Distinct regulation of murine lupus susceptibility genes by the IRF5/Blimp-1 axis

Genome-wide association studies have identified lupus susceptibility genes such as IRF5 and PRDM1 (encoding for IFN regulatory factor 5 [IRF]5 and Blimp-1) in the human genome. Accordingly, the murine Irf5 and Prdm1 genes have been shown to play a role in lupus susceptibility. However, it remains unclear how IRF5 and Blimp-1 (a transcriptional target of IRF5) contribute to lupus susceptibility. Given that the murine lupus susceptibility locus Nba2 includes the IFN-regulated genes Ifi202 (encoding for the p202 protein), Aim2 (encoding for the Aim2 protein), and Fcgr2b (encoding for the FcγRIIB receptor), we investigated whether the IRF5/Blimp-1 axis could regulate the expression of these genes. We found that an Irf5 deficiency in mice decreased the expression of Blimp-1 and reduced the expression of the Ifi202. However, the deficiency increased the expression of Aim2 and Fcgr2b. Correspondingly, increased expression of IRF5 in cells increased levels of Blimp-1 and p202 protein. Moreover, Blimp-1 expression increased the expression of Ifi202, whereas it reduced the expression of Aim2. Interestingly, an Aim2 deficiency in female mice increased the expression of IRF5. Similarly, the Fcgr2b-deficient mice expressed increased levels of IRF5. Moreover, increased expression of IRF5 and Blimp-1 in lupus-prone C57BL/6.Nba2, New Zealand Black, and C57BL/6.Sle123 female mice (as compared with age-matched C57BL/6 female mice) was associated with increased levels of the p202 protein. Taken together, our observations demonstrate that the IRF5/Blimp-1 axis differentially regulates the expression of Nba2 lupus susceptibility genes, and they suggest an important role for the IRF5/Blimp-1/p202 axis in murine lupus susceptibility.