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Purpose of review Lipid rafts on monocytes/macrophages provide a dynamic microenvironment for an integrated lipopolysaccharide receptor (CD14)-dependent clustering of a set of receptors involved in innate immunity and clearance of atherogenic lipoproteins. The purpose of this review is to summarize the recent advances in our understanding of CD14-dependent receptor clustering and its relevance in atherogenesis. Recent findings Upon binding of various ligands, CD14 as a multiligand pattern recognition receptor induces specific coassembly of additional receptors present on circulating monocytes. Summary The composition of the receptor cluster and thus the associated signalling pathways defines a ligand specific cellular response, linking endogenous and exogenous host defense to a common recognition platform in rafts.

ATP-binding cassette (ABC) transporters constitute a group of evolutionary highly conserved cellular transmembrane transport proteins. Recent work has implicated ABC transporters in cellular transmembrane lipid transport and hereditary diseases have been causatively linked to defective ABC transporters translocating lipid compounds. The emerging concept that a defined subset of ABC transporters is intimately involved in cellular lipid trafficking has recently been substantiated convincingly by the finding that ABCA1 plays a central role in the regulation of HDL metabolism and macrophage targeting to the RES or the vascular wall. Differentiation dependent expression of a large number of ABC transporters in monocytes/macrophages and their regulation by sterol flux render these transporter molecules potentially critical players in atherogenesis and other chronic inflammatory diseases.

Integrins are in physical association and functional cooperation with other membrane proteins that include receptors with scavenger functions, glycosyl-phosphatidylinositol-linked receptors, the family of integrin associated multimembrane spanning signalling proteins and possibly other less characterized proteins with a coupling or signalling function. Monocyte adhesion, migration and differentiation to phagocytically active scavenger cells are directly coupled processes, involving integrins as common transducers for a panel of integrin-linked specific receptors, which assemble a master cluster to coordinate adhesion, migration, scavenging and associated metabolic pathways of the lysosomal and secretory route, and also processes involved in host response. As macrophages represent highly heterogeneous cells that have major phenotypical and functional differences associated with specific patterns of integrin expression, the functional cooperation of integrins with scavenger receptors has to be related to specialized subsets of monocytes and macrophages as well as to ligand specific effects which mediate receptor coupling.