Granulocyte-colony stimulating factor and lipopolysaccharide regulate the expression of interleukin 8 receptors on polymorphonuclear leukocytes

Interleukin 8 (IL-8) is a potent chemoattractant and activating factor for human polymorphonuclear leukocytes (PMN) and hence plays a critical role in the pathogenesis of acute inflammation. Two unique but homologous receptors for IL-8 have been cloned (IL-8RA and -B), each of which binds the IL-8 ligand with high affinity. PMN stimulated by cytokines or lipopolysaccharide (LPS) exhibit changes in IL-8R mRNA and 125I-IL-8 binding. Granulocyte-colony stimulating factor (G-CSF) treatment of PMN enhances, and LPS inhibits, IL-8R mRNA expression. Similarly, 125I-IL-8 ligand binding to PMN is increased by G-CSF and decreased by LPS treatment. The stimulatory effect of G-CSF on IL-8R expression is transcriptional as it is inhibited by actinomycin D and is evident in nuclear run-on analyses. In contrast, LPS down-regulates IL-8R by both transcriptional and post-transcriptional mechanisms. The alterations in IL-8R expression are associated with similar changes in the IL-8-induced chemotactic responses of PMN. In conclusion, the two types of IL-8 receptor differ in their cellular distribution and are regulated in response to cytokines and LPS. Regulation of IL-8R expression by endogenous and exogenous immunomodulators may be important in the in vivo control of PMN effector functions in inflammation.

Promoter analysis of the human interleukin-8 receptor genes, IL-8RA and IL-8RB

Two distinct receptors for the neutrophil chemoattractant IL-8 have been cloned, designated IL-8RA and -B. Both receptors are abundantly expressed on unstimulated mature neutrophils. To understand the tissue-specific expression and to identify gene-regulatory elements we have cloned, sequenced and characterized both human IL-8R genes, IL-8RA and -B. The open reading frames and 3'-untranslated regions were entirely encoded by a single exon. The promoters of both IL-8R-genes appeared to be very similar: A non-classical TATA-box and a GC-rich 5'-flanking region was identified immediately upstream of the transcription start site. These minimal promoters were sufficient to generate constitutive activity in CAT-expression assays. A G-CSF responsive element was mapped within the first 118 nucleotides upstream of the transcription start site of the IL-8RB gene. Expression analyses of additional upstream regions suggested that both IL-8R-promoters are negatively controlled by silencer elements, which could be counteracted by stimulation with G-CSF.

Genomic structure, characterization, and identification of the promoter of the human IL-8 receptor A gene

Two unique but homologous receptors for the neutrophil chemoattractant, IL-8 have been cloned (designated IL-8RA and IL-8RB), each of which binds IL-8 with high affinity. IL-8RA mRNA expression was found to be regulated by granulocyte-CSF and LPS. In an attempt to understand the tissue-specific expression and to identify transcriptional regulatory elements, we have cloned, sequenced, and characterized the human IL-8RA gene. A lambda-DASH clone encoding the entire human IL-8RA gene was isolated by screening a genomic library with a PCR-generated cDNA. After mapping, subcloning, and sequencing several restriction fragments, a 9.2-kb continuous DNA sequence was obtained. As the sizes of the published cDNA (1.9 kb) and the mRNA determined by Northern blot analysis (2.1 kb) were not in agreement, a full-length cDNA was cloned by using a modified rapid amplification of cDNA ends technique. We identified a 5'-untranslated region of 119 bp. After comparison with the genomic sequence, we found the gene consisted of two exons interrupted by an intron of 1.7 kb. A 1050-bp ORF was encoded entirely in the second exon together with a 834-bp 3'-untranslated region. The immediate GC-rich 5'-flanking region upstream of exon 1 could serve as a constitutively active promoter in chloramphenicol-acetyl-transferase-expression assays. Expression analysis of additional upstream regions suggested the presence of silencer elements between positions -841 and -280. In conclusion, cloning a full-length cDNA permitted us to clone the human IL-8RA gene, identify the genomic structure, and characterize the promoter region.

