title: Antigen recognition induces phosphatidylserine exposure on the cell surface of human CD8+ T cells.
abstract: In eukaryotic cells the phospholipid phosphatidylserine (PS) is restricted to the inner plasma-membrane leaflet. This lipid asymmetry, which is maintained by the concerted action of phospholipid transport proteins, is mainly lost during apoptosis. Here, we demonstrate that primary human CD8+ cytotoxic T lymphocytes (CTLs) expose PS on T-cell receptor (TCR)-mediated antigen (Ag) recognition. In contrast to PS externalization on apoptotic cells, activation-induced PS exposure is less pronounced and reversible. Fluorescence microscopic analysis revealed that PS is distributed nonhomogenously over the plasma membrane and concentrated in membrane lipid raft domains at the immunologic synapse. By studying the activity of PS transport proteins using a fluorescence-labeled PS analogue, we found that activation of CTLs inhibited the flippase-mediated inward-directed PS transport without affecting the outward transport. Shielding of exposed PS by annexin V protein during Ag recognition diminished cytokine secretion, activation, and cell-to-cell clustering of Ag-specific CTLs. In summary, our data demonstrate for the first time that externalized PS on Ag-stimulated CTLs is linked to T-cell activation and probably involved in cell-to-cell contact formation at the immunologic synapse.
authors.affiliation: Department of Hematology and Oncology, University of Regensburg, Franz-Josef-Strauss-Allee 11, D-93042 Regensburg, Germany. karin.fischer@klinik.uni-regensburg.de
authors.forename: Karin
authors.initials: K
authors.lastname: Fischer
authors.forename: Simon
authors.initials: S
authors.lastname: Voelkl
authors.forename: Jana
authors.initials: J
authors.lastname: Berger
authors.forename: Reinhard
authors.initials: R
authors.lastname: Andreesen
authors.forename: Thomas
authors.initials: T
authors.lastname: Pomorski
authors.forename: Andreas
authors.initials: A
authors.lastname: Mackensen
mesh_terms: D017304:Annexin A5 / Q000276:immunology; D017951:Antigen Presentation / Q000276:immunology*; D000941:Antigens / Q000276:immunology; D000951:Antigens, Neoplasm / Q000276:immunology; D017209:Apoptosis / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology*; D002450:Cell Communication / Q000276:immunology; D002460:Cell Line; D016207:Cytokines / Q000276:immunology; D006801:Humans; D008213:Lymphocyte Activation / Q000276:immunology*; D058965:MART-1 Antigen; D021962:Membrane Microdomains / Q000276:immunology; D009363:Neoplasm Proteins / Q000276:immunology; D010718:Phosphatidylserines / Q000276:immunology*; D021381:Protein Transport / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000276:immunology*
chemical_list: D017304:Annexin A5; D000941:Antigens; D000951:Antigens, Neoplasm; D016207:Cytokines; D058965:MART-1 Antigen; C548667:MLANA protein, human; D009363:Neoplasm Proteins; D010718:Phosphatidylserines; D011948:Receptors, Antigen, T-Cell