Human Monocyte-like Cell Line Research Articles

Glucocorticoids enhance the gamma-interferon augmentation of human monocyte immunoglobulin G Fc receptor expression.

At physiologic and therapeutic concentrations, glucocorticoids decrease the number of Fc receptors for IgG (Fc gamma R) on human monocyte-like cell lines. In comparison, gamma-interferon (IFN-gamma) increases Fc gamma R expression on both human monocytes and monocyte-like cell lines. In this study, we examined the combined effects of glucocorticoids and IFN-gamma on human monocyte expression of the high affinity (72 kDa) Fc gamma R. Mononuclear cells prepared from heparinized venous blood of normal donors were treated for up to 90 hr with or without recombinant IFN-gamma and/or steroids. Monocyte Fc gamma R were measured by Scatchard analysis of the binding of human monomeric 125I-IgG1; indirect immunofluorescence plus flow cytometry, utilizing a monoclonal antibody (MoAb 32) which is specific for the high affinity Fc gamma R; and direct immunofluorescence using fluorescein isothiocyanate-labeled human monomeric IgG1 and flow cytometry quantitated using U-937 cells as a standard. Cultured monocytes incubated in the presence of both glucocorticoids and IFN-gamma for 18 hr had significantly higher (p less than 0.01) Fc gamma R levels than monocytes treated with IFN-gamma alone. The effect of combined treatment reached a plateau by 42 hr of incubation without increasing expression of other surface markers tested. Treatment with glucocorticoids alone did not consistently decrease monocyte Fc gamma R levels after either 18 or 42 hr of culture. Only glucocorticoids augmented the IFN-gamma increase in Fc gamma R; other steroids tested had no effect on IFN-gamma action. Furthermore, the effect was observed after treatment with only one type of interferon, IFN-gamma. These results describe a glucocorticoid immunoregulatory effect that may explain why combined IFN-gamma plus glucocorticoid treatment enhances mononuclear phagocyte Fc-mediated functions.

A requirement for cholesterol for phorbol ester-induced adhesion of a human monocyte-like cell line

The human monocyte/macrophage-like cell line U937, which is a cholesterol auxotroph, is nonadherent. However, it becomes adherent after treatment with phorbol 12-myristate 13-acetate (phorbol ester). We investigated the effects of cellular cholesterol depletion and repletion on the effectiveness of phorbol ester to induce adhesion to substratum. Almost 70% of cellular cholesterol is depleted by incubation of the cells for 24 hrs in the growth medium in which delipidated fetal calf serum is substituted for fetal calf serum without affecting viability or the rate of growth. The use of delipidated fetal calf serum inhibited phorbol ester-induced adhesion by 40%. If the cells were preincubated in the medium containing delipidated fetal calf serum 6 hrs prior to addition of phorbol ester, adhesion was inhibited by 90%. Addition of cholesterol to the medium containing delipidated fetal calf serum, which replenishes cellular cholesterol, restored the ability of phorbol ester to induce adhesion to levels seen in cells cultured in the medium containing fetal calf serum. Epicholesterol was not as effective as cholesterol in supporting adhesion. Cholesterol depletion did not inhibit phorbol ester stimulation of superoxide anion production. These observations indicate a function for cholesterol in phorbol ester-induced adhesion that is independent of phorbol ester-induced superoxide anion production. It is proposed that cholesterol is required for synthesis and/or proper orientation and distribution, in the plasma membrane, of macromolecule(s) that mediate phorbol ester-induced adhesion.

The chemoattractant des-Arg74-C5a regulates the expression of its own receptor on a monocyte-like cell line.

The interaction of the chemoattractant des-Arg74-C5a (C5a des Arg) with its receptor on a human monocyte-like cell line, U-937, was examined. The data obtained suggest that C5a des Arg receptor expression is regulated by the extracellular concentration of C5a des Arg itself.

Phosphorylation of class I HLA antigens in U-937 monocyte-like cells: Role of protein kinase C

Phorbol esters and 1-oleoyl-2-acetylglycerol induce an increase in phosphorylation of a series of 44-kD proteins in the U-937 human monocyte-like cell line. The phenomenon is rapid at 37 °C, starting 0.5 min after adding the inducer, increasing to a maximum of 5–10 min and decreasing to the basal level at 30 min. It is also observed at 4 °C, though much more slowly. Immunoprecipitation and two-dimensional electrophoresis demonstrated that these phosphorylated proteins belong to the class I HLA antigens.

Purification and characterization of a membrane protein (gp45-70) that is a cofactor for cleavage of C3b and C4b.

