Interleukin-33-activated dendritic cells induce the production of thymus and activation-regulated chemokine and macrophage-derived chemokine.

BACKGROUND: Interleukin (IL)-33, a new member of the IL-1 cytokine family, is involved in T helper (Th)2-type responses in a wide range of diseases and is mediated by expression of the ST2 receptor in many immune cells. As the effects of IL-33 on dendritic cells (DCs) remain controversial, we investigated the ability of IL-33 to modulate the functions of these cells. METHODS: DCs were derived from mouse bone marrow, and the expression of the IL-33 receptor ST2 was examined by fluorescence-activated cell sorting and RT-PCR. The responses of the DCs to IL-33 were examined by RT-PCR and ELISA, and activation of mitogen-activated protein kinases (MAPKs) was determined by Western blotting. RESULTS: ST2 ligand mRNA and protein were detectable in DCs. IL-33 induced the production of thymus and activation-regulated chemokine/CCL17 and macrophage-derived chemokine/CCL22 and the activation of extracellular signal-regulated kinase 1/2, c-Jun N-terminal kinase and p38 MAPK. CONCLUSIONS: DCs respond directly to IL-33 through ST2. The interaction between IL-33 and DCs may represent a new pathway to initiate Th2-type immune responses. IL-33 and ST2 may play important roles in allergic inflammation.

Basic research on virus-induced asthma exacerbation: inhibition of inflammatory chemokine expression by fluticasone propionate.

BACKGROUND: Viral infection can exacerbate asthma by inducing the accumulation of inflammatory cells in the airway. We have previously reported that double-stranded RNA (dsRNA), a viral product and ligand of the Toll-like receptor-3 (TLR3), activates the transcription factors NF-κB and IRF-3 and upregulates the expression of inflammatory chemokines in airway epithelial cells. Here, we examined the effects of the glucocorticoid fluticasone propionate (FP) on the expression of the inflammatory chemokines CCL5, CXCL8 and CXCL10. METHODS: The airway epithelial cell line BEAS-2B was used for this study. Expression of CCL5, CXCL8 and CXCL10 mRNA and protein was quantified by real-time PCR and ELISA assay, respectively. To examine the association of FP with the physiology of chemokine production, we included several methods. Nuclear translocation of transcription factors was determined by performing Western blot analysis. Histone deacetylase (HDAC) activity in nuclear extracts was measured using a colorimetric assay. Stability of the chemokine mRNAs was examined in cells incubated with actinomycin D. The activities of the CCL5 promoter and the transcription factors NF-κB and IRF-3 were assessed using luciferase reporter assays. RESULTS: Treatment of BEAS-2B cells with FP significantly and dose-dependently (10(-9) to 10(-6)M) inhibited dsRNA-induced expression of CCL5, CXCL8 and CXCL10 protein and mRNA, but did not affect mRNA stability. FP also significantly inhibited dsRNA-stimulated CCL5 promoter activity. However, FP had no effect on the activity of HDAC or the nuclear translocation of NF-κB and IRF-3. CONCLUSIONS: FP inhibits the dsRNA-stimulated expression of inflammatory chemokines in airway epithelial cells. FP may act by inhibiting chemokine transcription through an as yet unidentified mechanism.

Expression and effects of IL-33 and ST2 in allergic bronchial asthma: IL-33 induces eotaxin production in lung fibroblasts.

BACKGROUND: Interleukin (IL)-33, a new member of the IL-1 cytokine family, has been recognized as a key cytokine that enhances T helper 2-balanced immune regulation through its receptor ST2; however, the function and relationship of the IL-33 and ST2 pathways in bronchial asthma are still unclear. We investigated the cellular origin and regulation of IL-33 and ST2 in allergic bronchial asthma in vivo and in vitro. METHODS: BALB/c mice were sensitized by intraperitoneal injections of ovalbumin (OVA) with alum. Mice were exposed to aerosolized 1% OVA for 30 min a day for 7 days. These mice were then challenged with aerosolized 1% OVA 2 days after the last day of exposure. After the OVA challenge, the mice were sacrificed and their lung tissues were obtained. Mouse lung fibroblasts were cultured and treated with IL-33 or IL-13. RESULTS: The levels of IL-33 mRNA and IL-33 protein in lung tissue increased after the OVA challenge. Most IL-33-expressing cells were CD11c+ cells and epithelial cells, and many ST2-expressing cells were stained lung fibroblasts and inflammatory cells. IL-33 induced eotaxin/CCL11 production in lung fibroblasts. IL-33 and IL-13 synergistically induced eotaxin expression. CONCLUSIONS: IL-33 may contribute to the induction and maintenance of eosinophilic inflammation in the airways by acting on lung fibroblasts. IL-33 and ST2 may play important roles in allergic bronchial asthma.