Genomic structure, characterization, and identification of the promoter of the human IL-8 receptor A gene

Two unique but homologous receptors for the neutrophil chemoattractant, IL-8 have been cloned (designated IL-8RA and IL-8RB), each of which binds IL-8 with high affinity. IL-8RA mRNA expression was found to be regulated by granulocyte-CSF and LPS. In an attempt to understand the tissue-specific expression and to identify transcriptional regulatory elements, we have cloned, sequenced, and characterized the human IL-8RA gene. A lambda-DASH clone encoding the entire human IL-8RA gene was isolated by screening a genomic library with a PCR-generated cDNA. After mapping, subcloning, and sequencing several restriction fragments, a 9.2-kb continuous DNA sequence was obtained. As the sizes of the published cDNA (1.9 kb) and the mRNA determined by Northern blot analysis (2.1 kb) were not in agreement, a full-length cDNA was cloned by using a modified rapid amplification of cDNA ends technique. We identified a 5'-untranslated region of 119 bp. After comparison with the genomic sequence, we found the gene consisted of two exons interrupted by an intron of 1.7 kb. A 1050-bp ORF was encoded entirely in the second exon together with a 834-bp 3'-untranslated region. The immediate GC-rich 5'-flanking region upstream of exon 1 could serve as a constitutively active promoter in chloramphenicol-acetyl-transferase-expression assays. Expression analysis of additional upstream regions suggested the presence of silencer elements between positions -841 and -280. In conclusion, cloning a full-length cDNA permitted us to clone the human IL-8RA gene, identify the genomic structure, and characterize the promoter region.

Structure, genomic organization, and expression of the human interleukin-8 receptor B gene

Two distinct receptors for the chemoattractant interleukin-8 (designated IL-8RA and -B) have been cloned recently. The receptors are expressed almost exclusively on neutrophils and myelomonocytic cell lines. In an attempt to understand the tissue-specific expression and to identify transcriptional regulatory elements we have cloned, sequenced, and characterized the human IL-8RB gene. The gene consists of 3 exons, interrupted by two introns of 3 and 5.4 kilobases (kb). A 1065-base pair open reading frame is encoded entirely in the third exon. A 1.4-kb 3'-untranslated region contains clustered AU-rich elements, similar to those described for genes regulated by altering mRNA stability. The start site of transcription was mapped by a modified rapid amplification of cDNA ends technique and revealed an unexpectedly long 5'-untranslated region of 423 base pairs. A TATA box equivalent was found in the 5'-flanking region 20 nucleotides upstream of the start of the first exon. The promoter was separated from the ATG-initiation codon by 8.75 kb. Comparison of the IL-8RB promoter with the promoter region of the receptor for another chemoattractant ligand, the bacterial peptide f-Met-Leu-Phe, revealed 3 novel but conserved motifs occupying similar positions. The immediate 5'-flanking region was GC-rich with 3 SP-1-like and 2 AP-2 sites identified in close proximity to the transcription start site. This essential promoter region was found to be responsible for constitutive expression, inducible by granulocyte colony-stimulating factor and controlled by silencer elements located further upstream between positions -779 and -118.

Purification and cloning of a novel serine protease, RNK-Tryp-2, from the granules of a rat NK cell leukemia

We have biochemically purified a 27-kDa serine protease (designated RNK-Tryp-2) from the granules of the rat large granular lymphocyte leukemia cell line (RNK-16) which has tryptase activity. Utilizing molecular sieve chromatography and reverse-phase HPLC, we purified RNK-Tryp-2 to homogeneity and sequenced 33 NH2-terminal amino acids. Oligonucleotide primers were used in the PCR to generate a 528-bp cDNA clone encoding a novel serine protease from RNK-16 mRNA. This cDNA clone was used to isolate an 884-bp RNK-Tryp-2 cDNA from an RNK-16 lambda-gt11 library. The open reading frame predicts a mature protein of 233 amino acids which does not have potential sites for N-linked glycosylation. The cDNA encodes a leader peptide of at least 25 amino acids. The characteristic Ile-Ile-Gly-Gly amino acids of the N-terminus, and the His, Asp, and Ser amino acids that form the catalytic triad of serine proteases, are conserved. The amino acid sequence has less than 45% identity with any other member of the serine protease family, indicating that RNK-Tryp-2 is distinct protease. Southern blot analysis suggests the existence of one or more related genes. A single 1.3-kb mRNA transcript was detected by Northern blot analysis of total cellular RNA from the in vivo passaged RNK-16, rat splenocytes, lung and liver nonparenchymal cells, as well as in highly purified rat LGL and T cells. RNK-Tryp-2 is a novel serine protease that is expressed in the granules of large granular lymphocytes.

