thromboxane-b2 and Leukemia--Monocytic--Acute

Endotoxin [lipopolysaccharide (LPS)] tolerance suppresses macrophage/monocyte proinflammatory-mediator production. This phenomenon also confers cross-tolerance to other stimuli including tumor necrosis factor (TNF) alpha and interleukin (IL)-1beta. Post-receptor convergence of signal transduction pathways might occur after LPS, IL-1beta, and TNF-alpha stimulation. Therefore, it was hypothesized that down-regulation of common signaling molecules induces cross-tolerance among these stimuli. LPS tolerance and cross-tolerance were examined in THP-1 cells. Phosphorylation of MAP kinases and degradation of inhibitor kappaBalpha (IkappaBalpha) DNA binding of nuclear factor-kappaB (NF-kappaB), and mediator production were examined. In naive cells, LPS, TNF-alpha, and IL-1beta induced IkappaBalpha degradation, kinase phosphorylation, and NF-kappaB DNA binding. LPS stimulation induced production of TNF-alpha or TxB2 and degradation of IRAK. However, neither TNF-alpha nor IL-1beta induced IRAK degradation or stimulated TNF-alpha or TxB2 production in naive cells. Pretreatment with each stimulus induced homologous tolerance to restimulation with the same agonist. LPS tolerance also suppressed LPS-induced TxB2 and TNF-alpha production. LPS pretreatment induced cross-tolerance to TNF-alpha or IL-1beta stimulation. Pretreatment with TNF-alpha induced cross-tolerance to LPS-induced signaling events and TxB2 production. Although pretreatment with IL-1beta did not induce cross-tolerance to LPS-induced signaling events, it strongly inhibited LPS TNF-alpha and TxB2 production. These data demonstrate that IL-1beta induces cross-tolerance to LPS-induced mediator production without suppressing LPS-induced signaling to MAP kinases or NF-kappaB activation.

Topics: Culture Media, Conditioned; DNA-Binding Proteins; Drug Interactions; Drug Tolerance; Electrophoretic Mobility Shift Assay; Endotoxins; Gene Expression Regulation, Leukemic; I-kappa B Proteins; Interleukin-1; Interleukin-1 Receptor-Associated Kinases; JNK Mitogen-Activated Protein Kinases; Leukemia, Monocytic, Acute; MAP Kinase Signaling System; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Monocytes; Neoplasm Proteins; NF-kappa B; NF-KappaB Inhibitor alpha; Phosphorylation; Protein Kinases; Protein Processing, Post-Translational; Thromboxane B2; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha

The early events triggered in interleukin-4 (IL-4)-stimulated U937 cells by ligation of CD23/Fc epsilon RII with specific monoclonal antibodies (mAb) were analysed, as a model of the action of this molecule on the differentiation of promonocytic cells. As well as IL-4-activated human monocytes, addition of anti-CD23 mAb to IL-4-treated U937 cells triggered cAMP accumulation but did not evoke significant polyphosphoinositide hydrolysis. However, by a microspectrofluorometric technique allowing single cell analysis, anti-CD23 mAb was found to elicit calcium mobilization in these cells. In addition, the treatment induced phenotypic alterations in these cells, as evidenced by the acquisition of the monocyte marker CD14 and the increase of the alpha-chain (CD11a) and of the common beta-chain (CD18) of the leucocyte function-associated antigen 1 (LFA-1) family antigens. Although weaker than in monocytes, CD23 ligation evoked a small secretion of the pro-inflammatory mediators IL-6 and thromboxane B2. These data suggest that a significant maturation of promonocytic cells towards a more mature monocytic phenotype can be achieved through successive exposure to IL-4 and CD23 ligation.

Topics: Antibodies, Monoclonal; Antigens, CD; Antigens, Differentiation, Myelomonocytic; Calcium; CD11 Antigens; CD18 Antigens; Cell Division; Cyclic AMP; Humans; Inositol 1,4,5-Trisphosphate; Interleukin-4; Interleukin-6; Leukemia, Monocytic, Acute; Lipopolysaccharide Receptors; Monocytes; Receptors, IgE; Thromboxane B2; Tumor Cells, Cultured

The U937 monocytic cell line and its differentiated macrophage-like form have been well characterized, illustrating many similarities with their analogous in vivo cells. We examined the release of thromboxane B2 (TXB2) from undifferentiated and differentiated cells after stimulation with opsonized zymosan and investigated whether the release of this mediator could be modified by isoprenaline. After stimulation, the U937 cells released TXB2 in a dose-dependent manner, with the release greater from the differentiated cells. The TXB2 released was inhibited by flurbiprofen (> 10(-8) M; P < .01) and isoprenaline (> 10(-6) M; P < .01), and the inhibition was reversed by propranolol (10(-6) M; P < .02). Thus, it is clear that undifferentiated and differentiated U937 cells release TXB2, which can be inhibited by beta 2-adrenoceptor stimulation. These findings illustrate an important functional difference between the in vivo macrophages and differentiated U937 cells because beta 2-adrenoceptor stimulation does not inhibit mediator release from macrophages.

Topics: Cell Transformation, Neoplastic; Dose-Response Relationship, Drug; Flurbiprofen; Humans; Isoproterenol; Leukemia, Monocytic, Acute; Macrophages; Opsonin Proteins; Propranolol; Receptors, Adrenergic, beta; Thromboxane B2; Tumor Cells, Cultured; Urinary Bladder Neoplasms; Zymosan

The primary objective of this study was to explore if the CD23 antigen is a functional low affinity IgE receptor on macrophages for the release of thromboxane B2 (TXB2). The responsiveness of U937 monocytic cells and their macrophage-like inducible forms to platelet-activating factor (Paf), the chemotactic peptide fMLP, and low affinity IgE-receptor occupation was examined. Differentiation of U937 cells by phorbol myristate acetate (PMA) and a cancer cell line (HBT 5637) conditioned medium (5637-CM), but not INFg or IL4, resulted in a macrophage-like cell line which released TXB2. A high basal release of TXB2 with no significant response to Paf or fMLP challenge was seen following culture of cells with PMA. In 5637-CM-differentiated cells, Paf and fMLP induced a rapid release of TXB2, about 10 fold above basal activity. There was a slow Ca-independent response to short-term treatment with PMA and a rapid Ca-dependent response to the ionophore A23187. Both stimulants acted synergistically on TXB2 synthesis in 5637-CM differentiated cells. Although low affinity receptors for IgE (Fc epsilon RII/CD23) were induced by 5637-CM, no TXB2 was released in response to soluble or latex-bound IgE-antigen complexes or to anti-Fc epsilon RII/CD23-antibodies. IL4 and to a lesser extent INFg both induced Fc epsilon RII/CD23 receptor expression, but inhibited release of TXB2 in response to Paf, fMLP, or PMA. We conclude that the functional receptors for IgE on mature macrophages are most probably not Fc epsilon RII/CD23.

Topics: Antibodies, Anti-Idiotypic; Antigens, Differentiation, B-Lymphocyte; Calcimycin; Drug Synergism; Humans; Immunoglobulin E; Interferon-gamma; Interleukin-4; Leukemia, Monocytic, Acute; Lymphokines; N-Formylmethionine Leucyl-Phenylalanine; Platelet Activating Factor; Protein Binding; Receptors, Fc; Receptors, IgE; Tetradecanoylphorbol Acetate; Thromboxane B2; Tumor Cells, Cultured