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Biomedical subjects

E Huberman

Publications and source records attributed to E Huberman.

At least 91 records · Page 5Linked to original sources
PubMed1986

Translocation of protein kinase C in human leukemia cells susceptible or resistant to differentiation induced by phorbol 12-myristate 13-acetate.

We investigated the possible relationship between the susceptibility of cells to differentiation induced by phorbol 12-myristate 13-acetate (PMA) and the subcellular translocation of calcium- and phospholipid-dependent protein kinase (protein kinase C) activity from the cytosol to the membrane. These two events were analyzed in a number of human leukemia cell lines, including four cell variants of the promyelocytic cell line HL-60 that exhibit different degrees of susceptibility to PMA-induced differentiation. The phenotype of the differentiated cells was characterized by increased reactivity with monoclonal antibodies against maturation-specific cell surface antigens, increased nonspecific esterase activity, and acquisition of morphological cell maturation. Analysis of the subcellular distribution of protein kinase C activity in each of these cell types revealed that 90% of the kinase activity was present in the cytosolic fraction, with the remaining activity in the membrane fraction. Treatment of the differentiation-susceptible cells with 160 nM PMA resulted, within 5 min after treatment, in a greater than 60% decrease in protein kinase C activity in the cytosolic fraction and a greater than 1500% increase in the activity in the membrane fraction. No such subcellular redistribution of protein kinase C activity was found after treatment of the differentiation-resistant cells. On the basis of these findings, we suggest that the process of subcellular translocation of protein kinase C activity, initiated after the binding of PMA to this kinase, is required for the induction of cell differentiation by this phorbol diester.

Cell Compartmentation↗
PubMed1986

Alteration in glycosphingolipid pattern during phorbol-12-myristate-13-acetate-induced cell differentiation in human T-lymphoid leukemia cells.

We analyzed the patterns of glycosphingolipids (GSLs) from a line of cells derived from a clone of the human T-cell leukemia cells (CEM) that had been induced to differentiate by phorbol-12-myristate-13-acetate (PMA) into cells with a suppressor-like phenotype. We characterized the differentiation state of the cells by immunofluorescence by using anti-cell surface differentiation-specific monoclonal antibodies (OKT3, OKT4, OKT6, and OKT8). The GSLs were extracted and separated by thin-layer chromatography and the individual bands were quantitated by a dual-wavelength densitometer or by autoradiography of GSLs labeled with [14C]glucosamine and [14C]galactose. Treatment of the CEM cells with 0.16-16 nM PMA for 6 h to 6 days resulted in a dose- and time-dependent increase in the amount of two neutral GSLs [ceramide monohexoside and ceramide dihexoside] and three gangliosides [monosialoganglioside (GM3), sialosylparagloboside, and disialoganglioside (GD3)]. The increase in the neutral GSLs after PMA treatment reached its maximum at 30 h while GM3 peaked at 96 h. The increases in GM3 and sialosylparagloboside are presumably due to an increase in their synthesis levels because PMA promoted an elevated incorporation of glucosamine and galactose into these GSLs. The increase in the amount of GD3, on the other hand, is due to either a decrease in its degradation or use in other metabolic pathways because no detectable increase in glucosamine and galactose incorporation into this ganglioside could be found. Incubation of control or PMA-induced CEM cells with GM3 fractions purified from either CEM cells, human brain, or dog erythrocytes caused a reduction in cell growth and prevented the increase in reactivity of the induced cells with the OKT3 antibody. Incubation with semisynthetic ceramide dihexoside, however, prevented the decrease in reactivity with the OKT4 antibody. The observed changes in GSL patterns during PMA-induced differentiation of the CEM cells into suppressor-like cells and the inhibition of CEM cell growth by GM3 fractions suggest that the GSLs play a role in the control of cell growth and differentiation in the PMA-treated CEM cells.

Antibodies, Monoclonal↗
PubMed1986

Activation of the colon carcinogen 1,2-dimethylhydrazine in a rat colon cell-mediated mutagenesis assay.

