OBJECTIVES: The goal of this study was to determine whether endosomal Toll-like receptors (TLRs) contribute to the clinical manifestation of systemic autoimmunity exhibited by mice that lack the lysosomal nuclease DNaseII.

METHODS: DNaseII/IFNaR double deficient mice were intercrossed with Unc93b13d/3d mice to generate DNaseII-/-mice with non-functional endosomal TLRs. The resulting triple deficient mice were evaluated for arthritis, autoantibody production, splenomegaly, and extramedullary haematopoiesis. B cells from both strains were evaluated for their capacity to respond to endogenous DNA by using small oligonucleotide based TLR9D ligands and a novel class of bifunctional anti-DNA antibodies.

RESULTS: Mice that fail to express DNaseII, IFNaR, and Unc93b1 still develop arthritis but do not make autoantibodies, develop splenomegaly, or exhibit extramedullary haematopoiesis. DNaseII-/- IFNaR-/- B cells can respond to synthetic ODNs, but not to endogenous dsDNA.

CONCLUSIONS: RNA-reactive TLRs, presumably TLR7, are required for autoantibody production, splenomegaly, and extramedullary haematopoiesis in the DNaseII-/- model of systemic autoimmunity.