JS Bromberg, G Lal, B Burrell, N Yin, Y Nakayama, J Xu, Y Ding

Departments of Microbiology and Immunology and Surgery, and the Center for Vascular and Inflammatory Disease, University of Maryland School of Medicine, Baltimore, MD USA 21201.

CD4+CD25+Foxp3+ Treg are important regulators for virtually all immune responses, and are key elements for establishing and maintaining antigen specific tolerance. We have established a number of important principles of Treg, revealing that during tolerization, naïve T cells migrate to LN, where they are stimulated in the cortical area by specific alloantigen presenting pDC, next to the abluminal surface of the HEV, to generate aTreg. We elucidated several important molecular mechanisms in these interactions including roles for IL-2, TGFβ, T cell receptor (TCR), chemokines (CCL17, CCL19, CCL21), chemokine receptors (CCR4, CCR7), sphingosine-1-phosphate (S1P), and S1P receptor-1 (S1P1).  Investigation of molecular factors that control Foxp3 expression revealed an upstream CpG island enhancer that is epigenetically regulated by DNA methylation, and that is completely methylated in aTreg versus being unmethylated in thymus derived nTreg. Manipulation of this enhancer by using DNMT inhibitors drives Foxp3 expression, allowing us to generate Treg subsets that resemble either aTreg or nTreg.  Foxp3 expression is regulated in an epigenetic fashion by signals mediated by IL-6R and TLR2 receptor pathways.  These signals result in alternative structures for the Foxp3 gene, and differential fates and functions for Treg.  Investigation of trafficking properties demonstrated that nTreg migrate sequentially from the blood through microvascular endothelium into the site of tissue inflammation, and then subsequently from tissue into afferent lymphatics and then the dLN, in order to become activated and display suppressor functions for islet allograft survival. Sequential tissue and dLN migration are key components of nTreg function, and migration is coupled to Treg developmental and differentiative steps. In contrast, aTreg precursors migrate first to the LN, and then to sites of inflammation. We hypothesize that aTreg and nTreg have distinct requirements for induction, migration, trafficking and suppressive function, and that these distinctions are critically important for their separate roles in immune suppression and regulation.

1.) Ochando JC, Homma C, Yang Y, Hidalgo A, Garin A, Tacke F, Angeli V, Li Y, Boros P, Ding Y, Jessberger R, Lira SA, Randolph GJ, and Bromberg JS. Alloantigen-presenting plasmacytoid dendritic cells mediate tolerance to vascularized grafts. Nature Immunology, 2006, 7:652-662.

2.) Zhang N, Schroppel B, Lal G, Jakubzick C, Mao X, Chen D, Jessberger R, Ochando JC, Bromberg JS.  Regulatory T cells sequentially migrate from the site of tissue inflammation to the draining LN to suppress allograft rejection. Immunity, 2009,30:458-469.

3.) Lal G, Zhang N, van der Touw W, Ding Y, Ju W, Bottinger E, Reid SP, Levy DE, Bromberg JS.  Epigenetic regulation of Foxp3 expression in regulatory T cells by DNA methylation. J. Immunol., 2009; 182:259-273.

Supported by NIH RO1 AI072039, AI41428, and AI62765; JDRFI 1-2008-90, and the Emerald Foundation.