Oxaliplatin-induced lung injury with allergic reaction.

A 79-year-old man was diagnosed as stage IV colon cancer and treated with a modified FOLFOX6 (mFOLFOX6) regimen. On the 12th cycle, we observed erythema and dyspnea. Radiographs showed ground grass opacities. Blood tests showed elevated levels of eosinophils and immunoglobulin E. We diagnosed this finding as response to drug allergy and administered high-dose methylprednisolone. The treatment was successful and he was discharged. The drug lymphocyte stimulating test against oxaliplatin was positive, indicating a type I and IV allergic reaction due to oxaliplatin. Regimens including oxaliplatin must be carefully monitored and frequent blood tests and chest radiographs are needed.

Cooperative activation of CCL5 expression by TLR3 and tumor necrosis factor-alpha or interferon-gamma through nuclear factor-kappaB or STAT-1 in airway epithelial cells.

BACKGROUND: CCL5/RANTES contributes to prolonged eosinophilic inflammation and asthma exacerbation after a viral infection. We studied the mechanism of CCL5 expression using viral product double-stranded RNA (dsRNA), a ligand of Toll-like receptor 3 (TLR3), and inflammatory cytokines in airway epithelial cells. METHODS: The airway epithelial cell line BEAS-2B was used in our in vitro study, and the levels of CCL5 mRNA and CCL5 protein expression were determined using real-time PCR and ELISA. The activity of the CCL5 promoter region and nuclear factor (NF)-kappaB was assessed by dual luciferase assay using specific luciferase reporter plasmids. We used actinomycin D to assess the stability of mRNA. Phosphorylation of signal transducer and activator of transcription 1 (STAT-1) was analyzed by Western blot. RESULTS: Synthetic dsRNA up-regulated the expression of CCL5 mRNA and CCL5 protein. Adding TNF-alpha or IFN-gamma to dsRNA further increased the expression of CCL5. The combination of TNF-alpha and dsRNA cooperatively activated the CCL5 promoter region and the NF-kappaB-specific reporter. IFN-gamma did not activate these reporters. However, it increased the stability of CCL5 mRNA induced by dsRNA. IFN-gamma phosphorylated STAT-1, but dsRNA did not. The effects of IFN-gamma were not evident in the cells transfected with short interfering RNA for STAT-1. CONCLUSIONS: Cross-talk between TLR3 signaling and inflammatory cytokines regulates the expression of CCL5 in airway epithelial cells. In this mechanism, TNF-alpha may activate NF-kappaB, in cooperation with TLR3 signaling. IFN-gamma may stabilize CCL5 mRNA up-regulated by TLR3. This mechanism may depend on STAT-1.

Effects of corticosteroids on osteopontin expression in a murine model of allergic asthma.

BACKGROUND: Osteopontin (OPN) contributes to the development of T helper 1 (Th1)-mediated immunity and Th1-associated diseases. However, the role of OPN in bronchial asthma is unclear. Corticosteroids reduce airway inflammation, as reflected by the low eosinophil and T-cell counts, and the low level of cytokine expression. We investigated OPN production and the inhibitory effects of corticosteroids on OPN production in a murine model of allergic asthma. METHODS: BALB/c mice were sensitized by intraperitoneal injections of ovalbumin (OVA) with alum. Some mice received daily injections of dexamethasone (DEX) or phosphate-buffered saline for 1 week. All OVA-challenged mice were exposed to aerosolized 1% OVA for 30 min an hour after these injections. After the OVA challenge, the mice were killed, and bronchoalveolar lavage (BAL) fluid and lung tissue were examined. RESULTS: The levels of OPN protein in BAL fluid and OPN mRNA in lung tissue increased after OVA challenge. Most OPN-expressing cells were CD11c+ cells and some were T cells. DEX decreased the levels of OPN protein in the BAL fluid, and those of OPN mRNA and OPN protein in lung tissue. CONCLUSIONS: OPN may play an important role in allergic bronchial asthma. Corticosteroids inhibit OPN production in mice with allergic asthma. The beneficial effect of corticosteroids in bronchial asthma is partly due to their inhibitory effects on OPN production.