Suspensions of rat colon epithelial cells metabolized the potent colon carcinogen, 1,2-[14C]dimethylhydrazine (DMH), into 14C-labeled, alkali-soluble volatile products, presumably CO2. The colon cell suspensions, however, were less effective than rat hepatocyte suspensions. In addition, we used a cell-mediated mutagenesis assay to test rat colon epithelial cells grown from tissue explants for their ability to metabolize DMH into products mutagenic for human P3 teratoma cells. Mutagenesis in the P3 cells was indicated by an acquired resistance to 6-thioguanine. Cocultivation of the colon cells with the P3 cells in the cell-mediated assay resulted in mutagenesis, whereas in the absence of the colon cells, no mutagenesis by DMH was observed. Similar results were obtained in a hepatocyte-mediated mutagenesis assay. Colon cells were also able to activate another carcinogen, benzo(a)pyrene, into products mutagenic for the P3 cells. Individual epithelial clonal populations isolated from the colon cultures grown from tissue explants, however, expressed different capacities to activate DMH and benzo(a)pyrene into mutagens, and a high degree of DMH activation by cells from a colon clone was not necessarily associated with a similar degree of benzo(a)pyrene activation. Our results indicate that the colon itself contains epithelial cell types capable of effectively converting DMH into mutagenic (and presumably carcinogenic) products without necessarily involving intermediary metabolism by hepatocytes as previously thought.

1,2-Dimethylhydrazine↗
PubMed1985

Specific protein phosphorylation in human promyelocytic HL-60 leukemia cells susceptible or resistant to induction of cell differentiation by phorbol-12-myristate-13-acetate.

The pattern of protein phosphorylation induced by phorbol-12-myristate-13-acetate (PMA) was analyzed by two-dimensional gel electrophoresis in human HL-60 leukemia cells, which are susceptible to induction of cell differentiation by PMA, and in cells from an HL-60 cell variant designated R-94 that are resistant to such an induction. Protein phosphorylation was detected by observing either a rapid acid-directed charge shift of [35S]methionine-labeled protein or an increase in the amount of phosphate label in a 32P-labeled protein. The results indicated that PMA at 10(-7) M causes within 30 min after treatment the phosphorylation of at least ten different proteins in both the HL-60 and R-94 cells. Among these ten phosphorylated proteins, we identified a major cytoplasmic polypeptide (Mr approximately 64,000), a cytoskeletal protein (Mr approximately 56,000), a nonmuscle myosin light chain, and two proteins (Mr approximately 60,000 and 64,000) localized in or around the cell nucleus. Phosphoamino acid analysis of six of the ten phosphoproteins showed that they contain phosphoserine. None of these proteins contained phosphotyrosine or phosphothreonine. The R-94 cell variant was found to be capable of increased protein phosphorylation after PMA treatment; however, the level of phosphate incorporation reached only the level of the untreated HL-60 cells and thus fell far short of the level observed in the HL-60 cells after PMA treatment. It is suggested that the basis for the acquired resistance in R-94 cells towards induction of cell differentiation by PMA is a block in signal transmission involving phosphorylation of nuclear protein(s) following the binding of the inducer PMA to its receptor (protein kinase C).

Caenorhabditis elegans Proteins↗
PubMed1985

Expression of maturation-specific nuclear antigens in differentiating human myeloid leukemia cells.

The expression of three myeloid-specific nuclear antigens was studied by indirect immunofluorescence with murine monoclonal antibodies in human myeloid (HL-60, ML-2, KG-1, and B-II) leukemia cells treated with chemical inducers of cell differentiation. Treatment of the promyelocytic HL-60 cells with dimethyl sulfoxide or 1,25-dihydroxyvitamin D3 induced the cells to acquire a phenotype that resembled that of granulocytes and monocytes-macrophages, respectively. These phenotypes were characterized by changes in cell growth, cell morphology, expression of specific cell surface antigens, and activities of lysozyme and nonspecific esterase enzymes. Induction of these differentiation markers in the HL-60 cells was associated with induction of the myeloid-specific nuclear antigens. The ML-2 cells, which are arrested at the myeloblast-promyelocyte stage, were also susceptible to the induction of cell differentiation and to changes in the expression of the nuclear antigens, but the degree of susceptibility was less than in the HL-60 cells. The less-differentiated KG-1 and B-II myeloid cells were either not responsive or responded only in a limited degree to the induction of cell differentiation or to changes in the expression of the nuclear antigens. We suggest that the reactivity of cells with monoclonal antibodies to specific nuclear antigens can be used as a maturational marker in cell differentiation studies. Furthermore, nuclear antigens expressed early in cellular differentiation may provide information about changes in regulatory elements in normal and malignant cells.

