Objective: To investigate peripheral blood (PB) cell transcript profiles of systemic sclerosis (SSc) and its subtypes in direct comparison with systemic lupus erythematosus (SLE).
Methods: We investigated PB cell samples from 74 SSc patients, 21 healthy controls, and 17 SLE patients using Illumina Human Ref-8 BeadChips and quantitative polymerase chain reaction confirmation. None of the study participants were receiving immunosuppressive agents other than low-dose steroids and hydroxychloroquine. In addition to conventional statistical and modular analysis, a composite score for the interferon (IFN)-inducible genes was calculated. Within the group of patients with SSc, the correlation of the IFN score with the serologic and clinical subtypes was investigated, as were single-nucleotide polymorphisms in a selected number of IFN pathway genes.
Results: Many of the most prominently overexpressed genes in SSc and SLE were IFN-inducible genes. Forty-three of 47 overexpressed IFN-inducible genes in SSc (91%) were similarly altered in SLE. The IFN score was highest in the SLE patients, followed by the SSc patients, and then the controls. The difference in IFN score among all 3 groups was statistically significant (P < 0.001 for all 3 comparisons). SSc and SLE PB cell samples showed striking parallels to our previously reported SSc skin transcripts in regard to the IFN-inducible gene expression pattern. In SSc, the presence of antitopoisomerase and anti-U1 RNP antibodies and lymphopenia correlated with the higher IFN scores (P = 0.005, P = 0.001, and P = 0.004, respectively); a missense mutation in IFNAR2 was significantly associated with the IFN score.
Conclusion: SLE and SSc fit within the same spectrum of IFN-mediated diseases. A subset of SSc patients shows a "lupus-like" high IFN-inducible gene expression pattern that correlates with the presence of antitopoisomerase and anti-U1 RNP antibodies.