Revisiting the role of IL-2 in autoimmunity

Department of Pathology, University of California, San Francisco, CA 94143-0511, USA.
European Journal of Immunology (Impact Factor: 4.03). 06/2010; 40(6):1538-40. DOI: 10.1002/eji.201040617
Source: PubMed


IL-2 was discovered as a T-cell growth factor that promoted T-cell-dependent immune responses; however, more recent studies suggest that the essential role of IL-2 is to maintain functional Treg and thus control immune responses. These results are leading to new ideas about the potential of IL-2 as a therapeutic strategy in autoimmune diseases. In this issue of the European Journal of Immunology, a study further examines the role of IL-2 in immune regulation and shows for the first time that IL-2 complexes can ameliorate autoantibody-mediated autoimmunity. This commentary examines the current findings in relation to what we already know about IL-2 complexes.

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    • "Expression of IL-2 is tightly regulated in naïve CD4 T cells and requires an extensive period of antigen stimulation [3]. Most activated CD4 T cells die after 5–7 days of stimulation by activation induced cell death (AICD), and IL-2 also plays a critical role in AICD to induce cell death [4]. Moreover, IL-2 is essential for functional naturally arising regulatory T cells (nTregs) [5] [6]. "
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    ABSTRACT: IL-2 is a growth factor for activated T cells and is required for maintenance of naturally arising regulatory T cells (nTregs). Mice defective in IL-2/IL-2 receptor signaling pathways have impaired nTregs and suffer from lymphoproliferative disorders, suggesting that IL-2 is present and functional in healthy animals. However, the cellular source of IL-2 is currently unknown. To determine which cells produce IL-2 in healthy animals, we established mice carrying cre gene knock in at the il-2 locus (termed IL-2(cre)). When IL-2(cre) mice were crossed with EGFP reporter mice, EGFP was exclusively expressed by a fraction of CD4 T cells present in both lymphoid and non-lymphoid tissues. Live imaging of IL-2(cre) mice that carry the luciferase reporter showed concentrated localization of luciferase(+) cells in Peyer's patches. These cells were not observed in new born mice but appeared within 3days after birth. Reduction of antigen receptor repertoire by transgene expression reduced their number, indicating that recognition of environmental antigens is necessary for generation of these IL-2 producers in healthy animals. A substantial fraction of EGFP(+) cells also produce IL-10 and IFN-γ, a characteristic profile of type 1 regulatory T cells (Tr1). The data suggest that a group of Tr1 cells have addition roles in immune homeostasis by producing IL-2 along with other cytokines and help maintaining Tregs.
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    • "It has been suggested that Tregs have the capacity to specifically target and suppress effector T cells, such as Th1, Th2 and Th17 cells [19] [20]. To evaluate whether the IL-2 complex expanded Tregs inhibit a specific T cell subset in vivo during initiation of atherosclerosis , splenocytes were stained for the transcription factors T-bet, GATA-3, and RORt, which control the differentiation of Th0 cells into Th1, Th2 and Th17 cells, respectively. "
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    ABSTRACT: Regulatory T cells (Tregs) play an important role in the regulation of T cell-mediated immune responses through suppression of T cell proliferation and cytokine production. In atherosclerosis, a chronic autoimmune-like disease, an imbalance between pro-inflammatory cells (Th1/Th2) and anti-inflammatory cells (Tregs) exists. Therefore, increased Treg numbers may be beneficial for patients suffering from atherosclerosis. In the present study, we determined the effect of a vast expansion of Tregs on the initiation and regression of well-established lesions. For in vivo Treg expansion, LDL receptor deficient (LDLr(-/-)) mice received repeated intraperitoneal injections of a complex of IL-2 and anti-IL-2 mAb. This resulted in a 10-fold increase in CD4(+)CD25(hi)Foxp3(+) T cells, which potently suppressed effector T cells ex vivo. During initial atherosclerosis, IL-2 complex treatment of LDLr(-/-) mice fed a Western-type diet reduced atherosclerotic lesion formation by 39%. The effect on pre-existing lesions was assessed by combining IL-2 complex treatment with a vigorous lowering of blood lipid levels in LDLr(-/-) mice. This did not induce regression of atherosclerosis, but significantly enhanced lesion stability. Our data show differential roles for Tregs during atherosclerosis: Tregs suppress inflammatory responses and attenuate initial atherosclerosis development, while during regression Tregs can improve stabilization of the atherosclerotic lesions.
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