Alterations of ambient oxygen tension modulate the expression of tumor necrosis factor and macrophage inflammatory protein-1 alpha from murine alveolar macrophages.

Tissue injury that occurs as a result of ischemia and subsequent reperfusion is characterized by endothelial cell injury, edema formation, and the influx of inflammatory leukocytes. Two macrophage-derived proinflammatory cytokines which may play a critical role in cellular injury and leukocyte recruitment/activation that occurs in the setting of ischemia-reperfusion injury are tumor necrosis factor alpha (TNF) and macrophage inflammatory protein-1 alpha (MIP-1 alpha). To determine if modulation of ambient oxygen tensions in vitro alters the expression of proinflammatory cytokines from activated macrophages, murine alveolar macrophages (AMO) were cultured in various combinations of ambient oxygen concentrations, then the supernatant fluid and cell pellet assayed for the presence of TNF and MIP-1 alpha messenger RNA (mRNA) and protein. We demonstrated that conditions of anoxia (95% nitrogen/5% CO2) or hyperoxia (95% oxygen/5% CO2) independently resulted in the increased expression of both TNF and MIP-1 alpha mRNA and protein from lipopolysaccharide (LPS)-stimulated AMO, as compared with cells cultured in room air. The specific culture condition of anoxia (x 6 h) followed by hyperoxia (x 18 h) produced the greatest increases in both TNF and MIP-1 alpha, suggesting that when following a period of anoxic priming, oxygen stress results in exaggerated cytokine production. A period of at least 4.5 to 6 h of anoxia prior to hyperoxic exposure was found to be the minimal time required for anoxic priming. Furthermore, the coincubation of LPS-treated AMO with dimethyl sulfoxide (DMSO) attenuated the anoxia-hyperoxia-induced increases in TNF and MIP-1 alpha mRNA by 23% and 34%, respectively. These findings suggested that alterations in ambient oxygen tension can regulate the expression of TNF and MIP-1 alpha from activated AMO, and that oxidant-related cytokine production may represent an important mechanism by which inflammation occurs in the clinical settings of ischemia-reperfusion injury and hyperoxia.

Compartmentalized expression of RANTES in a murine model of endotoxemia.

Systemic exposure to LPS initiates a complex sequence of events culminating in organ-specific leukocyte recruitment and end organ injury. We hypothesized that RANTES, a C-C chemokine with potent M phi (mononuclear phagocyte) chemotactic activity, is expressed in vivo in response to endotoxemia, and that this protein may play an important role in the recruitment of M phi to the lung. CD-1 mice were challenged with LPS (200 micrograms), resulting in a maximal fourfold increase in polymorphonuclear leukocyte (neutrophils) at 6 h post LPS, and a 2.4-fold increase in numbers of M phi within lung minces at 24 h. A time-dependent increase in RANTES mRNA was detected in lung after LPS treatment, whereas minimal quantities of RANTES mRNA were detected in blood buffy coats and liver. Furthermore, treatment with LPS resulted in time-dependent increase in RANTES protein within lung homogenates, with immunolocalization to alveolar epithelial cells. The pretreatment of mice with goat anti-RANTES Ab significantly inhibited the influx of lung M phi, but not polymorphonuclear leukocyte and lymphocytes, at 24 h post-LPS challenge. Lastly, the pretreatment of animals with soluble TNF receptor: Ig construct 2 h before LPS resulted in a 60% reduction in steady state levels of RANTES mRNA within lung homogenates at 4 h post-LPS. Our observations suggest that RANTES represents an important mediator of lung M phi recruitment in the setting of endotoxemia, and that the expression of RANTES in vivo is dependent upon the endogenous production of TNF.

Macrophage inflammatory protein-1 alpha expression in vivo and in vitro: the role of lipoteichoic acid.

