The inflammatory response is a protective process of the body to counteract xenobiotic penetration and injury, although in disease this response can become deregulated. There are endogenous biochemical pathways that operate in the host to keep inflammation under control. Here we demonstrate that the counterregulator annexin 1 (AnxA1) is critical for controlling experimental endotoxemia. Lipopolysaccharide (LPS) markedly activated the AnxA1 gene in epithelial cells, neutrophils, and peritoneal, mesenteric, and alveolar macrophages--cell types known to function in experimental endotoxemia. Administration of LPS to AnxA1-deficient mice produced a toxic response characterized by organ injury and lethality within 48 hours, a phenotype rescued by exogenous application of low doses of the protein. In the absence of AnxA1, LPS generated a deregulated cellular and cytokine response with a marked degree of leukocyte adhesion in the microcirculation. Analysis of LPS receptor expression in AnxA1-null macrophages indicated an aberrant expression of Toll-like receptor 4. In conclusion, this study has detailed cellular and biochemical alterations associated with AnxA1 gene deletion and highlighted the impact of this protective circuit for the correct functioning of the homeostatic response to sublethal doses of LPS.

The recent appreciation of the role played by endogenous counterregulatory mechanisms in controlling the outcome of the host inflammatory response requires specific analysis of their spatial and temporal profiles. In this study, we have focused on the glucocorticoid-regulated anti-inflammatory mediator annexin 1. Induction of peritonitis in wild-type mice rapidly (4 h) produced the expected signs of inflammation, including marked activation of resident cells (e.g., mast cells), migration of blood-borne leukocytes, mirrored by blood neutrophilia. These changes subsided after 48–96 h. In annexin 1null mice, the peritonitis response was exaggerated (∼40% at 4 h), with increased granulocyte migration and cytokine production. In blood leukocytes, annexin 1 gene expression was activated at 4, but not 24, h postzymosan, whereas protein levels were increased at both time points. Locally, endothelial and mast cell annexin 1 gene expression was not detectable in basal conditions, whereas it was switched on during the inflammatory response. The significance of annexin 1 system plasticity in the anti-inflammatory properties of dexamethasone was assessed. Clear induction of annexin 1 gene in response to dexamethasone treatment was evident in the circulating and migrated leukocytes, and in connective tissue mast cells; this was associated with the steroid failure to inhibit leukocyte trafficking, cytokine synthesis, and mast cell degranulation in the annexin 1null mouse. In conclusion, understanding how inflammation is brought under control will help clarify the complex interplay between pro- and anti-inflammatory pathways operating during the host response to injury and infection.

Retinoid X receptors (RXRs) are important transcriptional nuclear hormone receptors, acting as either homodimers or the binding partner for at least one fourth of all the known human nuclear receptors. Functional nongenomic effects of nuclear receptors are poorly understood; however, recently peroxisome proliferator-activated receptor (PPAR) γ, PPARβ, and the glucocorticoid receptor have all been found active in human platelets. Human platelets express RXRα and RXRβ. RXR ligands inhibit platelet aggregation and TXA2 release to ADP and the TXA2 receptors, but only weakly to collagen. ADP and TXA2 both signal via the G protein, Gq. RXR rapidly binds Gq but not Gi/z/o/t/gust in a ligand-dependent manner and inhibits Gq-induced Rac activation and intracellular calcium release. We propose that RXR ligands may have beneficial clinical actions through inhibition of platelet activation. Furthermore, our results demonstrate a novel nongenomic mode for nuclear receptor action and a functional cross-talk between G-protein and nuclear receptor signaling families.

