Macrophage-mediated Inflammatory Responses Research Articles

Macrophage-mediated endothelial inflammatory responses to airborne particulates: impact of particulate physicochemical properties.

Epidemiological studies have implicated a role for airborne particulates of <2.5 microm diameter in the development/exacerbation of chronic cardiopulmonary disease; however, specific pathogenic mechanisms and the etiological significance of particle physicochemical properties remain unresolved. Using a microporous aluminosilicate zeolite Y as a manifold, we have synthesized 1 microm particulates of pure carbon (C), carbon-iron (C/Fe), and carbon-iron/fluoro-aluminum silicate (C-Fe/F-Al-Si). We have used these particulates, as well as coal fly ash (CFA) and diesel exhaust particulates (DEP), to test the hypotheses that human macrophages treated with particulates elaborate proinflammatory cytokines in quantities sufficient to induce endothelial adhesion molecule expression and that macrophage responses to particulate exposure vary as a function of particulate physicochemical properties. Human monocyte-derived macrophages (Mø) were exposed for 24 h to sublethal concentrations of particulates, at which time phagocytosis was evident from optical microscopy. Human arterial, microvascular, or venous endothelial cells (EC) were treated with clarified supernatants recovered from Mø cultures, stained with fluorescein-conjugated mononclonal antibodies specific for endothelial adhesion molecules intercellular adhesion molecule-1, vascular cell adhesion molecule-1, or E-selectin, and assayed by fluorescence flow cytometry. Data generated by these experiments demonstrate that while supernatants of Mø exposed to CFA and C particulates are relatively ineffective, supernatants from DEP, C/Fe, or C-Fe/F-Al-Si strongly induced adhesion molecule expression on EC, responses which were completely attenuated by antibody with blocking specificity for tumor necrosis factor alpha. Because the only difference between C and C/Fe particulates is the presence of surface iron on C/Fe, these findings suggest particulate-induced oxidative stress as a contributing factor in Mø activation and implicate redox active iron as a major determinant of particulate bioreactivity.

The peroxisome proliferator activated receptor δ is required for the differentiation of THP-1 monocytic cells by phorbol ester

BackgroundPPARδ (NR1C2) promotes lipid accumulation in human macrophages in vitro and has been implicated in the response of macrophages to vLDL. We have investigated the role of PPARδ in PMA-stimulated macrophage differentiation.The THP-1 monocytic cell line which displays macrophage like differentiation in response to phorbol esters was used as a model system. We manipulated the response to PMA using a potent synthetic agonist of PPARδ , compound F. THP-1 sub-lines that either over-expressed PPARδ protein, or expressed PPARδ anti-sense RNA were generated. We then explored the effects of these genetic modulations on the differentiation process.ResultsThe PPARδ agonist, compound F, stimulated differentiation in the presence of sub-nanomolar concentrations of phorbol ester. Several markers of differentiation were induced by compound F in a synergistic fashion with phorbol ester, including CD68 and IL8. Over-expression of PPARδ also sensitised THP-1 cells to phorbol ester and correspondingly, inhibition of PPARδ by anti-sense RNA completely abolished this response.ConclusionsThese data collectively demonstrate that PPARδ plays a fundamental role in mediating a subset of cellular effects of phorbol ester and supports observations from mouse knockout models that PPARδ is involved in macrophage-mediated inflammatory responses.

Comparisons of CapG and gelsolin-null macrophages

Capping the barbed ends of actin filaments is a critical step for regulating actin-based motility in nonmuscle cells. The in vivo function of CapG, a calcium-sensitive barbed end capping protein and member of the gelsolin/villin family, has been assessed using a null Capg allele engineered into mice. Both CapG-null mice and CapG/gelsolin double-null mice appear normal and have no gross functional abnormalities. However, the loss of CapG in bone marrow macrophages profoundly inhibits macrophage colony stimulating factor–stimulated ruffling; reintroduction of CapG protein by microinjection fully restores this function. CapG-null macrophages also demonstrate ∼50% impairment of immunoglobulin G, and complement-opsonized phagocytosis and lanthanum-induced vesicle rocketing. These motile functions are not impaired in gelsolin-null macrophages and no additive effects are observed in CapG/gelsolin double-null macrophages, establishing that CapG function is distinct from, and does not overlap with, gelsolin in macrophages. Our observations indicate that CapG is required for receptor-mediated ruffling, and that it is a major functional component of macrophage phagocytosis. These primary effects on macrophage motile function suggest that CapG may be a useful target for the regulation of macrophage-mediated inflammatory responses.

Inhibition of mesangial cell nitric oxide in MRL/lpr mice by prostaglandin J2 and proliferator activation receptor-gamma agonists.

MRL/Mp-lpr/lpr (MRL/lpr) mice develop immune complex glomerulonephritis similar to human lupus. Glomerular mesangial cells are key modulators of the inflammatory response in lupus nephritis. When activated, these cells secrete inflammatory mediators including NO and products of cyclooxygenase perpetuating the local inflammatory response. PGJ2, a product of cyclooxygenase, is a potent in vitro inhibitor of macrophage inflammatory functions and is postulated to function as an in vivo inhibitor of macrophage-mediated inflammatory responses. We hypothesized that in lupus, a defect in PGJ2 production allows the inflammatory response to continue unchecked. To test this hypothesis, mesangial cells were isolated from MRL/lpr and BALB/c mice and stimulated with IL-1beta or LPS plus IFN-gamma. In contrast to the 2- to 3-fold increase in PGJ2 production by stimulated BALB/c mesangial cells, supernatant PGJ2 did not increase in MRL/lpr mesangial cell cultures. NO production in stimulated MRL/lpr and BALB/c mesangial cells, was blocked by PGJ2 and pioglitazone. These studies suggest that abnormalities in PGJ2 production are present in MRL/lpr mice and may be linked to the heightened activation state of mesangial cells in these mice.

