Objectives Arthritis is frequently seen in human lupus, but rarely in lupus models. Pristane-induced lupus (PIL) can be induced in various mouse strains such as BALB/c and C57Bl/6. We herein characterize clinical and histological features of arthritis in the context of systemic lupus and provide a prudent comparison with models of rheumatoid arthritis (RA).

Methods Arthritis is frequently seen in human lupus, but rarely in lupus models. Pristane-induced lupus (PIL) can be induced in various mouse strains such as BALB/c and C57Bl/6. We herein characterize clinical and histological features of arthritis in the context of systemic lupus and provide a prudent comparison with models of rheumatoid arthritis (RA).

Results In BALB/c, clinical arthritis started at 3 months, occurred finally in 79% of PIL (but not in controls, p<0.001) and correlated with areas of inflammation, erosion, cartilage damage, osteoclast numbers and total severity score (for all: r>0.7, p<0.001). After 8 months, 58% of PIL (but no controls, p<0.001) had mild-erosive arthritis: In contrast to murine RA, the most frequent inflammatory cell type of the pannus was granulocytes (17.7%), PIL had lower numbers of osteoclasts, erosions rarely affected both layers of the cortical bone and there was no progression to complete joint destruction (even after 1 year of observation). Serum auto-abs preceded arthritis and became significantly elevated in all PIL; affected joints showed increased deposits of IgG (and IgM) within the inflammatory tissue, indicative for an antibody-mediated process. All PIL mice with arthritis also had pulmonary (100%) and renal (46%) lupus. In contrast to BALB/c, Bl/6 mice did not develop any signs of arthritis.

Conclusions PIL in BALB/c mice is characterized by severe organ involvement, typical auto-abs and by a mild-erosive arthritis with similarities, but also with distinct differences to RA. PIL may help to study arthritis along with other key features of SLE after therapeutic interventions or in knockout models based on a BALB/c, but not on a Bl/6 background.

Disclosure of Interest None Declared