Dichotomic effects of IFN-γ on the development of systemic lupus erythematosus-like syndrome in MRL-lpr/lpr mice

Systemic lupus erythematosus (SLE)-prone female MRL-lpr/lpr (MRL-lpr) mice were treated with mouse or rat IFN-γ under different experimental conditions, both prophylactically in 6- to 8-week-old animals and therapeutically in 12- to 18-week-old SLE-affected mice. It was found that IFN-γ heterogeneously modulated the course of the disease in MRL-lpr mice. When administered prophylactically, IFN-γ favorably modulated the histological, serological and clinical signs of the disease. Relative to untreated or PBS-treated control animals, the MRL-lpr mice which received IFN-γ were virtually free of inflammatory infiltration of the kidneys and the lungs, had lower levels of azotemia with reduction of both circulating IgG1, IgG2a and IgG3 and anti-double strand (ds) and single strand (ss) DNA antibodies, milder skin vasculitis, significantly reduced enlargment of their lymph nodes and lower weight of the spleens. IFN-γ also lowered the rate of mortality of MRL-lpr mice. In contrast to these findings, therapeutically administered IFN-γ, worsened the course of the disease in MRL-lpr mice, which exhibited increased proteinuria, higher levels of IgG2a and IgG3 and anti-ds and -ss DNA antibodies, more aggressive nephritis and died at an earlier age than PBS-treated control mice. The dichotomic effect of IFN-γ on disease manifestation in MRL-lpr mice offers new insights into the complex role of this cytokine in the regulation of systemic autoimmunity such as SLE.