CTLA-4 is a crucial immune regulator that mediates both negative costimulation signals to T cells, and regulatory T (Treg)-cell extrinsic control of effector responses.Here we present evidence supporting a novel mechanism for this extrinsic suppression, executed by the alternatively spliced soluble CTLA-4 isoform (sCTLA-4). Analyses of human T cells in vitro show that sCTLA-4 secretion can be increased during responses, and has potent inhibitory properties, since isoform-specific blockade of its activity significantly increased Ag-driven proliferation and cytokine (IFN-γ, IL-17) secretion. Treg cells were demonstrated to be a prominent source of sCTLA-4, which contributed to suppression in vitro when their numbers were limiting. The soluble isoform was also produced by, and inhibited, murine T cells responding to Ag in vitro, and blockade of its activity in vivo protected against metastatic spread of melanoma in mice. We conclude that sCTLA-4 is an important immune regulator, responsible for at least some of the inhibitory effects previously ascribed to the membrane-bound isoform. These results suggest that the immune system exploits the different CTLA-4 isoforms for either intrinsic or extrinsic regulation of T-cell activity. Keywords: CD4 + T cells r Costimulatory molecules r Immune regulation r Treg cellsAdditional supporting information may be found in the online version of this article at the publisher's web-site Introduction CTLA-4 is an important regulator of T-cell responses [1][2][3][4]. Its critical role is highlighted by CTLA-4 knockout mice, which develop a fatal lymphoproliferative disorder soon after birth, arising from a profound failure of T-cell homeostasis [5,6]. Despite these potent effects, the activities of CTLA-4 are only partially understood.CTLA-4 shares sequence homology and B7 ligands (CD80/CD86) with the costimulatory molecule, CD28, but differs by delivering inhibitory, rather than activating, signals to the T cells on which it is expressed as a receptor [7,8]. Upregulation of CTLA-4 on activated T cells provides a mechanism for negative Correspondence: Dr. Frank J. Ward e-mail: mmd475@abdn.ac.uk feedback to control their responses. However, not all its regulatory effects are explained by inhibitory costimulation, since CTLA-4 can also suppress activated effector T-cell populations without the need for them to express it [9,10]. This latter, cell-extrinsic mechanism has been largely attributed to CD4 + regulatory T (Treg)-cell subsets, which constitutively express high levels of CTLA-4, and require it for their regulatory function [11][12][13][14][15][16].How Treg cells might use CTLA-4 to regulate effector T-cell responses remains controversial. It has been suggested that CTLA-4 on Treg cells binds B7 and thus blocks CD28-mediated effector T-cell costimulation, or that it induces inhibitory mechanisms in the APC such as the IDO tryptophan catabolic enzyme * These authors contributed equally to this work.www.eji-journal.eu Eur. J. Immunol. 2013. 43: 1274-1285 Immunomodulation 1275 cas...

Objectives: To characterize plasma cytokine responses in melioidosis and analyse their association with mortality. Methods: A prospective longitudinal study was conducted in two hospitals in Northeast Thailand to enrol 161 individuals with melioidosis, plus 13 uninfected healthy individuals and 11 uninfected individuals with diabetes to act as controls. Blood was obtained from all individuals at enrolment (day 0), and at days 5, 12 and 28 from surviving melioidosis patients. Interferon-g (IFN-g), interleukin-1b (IL-1b),

Tetrasaccharides mimicking Burkholderia pseudomallei and Burkholderia mallei lipopolysaccharide O-antigens were synthesized and found to be highly reactive with Thai melioidosis patient serum, highlighting their potential as vaccine candidates.