, TNF was cytotoxic for all cells except BT-20 cells. This suggests that different mechanisms are responsible for the cytostatic and cytocidal activities of TNF. The sensitivity of different cell lines could not be correlated with the number or affinity of TNF receptors. Some protease inhibitors completely protected human and murine cells from TNF cytotoxicity. Inhibitors of chymotrypsin-like proteases were more effective than inhibitors of trypsin-like proteases. Reversible and irreversible inhibitors (such as alkylating compounds) were both protective. The cells were best protected when pretreated with inhibitors before the addition of TNF. When the protease inhibitors were removed the cells gradually lost their resistance to TNF cytotoxicity. The inhibitors did not interfere with the functioning of TNF-receptor complexes, since SK-MEL-109 melanoma cells treated with a protease inhibitor synthesized TNF-induced proteins. These findings suggest that a protease is involved in the cytocidal activity of TNF.

Humans↗
PubMed1987

Protection from tumor necrosis factor cytotoxicity by protease inhibitors.

Tumor necrosis factor (TNF) is cytocidal for human and murine cells when protein synthesis is inhibited by cycloheximide, but some protease inhibitors completely protect these cells from TNF cytotoxicity. Inhibitors of chymotrypsin-like proteases are active at lower concentrations than inhibitors of trypsin-like proteases. Both irreversible inhibitors, such as alkylating compounds, and reversible inhibitors, such as substrates of proteases, protect cells from the cytocidal activity of TNF. This protection is most effective when the cells are pretreated with these inhibitors before addition of TNF. When the protease inhibitors are removed, the cells gradually lose resistance to TNF cytotoxicity. The inhibitors do not interfere with the functioning of TNF-receptor complexes, since SK-MEL-109 melanoma cells treated with a protease inhibitor synthesize a TNF-induced protein. These findings suggest that a protease in involved in the cytocidal action of TNF.

Animals↗
PubMed1987

Loss of (2'-5')oligoadenylate synthetase activity by production of antisense RNA results in lack of protection by interferon from viral infections.

An expression vector was constructed that carries part of the human BK papovavirus with 0.5 kilobases of (2'-5')oligoadenylate (2-5A) synthetase cDNA inserted in inverted orientation downstream from the virion proteins (VP) promoter and the neomycin-resistance gene neo under the control of a simian virus 40 promoter. Cells transfected with this vector and selected for resistance to the neomycin derivative G418 synthesized RNA complementary to 2-5A synthetase mRNA. These cells lacked 2-5A synthetase activity, and the enzyme was not inducible by interferon. In contrast, 2-5A synthetase was induced in cells transfected with a control vector without the cDNA insert. Such cells were protected by interferon from RNA viruses, whereas cells lacking 2-5A synthetase were not protected from encephalomyocarditis virus, vesicular stomatitis virus, and Sindbis virus but were fully protected from influenza virus. These findings show that a high level of 2-5A synthetase is required for interferon-induced protection from the cytoplasmic RNA viruses tested.

2',5'-Oligoadenylate Synthetase↗
PubMed1986

Translational regulation of the synthesis of a major heat shock protein in HeLa cells.

The synthesis of a major heat shock protein (HSP 70) was measured in HeLa cells incubated at 42.5 degrees C and then transferred to 37 degrees C or 30 degrees C. After 90 min, synthesis of HSP 70 decreased by 54 and 85%, respectively, whereas HSP 70 mRNA was reduced at most by 20%. Therefore, the reduced synthesis of HSP 70 could not be accounted for by mRNA turnover. HSP 70 was associated with large polyribosomes (6-10 ribosomes) in cells kept at 42.5 degrees C, but with medium or small polyribosomes in cells transferred to 37 degrees C or 30 degrees C (5-6 or 2-3 ribosomes, respectively). Addition of puromycin to these cells resulted in the release of all ribosomes from HSP 70 mRNA, indicating that they were translationally active. The regulation of HSP 70 synthesis was investigated in cell-free systems prepared from heat-shocked or control cells and incubated at 30 degrees C and 42 degrees C. After 5 min at 42 degrees C, the cell-free system from heat-shocked cells synthesized protein at 3 times the rate of the control cell-free system. This difference was in large part due to synthesis of HSP 70. Addition of HSP mRNA to the control cell-free system stimulated protein synthesis at 42 degrees C, but not at 30 degrees C. These findings suggest that translation of HSP 70 mRNA is specifically promoted at high temperature and repressed during recovery from heat shock by regulatory mechanisms active at the level of initiation.

Cell-Free System↗
PubMed1986

Species specificity of human and murine tumor necrosis factor. A comparative study of tumor necrosis factor receptors.

