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...
Calreticulin (CRT) is located predominantly in the endoplasmic reticulum (ER) of cells, where it functions as a quality control controller of protein folding. However, CRT is also a prevalent autoantigen in patients with systemic lupus erythematosus (SLE), where its release from the cell may arise as a results of dysfunctional apoptosis and inefficient removal of ER vesicles, which are an abundant source of CRT and other autoantigens. Indicative of this is the presence of autoantibodies against CRT in the sera of 40-60% of all SLE patients. Once released into the circulation, CRT might bind directly to C1q and we have suggested that this association may result in a defect in C1q-mediated clearance of antigen-antibody complexes. It has been previously shown that CRT under physiological salt conditions binds to the globular head of C1q. It is known that the globular head region of C1q binds to the CH2 domain in the Fc portion of immunoglobulin gamma (IgG). The N-terminal half of CRT contains a number of short regions of 7-10 amino acids that show sequence similarity to the putative C1q binding region in the CH2 domain of IgG. By use of a series of 92 overlapping CRT synthetic peptides, a number of C1q binding sites on the CRT molecule have been identified, including several containing a CH2-like motif similar to the ExKxKx C1q binding motif found in the CH2 domain of IgG. A number of these peptides were shown to inhibit binding of C1q to IgG and reduce binding of native CRT to C1q. Moreover, several of the peptides were capable of inhibiting the classical pathway of complement activation. These studies have identified specific binding sites on the CRT molecule for C1q and lend support to the hypothesis that interaction of CRT with C1q may interfere with the ability of C1q to associate with immune complexes in autoimmune-related disorders.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2025 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.