Molecular Immunology 43 (2006) 1761–1768 A possible new bridge between innate and adaptive immunity: Are the anti-mitochondrial citrate synthase autoantibodies components of the natural antibody network? Tam´ as Cz ¨ omp¨ oly a , Katalin Olasz a , Di´ ana Simon b , Zolt´ an Ny´ ar´ ady a,c , L´ aszl´ o P´ alink´ as a , L´ aszl´ o Czirj´ ak b , T´ ımea Berki a , P´ eter N´ emeth a,∗ a Department of Immunology and Biotechnology, Faculty of Medicine, University of P´ ecs, Szigeti ´ ut 12., P´ ecs H-7643, Hungary b Department of Immunology and Rheumatology, Hungarian Brothers of St. John of God and University of P´ ecs, Irgalmasok u. 1., P´ ecs H-7621, Hungary c Department of Oral and Maxillofacial Surgery, University of P´ ecs, Dischka Gy. u. 5., H-7621 P´ ecs, Hungary Received 19 September 2005; received in revised form 14 November 2005; accepted 16 November 2005 Available online 20 December 2005 Abstract Natural antibody (nAb) producing B-1 B cells are considered an intermediate stage of evolution between innate and adaptive immunity. nAbs are immunoglobulins that are produced without antigen priming. nAbs can recognize foreign targets and may serve in the first line of immune defense during an infection. Natural autoantibodies (nAAbs) present in the serum of both healthy humans and patients suffering from systemic autoimmune diseases recognize a set of evolutionarily conserved self-structures. Because of their endosymbiotic evolutionary origin, proteins compartmentalized into mitochondria represent an interesting transition from prokaryotic foreign (non-self) to essential (self) molecules. We investigated the possible overlap in recognized epitopes of innate and self-reactive nAbs and surveyed changes in physiological autoreactivity under pathological autoimmune conditions. Epitope mapping analysis of a mitochondrial inner membrane enzyme, citrate synthase (CS) (EC 2.3.3.1) by synthetic overlapping peptides and phage display libraries using sera from healthy individuals and from patients having systemic autoimmune disease revealed CS recognizing nAAbs with IgM isotype. We analyzed cross reactive epitopes on human CS, bacterial CS, and various standard autoantigens. The anti-CS nAAbs by participating in the nAb network, could function in innate defense mechanisms and at the same time recognize a target antigen (nucleosome) in a systemic autoimmune disease. Thus, at the level of recognized epitopes there is a possible new link between the innate like component and the adaptive-autoimmune arm of the humoral immune system. © 2005 Elsevier Ltd. All rights reserved. Keywords: Natural antibody; Mitochondrial inner membrane enzyme; Epitope mapping; Phage display; Multi-pin ELISA; Systemic lupus erythematosus; Autoim- munity 1. Introduction Several lines of evidence indicate that natural antibody pro- ducing B-1 B cells represent an intermediate stage of evolution between innate and adaptive immunity. In fact they play an important role during the early phases of immune responses (Martin et al., 2001; Wardemann et al., 2002; Baumgarth et al., 1999). While they need to be under control and regulation because of their autoreactivity, these innate B cells themselves ∗ Corresponding author. Tel.: +36 72 536290; fax: +36 72 536289. E-mail address: peter.nemeth@aok.pte.hu (P. N´ emeth). play an important role in controlling autoimmunity (Boes et al., 2000; Cocca et al., 2001). Natural antibodies (nAbs) are immunoglobulins that are pro- duced without immunization with antigen (Coutinho et al., 1995). These molecules can recognize foreign targets and may serve in the first line of immune defense during an infection (Ochsenbein et al., 1999). In contrast, natural autoantibodies (nAAbs) present in the serum of both healthy humans and patients suffering from systemic autoimmune diseases recog- nize a set of self-structures that have been conserved during evolution (Cohen and Young, 1991). Most nAAbs belong to the IgM or IgG isotype (Mouthon et al., 1995; Avrameas, 1991) and show polyreactivity with a broad range of affinities for the 0161-5890/$ – see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.molimm.2005.11.004