Purification and cloning of a novel serine protease, RNK-Tryp-2, from the granules of a rat NK cell leukemia

We have biochemically purified a 27-kDa serine protease (designated RNK-Tryp-2) from the granules of the rat large granular lymphocyte leukemia cell line (RNK-16) which has tryptase activity. Utilizing molecular sieve chromatography and reverse-phase HPLC, we purified RNK-Tryp-2 to homogeneity and sequenced 33 NH2-terminal amino acids. Oligonucleotide primers were used in the PCR to generate a 528-bp cDNA clone encoding a novel serine protease from RNK-16 mRNA. This cDNA clone was used to isolate an 884-bp RNK-Tryp-2 cDNA from an RNK-16 lambda-gt11 library. The open reading frame predicts a mature protein of 233 amino acids which does not have potential sites for N-linked glycosylation. The cDNA encodes a leader peptide of at least 25 amino acids. The characteristic Ile-Ile-Gly-Gly amino acids of the N-terminus, and the His, Asp, and Ser amino acids that form the catalytic triad of serine proteases, are conserved. The amino acid sequence has less than 45% identity with any other member of the serine protease family, indicating that RNK-Tryp-2 is distinct protease. Southern blot analysis suggests the existence of one or more related genes. A single 1.3-kb mRNA transcript was detected by Northern blot analysis of total cellular RNA from the in vivo passaged RNK-16, rat splenocytes, lung and liver nonparenchymal cells, as well as in highly purified rat LGL and T cells. RNK-Tryp-2 is a novel serine protease that is expressed in the granules of large granular lymphocytes.

Characterization of a high molecular weight tumor necrosis factor-alpha mRNA in influenza A virus-infected macrophages

Infection by influenza A virus has previously been shown to prime macrophages for a high TNF-alpha production. Influenza A virus induced a TNF-alpha mRNA accumulation that consisted of two types: a regular 1.7 kb and an additional high m.w. 2.4 kb species in murine macrophages, and a high m.w. 3.6 kb species in human monocytes. In this study, we further characterized this virus-induced, novel high m.w. TNF-alpha mRNA. The additional high m.w. TNF-alpha mRNA represented a true polyadenylated mRNA and its induction required exposure to infectious viruses. The regular and the high m.w. TNF-alpha mRNA were both found in the nuclear fraction and the cytoplasm. We excluded that the novel high m.w. TNF-alpha mRNA was an intron-containing precursor TNF-alpha mRNA that could have persisted in virus-infected macrophages. When TNF-alpha exons 1 to 4 and TNF-alpha exons 2 to 4 were amplified by polymerase chain reaction, only regular and no high m.w. bands were detected. By use of specific TNF-alpha intron I and intron III cDNA we could definitely demonstrate the absence of introns in the high m.w. TNF-alpha mRNA. The high m.w. TNF-alpha mRNA was free of TNF-beta and TNF intergenic region elements but contained the 5' and 3' untranslated region of TNF-alpha. Influenza A virus infection also induced a double band of IL-1 beta and IL-6 mRNA. Whether this novel high m.w. TNF-alpha mRNA represents a virus-induced abnormality or a superinduction of an otherwise normal but minor TNF-alpha transcript, and whether this high m.w. TNF-alpha mRNA species codes for a biologically active product, remains to be examined.

Flumazenil as a diagnostic tool in the differential diagnosis of coma in a critically ill patient

The purpose of this report is to describe the use of flumazenil as a diagnostic aid in the differential diagnosis of coma in a patient with an inadvertent overdose of benzodiazepines. We report a patient with suspected septic encephalopathy whose level of consciousness markedly improved following flumazenil administration. Subsequent analysis revealed the presence of benzodiazepines and their metabolites in the blood and urine although the patient had not received benzodiazepines for over two weeks. The critically ill patient with multiorgan failure may have considerable derangement of benzodiazepine metabolism; therefore, if an obtunded patient's level of consciousness improves following flumazenil administration, benzodiazepine intoxication must be considered.

