K͞BxN mice develop an inflammatory joint disease with many features characteristic of rheumatoid arthritis. In this model, the KRN transgenic T cells and nontransgenic B cells both recognize the glycolytic enzyme glucose-6-phosphate-isomerase (GPI) as an autoantigen. Here, we followed the anti-GPI B cell response that naturally arises in K͞BxN mice. The anti-GPI B cell response was robust and arose at the same time as the development of serum anti-GPI autoantibody and joint inflammation. Surprisingly, although GPI was expressed systemically, the anti-GPI B cell response was focused to the lymph nodes (LN) draining the distal joints where arthritis was evident. In lymphotoxin-␤ receptor-Ig-treated mice, which lack LNs, the development of arthritis was completely inhibited up to 5-6 weeks. At later times, some arthritis did develop, but at a significantly reduced level. Thus, in this spontaneous model of autoimmunity, the LNs draining the distal joints are essential for both the inhibition and amplification of the arthritogenic B cell response. These findings imply that the immune physiology of a joint is unique, resulting in a local immune response to a systemic autoantigen.

Objective. Juvenile dermatomyositis (DM) is a chronic inflammatory myopathy of childhood primarily affecting the muscles and skin. Treatment for juvenile DM is often difficult, and conventional therapies include corticosteroids and other immune suppressants. We reviewed the records of 4 patients with juvenile DM who received the B cell-depleting anti-CD20 monoclonal antibody rituximab to determine whether this therapy resulted in improved control of their juvenile DM.Methods. This is a retrospective review of 4 pediatric patients ages 10-17 years with juvenile DM who were treated with rituximab. All patients were tested for myositis autoantibodies and received weekly rituximab infusions for a total of 4 doses. Two patients received repeat courses of rituximab 1 year after their first dose. Patients were followed up between 12 and 24 months after their first course of rituximab, and their strength, muscle enzymes, and rash were reviewed.Results. One patient was positive for a myositisspecific antibody, anti-Mi-2, and demonstrated striking reductions in her muscle enzyme levels for 1 year after rituximab therapy. Following a second course of rituximab, this patient remained disease free for 14 months before requiring a third course of rituximab. Two myositis antibody-negative patients showed clinical improvement and tolerated lower doses of corticosteroids following treatment with rituximab. Finally, 1 patient had worsening of her disease following rituximab.Conclusion. These cases highlight the potential for anti-B cell therapies in the treatment of juvenile DM in both myositis-specific autoantibody-positive and -negative patients.

Incomplete deletion of KRN T cells that recognize the ubiquitously expressed self-antigen glucose-6-phosphate-isomerase (GPI) initiates an anti-GPI autoimmune cascade in K/BxN mice resulting in a humorally mediated arthritis. Transgenic (Tg) expression of a KRN T cell receptor (TCR) agonist under the major histocompatibility complex class II promoter resulted in thymic deletion with loss of anti-GPI T and B cell responses and attenuated arthritis course. However, double Tg mice succumbed to systemic autoimmunity with multiorgan inflammation and autoantibody production. Extensive thymic deletion resulted in lymphopenia and elimination of CD4+ CD25+ regulatory T cells (Tregs), but spared some CD4+ T cells expressing endogenous TCR, which oligoclonally expanded in the periphery. Disease was transferred by these T cells and prevented by cotransfer of CD4+ CD25+ Tregs. Moreover, we extended our findings to another TCR system (anti–hen egg lysozyme [HEL] TCR/HEL mice) where similarly extensive thymic deletion also resulted in disease. Thus, our studies demonstrated that central tolerance can paradoxically result in systemic autoimmunity through differential susceptibility of Tregs and autoreactive T cells to thymic deletion. Therefore, too little or too much negative selection to a self-antigen can result in systemic autoimmunity and disease.

The specificity with which CD4+ T cells recognize self peptides in vivo was examined in transgenic mice that express an influenza virus PR8 hemagglutinin (HA) polypeptide in many tissues, including the thymus (HA Tg mice). HA Tg and non-Tg mice were analyzed for their T cell responses to the major PR8 HA I-E(d)-restricted CD4+ T cell determinant S1. Negative selection eliminated S1-specific T cells from HA Tg mice. Nevertheless, HA Tg mice retained the ability to mount a T cell response to a closely related analog of the S1 determinant [S1(K113)], and some S1(K113)-specific TCRs displayed a partial reactivity with S1 as indicated by their ability to transmit signals for IL-3 but not IL-2 secretion in response to the neo-self peptide. Moreover, the neo-self S1 peptide antagonized the ability of these TCRs to signal IL-2 secretion in response to the foreign S1(K113) determinant. Thus, TCRs that exhibit a partial reactivity with a self peptide are present in the peripheral T cell repertoire and can be activated by a virus containing an analog of the self peptide. These findings provide a model for the induction of autoimmunity by viruses that are close homologs of self peptides, and suggest a way in which TCRs could react with self peptides during positive selection of developing thymocytes.

Objective CD4+CD25+FoxP3+ regulatory T cells (TR) are critical regulators of autoimmunity. Yet, TR are paradoxically increased in RA patients and show variable activity in human studies. Our objective is to characterize the expansion and function of TR during the initiation and progression of experimental arthritis. Methods To unequivocally identify TR, we crossed FoxP3gfp mice to K/BxN to generate arthritic mice in which TR express green fluorescence protein. We examined the expansion and function of TR and effector T cells (TE) during different stages of arthritis by flow cytometry and cell proliferation. Results In K/BxN mice, thymic selection of KRN T cells resulted in an enrichment of FoxP3+ TR. TR numbers increased during arthritis with significant increases in the spleen and draining lymph node, indicating selective tropism to sites of disease. In contrast to the in vitro unresponsiveness when cultured by themselves, substantial fractions of TR proliferated in both non-arthritic and arthritic mice. However, they also underwent greater apoptosis thereby maintaining equilibrium with TE. Similarly, enhanced TR suppressive activity during arthritis was offset by greater resistance by their TE counterparts and antigen presenting cells. Conclusion In this well established model of RA, the interplay of TE and TR in K/BxN mice recapitulated many features of human disease. We demonstrated an ordered expansion of TR during arthritis and the dynamic changes in TR and TE functions. By elucidating factors that govern TR and TE development in K/BxNgfp mice, we will gain insight into the pathophysiology and develop novel therapeutics for human RA.