The 37-kDa protein annexin 1 (Anx-1; lipocortin 1) has been implicated in the regulation of phagocytosis, cell signaling, and proliferation and is postulated to be a mediator of glucocorticoid action in inflammation and in the control of anterior pituitary hormone release. Here, we report that mice lacking the Anx-1 gene exhibit a complex phenotype that includes an altered expression of other annexins as well as of COX-2 and cPLA2. In carrageenin- or zymosan-induced inflammation, Anx-1-/- mice exhibit an exaggerated response to the stimuli characterized by an increase in leukocyte emigration and IL-1beta generation and a partial or complete resistance to the antiinflammatory effects of glucocorticoids. Anx-1-/- polymorphonuclear leucocytes exhibited increased spontaneous migratory behavior in vivo whereas in vitro, leukocytes from Anx-1-/- mice had reduced cell surface CD 11b (MAC-1) but enhanced CD62L (L-selectin) expression and Anx-1-/- macrophages exhibited anomalies in phagocytosis. There are also gender differences in activated leukocyte behavior in the Anx-1-/- mice that are not seen in the wild-type animals, suggesting an interaction between sex hormones and inflammation in Anx-1-/- animals.

The human formyl-peptide receptor (FPR)-2 is a G protein-coupled receptor that transduces signals from lipoxin A4, annexin A1, and serum amyloid A (SAA) to regulate inflammation. In this study, we report the creation of a novel mouse colony in which the murine FprL1 FPR2 homologue, Fpr2, has been deleted and describe its use to explore the biology of this receptor. Deletion of murine fpr2 was verified by Southern blot analysis and PCR, and the functional absence of the G protein-coupled receptor was confirmed by radioligand binding assays. In vitro, Fpr2−/− macrophages had a diminished response to formyl-Met-Leu-Phe itself and did not respond to SAA-induced chemotaxis. ERK phosphorylation triggered by SAA was unchanged, but that induced by the annexin A1-derived peptide Ac2–26 or other Fpr2 ligands, such as W-peptide and compound 43, was attenuated markedly. In vivo, the antimigratory properties of compound 43, lipoxin A4, annexin A1, and dexamethasone were reduced notably in Fpr2−/− mice compared with those in wild-type littermates. In contrast, SAA stimulated neutrophil recruitment, but the promigratory effect was lost following Fpr2 deletion. Inflammation was more marked in Fpr2−/− mice, with a pronounced increase in cell adherence and emigration in the mesenteric microcirculation after an ischemia–reperfusion insult and an augmented acute response to carrageenan-induced paw edema, compared with that in wild-type controls. Finally, Fpr2−/− mice exhibited higher sensitivity to arthrogenic serum and were completely unable to resolve this chronic pathology. We conclude that Fpr2 is an anti-inflammatory receptor that serves varied regulatory functions during the host defense response. These data support the development of Fpr2 agonists as novel anti-inflammatory therapeutics.

Polymorphonuclear leukocyte (PMN) migration into sites of inflammation is fundamental to the host defense response. Activation of endothelial cells and PMNs increases the expression or activation of adhesion molecules, culminating in rolling and subsequent adherence of these cells to the vascular wall. Further activation of adherent PMNs, possibly by endothelial cell ligands, leads, within a few minutes, to extravasation itself. This process is not clearly understood, but adhesion molecules or related proteins, as well as endogenous chemokines, may play an important role. The anti-inflammatory glucocorticoids delay extravasation, which implies that an inhibitory regulatory system exists. Resting PMNs contain abundant cytoplasmic lipocortin 1 (LC1, also called annexin I)', and the activity profile of this protein suggests that it could reduce PMN responsiveness. To investigate this we have assessed neutrophil transmigration both in vivo and in vitro and examined the content and subcellular distribution of LC1 in PMNs by fluorescence-activated cell-sorting (FACS) analysis, western blotting and confocal microscopy. We report that LC1 is mobilized and externalized following PMN adhesion to endothelial monolayers in vitro or to venular endothelium in vivo and that the end point of this process is a negative regulation of PMN transendothelial passage.

Objective. Annexin 1 (Anx-1) is a putative mediator of the antiinflammatory actions of glucocorticoids (GCs). This study investigated the role of Anx-1 in experimental arthritis and in GC-mediated inhibition of inflammation, using antigen-induced arthritis (AIA) in Anx-1 knockout (Anx-1 ؊/؊ ) mice. Methods. Arthritis was induced by intraarticular injection of methylated BSA (mBSA) in mice preimmunized with mBSA. Disease was assessed after 7 days by histologic examination of the knee joints. Serum levels of anti-mBSA IgG were determined by enzyme-linked immunosorbent assay. Cytokine messenger RNA (mRNA) expression was detected by real-time polymerase chain reaction.Results. A significant exacerbation of arthritis was observed in the Anx-1 ؊/؊ mice compared with wild-type (WT) mice. This was associated with increased mRNA expression of synovial interleukin-1␤, tumor necrosis factor ␣, interleukin-6, and macrophage migration inhibitory factor. Dexamethasone significantly reduced the histologic severity of synovitis and bone damage in the WT mice, but exerted no inhibitory effects in the Anx-1 ؊/؊ mice, and also significantly reduced the serum levels of anti-mBSA IgG and the numbers of peripheral blood neutrophils and lymphocytes in WT mice, but had no such effect in Anx-1Conclusion. Anx-1 exerts endogenous antiinflammatory effects on AIA via the regulation of cytokine gene expression, and also mediates the antiinflammatory actions of dexamethasone in AIA.