Systemic Sclerosis (SSc) is a clinically heterogeneous disorder with inflammatory, fibrotic, and vascular manifestations and a highly variable prognosis and response to therapies. Biomarkers that segregate with disease manifestations and which may predict prognosis or response to therapy are needed. SSc shares a type I interferon (IFN) mRNA signature with Systemic Lupus (SLE). We have previously developed a panel of chemokines which correlate with the IFN signature in SLE, and which predicts SLE disease course. We now report the initial testing of this chemokine panel, and additional potentially relevant biomarkers in SSc patients.
Serum samples from 57 SSc patients, 5 healthy controls, and 6 autoimmune controls were obtained from the Scleroderma biorepository at the Benaroya Research Institute. Autoantibody status and presence/absence of interstitial lung disease(ILD) was determined by initial chart review at time of sample acquisition. Four IFN-regulated chemokines(IP-10, I-TAC, MCP-1, and MIP-3β) were measured by Searchlight multiplexed immunoassays, and 14 additional cytokines, chemokines, and growth factors were measured by multiplexed bead-based immunoassays (Luminex). Samples were run in duplicate and recombinant proteins were used to generate standard curves. Due to non-normal distribution of analyte values, nonparametric Mann-Whitney tests were used for group comparisons with p<0.05 considered significant. Significant variables from the univariate analysis were tested in a stepwise multiple logistic regression model.
In our initial study, IP-10 and MIP-3β were significantly elevated in SSc patients compared to healthy controls. These two chemokines and I-TAC were also significantly elevated in SSc compared to autoimmune controls. A chemokine score (calculated from summed levels of the four chemokines) was significantly higher in SSc compared to both control groups. MCP-1 levels were significantly higher in both anti-topoisomerase (topo) + patients (n=25) and topo-, CENP- patients (n=16) as compared to anti-centromere (CENP) + patients (n=15). Among 14 additional proteins, IL-1ra, VEGF, and Eotaxin were significantly increased in SSc vs. autoimmune controls, but none were found at altered levels in SSc patients compared to healthy controls. IL-1ra, VEGF, and IL-12p70 were elevated in SSc patients with ILD (n=34) compared to patients without ILD (n=18).IL-1ra and VEGF were also lower in CENP+ patients as compared to both Topo+ patients and Topo-, CENP- patients. In multivariate analysis of SSc vs. healthy controls, only IP-10 was retained in the model (p=0.0047); the model for SSc vs. autoimmune controls included both IP-10 and IL-1ra (p=0.0006). MCP-1 was the only significant variable retained in the model of ILD (p=0.0004).
Serum levels of IFN-regulated chemokines and other cytokines associate with specific autoantibodies and with important clinical manifestations of SSc. Further studies are needed to determine whether these putative biomarkers will predict disease course or response to therapy.
Disclosure: E. Baechler Gillespie, None; J. H. Buckner, None; J. C. Wilson, None; J. A. Molitor, None.