A <em>Tlr7</em> translocation accelerates systemic autoimmunity in murine lupus

Srividya Subramanian

Katalin Tus

Quan Li

Andrew Wang

Lisa McDaniel+3 authors

*Center for Immunology and

^{Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX 75235}

^{To whom correspondence should be addressed. E-mail:}ude.nretsewhtuostu@dnalekaw.drawde

Communicated by Diane Mathis, Harvard Medical School, Boston, MA, May 11, 2006.

Author contributions: S.S., K.T., A.W., and E.K.W. designed research; S.S., K.T., Q.-Z.L., A.W., X.-H.T., J.Z., C.L., G.B., L.D.M., and X.J.Z. performed research; R.A.S. contributed new reagents/analytic tools; S.S., K.T., and A.W. analyzed data; and S.S., K.T., A.W., and E.K.W. wrote the paper.

Received 2006 Apr 18

Abstract

The y-linked autoimmune accelerating (yaa) locus is a potent autoimmune disease allele. Transcription profiling of yaa-bearing B cells revealed the overexpression of a cluster of X-linked genes that included Tlr7. FISH analysis demonstrated the translocation of this segment onto the yaa chromosome. The resulting overexpression of Tlr7 increased in vitro responses to Toll-like receptor (TLR) 7 signaling in all yaa-bearing males. B6.yaa mice are not overtly autoimmune, but the addition of Sle1, which contains the autoimmune-predisposing Slam/Cd2 haplotype, causes the development of fatal lupus with numerous immunological aberrations. B6.Sle1yaa CD4 T cells develop the molecular signature for T_FH cells and also show expression changes in numerous cytokines and chemokines. Disease development and all component autoimmune phenotypes were inhibited by Sles1, a potent suppressor locus. Sles1 had no effect on yaa-enhanced TLR7 signaling in vitro, and these data place Sles1 downstream from the lesion in innate immune responses mediated by TLR7, suggesting that Sles1 modulates the activation of adaptive immunity in response to innate immune signaling.

Keywords: Sle1, Sles1, Toll-like receptor 7, yaa

Abstract

Susceptibility to systemic lupus erythematosus is mediated by complex genetic and environmental interactions (1, 2). Because of this complexity, we and others have used congenic dissection of lupus-prone mouse strains to characterize the underlying immune abnormalities responsible for lupus susceptibility (3 –11). These analyses have provided important insights into the component phenotypes associated with individual disease alleles and allowed an assessment of genetic interactions that mediate severe lupus. In addition, congenic dissection can be a key step in the identification of causative alleles, as demonstrated by the association of polymorphisms in the SLAM/CD2 gene cluster with Sle1b, the most potent lupus susceptibility locus in Sle1 (12).

The BXSB lupus model is a recombinant inbred mouse strain produced from an intercross of C57BL/6J (B6) and SB/Le (13, 14). BXSB male mice develop a severe form of murine lupus because of interactions between the y-linked autoimmune accelerator (yaa) locus on the Y chromosome and other autoimmune disease alleles in the BXSB genome (reviewed in ref. 15). yaa is the most potent disease allele detected in the BXSB strain (14). Previous studies found that yaa dysregulated the B cell lineage and that CD4 T cells were necessary for disease but need not carry the yaa mutation (16 –18). Introgression of yaa onto the nonautoimmune C57BL/6J (B6) background revealed that yaa could produce disease only when combined with other autoimmune-promoting genes (3, 8, 19 –21). In our B6 congenic system we found that the bicongenic B6.Sle1yaa strain developed severe disease, indicative of strong epistatic interactions between these two susceptibility loci (8).

We previously described four suppressive modifier loci, Sles1–4, which suppressed autoimmunity in NZW mice (22). Sles1 was the most potent of these loci, and we recently fine-mapped it into an ≈956-kb region at the proximal end of the murine MHC. Genetic complementation studies indicated that the suppressive effects of Sles1 were not mediated by MHC class II molecules and that mice expressing Sles1 mounted normal immune responses to exogenous stimulation, indicating that this suppressive modifier did not broadly inhibit the immune system (23).

Here we present data demonstrating that the causative genetic lesion for yaa involves a translocation of the Toll-like receptor (TLR) Tlr7 from the X chromosome onto the yaa Y chromosome. This translocation causes a 2-fold overexpression of Tlr7 in male mice bearing yaa, which is sufficient to dysregulate TLR7-mediated activation of innate immune responses. We further demonstrate that the introduction of Sle1 synergizes with this regulatory lesion in innate signaling to cause profound dysregulation of the adaptive immune system. Finally, the introduction of Sles1 onto the B6.Sle1yaa lupus model (B6.Sle1yaaSles1) eliminated pathogenic autoimmunity and associated phenotypes without suppressing the hyperresponsive properties of the TLR7 dysregulation caused by yaa.

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Acknowledgments

We are grateful to Dr. Jose Casco for excellent management of the mouse colony and to Angie Mobley for cell sorting. We thank the members of the E.K.W. laboratory for discussions, critical comments, and technical advice, in particular Alice Chan and Miwako Yamamoto. These studies were supported by grants from the National Institutes of Health, the Lupus Research Institute, and the Alliance for Lupus Research (to E.K.W.).

Acknowledgments

Abbreviations

TLR	Toll-like receptor
BAC	bacterial artificial chromosome
T_FH	follicular T helper.

Abbreviations

Footnotes

Conflict of interest statement: No conflicts declared.

Footnotes

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