title: P-glycoprotein (P-gp) is upregulated in peripheral T-cell subsets from solid organ transplant recipients.
abstract: Immunosuppressive agents such as cyclosporine, tacrolimus, sirolimus, and corticosteroids are substrates for the transmembrane multidrug resistance pump P-glycoprotein (P-gp). Experience in oncologyhas suggested that chronic exposure to P-gp substrates induces upregulation of P-gp activity, which could result in resistance to immunosuppressive drugs. The authors investigated P-gp function in CD4+ and CD8+ T cells from the peripheral blood of solid organ transplant recipients (SOTX). Subjects included 14 stable SOTX (10 liver, 4 lung) and 16 healthy controls. Four-color flow cytometry was used to simultaneously measure intracellular concentration of the fluorescent P-gp substrate Rhodamine 123 (Rh123) and surface expression of CD45RO (nominal memory/effector), CD45RA (naive), and either CD4 or CD8. P-glycoprotein function was measured by a dye efflux assay in which activity was inferred from a decrease in Rh123 fluorescence. CD4+ and CD8+ T cells from patients and control subjects eliminated Rh123, and this activity was inhibited by verapamil, a known P-gp substrate. CD8+ T cells had greater P-gp activity than CD4+ cells, and naive and transitional T cells displayed greater activity than memory T cells. Activity was bimodal in CD8+ CD45RO+ T cells, with a subset of these cells expressing the greatest P-gp activity. Patient CD8+ naive and transitional T cells had upregulated P-gp activity compared to control subjects. We conclude that (1) P-gp activityis significantly upregulated in specific T-cell subsets (CD8+/CD45RA+) in the peripheral blood of SOTX, and (2) the bimodal nature of P-gp response in CD8+ T cells complicates analysis of the effect of chronic administration of P-gp substrates to SOTX.
authors.affiliation: Department of Medicine, School of Pharmacy, University of Pittsburgh, Pennsylvania 15213, USA.
authors.forename: V S
authors.initials: VS
authors.lastname: Donnenberg
authors.forename: G J
authors.initials: GJ
authors.lastname: Burckart
authors.forename: B P
authors.initials: BP
authors.lastname: Griffith
authors.forename: A B
authors.initials: AB
authors.lastname: Jain
authors.forename: A
authors.initials: A
authors.lastname: Zeevi
authors.forename: A D
authors.initials: AD
authors.lastname: Berg
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis* / Q000235:genetics; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000378:metabolism; D003430:Cross-Sectional Studies; D005434:Flow Cytometry; D006801:Humans; D066298:In Vitro Techniques; D016377:Organ Transplantation / Q000502:physiology*; D016176:T-Lymphocyte Subsets / Q000378:metabolism*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1