The microvasculature assumes an inflammatory and procoagulant state in a variety of different diseases, including sickle cell disease (SCD), which may contribute to the high incidence of ischemic stroke in these patients. This study provides evidence for accelerated thrombus formation in arterioles and venules in the cerebral vasculature of mice that express hemoglobin-S (␤ s mice). Enhanced microvascular thrombosis in ␤ s mice was blunted by immunologic or genetic interventions that target tissue factor, endothelial protein C receptor, activated protein C, or thrombin. Platelets from ␤ s mice also exhibited enhanced aggregation velocity after stimulation with thrombin but not ADP. Neutropenia also protected against the enhanced thrombosis response in ␤ s mice. These results indicate that the cerebral microvasculature is rendered vulnerable to thrombus formation in ␤ s mice via a neutrophil-dependent mechanism that is associated with an increased formation of and enhanced platelet sensitivity to thrombin. (Blood. 2011;117(15):4125-4133) IntroductionSickle cell disease (SCD) is a chronic, genetic disease affecting the vasculature of various organs, including the lungs and brain, with affected tissues assuming an inflammatory phenotype. 1 Sickle cell anemia is characterized by recurring acute vasoocclusive episodes and chronic damage to multiple organs. 2 Many morbid consequences of SCD, such as stroke (the prevalence of stroke in SCD patients is 8%-10%), are believed to result from microvascular blood flow impairment. 3,4 Histopathologic evaluation indicates that large vessel narrowing with superimposed thrombosis is the most common cause of ischemic stroke in children with SCD. 5 Risk factors for ischemic stroke in SCD patients include: a hemoglobin-S (HbS) phenotype, low steady-state Hb concentrations, high leukocyte counts, and elevated systolic blood pressure. 6 A fine balance normally exists between the procoagulant and anticoagulant functions of blood, allowing vessel walls to prevent unwanted hemorrhage and thrombosis. 3 SCD is associated with abnormalities in coagulant/anticoagulant pathways that tend to favor thrombus formation; these include: increased tissue factor (TF), accelerated thrombin generation, increased D-dimer (a marker of increased fibrolysis) and prothrombin fragment 1.2 (a marker of thrombin generation), and increased circulating fibrinogen, VWF, and clotting factors Patients with SCD also have reduced protein C and S levels. 10 Despite the large body of evidence supporting a hypercoagulable and prothrombotic state in SCD, it remains unclear whether increased thrombin and fibrin generation and platelet activation are primary or secondary events in this disease. 11 Furthermore, the few clinical studies on the use of antiplatelet agents (eg, aspirin and ticlopidine) and anticoagulant agents (eg, heparin and warfarin) in SCD patients have not provided convincing evidence to support this therapeutic strategy for the prevention or treatment of vasoocclusive complications. 11 Whereas mechanism...

We evaluated the role of estradiol and progesterone in allergic lung inflammation. Rats were ovariectomized (Ovx) and, 7 days later, were sensitized with ovalbumin (OA) and challenged after 2 wk with inhaled OA; experiments were performed 1 day thereafter. Ovx-allergic rats showed reduced cell recruitment into the bronchoalveolar lavage (BAL) fluid relative to sham-Ovx allergic rats, as was observed in intact allergic rats treated with ICI-182,780. Estradiol increased the number of cells in the BAL of Ovx-allergic rats, whereas progesterone induced an additional reduction. Cells of BAL and bone marrow (BM) of Ovx-allergic rats released elevated amounts of IL-10 and reduced IL-1beta and TNF-alpha. BM cells of Ovx-allergic rats released increased amounts of IL-10 and lower amounts of IL-4. Estradiol treatment of Ovx-allergic rats decreased the release of IL-10 but increased that of IL-4 by BM cells. Estradiol also caused an increased release of IL-1beta and TNF-alpha by BAL cells. Progesterone significantly increased the release of IL-10, IL-1beta, and TNF-alpha by BAL cells and augmented that of IL-4 by BM cells. Degranulation of bronchial mast cells from Ovx rats was reduced after in vitro challenge, an effect reverted by estradiol but not by progesterone. We suggest that the serum estradiol-to-progesterone ratio might drive cellular recruitment, modulating the pulmonary allergy and profile of release of anti-inflammatory or inflammatory cytokines. The existence of such dual hormonal effects suggests that the hormone therapy of asthmatic postmenopausal women and of those suffering of premenstrual asthma should take into account the possibility of worsening the pulmonary conditions.

