Interleukin-10-deficient mice develop chronic enterocolitis

Interleukin-10 (IL-10) affects the growth and differentiation of many hemopoietic cells in vitro; in particular, it is a potent suppressor of macrophage and T cell functions. In IL-10-deficient mice, generated by gene targeting, lymphocyte development and antibody responses are normal, but most animals are growth retarded and anemic and suffer from chronic enterocolitis. Alterations in intestine include extensive mucosal hyperplasia, inflammatory reactions, and aberrant expression of major histocompatibility complex class II molecules on epithelia. In contrast, mutants kept under specific pathogen-free conditions develop only a local inflammation limited to the proximal colon. These results indicate that the bowel inflammation in the mutants originates from uncontrolled immune responses stimulated by enteric antigens and that IL-10 is an essential immunoregulator in the intestinal tract.

Interleukin-10-deficient mice develop chronic enterocolitis

Interleukin-10 (IL-10) affects the growth and differentiation of many hemopoietic cells in vitro; in particular, it is a potent suppressor of macrophage and T cell functions. In IL-10-deficient mice, generated by gene targeting, lymphocyte development and antibody responses are normal, but most animals are growth retarded and anemic and suffer from chronic enterocolitis. Alterations in intestine include extensive mucosal hyperplasia, inflammatory reactions, and aberrant expression of major histocompatibility complex class II molecules on epithelia. In contrast, mutants kept under specific pathogen-free conditions develop only a local inflammation limited to the proximal colon. These results indicate that the bowel inflammation in the mutants originates from uncontrolled immune responses stimulated by enteric antigens and that IL-10 is an essential immunoregulator in the intestinal tract.

Anti-IL-6 antibodies suppress myeloid cell production and the generation of CFU-c in long-term bone marrow cultures

Interleukin 6 (IL-6) is one of several hemopoietic growth factors produced by stromal cell lines derived from the adherent layer of long-term bone marrow cultures (LTBMCs). To evaluate the potential role of IL-6 in stromal cell-dependent myelopoiesis, we established LTBMCs and verified that IL-6 mRNA is transcribed by heterogeneous adherent cell layers and that IL-6 protein is present in culture supernatants. Established LTBMCs were then depleted of IL-6 by using a specific neutralizing monoclonal antibody (mAb). Cultures treated for 2-3 weeks with anti-IL-6 mAb showed decreased production of maturing myeloid cells and colony-forming progenitor cells (colony-forming units in culture, CFU-c) but not stem cells (spleen colony-forming units, CFU-s). In parallel experiments, it was also found that the addition of IL-6 to LTBMCs stimulated a marked increase in total cell production, CFU-c, and day-8 CFU-s. In sum, it appears that endogenous production of IL-6, although limiting, is essential for the normal level of myelopoiesis associated with stromal cell function in LTBMCs.

Interleukin 10: an overview

Since the original description of interleukin-10, a wealth of information concerning its biological properties has been gathered. Studies in vitro have rapidly identified both immunostimulatory and immunosuppressive activities for IL-10. Based on these findings, in vivo studies were initiated in a variety of animal disease models to assess the importance of these activities. This review will summarize the pleiotropic properties of IL-10 and will survey current research regarding the potential of IL-10 to regulate acute and chronic inflammatory reactions.

The in vitro response of phenotypically defined mouse stem cells and myeloerythroid progenitors to single or multiple growth factors