Based on preliminary evidence indicating that a cell-associated protein of U937 (a human monocyte-like cell line) possessed cofactor activity and was not the C3b/C4b receptor, we sought to further characterize this protein. A sequential four-column purification procedure was devised that includes C3(H2O) affinity chromatography to isolate in reasonable yields and purity a cell-associated protein of U937 and several other human cell lines. Based on its pattern and Mr on SDS-PAGE, acidic pI, and ligand specificity, it is identical to a recently described C3(H2O) or C3b-binding membrane glycoprotein of human PBL and cell lines; having no presently identified function, it was termed gp45-70. After purifying this protein, we determined its functional capabilities and compared them to those of the other complement proteins with regulatory activity directed at components comprising the C3 convertases. This protein was the most efficient (50 times that of H) yet-described cofactor for the I-mediated first cleavage of C3b. It also was a cofactor for the first cleavage of C4b, but was not as efficient as C4bp. The second cleavage of C3b and C4b was not efficiently mediated. It had no ability to accelerate decay in the classical or alternative pathway C3 convertases. Based on this unique activity profile and ability to be surface labeled, we have renamed this molecule membrane cofactor protein (MCP). We suggest that this protein plays a major role in preventing autologous complement activation.

Characterization of human IgG Fc receptors.

A murine monoclonal antibody, KuFc79, has been developed that reacts with human IgG Fc receptors on monocytes, B lymphocytes, and granulocytes. The specificity of KuFc79 for Fc receptors was demonstrated by the ability of Fab fragments to block Fc-mediated phagocytosis by monocytes. This finding was further substantiated by the decrease of KuFc79 binding to monocytes and granulocytes (58 and 70%, respectively) after modulation of surface IgG receptors with aggregated IgG. In addition, Fab KuFc79-conjugated Sepharose was used to isolate functional IgG Fc-binding molecules from soluble extracts of the human monocyte-like cell line U937. By immunoprecipitation, it was further shown that KuFc79 immunoprecipitated molecules of 42,000 and 70,000 daltons from U937 and a human lymphoblastoid cell line, SB. A lower m.w. species of approximately 33,000 was also precipitable from granulocytes. Extensive microheterogeneity of these molecules was noted by isoelectric focusing, which appears to be due to differential sialation.

A fast-acting elastase inhibitor in human monocytes.

A proteinase inhibitor active against neutrophil and pancreatic elastase was detected in extracts of cultured human monocytes and the human monocyte-like cell line U937. This component forms a covalent complex with the active site of elastase; the complex is stable in boiling sodium dodecyl sulfate solution, and is susceptible to nucleophilic cleavage. The activity of the elastase inhibitor is not detected in extracts of freshly isolated monocytes, but becomes detectable when the monocytes are allowed to mature in culture, with maximum levels occurring at 5-7 d. The monocyte inhibitor is fast-acting; its reaction with 125I-labeled elastase is complete in less than 1 min at 37 degrees C. Analysis by electrophoresis and studies using a heteroantiserum to alpha 1-proteinase inhibitor demonstrated that the elastase inhibitor of monocytes/U937 cells is not identical to alpha 1-proteinase inhibitor, the major elastase inhibitor of blood plasma. The extent of conversion of 125I-elastase to the 125I-elastase-inhibitor complex is proportional to the amount of U937 extract or cultured monocyte extract, indicating that this reaction can serve to quantify the elastase inhibitor. The elastase inhibitor is an abundant component in mature monocytes, with greater than or equal to 1.5 X 10(6) molecules/cell (greater than or equal to 12 micrograms per 10(8) cells, greater than 0.1% of total cell protein). Its mol wt is estimated at 50,000. Thus, the monocyte inhibitor should be classified as a putative regulator of neutrophil (and monocyte) elastase activity at inflammatory sites. This designation is based on the properties of the molecule, including its high concentration in maturing monocytes, its affinity for elastase, and its fast reaction with this enzyme.

Synthesis of C1 inhibitor (C1-INA) by a human monocyte-like cell line, U937.

