Use of SAG2A recombinant Toxoplasma gondii surface antigen as a diagnostic marker for human acute toxoplasmosis: analysis of titers and avidity of IgG and IgG1 antibodies Samantha Ribeiro Béla a , Deise A. Oliveira Silva a , Jair Pereira Cunha-Júnior b , Carlos P. Pirovani c , Flávia Andrade Chaves-Borges a , Fernando Reis de Carvalho a , Taísa Carrijo de Oliveira a , José Roberto Mineo a, ⁎ a Laboratory of Immunoparasitology, Institute of Biomedical Sciences, Federal University of Uberlândia, Uberlândia, MG, 38401-136, Brazil b Division of Immunology, Federal University of Tocantins, Palmas, TO, 77020-210, Brazil c Division of Microbiology and Immunology, Department of Biological Sciences, State University of Santa Cruz, Ilhéus, BA, 45662-000, Brazil Received 11 January 2008; accepted 26 May 2008 Abstract We evaluated the reactivity of IgG and IgG1 antibodies by immunoassays in sera from patients with acute and chronic phases of toxoplasmosis against 2 recombinant antigens, SAG2A (full molecule) and SAG2AΔ (truncated molecule from the epitope recognized by A4D12 monoclonal antibody [mAb]), in comparison with soluble Toxoplasma antigen (STAg). Results demonstrated higher IgG reactivity in acute sera with both STAg and SAG2A than in chronic phase sera, and this difference was more evident for IgG1 antibodies to SAG2A. Low reactivity to SAG2AΔ was found in sera from both phases. ELISA-IgG-SAG2A showed high sensitivity (95%) and specificity (100%). ELISA- IgG1-SAG2A sensitivity was significantly higher (90%) for acute than for chronic (67%) phases. ELISA-IgG avidity using STAg demonstrated high performance for characterizing sera with high avidity (N60%), whereas the ELISA-IgG1 avidity-SAG2A immunoassay was the best to define chronic phase infection. It can be concluded that SAG2A is an antigen that may be used as a diagnostic tool to characterize the acute phase Toxoplasma gondii infection. Also, the epitope recognized by A4D12 mAb may be critical for the recognition of this molecule. © 2008 Elsevier Inc. All rights reserved. Keywords: Toxoplasma gondii; Human toxoplasmosis; Antibody avidity; IgG subclasses; SAG2A molecule; Recombinant antigen; Serologic diagnosis 1. Introduction Toxoplasma gondii, a member of the phylum Apicom- plexa, is an obligate intracellular and ubiquitous protozoan parasite that infects a broad range of hosts, including humans and domestic animals (Dubey et al., 1998). In immunocom- petent individuals, acute infection commonly resolves with- out treatment, but the host remains chronically infected lifelong. In contrast, immunocompromised individuals, such as those infected with the human immunodeficiency virus or receiving immunosuppressive therapy, are at risk for life- threatening disease that develops after reactivation of quiescent brain cysts. In addition, T. gondii infection causes significant morbidity and mortality in congenitally infected subjects (Di Cristina et al., 2004; Golkar et al., 2007). The parasite exhibits 3 morphologically distinct infec- tious stages: tachyzoites, bradyzoites (in tissue cysts), and sporozoites (in oocysts) (Dubey et al., 1998). The surface of T. gondii tachyzoites and bradyzoites is covered with glycosylphosphatidylinositol-anchored antigens (Nagel and Boothroyd, 1989; Tomavo et al., 1989), most of which are members of the surface antigen 1 (SAG1) or SAG2 families (Boothroyd et al., 1998; Lekutis et al., 2000; Manger et al., 1998). These molecules appear to play a role in host cell invasion, immune modulation, and/or virulence attenuation, although they may also provide protection needed by the parasite to survive in the environment, and your native or recombinant shapes are used for the serologic diagnosis of toxoplasmosis (Harning et al., 1996; Available online at www.sciencedirect.com Diagnostic Microbiology and Infectious Disease 62 (2008) 245 – 254 www.elsevier.com/locate/diagmicrobio ⁎ Corresponding author. Tel.: +55-34-3218-2195; fax: +55-34-3218- 2333. E-mail address: jrmineo@ufu.br (J.R. Mineo). 0732-8893/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.diagmicrobio.2008.05.017