Pluripotential stem cells (Thylo Lin- Sca+; referred to as Sca+) and primitive myeloerythroid progenitor cells (Thylo Lin- Sca-; referred to as Sca-), defined by their in vivo repopulating properties, have been purified from mouse bone marrow. In this study, the growth factor requirements of these two subsets were compared in colony-forming assays. Sca- progenitor cells grew well in interleukin (IL) 3 alone and showed maximum growth when two factors, IL-3 plus IL-1 or IL-3 plus IL-6, were combined. In contrast, Sca+ stem cells were generally not responsive to any single factor tested. Some colony formation was found when IL-3 was paired with either IL-1 or IL-6, and this was significantly enhanced as additional factors were included. A remarkable frequency of as much as 1 colony per 1.7 input Sca+ cells was achieved when IL-1, IL-3, IL-6, and colony-stimulating factors were used together. These differences in factor requirements presumably reflect the need for multiple factor signaling in the more primitive stem cell population. In most other aspects of colony formation, Sca+ and Sca- cells were very similar. They generated colonies that had equivalent distributions in size and cellular composition. One notable difference was found in the kinetics of their response. Whereas nearly all Sca- cells formed colonies within 7 days, a significant fraction of Sca+ cells delayed colony formation for greater than 1 week. During this quiescent period, cell survival was absolutely dependent on the presence of factors in the medium.

Antibody to interleukin-5 inhibits helminth-induced eosinophilia in mice

When rodents are infected with the nematode Nippostrongylus brasiliensis, large numbers of eosinophils appear in their blood and lungs and their serum immunoglobulin E (IgE) is increased. Injection of a monoclonal antibody to interleukin-5 completely suppressed the blood eosinophilia and the infiltration of eosinophils in the lungs of parasitized mice but had no effect on serum IgE. In contrast, an antibody to interleukin-4 inhibited parasite-induced IgE but not the eosinophilia. These results show that interleukin-5 is important in eosinophil production in vivo and that IgE and eosinophil production are regulated by different cytokines produced by the TH2 subset of CD4-expressing T cells.

Interleukin-6 interacts with interleukin-4 and other hematopoietic growth factors to selectively enhance the growth of megakaryocytic, erythroid, myeloid, and multipotential progenitor cells

The growth-promoting activities of interleukin-6 (IL-6) in combination with different factors were assessed in bone marrow (BM) cultures prepared from normal mice and from mice treated with 5-fluorouracil (5-FU). Effects on hematopoietic colony formation with respect to number, size, and cellular composition were evaluated. In agreement with previous reports, IL-6 acts synergistically with IL-3 to stimulate increased numbers of granulocyte/macrophage (GM) and multilineage colonies in day-2 and day-4 post-5-FU BM cultures. Furthermore, day 4 but not day 2 post-5-FU BM showed enhanced GM colony formation when stimulated with IL-6 plus interleukin-4 (IL-4) or granulocyte colony-stimulating factor (G-CSF). In contrast, IL-6 did not increase the number of colonies supported by M-CSF or GM-CSF. Nevertheless IL-6 interacted with all factors, including M-CSF and GM-CSF, to stimulate an increase in colony size. Many of these myeloid colonies attained a diameter of greater than or equal to 0.5 mm, suggesting they derive from high proliferative potential cells (HPP-CFC). The response of normal and day-8 post-5-FU BM containing high numbers of more mature progenitors was also assessed. We found IL-6 enhanced colony formation by lineage-restricted megakaryocytic and erythroid progenitors in the presence of IL-3 and IL-4 plus erythropoietin (Epo), respectively. The sum of these results shows that IL-6 interacts with a variety of factors to regulate the growth of progenitor cells at different stages of lineage commitment and maturation.

IL-3 and stromal cell-derived factor synergistically stimulate the growth of pre-B cell lines cloned from long-term lymphoid bone marrow cultures

The addition of IL-3 to modified Whitlock-Witte long-term lymphocyte cultures was found to enhance the growth of a small but significant number of B cell precursors supported by an adherent stromal cell monolayer. Several pre-B cell lines were cloned from IL-3-treated long-term lymphocyte cultures. The growth requirements and physical properties of one representative clone, BL/3, are described. BL/3 cells were shown to be unresponsive to IL-3 except when it is used at very high concentrations. In contrast, significant growth was stimulated by stromal cell conditioned medium previously shown to contain a pre-B cell growth factor. Optimal growth of the pre-B cell clone was stimulated by stromal cell conditioned medium plus IL-3. Synergy between the stromal cell-derived factor and IL-3 occurred when IL-3 was used over a wide range of concentrations including a relatively low amount that was ineffective as a growth stimulus by itself. The finding that more than one factor is required to sustain optimal growth of some pre-B cells parallels the complex growth requirements reported for some primitive myeloid/erythroid progenitors.