Human monocytes are known to synthesize many of the components of complement, including C1-INA. In this report we demonstrate that the human monocyte-like cell line U937 is also capable of synthesizing functional C1-INA. This was shown in several ways, including 1) incorporation of tritiated amino acids into antigenic C1-INA, immunoprecipitation, and detection by fluorography; 2) a sensitive ELISA, which allowed quantitation of antigenic C1-INA in cell lysates, and 3) a C2-dependent hemolytic assay in which the functional activity of U937 C1-INA was assayed. Data from the ELISA indicate that U937 cells contain between 2.1 to 12.8 ng of C1-INA per 1 X 10(6) cells. Furthermore, fluorescence-activated cell sorter analysis revealed that approximately 16% of U937 cells carry C1-INA as a surface bound antigen. Other proteins found to be synthesized by U937 cells include C1r, C8, and possibly alpha-2-macroglobulin. These results suggest that the U937 cell line could be a convenient and valuable model for the study of monocyte C1-INA synthesis and physiology.

The characteristics of binding of human recombinant interferon-gamma to its receptor on human monocytes and human monocyte-like cell lines.

Interferon-gamma (IFN-gamma) induces many effector functions in macrophages, presumably through binding to cell surface receptors. Such receptors have been documented in murine macrophages. This report demonstrates that IFN-gamma interacts with a specific receptor on human monocytes and monocyte-like cell lines, U937 and HL60. Recombinant IFN-gamma (rIFN-gamma) was radioiodinated by using Bolton-Hunter reagent to high specific activity. 125I-rIFN-gamma bound in a specific and saturable manner. Saturation of binding sites occurred at 10(-9) M (300 U/ml); there were 4000 specific binding sites per cell for both monocytes and the cell lines. Purified lymphocyte-derived IFN-gamma as well as rIFN-gamma competed for binding sites with 125I-rIFN-gamma. There was no inhibition of binding of the 125I-rIFN-gamma by rIFN-alpha or rIFN-beta. The forward rate constant, k1, at 4 degrees C was about 8 X 10(5) M-1 sec-1 for each cell type studied. In the presence of excess ligand, the dissociation rate constant, k-1, was about 2 X 10(-4) sec-1. The Ka calculated from these constants (4 X 10(9) M-1) agreed closely with that calculated from experiments performed at equilibrium (8 X 10(9) M-1). Because the dissociation of rIFN-gamma from cells was enhanced in the presence of ligand, interactions between binding sites of a negative cooperative type could be operative. These studies demonstrate that rIFN-gamma binds in a specific and saturable manner and with high affinity to a receptor on human monocytes as well as monocyte-like cell lines.

Structure of human ferritin light subunit messenger RNA: comparison with heavy subunit message and functional implications.

Ferritin has a protein shell of 5 X 10(6) Da consisting of 24 subunits of two types, a heavier (H) chain of 21,000 Da and a lighter (L) chain of 19,000 Da. A cDNA clone of the messenger for the L subunit has been isolated from a human monocyte-like leukemia cell line. The clone contains an open reading frame of 522 nucleotides coding for an amino acid sequence matching 97% of the published sequence of human liver ferritin L subunit determined by sequenator, but it corresponds to only 55% of the reported amino acid sequence of a human liver H-subunit clone. Nevertheless, computer analysis of the subunit conformations predicted from the open reading frames of the L and H clones shows that most of the amino acid differences are conservative and would allow both subunits to form the five alpha-helices and beta-turns established by x-ray crystallography for horse spleen ferritin subunits. This suggests that L and H subunits are structurally interchangeable in forming an apoferritin shell. The 5' untranslated region of our human ferritin L clone has considerable homology with that of the rat liver ferritin L clone in the region immediately upstream from the initiator codon, notably showing an identical sequence of 10 nucleotides at the same position in both subunit clones that may participate in regulating the known activation of ferritin mRNA after iron administration. Extensive homology, including several blocks of nucleotides, was identified between the 3' untranslated regions of the human and rat L clones. The common structural features of the H and L subunits lead us to conclude that they have diverged from a single ancestral gene.

Differentiation of U-937 human monocyte-like cell line by 1α,25-dihydroxyvitamin D 3 or by retinoic acid : Opposite effects on insulin receptors

The monocyte-like human cell line U-937 has been differentiated in vitro by incubation with either 1α,25-dihydroxyvitamin D 3 or retinoic acid (RA) plus dibutyryl cyclic AMP (db-cAMP). Both methods were effective in inducing the appearance of maturation markers. Their actions on insulin receptors were the opposite, however; 1α,25-dihydroxyvitamin D 3 increased the binding of the hormone, while RA plus db-cAMP decreased the binding. These effects were specific for insulin, since the transferrin receptors were reduced by both methods of differentiation. Thus, the changes in insulin receptors during maturation in vitro depend on the inducing agent and are not causally related to the differentiation process.