Substance P Diminishes Lipopolysaccharide and Interferon-γ-Induced TGF-β1 Production by Cultured Murine Macrophages

Recent evidence has demonstrated the importance of substance P and its receptor in macrophage-mediated inflammatory responses. While previous studies have shown that substance P can augment proinflammatory monokine production, little is known about the effects of this neuropeptide on the production of monokines that might limit inflammation. In the present study we have investigated the effect of substance P treatment on the production of transforming growth factor-β1 (TGF-β1) in cultured murine macrophages. We report that, while substance P agonist alone elicited increases in TGF-β1 mRNA expression and modest increases in TGF-β1 secretion, substance P dramatically diminished LPS- or IFN-γ-induced TGF-β1 production. These results suggest a previously unrecognized mechanism where substance P may act as a proinflammatory mediator by limiting the production of excessive levels of TGF-β1 by LPS- or IFN-γ-activated macrophages.

Components of the angiotensin system cause release of a neutrophil chemoattractant from cultured bovine and human endothelial cells

Evidence suggests that angiotensin II can affect macrophage-mediated inflammatory responses; however, whether it can affect neutrophil-mediated inflammatory responses is not yet clear. We have previously demonstrated that components of the angiotensin system simulate bovine aortic and human umbilical vein endothelial cells to release a neutrophil chemoattractant. In the current study, we examined the effect of components of the angiotensin system on bovine and human pulmonary arterial and human aortic endothelial cells, and partially characterized this neutrophil chemoattractant. All endothelial cell types incubated with angiotensin II released neutrophil chemoattractant activity. This activity appeared within 1 min of exposure to angiotensin II, and was blocked by saralasin, an angiotensin II antagonist. The neutrophil chemoattractant also appeared after exposure to angiotensin I, but this effect required conversion to angiotensin II. Incubation with bradykinin, another substrate for angiotensin-converting enzyme, did not cause release of the neutrophil chemoattractant. Chemoattractant release was not inhibited by indomethacin but was blocked by diethylcarbamazine or 5,8,11,14-eicosatetraynoic acid. Following extraction, the neutrophil chemoattractant partitioned completely into the organic phase. High-pressure liquid chromatography demonstrated several peaks of chemoactivity, none of which co-eluted with known eicosanoid or phospholipid neutrophil chemoattractants. This study demonstrates that angiotensin II may influence neutrophil accumulation via production of neutrophil chemoattractant activity by vascular endothelial cells.

The role of arachidonic acid metabolites in mononuclear phagocytic cell interactions.

Numerous investigations support the theory that arachidonic acid metabolites play a critical role in dictating the progression of chronic immune reactions. With regard to macrophage-mediated inflammatory responses, enzymatic oxygenation of arachidonic acid via the lipoxygenase or cyclooxygenase pathway can result in the production of compounds that may potentiate or suppress the inflammatory lesion. We recently have presented data demonstrating that lipoxygenase derived leukotriene B4 and C4 can induce the release of IL-1 by macrophages, while PGE2 and PGI2 can suppress the production of IL-1. Macrophages are central to the induction of immune responses and the progression of chronic inflammatory reactions. Therefore, an understanding of the role that macrophage-derived arachidonic acid metabolites play in the initiation, maintenance, and resolution of chronic immune responses is essential. As shown in Figure 3, there are a number of chemical signals that occur between macrophages and lymphocytes that are critical for immune cell communication. The investigations described above have demonstrated that the macrophage may regulate the production and expression of any or all of these signals, such that the inflammatory response is potentiated, sustained, suppressed, or resolved. A better comprehension of the activity of these potent arachidonate derivates will undoubtedly aid in the therapeutic manipulation of inflammatory disease.

Bovine and human endothelial cell production of neutrophil chemoattractant activity in response to components of the angiotensin system.

Although there is growing evidence that angiotensin II affects macrophage-mediated inflammatory responses, it is unclear whether it can affect neutrophil-mediated inflammatory responses. Because vascular endothelial cells are capable of releasing neutrophil chemoattractant activity, we attempted to determine whether components of the angiotensin system could affect neutrophil-mediated responses indirectly by stimulating endothelial cells to release neutrophil chemoattractant substances. Cultured bovine and human endothelial cells incubated with angiotensin II released neutrophil chemoattractant activity. This activity appeared within 1 minute of exposure to angiotensin II, and was blocked by saralasin, an angiotensin II antagonist. Angiotensin I also caused release of neutrophil chemoattractant activity, but its effect required conversion to angiotensin II. Bradykinin, another substrate for angiotensin-converting enzyme, did not stimulate appearance of chemoattractant. Chemoattractant generation was not inhibited by indomethacin but was blocked by diethylcarbamazine and 5,8,11,14-eicosatetraynoic acid. This study demonstrates that angiotensin II may influence neutrophil accumulation, via production of neutrophil chemoattractant activity by vascular endothelial cells.