Interleukin 8 (IL-8) selectively inhibits immunoglobulin E production induced by IL-4 in human B cells.

The effect of interleukin 8 (IL-8) on IL-4-induced immunoglobulin E (IgE) production was studied. IL-4 induced IgE and IgG4 production by tonsillar mononuclear cells (MNC) without affecting IgM, IgG1, IgA, IgG2, or IgG3 production. IL-8 inhibited IL-4-induced IgE and IgG4 production, whereas it had no effect on IgM, IgG1, IgA, IgG2, and IgG3 production. The inhibitory effect by IL-8 was specific, since it was blocked by anti-IL-8 mAb, but not by control IgG1. Although interferon gamma (IFN-gamma) also inhibited IgE and IgG4 production by MNC stimulated with IL-4, the inhibitory effect of IL-8 was not mediated by IFN-gamma, since the IL-8-induced inhibition could not be blocked by anti-IFN-gamma. Furthermore, anti-IL-8 mAb had no effect on IFN-gamma-induced inhibition. Moreover, addition of IL-5 or IL-6 did not reverse IL-8-induced inhibition of IgE production. In contrast to these observations with MNC, IL-4 failed to induce IgE and IgG4 production by purified B cells. However, combined treatment of purified B cells cells with IL-4 and anti-CD40 antibody resulted in IgE but not IgG4 production. IL-8 inhibited this IgE production without affecting IgM, IgG1, IgG2, IgG3, IgG4, or IgA production, whereas IFN-gamma, IFN-alpha, or prostaglandin E2 (PGE2) failed to do so. These results indicate that IL-8 antagonizes IL-4-induced IgE production by directly affecting B cells through a specific mechanism that is different from IFN-gamma, IFN-alpha, or PGE2.

The neutrophil-activating peptide NAF/NAP-1 induces histamine and leukotriene release by interleukin 3-primed basophils.

IgE-independent mediator release from basophils is considered an important event in inflammation, particularly in nonallergic immediate hypersensitivity and in allergic late-phase reactions. This study demonstrates that after exposure to IL-3, basophils release histamine and leukotrienes in response to the neutrophil-activating peptide NAF/NAP-1. Thus, the sequential action of two pure cytokines can promote basophils mediator release. In the presence of IL-3, NAF/NAP-1 functions like a "histamine-releasing factor" and may therefore not only induce cellular infiltration but also provoke symptoms of hypersensitivity reactions.

RANTES and macrophage inflammatory protein 1 alpha selectively enhance immunoglobulin (IgE) and IgG4 production by human B cells.

We studied the effects of various chemokines including neutrophil-activating peptide 2 (NAP-2), beta-thromboglobulin (beta-TG), platelet factor 4 (PF-4), melanoma growth stimulating activity (GRO), gamma interferon-induced protein (IP-10), regulated on activation, normal T expressed and secreted (RANTES), macrophage inflammatory protein 1 alpha (MIP-1 alpha), MIP-1 beta, and monocyte chemotactic protein 1 (MCP-1) on Immunoglobulin (IgE) and IgG4 production by human B cells. None of these chemokines with or without interleukin (IL-4), anti-CD40 or -CD58 monoclonal antibody (mAb), induced IgE and IgG4 production by B cells from nonatopic donors. However, RANTES and MIP-1 alpha selectively enhanced IgE and IgG4 production induced by IL-4 plus anti-CD40 or -CD58 mAb without affecting production of IgM, IgG1, IgG2, IgG3, IgA1, or IgA2, whereas other chemokines failed to do so. Enhancement of IgE and IgG4 production by RANTES and MIP-1 alpha was specifically blocked by anti-RANTES mAb and anti-MIP-1 alpha antibody (Ab), respectively, whereas anti-IL-5 mAb, anti-IL-6 mAb, anti-IL-10 Ab, anti-IL-13 Ab, and anti-tumor necrosis factor-alpha mAb failed to do so. Purified surface IgE positive (slgE4) and slgG4+ B cells generated either in vitro or in vivo spontaneously produced IgE and IgG4, respectively, whereas sIgE- and sIgG4- B cells failed to do so. RANTES and MIP-1 alpha enhanced spontaneous IgE and IgG4 production in slgE+ and slgG4- B cells, respectively, whereas neither RANTES nor MIP-1 alpha did so in sIgE- or sIgG4- B cells. Purified sIgE4+ and sIgG4+, but not sIgE- or sIgG4- B cells, generated in vitro and in vivo expressed receptors for RANTES and MIP-1 alpha, whereas they failed to express receptors for other chemokines. These findings indicate that RANTES and MIP-1 alpha enhance IgE and IgG4 production by directly stimulating sIgE+ and sIgG4+ B cells.

