MicroRNA-126 inhibits invasion in non-small cell lung carcinoma cell lines.

Crk is a member of a family of adaptor proteins that are involved in intracellular signal pathways altering cell adhesion, proliferation, and migration. Increased expression of Crk has been described in lung cancer and associated with increased tumor invasiveness. MicroRNAs (miRNAs) are a family of small non-coding RNAs (approximately 21-25 nt long) that are capable of targeting genes for either degradation of mRNA or inhibition of translation. Crk is a predicted putative target gene for miR-126. Over-expression of miR126 in a lung cancer cell line resulted in a decrease in Crk protein without any alteration in the associated mRNA. These lung cancer cells exhibit a decrease in adhesion, migration, and invasion. Decreased cancer cell invasion was also evident following targeted knockdown of Crk. MiR-126 alters lung cancer cell phenotype by inhibiting adhesion, migration, and invasion and the effects on invasion may be partially mediated through Crk regulation.

Antineutrophil cytoplasmic antibodies induce monocyte IL-8 release. Role of surface proteinase-3, alpha1-antitrypsin, and Fcgamma receptors.

Cytoplasmic antineutrophil cytoplasmic antibodies (cANCA) that accompany the neutrophilic vasculitis seen in Wegener's granulomatosis (WG), are directed against proteinase-3 (PR-3), a serine proteinase which is located in azurophilic granules of neutrophils and monocytes. PR-3, when expressed on the surface of TNFalpha-primed neutrophils, can directly activate neutrophils by complexing cANCA and promoting concomitant Fcgamma receptor (FcgammaR) cross-linking. Although the neutrophil's pathogenic role in WG has been studied, the role of the monocyte has not been explored. The monocyte, with its ability to release cytokines and regulate neutrophil influx, also expresses PR-3. Therefore, the monocyte may play a significant role in WG via the interaction of surface PR-3 with cANCA, inducing cytokine release by the monocyte. To test this hypothesis, monocytes were studied for PR-3 expression and for IL-8 release in response to cANCA IgG. PBMC obtained from healthy donors displayed dramatic surface PR-3 expression as detected by immunohistochemistry and flow cytometry in response to 0. 5-h pulse with TNFalpha (2 ng/ml). Purified monoclonal anti-PR-3 IgG added to TNFalpha-primed PBMC induced 45-fold more IL-8 release than an isotype control antibody. Furthermore, alpha 1-antitrypsin (alpha1-AT), the primary PR-3 antiprotease, inhibited the anti-PR-3 induced IL-8 release by 80%. Importantly, Fab and F(ab')2 fragments of anti-PR-3 IgG, which do not result in Fcgamma receptor cross-linking, do not induce IL-8 release. As a correlate, IgG isolated from cANCA positive patients with WG induced six times as much PBMC IL-8 release as compared to IgG isolated from normal healthy volunteers. Consistent with PR-3 associated IL-8 induction, alpha1-AT significantly inhibited this effect. These observations suggest that cANCA may recruit and target neutrophils through promoting monocyte IL-8 release. This induction is mediated via Fcgamma receptor cross-linking and is regulated in part by alpha1-AT.

Lymphocytes induce monocyte chemoattractant protein-1 production by renal cells after Fc gamma receptor cross-linking: role of IL-1beta.

Leukocyte recruitment to the kidney in immune complex disease like systemic lupus erythematosus (SLE) is mediated in part by local expression of chemokines such as monocyte chemoattractant protein-1 (MCP-1). Recent studies from this laboratory demonstrated that cross-linking Fc gammaR on lymphocytes causes release of a soluble factor that induces monocyte chemokine production. To explain the induction of renal chemokine expression in immune complex disease, we postulated that this lymphocyte factor stimulates renal parenchymal cell MCP-1 expression. To test this hypothesis, human peripheral blood lymphocytes were incubated on immobilized IgG, a model for immune complex Fc gammaR cross-linking. Supernatants from these lymphocyte cultures significantly increased MCP-1 production by human mesangial, glomerular capillary endothelial, and proximal tubular epithelial cells. Mesangial cells incubated on immobilized IgG or with soluble, preformed immune complexes did not secrete MCP-1 above control levels. Lymphocyte supernatant-induced MCP-1 production appeared to be dependent on the presence of interleukin (IL)-1beta in the supernatant. Removing IL-1beta from the supernatants, antagonizing its activity, or preventing conversion to mature IL-1beta abrogated renal cell MCP-1 expression by the lymphocyte supernatants. These data demonstrate that in response to cross-linking Fc gammaR, lymphocytes induce renal cell MCP-1 expression by secreting IL-1beta. Renal chemokine expression in immune complex disease may thus be triggered as lymphocytes traffic through the kidney and encounter deposited immune complexes.