Increase in reactive oxygen metabolite level in acute exacerbations of asthma.

BACKGROUND: Oxidants including reactive oxygen species have been indicated to play an important role in the pathogenesis of asthma. OBJECTIVE: We investigated oxidative status in patients with acute exacerbations of asthma and evaluated the therapeutic response using the D-ROM test which is simple to use and quick. METHODS: We measured reactive oxygen metabolite (ROM) levels in the serum of 42 outpatients with acute exacerbations of asthma, 11 outpatients with stable asthma and 40 healthy subjects using the D-ROM test. Seven inpatients admitted due to acute exacerbations of asthma were also enrolled to evaluate the effects of treatment. Serum eosinophil cationic protein and plasma polymorphonuclear elastase were also measured by EIA or ELISA to evaluate the correlation between inflammation and oxidative status. RESULTS: Serum ROM levels were significantly higher in patients with acute exacerbation of asthma than in patients with stable asthma or healthy subjects. Levels of serum eosinophil cationic protein and plasma polymorphonuclear elastase were increased in acute exacerbation and moderately correlated to ROM levels. Levels of ROM were significantly decreased after treatment with systemic steroids and bronchodilators. CONCLUSION: These findings suggest that acute exacerbation of asthma is associated with increased oxidative stress. Serum ROM levels would partly reflect the inflammation with eosinophils and neutrophils and may be useful as biomarkers of asthma.

Role of RIG-I, MDA-5, and PKR on the expression of inflammatory chemokines induced by synthetic dsRNA in airway epithelial cells.

BACKGROUND: We hypothesized that synthetic double-stranded (ds)RNA may mimic viral infection and reported that dsRNA stimulates expression of inflammatory chemokines through a receptor of dsRNA Toll-like receptor (TLR) 3 in airway epithelial cells. In this study, we focused our study on the role of other receptors for dsRNA, such as retinoic acid-inducible gene I (RIG-I), melanoma differentiation-associated gene 5 (MDA-5), and double-stranded RNA-dependent protein kinase (PKR). METHODS: Airway epithelial cell BEAS-2B was cultured in vitro. Expression of target RNA and protein were analyzed by PCR and ELISA. To analyze the role of receptors for dsRNA, knockdown of theses genes was performed with short interfering RNA (siRNA). RESULTS: We first investigated the effects of chloroquine, an inhibitor of lysosomal acidification, on the expression of chemokines. Preincubation with 100 microM chloroquine significantly inhibited the expression of mRNA for RANTES, IP-10, and IL-8, stimulated by poly I:C, indicating that poly I:C may react with a receptor expressed inside the cells. RIG-I, MDA-5, and PKR are supposed to be expressed inside the airway epithelial cells. However, the expression of chemokines stimulated with poly I:C was not significantly inhibited for these putative receptors in the cells which were transfected with siRNA. CONCLUSIONS: Synthetic dsRNA poly I:C stimulates the expression of inflammatory chemokines in airway epithelial cells, but the putative receptors for dsRNA such as RIG-I, MDA-5, or PKR may not play pivotal roles in this process. TLR3 may play a major role as reported previously.

Differential regulation of chemokine expression by Th1 and Th2 cytokines and mechanisms of eotaxin/CCL-11 expression in human airway smooth muscle cells.