Activated human T lymphocytes express MHC class I heavy chains not associated with beta 2-microglobulin.

We present here the molecular characterization of a new activation-induced surface structure on human T lymphocytes, termed LA45, with high homology (93% at protein level) to MHC class I molecules. Antigen modulation and sequential immunoprecipitation experiments revealed that LA45 and HLA class I proteins do not crossreact with the corresponding antibodies. Furthermore, LA45 is not associated with beta 2-m. On the other hand, we could show that the separation of HLA-A,B,C and beta 2m molecules, induced by SDS-denaturation, leads to a conformational change in the heavy chain in such a way that it becomes reactive with LA45. The 90/45 kD LA45 proteins thus appear to be non-beta 2m-associated MHC class I alpha chains that are selectively expressed by activated but not by resting human T lymphocytes.

Improved survival of lethally irradiated recipient mice transplanted with circulating progenitor cells mobilized by IL-8 after pretreatment with stem cell factor.

We have demonstrated previously that a single bolus-injection of interleukin (IL)-8 induces instant mobilization of hematopoietic progenitor cells (HPC) in mice and primates. To further improve the mobilization of HPC, we treated mice with hematopoietic growth factors (HGF) before IL-8-administration. The mobilized HPC were transplanted into lethally irradiated recipient mice to study the effects on survival. Male donor mice (age 8-12 weeks, weight 20-25 grams) were pretreated intraperitoneally (ip) with a fixed dose of 2.5 micrograms of either granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-3, stem cell factor (SCF), or saline administered twice daily for 2 to 4 days. Then a fixed dose of 30 micrograms of IL-8 was administered ip at various time intervals before harvesting blood, bone marrow, and spleen. Cell counts and numbers of colony-forming units granulocyte/macrophage (CFU-GM) of these organs were assessed. Donor mice pretreated with HGF for 2 days and subsequently injected with IL-8 showed an increase in the numbers of circulating CFU-GM per mL blood from 168 +/- 98 to 402 +/- 201 (mean +/- SD, CFU-GM/mL blood) when GM-CSF was used, 314 +/- 133 to 2502 +/- 513 with G-CSF, and 27 +/- 15 to 524 +/- 339 with SCF compared with saline-pretreated controls (28 +/- 17 to 462 +/- 335 CFU-GM/mL blood, mean +/- SD; n = 42 and 40 per interval). Donor-mice pretreated for 4 days with IL-3 or GM-CSF showed an increase in the numbers of circulating HPC from 62 +/- 52 to 368 +/- 118 and 859 +/- 387 to 1034 +/- 421, respectively (CFU-GM/mL, mean +/- SD, n = 4 per group). Lethally irradiated (8.5 Gy) female Balb/c mice were then injected with decreasing numbers of peripheral blood mononuclear cells (PBMNC). Transplantation of 1.5 x 10(5) MNC obtained from donors pretreated with SCF for 2 days prior to IL-8 mobilization resulted in a significantly enhanced survival of 100% of the recipients, whereas recipients of PBM-NCs derived from donors treated with SCF only or IL-8 as a single injection had a survival rate at day 60 of only 50% and 60% respectively. When equal numbers of IL-8 mobilized MNCs from G-CSF, GM-CSF, or IL-3 pretreated donors were transplanted into lethally irradiated recipients, no such survival-advantage was observed. We conclude that pretreatment with SCF for 2 days improves the mobilizing effect induced by IL-8 and that transplantation of these cells enhances survival of lethally irradiated recipients.

Interleukin-8 stimulates calcium transients and promotes epidermal cell proliferation.

