Comment on "The inhibiting Fc receptor for IgG, FcgammaRIIB, is a modifier of autoimmune susceptibility"

Interferon-inducible Ifi200-family genes as modifiers of lupus susceptibility

Both genetic and environmental factors contribute to the development and progression of systemic lupus erythematosus (SLE), a complex autoimmune disease. The disease exhibits a strong gender bias and develops predominantly in females. Additionally, most SLE patients exhibit increased serum levels of interferon-α (IFN-α) and the "IFN signature". Studies using the mouse models of lupus have identified several lupus susceptibility loci, including the New Zealand Black (NZB)-derived autoimmunity 2 (Nba2) interval on the chromosome 1. The interval, which is syntenic to the human chromosome 1q region, harbors the FcγR family, SLAM/CD2-family, and the IFN-inducible Ifi200-family genes (encoding for the p200-family proteins). Studies involving the B6.Nba2 congenic mice revealed that the development of antinuclear autoantibodies (ANAs) depends on the age, gender, and activation of type I IFN-signaling. Interestingly, recent studies involving the generation of Nba2 subcongenic mouse lines and generation of mice deficient for the Fcgr2b or Aim2 gene within the interval have provided evidence that epistatic interactions among the Nba2 genes contribute to increased lupus susceptibility. Given that the expression of some of the p200-family proteins is differentially regulated by sex hormones and these proteins differentially regulate cytosolic DNA-induced production of type I IFN and proinflammatory cytokines (IL-1β and IL-18), the major known contributors of SLE-associated inflammation, we discuss the recent advancements in our understanding of the role of p200-family proteins in lupus susceptibility modification. An improved understanding of the role of p200-family proteins in the development of autoimmunity is likely to identify new approaches to treat SLE patients.

Murine BAFF expression is up-regulated by estrogen and interferons: implications for sex bias in the development of autoimmunity

Systemic lupus erythematosus (SLE) in patients and certain mouse models exhibits a strong sex bias. Additionally, in most patients, increased serum levels of type I interferon (IFN-α) are associated with severity of the disease. Because increased levels of B cell activating factor (BAFF) in SLE patients and mouse models are associated with the development of SLE, we investigated whether the female sex hormone estrogen (E2) and/or IFNs (IFN-α or γ) could regulate the expression of murine BAFF. We found that steady-state levels of BAFF mRNA and protein were measurably higher in immune cells (CD11b(+), CD11c(+), and CD19(+)) isolated from C57BL/6 females than the age-matched male mice. Treatment of immune cells with IFN or E2 significantly increased levels of BAFF mRNA and protein and a deficiency of estrogen receptor-α, IRF5, or STAT1 expression in splenic cells decreased expression of BAFF. Moreover, treatment of RAW264.7 macrophage cells with IFN-α, IFN-γ, or E2 induced expression of BAFF. Interestingly, increased expression of p202, an IFN and estrogen-inducible protein, in RAW264.7 cells significantly increased the expression levels of BAFF and also stimulated the activity of the BAFF-luc-reporter. Accordingly, the increased expression of the p202 protein in lupus-prone B6.Nba2-ABC than non lupus-prone C57BL/6 and B6.Nba2-C female mice was associated with increased expression levels of BAFF. Together, our observations demonstrated that estrogen and IFN-induced increased levels of the p202 protein in immune cells contribute to sex bias in part through up-regulation of BAFF expression.