Cutting edge: autoimmune disease risk variant of STAT4 confers increased sensitivity to IFN-alpha in lupus patients in vivo

Abstract

Increased IFN-alpha signaling is a primary pathogenic factor in systemic lupus erythematosus (SLE). STAT4 is a transcription factor that is activated by IFN-alpha signaling, and genetic variation of STAT4 has been associated with risk of SLE and rheumatoid arthritis. We measured serum IFN-alpha activity and simultaneous IFN-alpha-induced gene expression in PBMC in a large SLE cohort. The risk variant of STAT4 (T allele; rs7574865) was simultaneously associated with both lower serum IFN-alpha activity and greater IFN-alpha-induced gene expression in PBMC in SLE patients in vivo. Regression analyses confirmed that the risk allele of STAT4 was associated with increased sensitivity to IFN-alpha signaling. The IFN regulatory factor 5 SLE risk genotype was associated with higher serum IFN-alpha activity; however, STAT4 showed dominant influence on the sensitivity of PBMC to serum IFN-alpha. These data provide biologic relevance for the risk variant of STAT4 in the IFN-alpha pathway in vivo.

FIGURE 1

Serum IFN-α activity in SLE patients in relation to STAT4 genotype. SLE patients are stratified by STAT4 rs7574865 genotype and presence or absence of anti-RBP or dsDNA autoantibodies, with p values calculated using the extra sum-of-squares F test. Serum IFN-α activity is measured as a summed score of IFN-α-induced gene expression in the reporter cells (see Materials and Methods). RBP–/DNA– indicates subjects lacking both anti-RBP and anti-dsDNA Abs; RBP+ or DNA+ indicates subjects with either anti-RBP or anti-dsDNAAbs; and RBP +/DNA+ indicates subjects with both anti-RBP and anti-dsDNA Abs. Lines show the mean with SD, p values were corrected for multiple comparisons using a Bonferroni correction.

FIGURE 2

IFN-α-induced gene expression in PBMC vs serum IFN-α activity in SLE patients stratified by STAT4 genotype. Multiple linear regression plots showing PBMC IFN-α-induced gene expression vs induction of the same gene by serum in reporter cells in simultaneous samples. All patients are stratified by STAT4 genotype and the best-fit lines and slopes for each genotype as determined by linear regression, with a p value by extra sum-of-squares F test for a difference in either y-intercept (IFIT-1) or slope (MX-1 and PKR).

FIGURE 3

Serum IFN-α activity and serum vs PBMC data in SLE patients stratified by both STAT4 and IRF5 genotype and autoantibody status. Multiple linear regressions showing PBMC IFN-α-induced gene expression vs induction of the same gene by serum in reporter cells in simultaneous samples. p value by extra sum-of-squares F test for a difference in either y-intercept (IFIT-1) or slope (MX-1 and PKR).

FIGURE 4

Proposed model of IFN-α signaling in SLE including autoantibodies, IRF5, and STAT4. Anti-RBP and anti-dsDNA Abs form immune complexes containing nucleic acid, which can be taken into plasmacytoid dendritic cells via Fc receptors and result in ligation of endosomal TLRs. Downstream TLR signaling is augmented by IRF5 SLE risk variants, resulting in increased IFN-α production. IFN-α is released, and STAT4 SLE risk variants result in increased sensitivity to IFN-α downstream of the type IIFN receptor.