Characterization of a high molecular weight tumor necrosis factor-alpha mRNA in influenza A virus-infected macrophages

Infection by influenza A virus has previously been shown to prime macrophages for a high TNF-alpha production. Influenza A virus induced a TNF-alpha mRNA accumulation that consisted of two types: a regular 1.7 kb and an additional high m.w. 2.4 kb species in murine macrophages, and a high m.w. 3.6 kb species in human monocytes. In this study, we further characterized this virus-induced, novel high m.w. TNF-alpha mRNA. The additional high m.w. TNF-alpha mRNA represented a true polyadenylated mRNA and its induction required exposure to infectious viruses. The regular and the high m.w. TNF-alpha mRNA were both found in the nuclear fraction and the cytoplasm. We excluded that the novel high m.w. TNF-alpha mRNA was an intron-containing precursor TNF-alpha mRNA that could have persisted in virus-infected macrophages. When TNF-alpha exons 1 to 4 and TNF-alpha exons 2 to 4 were amplified by polymerase chain reaction, only regular and no high m.w. bands were detected. By use of specific TNF-alpha intron I and intron III cDNA we could definitely demonstrate the absence of introns in the high m.w. TNF-alpha mRNA. The high m.w. TNF-alpha mRNA was free of TNF-beta and TNF intergenic region elements but contained the 5' and 3' untranslated region of TNF-alpha. Influenza A virus infection also induced a double band of IL-1 beta and IL-6 mRNA. Whether this novel high m.w. TNF-alpha mRNA represents a virus-induced abnormality or a superinduction of an otherwise normal but minor TNF-alpha transcript, and whether this high m.w. TNF-alpha mRNA species codes for a biologically active product, remains to be examined.

Chemokines and serpentines: the molecular biology of chemokine receptors

Chemokines are pro-inflammatory molecules with a diverse array of biological and biochemical functions. These molecules induce the migration of a number of leukocyte subsets including monocytes, neutrophils, and T-cells. The recent cloning of the IL-8, GRO, and MIP-1 alpha chemokine receptors revealed that these glycoproteins belong to the serpentine family of seven transmembrane G-protein-coupled receptors. Other members of this family include the chemotactic receptors for fMLP and C5a, indicating that a common pathway for eliciting the directional migration of leukocytes is probably transduced via G proteins. Ligand binding to chemokine receptors is complex, featured by multiple chemokines binding to a single receptor and multiple receptors binding a specific ligand. Future directions in this field appear to be focused on the cloning of novel receptors and the identification of ligands for orphaned receptors.

The potentiating effect of LPS on tumor necrosis factor-alpha production by influenza A virus-infected macrophages

Infection of murine PU5-1.8 macrophages and human monocytes by influenza A virus was associated with virus replication, release of tumor necrosis factor-alpha (TNF-alpha) and subsequent cell death. In the presence of small and by itself rather inefficient concentrations of lipopolysaccharide (LPS) or free lipid A (1 to 10 ng/ml), TNF-alpha production of virus-infected macrophages was strongly potentiated. LPS-triggered and enhanced TNF-alpha release from virus-infected macrophages was neither due to increased cell survival nor altered virus replication, potentiated TNF-alpha gene transcription, release of intracellularly stored TNF-alpha or shifts in the kinetics of TNF-alpha secretion. Influenza A virus infection alone induced a massive TNF-alpha mRNA accumulation which, however, was only weakly translated into bioactive TNF-alpha protein. When these virus-primed macrophages were exposed to LPS either simultaneously or up to 4 h after infection, an efficient and high translation into TNF-alpha protein occurred. Although the LPS-induced biochemical pathways leading to an augmented TNF-alpha production by virus-infected macrophages still remains unsolved, the findings suggest that the frequently observed serious clinical complications in the course of combined influenza A virus and bacterial infections may be due, at least in part, to an excessive release of cytokines such as TNF-alpha.

Assignment of genes for interleukin-8 receptors (IL8R) A and B to human chromosome band 2q35

The human genes encoding the interleukin 8 receptors type A and B were assigned to chromosome 2 by polymerase chain reaction amplification and by Southern analysis of a panel of human x rodent somatic cell hybrid DNAs. The IL8R genes were further localized by in situ hybridization to band 2q35.

Enhanced release of cytokines, interleukin-2 receptors, and neopterin after long-distance running

This study was designed to examine cytokine production in a group of 22 well-trained runners covering a distance of 20 km within 2 hr. After running, all participants displayed a marked granulocytosis for 7 hr. Plasma neopterin levels increased 1 hr after exercise for 24 hr. Except for interleukin-6 (IL-6), cytokines were not reliably detected in plasma but were present in urine. Already before exercise, cytokines were detected in the urine of runners when compared to sedentary controls. Directly after running, interferon-gamma and tumor necrosis factor-alpha were further elevated but rapidly declined to preexercise levels. Interleukin-1 beta and interleukin-6 increased at a slower rate after exercise but secretion into urine persisted longer until 12 and 7 hr, respectively. Interleukin-2 (IL-2) was not detected but soluble IL-2 receptors appeared in the urine directly after running. Enhanced cytokine levels were accompanied by an only low creatinin kinase increase, indicating little muscle damage. These data show that long-distance running elevates cytokine production which supports the concept that regular, but not excessive, physical exercise may be beneficial by maintaining a stimulated immune system.