BACKGROUND: Airway smooth muscle (ASM) cells may contribute to the pathogenesis of asthma including airway inflammation and remodeling. We focused our study on the regulation of chemokine expression by cytokines and analyzed the mechanisms of eotaxin/CCL-11 expression in ASM cells. METHODS: Human ASM cells were cultured in vitro and treated with IL-4, interferon-gamma (IFNgamma), and tumor necrosis factor-alpha (TNFalpha). Secretion of chemokines into the culture medium was analyzed by ELISA. Expression of eotaxin mRNA was analyzed by reverse transcription-polymerase chain reaction (RT-PCR). Binding of transcription factor signal transducer activator of transcription (STAT) 6 to the eotaxin promoter-derived DNA was analyzed by pull-down Western blot. To assess transcriptional regulation of eotaxin, cells were transfected with eotaxin promoter-luciferase reporter plasmids, and activity was determined by dual luciferase assay. RESULTS: The Th2 cytokine IL-4 preferentially stimulated the expression of the CC chemokine receptor (CCR) 3-ligand chemokines eotaxin, eotaxin-3, and MCP-4. The Th1 cytokine IFNgamma stimulated the expression of chemokines IP-10 and RANTES. IL-4 stimulated nuclear translocation of signal transducer activator of transcription 6 (STAT6) and its binding to the eotaxin promoter region. IL-4 activated the eotaxin promoter and its activity was inhibited by mutation of the binding site for STAT6 in the promoter. CONCLUSIONS: The Th2 cytokine IL-4 preferentially stimulated the expression of CCR3 ligand chemokines including eotaxin in ASM cells. The transcription factor STAT6 may play a pivotal role in the activation of eotaxin transcription in response to IL-4.

The IL-17F signaling pathway is involved in the induction of IFN-gamma-inducible protein 10 in bronchial epithelial cells.

BACKGROUND: IL-17F is involved in airway inflammation, but its biologic activity and signaling pathway remain incompletely defined. Interferon-gamma-inducible protein 10 (IP-10) is widely expressed and plays a role in airway inflammatory diseases. OBJECTIVE: We sought to investigate the functional linkage between IL-17F and IP-10 expression in bronchial epithelial cells. METHODS: Bronchial epithelial cells were cultured in the presence or absence of IL-17F, and/or a T(H)1 cytokine, T(H)2 cytokines, proinflammatory cytokines, various kinase inhibitors, or a Raf1 dominant-negative mutant to analyze the expression of IP-10. Moreover, the involvement of p90 ribosomal S6 kinase (p90RSK) and cyclic AMP response element-binding protein (CREB) in IL-17F-induced IP-10 expression were investigated. RESULTS: IL-17F induces the gene and protein expression of IP-10. The addition of IFN-gamma, IL-1beta, and TNF-alpha augmented IL-17F-induced IP-10 expression. The mitogen-activated protein kinase kinase (MEK) inhibitors PD98059, U0126, and Raf1 kinase inhibitor I significantly inhibited its production. In contrast, a p38 inhibitor, a JNK inhibitor, protein kinase C inhibitors, and a phosphatidylinositol 3-kinase inhibitor, showed no inhibitory effect. Furthermore, overexpression of a Raf1 dominant-negative mutant inhibited its expression. Of interest, IL-17F phosphorylated p90RSK and CREB, and transfection of the cells with a short interfering RNA for p90RSK or CREB inhibited its expression, suggesting p90RSK and CREB as novel signaling molecules of IL-17F. CONCLUSION: IL-17F is a potent inducer of IP-10 in bronchial epithelial cells through the activation of the Raf1-MEK1/2-extracellular signal-regulated kinase 1/2-p90RSK-CREB pathway, supporting its regulatory role in airway inflammation. CLINICAL IMPLICATIONS: The IL-17F-IP-10 axis might be a novel and critical therapeutic target for airway inflammatory diseases.

Effects of corticosteroid on the expression of thymus and activation-regulated chemokine in a murine model of allergic asthma.

BACKGROUND: Thymus and activation-regulated chemokine (TARC; CCL17) is a lymphocyte-directed CC chemokine that specifically attracts T-helper (Th) 2 cells positive for the CC chemokine receptor 4 (CCR4(+)). Corticosteroids reduce airway inflammation, as reflected by reduced numbers of eosinophils and T cells and reduced expression of cytokines. We investigated TARC production and the inhibitory effects of corticosteroids on TARC expression in a murine model of allergic asthma. METHODS: BALB/c mice were sensitized by intraperitoneal injection of ovalbumin (OVA) with alum. Once daily for 1 week, mice received injections of dexamethasone or 0.2 ml saline (control), then 1 h later inhaled aerosolized 1% OVA for 30 min. Mice were killed 24 h after OVA challenge for bronchoalveolar lavage and lung tissue examination. RESULTS: TARC was expressed mainly in the bronchial epithelial cells. Dexamethasone attenuated OVA-induced airway eosinophilia, lymphocyte infiltration, and airway hyperresponsiveness. Dexamethasone also decreased TARC production in the bronchoalveolar lavage fluid and decreased expression of TARC mRNA and TARC protein in lung tissue. CONCLUSIONS: The corticosteroid dexamethasone inhibits TARC production in a murine model of allergic asthma in vivo. The beneficial effect of corticosteroids in bronchial asthma is due in part to their direct inhibitory effects on TARC production.

