title: Human CD8+ T cells do not require the polarization of lipid rafts for activation and proliferation.
abstract: Lipid rafts are important signaling platforms in T cells. Little is known about their properties in human CD8(+) T cells. We studied polarization of lipid rafts by digital immunofluorescence microscopy in primary human T cells, using beads coated with anti-CD3 and anti-CD28 mAbs (CD3/28 beads). Unlike CD4(+) T cells, CD8(+) T cells did not polarize lipid rafts when stimulated with CD3/28 beads, when the anti-CD28 antibody was substituted with B7.2Ig, or if an anti-CD8 antibody was added to the CD3/28 beads. This phenomenon was also observed in human antigen-specific CD8(+) T cells. On stimulation with CD3/28 beads, the T cell antigen receptor clustered at the cell/bead contact area in both CD4(+) and CD8(+) T cells. Examination of lipid rafts isolated by sucrose density gradient centrifugation revealed the constitutive expression of p(56)Lck in the raft fractions of unstimulated CD8(+) T cells, whereas p(56)Lck was recruited to the raft fraction of CD4(+) T cells only after stimulation with CD3/28 beads. Stimulation with CD3/28 beads induced marked calcium flux, recruitment of PKC-theta and F-actin to the cell/bead contact site, and similar proliferation patterns in CD4(+) and CD8(+) T cells. Thus, polarization of lipid rafts is not essential for early signal transduction events or proliferation of human CD8(+) lymphocytes. It is possible that the lower stringency of CD8(+) T cell activation obviates a requirement for raft polarization.
authors.affiliation: Division of Rheumatology, Department of Pediatrics, Children's Hospital of Philadelphia, PA 19104, USA.
authors.forename: Birgit
authors.initials: B
authors.lastname: Kovacs
authors.forename: Marcela V
authors.initials: MV
authors.lastname: Maus
authors.forename: James L
authors.initials: JL
authors.lastname: Riley
authors.forename: Geo S
authors.initials: GS
authors.lastname: Derimanov
authors.forename: Gary A
authors.initials: GA
authors.lastname: Koretzky
authors.forename: Carl H
authors.initials: CH
authors.lastname: June
authors.forename: Terri H
authors.initials: TH
authors.lastname: Finkel
mesh_terms: D015703:Antigens, CD / Q000276:immunology; D015704:CD4 Antigens / Q000276:immunology; D016827:CD8 Antigens / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology* / Q000502:physiology; D002458:Cell Fractionation; D016764:Cell Polarity / Q000502:physiology*; D002469:Cell Separation / Q000379:methods; D002499:Centrifugation, Density Gradient; D006801:Humans; D008213:Lymphocyte Activation; D021962:Membrane Microdomains / Q000502:physiology* / Q000648:ultrastructure; D008856:Microscopy, Fluorescence; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology
chemical_list: D015703:Antigens, CD; D015704:CD4 Antigens; D016827:CD8 Antigens; D011948:Receptors, Antigen, T-Cell