Activation of the Interferon Pathway is Dependent Upon Autoantibodies in African-American SLE Patients, but Not in European-American SLE Patients

Abstract

Background: In systemic lupus erythematosus (SLE), antibodies directed at RNA-binding proteins (anti-RBP) are associated with high serum type I interferon (IFN), which plays an important role in SLE pathogenesis. African-Americans (AA) are more likely to develop SLE, and SLE is also more severe in this population. We hypothesized that peripheral blood gene expression patterns would differ between AA and European-American (EA) SLE patients, and between those with anti-RBP antibodies and those who lack these antibodies.

Methods: Whole blood RNA from 33 female SLE patients and 16 matched female controls from AA and EA ancestral backgrounds was analyzed on Affymetrix Gene 1.0 ST gene expression arrays. Ingenuity Pathway Analysis was used to compare the top differentially expressed canonical pathways amongst the sample groups. An independent cohort of 116 SLE patients was used to replicate findings using quantitative real-time PCR (qPCR).

Results: Both AA and EA patients with positive anti-RBP antibodies showed over-expression of similar IFN-related canonical pathways, such as IFN Signaling (P = 1.3 × 10(-7) and 6.3 × 10(-11) in AA vs. EA respectively), Antigen Presenting Pathway (P = 1.8 × 10(-5) and 2.5 × 10(-6)), and a number of pattern recognition receptor pathways. In anti-RBP negative (RBP-) patients, EA subjects demonstrated similar IFN-related pathway activation, whereas no IFN-related pathways were detected in RBP-AA patients. qPCR validation confirmed similar results.

Conclusion: Our data show that IFN-induced gene expression is completely dependent on the presence of autoantibodies in AA SLE patients but not in EA patients. This molecular heterogeneity suggests differences in IFN-pathway activation between ancestral backgrounds in SLE. This heterogeneity may be clinically important, as therapeutics targeting this pathway are being developed.

Keywords: ancestral background; autoantibodies; interferon alpha; interferon gamma; systemic lupus erythematosus.

Figure 1

Pathway diagram illustrating the type I and type II IFN pathways in SLE patient subsets. Genes which are up-regulated are shaded red, with increasingly dark red shading indicating a greater degree of over-expression in cases as compared to controls of the same ancestral background. AA, African-American; EA, European-American; RBP+, anti-RNA-binding-protein (RBP) antibody positive; and RBP−, RBP antibody negative. Pictures generated using Ingenuity Pathway Analysis software.

Figure 2

Type I IFN-induced gene expression in SLE patient subgroups and controls. Expression of three genes (IFIT1, MX1, and PKR) are shown in both patients with anti-RNA-binding protein antibodies (RBP+), and those who lack those antibodies (RBP−). Central tendency shown is a median, with error bars representing the interquartile range. P values generated by Mann–Whitney U test.

Figure 3

Type I IFN-induced gene expression in RBP–SLE patient subgroups and controls in regards to of anti-dsDNA antibodies. Expression of three genes (IFIT1, MX1, and PKR) are shown in both patients with anti-dsDNA antibodies (DNA+), and those who lack those antibodies (DNA−). Central tendency shown is a median, with error bars representing the interquartile range. P values generated by Mann–Whitney U test.