Induction of granulocyte-macrophage colony-stimulating factor by a new cytokine, ML-1 (IL-17F), via Raf I-MEK-ERK pathway.

BACKGROUND: ML-1 (IL-17F) is a recently discovered cytokine, and its function remains elusive. GM-CSF is a crucial cytokine for the maturation of various cell types and regulates allergic airway inflammation. OBJECTIVE: The functional effect of ML-1 in the expression of GM-CSF was investigated. METHODS: The levels of gene and protein expression in normal human bronchial epithelial cells (NHBEs) in the presence or absence of various kinase inhibitors or, in some cases, of a Raf1 dominant-negative mutant were determined by RT-PCR and ELISA, respectively. Western blotting was performed to investigate kinase activation. RESULTS: The results showed first that ML-1 induces, in a time-dependent and dose-dependent manner, the gene and protein expression for GM-CSF NHBEs, which are associated with activation of Raf1 and MAP kinase kinase (MEK) kinases. Selective MEK inhibitors, PD98059 and U0126, and Raf1 kinase inhibitor I significantly inhibited ML-1-induced GM-CSF production. Furthermore, overexpression of Raf1 dominant-negative mutants inhibited IL-17F-induced GMCSF expression. The combination of PD98059 and Raf1 kinase inhibitor I completely blocked GM-CSF production, whereas 2 protein kinase C inhibitors, Ro-31-7549 and GF109203X, and a phosphatidylinositol 3-kinase inhibitor, LY294002, showed no inhibitory effect. CONCLUSION: These findings suggest that ML-1 induces GM-CSF expression through the activation of the Raf1-MEK-extracellular signal-regulated kinase 1/2 pathway.

[Comparison of the inhibitory effects of glucocorticoids on the expression of eotaxin in airway epithelial cell line BEAS-2B].

OBJECTIVE: Inhaled corticosteroids play a pivotal role in the treatment of asthma. To observe the mechanisms of glucocorticoids, we focused our study on the comparison of several glucocorticoids' effects on eotaxin expression in the airway epithelial cells. METHODS: Airway epithelial cell line BEAS-2B was cultured in vitro. Cells were preincubated with or without glucocorticoids (becromethasone dipropionate; BDP, budesonide; BUD, fluticasone propionate; FP) and stimulated with TNFalpha and/or IL-4. Protein levels of eotaxin in the supernatants of the cultured cells were determined by ELISA. RESULTS AND CONCLUSIONS: TNFalpha and IL-4 increased the levels of eotaxin in BEAS-2B cells. Combination of these cytokines synergistically upregulated the eotaxin expression as reported previously. Each glucocorticoid significantly inhibited the expression of eotaxin protein induced with TNFalpha and IL-4 and the compared efficacy was in order of FP>BUD>BDP. FP seemed most potent and the inhibitory effect was also observed with relatively low concentration such as 10 (-10)M. Taken together, the comparison of the potency of each glucocorticoid using airway epithelial cells may reflect the efficacy of these drugs in asthmatics.

Molecular mechanisms of repression of eotaxin expression with fluticasone propionate in airway epithelial cells.

BACKGROUND: Glucocorticoids are known to repress the expression of CC chemokine eotaxin in airway epithelial cells. We focused our study on the molecular mechanisms of the glucocorticoid, fluticasone, in the inhibition of the expression of the eotaxin gene in the cells. METHODS: The airway epithelial cell line, BEAS-2B, was stably transfected with signal transducers and activators of transcription 6 (STAT6)-expressing vector and used in the following experiments to clarify the function of STAT6. Levels of eotaxin mRNA and protein expression were determined with RT-PCR and ELISA. Mechanisms of transcriptional regulation were assessed by the electrophoretic mobility shift assay and dual luciferase assay using eotaxin promoter-luciferase reporter plasmids. RESULTS: Fluticasone significantly inhibited the induction of eotaxin protein stimulated with TNF-alpha and IL-4 in the cells. Fluticasone also repressed the induction of eotaxin mRNA with these stimuli. It partially inhibited the activity of eotaxin promoter; however, it did not inhibit the nuclear translocation and binding of transcription factors, nuclear factor-kappa B (NF-kappaB) or STAT6, to the DNA derived from the proximal promoter region of the eotaxin gene. Moreover, the inhibitory effect was also conserved in the experiments using the reporter plasmid of which the putative glucocorticoid-responsive element was mutated. CONCLUSIONS: Fluticasone inhibits the expression of eotaxin gene in airway epithelial cells in part through repression of the transcription. However, the mechanisms depend neither on the inhibition of transcription factors' translocation into nuclei nor the function of the putative glucocorticoid-responsive element in the promoter, indicating that other mechanisms would be related to the transcriptional repression of the eotaxin gene in airway epithelial cells.

