Transforming growth factor β-producing Foxp3+CD8+CD25+ T cells induced by iris pigment epithelial cells display regulatory phenotype and acquire regulatory functions
Introduction
Ocular immune privilege protects the delicate internal structures of the eye from the blinding consequences of innate and adaptive immune inflammation (Niederkorn, 2002, Streilein, 2003). One of the factors responsible for creating ocular immune privilege is the pigment-containing epithelium of the iris, the ciliary body, and the neural retina. The ocular pigment epithelial (PE) cells contribute to the integrity of the blood-ocular barrier, and thereby secure immune privilege within the eye. T cells that encounter PE cells in vitro are inhibited from undergoing TCR-triggered activation (Sugita and Streilein, 2003, Sugita et al., 2004) and are converted into regulators (Yoshida et al., 2000). We recently showed that iris PE (IPE) cells produce B7 costimulatory molecules and membrane-bound transforming growth factor β (TGFβ) that is delivered to CD8+ T regulators (CD8+ IPE-induced Tregs) (Sugita et al., 2006a). The CD8+ IPE-induced Tregs engage CTLA-4+ bystander T cells by B7 interactions for targeted delivery of membrane-bound TGFβ. Importantly, IPE-induced Tregs express their own B7 and membrane-bound TGFβ in order to suppress bystander T cells. In addition, we showed that thrombospondin-1 (TSP-1) produced by IPE and the IPE-induced Tregs binds and activates TGFβ (Futagami et al., 2007). The TSP-1 is essential to the induction of eye-specific Tregs and the subsequent suppression of bystander T cells in vitro. The CD8+ T cells that encounter ocular PE express immunoregulatory molecules to achieve suppression of T-cell activation.
CD4+CD25+ T regulatory cells have emerged as a unique population of suppressor T cells that maintain peripheral immune tolerance (Sakaguchi, 2000, Shevach, 2000). These regulatory T cells develop spontaneously in the thymus and suppress T- and B-cell activation in vitro by a cell contact-dependent mechanism (Mason and Powrie, 1998, Nakamura et al., 2001, Suri-Payer et al., 1998). More importantly, mice depleted of CD4+CD25+ T cells are vulnerable to a variety of autoimmune diseases (Maloy and Powrie, 2001, McHugh and Shevach, 2002, Salomon et al., 2000). Mice that are thymectomized on their 3rd postnatal day (a procedure that depletes their CD4+CD25+ T-cell population) develop immune-mediated inflammation in a variety of organs, including the uveal tract of the eye (Asano et al., 1996, Takeuchi et al., 1998). This finding raises some critical questions: (I) can the ocular PE cells induce regulatory T cells that express CD25 molecules, (II) can the PE-induced Tregs be induced or converted from peripheral naturally arising CD25+ Tregs, and (III) if this latter situation occurs, which molecules and/or cytokines are responsible for the conversion?
Because the T cells exposed to ocular PE (PE-induced Tregs) suppress bystander effecter T cells, we questioned whether the PE-induced Tregs are related to, or perhaps even derived from, the natural CD25+ T-cell population. We designed a series of experiments to examine this possibility. We found that T cells exposed to IPE proliferate due to TCR-trigged activation via costimulatory interactions. The T cells exposed to IPE are converted into CD25+ T regulatory cells. The Tregs that emerge in the presence of IPE are not necessarily derived from naturally arising CD25+ Tregs. Instead, IPE-induced Tregs can arise independently from T cells that are CD25− precursors. These eye-derived CD25+ Tregs greatly express Foxp3 transcripts through TGFβ–TGFβ receptor interactions, and produce immunoregulatory cytokines.
