Granulocyte Colony-stimulating Factor mRNA Levels Research Articles

Myeloperoxidase-deficient mice exposed to Zymosan exhibit severe neutrophilia and anemia with enhanced granulopoiesis and reduced erythropoiesis, accompanied by pulmonary inflammation

We previously reported that myeloperoxidase-deficient (MPO-/-) mice develop more severe neutrophil-rich lung inflammation than wild-type mice following intranasal Zymosan administration. Interestingly, we found that these mutant mice with severe lung inflammation also displayed pronounced neutrophilia and anemia, characterized by increased granulopoiesis and decreased erythropoiesis in the bone marrow, compared to wild-type mice. This condition was associated with higher concentrations of granulocyte-colony stimulating factor (G-CSF) in both the lungs and serum, a factor known to enhance granulopoiesis. Neutrophils accumulating in the lungs of MPO-/- mice produced greater amounts of G-CSF than those in wild-type mice, indicating that they are a significant source of G-CSF. In vitro experiments using signal transduction inhibitors and Western blot analysis revealed that MPO-/- neutrophils express higher levels of G-CSF mRNA in response to Zymosan, attributed to the upregulation of the IκB kinase/nuclear factor (NF)-κB pathway and the extracellular-signal-regulated kinase/NF-κB pathway. These findings highlight MPO as a critical regulator of granulopoiesis and erythropoiesis in inflamed tissues.

Altered Peripheral Immune Profiles in First-Episode, Drug-Free Patients With Schizophrenia: Response to Antipsychotic Medications.

Previous research has demonstrated aberrations in the levels of inflammatory cytokines in patients with schizophrenia (SCZ), but most of the respective studies have tested a narrow set of inflammatory cytokines. Here, we aimed to analyze broad immune profiles in the peripheral blood of the first-episode drug-free (FEDF) patients with SCZ at baseline and after an 8-week treatment with atypical antipsychotics. Serum samples from 24 FEDF patients with SCZ and 25 healthy control (HC) subjects were tested using Luminex multiplex analysis for 30 cytokines, chemokines, and growth factors. Multiple comparison tests demonstrated that interleukin-2 (IL-2), IL-4, interferon-gamma (IFN-γ), monokine induced by IFN-γ, and granulocyte colony-stimulating factor (G-CSF) levels were significantly increased, whereas those of the epidermal growth factor were significantly decreased in the FEDF patients with SCZ. Moreover, the levels of the 6 dysregulated cytokines as well as those of 12 additional soluble factors in FEDF patients with SCZ were significantly decreased after 8 weeks of antipsychotic treatment. Furthermore, the transcription of G-CSF and IFN-γ was significantly increased in FEDF patients with SCZ when compared with controls, and G-CSF and IFN-γ mRNA levels were highly correlated with their respective protein concentrations. Receiver operating characteristic curves showed that G-CSF and IFN-γ had good performance in differentiating between FEDF patients with SCZ and HC subjects. Taken together, our data revealed that FEDF patients with SCZ were accompanied by a unique pattern of immune profile, and antipsychotic medications seemed to suppress the immune function in these patients, which could be used to develop novel targets for the diagnosis and treatment of SCZ.

SB203580 increases G-CSF production via a stem-loop destabilizing element in the 3' untranslated region in macrophages independently of its effect on p38 MAPK activity.