Hormones play a modulating role in allergic inflammation. An inverse relationship between atopy and diabetes mellitus was reported. The mechanisms regulating this interaction are not completely understood. This study examined whether insulin influences mast cell activation following antigen challenge in rats.The experimental design included alloxan-induced diabetic rats and matching controls. Experiments were performed 30 days after alloxan injection. The animals were sensitised by s.c. injection of ovalbumin (OA) and aluminium hydroxide. OAinduced airway contraction, morphometric analysis of airway mast cells and tissue histamine quantification were evaluated in the isolated main bronchus and intrapulmonary bronchus upon exposure to antigen in vitro.Relative to controls, a reduced contraction to OA was observed in bronchial segments isolated from diabetic rats. This was accompanied by a 50% reduction in the number of degranulated mast cells and in histamine release. A complete recovery of the impaired responses was observed under the influence of insulin.In conclusion, the data suggested that insulin might modulate the controlling of mast cell degranulation; therefore, the early-phase response to antigen provocation, which represents a new insight into a better understanding of the mechanisms, accounted for the decreased risk of asthma among type-1 diabetic patients.

The purpose of this study was twofold: to reveal cellular events associated with the protective role of endogenous annexin A1 (AnxA1) in inflammation and to highlight the potential involvement of members of the formyl peptide receptor (Fpr) family in this process. We found that wild-type, AnxA1-null, and Fpr1-null mice all displayed an intense neutrophil recruitment into the peritoneal cavity as assessed 4 hours after carrageenin injection, and that this recruitment was most pronounced in AnxA1-null mice. In addition, this cell influx could be inhibited by the AnxA1 pharmacophore peptide, Ac2-26, in wild-type, AnxA1-null, and Fpr1-null mice, but was restored when co-treated with the pan-receptor antagonist Boc2. Using the LacZ gene reporter assay, an enhancement of AnxA1 gene promoter activity in extravasated neutrophils was evident in AnxA1-null mice; again this response was reduced after peptide treatment. The lack of functional involvement of Fpr1 prompted us to monitor the structurally related receptor Fpr2. We report, for the first time, the ultrastructural immunocytochemical co-localization of Fpr2 with AnxA1 in neutrophils that migrate into the mesenteric microcirculation and extravasate into the peritoneal fluid. Collectively , these data provide in vivo support to the hypothesis that endogenous AnxA1 is an essential effector of endogenous antiinflammation and provide an ultrastructural indication that this mediator interacts with Fpr2 in murine neutrophils. We believe that these findings could significantly affect the development of novel therapeutics, which are modeled after the anti-migratory actions

BackgroundThe balancing functions of pro/anti-inflammatory mediators of the complex innate responses have been investigated in a variety of experimental inflammatory settings. Annexin-A1 (AnxA1) is one mediator of endogenous anti-inflammation, affording regulation of leukocyte trafficking and activation in many contexts, yet its role in lung pathologies has been scarcely investigated, despite being highly expressed in lung cells. Here we have applied the bleomycin lung fibrosis model to AnxA1 null mice over a 21-day time-course, to monitor potential impact of this mediator on the control of the inflammatory and fibrotic phases.ResultsAnalyses in wild-type mice revealed strict spatial and temporal regulation of the Anxa1 gene, e.g. up-regulation in epithelial cells and infiltrated granulocytes at day 7, followed by augmented protein levels in alveolar macrophages by day 21. Absence of AnxA1 caused increases in: i) the degree of inflammation at day 7; and ii) indexes of fibrosis (assessed by deposition of hydroxyproline in the lung) at day 7 and 21. These alterations in AnxA1 null mice were paralleled by augmented TGF-β1, IFN-γ and TNF-α generation compared to wild-type mice. Finally, treatment of wild type animals with an AnxA1 peptido-mimetic, given prophylactically (from day 0 to 21) or therapeutically (from day 14 onward), ameliorated both signs of inflammation and fibrosis.ConclusionCollectively these data reveal a pathophysiological relevance for endogenous AnxA1 in lung inflammation and, more importantly, fibrosis, and may open new insights for the pharmacological treatment of lung fibrosis.