title: Trafficking of liposomal antigen to the trans-Golgi of murine macrophages requires both liposomal lipid and liposomal protein.
abstract: Major histocompatibility complex (MHC) class I molecules found on antigen-presenting cells present peptides derived from cytoplasmic proteins to T cells. In contrast, peptides from exogenous proteins are mostly presented by class II molecules. It has been well established that liposomes can serve as an efficient delivery system for entry of exogenous protein antigens into the MHC class I pathway. Our previous studies utilizing fluorophore-labeled proteins encapsulated in liposomes demonstrated that after phagocytosis of the liposomes by bone marrow-derived macrophages (BMs), the processed peptides were subsequently visualized in the trans-Golgi, while free conalbumin was excluded from the trans-Golgi area. In the present study, we investigated whether liposomal lipids follow the same intracellular route as the liposomal proteins after phagocytosis by BMs. Multilamellar liposomes with different lipid compositions that also contained fluorescent phospholipids (empty liposomes) were incubated with murine BMs. Our results indicate that although empty liposomes were avidly phagocytosed by macrophages, the fluorescent liposomal lipids did not localize to any particular area of the cell but were distributed throughout the cell. In contrast, when a protein was encapsulated in the liposomes, the liposomal lipids were no longer dispersed throughout the cell, but were concentrated and localized in the trans-Golgi area. Furthermore, when the liposomes contained a fluorescent-labeled protein, the fluorescent peptides also localized to the trans-Golgi. These results demonstrate that the combination of both liposomal lipids and liposomal protein is required for Golgi-specific targeting of liposomal antigens. Transport of both liposomal lipids and liposomal proteins to the Golgi complex, a major subcellular organelle in the passage of MHC class I molecules, might explain why antigens encapsulated in liposomes readily induce cytotoxic T lymphocytes.
authors.affiliation: Department of Membrane Biochemistry, Walter Reed Army Institute of Research, Washington, DC, 20307-5100, USA. Dr._Mangala_Rao@wrsmtp-ccmail.army.mil
authors.forename: M
authors.initials: M
authors.lastname: Rao
authors.forename: S W
authors.initials: SW
authors.lastname: Rothwell
authors.forename: N M
authors.initials: NM
authors.lastname: Wassef
authors.forename: A B
authors.initials: AB
authors.lastname: Koolwal
authors.forename: C R
authors.initials: CR
authors.lastname: Alving
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000378:metabolism; D000941:Antigens / Q000276:immunology / Q000378:metabolism; D001692:Biological Transport; D001854:Bone Marrow Cells; D002478:Cells, Cultured; D003207:Conalbumin / Q000493:pharmacokinetics*; D003593:Cytoplasm / Q000378:metabolism; D005227:Fatty Acids / Q000502:physiology; D005260:Female; D005456:Fluorescent Dyes / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism*; D008081:Liposomes / Q000493:pharmacokinetics*; D008264:Macrophages / Q000378:metabolism*; D008563:Membrane Lipids / Q000493:pharmacokinetics*; D051379:Mice; D008815:Mice, Inbred Strains; D010587:Phagocytosis; D013997:Time Factors
chemical_list: D000941:Antigens; D005227:Fatty Acids; D005456:Fluorescent Dyes; D008081:Liposomes; D008563:Membrane Lipids; D003207:Conalbumin