Signal transduction in macrophages. Intracellular pathways activated by microbial constituents

Abstract: Macrophages play an essential role in the defense against infection by phagocytosis and by production of inflammatory mediators. Such mediators are TNF? and eicosanoids. Many microbial agents elicit arachidonate release in macrophages that lead to the formation of eicosanoids. This thesis is based on studies performed with the use of microbial constituents which induce arachidonate release or/and TNF? production. Whole gram-positive bacteria S.aureus, the bacterial products LPS and peptidoglycan, the yeast preparation zymosan and ?-glucan were used to stimulate the cells. The main focus has been to elucidate the potential role of the non-receptor tyrosine kinases from the Src family (SFK) and the Tec kinase Btk. in signaling pathways induced by microbial constituents. SFK are important in bacteria and yeast induced arachidonate release and these studies bring forward that SFK has a pivotal role in acting proximally of several known members of the signaling like, ERK, p38 and PLC?2. Btk is also observed to be a part signaling pathway downstream of SFK. Differences were detected between bacteria and zymosan elicted responses, probably due to use of different receptors. Zymosan can bind to several receptors and our results suggest that zymosan-induced arachidonate release is mediated by the ?-glucan receptor dectin-1. Furthermore we show that the adaptor protein gab-2 is affected by ?-glucan and zymosan stimulation, indicating a role in dectin-1 signaling. SFK are also seen to be involved in TNF? production induced by microbial constituents, but their mode of action is still unknown. In summery this thesis has contributed to an increased understanding of the role of SFK in eicosanoid and TNF? production in macrophages. Furthermore has we contributed to knowledge about the signaling pathway resulting in arachidonate release.