Toll-like receptor 9 signaling protects against murine lupus
Article first published online: 29 DEC 2005
Copyright © 2006 by the American College of Rheumatology
Arthritis & Rheumatism
Volume 54, Issue 1, pages 336–342, January 2006
How to Cite
Wu, X. and Peng, S. L. (2006), Toll-like receptor 9 signaling protects against murine lupus. Arthritis & Rheumatism, 54: 336–342. doi: 10.1002/art.21553
- Issue published online: 29 DEC 2005
- Article first published online: 29 DEC 2005
- Manuscript Accepted: 13 OCT 2005
- Manuscript Received: 1 SEP 2005
- NIH. Grant Numbers: AI-01803, AI-057471
Hypomethylated CpG–containing DNA, which is recognized by Toll-like receptor 9 (TLR-9), has been strongly implicated in the pathogenesis of autoantibody-mediated diseases such as systemic lupus erythematosus. This study was undertaken to determine the role of TLR-9 in the MRL/+ and MRL/lpr models of murine lupus.
TLR-9–deficient MRL mice were generated by backcrossing a TLR-9–deficient allele against the MRL backgrounds by a speed congenic technique. Parameters of murine lupus were examined by routine methods. Regulatory T cell activity was assessed by autologous mixed lymphocyte reaction (AMLR), an in vitro assay for autoreactivity.
Surprisingly, TLR-9–deficient animals of both the MRL/+ and the MRL/lpr backgrounds developed more severe lupus, as judged by anti-DNA and rheumatoid factor autoantibodies, total serum Ig isotypes, lymphadenopathy, inflammatory infiltrates in the salivary gland and kidney, proteinuria, and mortality, in comparison with their TLR-9–sufficient littermates. In vitro, regulatory T cells from TLR-9–deficient animals were impaired in their ability to suppress the AMLR.
In the MRL model of murine lupus, TLR-9 signaling plays a protective role, perhaps by modulating the activity of regulatory T cells. These results contrast with findings of recent studies that implicate TLR-9 in the pathogenesis of anti-DNA responses, based in part on investigations in incompletely backcrossed TLR-9–deficient MRL/lpr mice in vivo or transgenic B cells in vitro. The present results highlight the need for caution in the assessment of disease paradigms based on the study of isolated cell populations in vitro, as well as in vivo studies of knockout animals involving non-ideal genetic models.