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Background: We have previously shown that critically ill children transfused with red blood cells (RBCs) of longer storage durations have more suppressed monocyte function after transfusion compared to children transfused with fresher RBCs and that older stored RBCs directly suppress monocyte function in vitro, through unknown mechanisms. We hypothesized that RBC-derived microvesicles (MVs) were responsible for monocyte suppression., Study Design and Methods: To determine the role of stored RBC unit-derived MVs, we cocultured monocytes with supernatants, isolated MVs, or supernatants that had been depleted of MVs from prestorage leukoreduced RBCs that had been stored for either 7 or 30 days. Isolated MVs were characterized by electron microscopy and flow cytometry. Monocyte function after coculture experiments was measured by cytokine production after stimulation with lipopolysaccharide (LPS)., Results: Monocyte function was suppressed after exposure to supernatants from 30-day RBC units compared to monocytes cultured in medium alone (LPS-induced tumor necrosis factor-α production, 17,611 ± 3,426 vs. 37,486 ± 5,598 pg/mL; p = 0.02). Monocyte function was not suppressed after exposure to MV fractions. RBC supernatants that had been depleted of MVs remained immunosuppressive. Treating RBC supernatants with heat followed by RNase (to degrade protein-bound RNA) prevented RBC supernatant-induced monocyte suppression., Conclusion: Our findings implicate soluble mediators of stored RBC-induced monocyte suppression outside of MV fractions and suggest that extracellular protein-bound RNAs (such as microRNA) may play a role in transfusion-related immunomodulation., (© 2015 AABB.)

Reports demonstrate the role of M-CSF (CSF1) in tumor progression in mouse models as well as the prognostic value of macrophage numbers in breast cancer patients. Recently, a subset of CD14+ monocytes expressing the Tie2 receptor, once thought to be predominantly expressed on endothelial cells, has been characterized. We hypothesized that increased levels of CSF1 in breast tumors can regulate differentiation of Tie2- monocytes to a Tie2+ phenotype. We treated CD14+ human monocytes with CSF1 and found a significant increase in CD14+/Tie2+ positivity. To understand if CSF1-induced Tie2 expression on these cells improved their migratory ability, we pre-treated CD14+ monocytes with CSF1 and used Boyden chemotaxis chambers to observe enhanced response to angiopoietin-2 (ANG2), the chemotactic ligand for the Tie2 receptor. We found that CSF1 pre-treatment significantly augmented chemotaxis and that Tie2 receptor upregulation was responsible as siRNA targeting Tie2 receptor abrogated this effect. To understand any augmented angiogenic effect produced by treating these cells with CSF1, we cultured human umbilical vein endothelial cells (HUVECs) with conditioned supernatants from CSF1-pre-treated CD14+ monocytes for a tube formation assay. While supernatants from CSF1-pre-treated TEMs increased HUVEC branching, a neutralizing antibody against the CSF1R abrogated this activity, as did siRNA against the Tie2 receptor. To test our hypothesis in vivo, we treated PyMT tumor-bearing mice with CSF1 and observed an expansion in the TEM population relative to total F4/80+ cells, which resulted in increased angiogenesis. Investigation into the mechanism of Tie2 receptor upregulation on CD14+ monocytes by CSF1 revealed a synergistic contribution from the PI3 kinase and HIF pathways as the PI3 kinase inhibitor LY294002, as well as HIF-1α-deficient macrophages differentiated from the bone marrow of HIF-1αfl/fl/LysMcre mice, diminished CSF1-stimulated Tie2 receptor expression.

Macrophage colony-stimulating factor (M-CSF) promotes mononuclear phagocyte survival and proliferation. The transcription factor Nuclear Factor-kappaB (NF-κB) is a key regulator of genes involved in M-CSF-induced mononuclear phagocyte survival and this study focused at identifying the mechanism of NF-κB transcriptional activation. Here, we demonstrate that M-CSF stimulated NF-κB transcriptional activity in human monocyte-derived macrophages (MDMs) and the murine macrophage cell line RAW 264.7. The general protein kinase C (PKC) inhibitor Ro-31-8220, the conventional PKCα/β inhibitor Gö-6976, overexpression of dominant negative PKCα constructs and PKCα siRNA reduced NF-κB activity in response to M-CSF. Interestingly, Ro-31-8220 reduced Ser276 phosphorylation of NF-κBp65 leading to decreased M-CSF-induced monocyte survival. In this report, we identify conventional PKCs, including PKCα as important upstream kinases for M-CSF-induced NF-κB transcriptional activation, NF-κB-regulated gene expression, NF-κB p65 Ser276 phosphorylation, and macrophage survival. Lastly, we find that NF-κB p65 Ser276 plays an important role in basal and M-CSF-stimulated NF-κB activation in human mononuclear phagocytes., (© 2011 Wang et al.)

