Background Despite the numerous murine models of SLE, models that accurately reflect the central features of CLE are much more limited. The MRL/lpr line is commonly studied in this context, but the onset of cutaneous disease in MRL/lpr mice is highly variable, colony dependent, and takes 6 months or more to develop. Endosomal TLRs play a key role in the development of murine models of SLE and mice lacking all endosomal TLR function have markedly attenuated disease. However autoimmune-prone mice deficient for only TLR9 invariably develop more severe SLE.
Materials and methods We have generated TLR9WT and TLR9KO mice that express a membrane-bound OVA fusion protein on MHC class II+ cells under the control of a doxycycline (DOX) inducible promoter. These mice were given DOX chow, sublethally irradiated and injected with activated OVA-specific DO11 T cells and then monitored for indications of systemic autoimmune disease.
Results 3–4 weeks following T cell transfer, the TLR9KO recipients develop cutaneous manifestation of SLE characterised by a mononuclear interface dermatitis associated with mucin deposition, absence of skin-associated Tregs, accumulation of IFNγ-producing DO11 T cells, elevated MHC class II expression by LCs and keratinocytes, and excessive keratinocyte death. Many more DO11 T cells are found in the epidermis of the TLR9KO recipients compared to the TLR9WT recipients, and the TLR9WT recipients have a higher frequency of DO11 Tregs. Importantly, the TLR9KO recipients have more germinal centre B cells in the spleen and more ELIspot+ cells in the bone marrow, and make autoantibodies specific for Ro52, a self-reactivity commonly detected in human CLE patients. An additional key feature of the model is our ability to turn disease on and then off, simply by providing, or not providing, DOX. In mice on DOX for 4 wks and then off DOX for 2 wks, autoantibody titers markedly decrease and skin lesions resolve with minimal if any residual scarring. Subsequent DOX re-administration, without the transfer of additional T cells or any additional irradiation, leads to the rapid recurrence of autoantibody production and skin disease, thereby recapitulating lupus flares.
Conclusions We have now leveraged the hyperactivity of TLR9-deficient mice to develop a novel T cell dependent model of cutaneous inflammation that is strikingly similar to human CLE. This model provides a means for characterising both T and B cell memory responses elicited by autoantigens, and determining to what extent the primary vs secondary responses can be limited by TLR antagonists.
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