The pathogenesis of sepsis. Factors that modulate the response to gram-negative bacterial infection.

Gram-negative bacteria gain access to the bloodstream by evading host defenses. Once in circulation, lipopolysaccharide interacts with the host receptor CD14 and initiates the host's immune response. Lipolysaccharide stimulates the host to produce a cascade of mediators that activate and target leukocytes, opsonize the bacteria, and induce fever to defend against the invading bacteria. Unregulated release of these mediators, however, leads to the production of vasoactive substances, activation of the clotting cascade, and diminution of cardiac performance, which leads to the sepsis syndrome. This article discusses the pathogenic events that lead to sepsis syndrome and reviews critical steps in regulating these inflammatory mediators to allow the host to recover from gram-negative bacteremia.

Measurement of outcomes in adults receiving pharmaceutical care in a comprehensive asthma outpatient clinic.

We hypothesized that a pharmacist-provided comprehensive education program in conjunction with care provided by a pulmonologist would lead to improved economic, clinical, and humanistic outcomes in adults with asthma, compared with similar patients receiving care from a pulmonologist alone. The experimental group reported receiving more information about asthma self-management (p=0.001), were more likely to monitor peak flow readings (p=0.004), and had increased satisfaction with care, and perceived higher quality of care. Both groups had less lost productivity, fewer emergency department visits, fewer hospitalizations, and fewer physician visits, as well as improvement in symptoms scores within 45 days. Both groups improved in all functional status domains except the mental component score of the SF-12. Our results show a positive impact on outcomes in adults with asthma who received pharmaceutical care.

A database de-identification framework to enable direct queries on medical data for secondary use.

OBJECTIVE: To qualify the use of patient clinical records as non-human-subject for research purpose, electronic medical record data must be de-identified so there is minimum risk to protected health information exposure. This study demonstrated a robust framework for structured data de-identification that can be applied to any relational data source that needs to be de-identified. METHODS: Using a real world clinical data warehouse, a pilot implementation of limited subject areas were used to demonstrate and evaluate this new de-identification process. Query results and performances are compared between source and target system to validate data accuracy and usability. RESULTS: The combination of hashing, pseudonyms, and session dependent randomizer provides a rigorous de-identification framework to guard against 1) source identifier exposure; 2) internal data analyst manually linking to source identifiers; and 3) identifier cross-link among different researchers or multiple query sessions by the same researcher. In addition, a query rejection option is provided to refuse queries resulting in less than preset numbers of subjects and total records to prevent users from accidental subject identification due to low volume of data. This framework does not prevent subject re-identification based on prior knowledge and sequence of events. Also, it does not deal with medical free text de-identification, although text de-identification using natural language processing can be included due its modular design. CONCLUSION: We demonstrated a framework resulting in HIPAA Compliant databases that can be directly queried by researchers. This technique can be augmented to facilitate inter-institutional research data sharing through existing middleware such as caGrid.

Reprogramming of the tumour microenvironment by stromal PTEN-regulated miR-320.

PTEN (Phosphatase and tensin homolog deleted on chromosome 10) expression in stromal fibroblasts suppresses epithelial mammary tumours, but the underlying molecular mechanisms remain unknown. Using proteomic and expression profiling, we show that Pten loss from mammary stromal fibroblasts activates an oncogenic secretome that orchestrates the transcriptional reprogramming of other cell types in the microenvironment. Downregulation of miR-320 and upregulation of one of its direct targets, ETS2 (v-ets erythroblastosis virus E26 oncogene homolog 2) are critical events in Pten-deleted stromal fibroblasts responsible for inducing this oncogenic secretome, which in turn promotes tumour angiogenesis and tumour-cell invasion. Expression of the Pten-miR-320-Ets2-regulated secretome distinguished human normal breast stroma from tumour stroma and robustly correlated with recurrence in breast cancer patients. This work reveals miR-320 as a critical component of the Pten tumour-suppressor axis that acts in stromal fibroblasts to reprogramme the tumour microenvironment and curtail tumour progression.

