TGF-beta-mediated suppression by CD4+CD25+ T cells is facilitated by CTLA-4 signaling.
CD4+CD25+ T cells play a pivotal role in immunological homeostasis by their capacity to exert immunosuppressive activity. However, the mechanism by which these cells function is still a subject for debate. We previously reported that surface (membrane) TGF-beta produced by CD4+CD25+ T cells was an effector molecule mediating suppressor function. We now support this finding by imaging surface TGF-beta on Foxp3+CD4+CD25+ T cells in confocal fluorescence microscopy. Then, using a TGF-beta-sensitive mink lung epithelial cell (luciferase) reporter system, we show that surface TGF-beta can be activated to signal upon cell-cell contact. Moreover, if such TGF-beta signaling is blocked in an in vitro assay of CD4+CD25+ T cell suppression by a specific inhibitor of TGF-betaRI, suppressor function is also blocked. Finally, we address the role of CTLA-4 in CD4+CD25+ T cell suppression, showing first that whereas anti-CTLA-4 does not block in vitro suppressor function, it does complement the blocking activity of anti-TGF-beta. We then show with confocal fluorescence microscopy that incubation of CD4+CD25+ T cells with anti-CTLA-4- and rB7-1/Fc-coated beads results in accumulation of TGF-beta at the cell-bead contact site. This suggests that CTLA-4 signaling facilitates TGF-beta-mediated suppression by intensifying the TGF-beta signal at the point of suppressor cell-target cell interaction.
Oida
Takatoku
T
Mucosal Immunity Section, Laboratory of Clinical Investigation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 10 Center Drive, Bethesda, MD 20892, USA.
Xu
Lili
L
Weiner
Howard L
HL
Kitani
Atsushi
A
Strober
Warren
W
D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000502:physiology*; D060908:CTLA-4 Antigen; D002460:Cell Line; D007108:Immune Tolerance; D051379:Mice; D008805:Mice, Inbred A; D015398:Signal Transduction / Q000276:immunology*; D050378:T-Lymphocytes, Regulatory / Q000276:immunology*; D016212:Transforming Growth Factor beta / Q000096:biosynthesis / Q000502:physiology*
D015703:Antigens, CD; D000943:Antigens, Differentiation; D060908:CTLA-4 Antigen; C556707:Ctla4 protein, mouse; D016212:Transforming Growth Factor beta