Pro- and Anti-inflammatory Regulation of β2 Integrin Signalling in Human Neutrophils

The body is under constant attack from pathogens trying to slip by our immune defence. If the barrier is breached, invading pathogens enter the tissues and cause inflammation. During this process neutrophils, constituting the first line of defence, leave the bloodstream and seek out and kill the invading pathogens. The mechanisms leading to activation of receptors on neutrophils must be closely orchestrated. Proand anti-inflammatory substances can influence the outcome of the inflammation process by affecting the involved players. If not well balanced, inflammatory diseases, such as atherosclerosis and rheumatoid arthritis, can be the outcome. The aim of this thesis was to elucidate the effect of pro(fMLP, Leukotriene B4, and Interleukin-8) and anti(lipoxins, aspirin and statins) inflammatory substances on the β2 integrins, mediating adhesion of neutrophils both under “normal” conditions and during coronary artery disease. More specifically, the effect of these substances on the β2 integrins were studied in regard to: i) the activity (i.e. affinity and avidity) of β2 integrins, ii) the signalling capacity of β2 integrins (i.e. detected as release of arachidonic acid, and the production of reactive oxygen species, and iii) the signal transduction mediated by the β2 integrins (i.e. phosphorylation of Pyk2). The pro-inflammatory substances belong to the family of chemoattractants that induces transmigration and chemotaxis. A hierarchy exists between the different family members; the end-target chemoattractants (e.g. fMLP) being more potent than intermediary chemoattractants (e.g. IL-8 and LTBB4). It was found that intermediary chemoattractants regulate β2 integrins by mainly affecting the avidity of β2 integrins. End-target chemoattractants on the other hand, affected the β2 integrins by increasing the avidity and the affinity, as well as their signalling capacity. The anti-inflammatory substances used in this study were the exogenous aspirin and statins, and the endogenous lipoxins. In the presence of aspirin, stable analogues of lipoxin (i.e. epilipoxins) are formed in a trans-cellular process. Lipoxin inhibited the signalling capacity of β2