Antibodies, Monoclonal↗
PubMed1985

Recombinant gamma-interferon and lipopolysaccharide enhance 1,25-dihydroxyvitamin D3-induced cell differentiation in human promyelocytic leukemia (HL-60) cells.

The induction of cell differentiation by a combination of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], recombinant gamma-interferon (rec gamma-IFN), and a lipopolysaccharide from E. coli (LPS) was studied in a clonal population (clone-9) of human promyelocytic HL-60 leukemia cells in vitro. Treatment of clone-9 cells with 10(-9) to 10(-7)M 1,25-(OH)2D3 yielded a macrophage cell differentiation. The addition of 10 or 100 U/ml of gamma-IFN and 2 or 10 micrograms/ml LPS caused a further increase in expression of the different differentiation markers. The most pronounced effects involved increases in cell attachment to the surface of tissue-culture Petri dishes and in lysozyme, nonspecific esterase, and cytolytic activities. The combined treatment with 1,25-(OH)2D3 and rec gamma-IFN and LPS also caused an increase in the percent of multinucleated giant cells. These results indicate the effectiveness of combining different agents in inducing cell differentiation in HL-60 cells. A similar approach may be useful in controlling myeloid leukemias in vivo.

24,25-Dihydroxyvitamin D 3↗
PubMed1984

Induction of mutations by chemical agents at the hypoxanthine-guanine phosphoribosyl transferase locus in human epithelial teratoma cells.

Induction of 6-thioguanine (TG) resistance by chemical mutagens was examined in a line of cells derived from a human epithelial teratocarcinoma cell clone. The cells, designated as P3 cells, have a stable diploid karyotype with 46(XX) chromosomes, including a translocation between chromosomes 15 and 20. Efficient recovery of TG-resistant mutants induced by the direct-acting mutagens: N-methyl-N'-nitro-N-nitrosoguanidine (MNNG); 7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10 -tetrahydrobenzo[a]pyrene (BPDE); and benzo[a]pyrene (B[a]P); activated in a cell-mediated assay, required an expression time of 7 days and a saturation density of 2 X 10(4) cells/60-mm petri dish. The TG-resistant mutant cells induced by MNNG and BPDE maintained their resistant phenotype 4-6 weeks after isolation. This mutant phenotype was associated with a more than 10-fold reduction in hypoxanthine-guanine phosphoribosyl transferase (HGPRT) activity relative to that of the parental P3 cell line, which was shown to catalyze the formation of 4.6 pmoles inosine-5'-monophosphate (IMP)/min/microgram protein. Induction of TG resistance was also observed in P3 cells cocultivated in a cell-mediated assay with human breast carcinoma cells, which are capable of polycyclic aromatic hydrocarbon (PAH) metabolism, after treatment with the carcinogenic PAHs: B[a]P, chrysene, 7,12-dimethylbenz[a]anthracene (DMBA), and 3-methylcholanthrene (MCA). The degree of mutant induction in this assay was related to the carcinogenic potency of these PAHs in experimental animals. The most potent mutagen was DMBA, followed in decreasing order by MCA, B[a]P, and chrysene. DMBA, at 0.4 microM, increased the frequency of mutants for TG resistance from 2 for the control to about 200 TG-resistant mutants/10(6) colony-forming cells (CFC). Benzo[e]pyrene (B[e]P) and pyrene, which are not carcinogenic, were not effective in the assay. None of the PAHs was mutagenic in the P3 cells cultivated in the absence of the PAH-metabolizing cells. These results indicate that the P3 cells can be useful for the study of mutagenesis at the HGPRT locus by direct-acting chemical mutagens, as well as by chemicals activated in a cell-mediated assay.

Biotransformation↗
PubMed1984

Enhancement of chemical-carcinogen-induced cell transformation in hamster embryo cells by 1 alpha,25-dihydroxycholecalciferol, the biologically active metabolite of vitamin D3.