The presence of large amounts of biologically active interleukin-8 (IL-8) in psoriatic involved skin suggests that it may contribute, in part, to the changes observed in psoriasis, including hyperproliferation of keratinocytes. To examine the effect of IL-8 on epidermal growth, we monitored cytosolic free Ca++ transients in human keratinocytes adult skin epidermis calcium reduced level, temperature elevated (HaCat) cells and normal keratinocytes loaded with the cell permeable, acetoxymethyl derivative, indo-1AM. Addition of IL-8 (0.06-47 nM) to the HaCat cells induced rapid rises in cytosolic free Ca++ from resting levels of 145 +/- 38 to peak levels of 889 +/- 10 nM. The induced rises in Ca++ were transient and concentration dependent. Half maximal effect was observed at 1.2 nM. Normal keratinocytes also responded to IL-8 (6 nM) by rises in cytosolic free Ca++ from a pre-stimulated level of 269 nM to transient peak value of 393 nM. In addition, IL-8 promoted epidermal cell proliferation. Polyclonal anti-IL-8 antibody blocked IL-8-induced calcium changes and proliferation. Under similar conditions, human neutrophils also responded to IL-8 in a similar dose range by a rapid and transient mobilization of Ca++. The findings indicate that IL-8 has a wider range of responsive target cells than hitherto thought and acts as an autocrine growth factor.

Human macrophage inflammatory protein-3alpha/CCL20/LARC/Exodus/SCYA20 is transcriptionally upregulated by tumor necrosis factor-alpha via a non-standard NF-kappaB site.

The 5'-flanking sequences of the human macrophage inflammatory protein-3alpha/CCL20 gene were cloned and transfected into G-361 human melanoma cells in a luciferase reporter construct. Tumor necrosis factor-alpha (TNF-alpha) treatment stimulated luciferase expression, and promoter truncations demonstrated that TNF-alpha inducibility is conferred by a region between nt -111 and -77, which contains a non-standard nuclear factor-kappaB (NF-kappaB) binding site. The requirement for NF-kappaB was demonstrated as follows: (i) mutations in this NF-kappaB site abrogated TNF-alpha responsiveness; (ii) TNF-alpha activated a construct containing two copies of the CCL20 NF-kappaB binding site; (iii) overexpression of NF-kappaB p65 activated the CCL20 promoter; (iv) NF-kappaB from nuclear extracts of TNF-alpha-stimulated cells bound specifically to this NF-kappaB site.

1Alpha,25-dihydroxyvitamin D3 decreases DNA binding of nuclear factor-kappaB in human fibroblasts.

1Alpha,25-dihydroxyvitamin D3 (1,25-(OH)2-D3), the active metabolite of vitamin D, can inhibit NF-kappaB activity in human MRC-5 fibroblasts, targeting DNA binding of NF-kappaB but not translocation of its subunits p50 and p65. The partial inhibition of NF-kappaB DNA binding by 1,25-(OH)2-D3 is dependent on de novo protein synthesis, suggesting that 1,25-(OH)2-D3 may regulate expression of cellular factors which contribute to reduced DNA binding of NF-kappaB. Although NF-kappaB binding is decreased by 1,25-(OH)2-D3 in MRC-5 cells, IL-8 and IL-6 mRNA levels are only moderately downregulated, demonstrating that inhibition of NF-kappaB DNA binding alone is not sufficient for optimal downregulation of these genes.

Crystallization and preliminary X-ray crystallographic study of interleukin-8.

Interleukin-8 (neutrophil-activating factor; NAP-1) has been crystallized by the vapour diffusion technique to give single crystals suitable for three-dimensional structural study at a resolution higher than 2.4 A. The crystals belong to the space group P3(1)21 or P3(2)21 and have unit cell dimensions a = b = 40.9 A, c = 90.3 A.

The structure of procalcitonin of the salmon as deduced from its cDNA sequence.

Oligonucleotide probes based on the known amino acid sequence of salmon calcitonin were used to screen a cDNA library obtained from ultimobranchial glands of salmon for clones encoding salmon calcitonin. From the cDNA sequence of strongly hybridizing clones the complete primary structure of the calcitonin precursor could be deduced. Its overall structure is identical with the structures of procalcitonins from other vertebrates and has the highest homology with the chicken precursor.

Intensity-independent fluorometric detection of cellular nitric oxide release.

A new fluorescence method is introduced in which nitric oxide (NO)-derived higher-order oxygen complexes (NO(x)) are quantified at physiological pH. Detecting the fluorescence lifetime shift between 2,3-diaminonaphthalene and the NO(x)-derived protonated 2,3-naphthotriazole allows an intensity independent determination of the NO(x) concentration. The NO release from LPS and IFNgamma-stimulated murine macrophages and iNOS transfected hamster cells was quantified. The lower detection limit for NO2- was found to be 800 pmol/ml. Since the influence of static fluorescence quenching due to cellular components can be neglected, the method is applicable for clear cellular supernatants as well as turbid cellular suspensions.