The receptor for advanced glycation end products (RAGE) is produced either as a transmembrane or soluble form (sRAGE). Substantial evidence supports a role for RAGE and its ligands in disease. sRAGE is reported to be a competitive, negative regulator of membrane RAGE activation, inhibiting ligand binding. However, some reports indicate that sRAGE is associated with inflammatory disease. We sought to define the biological function of sRAGE on inflammatory cell recruitment, survival, and differentiation in vivo and in vitro. To test the in vivo impact of sRAGE, the recombinant protein was intratracheally administered to mice, which demonstrated monocyte- and neutrophil-mediated lung inflammation. We also observed that sRAGE induced human monocyte and neutrophil migration in vitro. Human monocytes treated with sRAGE produced proinflammatory cytokines and chemokines. Our data demonstrated that sRAGE directly bound human monocytes and monocyte-derived macrophages. Binding of sRAGE to monocytes promoted their survival and differentiation to macrophages. Furthermore, sRAGE binding to cells increased during maturation, which was similar in freshly isolated mouse monocytes compared with mature tissue macrophages. Because sRAGE activated cell survival and differentiation, we examined intracellular pathways that were activated by sRAGE. In primary human monocytes and macrophages, sRAGE treatment activated Akt, Erk, and NF-kappaB, and their activation appeared to be critical for cell survival and differentiation. Our data suggest a novel role for sRAGE in monocyte- and neutrophil-mediated inflammation and mononuclear phagocyte survival and differentiation.

Francisella tularensis is a gram-negative facultative bacterium that causes the disease tularemia, even upon exposure to low numbers of bacteria. One critical characteristic of Francisella is its ability to dampen or subvert the host immune response. In order to help understand the mechanisms by which this occurs, we performed Affymetrix microarray analysis on transcripts from blood monocytes infected with the virulent Type A Schu S4 strain. Results showed that expression of several host response genes were reduced such as those associated with interferon signaling, Toll-like receptor signaling, autophagy and phagocytosis. When compared to microarrays from monocytes infected with the less virulent F. tularensis subsp. novicida, we found qualitative differences and also a general pattern of quantitatively reduced pro-inflammatory signaling pathway genes in the Schu S4 strain. Notably, the PI3K/Akt1 pathway appeared specifically down-regulated following Schu S4 infection and a concomitantly lower cytokine response was observed. This study identifies several new factors potentially important in host cell subversion by the virulent Type A F. tularensis that may serve as novel targets for drug discovery.

We previously demonstrated that monocytes produce IL-23 during Francisella infection, and that IL-23 induces IFNgamma from NK cells. Here, we demonstrate that IFNgamma-priming of monocytes enhances IL-23 production during Francisella infection. This effect was seen on the IL12/23 p40 subunit. Induction of IL-12/23 p40 is reported to be enhanced by IRF-1 and IRF-8. Consistently, microarray analysis of IFNgamma-treated monocytes revealed a significant induction of the IRFs. Interestingly, IFNgamma-primed monocytes produced IL-12 p70, a more potent inducer of IFNgamma than IL-23. We propose that there exists an amplification loop between monocyte IL-23 and NK/T cell IFNgamma that leads to IL-12 p70 production.

M-CSF induces PI 3-kinase activation, resulting in reactive oxygen species (ROS) production. Previously, we reported that ROS mediate macrophage colony-stimulating factor (M-CSF)-induced extracellular regulated kinase (Erk) activation and monocyte survival. In this work, we hypothesized that M-CSF-stimulated ROS products modulated Akt1 and p38 activation. Furthermore, we sought to clarify the source of these ROS and the role of ROS and Akt in monocyte/macrophage survival. Macrophages from p47(phox-/-) mice, lacking a key component of the NADPH oxidase complex required for ROS generation, had reduced cell survival and Akt1 and p38 mitogen-activated protein kinase (MAPK) phosphorylation compared with wild-type macrophages in response to M-CSF stimulation, but had no difference in M-CSF-stimulated Erk. To understand how ROS affected monocyte survival and signaling, we observed that NAC and DPI decreased cell survival and Akt1 and p38 MAPK phosphorylation. Using bone marrow-derived macrophages from mice expressing constitutively activated Akt1 (Myr-Akt1) or transfecting Myr-Akt1 constructs into human peripheral monocytes, we concluded that Akt is a positive regulator of monocyte survival. Moreover, the p38 MAPK inhibitor, SB203580, inhibited p38 activity and M-CSF-induced monocyte survival. These findings demonstrate that ROS generated from the NADPH oxidase complex contribute to monocyte/macrophage survival induced by M-CSF via regulation of Akt and p38 MAPK.