Recombinant murine and human tumor necrosis factor (mTNF and hTNF, respectively) were radioiodinated to high specific activity using a solid-phase lactoperoxidase method. A single class of high affinity receptors for 125I-TNF was identified on TNF-sensitive murine L cells and human HeLa S2 cells. Competitive radioligand binding assays were used to study the species specificity of TNF preparations. Unlabeled hTNF competed 30-fold less effectively than mTNF for binding to L cell receptors, whereas mTNF competed to approximately the same extent as hTNF for binding to HeLa cell receptors. A similar species specificity was observed in cytotoxicity assays; hTNF was more cytotoxic for HeLa cells than mTNF. Conversely, mTNF was more growth inhibitory and cytotoxic for L cells than hTNF. mTNF. and hTNF.receptor complexes were compared by gel filtration chromatography and polyacrylamide gel electrophoresis before and after cross-linking with bis[2-(succinimidooxycarbonyloxy)ethyl]sulfone (BSOCOES). These complexes eluted in gel filtration at a position corresponding to a globular protein of 350,000 Mr. Gel autoradiographs of the fractions containing cross-linked complexes showed bands of 95,000 and 75,000 Mr as well as small amounts of higher Mr bands. mTNF and hTNF treated with BSOCOES formed cross-linked dimers and trimers. Therefore, we were unable to determine whether the 95,000 and 75,000 Mr bands represented two distinct subunits of receptors or one subunit to which either a dimer or a monomer of TNF was cross-linked. These results demonstrate species specificity in the TNF-receptor interaction. In addition, the affinity labeling studies in two species give an identical pattern for the TNF X receptor complexes, suggesting that the receptors have similar subunit composition.

Animals↗
PubMed1986

Growth inhibition and cytotoxicity of tumor necrosis factor in L929 cells is enhanced by high cell density and inhibition of mRNA synthesis.

L929 cells were growth-inhibited after 1 to 2 days of treatment with human recombinant tumor necrosis factor (rTNF). This effect of rTNF was largely reversible, and L929 cells resumed normal growth when rTNF was removed. The rTNF showed growth inhibitory and cytotoxic activity when L929 cells approached a high cell density and grew slowly. This was shown in experiments in which L929 cells approached confluency at different times after being seeded at increasing initial densities. The rTNF had little effect on the growth of cells seeded at the lowest density tested. L929 cells cultured to high density synthesized RNA at a reduced rate. This suggested that a reduced rate of RNA synthesis may be at least in part responsible for the growth inhibitory and cytotoxic activities of rTNF on cells grown to high density. Treatment with inhibitors of RNA synthesis potentiated the cytotoxic activity of rTNF. Inhibition of mRNA synthesis was apparently responsible for the enhanced sensitivity to rTNF, as shown by experiments with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole, an inhibitor of the synthesis of poly(A)-containing RNA.

Animals↗
PubMed1986

Tumor necrosis factor induces synthesis of two proteins in human fibroblasts.

Human fibroblasts were insensitive to tumor necrosis factor (TNF) alone but were killed when treated with TNF together with the inhibitor of protein synthesis cycloheximide. However, incubation with TNF before addition of cycloheximide protected these cells from cytotoxicity. This suggested that TNF induced some protective mechanism(s) and that protein synthesis was required for this induction. By labeling fibroblasts with [35S]methionine, we observed that TNF induced in these cells the synthesis of two proteins of Mr 36,000 and 42,000 (p36 and p42). This induction was dependent on the TNF concentration and was observed within a few hours after addition of TNF. Actinomycin D prevented synthesis of these proteins, suggesting that TNF induced transcription of the corresponding mRNAs. p42 appeared to be stable, whereas p36 turned over within a few hours. The physiological role of these proteins in the cellular response to TNF remains to be established.

Cycloheximide↗
PubMed1986

Induction of the synthesis of tumor necrosis factor receptors by interferon-gamma.

Human HT-29 colon carcinoma and HeLa D98/AH2 and SK-MEL-109 melanoma cells were sensitive to synergistic growth inhibition by concentrations of recombinant human tumor necrosis factor (rTNF) and interferon-gamma (rIFN-gamma) which individually were only slightly inhibitory. We investigated whether this synergism could be explained by the presence of an increased number of TNF receptors in cells treated with rIFN-gamma. These receptors were measured by incubating cells resuspended from monolayers with 125I-rTNF. HT-29 cells treated for a few hours with rIFN-gamma could bind more 125I-rTNF than control untreated cells, but this binding returned to the level of control cells after 24 hr. The treatment with rIFN-gamma did not change the binding affinity of TNF receptors, but increased their number to 1800 per cell from a basal level of about 800 per cell. Inhibitors of RNA synthesis prevented this increase. HT-29 cells were significantly more growth-inhibited when treated first for 6 to 12 hr with rIFN-gamma and then with rTNF, than when treated first with rTNF and then with rIFN-gamma. Untreated HeLa D98/AH2 and SK-MEL-109 cells had 2400 and 9000 receptors per cell, with a KD similar to that of HT-29 cells (approximately 2 X 10(-10)M). A significant increase in TNF receptors after treatment with rIFN-gamma was observed in HeLa D98/AH2, but not in SK-MEL-109 cells. No increase in TNF receptors was detected in cells treated with rIFN-alpha 2. These results indicate that the synergism between rTNF and rIFN-gamma may be due, at least in part, to a transient induction of the synthesis of TNF receptors by rIFN-gamma in cells with a relatively low number of these receptors.