BackgroundGranulocyte-colony stimulating factor (G-CSF) is a major regulator of the production and survival of neutrophils. Regulation of G-CSF expression is complex and occurs at both transcription and post-transcription levels. Two distinct types of cis-acting elements in the 3’ untranslated region (3’UTR) of G-CSF mRNA have been identified as destabilizing elements; these consist of adenylate uridylate-rich elements (AUREs) and a stem–loop destabilizing element (SLDE). Regulation of the stability of mRNA by p38 mitogen-activated protein kinase (MAPK) has been indicated to be linked to AUREs in the 3’UTR. However, whether p38 MAPK is involved in the regulation of the stability of G-CSF mRNA has not been elucidated. This study investigated the effect of SB203580, an inhibitor of p38 MAPK, on the lipopolysaccharide-induced G-CSF expression in macrophages at the post-transcription level.ResultsOur study showed surprising results that SB203580 augmented the lipopolysaccharide-induced increase in the G-CSF mRNA levels in RAW264.7 mouse macrophages, mouse bone marrow-derived macrophages and in THP-1 human macrophages. This effect was also seen in p38α MAPK knockdown RAW264.7 cells, showing that it was not due to inhibition of p38 MAPK activity. In the presence of actinomycin D, the decay of G-CSF mRNA was slower in SB203580-treated cells than in control cells, showing that SB203580 increased the stability of G-CSF mRNA. Reporter genes containing luciferase with or without the 3’UTR of G-CSF were constructed and transfected into RAW264.7 cells and the results showed that the presence of the 3’UTR reduced the luciferase mRNA levels and luciferase activity. Furthermore, SB203580 increased the luciferase mRNA levels and activity in RAW264.7 cells transfected with the luciferase reporter containing the 3’UTR, but not in cells transfected with the luciferase reporter without the 3’UTR. Mutations of the highly conserved SLDE in the 3’UTR abolished these effects, showing that the SLDE was essential for the SB203580-induced increase in the stability of mRNA.ConclusionsSB203580 increases G-CSF expression in macrophages by increasing the stability of G-CSF mRNA via its 3’UTR, and the effect was not due to its inhibition of p38 MAPK activity. The results of this study also highlight a potential target for boosting endogenous production of G-CSF during neutropenia.

Circumventing Y. pestis Virulence by Early Recruitment of Neutrophils to the Lungs during Pneumonic Plague

Pneumonic plague is a fatal disease caused by Yersinia pestis that is associated with a delayed immune response in the lungs. Because neutrophils are the first immune cells recruited to sites of infection, we investigated the mechanisms responsible for their delayed homing to the lung. During the first 24 hr after pulmonary infection with a fully virulent Y. pestis strain, no significant changes were observed in the lungs in the levels of neutrophils infiltrate, expression of adhesion molecules, or the expression of the major neutrophil chemoattractants keratinocyte cell-derived chemokine (KC), macrophage inflammatory protein 2 (MIP-2) and granulocyte colony stimulating factor (G-CSF). In contrast, early induction of chemokines, rapid neutrophil infiltration and a reduced bacterial burden were observed in the lungs of mice infected with an avirulent Y. pestis strain. In vitro infection of lung-derived cell-lines with a YopJ mutant revealed the involvement of YopJ in the inhibition of chemoattractants expression. However, the recruitment of neutrophils to the lungs of mice infected with the mutant was still delayed and associated with rapid bacterial propagation and mortality. Interestingly, whereas KC, MIP-2 and G-CSF mRNA levels in the lungs were up-regulated early after infection with the mutant, their protein levels remained constant, suggesting that Y. pestis may employ additional mechanisms to suppress early chemoattractants induction in the lung. It therefore seems that prevention of the early influx of neutrophils to the lungs is of major importance for Y. pestis virulence. Indeed, pulmonary instillation of KC and MIP-2 to G-CSF-treated mice infected with Y. pestis led to rapid homing of neutrophils to the lung followed by a reduction in bacterial counts at 24 hr post-infection and improved survival rates. These observations shed new light on the virulence mechanisms of Y. pestis during pneumonic plague, and have implications for the development of novel therapies against this pathogen.

Inhibition by rapamycin of the lipoteichoic acid-induced granulocyte-colony stimulating factor expression in mouse macrophages

Granulocyte-colony stimulating factor (G-CSF) is a cytokine which involves in anti-inflammation and inflammation as well. Rapamycin is an inhibitor of mTOR which also plays a role in innate immunity. This study investigated the effect of rapamycin on the lipoteichoic acid (LTA)-induced expression of G-CSF in macrophages and its underlying mechanism. Our data show that LTA induced G-CSF expression in RAW264.7 and bone marrow-derived macrophages and that this effect was inhibited by rapamycin. Analysis of the G-CSF 5′ flanking sequence revealed that the −283 to +35 fragment, which contains CSF and octamer elements, was required for maximal promoter activity in response to LTA stimulation. Western blot analyses of proteins that bind to the CSF and octamer element show that LTA increased protein levels of NF-κB, C/EBPβ and Oct-2, and that rapamycin inhibited the LTA-induced increase in Oct-2 protein levels, but not the others. Knockdown of Oct-2 by RNA interference resulted in a decrease in LTA-induced G-CSF mRNA levels. Moreover, forced expression of Oct-2 by transfection with the pCG-Oct-2 plasmid overcame the inhibitory effect of rapamycin on the LTA-induced increase in G-CSF mRNA levels and promoter activity. This study demonstrates that rapamycin reduces G-CSF expression in LTA-treated macrophages by inhibiting Oct-2 expression.