IL-3 and stromal cell-derived factor synergistically stimulate the growth of pre-B cell lines cloned from long-term lymphoid bone marrow cultures

The addition of IL-3 to modified Whitlock-Witte long-term lymphocyte cultures was found to enhance the growth of a small but significant number of B cell precursors supported by an adherent stromal cell monolayer. Several pre-B cell lines were cloned from IL-3-treated long-term lymphocyte cultures. The growth requirements and physical properties of one representative clone, BL/3, are described. BL/3 cells were shown to be unresponsive to IL-3 except when it is used at very high concentrations. In contrast, significant growth was stimulated by stromal cell conditioned medium previously shown to contain a pre-B cell growth factor. Optimal growth of the pre-B cell clone was stimulated by stromal cell conditioned medium plus IL-3. Synergy between the stromal cell-derived factor and IL-3 occurred when IL-3 was used over a wide range of concentrations including a relatively low amount that was ineffective as a growth stimulus by itself. The finding that more than one factor is required to sustain optimal growth of some pre-B cells parallels the complex growth requirements reported for some primitive myeloid/erythroid progenitors.

Multiple biological activities are expressed by a mouse interleukin 6 cDNA clone isolated from bone marrow stromal cells

Interleukin 6 (IL-6) refers to the gene product that was characterized initially as beta 2 interferon/26-kDa protein produced by human fibroblasts and later was found to be identical to B-cell stimulatory factor 2, hybridoma/plasmacytoma growth factor, and probably hepatocyte-stimulating factor. Using the human IL-6 cDNA as a probe, we have isolated functional cDNA clones from mouse bone marrow stromal cell cDNA libraries. Sequence analysis of the mouse cDNA insert revealed significant homology between the human and mouse IL-6 cDNA clones both at the level of nucleotide (65%) and deduced amino acid (41%) sequences. The NH2-terminal sequence of the deduced protein is identical to a partial NH2-terminal sequence determined previously for a hybridoma/plasmacytoma growth factor and a plasmacytoma growth factor isolated from mouse T cells and macrophages, respectively. The mRNA for mouse IL-6 is expressed in IL-1-treated stromal cells and in activated T-cell and macrophage cell lines. Supernatants from COS-7 monkey cells transfected with the cDNA clone have plasmacytoma growth factor, hepatocyte-stimulating factor, and colony-stimulating factor activities, as well as the ability to support the growth of a factor-dependent myeloid cell line, thus revealing an additional biological activity for IL-6.

The molecular cloning of interleukins 4, 5 and 6: multifunctional hemopoietic growth factors

We summarize here our recent studies on the cloning and characterization of three lymphokines which are produced by activated T cells. Interleukins 4, 5 and 6 are involved in the regulation of B cell activation, proliferation and differentiation. IL-4 can activate resting B cells, while IL-5 stimulates the proliferation of activated B cells. Both of these factors also have a role in regulating the isotype of immunoglobulin produced by cultures of D cells. IL-6 appears to induce the differentiation of B cells to secrete high levels of immunoglobulin. In addition, each of these factors is involved in the regulation of other lineages of hemopoietic cells. Thus, T cells control multiple lineages of myeloid and lymphoid cells through the diverse actions of multiple lymphokines. IL-6 is exceptional because it is produced by a variety of cell types, and its action is not restricted to hemopoietic cells.