GM-CSF promotes homeostasis of myeloid cells. We report that GM-CSF upregulates mRNA and protein production of the soluble form of membrane bound VEGF receptor-1 (sVEGFR-1) in human monocytes. This sVEGFR-1 was biologically active, as cell-free supernatants from GM-CSF-stimulated monocytes blocked detection of endogenously expressed VEGF and inhibited endothelial cell migration and tube formation, even in the presence of exogenous rhVEGF. VEGF activity was recovered by neutralizing sVEGFR-1. To determine whether these events were important in vivo, Matrigel plugs were incubated with rhVEGF, rhGM-CSF, or rhGM-CSF/rhVEGF and injected into mice. Plugs containing GM-CSF or GM-CSF/VEGF had less endothelial cell invasion than plugs containing rhVEGF and were similar to plugs incubated with PBS alone. Neutralizing antibodies specific for sVEGFR-1 injected in these plugs reversed the effects of GM-CSF or GM-CSF/VEGF, while an isogenic antibody did not. Thus, GM-CSF and monocytes play a vital role in angiogenesis through the regulation of VEGF and sVEGFR-1.

Alveolar macrophages (AMs) are a subset of tissue macrophages situated in the alveolar milieu. Compared with their precursor blood monocytes, AMs exhibit distinct physiologic functions unique to their anatomic location. However, the molecular details that control monocyte differentiation into AMs remain unknown. This study employed a proteomic approach to define protein characteristics that distinguish AMs from monocytes. AMs and monocytes were obtained from six nonsmoking, healthy donors. Whole cell lysates from each donor's AMs and monocytes were analyzed by two-dimensional (2D) gel electrophoreses. The protein density for each protein spot in a 2D gel was compared between these two cell types. Proteins that demonstrated consistent level changes of greater than 2.5-fold in all six donors were subjected to tandem mass spectrometry for protein identity. Using this process, we revealed proteome changes in AMs that relate to their physiologic roles in proteolysis, actin reorganization, and cellular adaptation in the unique alveolar milieu. By comparison, blood monocytes displayed higher levels of the proteins involved in transcription, metabolism, inflammation, and in the control of proteolysis. These results provide new insights into the biology of mononuclear phagocytes and set a basis for future causality studies.

The ability to target and accumulate monocytes and macrophages in areas of tissue inflammation plays an important role in innate and humoral immunity. However, when this process becomes uncontrolled, tissue injury and dysfunction may ensue. This paper will focus on understanding the role and action of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in regulating the molecular and biochemical pathways responsible for the regulation of the survival of human monocytes. We and others have found that ROS and RNS serve as important intracellular signaling molecules that influence cellular survival. Human monocytes are influenced by intracellular production of ROS and RNS, which affects both monocyte survival and death, depending on the form of nitric oxide presented to the cell. This review will address potential mechanisms by which ROS and RNS promote the survival of human monocytes and macrophages.

The impact of the immune response in malignancy is poorly understood. While immune cells can destroy transformed cells, the targeting and accumulation of monocytes and macrophages at tumor sites may promote tumor metastases. The growth factor M-CSF is important in promoting monocyte survival. Since M-CSF(-/-) mice are protected against tumor metastases, we hypothesized that M-CSF induced monocytes to produce angiogenic factors that facilitate metastases. In this study we demonstrate that recombinant human M-CSF induces freshly isolated normal human monocytes to produce and release the growth factor vascular endothelial growth factor (VEGF) in a dose-dependent manner, which peaked at 5 days in culture. VEGF released by these monocytes is biologically active, as cell-free supernatants from these M-CSF-stimulated monocytes induced tube formation in HUVEC. Network formation by these HUVECs after treatment with supernatants from monocytes stimulated with M-CSF were inhibited by anti-VEGF, but not by the isogenic control, Abs. Collectively, these data support an important role for M-CSF and monocytes in VEGF production and angiogenesis.

In the absence of survival factors, blood monocytes undergo spontaneous apoptosis, which involves the activation of caspase-3. Although nitric oxide can block caspase-3 activation and promote cell survival, it can also induce apoptosis. We hypothesized that nitrosothiols that promote protein S-nitrosylation would reduce caspase-3 activation and cell survival, whereas nitric oxide donors (such as 1-propamine 3-(2-hydroxy-2-nitroso-1-propylhydrazine (PAPA) NONOate and diethylamine (DEA) NONOate) that do not target thiol residues would not. Using human monocytes as a model, we observed that nitrosothiol donors S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine suppressed caspase-9 and caspase-3 activity and DNA fragmentation. In contrast, PAPA or DEA NONOate did not promote monocyte survival events and appeared to inhibit monocyte survival induced by macrophage colony-stimulating factor. The caspase-3-selective inhibitor DEVD-fluoromethyl ketone reversed DNA fragmentation events, and the caspase-9 inhibitor LEHD-fluoromethyl ketone reversed caspase-3 activity in monocytes treated with PAPA or DEA NONOate in the presence of macrophage colony-stimulating factor. These results were not caused by differences in glutathione levels or the kinetics of nitric oxide release. Moreover, S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine directly blocked the activity of recombinant caspase-3, which was reversed by the reducing agent dithiothreitol, whereas PAPA or DEA NONOate did not block the enzymatic activity of caspase-3. These data support the hypothesis that nitrosylation of protein thiol residues by nitric oxide is critical for promoting the survival of human monocytes.

