Regulated recruitment of MHC class II and costimulatory molecules to lipid rafts in dendritic cells.

T cell activation has long been associated with the partitioning of Ag receptors and associated molecules to lipid microdomains. We now show that dendritic cells (DCs) also accomplish the selective recruitment to lipid rafts of molecules critical for Ag presentation. Using mouse bone marrow-derived DCs, we demonstrate that MHC class II molecules become substantially localized to rafts upon DC maturation. Even more striking is the fact that CD86 is recruited to rafts upon T cell-DC interaction. Recruitment is Ag dependent and requires CD28 on T cells. Despite the regulated recruitment of MHC class II and CD86 to rafts, unlike the counter-receptors in T cells, DCs do not polarize these molecules to sites of DC-T cell contact. This difference may reflect the necessity for DCs to interact with multiple T cells simultaneously and emphasizes that the biochemical and morphological correlates of lipid rafts are not necessarily equivalent.