Proliferation and differentiation of highly enriched mouse hematopoietic stem cells and progenitor cells in response to defined growth factors

Three distinct hematopoietic populations derived from normal bone marrow were analyzed for their response to defined growth factors. The Thy-1loT- B- G- M-population, composing 0.2% of bone marrow, is 370-fold enriched for pluripotent hematopoietic stem cells. The two other populations, the Thy-1- T- B- G- M- and the predominantly mature Thy-1+ T+ B+ G+ M+ cells, lack stem cells. Thy-1loT- B- G- M- cells respond with a frequency of one in seven cells to IL-3 in an in vitro CFU-C assay, and give rise to many mixed colonies as expected from an early multipotent or pluripotent progenitor. The Thy-1- T- B- G- M- population also contains progenitor cells which responded to IL-3. However, colonies derived from Thy-1- T- B- G- M- cells are almost exclusively restricted to the macrophage/granulocyte lineages. This indicates that IL-3 can stimulate at least two distinct clonogenic early progenitor cells in normal bone marrow: multipotent Thy-1loT- B- G- M- cells and restricted Thy-1- T- B- G- M- cells. Thy-1loT- B- G- M-cells could not be stimulated by macrophage colony-stimulating factor (M-CSF), granulocyte CSF (G-CSF) or IL-5 (Eosinophil-CSF). The hematopoietic precursors that react to these factors are enriched in the Thy-1- T- G- B- M- population. Thus, multipotent and restricted progenitors can be separated on the basis of the expression of the cell surface antigen Thy-1.

Role of interleukin 2, interleukin 4, and alpha, beta, and gamma interferon in stimulating macrophage antibody-dependent tumoricidal activity

Pretreatment of murine peritoneal exudate macrophages with 1-5 U/ml rIFN-gamma or rIL-2, or higher concentrations of IFN-alpha or IFN-beta greatly stimulated ADCC to Rl lymphoma targets. The assay was direct counting of viable target cells after 9 and 24 h using an E/T ratio of 5:1. 2d of pretreatment was optimal for enhancing ADCC. rIL-4 was inactive and IL-4-depleted Con A-induced spleen lymphokine retained its ADCC-stimulating activity. Antibody to IFN-gamma blocked the ADCC-promoting effect of the lymphokine, suggesting a major role for this factor.

Expression of high affinity receptors for murine interleukin 4 (BSF-1) on hemopoietic and nonhemopoietic cells

In this report a method for the affinity purification and radiolabeling of recombinant mouse interleukin (IL)-4 is described. It is shown on the basis of several criteria that IL-4 retains full biologic activity after radioiodination and can therefore be used as a valid model for measuring the binding characteristics of native IL-4. By using Scatchard plot analysis of equilibrium binding data, it is demonstrated that 125I-IL-4 binds to a high affinity cell surface receptor which is expressed by both hemopoietic and nonhemopoietic cells. The dissociation constant for 125I-IL-4 (Kd = 20 to 60 pM) corresponds to the concentration of IL-4 which gives 50% biologic activity (i.e., 10 to 30 pM). Binding of 125I-IL-4 is rapid (t1/2 of 2 min), whereas dissociation occurs at a slow rate (t1/2 approximately 4 hr). The IL-4 receptor shows a high degree of specificity. Whereas unlabeled mouse IL-4 competed with mouse 125I-IL-4 in an equimolar fashion for binding to IL-4 receptors, several other lymphokines, including mouse IL-2, IL-3, interferon-gamma, granulocyte-macrophage colony-stimulating factor, and human IL-1, IL-2, and IL-4 were unable to inhibit, even at molar excesses of 400 to 800-fold. At 37 degrees C, 125I-IL-4 is rapidly internalized (approximately 200 molecules/cell/min) by HT-2 cells, with at least 85% of cell surface receptors being functional in this respect. Receptors for IL-4 were found to be expressed by subclasses of T and B cells, mast cells, macrophages, and by cells of the myeloid and erythroid lineages. This wide distribution of receptor expression closely matches the known spectrum of biologic activities of IL-4, including proliferation and/or differentiation of T and B cells, mast cells and granulocytes, and induction of macrophage antigen-presenting capacity. IL-4 receptors were also found on a variety of nonhemopoietic cells such as cloned stromal cell lines from the bone marrow, spleen, thymus, and brain, and on muscle, brain, melanoma, fibroblast, and liver cells. Indeed, only 5 of more than 90 cell types tested have undetectable numbers of IL-4 receptors. The biologic effects of IL-4 on nonhemopoietic cells have not yet been reported and await elucidation.