Adenocarcinoma↗
PubMed1986

Activation of hemin-regulated initiation factor-2 kinase in heat-shocked HeLa cells.

Protein synthesis was drastically inhibited in HeLa cells incubated for 5 min at 42.5 degrees C, but it resumed after 20 min at a rate about 50% that of control cells. After 10 min of heat shock, the binding of Met-tRNAf to 40 S ribosomal subunits was greatly reduced and a polypeptide identified by immunoprecipitation with the alpha subunit of eukaryotic initiation factor-2 (eIF-2) was phosphorylated. Extracts prepared from control and heat-shocked cells were assayed for in vitro protein synthesis. Both extracts were active when supplemented with hemin, but the extract from heat-shocked cells had little initiation activity without this addition. A Mr 90,000 polypeptide and eIF-2 alpha were phosphorylated in this extract, but hemin or an antibody which inhibits the protein kinase designated heme-controlled repressor reduced this phosphorylation. These findings implicated heme-controlled repressor as the kinase at least in part responsible for eIF-2 alpha phosphorylation. Furthermore, the initial inhibition of protein synthesis and eIF-2 alpha phosphorylation after heat shock were reduced by adding hemin to intact HeLa cells. These cells synthesized heat-shock proteins with some delay relative to cells without added hemin. The binding of Met-tRNAf to 40 S ribosomal subunits was inhibited by about 50% in extracts prepared from cells heat-shocked for 40 min, and eIF-2 alpha phosphorylation was increased in these cells. These results suggest that heme-controlled repressor is activated in heat-shocked cells and that eIF-2 alpha phosphorylation limits mRNA translation even after partial recovery of protein synthesis.

Electrophoresis, Polyacrylamide Gel↗
PubMed1986

Inhibition of 2',5'-oligo(A)-dependent endoribonuclease by 2',5'-oligo(A) degradation products.

Addition of extract of interferon (IFN)-treated HeLa cells to transcription reactions containing activated reovirion cores decreases the yield of viral mRNA (C. Baglioni, A. De Benedetti, and G. J. Williams, 1984, J. Virol. 52, 865-871). The 2'5'-oligo(A) (2-5A)-dependent endonuclease (RNase L) cleaves specifically viral mRNA, but little 5'-triphosphate 2-5A is recovered from these reactions by DEAE-cellulose chromatography. However, in the present study we detected microM concentrations of 2-5A derivatives by binding to RNase L. Similar results were obtained when the synthetic double-stranded RNA poly(I) X poly(C) was incubated with extract from IFN-treated cells: microM concentrations of 2-5A were detected by the binding assay, but little rRNA was degraded by RNase L. 2-5A derivatives which inhibited the activation of RNase L by authentic 2-5A were eluted from DEAE-cellulose with 90 mM KCl. These inhibitors were also formed by incubating purified 2-5A with HeLa cell extract. These results indicated that 2-5A was synthesized in the incubations with reovirion cores or poly(I) X poly(C), but that it was in large part degraded to compounds inhibitory for RNase L. IFN-treated HeLa cells were incubated with poly(I X C), but little rRNA degradation was detected in spite of the presence of high concentrations of 2-5A in these cells. Most of this 2-5A was eluted with 90 mM KCl from DEAE-cellulose and was inhibitory for RNase L. This indicated that 2-5A was degraded to inhibitory derivatives also in intact cells. The structure of the degradation products of 2-5A has not been established, but they contain free terminal phosphate(s), since their binding to RNase L and the inhibition of this enzyme is abolished by digestion with phosphatase.

Adenine Nucleotides↗
PubMed1985

Binding of human tumor necrosis factor to high affinity receptors on HeLa and lymphoblastoid cells sensitive to growth inhibition.

Purified human tumor necrosis factor (TNF) was iodinated to high specific activity with good retention of its biological activity, as determined by the cytotoxic titer on murine L929 cells. The binding of 125I-TNF to L929 and human HeLa S2 cells grown in monolayer was initially measured, but high levels of nonspecific binding were observed. Specific binding to high affinity receptors of HeLa S2 cells grown in suspension culture was demonstrated by competitive displacement experiments and analysis of the binding data with the LIGAND program. A KD of 2 X 10(-10) M and 6000 receptors/cell were calculated in this way. These observations provide the first direct evidence for a cellular receptor for TNF. The cell-bound 125I-TNF was internalized at 37 degrees C, presumably by receptor-mediated endocytosis, and subsequently degraded to acid-soluble products. Three lines of human lymphoblastoid cells were examined for sensitivity to the cytostatic effect of TNF and for the presence of high affinity receptors. Daudi and Raji cells were insensitive to TNF and showed very few specific binding sites when incubated with 125I-TNF. Jurkat cells were growth-inhibited by TNF and showed a significantly greater number of specific binding sites than the other lymphoblastoid cells. These findings suggest that the sensitivity of some cell lines to the biological effects of TNF may be correlated with the presence of a relatively high number of receptors for this factor.

Animals↗