Section snippets
Mice
Adult C57BL/6 mice, purchased from CLEA Japan Inc. (Tokyo, Japan), were used as donors of lymphoid cells and ocular PE. Mice of the C57BL/6 background with disrupted CD28 genes were purchased from Jackson Laboratories. Drs. Philip J. Lucas and Ronald E. Gress (National Cancer Institute, Bethesda, MD) kindly provided dominant negative TGFβ type II receptor (TGFβ RII) transgenic mice (Lucas et al., 2000). Dr. James P. Allison (Univ. California at Berkeley) kindly provided C57BL/6 background CTLA-4
IPE cells promote T-cell proliferation in vitro after 24-h culture
We first examined whether cultured IPE cells suppress or promote T-cell activation. To assess the influence of IPE on T-cell proliferation, different types of T-cell assays were performed. The initial results showed that primary cultured IPE cells promote T-cell proliferation after 24-h culture with a low concentration (0.01–0.1 μg/ml) of anti-CD3 antibodies (Fig. 1A). IPE also profoundly promoted the proliferation of the CD8+ population induced by anti-CD3 after 24-h culture, whereas IPE did
Discussion
In this study, we showed that iris pigment epithelium converts CD8+ T cells into CD25+ Tregs by inducing the transcription factor Foxp3. The CD8+CD25+ IPE-induced Tregs fully suppress bystander T cells in vitro. We suspect that the peripherally arising CD25+ Tregs that develop in the presence of ocular resident cells/tissues protect the delicate internal structures of the eye from intraocular inflammation. Mice possess a population of native T regulators that express surface markers for CD4 and
Acknowledgments
The authors thank Professor J. Wayne Streilein of the Schepens Eye Research Institute for many useful ideas that contributed to this project. Dr. Streilein passed away on March 15, 2004. We greatly appreciate the expert technical assistance of Ms. Tomoko Yoshida and Mrs. Ikuyo Yamamoto.
References (39)
- et al.
Control of immune pathology by regulatory T cells
Curr. Opin. Immunol
(1998) Regulatory T cells: key controllers of immunologic self-tolerance
Cell
(2000)- et al.
B7/CD28 costimulation is essential for the homeostasis of the CD4+CD25+ immunoregulatory T cells that control autoimmune diabetes
Immunity
(2000) - et al.
Retinal and ciliary body pigment epithelium suppress activation of T lymphocytes via transforming growth factor beta
Exp. Eye. Res.
(2006) - et al.
Interleukin-2 receptor alpha chain regulates the size and content of the peripheral lymphoid compartment
Immunity
(1995) - et al.
Autoimmune disease as a consequence of developmental abnormality of a T cell subpopulation
J. Exp. Med
(1996) - et al.
Engagement of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) induces transforming growth factor beta (TGF-beta) production by murine CD4+ T cells
J. Exp. Med
(1998) - et al.
Conversion of peripheral CD4+CD25− naive T cells to CD4+CD25+ regulatory T cells by TGF-beta induction of transcription factor Foxp3
J. Exp. Med
(2003) - et al.
Foxp3 programs the development and function of CD4+CD25+ regulatory T cells
Nat. Immunol
(2003) - et al.
Role of thrombospondin-1 in T cell response to ocular pigment epithelial cells
J. Immunol
(2007)
CD4+ T-cell subset inhibits antigen-specific T-cell responses and prevents colitis
Nature
Control of regulatory T cell development by the transcription factor Foxp3
Science
Identification and functional characterization of human CD4+CD25+ T cells with regulatory properties isolated from peripheral blood
J. Exp. Med
The TGF-beta superfamily: new members, new receptors, and new genetic tests of function in different organisms
Genes Dev.
Human CD25+CD4+ T suppressor cell clones produce transforming growth factor beta, but not interleukin 10, and are distinct from type 1 T regulatory cells
J. Exp. Med
Spontaneous elaboration of transforming growth factor beta suppresses host defense against bacterial infection in autoimmune MRL/lpr mice
J. Exp. Med
Disruption of T cell homeostasis in mice expressing a T cell-specific dominant negative transforming growth factor beta II receptor
J. Exp. Med
Regulatory T cells in the control of immune pathology
Nat. Immunol
Cutting edge: depletion of CD4+CD25+ regulatory T cells is necessary, but not sufficient, for induction of organ-specific autoimmune disease
J. Immunol
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