Intermittent hypoxia suppresses adiponectin secretion by adipocytes.

Obstructive sleep apnea (OSA), characterized by cyclic intermittent hypoxia (IH) during sleep, is an independent risk factor for cardiovascular disease. Adiponectin (APN), an adipocytokine secreted exclusively by adipocytes, possesses antiatherogenic properties. Low levels of APN, particularly the high-molecular-weight (HMW) form, are associated with an increased risk of cardiovascular disease. Here, we hypothesized that IH would result in the dysregulation of APN expression and secretion. 3T3-L1 adipocytes were exposed to IH at 12 cycles/h for 6 h/d to simulate the IH condition similar to that encountered in OSA. Control adipocytes were exposed to 21% O(2) under identical conditions. After 48 h of incubation, IH caused a decrease in the secretion of total and HMW APN in spite of a significant upregulation of APN mRNA expression by adipocytes. This study suggested a novel mechanism of how the cyclic hypoxemia in OSA predisposes OSA patients to cardiovascular disease through the dysregulation of secretion of APN by adipocytes. Further studies are needed to determine the exact molecular mechanism how IH reduces the release of APN by adipocytes.

Polymyositis leading to diagnosis and resection of occult localized carcinoma of the cecum.

Polymyositis in an elderly but alert man led to an intensive search for an occult malignancy, which was found and removed. A five-year follow-up without evidence of metastasis supports the concept that polymyositis may antedate metastasis of underlying carcinoma and provide an opportunity for diagnosis and excision of the tumor before it has spread.

Cytokine-induced interleukin-1 receptor antagonist release in mononuclear phagocytes.

IL-1ra has recently been shown to suppress both cytokine- and endotoxin-induced IL-1 beta and TNF-alpha release from monocytes. Given that mononuclear phagocytes can produce both the proinflammatory cytokines IL-1 alpha, IL-1 beta, and TNF-alpha as well as the suppressive cytokine IL-1ra, we proposed that IL-1 alpha, IL-1 beta, and TNF-alpha may induce IL-1ra from mononuclear phagocytes. To test this hypothesis, human mononuclear cells were stimulated for 18 h with IL-1 alpha, IL-1 beta, or TNF-alpha, and the supernatants assayed for IL-1ra by ELISA. Each cytokine induced IL-1ra secretion in a dose-response manner. However, IL-1 alpha and IL-1 beta were better inducers of IL-1ra than was TNF-alpha. IL-1 alpha or IL-1 beta at a dose of 10 ng/ml induced 3 to 6 ng/ml of IL-1ra, while TNF-alpha at a dose of 100 ng/ml stimulated only 1.4 ng/ml of IL-1ra. This induction was not due to endotoxin, as all cytokines contained less than 10 pg/ml of contaminating LPS. Furthermore, for IL-1 beta-induced IL-1ra, immunoprecipitation of IL-1 beta with an anti-IL-1 beta antibody, but not a preimmune antibody, blocked the induction of IL-1ra. In contrast to mononuclear phagocytes, IL-1 alpha, IL-1 beta, and TNF-alpha did not induce further IL-1ra production in alveolar macrophages. This lack of macrophage responsiveness may relate to the constitutive production of IL-1ra by these mature mononuclear phagocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Fc gamma receptor cross-linking down-regulates IL-1 receptor antagonist and induces IL-1 beta in mononuclear phagocytes stimulated with endotoxin or Staphylococcus aureus.

The cross-linking of monocyte Fc gamma R is a potent stimulus for IL-1ra production but does not induce IL-1 beta. However, during systemic infection, IgG-coated bacteria can activate mononuclear phagocytes via both cell wall components and opsonized IgG. Therefore, we analyzed the effect of combinations of Fc gamma R cross-linking and bacterial cell wall components on mononuclear phagocyte IL-1 beta and IL-1ra production. Human mononuclear cells and monocytes were cultured either alone or with combinations of immobilized IgG, LPS, or heat-killed Staphylococcus aureus (HKSA). Cells cultured on immobilized IgG released large amounts of IL-1ra but no detectable IL-1 beta. In response to LPS, mononuclear cells released IL-1ra at 1000-fold lower doses of LPS than was required to induce IL-1 beta. However, when measured in the presence of immobilized IgG, the LPS sensitivity for IL-1 beta release increased 100-fold, whereas IL-1ra release correlated inversely with the LPS dose. Furthermore, HKSA, a nonendotoxin stimulus, affected mononuclear cell IL-1 beta and IL-1ra release similarly. In addition, polymyxin B, a specific endotoxin inhibitor, blocked the LPS, but not the HKSA-induced changes in IL-1 beta and IL-1ra secretion, irrespective of immobilized IgG co-stimulation. In summary, these results suggest that mononuclear phagocyte stimulation with immobilized IgG favors IL-1ra over IL-1 beta production. Conversely, the addition of LPS or HKSA to the Fc gamma R-stimulated cells augments IL-1 beta but suppresses IL-1ra production.