Coxsackievirus B3-induced production of tumor necrosis factor-alpha, IL-1 beta, and IL-6 in human monocytes

Infections by coxsackievirus B3 (CVB3) have previously been shown to cause acute and chronic myocarditis characterized by a heavy mononuclear leukocyte infiltration and myocyte necrosis. Because clinical and experimental evidence suggested that cardiac damage may result from immunologic rather than viral mechanisms, we examined in this study the in vitro interaction of CVB3 with human monocytes. CVB3 was capable of infecting freshly harvested monocytes as revealed by immunofluorescence and release of infectious virus particles. Virus infection did not reduce monocyte viability but, on the contrary, enhanced spreading and adherence. In a dose-dependent manner, CVB3 stimulated the release of cytokines from monocytes. Whereas a potent production of TNF-alpha, IL-1 beta, and IL-6 was dependent on exposure to infectious CVB3, IFN release was also induced by UV-inactivated virus. On a molecular level, CVB3 stimulated cytokine gene expression as shown by a marked TNF-alpha, IL-1 beta, and IL-6 mRNA accumulation. Supernatants of CVB3-infected monocytes displayed cytotoxic activity against Girardi heart cells which could be abrogated by an anti-TNF-alpha antiserum. These data suggest that CVB3-induced cytokine release from monocytes may participate in virus-induced organ damage such as myocarditis, which may either occur by a direct cytotoxicity of cytokines or by activation of cytotoxic lymphocytes.

Coxsackievirus B3-induced production of tumor necrosis factor-alpha, IL-1 beta, and IL-6 in human monocytes

Infections by coxsackievirus B3 (CVB3) have previously been shown to cause acute and chronic myocarditis characterized by a heavy mononuclear leukocyte infiltration and myocyte necrosis. Because clinical and experimental evidence suggested that cardiac damage may result from immunologic rather than viral mechanisms, we examined in this study the in vitro interaction of CVB3 with human monocytes. CVB3 was capable of infecting freshly harvested monocytes as revealed by immunofluorescence and release of infectious virus particles. Virus infection did not reduce monocyte viability but, on the contrary, enhanced spreading and adherence. In a dose-dependent manner, CVB3 stimulated the release of cytokines from monocytes. Whereas a potent production of TNF-alpha, IL-1 beta, and IL-6 was dependent on exposure to infectious CVB3, IFN release was also induced by UV-inactivated virus. On a molecular level, CVB3 stimulated cytokine gene expression as shown by a marked TNF-alpha, IL-1 beta, and IL-6 mRNA accumulation. Supernatants of CVB3-infected monocytes displayed cytotoxic activity against Girardi heart cells which could be abrogated by an anti-TNF-alpha antiserum. These data suggest that CVB3-induced cytokine release from monocytes may participate in virus-induced organ damage such as myocarditis, which may either occur by a direct cytotoxicity of cytokines or by activation of cytotoxic lymphocytes.

Influenza A virus infection of macrophages. Enhanced tumor necrosis factor-alpha (TNF-alpha) gene expression and lipopolysaccharide-triggered TNF-alpha release

We have previously shown that infection of macrophages by influenza A virus is capable of priming for a high TNF-alpha production in response to LPS. The present study was designed to examine in more detail TNF-alpha gene expression and TNF-alpha protein release of virus-infected, murine PU5-1.8 macrophages in the presence or absence of low and by itself rather inefficient concentrations of LPS (10 ng/ml). Although influenza A virus infection alone induced a massive TNF-alpha mRNA accumulation, translation into the bioactive TNF-alpha protein was low as intra- and extracellularly determined by bioassay, specific ELISA and Western blot. However, when LPS was added simultaneously or up to 4 h after infection, a high TNF-alpha production was initiated. The virus-induced TNF-alpha mRNA accumulation appeared to be due to both transcriptional and post-transcriptional changes: an enhanced TNF-alpha gene transcription as determined by nuclear run-on transcription assay and a markedly prolonged half-life of TNF-alpha mRNA as shown in actinomycin D-treated macrophages. These findings imply that influenza A virus may 1) either directly or indirectly stimulate TNF-alpha gene transcription activators or may interfere with labile transcription repressor proteins and 2) may stabilize TNF-alpha mRNA by delaying its degradation. Both mechanisms, taken together, prime influenza A virus-infected macrophages for a high TNF-alpha release in response to LPS which, as clinical cases show, may adversely affect patients with combined influenza A virus and bacterial infections.