Rapamycin inhibits lipopolysaccharide induction of granulocyte-colony stimulating factor and inducible nitric oxide synthase expression in macrophages by reducing the levels of octamer-binding factor-2

This article reports an inhibitory effect of rapamycin on the lipopolysaccharide (LPS)-induced expression of both inducible nitric oxide synthase (iNOS) and granulocyte-colony stimulating factor (G-CSF) in macrophages and its underlying mechanism. The study arose from an observation that rapamycin inhibited the LPS-induced increase in octamer-binding factor-2 (Oct-2) protein levels through a mammalian target of rapamycin (mTOR)-dependent pathway in mouse RAW264.7 macrophages. As both iNOS and G-CSF are potential Oct-2 target genes, we tested the effect of rapamycin on their expression and found that it reduced the LPS-induced increase in iNOS and G-CSF mRNA levels and iNOS and G-CSF protein levels. Blocking of mTOR-signaling using a dominant-negative mTOR expression plasmid resulted in inhibition of the LPS-induced increase in iNOS and G-CSF protein levels, supporting the essential role of mTOR. Forced expression of Oct-2 using the pCG-Oct-2 plasmid overcame the inhibitory effect of rapamycin on the LPS-induced increase in iNOS and G-CSF mRNA levels. Chromatin immunoprecipitation assays showed that LPS enhanced the binding of Oct-2 to the iNOS and G-CSF promoters and that this effect was inhibited by pretreatment with rapamycin. Moreover, RNA interference knockdown of Oct-2 reduced iNOS and G-CSF expression in LPS-treated cells. The inhibitory effect of rapamycin on the LPS-induced increase in Oct-2 protein levels and on the iNOS and G-CSF mRNA levels was also detected in human THP-1 monocyte-derived macrophages. This study demonstrates that rapamycin reduces iNOS and G-CSF expression at the transcription level in LPS-treated macrophages by inhibiting Oct-2 expression.

Interleukin-6 Infusion Blunts Proinflammatory Cytokine Production Without Causing Systematic Toxicity in a Swine Model of Uncontrolled Hemorrhagic Shock

Serum elevations of interleukin-6 (IL-6) correlate with multiple organ dysfunction syndrome and mortality in critically injured trauma patients. Data from rodent models of controlled hemorrhage suggest that recombinant IL-6 (rIL-6) infusion protects tissue at risk for ischemia-reperfusion injury. Exogenous rIL-6 administered during shock appears to abrogate inflammation, providing a protective rather than a deleterious influence. In an examination of this paradox, the current study aimed to determine whether rIL-6 decreases inflammation in a clinically relevant large animal model of uncontrolled hemorrhagic shock, (UHS), and to investigate the mechanism of protection. Swine were randomized to four groups (8 animals in each): (1) sacrifice, (2) sham (splenectomy followed by hemodilution and cooling to 33 degrees C), (3) rIL-6 infusion (sham plus UHS using grade 5 liver injury with packing and resuscitation plus blinded infusion of rIL-6 [10 mcg/kg]), and (4) placebo (UHS plus blinded vehicle). After 4 hours, blood was sampled, estimated blood loss determined, animals sacrificed, and lung harvested for RNA isolation. Quantitative reverse transcriptase-polymerase chain reaction was used to assess granulocyte colony-stimulating factor (G-CSF), IL-6, and tumor necrosis factor-alpha (TNFalpha) messenger ribonucleic acid (mRNA) levels. Serum levels of IL-6 and TNFalpha were measured by enzyme-linked immunoassay (ELISA). As compared with placebo, IL-6 infusion in UHS did not increase estimated blood loss or white blood cell counts, nor decrease hematocrit or platelet levels. As compared with the sham condition, lung G-CSF mRNA production in UHS plus placebo increased eightfold (*p < 0.05). In contrast, rIL-6 infusion plus UHS blunted G-CSF mRNA levels, which were not significantly higher than sham levels (p = 0.1). Infusion of rIL-6 did not significantly affect endogenous production of either lung IL-6 or mRNA. As determined by ELISA, rIL-6 infusion did not increase final serum levels of IL-6 or TNFalpha over those of sham and placebo conditions. Exogenous rIL-6 blunts lung mRNA levels of the proinflammatory cytokine G-CSF. The administration of rIL-6 does not increase the local expression of IL-6 nor TNFalpha mRNA in the lung. Additionally, rIL-6 infusion does not appear to cause systemic toxicity.