The biologically active metabolite of vitamin D3, 1 alpha,25-dihydroxycholecalciferol [1,25-(OH)2D3], which by itself was not effective in inducing morphological cell transformation in vitro in the Syrian hamster embryo colony assay, enhanced such a transformation in a dose-dependent manner in cells pretreated with a series of known chemical carcinogens. Treatment of the hamster embryo cells with either benzo[a]-pyrene (B[a]P), (+/-)7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, or N-methyl-N'-nitro-N-nitroso-guanidine for 3 days (stage 1) followed by treatment with 1,25-(OH)2D3 for 4 days (stage 2) increased the transformation frequency compared to the transformation frequency for cells treated with the carcinogen only. Reversing the order of the treatment (i.e., incubating the cells with 1,25-(OH)2D3 prior to B[a]P treatment) did not result in an effective enhancement. Vitamin D3 and 24,25-dihydroxycholecalciferol, another metabolite of this vitamin, also enhanced the frequency of cell transformation but to a lesser degree than did 1,25-(OH)2D3. Pyrene, which is not a carcinogen, did not induce transformed colonies either by itself or when combined with 1,25-(OH)2D3. Benzo[e]pyrene (B[e]P), which is not considered to be a complete carcinogen but can act as a tumor initiator, also was not effective by itself. However, in the two-stage protocol with 1,25-(OH)2D3, B[e]P did induce transformed colonies. Comparison of the enhancing effect of 1,25-(OH)2D3 to that of phorbol-12-myristate-13-acetate (PMA), a known tumor promoter, revealed a heterogeneity in the response to these agents. A high or low responsiveness of the cells to 1,25-(OH)2D3 was not necessarily indicative of a similar responsiveness to PMA. These results indicate that 1,25-(OH)2D3 can act as a promoter of cell transformation in fibroblasts and perhaps other cell types but through a mechanism not necessarily identical to that involving PMA.

24,25-Dihydroxyvitamin D 3↗
PubMed1984

Membrane lipid dynamics in human promyelocytic leukemia cells sensitive and resistant to 12-O-tetradecanoylphorbol-13-acetate induction of differentiation.

A series of fluorescent probes was used to analyze membrane lipid dynamics in promyelocytic leukemic cells sensitive (HL-60) or resistant (R-55) to phorbol diester induction of cell differentiation. When examined with the probe 1,6-diphenyl-1,3,5-hexatriene, which can penetrate the plasma membrane and intercalate in the lipids of both leaflets of the plasma membrane, as well as in organellar membranes, R-55 cells were found to have higher fluorescence anisotropy values, indicative of decreased lipid fluidity, as compared to HL-60 cells. In contrast, when HL-60 and R-55 cells were compared using a series of membrane-impermeant fluorophores (stachyose derivatives of anthroyloxystearate and pyrenebutyryl hydrazide) that incorporate only into the outer hemileaflet of the plasma membrane, no difference was observed in membrane lipid fluidity. Exposure to 12-O-tetradecanoylphorbol-13-acetate (10 ng/ml) for 24 hr decreased the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene in both HL-60 and R-55 cells, whereas by 48 hr only the HL-60 cells displayed the reduction. No effect on the fluorescence anisotropy of 1-(4'-trimethylammonium phenyl)-6-phenyl-1,3,5-hexatriene, which is believed to localize in the plasma membrane, was observed in R-55 cells exposed to 12-O-tetradecanoylphorbol-13-acetate (10 or 100 ng/ml), whereas HL-60 cells treated with 12-O-tetradecanoylphorbol-13-acetate (10 ng/ml) showed a marked reduction in the fluorescence anisotropy. These observations suggest that the ability of HL-60 cells to respond to 12-O-tetradecanoylphorbol-13-acetate may be affected by the physical state of the plasma membrane lipids and that the resistant phenotype is associated with decreased fluidity of either the inner leaflet of the plasma membrane and/or of the cytosolic organellar membranes.

Cell Differentiation↗
PubMed1983

A microtiter plate assay for the selection of 6-thioguanine-resistant mutants in Chinese hamster V79 cells in the presence of phorbol-12-myristate-13-acetate.