Expression of high affinity receptors for murine interleukin 4 (BSF-1) on hemopoietic and nonhemopoietic cells

In this report a method for the affinity purification and radiolabeling of recombinant mouse interleukin (IL)-4 is described. It is shown on the basis of several criteria that IL-4 retains full biologic activity after radioiodination and can therefore be used as a valid model for measuring the binding characteristics of native IL-4. By using Scatchard plot analysis of equilibrium binding data, it is demonstrated that 125I-IL-4 binds to a high affinity cell surface receptor which is expressed by both hemopoietic and nonhemopoietic cells. The dissociation constant for 125I-IL-4 (Kd = 20 to 60 pM) corresponds to the concentration of IL-4 which gives 50% biologic activity (i.e., 10 to 30 pM). Binding of 125I-IL-4 is rapid (t1/2 of 2 min), whereas dissociation occurs at a slow rate (t1/2 approximately 4 hr). The IL-4 receptor shows a high degree of specificity. Whereas unlabeled mouse IL-4 competed with mouse 125I-IL-4 in an equimolar fashion for binding to IL-4 receptors, several other lymphokines, including mouse IL-2, IL-3, interferon-gamma, granulocyte-macrophage colony-stimulating factor, and human IL-1, IL-2, and IL-4 were unable to inhibit, even at molar excesses of 400 to 800-fold. At 37 degrees C, 125I-IL-4 is rapidly internalized (approximately 200 molecules/cell/min) by HT-2 cells, with at least 85% of cell surface receptors being functional in this respect. Receptors for IL-4 were found to be expressed by subclasses of T and B cells, mast cells, macrophages, and by cells of the myeloid and erythroid lineages. This wide distribution of receptor expression closely matches the known spectrum of biologic activities of IL-4, including proliferation and/or differentiation of T and B cells, mast cells and granulocytes, and induction of macrophage antigen-presenting capacity. IL-4 receptors were also found on a variety of nonhemopoietic cells such as cloned stromal cell lines from the bone marrow, spleen, thymus, and brain, and on muscle, brain, melanoma, fibroblast, and liver cells. Indeed, only 5 of more than 90 cell types tested have undetectable numbers of IL-4 receptors. The biologic effects of IL-4 on nonhemopoietic cells have not yet been reported and await elucidation.

Interleukin 4 (B-cell stimulatory factor 1) can enhance or antagonize the factor-dependent growth of hemopoietic progenitor cells

Our studies show that although interleukin 4 (IL-4) fails to stimulate significant colony formation by bone marrow progenitor cells, it enhances erythroid, granulocyte, macrophage, and mast-cell colony formation when used as a costimulant with erythropoietin, granulocyte colony-stimulating factor, macrophage colony-stimulating factor, and interleukin 3 (IL-3), respectively. In contrast, IL-4 suppresses IL-3-dependent colony formation by granulocyte and macrophage progenitor cells and by multipotential progenitor cells. Furthermore, it appears to inhibit the in vitro generation of colony-forming progenitor cells from immature IL-3-dependent stem cells. We also found that IL-4 inhibits stromal cell-dependent growth of bone marrow-derived pre-B cells. The ability of IL-4 to directly or indirectly regulate both positive and negative aspects of progenitor cell growth is discussed.

Identification of a signal-transduction pathway shared by haematopoietic growth factors with diverse biological specificity

The haematopoietic growth factors multi-colony-stimulating factor, granulocyte/macrophage colony-stimulating factor, granulocyte colony-stimulating factor and interleukin 2 specifically control the production and proliferation of distinct leucocyte series. Each growth factor acts on a unique surface receptor associated with an appropriate signal-transduction apparatus. In this report we identify a 68 kDa substrate which is phosphorylated after stimulation of different cell types with multi-colony-stimulating factor, granulocyte colony-stimulating factor and interleukin 2. The 68 kDa substrate is also phosphorylated in each cell line stimulated with synthetic diacylglycerol, a direct activator of protein kinase C. Interestingly, granulocyte/macrophage colony-stimulating factor does not induce phosphorylation of the 68 kDa molecule. The 68 kDa molecule that is phosphorylated after stimulation with each ligand yielded similar peptide maps after chymotryptic digestion; furthermore, the substrate was always phosphorylated on threonine residues. Phosphorylation of the same residues in the 68 kDa substrate suggests that activation of protein kinase C is one common signal-transduction event associated with the action of multi-colony-stimulating factor, granulocyte colony-stimulating factor and interleukin 2.

