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* Department of Pathology and Immunology, University of Geneva, Geneva, Switzerland;
Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan; and
University of Colorado Health Sciences Center, Denver, CO 80262
The accelerated development of systemic lupus erythematosus (SLE) in male BXSB mice is associated with the genetic abnormality in its Y chromosome, designated Yaa (Y-linked autoimmune acceleration). Recently, the Yaa mutation was identified to be a translocation from the telomeric end of the X chromosome (containing the gene encoding TLR7) onto the Y chromosome. In the present study, we determined whether the Tlr7 gene duplication is indeed responsible for the Yaa-mediated acceleration of SLE. Analysis of C57BL/6 mice congenic for the Nba2 (NZB autoimmunity 2) locus (B6.Nba2) bearing the Yaa mutation revealed that introduction of the Tlr7 null mutation on the X chromosome significantly reduced serum levels of IgG autoantibodies against DNA and ribonucleoproteins, as well as the incidence of lupus nephritis. However, the protection was not complete, because these mice still developed high titers of anti-chromatin autoantibodies and retroviral gp70-anti-gp70 immune complexes, and severe lupus nephritis, which was not the case in male B6.Nba2 mice lacking the Yaa mutation. Moreover, we found that the Tlr7 gene duplication contributed to the development of monocytosis, but not to the reduction of marginal zone B cells, which both are cellular abnormalities causally linked to the Yaa mutation. Our results indicate that the Yaa-mediated acceleration of SLE as well as various Yaa-linked cellular traits cannot be explained by the Tlr7 gene duplication alone, and suggest additional contributions from other duplicated genes in the translocated X chromosome.
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1 This work was supported by grants from the Swiss National Foundation for Scientific Research and the Alliance for Lupus Research.
2 Current address: Amgen Inc., 1 Amgen Center Drive, Thousand Oaks, CA 91320.
3 Address correspondence and reprint requests to Dr. Shozo Izui, Department of Pathology and Immunology, Centre Médicale Universitaire, 1211 Geneva 4, Switzerland. E-mail address: Shozo.Izui{at}medecine.unige.ch
4 Abbreviations used in this paper: SLE, systemic lupus erythematosus; MZ, marginal zone; B6, C57BL/6; RNP, ribonucleoproteins; gp70 IC, gp70-anti-gp70 immune complexes.
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