Cyclic changes of granulocyte colony-stimulating factor (G-CSF) mRNA in the human follicle during the normal menstrual cycle and immunolocalization of G-CSF protein.

Ovulation has several similarities with inflammation and is closely connected to the activity of leukocytes and inflammatory cytokines. Since granulocytes are one of the major leukocytes, we focused our attention on the presence and local production of granulocyte colony-stimulating factor (G-CSF) in the human ovary. The presence of G-CSF protein in the follicular fluid and perifollicular tissues was examined by Western blot analysis (n = 5) and immunohistochemical staining (n = 10). The relative expression levels of G-CSF mRNA in relation to GAPDH in granulosa, theca and luteal cells during the menstrual cycle were measured by quantitative RT-PCR using TaqMan technology (n = 15). G-CSF protein was detected in all follicular fluid and located mainly in granulosa cells of the follicle and luteal cells. The expression level of G-CSF mRNA in the late follicular phase was 137.6 +/- 18.5, which was approximately 10-fold greater than other phases during the menstrual cycle (P < 0.05). These results demonstrate that G-CSF is produced in the human follicle shortly before the ovulatory phase and may play an important role in the mechanism of ovulation.

CHRONIC NEUTROPHILIC LEUKAEMIA: A DISTINCT CLINICAL ENTITY?

CHRONIC NEUTROPHILIC LEUKAEMIA: A DISTINCT CLINICAL ENTITY?

Regulation of granulocyte colony-stimulating factor gene expression by interleukin-17

Interleukin-17 (IL-17) has been previously reported to induce stromal cells to produce a number of hematopoietic and proinflammatory cytokines, including granulocyte colony-stimulating factor (G-CSF). Here, we have evaluated the mechanisms responsible for the augmentation of G-CSF gene expression by IL-17, using the murine 3T3 fibroblast cell line. Treatment of 3T3 cells, but not primary bone marrow-derived macrophages or murine monocyte/macrophage cell lines, resulted in increased steady-state G-CSF mRNA levels within 2–4 h and augmented G-CSF protein production. The combination of IL-17 and LPS enhanced G-CSF expression in an additive fashion. Stability studies revealed that IL-17 stabilized G-CSF mRNA levels, with a t 1/2 of 4 h, compared to a t 1/2 of less than 2 h in medium or LPS-treated cells. Induction of G-CSF expression in 3T3 cells by IL-17 did not appear to require tyrosine kinase activation or de novo protein synthesis. These studies indicate that post-transcriptional mechanisms play an important role in IL-17-induced G-CSF expression in fibroblasts and suggest that IL-17 may be useful for further delineating mechanisms of G-CSF gene regulation.

G-CSF instillation into rat lungs mediates neutrophil recruitment, pulmonary edema, and hypoxia.

Activated neutrophils (PMN) have been implicated in the pathogenesis of adult respiratory distress syndrome (ARDS). Granulocyte colony-stimulating factor (G-CSF) is essential for PMN production and activation of PMN functions. We have recently shown that levels of G-CSF mRNA in a rat model of hemorrhagic shock correlated with severity of shock, PMN infiltration, pulmonary edema, and hypoxia. To determine whether increased tissue levels of G-CSF contribute to PMN recruitment and PMN-mediated injury, we instilled G-CSF into the lungs by intratracheal injection. Animals treated with G-CSF became hypoxic, hypocapnic, and alkalotic and demonstrated increased BAL fluid cellularity compared with control animals. The wet-to-dry ratio increased significantly after G-CSF instillation and peaked at 12 h. Histological examination of the lungs from G-CSF-treated rats revealed marked edema and increased PMN within the interstitium and alveoli. These results indicate that the presence of G-CSF alone in the lung can lead to recruitment of PMN, lung injury, and impaired pulmonary function, suggesting that local production of G-CSF may contribute to the development of lung damage and possibly ARDS in the setting of resuscitated hemorrhagic shock.

