Brief Definitive Report Characterization of Leishmania infantum thiol-dependent reductase 1 and evaluation of its potential to induce immune protection A. M. SILVA, 1,2,3 J. TAVARES, 1,2 R. SILVESTRE, 1 A. OUAISSI, 4 G. H. COOMBS 3 & A. CORDEIRO-DA-SILVA 1,2 1 IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal, 2 Laboratório de CiÞncias Biológicas, Facul- dade de Farmµcia da Universidade do Porto, Porto, Portugal, 3 Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK, 4 INSERM, UMR CNRS 5235, UniversitØ de Montpellier 2, Montpellier Cx 5, France SUMMARY The need to develop an effective vaccine against leishmania- sis to prevent the 2 million new cases each year led to the search for antigens able to elicit protection against infection with Leishmania. In this study, we have characterized a par- asite-specific protein of Leishmania infantum named thiol- dependent reductase 1 (TDR1). The protein is present in both life cycle stages of L. infantum with a notable higher expression in the amastigote forms, suggesting a role in the interaction between the parasite and the mammalian host. Thiol-dependent reductase 1 is localized in the cytosol, although we were able to detect the protein in the culture medium of both promastigotes and axenic amastigotes, and consequently, TDR1 is considered an excreted ⁄ secreted mol- ecule of the parasite. Therefore, we have evaluated the potential of TDR1 recombinant protein to protect against experimental challenge with L. infantum parasites using a murine model. Despite a reduction in spleen parasite load in the chronic phase of disease, TDR1 administration was not effective in the protection of Balb ⁄ c mice against visceral leishmaniasis and thus TDR1 do not have a crucial role in the modulation of mammalian host immune response, as observed with its protein counterpart Tc52 of Trypanosoma cruzi. Keywords Leishmania infantum, TDR1, Visceral leishman- iasis INTRODUCTION The leishmaniases remain a major public health problem with 350 million people at risk worldwide and 2 million estimated new cases every year in 88 countries. Clinical manifestations of Leishmania infection range from self- healing cutaneous and mucocutaneous forms to visceral leishmaniasis (VL) which, if left untreated, is fatal (1). Leishmaniasis is also found as an opportunistic disease associated with human immunodeficiency virus (HIV). HIV infection increases the risk of developing active VL by between 100 and 2320 times (2). Unfortunately, there is no effective vaccine against this parasite; thus, control of the disease relies on chemotherapy. However, there are limitations in the use of available drugs because of high cost, toxicity, long courses of treatment and, in particular, the emergence of drug resistance (3). The clinical outcome of infection is determined by a combination of several fac- tors including parasite pathogenicity, determined by the Leishmania species, and the host’s immune status (4). Parasite fractions or defined protein subunits have been used in vaccination strategies as a mean to reduce the complexity of the host immune response to vaccines that included whole killed or lysed parasites. A number of can- didate antigens have been tested [reviewed in (5)] but only a few have entered clinical testing, such as Leish-111f, a fusion protein formulated with MPL-SE (6,7). Thus, it is still necessary to characterize other Leishmania antigens and determine the potential use of recombinant protein in vaccination strategies. The current study was undertaken to investigate the role of Leishmania infantum thiol-dependent reductase 1 (TDR1) in the parasite–host interaction. Thiol-dependent reductase 1 was first identified in Leishmania major as a par- asite-specific enzyme by Denton et al. (8). This enzyme has some similarities to human omega-glutathione S-tranferase (GST), including its thiol transferase and dehydroascorbate Correspondence: Anabela Cordeiro-da-Silva, Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal (e-mail: cordeiro@ibmc.up.pt). Disclosures: None. Received: 27 October 2011 Accepted for publication: 7 March 2012 Parasite Immunology, 2012, 34, 345–350 DOI: 10.1111/j.1365-3024.2012.01361.x Ó 2012 Blackwell Publishing Ltd 345