ARTHRITIS & RHEUMATISM Vol. 60, No. 6, June 2009, pp 1683–1693 DOI 10.1002/art.24501 © 2009, American College of Rheumatology Autoimmune Regulator Controls T Cell Help for Pathogenetic Autoantibody Production in Collagen-Induced Arthritis Ian K. Campbell, 1 Sarah A. Kinkel, 2 Sarah F. Drake, 1 Annemarie van Nieuwenhuijze, 1 Franc ¸ois-Xavier Hubert, 1 David M. Tarlinton, 1 William R. Heath, 1 Hamish S. Scott, 1 and Ian P. Wicks 1 Objective. Autoimmune regulator (Aire) promotes the ectopic expression of tissue-restricted antigens in medullary thymic epithelial cells (mTECs), leading to negative selection of autoreactive T cells. This study was undertaken to determine whether loss of central toler- ance renders Aire-deficient (Aire / ) mice more suscep- tible to the induction of autoimmune arthritis. Methods. Medullary TECs were isolated from Aire / and wild-type C57BL/6 mice for gene expression analysis. Collagen-induced arthritis (CIA) was elicited by injection of chick type II collagen (CII) in adjuvant. Cellular and humoral immune responses to CII were evaluated. Chimeric mice were created by reconstituting lymphocyte-deficient mice with either Aire / or wild- type CD4 T cells and wild-type B cells. Results. Wild-type, but not Aire / , mTECs ex- pressed the CII gene Col2a1. Aire / mice developed more rapid and severe CIA, showing elevated serum anti-CII IgG levels, with earlier switching to arthrito- genic IgG subclasses. No evidence was found of en- hanced T cell responsiveness to CII in Aire / mice; however, Aire / CD4 T cells were more efficient at stimulating wild-type B cells to produce anti-CII IgG following immunization of chimeric mice with CII. Conclusion. Our findings indicate that Aire- dependent expression of CII occurs in mTECs, implying that there is central tolerance to self antigens found in articular cartilage. Reduced central tolerance to CII in Aire / mice manifests as increased CD4 T cell help to B cells for cross-reactive autoantibody production and enhanced CIA. Aire and central tolerance help prevent cross-reactive autoimmune responses to CII initiated by environmental stimuli and limit spontaneous autoim- munity. Several mechanisms have evolved to enable T cells to discriminate between self and non-self. At the forefront is central tolerance in the thymus, resulting in the clonal deletion of developing T cells bearing rear- ranged T cell receptor (TCR) with high affinity for self antigen and the production of Treg cells. While circu- lating self antigens are accessible for presentation by antigen-presenting cells (APCs) and deletion of cognate T cells in the thymus, deletion of T cells with high affinity for tissue-restricted antigens (TRAs) is depen- dent on ectopic expression by specialized thymic cells, most notably medullary thymic epithelial cells (mTECs). Recently, it was shown that extrathymic Aire-expressing stromal cells within secondary lymphoid organs can also present TRAs, thereby helping to control any self- reactive T cells in the periphery (1). Autoimmune regulator (Aire) was first identified as a loss-of-function mutation in patients with auto- Supported by the Reid Charitable Trusts, the National Health and Medical Research Council of Australia, the Rebecca L. Cooper Medical Research Foundation, and the European Union Sixth Frame- work Programme EuroThymaide and EURAPs Projects. 1 Ian K. Campbell, PhD, Sarah F. Drake, BSc (Hons), Anne- marie van Nieuwenhuijze, MSc, Franc ¸ois-Xavier Hubert, PhD (current address: INSERM Unite ´ 643, CHU de Nantes, Universite ´ de Nantes, Nantes, France), David M. Tarlinton, PhD, William R. Heath, PhD, Hamish S. Scott, PhD (current address: Institute of Medical and Veterinary Science, and The Hanson Institute, Adelaide, South Aus- tralia, Australia), Ian P. Wicks, MBBS, FRACP, PhD: The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia; 2 Sarah A. Kinkel, BSc (Hons): The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia, and The University of Melbourne, Melbourne, Victoria, Australia. Address correspondence and reprint requests to Ian P. Wicks, MBBS, FRACP, PhD, Reid Rheumatology Laboratory, Division of Autoimmunity and Transplantation, The Walter and Eliza Hall Insti- tute of Medical Research, 1G Royal Parade, Parkville, Victoria 3050, Australia (e-mail: wicks@wehi.edu.au.); or to Hamish S. Scott, PhD, Division of Molecular Pathology, The Institute of Medical and Veter- inary Science, and The Hanson Institute, Box 14 Rundle Mall PO, Adelaide, South Australia 5000, Australia (e-mail: hamish.scott@ imvs.sa.gov.au). Submitted for publication September 10, 2008; accepted in revised form February 12, 2009. 1683