Purification, crystallization and preliminary X-ray diffraction analysis of recombinant human neutrophil-activating peptide 2 (rhNAP-2).

The potent activator and chemoattractant for human neutrophils, neutrophil-activating peptide 2 (NAP-2), has been cloned and expressed in Escherichia coli. The protein has been purified to homogeneity (> 98%) by a series of chromatographic techniques, including reversed phase HPLC. The biological activity of recombinant human NAP-2 (rhNAP-2), characterized by the induction of elastase release from human neutrophils, was found to be comparable to natural NAP-2. rhNAP-2 has been crystallized by the hanging drop vapor diffusion method. The crystals belong to space group P222 with unit cell dimensions of a = 30.8 A, b = 39.5 A and c = 95.3 A. A packing density of 3.8 A3/Da with a solvent content of approximately 68% is obtained when one molecule per asymmetric unit is assumed. The crystals were shown to diffract to beyond 2.0 A on a conventional X-ray source. They are stable to X-rays for several days and are thus suitable for high resolution structure determination.

Up-regulation of interleukin-1beta-stimulated interleukin-8 in human keratinocytes by nitric oxide.

Nitric oxide (NO) is able to regulate the expression of a number of inflammatory mediators. In this study, the effect of NO on the expression of the chemokine interleukin-8 (IL-8) by primary human keratinocytes and the lines KB and HaCaT was examined. Incubation with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) for 24 hr increased IL-8 protein only in HaCaT cells, partly due to the presence of constitutive interleukin-1 (IL-1). However, in combination with IL-1beta, SNAP enhanced both IL-8 mRNA and protein in all three cell types. Transfection of cells with an IL-8 promoter reporter gene construct showed that the effect of NO was at least partly due to transcriptional activation. Despite small variations in the response to NO by the three cell types, these results demonstrate that NO can up-regulate IL-1beta-stimulated IL-8 expression in human keratinocytes. This study provides a regulatory mechanism which may be important in the context of skin inflammation, and supports the role of NO as an inflammatory mediator in the skin.

CagA/cytotoxic strains of Helicobacter pylori and interleukin-8 in gastric epithelial cell lines.

AIMS: To investigate: (1) whether Helicobacter pylori directly induces interleukin-8 (IL-8) message expression and protein secretion in established gastric epithelial cell lines; and (2) if CagA/cytotoxin positive and negative strains of H pylori differ in their ability to induce epithelial IL-8. METHODS: Gastric epithelial cell lines were co-cultured with H pylori NCTC 11637 and 10 clinical isolates (four cytotoxic, six non-cytotoxic) and secreted IL-8 was measured by enzyme linked immunosorbent assay (ELISA). Specific induction of gastric epithelial IL-8 mRNA was examined by reverse transcription and polymerase chain reaction (RT-PCR) amplification. RESULTS: H pylori (NCTC 11637) induced IL-8 secretion from three gastric epithelial cell lines (KATO-3, ST42, AGS) but not from MKN 45 (gastric) or intestinal (SW480, HT29) cell lines. H mustelae did not stimulate IL-8 secretion from KATO-3, ST42, and AGS cells. H pylori induced IL-8 secretion was reduced by heat killing, sonication, freeze thawing or formalin fixation of the bacteria. CagA/cytotoxin positive strains of H pylori induced significantly higher IL-8 secretion than CagA/cytotoxin negative strains in the three positive gastric epithelial cell lines (KATO-3, ST42: p < 0.01; AGS: p < 0.02). A significant increase (p < 0.01) in the expression of IL-8 mRNA relative to G3PDH mRNA was observed in KATO-3 cells after three hours of co-culture with CagA/cytotoxin positive strains. CONCLUSIONS: H pylori directly increases gastric epithelial IL-8 mRNA expression and IL-8 protein secretion in a strain specific manner. Induction of epithelial IL-8 by CagA/cytotoxin positive strains is likely to result in neutrophil chemotaxis and activation and thus mucosal damage. These observations on epithelial IL-8 may explain the association between CagA/cytotoxin positive strains and gastroduodenal disease.

