No abstract

Compelling evidence suggests that Foxp3 + CD25 + CD4 + Treg play a fundamental role in immunoregulation. We have previously demonstrated that Treg have to enter peripheral tissues to suppress ongoing inflammation. However, relatively little is known about how Treg acquire the expression of homing receptors required for tissue-or inflammationspecific migration. Migratory properties of conventional naïve T cells are shaped by the tissue microenvironment and organ-specific dendritic cells during priming. Here, we show that this basic concept also holds true for CD25 + CD4 + Treg: Priming of Treg within peripheral LN led to the expression of selectin ligands, which facilitate migration into inflamed skin, whereas activation within mesenteric LN led to induction of the integrin a 4 b 7 , which is required for migration into mucosal tissues. Furthermore, we could establish in vitro culture systems containing either dendritic cells from mesenteric and peripheral LN, or retinoic acid and IL-12 as polarizing compounds to induce mucosa-and skin-seeking Treg, respectively. Together, our results demonstrate that Treg, similarly to conventional T cells, can be configured with organ-selective homing properties allowing efficient targeting into distinct tissues. IntroductionMigration of T cell subsets to different tissues is determined by the combined expression of adhesion molecules and chemokine receptors (CCR) on the cell surfaces [1][2][3][4]. Among these homing receptors (HR), the integrin a 4 b 7 [5,6] and the chemokine receptor CCR9 [7][8][9] mediate the homing of T cell subsets to GALT such as mesenteric LN (mLN) and Peyer's patches (PP) and to the small intestinal lamina propria and the mucosal epithelium. In contrast, T cell trafficking to the skin is mediated by P-(P-lig) and E-(E-lig) selectin ligands [10,11] as well as .Recently, a number of studies have described that antigen-dependent differentiation of naïve T cells in lymphoid organs leads to the generation of effector T cells exhibiting a capacity to enter peripheral extralymphoid tissues [2]. Effector T cells generated in different lymphoid organs display distinct tissue tropism, which is regulated by an organ-specific induction of adhesion molecules and chemokine receptors during T cell priming [4,[15][16][17][18][19][20][21]. For example, T cells activated in mLN and PP draining the gut acquire high levels of the integrin a 4 b 7 , whereas activation in skin-draining peripheral LN (pLN) results in the upregulation of selectin ligands such as P-lig. Tissuespecific DC have been shown in a number of in vitro and in vivo studies to be involved in the instruction of naïve T cells [4,[17][18][19][20][22][23][24] reported that GALT DC were capable of converting metabolites of dietary vitamin A into retinoic acid (RA), which in turn induced T cell expression of a 4 b 7 and CCR9, leading to the generation of gut-tropic T cells. However, the factors, which are involved in the generation of skin-specific T cell homing in vivo, are largely unknown, although important ...

Repeatedly activated T helper 1 (Th1) cells present during chronic inflammation can efficiently adapt to the inflammatory milieu, for example, by expressing the transcription factor Twist1, which limits the immunopathology caused by Th1 cells. Here, we show that in repeatedly activated murine Th1 cells, Twist1 and T-bet induce expression of microRNA-148a (miR-148a). miR-148a regulates expression of the proapoptotic gene Bim, resulting in a decreased Bim/Bcl2 ratio. Inhibition of miR-148a by antagomirs in repeatedly activated Th1 cells increases the expression of Bim, leading to enhanced apoptosis. Knockdown of Bim expression by siRNA in miR-148a antagomir-treated cells restores viability of the Th1 cells, demonstrating that miR-148a controls survival by regulating Bim expression. Thus, Twist1 and T-bet not only control the differentiation and function of Th1 cells, but also their persistence in chronic inflammation.

The endothelium plays an important role in the exchange of molecules, but also of immune cells between blood and the underlying tissue. The endothelial molecule S-Endo 1 antigen (CD146) is preferentially located at endothelial junctions and has been claimed to support endothelial integrity. In this study we show that the monoclonal antibody ME-9F1 recognizes the extracellular portion of murine CD146. Making use of ME-9F1 we found CD146 highly expressed and widely spread on endothelial cells in the analyzed murine tissues. In contrast to humans that express CD146 also on T cells or follicular dendritic cells, murine CD146 albeit at low levels was only found on a subset of NK1.1 + cells. The antibody against murine CD146 is useful for immunomagnetic sorting of primary endothelial cells not only from the liver but from various other organs. In vitro, no evidence was seen that the formation and integrity of endothelial monolayers or the transendothelial migration of T cells was aVected by antibody binding to CD146 or by crosslinking of the antigen. This makes the antibody ME-9F1 an excellent tool especially for the ex vivo isolation of murine endothelial cells intended to be used in functional studies.