Macrophage and monocyte IL-1 beta regulation differs at multiple sites. Messenger RNA expression, translation, and post-translational processing.

Maturation of blood monocytes into macrophages is accompanied by a number of functional changes including decreased IL-1 beta release in response to LPS. This limitation has previously been ascribed to transcriptional regulation. However, in seeming conflict with the observed depression in IL-1 beta mRNA levels, recent work demonstrates increased intracellular IL-1 beta in macrophages. Therefore, the present study sought to explain these differences by comparing IL-1 beta production from autologous alveolar macrophage and blood monocyte pairs at multiple regulatory sites, including endotoxin responsiveness, mRNA expression, protein translation, and post-translational processing. Macrophages did not differ from monocytes in endotoxin sensitivity, but when analyzed by both ELISA and Western blot, were confirmed to have limitations in IL-1 beta release. Gene expression studies demonstrated that at 4 h, macrophage IL-1 beta steady state mRNA levels were 3-fold lower than the monocyte's. However, total IL-1 beta protein production, as measured by [35S]methionine labeling with immunoprecipitation, demonstrated three- to sixfold higher amounts in macrophages at comparable time points. The enhanced protein production in the face of relatively low mRNA levels suggests that macrophages translate IL-1 beta mRNA more efficiently. Furthermore, characterization of IL-1 beta release into supernatants revealed that whereas monocyte release occurred early, represented 5 to 20% of the intracellular amounts, and contained largely processed IL-1 beta, macrophage release was delayed, represented 1 to 5% of the intracellular amounts, and contained primarily unprocessed IL-1 beta. Taken together, these data demonstrate that the limitations in alveolar macrophage IL-1 beta release occur due to slower export and conversion of 35- to 17-kDa protein and are not due to differences in sensitivity to endotoxin or to transcriptional control mechanisms.

Monocyte IL-8 release is induced by two independent Fc gamma R- mediated pathways.

Cross-linking of PBMC and monocyte Fc gamma R on immobilized IgG stimulates IL-8 release. We used immobilized anti-Fc gamma R Abs to determine which of the three surface Fc gamma R regulated this IL-8 secretion. Fc gamma RIII cross-linking stimulated PBMC to release 5 times more IL-8 than did either Fc gamma RI or Fc gamma RII clustering (p = 0.001) and stimulated 77% more IL-8 release from PBMC than that from purified monocytes (p = 0.001). In contrast, only Fc gamma RI cross-linking significantly induced monocytes to release IL-8 (p = 0.05). Since purified lymphocytes release little IL-8 in response to immobilized IgG or anti-Fc gamma RIII Abs, we hypothesized that lymphocyte Fc gamma R cross-linking augmented monocyte IL-8 release. Supernatants from IgG- or Fc gamma RIII -stimulated lymphocytes induced monocytes to release more IL-8 than lymphocytes incubated on plastic alone (p = 0.002 and p = 0.003, respectively). THP-1 cells, which do not produce IL-8 in response to Fc gamma i]R cross-linking, also released IL-8 in response to supernatants from IgG- or Fc gamma RIII-stimulated lymphocytes, suggesting that the supernatant activity was not soluble immune complexes. The IL-8-stimulating activity was heat labile, suggesting that the activity is a protein. However, we could not reproduce or block this activity using recombinant cytokines or neutralizing anti-cytokine Abs. Thus, monocyte IL-8 is stimulated directly through Fc gamma RI cross-linking and indirectly through an Fc gamma RIII-stimulated soluble lymphocyte factor.

Fc(gamma) receptor cross-linking induces peripheral blood mononuclear cell monocyte chemoattractant protein-1 expression: role of lymphocyte Fc(gamma)RIII.