Induction of interleukin-8 secretion from gastric epithelial cells by a cagA negative isogenic mutant of Helicobacter pylori.

The ability of Helicobacter pylori strains to induce interleukin-8 (IL-8) gene expression and protein secretion from gastric epithelial cell lines in vitro is variable. This cellular response is associated with bacterial expression of the CagA protein present in type I H pylori strains. To determine the role of CagA in this host cell response, an isogenic cagA negative mutant, N6.XA3, was constructed. The cagA negative isogenic mutant and the wild-type parental cagA positive strain, N6, were cocultured with AGS, ST-42 and KATO-3 gastric epithelial cell lines and secreted interleukin-8 assayed by enzyme linked immunosorbent assay. In all three cell lines there was no significant difference in the IL-8 secretion induced by the cagA negative isogenic mutant, N6.XA3, and the wild-type parent strain, N6. These studies show that CagA is not the inducer of IL-8 secretion from gastric epithelial cells. As all wild-type CagA positive strains studied to date induce IL-8, the bacterial factor(s) inducing this inflammatory response is closely associated with the expression of CagA.

Modulation of Helicobacter pylori induced interleukin-8 synthesis in gastric epithelial cells mediated by cag PAI encoded VirD4 homologue.

BACKGROUND: Strains of Helicobacter pylori carrying the virulence associated cag pathogenicity island (PAI) induce gastric epithelial synthesis of the chemokine interleukin-8 (IL-8), a neutrophil chemoattractant, and thereby a strong inflammatory response during chronic infection of the human gastric mucosa. Previous mutational analyses have shown that many genes in the cag PAI are needed to elicit IL-8 synthesis in gastric epithelial cells, and also that some genes are not involved. AIM: To test the possibility that certain genes in the cag PAI also downregulate (modulate) the inflammatory response elicited by cag+ H pylori infection. METHODS: Cells of L5F11, a derivative of the Kato-3 gastric epithelial cell line that carries an engineered IL-8 promoter-luciferase reporter gene fusion, were cocultured with H pylori strain 26695 or with an isogenic mutant in which most of the cag PAI ORF 10 gene, an Agrobacterium virD4 homologue, was deleted. Luciferase activity was measured to assess IL-8 gene transcription and secreted IL-8 was measured by enzyme linked immunosorbent assay to assess synthesis and release of IL-8 protein from gastric epithelial cells. RESULTS: Inactivation of ORF10 led to a 2.8-fold increase in IL-8 gene transcription and a 3.6-fold increase in IL-8 synthesis and secretion. CONCLUSIONS: The results suggest that this VirD4 homologue participates in the control of inflammation that H pylori infection elicits by downregulating (modulating) the strong induction of IL-8 synthesis mediated by other cag encoded proteins.

Interleukin-8 expression in Helicobacter pylori infected, normal, and neoplastic gastroduodenal mucosa.

AIMS: To investigate the expression of interleukin-8 (IL-8) in Helicobacter pylori infected normal and neoplastic gastroduodenal mucosa, and in established gastric cancer cell lines. METHODS: Immunofluorescence techniques were used to localise IL-8 in cryosections of gastric (n = 25) and duodenal (n = 17) endoscopic biopsy specimens an in resected gastric tumour tissue samples from 16 patients. Two gastric cancer cell lines (Kato 3 and MKN 45) were examined for IL-8 protein expression by immunofluorescence and for the presence of IL-8 mRNA by reverse transcription followed by the polymerase chain reaction (RT-PCR). RESULTS: IL-8 was localised to the epithelium in histologically normal gastric mucosa, with particularly strong expression in the surface cells. IL-8 expression was also a feature of surface epithelium in the duodenal bulb, but was much reduced in the second part of the duodenum. In chronic H pylori-associated gastritis gastritis gastric epithelial IL-8 expression was increased and expression of IL-8 within the lamina propria was evident. By contrast, large areas of IL-8 negative epithelium were observed in the body mucosa of a subject with Ménétrier's disease. In gastric carcinoma the tumour cells were positive for IL-8. IL-8 was also detected by immunofluorescence in unstimulated Kato 3 and MKN 45 cells, and constitutive IL-8 gene expression in these cell lines was confirmed by detection of IL-8 mRNA by RT-PCR. CONCLUSIONS: Immunoreactive IL-8, a potent neutrophil chemotactic and activating factor, is present in the epithelium of both normal and inflamed gastric mucosa with increased expression in the latter. There is site dependent variation in epithelial IL-8 expression within the gastroduodenal mucosa. The expression of the pro-inflammatory cytokine IL-8 in gastric carcinoma cells may influence peritumoural cellular infiltrates.

