Induction of autoimmune valvulitis in Lewis rats following immunization with peptides from the conserved region of group A streptococcal M protein Robyn S. Lymbury a , Colleen Olive b , Kellie A. Powell c , Michael F. Good b , Robert G. Hirst a , Justin T. LaBrooy c , Natkunam Ketheesan a,c * a Microbiology and Immunology, School of Biomedical Sciences, James Cook University, Townsville, Australia b Division of Infectious Diseases and Immunology, Queensland Institute of Medical Research, Brisbane, Australia c School of Medicine, James Cook University, Townsville, Australia Received 28 October 2002; accepted 28 January 2003 Abstract Rheumatic heart disease (RHD) is considered to be an autoimmune disorder mediated by group A streptococcal (GAS) M protein-specific T cells and antibodies that cross-react with cardiac antigens and epitopes of the GAS M protein. In this study, Lewis rats were immunized with a pool of overlapping peptides spanning the conserved region of the GAS M protein in Complete Freund’s Adjuvant, followed by immunization with Bordetella pertussis. Controls received adjuvants alone. Spleen-derived lymphocytes from rats immunized with the conserved region peptides proliferated in response to the immunogen and to cardiac myosin. Moreover, histological examination of cardiac tissue from rats immunized with conserved region peptides revealed the presence of inflammatory lesions in both the myocardium and valve tissue indicating a role for GAS M protein-specific autoreactive T cells in the development of cardiac lesions. This study may support the use of the rat model of autoimmune valvulitis to investigate the immunopathogenesis of RHD and possible preventive strategies.  2003 Elsevier Science Ltd. All rights reserved. Keywords: Autoimmune valvulitis; Group A streptococcus; Lewis rat; M protein; Rheumatic heart disease 1. Introduction Group A streptococcal (GAS) infection can lead to several complications including the post-streptococcal sequelae- rheumatic fever (RF) and rheumatic heart disease (RHD). Acute rheumatic fever (ARF) occurs in approximately 3% of individuals following an unresolved GAS pharyngeal infection. Furthermore, repeated episodes of ARF can lead to RHD causing severe cardiovascular morbidity, and in many cases mortality. Recent annual statistics report that RF and RHD affect 12 million people worldwide with 400 000 deaths [1]. A major concern is the high incidence and prevalence of these diseases in developing countries and in indigenous communities within developed countries [2,3]. There is strong evidence that RHD is autoimmune in origin involving both T-cells and antibodies. Although the exact mechanism of the pathogenesis of RHD is yet to be elucidated, it is widely believed that molecular mimicry between GAS proteins and host proteins leads to a breakdown in immunological tolerance to self antigens [4,5]. In particular, the GAS surface M protein has been implicated in disease pathogenesis and several studies have demonstrated cross-reactivity at the cellular and humoral level between the M protein and host proteins, such as cardiac myosin [4,6], leading to the identification of cross-reactive B- and T-cell epitopes within the M protein [6–10]. The M protein is a major virulence factor during GAS infection and allows the bacteria to escape destruc- tion by phagocytosis in the absence of type-specific * Corresponding author. N. Ketheesan, School of Medicine, James Cook University, Queensland 4811, Australia. Tel.: +61-747-81-6876; fax: +61-747-79-1526 E-mail address: N.Ketheesan@jcu.edu.au (N. Ketheesan). Journal of Autoimmunity 20 (2003) 211–217 www.elsevier.com/locate/issn/08968411 0896-8411/03/$ - see front matter  2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0896-8411(03)00026-X