Lipoteichoic acid (LTA), a component of the cell wall of most gram-positive bacteria, has been shown to play a significant role in the initiation and progression of bacterial infection. However, little is known of its position in the cytokine network involved in the induction and perpetuation of inflammation. In this study, we assessed whether the macrophage activating and chemotactic cytokine macrophage inflammatory protein-1 alpha (MIP-1 alpha) was expressed in the setting of localized gram-positive infection. Furthermore, we determined whether LTA purified from either Staphylococcus aureus or Streptococcus pyogenes could induce the expression of MIP-1 alpha mRNA and protein from human blood monocytes. Immunohistochemical staining of human endocardial samples obtained from patients with acute S. aureus endocarditis revealed cell-associated MIP-1 alpha expression by neutrophils, macrophages, and fibroblasts. Treatment of human peripheral blood monocytes in vitro with LTA isolated from either S. aureus or S. pyogenes resulted in both the time- and dose-dependent expression of MIP-1 alpha mRNA. Similarly, staphylococcal and streptococcal LTA induced the dose-dependent production of MIP-1 alpha protein after 24 h in culture. These studies suggest that LTA may play an important role in triggering the recruitment and activation of leukocytes that characterizes the host response to gram-positive bacterial invasion.

Expression and regulation of macrophage inflammatory protein-1 alpha by murine alveolar and peritoneal macrophages.

A number of disease states are characterized by the accumulation of inflammatory cells at the site of tissue injury. Mononuclear phagocytes (M phi) represent key cellular mediators of inflammation via the production of regulatory and chemokinetic cytokines. One such cytokine, macrophage inflammatory protein-1 alpha (MIP-1 alpha), has been shown to be one of the major inducible chemotaxins expressed from murine macrophage cell lines (RAW 264.7). We postulated that MIP-1 alpha is a major monocyte chemoattractant produced by resident M phi, and the magnitude of production of this chemotaxin may depend upon the specific population of M phi studied. To test this hypothesis, we isolated alveolar macrophages (AM phi) and peritoneal macrophages (PM phi) from CD-1 mice by bronchoalveolar and peritoneal lavage, respectively. Recombinant murine MIP-1 alpha accounted for significant neutrophil chemokinetic rather than chemotactic activity, as assessed by checkerboard analysis. LPS-stimulated AM phi-derived monocyte chemotactic activity (MCA) was significantly neutralized by specific rabbit anti-murine MIP-1 alpha serum. In contrast, PM phi-derived conditioned media failed to produce MCA attributable to MIP-1 alpha. The production of MIP-1 alpha was then characterized from both AM phi and PM phi. While unstimulated AM phi and PM phi failed to express MIP-1 alpha mRNA, both AM phi and PM phi challenged with lipopolysaccharide (LPS) expressed MIP-1 alpha mRNA in a time-dependent fashion.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoteichoic acid induces secretion of interleukin-8 from human blood monocytes: a cellular and molecular analysis.

Invasion by gram-positive and gram-negative bacterial organisms is characterized immunopathologically by the activation of mononuclear phagocytic cells, leading to the elaboration of macrophage-derived regulatory and chemotactic factors, and the resultant influx of inflammatory leukocytes. Little is known regarding the mechanisms by which gram-positive organisms initiate macrophage activation and subsequent inflammation. In this investigation, we postulated that lipoteichoic acid (LTA) purified from two different gram-positive bacterial species was an important signal for the expression of chemotactic cytokines from human peripheral blood monocytes (PBM). In initial experiments, we demonstrated that cell-associated interleukin-8 (IL-8) was expressed by mononuclear phagocytes present in inflamed areas of endocardium in cases of acute Staphylococcus aureus endocarditis. We next demonstrated that LTA purified from either Staphylococcus aureus or Streptococcus pyogenes induced the time- and dose-dependent expression of IL-8 mRNA and protein from human PBM. The expression of IL-8 mRNA from LTA- but not lipopolysaccharide (LPS)-treated PBM was superinduced by concomitant treatment with cycloheximide, indicating that the expression of IL-8 mRNA from LTA-treated PBM was negatively controlled by repressor proteins. Furthermore, mRNA stability studies indicated that IL-8 mRNA was less stable in the presence of LTA than in the presence of LPS. Our findings indicate that LTA can induce the secretion of the polymorphonuclear leukocyte chemotactic factor IL-8 and that LTA may be an important cellular mediator of inflammatory cell recruitment that characterizes immune responses to gram-positive bacterial infections.