Chemistry of a Human Monocyte-Derived Cell Line (U937): Identification of the Angiotensin I-Converting Activity as Leukocyte Cathepsin G

Angiotensin-converting enzyme, a dipeptidyl carboxypeptidase, catalyzes the conversion of angiotensin I to the vasoactive peptide angiotensin II. The finding of angiotensin-converting enzyme in dexamethasone-stimulated cultured monocytes and alveolar macrophages prompted the examination of a human monocyte-like cell line (U937) for angiotensin I-converting activity. Conversion of angiotensin I (5 X 10(-5) mol/L) to angiotensin II by U937 cell extracts (10(4) - 4 X 10(6) cells) was detected, and the pH optimum for the reaction was 7.0 to 8.0. The U937 cell angiotensin I-converting activity was purified to homogeneity by carboxymethylcellulose chromatography and trasylol affinity chromatography. The purified protein performed similarly to purified human neutrophil cathepsin G on sodium dodecyl sulfate-gradient polyacrylamide gel electrophoresis (SDS-gradient PAGE), elicited a reaction of complete identity with neutrophil cathepsin G when diffused against anti-cathepsin G antiserum, and had quantitatively similar angiotensin I-converting activity as neutrophil cathepsin G. Neutrophils and U937 cells had 143 and 52 times greater angiotensin I-converting capability than cultured monocytes or peripheral blood mononuclear cells, suggesting the relative importance of mobile cells containing cathepsin G in the local generation of angiotensin II. These data identify the angiotensin I-converting activity of the U937 cell as leukocyte cathepsin G and provide evidence that the U937 cell has neutrophil-like as well as monocyte-like characteristics.

Chemistry of a human monocyte-derived cell line (U937): identification of the angiotensin I-converting activity as leukocyte cathepsin G

Angiotensin-converting enzyme, a dipeptidyl carboxypeptidase, catalyzes the conversion of angiotensin I to the vasoactive peptide angiotensin II. The finding of angiotensin-converting enzyme in dexamethasone- stimulated cultured monocytes and alveolar macrophages prompted the examination of a human monocyte-like cell line (U937) for angiotensin I- converting activity. Conversion of angiotensin I (5 X 10(-5) mol/L) to angiotensin II by U937 cell extracts (10(4) - 4 X 10(6) cells) was detected, and the pH optimum for the reaction was 7.0 to 8.0. The U937 cell angiotensin I-converting activity was purified to homogeneity by carboxymethylcellulose chromatography and trasylol affinity chromatography. The purified protein performed similarly to purified human neutrophil cathepsin G on sodium dodecyl sulfate-gradient polyacrylamide gel electrophoresis (SDS-gradient PAGE), elicited a reaction of complete identity with neutrophil cathepsin G when diffused against anti-cathepsin G antiserum, and had quantitatively similar angiotensin I-converting activity as neutrophil cathepsin G. Neutrophils and U937 cells had 143 and 52 times greater angiotensin I- converting capability than cultured monocytes or peripheral blood mononuclear cells, suggesting the relative importance of mobile cells containing cathepsin G in the local generation of angiotensin II. These data identify the angiotensin I-converting activity of the U937 cell as leukocyte cathepsin G and provide evidence that the U937 cell has neutrophil-like as well as monocyte-like characteristics.

Direct stimulation of adcc by cloned gamma interferon is not ablated by glucocorticoids: Studies using a human monocyte-like cell line (U-937)

We have used the macrophage-like cell line U-937 to demonstrate that recombinant gamma (immune) interferon (γ-IFN) acts directly on the mononuclear phagocyte in the absence of other cell types to increase Fc receptor sites and antibody-dependent cellular cytotoxicity (ADCC). Incubation of U-937 for 18hr with 2% γ-IFN-rich supernatant, or with 10 U/ml of pure recombinant γ-IFN, resulted in a seven-fold increase in Fc receptors as measured by the binding of radiolabeled IgG or fluoresceinated IgG and cytofluorography. Simultaneous measurement of ADCC for chick erythrocytes showed a seven-fold increase. This augmentation of Fc receptors and function was not ablated by an immunosuppressive concn of the glucocorticoid dexamethasone. The potent effects of γ-IFN both on surface receptors and effector functions of macrophages suggest that it is an important mediator in the efferent limb of immunity. Moreover, our findings that physiologic levels of glucocorticoids do not block activation of the mononuclear phagocyte support our view that glucocorticoids are immunosuppressive as a result of their action on γ-IFN-producing cells. This would seem an important consideration in the development of potential strategies for obviating steroid-induced immunosuppression.

