1. ¹Faculty of Medicine, Molecular Genetics and Rheumatology Section, Imperial College, Hammersmith Campus, London, UK
2. ²Department of Histopathology, Imperial College, Hammersmith Campus, London, UK

Correspondence: Professor M Botto, Faculty of Medicine, Molecular Genetics and Rheumatology Section, Imperial College, Hammersmith Campus, Du Cane Road, London W12 0NN, UK. E-mail: m.botto@imperial.ac.uk

³Current address: The Wellcome Trust, London, UK.

Received 29 April 2008; Revised 3 July 2008; Accepted 10 September 2008; Published online 9 October 2008.

Abstract

Epistatic interactions between the non-autoimmune strains 129 and C57BL/6 (B6), used for generating gene-targeted animals, can induce a lupus-like disease. Genome-wide scan analyses of testcross progeny between these two strains have identified several lupus susceptibility loci, with the strongest linkage to the production of autoantibodies (auto-Abs) displayed by an interval on chromosome 1 of 129 origin (Sle16). However, the contribution of B6 loci to the lupus phenotype remained unknown. We used a congenic approach to deduce the contribution to the autoimmune traits of the B6 genomic interval on chromosome 3 (Sle18), previously shown to be linked to antinuclear Ab production. This interval, when transferred on a 129 background (a strain termed 129.B6–Sle18), promoted auto-Ab production targeting a broad spectrum of autoantigens, expansion of activated CD4⁺T and B cells and mild glomerulonephritis. Surprisingly, these immunological and serological defects were accompanied by a significant increase in the percentage of regulatory T cells (Tregs; CD4⁺ Foxp3⁺). However, these cells, that expressed lower levels of Foxp3, had no impaired regulatory function when tested in vitro. These findings illustrate further the efficacy of congenic dissection for functional characterisation of individual lupus susceptibility loci and highlight the contribution of loci derived from non-autoimmune strains to the disease pathogenesis.