A single bone marrow-derived stromal cell type supports the in vitro growth of early lymphoid and myeloid cells

A clonal cell line (ALC) derived from murine bone marrow stroma is capable of supporting the continuous, in vitro growth of early lymphoid and myeloid cell populations. The growth-promoting effects of ALC are in part mediated through M-CSF and a pre-B cell growth factor, both of which accumulate in ALC-culture supernatant. To analyze the lymphoid growth factor produced by ALC cells, we derived a pre-B cell indicator line that is dependent on ALC-growth-conditioned medium. Using a combination of biological and biochemical analyses, we have established that the pre-B cell growth factor produced by ALC cells is distinct from IL-1, IL-2, IL-3, and IL-4 (BSF-1), suggesting that the early stages of B-cell development are regulated by a unique stroma-derived growth factor.

Control of hemopoiesis by a bone marrow stromal cell clone: lipopolysaccharide- and interleukin-1-inducible production of colony-stimulating factors

A stromal cell line, GY30, was cloned from mouse bone marrow adherent cell layers. In culture, GY30 cells sustain the production of granulocyte-macrophage progenitor cells (GM-CFU) but fail to support the survival of pluripotential stem cells (CFU-S). GY30 cells secrete two growth factor activities distinct from interleukin-3 (IL-3), IL-2, and macrophage colony-stimulating factor (M-CSF) but functionally similar to GM-CSF and G-CSF. The production of both CSFs is increased 70- to 200-fold by treating GY30 cells with lipopolysaccharide or IL-1. RNA blot analysis reveals the presence of GM-CSF and G-CSF transcripts and demonstrates that IL-1 regulates the production of both factors at the mRNA level. Further, these studies show that the GM-CSF secreted by GY30 cells is structurally similar to the GM-CSF produced by activated T cells.

BSF1 induces membrane protein phosphorylation but not phosphoinositide metabolism, Ca2+ mobilization, protein kinase C translocation, or membrane depolarization in resting murine B lymphocytes

The findings presented in this study provide evidence that BSF1 receptors and mIg transmit signals via dissimilar transduction mechanisms that result in a common biologic response, hyper-Ia expression. Specifically, BSF1-containing supernatant does not induce PtdInsP2 hydrolysis as determined by measurement of PtdOH and InsP3. Additionally, BSF1 does not stimulate Ca2+ mobilization, PKC translocation from cytosol to membrane, or membrane depolarization. All of these metabolic events appear to play a central role in hyper-Ia expression mediated by mIg and are initiated after treatment of resting B cells with anti-Ig antibodies. In vitro phosphorylation studies with partially purified plasma membranes from resting B cells revealed that BSF1 interaction with membrane receptors stimulates a membrane-associated protein kinase that phosphorylates an endogenous protein of 44 KDa. Anti-Ig does not stimulate phosphorylation of the 44 KDa protein, suggesting that it does not activate the membrane-associated protein kinase. This observation provides the first evidence of a signal transduction mechanism associated with BSF1-receptor ligation. It indicates that although BSF1 does not modulate events associated with PKC activation, it may function via activation of a membrane-associated protein kinase. This provides a focal point for further studies directed at elucidating signal transduction resulting from BSF1-receptor interaction.