Differentiation of a human monocyte-like cell line by (2′–5′) oligoisoadenylate

Treatment of a human monocyte-like cell line (U-937) by (2′–5′)ApApA, the 5′dephosphorylated product of (2′–5′)oligo-isoadenylate [oligo(A)] synthetase, an interferon-induced enzyme, was able to induce differentiation, mimicking the effect of interferon treatment. Treatment of U-937 cells with (2′–5′)ApApA resulted in morphologic changes, new (monocyte-associated) membrane antigen expression, and acquisition of the capacity to mediate antibody-dependent cellular cytotoxicity (ADCC). (2′–5′)ApA and (3′–5′)ApApA were without effect. A myeloid cell line (HL-60) which differentiates in response to other agents, but not to α-interferon, was not able to differentiate in response to (2′–5′)ApApA, despite the ability of interferon to induce (2′–5′)oligo (A) synthetase.

LPS stimulation of complement (C3) synthesis by a human monocyte cell line.

The human monocyte-like cell line, U937, was utilized as a model system to assess the influence of lipopolysaccharides (LPS) from Escherichia coli and other immunomodulatory agents on the biosynthesis of complement component C3 by monocytoid cells. The amount of C3 accumulated in the medium of cultured cells was measured by an enzyme-linked immunoabsorbent assay (ELISA). In the presence of LPS (0.01 and 0.10 microgram/ml) C3 production by U937 cells was increased by 2- and 5-fold, respectively. C3 production was also increased in the presence of lymphokine-containing supernatants obtained from human peripheral blood mononuclear cells after their stimulation with concanavalin A-sepharose. Human gamma-interferon (50-500 units/ml) stimulated C3 production by U937 cells. Stimulation of C3 production by LPS or mononuclear cell supernatants was blocked by cycloheximide. LPS (0.10 and 1.0 microgram/ml) also stimulated PGE2 production by U937 cells but failed to increase PGE2 at the lowest concentration (0.01 micrograms/ml) shown to increase C3 biosynthesis. Although exogenous PGE1 (10(-7) and 10(-6) M) promoted a small increase in C3 production, the effect of LPS was not decreased by a concentration of indomethacin (10(-6) M) that inhibited biosynthesis of PGE2. Therefore, LPS-induced C3 synthesis is not mediated by an increase in PGE2 in U937 cells. In summary, these observations suggest that C3 biosynthesis by monocytes/macrophages can be modulated by mediators of cellular immune responses found in the microenvironment of a localized inflammatory reaction.

The insulin receptor of a human monocyte-like cell line: characterization and function.

Most clinical studies of the insulin receptor in man have been carried out in circulating cells, mainly monocytes. It is important to establish whether the function of the insulin receptor in blood cells reflects that of the major target tissues. Since peripheral monocytes do not divide, they cannot be studied under continuous cell culture conditions. We, therefore, studied the insulin receptor of a monocyte-like human cell line (U-937) to determine whether it could serve as a model for further investigation of the function of the insulin receptor. We found that the U-937 cells bind [125I]insulin specifically and in a time-, temperature-, concentration-, and pH-dependent fashion, similar to circulating monocytes. In addition, they internalize the hormone-receptor complex rapidly and extensively at 37 C in a fashion analogous to that of blood monocytes and hepatocytes. U-937 cells show a similar affinity for insulin as monocytes. Unlike hepatocytes, these cells do not appear to release extensive insulin-degrading activity and do not degrade cell surface-associated ligand during initial incubations. [125I] Insulin extracted or dissociated spontaneously from the cell surface shows full rebindability to fresh cells. The insulin receptor of the U-937 cells can be down-regulated as in the major target cells. As in cultured human lymphocytes, preincubation of U-937 cells with prednisolone results in significantly increased insulin binding. Incubation with a phorbol ester tumor promoter, in contrast, inhibits the extent of specific [125I]insulin binding to U-937 cells by altering the receptor affinity. The insulin receptor of the U-937 monocyte-like cell line mirrors the insulin receptor of blood monocytes and target cells; it is a useful tool for further in vitro studies of the insulin receptor.

Characterization of hydrogen peroxide-potentiating factor, a lymphokine that increases the capacity of human monocytes and monocyte-like cell lines to produce hydrogen peroxide.

