ARTHRITIS & RHEUMATISM Vol. 46, No. 5, May 2002, pp 1255–1263 DOI 10.1002/art.10264 © 2002, American College of Rheumatology Expression of Recombination Activating Genes 1 and 2 in Peripheral B Cells of Patients With Systemic Lupus Erythematosus Hermann J. Girschick, 1 Amrie C. Grammer, 2 Toshihiro Nanki, 2 Eduardo Vazquez, 2 and Peter E. Lipsky 2 Objective. To analyze immunoregulatory abnor- malities in patients with systemic lupus erythematosus (SLE) by assessing the expression of messenger RNA (mRNA) for types 1 and 2 recombination activating genes (RAG) in the peripheral blood of patients with active SLE. Methods. We examined B cell populations and also individual B cells from patients with SLE for the expression of RAG mRNA. Results. Analysis of bulk mRNA indicated that RAG1 and RAG2 mRNA were found routinely in peri- pheral B cells of patients with active SLE, but not in healthy subjects. When assessed on a single-cell basis, there was a 3-fold increase in the frequency of RAG1- and RAG2-expressing B cells in SLE patients compared with healthy subjects. Notably, B cells expressing both RAG1 and RAG2 mRNA expressed only IgD mRNA, but not IgG mRNA. Fifty percent of RAG-expressing B cells also expressed VpreB mRNA, whereas all expressed CD154 mRNA. Phenotypic analysis indicated that RAG- expressing B cells were activated, mature B cells. Conclusion. These results indicate that RAG ex- pression is up-regulated in peripheral IgD and VpreB B cells of patients with active SLE. These cells may contribute to the immunoregulatory abnormalities in patients with SLE. Numerous aberrations of the immune system have been reported in systemic lupus erythematosus (SLE) and have been implicated in the pathogenesis of this autoimmune disease (1,2). Included in these abnor- malities are immune-cell signaling defects resulting in hyperactivity of B and T cells (3), hypomethylation of DNA leading to abnormal autoreactive B cells (4), and changes in the immunoglobulin repertoire of lupus B cells leading to an increased number of B cell–producing autoantibodies (5). In addition, enhanced mutational activity of immunoglobulin genes has been implicated in the pathogenesis of SLE (6–8). Although the causes of autoantibody production have not been completely de- lineated, it has been suggested that one contributing feature might be a failure of editing or revision of autoreactive B cell receptors (BCRs) (5,9). On the other hand, recent data suggest that receptor editing/revision might be enhanced in patients with SLE (10,11). V–D–J rearrangement of immune-receptor genes is a feature of developing lymphocytes in the bone marrow (12) and depends on recombination activating gene (RAG) enzymes (13). RAG enzymes are expressed at high levels during ontogeny, but their expression diminishes in immature B cells and is usually absent in recirculating, mature, naive B cells (14,15). However, we (16) and others have demonstrated a marked reexpres- sion of the RAG-encoding endonucleases RAG1 and RAG2 during germinal center reactions in secondary lymphoid organs (17–28). This has led to the proposal that V–D–J editing/revision in secondary lymphoid or- gans might be a mechanism to rescue B cells whose antigen receptor avidity has been decreased as a result of somatic hypermutation or to rescue B cells in which somatic mutation has generated autoreactivity (8,21). In mice, in contrast to humans, peripheral transcription of Supported by NIH grant AI-31229. Dr. Girschick is a recipi- ent of a Deutsche Forschungsgemeinschaft grant, Gi-295/1-1. Dr. Grammer’s work is supported by a grant from the Arthritis Founda- tion. 1 Hermann J. Girschick, MD (current address: Children’s Hospital, University of Wuerzburg, Wuerzburg, Germany): University of Texas Southwestern Medical Center, Dallas; 2 Amrie C. Grammer, PhD, Toshihiro Nanki, MD, Eduardo Vazquez, BS, Peter E. Lipsky, MD: National Institute of Arthritis and Musculoskeletal and Skin Diseases, NIH, Bethesda, Maryland. Drs. Girschick and Grammer contributed equally to this work. Address correspondence and reprint requests to Peter E. Lipsky, MD, Scientific Director, NIAMS, National Institutes of Health, 9000 Rockville Pike, Building 10, Room 9N228, Bethesda, MD 20892-1820. E-mail: lipskyp@mail.nih.gov. Submitted for publication October 22, 2001; accepted in revised form January 11, 2002. 1255