BSF1 induces membrane protein phosphorylation but not phosphoinositide metabolism, Ca2+ mobilization, protein kinase C translocation, or membrane depolarization in resting murine B lymphocytes

The findings presented in this study provide evidence that BSF1 receptors and mIg transmit signals via dissimilar transduction mechanisms that result in a common biologic response, hyper-Ia expression. Specifically, BSF1-containing supernatant does not induce PtdInsP2 hydrolysis as determined by measurement of PtdOH and InsP3. Additionally, BSF1 does not stimulate Ca2+ mobilization, PKC translocation from cytosol to membrane, or membrane depolarization. All of these metabolic events appear to play a central role in hyper-Ia expression mediated by mIg and are initiated after treatment of resting B cells with anti-Ig antibodies. In vitro phosphorylation studies with partially purified plasma membranes from resting B cells revealed that BSF1 interaction with membrane receptors stimulates a membrane-associated protein kinase that phosphorylates an endogenous protein of 44 KDa. Anti-Ig does not stimulate phosphorylation of the 44 KDa protein, suggesting that it does not activate the membrane-associated protein kinase. This observation provides the first evidence of a signal transduction mechanism associated with BSF1-receptor ligation. It indicates that although BSF1 does not modulate events associated with PKC activation, it may function via activation of a membrane-associated protein kinase. This provides a focal point for further studies directed at elucidating signal transduction resulting from BSF1-receptor interaction.

Multilineage hematopoietic growth factor interleukin 3 and direct activators of protein kinase C stimulate phosphorylation of common substrates

In order to investigate early signal transduction events in myeloid cells, the phosphosubstrates of an interleukin 3 (IL 3)-dependent cell line, FDC-P1, have been analyzed. Using synthetic diacylglycerol as a direct activator of the unique calcium-phospholipid-dependent phosphotransferase protein kinase C (PK-C) and genetically engineered homogeneous IL 3, we have demonstrated a common element to signal transduction events associated with these stimulants. One novel substrate, p68 (68,000 kd), was rapidly phosphorylated in either IL 3- or diacylglycerol-stimulated cells. The phosphorylation of p68 was dose-dependent, with both the physiological ligand and diacylglycerol inducing the same maximal level of phosphorylation. Phosphorylation of p68 occurred in a time-dependent manner analogous to previously described kinetics of PK-C subcellular redistribution in the FDC-P1 cell line. The p68 substrate was also phosphorylated in a cell-free system under conditions designed to activate PK-C. Phosphoamino acid analysis demonstrated that the p68 molecule phosphorylated in intact cells as well as in a calcium-phospho-lipid-dependent cell-free system was phosphorylated on threonine residues, not tyrosine. These data support the hypothesis that the activation of PK-C that occurs after IL 3-receptor interaction which leads to the rapid phosphorylation of cellular proteins is an important element of the signal transduction mechanism in FDC-P1 cells. We propose that phosphorylation of the p68 molecule is a physiochemical marker for the activation of PK-C in myeloid cells, in response to the growth-promoting physiological ligand.

Regulation of expression of the interleukin-2 receptor on hematopoietic cells by interleukin-3

Remarkable similarities in the intracellular and genetic events occur when lymphoid and hematopoietic cells are exposed to their specific growth factors. The interleukin-2 (IL-2) receptor, whose cell-surface expression is an absolute requirement for the growth and differentiation of lymphoid cells, was detected on various nonlymphoid hematopoietic cell types in this study. Cell lines consisting either of granulocyte-macrophage precursors or mast cells, which are dependent on interleukin-3 (IL-3) for their growth, expressed high levels of the IL-2 receptor on their surface. Analysis of the binding characteristics of these receptors with 125I-labeled recombinant IL-2 revealed that only receptors with low affinity for IL-2 were present on these cells. Addition of purified recombinant IL-3 to these cell lines led to an increase in IL-2 receptor gene expression within 1 hour in isolated nuclei. This IL-3--induced increase in the number of IL-2 receptors on the cell surface is maximal within 24 hours. Addition of 10,000 units of IL-2 to these cells had no apparent effect on their growth or differentiation. The presence of the receptor with only low affinity for IL-2 on hematopoietic cells and the regulation by IL-3 suggest that this receptor is involved in some important metabolic event in hematopoiesis.