We previously reported that activation of the phosphatidylinositol (PI) 3-kinase pathway was important in M-CSF-induced monocyte survival. Because M-CSF also induces activation of the mitogen-activated protein (MAP) kinase extracellular-regulated kinase (Erk), we focused on dissecting the mechanism used by M-CSF to induce Erk activation in human monocytes. We found that, in addition to the MAP/Erk kinase inhibitor PD098059, the PI 3-kinase inhibitors LY294002 and wortmannin both suppressed Erk activation in M-CSF-treated monocytes, suggesting that 3-phosphorylated products of PI 3-kinase played a role in Erk activation. Investigating the biochemical pathways regulated by PI 3-kinase to activate Erk, we found that, in response to M-CSF, normal human monocytes induced reactive oxygen species (ROS), which were suppressed by the PI 3-kinase inhibitor wortmannin but not by the solvent control DMSO or the MAP/Erk kinase inhibitor PD098059. We next found that, in the absence of M-CSF, ROS could induce Erk activation in human monocytes. Exogenous H(2)O(2) induced Erk activation in human monocytes, which was suppressed by exogenous catalase. To determine whether ROS induced by M-CSF played a role in Erk activation, we found that N-acetylcysteine and diphenyleneiodonium both suppressed Erk activation in M-CSF-treated monocytes. Erk activation by M-CSF also seemed to play a role in cellular survival in monocytes. These data suggest that, in M-CSF-stimulated human monocytes, PI 3-kinase products and ROS production play a role in Erk activation and monocyte survival.

A number of inflammatory cytokines and growth factors promote monocyte survival; however, the biochemical events stimulated by these factors are poorly defined. We previously showed that the monocyte survival factor macrophage colony-stimulating factor (M-CSF) activated monocyte survival through a PI 3-kinase-dependent pathway resulting in the phosphorylation of Akt and the suppression of the activation of caspase-3. Because other cytokines and bacterial cell wall products also induce monocyte survival, we hypothesized that these factors may also suppress caspase-3 and caspase-9 activation and activate Akt in human monocytes. To test this hypothesis, we found that interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, lipopolysaccharide (LPS), granulocyte macrophage-colony-stimulating factor (GM-CSF), and IL-18 appeared to suppress DNA fragmentation, caspase-9, and caspase-3 activation in human monocytes. Moreover, these stimuli appeared to induce the serine and threonine phosphorylation of Akt, which was reduced by the PI 3-kinase inhibitor LY294002. Using in vitro kinase assays, M-CSF appeared to induce more Akt activity than did the other survival factors. Treatment of monocytes with either LY294002 or wortmannin resulted in caspase-3 activation in the presence of these survival factors. These results suggest that monocyte survival factors may suppress DNA fragmentation, caspase-9, and caspase-3 activation in a PI 3-kinase-dependent manner, perhaps through the activation of Akt.

IgG deposition at tissue sites characteristically leads to macrophage accumulation and organ injury. Although the mechanism by which deposited IgG induces tissue injury is not known, we have recently demonstrated that deposited IgG stimulates the release of IL-8 and monocyte chemoattractant protein-1 from normal human monocytes, which may drive inflammation. Since IgG also induces macrophage accumulation in these diseases, we hypothesized that deposited IgG protects monocytes from apoptosis. As an in vitro model of the effect of deposited IgG on monocyte survival, monocyte apoptosis was studied after FcgammaR cross-linking. Monocytes cultured on immobilized IgG, which induces FcgammaR cross-linking, were protected from apoptosis, whereas monocytes cultured with equivalent concentrations of F(ab')2 IgG or 50 times higher concentrations of soluble IgG, neither of which induces FcgammaR cross-linking, were not protected. Moreover, this protection was transferable, as supernatants from immobilized IgG-stimulated monocytes protected freshly isolated monocytes from apoptosis and contained functional M-CSF, a known monocyte survival factor. M-CSF mediated the monocyte survival induced by FcgammaR cross-linking, as neutralizing anti-human M-CSF Abs blocked the monocyte protection provided by either immobilized IgG or IgG-stimulated monocyte supernatants. These findings demonstrate a novel mechanism by which deposited IgG targets tissue macrophage accumulation through FcgammaR-mediated M-CSF release. This pathway may play an important role in promoting and potentiating IgG-mediated tissue injury.

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.

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.

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.

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.

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.

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)

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.