Turnover of immune complexes in liver

An important homeostatic liver function is to remove and degrade foreign molecules and cells from blood. This function is mediated by endocytosis-receptors expressed on parenchymal and nonparenchymal liver cells. Three important groups of such receptors a re Fc<.gamma.>-receptors (Fc<.gamma.>R), scavenger receptors (SR) and mannose receptors (MR). We have identified a MR, two types of Fc<.gamma.>Rs and two types of SR in rat liver cells (Kupifer cells (KC) and liver endothelial cells (LEC)). The ligands of these receptors are immune complexes, various denatured macromolecules (e.g. oxidized low density lipoproteins) and glycoproteins with terminal mannose, for respectively Fc<.gamma.>R, SR and MR. In the present project we wish (1) to clarify the intracellu lar transport of immune complexes in KC and LEC and to compare this itinerary with that followed by ligands of MR and SR, (2) to obtain information about the mechanisms of downregulation of the F c<.gamma.>R, (3) to identify possible signal molecules and transcription factors which regulate the expression of Fc<.gamma.>R and SR, and (4) to determine the role of the various endocytosis receptors (Fc<.gamma.>R and SR) in phagocytosis in KC. Methods: The studies will be performed with isolated liver cells and cell lines (COS cells, MIDCK cells, J774 cells). The cell lines offer the possibilities of transfecting genes for the receptors to be studies. Intracellular transport of ligands and receptors will be followed by means of confocal and electron microsc opy, and by subcellular fractionation. Phagocytosis will be studied using latex beads coated with IgG or SR and MR ligands. To study intracellular transport from endosomes to lysosomes (whichprobably takes place by fusion between late endosomes and lysoso mes) a cell free system will be employed. To study regulation of receptor expression the promoters of the receptor genes will be subcloned upstream of a reporter gen (luciferase) in J774 cel ls.