Influenza A virus infection of macrophages. Enhanced tumor necrosis factor-alpha (TNF-alpha) gene expression and lipopolysaccharide-triggered TNF-alpha release

We have previously shown that infection of macrophages by influenza A virus is capable of priming for a high TNF-alpha production in response to LPS. The present study was designed to examine in more detail TNF-alpha gene expression and TNF-alpha protein release of virus-infected, murine PU5-1.8 macrophages in the presence or absence of low and by itself rather inefficient concentrations of LPS (10 ng/ml). Although influenza A virus infection alone induced a massive TNF-alpha mRNA accumulation, translation into the bioactive TNF-alpha protein was low as intra- and extracellularly determined by bioassay, specific ELISA and Western blot. However, when LPS was added simultaneously or up to 4 h after infection, a high TNF-alpha production was initiated. The virus-induced TNF-alpha mRNA accumulation appeared to be due to both transcriptional and post-transcriptional changes: an enhanced TNF-alpha gene transcription as determined by nuclear run-on transcription assay and a markedly prolonged half-life of TNF-alpha mRNA as shown in actinomycin D-treated macrophages. These findings imply that influenza A virus may 1) either directly or indirectly stimulate TNF-alpha gene transcription activators or may interfere with labile transcription repressor proteins and 2) may stabilize TNF-alpha mRNA by delaying its degradation. Both mechanisms, taken together, prime influenza A virus-infected macrophages for a high TNF-alpha release in response to LPS which, as clinical cases show, may adversely affect patients with combined influenza A virus and bacterial infections.

The lack of receptors for atrial natriuretic peptides on human monocytes prevents a rise of cGMP and induction of tumor necrosis factor-alpha synthesis

Freshly harvested human monocytes were shown to produce tumor necrosis factor-alpha (TNF-alpha) in response to exogenously added or sodium nitroprusside-generated cGMP. In contrast, atrial natriuretic peptide (ANP) that acts by elevating cGMP in a variety of cells, was incapable of inducing TNF-alpha synthesis. This failure was due to a lack of ANP receptors and thus, to the inability of ANP to raise cGMP in human monocytes.

Influenza A virus infects macrophages and stimulates release of tumor necrosis factor-alpha

The clinical picture of influenza A virus infections indicates that release of tumor necrosis factor-alpha (TNF-alpha) may be involved. In the present study we exposed the murine macrophage line PU5-1.8 to influenza A virus and observed a productive infection which was followed by subsequent cell death. Infection of macrophages was accompanied by TNF-alpha mRNA accumulation and TNF-alpha release. TNF-alpha production could only be induced by live virus whereas interferon release was also stimulated by inactivated virus. When virus-infected macrophages were exposed to low amounts of lipopolysaccharide (LPS; 1-10 ng/ml) TNF-alpha production was strongly potentiated. These data show that low LPS concentrations could readily trigger a high TNF-alpha release from influenza-A-virus-infected macrophages which could, at least partially, explain the serious complications of combined influenza A virus and bacterial infections.

Enhancement of tumor necrosis factor-alpha gene expression by low doses of prostaglandin E2 and cyclic GMP

Macrophage-derived PGE2 is usually considered to be a down-regulator of TNF-alpha production. However, we recently demonstrated that PGE2 may display dual activities in that low concentrations stimulated whereas higher doses suppressed TNF-alpha synthesis in resident peritoneal macrophages. To examine the underlying molecular mechanisms, we studied TNF-alpha gene expression in rat peritoneal macrophages and the murine PU5-1.8 macrophage line. In both macrophage types, PGE2 enhanced TNF-alpha gene transcription and production at an optimal concentration of 1 ng/ml. Furthermore, evidence was obtained that PGE2 may stimulate TNF-alpha mRNA accumulation via a rise of the intracellular messenger cGMP. Both, exogenously added as well as endogenously, by sodium nitroprusside generated cGMP were found to enhance TNF-alpha gene expression and production. These findings lend further support to the concept that cGMP may represent one of the positive signals for TNF-alpha synthesis.