Helicobacter pylori induced interleukin-8 expression in gastric epithelial cells is associated with CagA positive phenotype.

AIMS: To use a range of natural phenotypically variant strains of Helicobacter pylori with disparate CagA and VacA (vacuolating cytotoxin) expression to determine which bacterial factors are more closely associated with epithelial interleukin-8 (IL-8) induction. METHODS: Gastric epithelial cells (AGS and KATO-3) were co-cultured with five H pylori strains which were variously shown to express the cagA gene/CagA protein, VacA and/or to exhibit biological cytotoxicity. Secreted IL-8 was assayed by enzyme leaked immunosorbent assay (ELISA) and IL-8 messenger RNA (mRNA) was assayed using a reverse transcription polymerase chain reaction based technique (RT-PCR). RESULTS: Strains expressing CagA, including a variant strain (D931) which is non-cytotoxic and does not express the VacA protein, were found to upregulate epithelial IL-8 secretion and gene expression. In contrast, strains with no CagA expression, even in the presence of VacA and/or biological cytotoxicity, (G104, BA142), failed to induce IL-8 protein or mRNA above control values. CONCLUSIONS: These results strongly support a role for H pylori CagA or coexpressed factors other than the cytotoxin in upregulation of gastric epithelial IL-8. Increased epithelial IL-8 secretion and concomitant neutrophil chemotaxis and activation in addition to direct cytotoxicity may be an important factor in tissue damage and ulceration.

Priming of normal human neutrophils by tachykinins: tuftsin-like inhibition of in vitro chemotaxis stimulated by formylpeptide or interleukin-8.

Tachykinins have priming effects on polymorphonuclear neutrophils, since they may activate the neutrophils to exhibit an exaggerated inflammatory response to phlogistic mediators. In order to investigate mechanisms involved in this action, we determined the influence of substance P and neurokinin A on chemotaxis of human neutrophils towards gradients of formymethionyl-leucyl-phenylalanine or recombinant human interleukin-8. As seen with other neutrophil-priming agents such as tumor necrosis factor-alpha, exposure of neutrophils to substance P or neurokinin A had an inhibitory effect upon a stimulated migration, with effective concentrations being in the nanomolar range. Tuftsin, a known neutrophil activating peptide, similarly inhibited stimulated migration. Analysis of structure-activity relationships revealed that activity of tachykinins is located in amino-terminal, tuftsin-like sequences. The inhibition of stimulated migration was partly reversed by (Pro1)-tuftsin, a partial tuftsin receptor antagonist, which suggests that the effects of amino-terminal tachykinins involves activation of tuftsin receptors of neutrophils.

Interleukin-8 down-regulates the oxidative burst induced by tumor necrosis factor alpha in neutrophils adherent to fibronectin.

Human neutrophils (5 x 10(4) incubated on fibronectin precoated wells released 2.83 +/- .25 nmoles of superoxide (0(2)-) (x +/- 1 SEM, n = 15) in response to 5.9 nM (100 ng/ml) Tumor Necrosis Factor Alpha (TNF). On the contrary, the 0(2)- production induced by interleukin-8 (IL-8) (doses ranging from 0.1 nM to 1 microM) was comparable to that of "resting" cells (< .6 nmoles/5 x 10(4) cells). IL-8 (100 nM) did not affect the TNF-dependent 0(2)- production when added with TNF at the beginning of the assay, but reduced it by approximately 80% when added with TNF on neutrophils previously incubated for 1 hour on fibronectin. As compared with IL-8, N-formyl-methionyl-leucyl-phenylalanine (FMLP, 100 nM) failed to suppress the TNF-triggering of the oxidative burst in neutrophils plated on fibronectin. The data suggest that the interaction of neutrophils with fibronectin uncovers the capacity of IL-8 to limit the cell response to TNF, without affecting the response to the combination of FMLP and TNF. Thus, although the chemotactic factors IL-8 and FMLP share the capacity of triggering the oxidative burst of neutrophils incubated in suspension, only IL-8 has the potential to down-regulate the responsiveness of fibronectin-adherent cells to TNF.