Background Systemic lupus erythematosus (SLE) is a severe systemic autoimmune disease with involvement of inner organs; autoreactive (CD4+) T cells, B cells and autoantibodies are crucial in its pathophysiology. CD4+FoxP3+ Treg, on the other hand, are important for maintaining peripheral tolerance to self-antigens. In human SLE, however, both the absolute numbers and the functionality of these cells are reduced and correlate inversely with disease activity, but direct evidence for a central role of Treg malfunction in SLE pathophysiology is still missing.

Objectives We therefore analyzed, if Treg-deficient scurfy mice share typical features of SLE.

Methods Scurfy mice have dysfunctional Treg due to a genetic defect in the transcription factor foxP3 which is crucial for their development and function. 9 scurfy and 9 matched controls (C57Bl/6) were analyzed at 4-5 weeks of age. By immunofluorescence we screened for autoantibodies and also performed hematological workup. Specimen of skin and inner organs were stained with H/E and screened for inflammation by a blinded pathologist; kidneys were also stained with PAS and by direct immunofluorescence. We analyzed joint pathology after staining with H/E (overview), tolloidin blue (cartilage) and TRAP (osteoclasts). Immunhistochemistry allowed for further analysis of the cellular composition of the inflammatory infiltrate, which was finally quantified by image analysis systems (Osteomeasure and HistoQuest, respectively).

Results We confirmed previous reports that scurfy mice spontaneously develop severe systemic autoimmune disease which includes pneumonitis and hematological abnormalities (anemia, lymphopenia) similar to those seen in SLE.

We here show that scurfy, but not WT control mice, exhibit various additional features typical for SLE: They develop severe interface dermatitis, show elevated serum levels of ANA and dsDNA-abs and develop mesangial glomerulonephritis (resembling lupus nephritis WHO2; seen in 8 out of 9 scurfy [88.9%] vs. 0/6 [0%] of controls, respectively, p=0.0014). In contrast to controls, scurfy mice showed increased cartilage degradation (destained/normal cartilage area 0.050±0.009 vs. 0.018±0.003, p=0.004) and developed inflammatory arthritic infiltrates (mean area 0.38±0.25mm²). There were no osteoclasts within the joint space and, consecutively, no erosions. Besides fibroblasts, the inflammatory infiltrate consisted mainly of CD3+ T lymphocytes (13%), with 7% B cells and <3% neutrophils and macrophages. In transfer experiments, CD4+ T cells from scurfy, but not from controls, led to pneumonitis, ANA and dsDNA-abs production in athymic nude mice.

Conclusions Our observations support the hypothesis that lupus-like disease develops in the absence of functional Treg.

References: Scheinecker C, Bonelli M, Smolen JS. Pathogenetic aspects of systemic lupus erythematosus with an emphasis on regulatory T cells. J Autoimmun. 2010 Nov;35(3):269-75. doi: 10.1016/j.jaut.2010.06.018. Epub 2010 Jul 16.

Disclosure of Interest: None Declared