Expression of Granulocyte Colony Stimulating Factor (G-CSF) and Granulocyte/Macrophage Colony Stimulating Factor (GM-CSF) mRNA upon Stimulation with Phorbol Ester

Stimulated human peripheral blood mononuclear cells (MNC) have been shown to express both G-CSF and GM-CSF. Furthermore, G-CSF is expressed by monocytes but not lymphocytes, whereas GM-CSF is expressed largely by T lymphocytes and at low levels in monocytes/macrophages. Here we present the effect of TPA (12-O-tetradecanoyl phorbol-13-acetate) on G-CSF and GM-CSF expression in stimulated human MNCs and T lymphocytes. We observed that TPA (30nM) decreased G-CSF mRNA levels in MNCs, while ionomycin increased G-CSF in a dose-dependent manner. TPA and ionomycin individually increased GM-CSF mRNA levels in T-lymphocytes and MNCs. Further, GM-CSF was induced synergistically by TPA plus ionomycin, whereas this combination markedly decreased G-CSF mRNA levels in MNCs. These data suggest at least two signaling pathways by which G-CSF and GM-CSF mRNA levels are modulated in a mixed population of monocytes and T lymphocytes, namely protein kinase C (PKC) and calcium. These signals seem to act synergistically in lymphocytes to increase GM-CSF, and not G-CSF mRNA levels specifically. It would also appear these signals act on MNCs in an opposing manner to decrease G-CSF mRNA levels, indicating that activation of PKC and the calcium signaling pathway lead to a cell-type specific modulation of individual cytokines and precise regulation of granulocyte production.

Maternal and umbilical serum concentrations of granulocyte colony-stimulating factor and its messenger RNA during clinical chorioamnionitis

To determine whether women with chorioamnionitis developed elevated serum granulocyte colony-stimulating factor (G-CSF) concentrations and, if so, whether the G-CSF crossed to the fetus. We quantified G-CSF before, during, and after delivery and in the cord blood of 12 women with clinical chorioamnionitis and 12 matched controls. We also measured G-CSF messenger RNA (mRNA) transcripts in mononuclear cells isolated from maternal and cord blood at delivery. At study entry, G-CSF concentrations were much higher in women with chorioamnionitis (1397 +/- 950 pg/mL, mean +/- standard error of mean) than in controls (17 +/- 5 pg/mL, P < .05). At delivery, concentrations had increased in both groups (2752 +/- 1100 pg/mL in the chorioamnionitis group, 165 +/- 61 pg/mL in controls; P < .05). After delivery, G-CSF concentrations had diminished to 839 +/- 594 pg/mL in women with chorioamnionitis and to 83 +/- 16 pg/mL in controls (P < .05). Concentrations in the cord blood were 2729 +/- 974 pg/mL for the chorioamnionitis group and 51 +/- 17 pg/mL for controls (P < .05). Granulocyte colony-stimulating factor mRNA transcripts were more abundant in women with chorioamnionitis than in controls but were scarce in all matched cord blood samples tested. Serum G-CSF concentrations were elevated during clinical chorioamnionitis, and similar levels were found in maternal and cord serum. Because G-CSF mRNA levels were very low in cord mononuclear cells, the G-CSF in cord serum might be maternal in origin.

G(AnH)MTetra, a naturally occurring 1,6-anhydro muramyl dipeptide, induces granulocyte colony-stimulating factor expression in human monocytes: a molecular analysis.

N-Acetylglucosaminyl-1,6-anhydro-N-acetylmuramyl-L-alanyl-D-isoglutam yl-m- diaminopimelyl-D-alanine [G (Anh)MTetra], a naturally occurring breakdown product of peptidoglycan from bacterial cell walls, was studied for its ability to induce granulocyte colony-stimulating factor (G-CSF) mRNA and protein expression in human adherent monocytes. Resting monocytes did not express G-CSF mRNA or secrete G-CSF protein. In contrast, monocytes exposed to G(Anh)MTetra showed a dose-dependent increase in G-CSF mRNA accumulation, which correlates with the secretion of G-CSF protein. Maximal levels of G-CSF mRNA were reached within 2 h of activation. Expression of G-CSF was mediated by an increase in the stability of G-CSF transcripts rather than by an increase in the transcription rate of the G-CSF gene. Experiments with the protein synthesis inhibitor cycloheximide revealed that G(Anh)MTetra-induced G-CSF mRNA expression was independent of new protein synthesis. Furthermore, it was shown that the effect of G(Anh)MTetra was regulated by a protein kinase C-dependent pathway, whereas protein kinase A and tyrosine kinases were not involved. Finally, it was shown that G(Anh)MTetra also induced G-CSF mRNA expression in human endothelial cells. The data indicate that, besides lipopolysaccharide, other naturally occurring bacterial cell wall components are able to induce G-CSF expression in different hematopoietic cells.