6-Thioguanine-resistant mutants can be efficiently recovered from Chinese hamster V79 cells incubated at high cell densities in microtiter plates (10(3)-10(4) cells/0.2 ml growth medium/0.4 cm2) when selected with 30 microM 6-thioguanine and 0.1 microgram/ml phorbol-12-myristate-13-acetate, an inhibitor of metabolic cooperation among V79 cells. Mutant frequencies in the microtiter plates were calculated from a direct count of mutant colonies. After treatment of the V79 cells with the carcinogen benzo[a]pyrene in a fibroblast-mediated assay, the mutation frequencies determined with the microtiter assay system were quantitatively similar to those obtained with a conventional procedure in which selection with 6-thioguanine was performed in petri dishes. The mutagenic activities of 3 polycyclic aromatic hydrocarbons (activated in the cell-mediated assay) were assessed with the microtiter plate selection procedure. The active carcinogen benzo[a]pyrene at 1 microgram/ml yielded about 100 mutants per 10(5) colony-forming cells. The same dose of a less active carcinogen, cyclopenta[c,d]pyrene, yielded about 20 mutants per 10(5) colony-forming cells, and benz[a]anthracene, not an active carcinogen, was inactive as a mutagen at all doses tested. Because of the small requirements for growth medium and tissue culture vessels compared with other assays, this microtiter plate assay can serve as an inexpensive system for detecting the mutagenic activity of environmental chemicals in mammalian cells.

Animals↗
PubMed1983

Cell specific activation of benzo[a]pyrene by fibroblasts and hepatocytes.

The cell specific activation of benzo[a]pyrene (BP) by embryonic fibroblasts and by mature hepatocytes to intermediates that can interact with DNA, or cause mutations in Chinese hamster V79 cells has been investigated. At BP concentrations of up to 15 muM, BP was activated to mutagenic intermediates for the V79 cells by embryonic fibroblasts but not by hepatocytes. However, hepatocytes from rats that had been pretreated with an inducer of the mixed function oxidases, 3-methylcholanthrene, did metabolize higher doses of BP (greater than 15 muM) to mutagenic intermediates. BP was extensively metabolized by both cell types, but the hepatocytes and fibroblasts showed differences both in the profiles of BP metabolites and the nature of the BP-DNA adducts formed. Hepatocytes metabolized BP principally to 4,5-dihydro-4,5-dihydroxybenzo[a]pyrene, phenols, and quinones, which underwent further metabolism to water-soluble metabolites. Metabolism of BP to 7,8-dihydro-7,8-dihydroxybenzo[a]-pyrene (BP-7,8-diol) occurred but proceeded rapidly to the formation of triols and tetraols. Fibroblasts metabolized BP predominantly toward the formation of BP-7,8-diol. The proportion of primary metabolites undergoing further metabolism to conjugates was less extensive than in the hepatocytes. Hepatocytes bound more BP to their DNA than the fibroblasts. In the hepatocytes the major DNA adducts formed were hydrophilic derivatives, and no [+/-]7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) adducts were detected even after treatment with BP-7,8-diol. In the fibroblasts, the major BP--DNA adduct was derived from the reaction of BPDE with deoxyguanosine. These results suggest that the differences in the response of embryonic fibroblasts and mature hepatocytes in the activation of BP to a mutagen for mammalian cells is determined at least in part by the overall balance of oxidation and detoxification processes in the cells and, hence, by the levels of critical oxidative intermediates that interact with DNA.

Animals↗
PubMed1983

Control of macrophage cell differentiation in human promyelocytic HL-60 leukemia cells by 1,25-dihydroxyvitamin D3 and phorbol-12-myristate-13-acetate.