Immune complexes activate cells by cross-linking leukocyte surface Fc(gamma)Rs. Diseases associated with immune complex deposition, such as rheumatoid arthritis, glomerulonephritis, or idiopathic pulmonary fibrosis, are characterized by compartmentalized monocyte infiltration. The factors that recruit monocytes to these compartments are not well characterized; however, monocyte chemoattractant protein-1 (MCP-1) has been found in areas of tissue injury. To account for these observations we hypothesized that PBMC Fc(gamma)R cross-linking may induce MCP-1 synthesis, which stimulates further monocyte recruitment. To test this hypothesis, PBMC were incubated on increasing concentrations of immobilized human IgG, a stimulus for Fc(gamma)R cross-linking. Immunoreactive MCP-1 was produced in a dose-dependent manner (p < 0.0001). MCP-1 was specifically induced by Fc(gamma)R cross-linking, since immobilized F(ab')2 fragments of human IgG did not activate MCP-1 production. This effect was reproduced by directly cross-linking PBMC Fc(gamma)RIII, but not by cross-linking Fc(gamma)RI or Fc(gamma)RII. PBMC-derived MCP-1 stimulated monocyte chemotaxis that was inhibited by a neutralizing anti-MCP-1 Ab. MCP-1 levels correlated with increased PBMC mRNA expression. Interestingly, Fc(gamma)R cross-linking with either immobilized IgG or anti-Fc(gamma)RIII induced more MCP-1 release from PBMC than from autologous monocytes (p = 0.02). Lymphocytes, the main cell type found in PBMC preparations, did not independently produce a significant amount of MCP-1, but when incubated on immobilized IgG or anti-Fc(gamma)RIII secreted a soluble factor(s) that induced monocyte MCP-1 production. These data suggest that cross-linking PBMC Fc(gamma)R induces the production of bioactive MCP-1. This occurs in part at the level of gene transcription and involves a cooperative interaction between monocytes and lymphocytes.

The combination of endotoxin and dexamethasone induces type II interleukin 1 receptor (IL-1r II) in monocytes: a comparison to interleukin 1 beta (IL-1 beta) and interleukin 1 receptor antagonist (IL-1ra).

Soluble type II interleukin 1 receptor (IL-1r II) and interleukin 1 receptor antagonist (IL-1ra) regulate inflammation by competitively inhibiting the binding of IL-1 beta to the signalling IL-1 receptor. In addition, glucocorticoids also regulate IL-1 beta by suppressing gene transcription. More recently, glucocorticoids have been shown to increase soluble IL-1r II concentrations, which may contribute to their anti-inflammatory properties. Interestingly, increased serum levels of soluble IL-1r II and IL-1ra have been measured in septic patients, although the mechanism is unclear. In this respect, the authors characterize new pathways in which IL-1r II and IL-1ra may be regulated in sepsis through combined stimulation with lipopolysaccharide (LPS) and dexamethasone of peripheral blood mononuclear cells (PBMC). This paper confirms that while dexamethasone induces release of IL-1r II, LPS augments dexamethasone-induced IL-1r II release 45-fold. Furthermore, LPS plus dexamethasone induces IL-1r II protein and mRNA, whereas LPS alone does not. Additionally, it was shown by flow cytometric analysis that the monocyte is the primary IL-1r II producer in response to LPS and dexamethasone administration. Therefore, LPS and dexamethasone synergism in IL-1r II induction may be important in controlling IL-1 beta effects. In contrast, LPS alone induces IL-1ra, while dexamethasone attenuates this LPS-induced response. Although IL-1r II and IL-1ra may work together to suppress IL-1 beta effects in sepsis, inflammatory cells differentially regulate these cytokines.

IL-1ra suppresses endotoxin-induced IL-1 beta and TNF-alpha release from mononuclear phagocytes.