Human arterial smooth muscle cells synthesize granulocyte colony- stimulating factor in response to interleukin-1 alpha and tumor necrosis factor-alpha

Vascular smooth muscle cells (SMC) are a major cell type comprising the walls of blood vessels. We report the synthesis of granulocyte colony- stimulating factor (G-CSF) by cultured human SMC obtained from the internal mammary artery and thoracic aorta. Interleukin-1 alpha (IL-1 alpha) greatly increased in a dose-dependent manner the amount of this cytokine produced by the SMC, with tumor necrosis factor-alpha (TNF- alpha) being less effective. Newly formed G-CSF could be detected in culture supernatants within 6 hours after IL-1 alpha or TNF-alpha treatment. Northern blot analysis of SMC stimulated with IL-1 alpha and TNF-alpha showed an increase in the amount of mRNA for G-CSF as compared with control cells. Enhanced G-CSF mRNA levels were observed when SMC were treated with cycloheximide in the absence or presence of added cytokine. In vasculitis, the walls of blood vessels become inflamed as evidenced by a leucocytic infiltrate usually dominated by polymorphonuclear neutrophil leukocytes (PMNs). G-CSF is known to stimulate PMNs, and our findings raise the possibility that G-CSF made by SMC contributes to the development of vasculitis lesions.

Human Arterial Smooth Muscle Cells Synthesize Granulocyte Colony-Stimulating Factor in Response to Interleukin-1α and Tumor Necrosis Factor-α

AbstractVascular smooth muscle cells (SMC) are a major cell type comprising the walls of blood vessels. We report the synthesis of granulocyte colony-stimulating factor (G-CSF) by cultured human SMC obtained from the internal mammary artery and thoracic aorta. Interleukin-1α (IL-1α) greatly increased in a dose-dependent manner the amount of this cytokine produced by the SMC, with tumor necrosis factor-α (TNF-α) being less effective. Newly formed G-CSF could be detected in culture supernatants within 6 hours after IL-1a or TNF-α treatment. Northern blot analysis of SMC stimulated with IL-1a and TNF-α showed an increase in the amount of mRNA for G-CSF as compared with control cells. Enhanced G-CSF mRNA levels were observed when SMC were treated with cycloheximide in the absence or presence of added cytokine. In vasculitis, the walls of blood vessels become inflamed as evidenced by a leucocytic infiltrate usually dominated by polymorphonuclear neutrophil leukocytes (PMNs). G-CSF is known to stimulate PMNs, and our findings raise the possibility that G-CSF made by SMC contributes to the development of vasculitis lesions.

Recombinant human TNF alpha stimulates production of granulocyte colony- stimulating factor

Tumor necrosis factor alpha (TNF alpha) stimulates production of granulocyte colony-stimulating factor (G-CSF) protein and mRNA in fibroblast cells. In contrast, TNF beta is at least 1,000-fold less potent than TNF alpha in increasing levels of G-CSF and GM-CSF activity and mRNA. The fibroblasts produce G-CSF and GM-CSF mRNA in a coordinate fashion after exposure to TNF. The ability of TNF alpha to stimulate production of CSF in fibroblasts may be pivotal to regulation of hematopoiesis.

Recombinant Human TNFαStimulates Production of Granulocyte Colony-Stimulating Factor

Abstract Tumor necrosis factor alpha (TNF alpha) stimulates production of granulocyte colony-stimulating factor (G-CSF) protein and mRNA in fibroblast cells. In contrast, TNF beta is at least 1,000-fold less potent than TNF alpha in increasing levels of G-CSF and GM-CSF activity and mRNA. The fibroblasts produce G-CSF and GM-CSF mRNA in a coordinate fashion after exposure to TNF. The ability of TNF alpha to stimulate production of CSF in fibroblasts may be pivotal to regulation of hematopoiesis.