Human promyelocytic leukemia cells (HL-60) were induced to differentiate into macrophage-like cells in a dose (3 X 10(-10) to 10(-7) M) and time (1 to 6 days)-dependent manner by 1,25-dihydroxyvitamin D3 and the tumor promoter, phorbol-12-myristate-13-acetate. Differentiation was determined by an increase in the percentage of morphologically mature cells, in lysozyme and nonspecific esterase activities, and in reactivity with the murine OKM1 monoclonal antibody. Two HL-60 cell variants, designated as R-80 and B-II, were also examined. R-80 cells, which are resistant to induction of cell differentiation by phorbol-12-myristate-13-acetate, also exhibited resistance, although to a lesser degree, to induction of cell differentiation by 1,25-dihydroxyvitamin D3. The resistance to the action of the two compounds is presumably not due to similar binding sites for the two inducers, since 1,25-dihydroxyvitamin D3 was unable to compete for the phorbol diester binding sites as measured by [3H]phorbol-12,13-dibutyrate binding. B-II cells were resistant to induction of cell differentiation by 1,25-dihydroxyvitamin D3, phorbol-12-myristate-13-acetate, retinoic acid, and dimethyl sulfoxide. Two-dimensional electrophoretic analysis of HL-60 cell protein patterns indicated that treatment of the HL-60 cells with 1,25-dihydroxyvitamin D3, phorbol-12-myristate-13-acetate, retinoic acid, and dimethyl sulfoxide caused the cells to express various monocyte-macrophage and granulocyte marker proteins. None of the inducers caused a protein pattern identical to that of peripheral monocytes or granulocytes in the HL-60 cells, but the protein pattern of the HL-60 cells treated with 1,25-dihydroxyvitamin D3 was the closest to that of peripheral blood monocytes. These results indicate that 1,25-dihydroxyvitamin D3 induces in the HL-60 cells a phenotype that resembles, but is not identical to, that of peripheral monocytes-macrophages.

Antibodies, Monoclonal↗
PubMed1983

Double minute chromatin bodies and other chromosome alterations in human myeloid HL-60 leukemia cells susceptible or resistant to induction of differentiation by phorbol-12-myristate-13-acetate.

An analysis of the chromosomal karyotype of the human promyelocytic HL-60 leukemia cell line and of a number of its sublines that exhibit varying degrees of resistance to induction of differentiation by phorbol-12-myristate-13-acetate was conducted. The HL-60 cell line and the derived sublines contained two consistent marker chromosomes [9p- and t(10;13)], which suggested that they have a common and possibly clonal origin. HL-60 cells that are susceptible to phorbol-12-myristate-13-acetate-induced cell differentiation contained double minute chromatin bodies. The sublines with different degrees of resistance showed a corresponding sequential reduction of double minute chromatin bodies in metaphase cells. This loss of double minute chromatin bodies was not associated with an appearance of homogeneously staining chromosomal regions. Resistant and susceptible HL-60 cells differed also in a number of other chromosomal alterations, including gains or losses involving chromosomes 5, 8, 11, 13, 16, and 17. Thus, it is suggested that acquisition of resistance to phorbol-12-myristate-13-acetate-induced cell differentiation in the HL-60 cells may involve one or more of the above chromosomal changes.

Cell Differentiation↗
PubMed1982

Differentiation of human T-lymphoid leukemia cells into cells that have a suppressor phenotype is induced by phorbol 12-myristate 13-acetate.

Treatment of cultured human T-lymphoid (CEM) leukemia cells with nanomolar concentrations of phorbol 12-myristate 13-acetate (PMA) resulted in a reduction in cell growth and in the acquisition of a surface antigenic pattern that is common to both suppressor and cytotoxic T lymphocytes. This antigenic pattern was detected by OKT monoclonal antibodies. PMA treatment did not cause the expression of a cytotoxic function but rather induced the expression of a suppressor cell marker. This marker was characterized by the ability of the treated CEM cells to suppress [3H]thymidine incorporation into phytohemagglutinin-activated peripheral blood lymphocytes. After 4 days of treatment of CEM cells from either cloned or the parental cell population with 16 nM PMA, 71-98% of the cells expressed reactivity with OKT3 and OKT8 antibodies whereas reactivity with OKT4 and OKT6 was detected in less than or equal to 1-8% of the cells. The CEM cells can be divided into five groups based on the antigenic patterns of cells from randomly isolated clones. The cells from four of these groups were characterized by either low or high reactivity with each of the four OKT antibodies. The antigenic pattern of the fifth group resembled that of the parent CEM cells. The acquisition of reactivity with the OKT3 antibody in the CEM cells after PMA treatment was dependent on both time and dose and did not require cell replication. Acquisition of reactivity with OKT3 antibody also occurred after treatment with phorbol 12,13-dibutyrate but not after treatment with phorbol 13-monoacetate, phorbol 12,13-diacetate, or dimethyl sulfoxide. These results indicate that treatment of CEM cells with PMA and related agents can cause the cells to express a phenotype that resembles that of a mature suppressor T lymphocyte.

Antibodies, Monoclonal↗