The proinflammatory effects of lipopolysaccharide (LPS) are modulated in large part through the induction of interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) release by mononuclear phagocytes. However, IL-1's target cell effects can be suppressed by IL-1 receptor agonist (IL-1ra). Because mononuclear phagocytes produce and respond to IL-1 via IL-1 receptors, we hypothesized that IL-1ra may also be able to block receptors on IL-1 producer cells and inhibit secondary IL-1-induced IL-1 production. To test this hypothesis, mononuclear cells and alveolar macrophages were stimulated with LPS in the presence of IL-1ra and analyzed for IL-1 beta and TNF-alpha production. For mononuclear cells, IL-1ra inhibited 6-h LPS- and IL-1 alpha-induced IL-1 beta release to 66 +/- 4% (P = 0.001 by paired t test) and 39 +/- 7% (P = 0.0005 by paired t test) of control, respectively. In addition, IL-1ra reduced both LPS- and IL-1 alpha-stimulated IL-1 beta mRNA levels to 78 and 37% of control, respectively. Furthermore, IL-1ra downregulated both LPS and IL-1 alpha-induced TNF-alpha release to 84 +/- 4% (P = 0.012 by paired t test) and 49 +/- 9% (P = 0.001 by paired t test) of control, respectively. Alveolar macrophages demonstrated variable IL-1ra-induced suppression of LPS-stimulated IL-1 beta and TNF-alpha release.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute phase levels of C-reactive protein enhance IL-1 beta and IL-1ra production by human blood monocytes but inhibit IL-1 beta and IL-1ra production by alveolar macrophages.

C-reactive protein (CRP), the major acute phase protein in humans, was purified free of endotoxin (LPS) (< 10 pg of LPS/mg of purified CRP) and evaluated for its ability to modulate LPS-induced production of IL-1 beta and IL-1 receptor antagonist (IL-1ra) from human PBMC and lung macrophages. PBMC (5 x 10(6)/ml) released low levels of IL-1 beta in response to either CRP (250 micrograms/ml) or LPS (100 ng/ml) for 18 h (0.3 +/- 0.1 and 1.5 +/- 0.7 ng/ml, respectively). However, when CRP (250 micrograms/ml) and LPS (100 ng/ml) were combined, PBMC released 9.7 +/- 2.9 ng/ml (p < 0.001 vs LPS alone). This synergy was removed by immunodepletion of CRP before stimulation. With respect to IL-1ra, although CRP induced IL-1ra production from PBMC (0.8 +/- 0.3 ng/ml control, 2.6 +/- 1.3 ng/ml with CRP), CRP did not synergize with LPS for IL-1ra production (15.0 +/- 0.7 ng/ml LPS alone vs 15.4 +/- 1.4 ng/ml LPS and CRP). In contrast, lung macrophages responded to CRP quite differently than PBMC. Macrophages (10(6)/ml) were not stimulated to produce IL-1 beta or IL-1ra by CRP alone. When combined with LPS, CRP inhibited IL-1 beta and IL-1ra release induced by LPS (for IL-1 beta release, LPS induced 3.0 +/- 1.7 ng/ml vs 1.1 +/- 0.4 for combined LPS and CRP; for IL-1ra release, LPS induced 12.9 +/- 2.3 ng/ml vs 7.6 +/- 2.3 ng/ml for combined LPS and CRP). These data suggest that acute phase levels of CRP may have divergent effects depending on the target population. CRP may be largely proinflammatory to blood monocytes responding to LPS since IL-1 beta production is augmented over IL-1ra production. However, in tissue compartments the effects of CRP may be largely immunosuppressive to LPS-induced tissue macrophage IL-1 beta production.

Monocyte Fc gamma receptor cross-linking induces IL-8 production.

In response to bacterial cell wall products such as LPS, monocytes produce IL-8, a powerful neutrophil chemotaxin. However, in the absence of bacterial pathogens, immune complex-mediated diseases such as rheumatoid arthritis are associated with high levels of IL-8 in monocyte-rich compartments. Since it is known that IgG-containing immune complexes can recruit neutrophils via an Fc gamma R-dependent process, we hypothesized that cross-linking of monocyte Fc gamma receptors may induce IL-8. To test this hypothesis, peripheral blood mononuclear cells were evaluated for IL-8 induction in response to immobilized LPS-free pooled human IgG. Immobilized IgG, but not soluble IgG, induced IL-8 in a dose-dependent manner (p < 0.05, r = 0.99). This induction corresponded with an up-regulation in IL-8 steady state mRNA levels that peaked at 4 h. The released IL-8 was functional, since supernatants induced concentration-dependent neutrophil migration that was inhibited by a monoclonal anti-IL-8 Ab. Evaluation of purified monocytes for IL-8 production, as well as FACS analysis of IgG-stimulated PBMC preparations, demonstrated that monocytes are the principal IL-8 producer cell. Thus, monocyte Fc gamma R cross-linking induces biologically active IL-8, which may participate in the pathogenesis of immune complex-mediated diseases.