Induction of C-X-C chemokines, growth-related oncogene alpha expression, and epithelial cell-derived neutrophil-activating protein-78 by ML-1 (interleukin-17F) involves activation of Raf1-mitogen-activated protein kinase kinase-extracellular signal-regulated kinase 1/2 pathway.

Neutrophil recruitment into the airway typifies pulmonary inflammation and is regulated through chemokine network, in which two C-X-C chemokines play a critical role. Airway epithelial cells and vein endothelial cells are major cell sources of chemokines. ML-1 (interleukin-17F) is a recently discovered cytokine and its function still remains elusive. In this report, we investigated the functional effect of ML-1 in the expression of growth-related oncogene (GRO)alpha and epithelial cell-derived neutrophil activating protein (ENA)-78. The results showed first that ML-1 induces, in time- and dose-dependent manners, the gene and protein expressions for both chemokines in normal human bronchial epithelial cells and human umbilical vein endothelial cells. Furthermore, selective mitogen-activated protein kinase kinase (MEK) inhibitors 2'-amino-3'-methoxyflavone (PD98059), 1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto) butadiene (U0126), and Raf1 kinase inhibitor I partially inhibited Ml-1-induced GROalpha and ENA-78 production. In contrast, the combination of PD98059 and Raf1 kinase inhibitor I completely abrogated the chemokine production, whereas a protein kinase C inhibitor, 2-(1-(3-aminopropyl) indol-3-yl)-3-(1-methylindol-3-yl) maleimide, acetate (Ro-31-7549), and a phosphatidylinositol 3-kinase inhibitor, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), did not affect their production. Together, these data indicates a role for Raf1-MEK-extracellular signal-regulated kinase 1/2 pathway in ML-1 induced C-X-C chemokine expression, suggesting potential pharmacological targets for modulation.

Differential regulation of eotaxin expression by IFN-gamma in airway epithelial cells.

BACKGROUND: Eotaxin is a chemokine that binds with high affinity and specificity to the chemokine receptor CCR3 and plays an important role in the pathogenesis of allergic disease. OBJECTIVE: We studied the regulation of eotaxin expression by the T(H)1 cytokine IFN-gamma and analyzed its molecular mechanisms. METHODS: Levels of eotaxin mRNA and protein expression in the airway epithelial cell line BEAS-2B were determined with RT-PCR and ELISA. Mechanisms of transcriptional regulation were assessed by means of electrophoretic mobility shift assays and luciferase assay with eotaxin promoter-luciferase reporter plasmids. RESULTS: Although IFN-gamma did not directly induce the expression of eotaxin protein, it increased the induction by TNF-alpha when these cytokines were added simultaneously. In contrast, preincubation of cells with IFN-gamma for 24 hours profoundly inhibited the production induced by TNF-alpha. IFN-gamma did not influence the TNF-alpha-induced binding of nuclear factor kappaB to a DNA probe derived from the eotaxin promoter. IFN-gamma did not increase the ability of TNF-alpha to activate the eotaxin promoter. Studies of eotaxin mRNA levels indicate that IFN-gamma combined with TNF-alpha increased the expression of eotaxin mRNA. When cells were preincubated with IFN-gamma, there was no inhibition of the appearance of eotaxin mRNA. CONCLUSION: These studies demonstrate that IFN-gamma enhances eotaxin expression when added in combination with TNF-alpha and profoundly inhibits eotaxin expression after preincubation. In both cases the available data indicate that the effect is mediated by a posttranscriptional mechanism.