The role of endogenous annexin A1 on leukocyte biology

Abstract

Inflammation is the body's innate immune response to the damage caused to its cells and vascularised tissue, either by injury or microbial pathogens. Although these processes cause pain, swelling, redness and an increase in body temperature, inflammation is generally a beneficial salutary response. Since the 1940's glucocorticoids have been widely prescribed in treating inflammatory diseases, e. g. for inflammatory bowel disease and anaphylactic shock hydrocortisone is prescribed, whereas for asthma and rheumatic disease, betametasone and prednisolone are the drugs of choice. During the late 1970's and early 1980's a novel glucocorticoid regulated protein, termed annexin Al, was identified. This protein mediates and shares many of the anti-inflammatory and prostaglandin suppressive properties with glucocorticoids. More recently annexin Al has been shown to be an endogenous ligand for the fMLP receptor, termed the FPR. This thesis questions the fundamental basis of annexin Al leukocyte biology by examining the behaviour of neutrophils and macrophages collected from mice lacking either the protein or its receptor. The major finding in this thesis can be divided into two sections, focusing on the neutrophil activation or the macrophage phagocytosis. Neutrophils from FPR deficient mice could be activated at high concentrations with fMLP, and pre-incubating cells with either the annexin Al mimetic or the FPR antagonist Boc 2 abrogates these effects. Blood neutrophils purified from annexin Al null mice were more susceptible to inflammatory stimuli, causing an excessive increase in cell adhesion molecule expression, chemotaxis and ROS production, compared to littermate (wild type) controls. In contrast neutrophils over expressing this protein exhibited an attenuated degree of activation. Annexin Al null peritoneal macrophages exhibited defects in phagocytosis in a stimulus-specific manner. Annexin Al null macrophages incubated with non-opsonised zymosan, Neisseria or opsonised sheep red blood cells exhibited a grossly impaired uptake of particles. This was further confirmed by electron and confocal microscopy analysis. Furthermore, specific alterations in annexin Al null macrophage plasma 2 membrane CD1lb and F4/80 expression was observed in macrophages lacking this protein. Upon activation these macrophages synthesised an augmented concentration of proinflammatory cytokines. Annexin Al null macrophages were resistant to glucocorticoid inhibition during phagocytosis. These results suggest that the participation of endogenous annexin Al during phagocytosis is critical. In summary, this thesis has investigated for the first time in genetically modified mice the potential effects that the lack of annexin Al may have on specific cellular functions with a major impact on the inflammatory response, finding that indeed this protein exerts a tonic inhibitory action, in a stimulus- and cell-specific fashion, on leukocyte biology.