Differential monocyte STAT6 activation and CD4 + CD25 + Foxp3 + T cells in kidney operational tolerance transplanted individuals Pedro Manoel M. Moraes-Vieira a,b , Hernandez M. Silva a,b , Maisa C.S. Takenaka a,b , Sandra Maria Monteiro a,b , Francine Lemos c , David Saitovitch b,d , Jorge Kalil a,b , VerÕnica Coelho a,b, * a Laboratory of Immunology, Heart Institute (InCor), University of Sâo Paulo Medical School, Sâo Paulo, Brazil b Institute for Investigation in Immunology, iii–National Institute of Science and Technology, Sâo Paulo, Brazil c Division of Nephrology, University of Sâo Paulo Medical School, Sâo Paulo, Brazil d Division of Nephrology, Sâo Lucas Hospital, Pontifìcia Universidade Catòlica do Rio Grande do Sul, Porto Alegre, RS, Brazil ARTICLE INFO Article history: Received 27 October 2009 Accepted 15 January 2010 Available online 13 February 2010 Keywords: Kidney transplantation Operational tolerance Foxp3 STAT6 Monocytes ABSTRACT In organ transplantation, the immunosuppression withdrawal leads, in most cases, to rejection. Nonetheless, a special group of patients maintain stable graft function after complete withdrawal of immunosuppression, achieving a state called “operational tolerance.” The study of such patients may be important to understand the mechanisms involved in human transplantation tolerance. We compared the profile of CD4 + CD25 + Foxp3 + T cells and the signaling pathways IL-6/STAT3 (signal transducers and activators of transcription) and IL-4/STAT6 in peripheral blood mononuclear cells of four kidney transplant groups: (i) operational tolerance (OT), (ii) chronic allograft nephropathy (CR), (iii) stable graft function under standard immunosuppression (Sta), (iv) stable graft function under low immunosuppression, and (v) healthy individuals. Both CR and Sta displayed lower numbers and percentages of CD4 + CD25 + Foxp3 + T cells compared with all other groups (p  0.05). The OT patients displayed a reduced activation of the IL-4/STAT6 pathway in monocytes, compared with all other groups (p  0.05). The lower numbers of CD4 + CD25 + Foxp3 + T cells observed in CR individuals may be a feature of chronic allograft nephropathy. The differential OT signaling profile, with reduced phosphorylation of STAT6, in monocytes’ region, suggests that some altered function of STAT6 signaling may be important for the operational tolerance state. Crown copyright  2010 Published by Elsevier Inc. on behalf of American Society for Histocompatibility and Immunogenetics. All rights reserved. 1. Introduction Transplantation has become a worldwide accepted treatment for irreversible organ failure. Nonetheless, one major drawback to this treatment is the need for continuous immunosuppression to prevent graft rejection. The improvement in the criteria used to select donors and the development of new immunosuppressors have contributed to increasing graft survival and limiting the risk of acute rejection [1]. However, long-term graft survival has persisted essentially unchanged, and an effective treatment for chronic allo- graft nephropathy remains one of the main challenges in organ transplantation. In human beings, immunosuppression withdrawal leads, in most cases, to rejection. Nonetheless, a special group of patients maintain stable graft function after the complete withdrawal of immunosuppression. These patients are in a state of “operational tolerance.” This indicates that tolerance may, indeed, be accom- plished in human transplantation [2– 4]. The study of operational tolerance patients may help the understanding of a variety of mechanisms involved in human allograft tolerance, as well as to identify parameters that may discriminate this homeostatic state in other transplanted individuals. Several immune response components have been reported to be associated with human allograft tolerance, including regulatory T cells [5,6]. In human beings, there are some reports describing protocols for the induction of graft acceptance, such as the induc- tion of mixed chimerism, the use of anti-CD52 (Campath-1), and anti-CD3 monoclonal antibodies [7–9] although, with little success. However, despite the effort to understand how transplantation tolerance might be accomplished in human beings, there are still limited data on potential mechanisms that lead to the state of operational tolerance. There are three works in which a participa- tion of peripheral CD4 + CD25 + T cells was suggested to be involved in this process [10 –12]. Although it has been reported that kidney transplanted individ- uals with long-term graft survival have an altered expression of molecules related with T-cell activation [13], it has not been inves- tigated whether these alterations modulate and activate different signaling pathways. We hypothesize that intracellular signaling pathways activated by cytokines might have an important role in * Corresponding author. E-mail address: vecoelho@usp.br (V. Coelho). Human Immunology 71 (2010) 442– 450 Contents lists available at ScienceDirect 0198-8859/10/$32.00 - see front matter Crown copyright  2010 Published by Elsevier Inc. on behalf of American Society for Histocompatibility and Immunogenetics. All rights reserved. doi:10.1016/j.humimm.2010.01.022