title: Kinetics and activation requirements of contact-dependent immune suppression by human regulatory T cells.
abstract: Naturally occurring regulatory T cells (Tregs) maintain self tolerance by dominant suppression of potentially self-reactive T cells in peripheral tissues. However, the activation requirements, the temporal aspects of the suppressive activity, and mode of action of human Tregs are subjects of controversy. In this study, we show that Tregs display significant variability in the suppressive activity ex vivo as 54% of healthy blood donors examined had fully suppressive Tregs spontaneously, whereas in the remaining donors, anti-CD3/CD2/CD28 stimulation was required for Treg suppressive activity. Furthermore, anti-CD3/CD2/CD28 stimulation for 6 h and subsequent fixation in paraformaldehyde rendered the Tregs fully suppressive in all donors. The fixation-resistant suppressive activity of Tregs operated in a contact-dependent manner that was not dependent on APCs, but could be fully obliterated by trypsin treatment, indicating that a cell surface protein is directly involved. By add-back of active, fixed Tregs at different time points after activation of responding T cells, the responder cells were susceptible to Treg-mediated immune suppression up to 24 h after stimulation. This defines a time window in which effector T cells are susceptible to Treg-mediated immune suppression. Lastly, we examined the effect of a set of signaling inhibitors that perturb effector T cell activation and found that none of the examined inhibitors affected Treg activation, indicating pathway redundancy or that Treg activation proceeds by signaling mechanisms distinct from those of effector T cells.
authors.affiliation: Centre for Molecular Medicine Norway, Nordic European Molecular Biology Laboratory Partnership, University of Oslo, N-0318 Oslo, Norway.
authors.forename: Morten
authors.initials: M
authors.lastname: Hagness
authors.forename: Karen
authors.initials: K
authors.lastname: Henjum
authors.forename: Johannes
authors.initials: J
authors.lastname: Landskron
authors.forename: Kristoffer Watten
authors.initials: KW
authors.lastname: Brudvik
authors.forename: Bjørn Atle
authors.initials: BA
authors.lastname: Bjørnbeth
authors.forename: Aksel
authors.initials: A
authors.lastname: Foss
authors.forename: Kjetil
authors.initials: K
authors.lastname: Taskén
authors.forename: Einar Martin
authors.initials: EM
authors.lastname: Aandahl
mesh_terms: D001782:Blood Donors / Q000145:classification; D015704:CD4 Antigens / Q000096:biosynthesis; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D002450:Cell Communication / Q000235:genetics / Q000276:immunology*; D049109:Cell Proliferation; D002478:Cells, Cultured; D018920:Coculture Techniques; D016207:Cytokines / Q000096:biosynthesis; D006801:Humans; D007108:Immune Tolerance / Q000235:genetics; D053645:Interleukin-2 Receptor alpha Subunit / Q000096:biosynthesis; D053699:Interleukin-7 Receptor alpha Subunit / Q000172:deficiency; D008213:Lymphocyte Activation / Q000276:immunology*; D011948:Receptors, Antigen, T-Cell / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D050378:T-Lymphocytes, Regulatory / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D014357:Trypsin / Q000494:pharmacology
chemical_list: D015704:CD4 Antigens; D016207:Cytokines; D053645:Interleukin-2 Receptor alpha Subunit; D053699:Interleukin-7 Receptor alpha Subunit; D011948:Receptors, Antigen, T-Cell; D014357:Trypsin