A study was made of a lymphokine produced by human T lymphocytes that mediates activation of human monocytes and monocyte-like cell lines, measured by increased production of H2O2. The lymphokine was produced either by stimulation of human nonadherent peripheral blood mononuclear cells with concanavalin A (Con A) or by stimulation of a human T cell line, HSB2, with Con A and phorbol myristic acetate (PMA). When incubated with freshly isolated peripheral blood monocytes for 48 to 72 hr, the H2O2-potentiating factor (HPPF) stimulated increased production of H2O2, measured in a PMA-triggered assay for H2O2 secretion. Because variations occurred in the response of normal blood donors to the HPPF, human monocyte-like cell lines were used as homogeneous and consistently responsive targets for the lymphokine to facilitate biochemical characterization studies of the factor. Two cell lines were studied: HL60, a human promyelocytic cell line, and U937, a human histiocytic cell line. When target cells of either type were incubated in the presence of the HPPF for 48 to 72 hr, they produced increased amounts of H2O2 in a dose-dependent fashion. H2O2 levels were assessed by means of a microassay that measures peroxide-mediated oxidation of phenol red after an oxidative burst triggered with PMA. By using this assay, HPPF was found to have an apparent m.w. of 54,000 and an isoelectric point of 5.5. The bouyant density was determined to be 1.307, indicating that HPPF is a protein. The utilization of cell lines for both the production and assay of HPPF should facilitate the purification of this lymphokine and the subsequent evaluation of its relationship to other lymphokines known to affect macrophage microbicidal and tumoricidal function.

Induction of selective biological responses to chemoattractants in a human monocyte-like cell line.

The availability of monocyte cell lines that can be induced to differentiate in a predictable fashion can provide important tools for the study of the biochemical mechanisms of specific cellular responses. The U937 human monocyte cell line was previously shown to differentiate into chemotactically responsive cells when incubated with supernatants of lectin-stimulated lymphocytes (conditioned medium). Considering the heterogeneous nature of stimulated lymphocyte supernatants, attempts were made to identify well-defined agents that could reproducibly induce U937 cell differentiation. Both dimethyl sulfoxide and dibutyryl cAMP induced expression of receptors for the N-formylated oligopeptide chemoattractants in U937 cells. Unstimulated U937 cells contained no detectable receptors. After cells were exposed to 1 mM dibutyryl cAMP, 1.3% dimethyl sulfoxide, or 5% conditioned medium for 72 h, the average number of oligopeptide chemoattractant receptors per U937 cell was 33,000, 4,000, and 3,400, respectively. Specific binding proteins for the chemoattractants were identified by covalent affinity labeling on the differentiated U937 cells as well as on normal human monocytes. Cells exposed to conditioned medium responded chemotactically, secreted lysosomal enzymes, and formed superoxide anion when incubated with the chemoattractant. Treatment of U937 cells with dibutyryl cAMP resulted in the most reproducible and rapid increase in the number of chemoattractant receptors as well as in chemotactic responsiveness. The receptors on dibutyryl cAMP-treated cells and on dimethyl sulfoxide-treated cells initiated chemotaxis and lysosomal enzyme secretion in response to chemoattractants, but not the formation of superoxide anion. These findings demonstrate that development of the chemotactic and respiratory burst functions during the differentiation of a monocyte-like cell line can occur independently.

Interferon-induced differentiation of U937 cells. Comparison with other agents that promote differentiation of human myeloid or monocytelike cell lines.

Effects of human fibroblast (beta) or leukocyte (alpha) interferon (IFN) on differentiations of a human histiocytic lymphoma-derived cell line (U937) or promyelocytic leukemia-derived cell line (HL-60) were studied. When cultured with beta-IFN (400-1,000 U/ml), U937 cells showed gross morphologic and microscopic changes consisting of clumping, increased cytoplasmic-to-nuclear ratio, enhanced prominence of cytoplasmic granules, and membrane ruffling. After culture with beta-IFN, the number of U937 cells reactive with B43.4.1 monoclonal antibody, which is specific for human monocytes, natural killer cells, and neutrophils, increased from less than 10% of U937 cells to 47% beta-IFN treatment also enhanced antibody-dependent cellular cytotoxicity against chicken erythrocytes by U937 cells. The same morphologic, phenotypic, and functional changes were also observed when U937 were treated with recombinant or natural alpha-IFN. The effects of alpha-IFN were totally abolished by anti-alpha-IFN serum. In contrast, HL-60, which differentiates toward cells of the monocyte lineage in response to phorbol 12-myristate 13-acetate (based on the above criteria), and toward granulocytes in response to dimethyl sulfoxide, did not differentiate when cultured with alpha- or beta-IFN. No consistent relationship between induction of differentiation and changes in phospholipid methylation were observed.