The influence of cyclosporin A on lymphocyte attenuator expression Chun Zeng a,b , Yu Zhen a,b , Shang-an Shu c , Tinghe Wu a,b , Huanfa Yi a,b , Zhe-Xiong Lian c , Yong Zhao a,d, * a Transplantation Biology Research Division, State Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China b Graduate School of the Chinese Academy of Sciences, Beijing, China c Division of Rheumatology, Allergy and Clinical Immunology, University of California School of Medicine, Davis, CA 95616, USA d Department of Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, USA Received 21 September 2006; revised 21 February 2007; accepted 26 February 2007 Abstract B and T lymphocyte attenuator (BTLA), a recently identified immune inhibitory receptor, has been demonstrated to have the ability to main- tain self-tolerance and transplant-tolerance in mice. However, little is known about the effects of immunosuppressive drugs on the expression of BTLA. In the present study, we observed that the immunosuppressive drug cyclosporin A (CsA) could significantly reduce BTLA but not CD25 and CD69 expression on CD4 þ T cells during activation in vitro, while rapamycin (RPM) had little effect on it. Exogenous interleukin-2 (IL-2) failed to reverse the inhibitory effect that CsA had on BTLA expression. Furthermore, phorbol 12-myristate 13-acetate (PMA) or ionomycin alone could efficiently induce BTLA protein expression on CD4 þ and CD8 þ T cells, while CsA significantly suppressed BTLA expression in this system. The present data indicate that the regulation of BTLA expression on CD4 þ T cells does not depend on IL-2 and T cell activation but depends on calcineurin-dependent and calcineurin-independent pathways. The observation that CsA significantly inhibits BTLA expression on CD4 þ T cells during activation, suggests that CsA might block the immune tolerance induced by BTLA and potentially increase the suscep- tibility to autoimmune diseases and graft rejection. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: BTLA; Cyclosporin A; Immunosuppression; Immune tolerance; Autoimmunity 1. Introduction Efficient and proper immune responses are achieved, at least in part, by the regulation of co-molecule signaling that provokes either positive or negative signals. Stimulatory sig- nals are crucial for initiating, augmenting and maintaining the expansion and proliferation of T cells, whereas inhibitory signals can attenuate, dampen and terminate the responses [1e4]. Therefore, the balance of both signals will dictate the outcomes of immune responses. BTLA is a recently identified co-inhibitory receptor of the CD28 superfamily [5]. It is highly induced on activated T cells and also expressed on B cells, macrophages, and bone marrow-derived dendritic cells [6,7]. The ligand of BTLA is herpes virus entry mediator (HVEM) [8e10], a co-stimulator of the TNFR family through the inter- action with LIGHT and lymphotoxin-a (LT-a) [11]. It has been reported that ligation of BTLA results in tyrosine phosphory- lation of BTLA, recruited Src homology domain 2-containing protein tyrosine phosphotases-1 (SHP-1) and SHP-2 and subsequently generated signals that dampen T and B cell Abbreviations: APC, antigen presenting cell; BTLA, B and T lymphocyte attenuator; ConA, Concanavalin A; Cpm, counts per minute; CsA, cyclosporin A; CTLA-4, cytotoxic T lymphocyte-associated antigen 4; FCM, flow cytom- etry; FITC, fluorescein isothiocyanate; HVEM, herpes virus entry mediator; IL-2, interleukin-2; MFI, mean fluorescence intensity; PE, phycoerythrin; PKC, protein kinase C; PMA, phorbol 12-myristate 13-acetate; PI, propidium iodide; TNFR, tumor necrosis factor receptor. * Corresponding author. Transplantation Biology Research Division, State Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, Chinese Academy of Sciences, Beisihuan Xi Road 25, Beijing, China 100080. Tel.: þ86 106253 8391; fax: þ86 10 6265 9958. E-mail address: zhaoy@ioz.ac.cn (Y. Zhao). 0896-8411/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaut.2007.03.002 Journal of Autoimmunity 28 (2007) 234e244 www.elsevier.com/locate/jautimm