Objective The interferon (IFN) system is activated in systemic sclerosis (SSc), but the driving mechanisms remain unclear. We asked whether type I and III IFN responses to Toll-like receptor (TLR)-7/8/9 stimulation of leukocytes from patients with SSc differ from healthy individuals, and if the IFN production is associated with clinical features.

Methods Peripheral blood mononuclear cells (PBMCs), monocyte-depleted PBMCs, and monocytes were prepared from 45 SSc patients and 47 healthy controls. Cells were stimulated with RNA-containing immune complexes (RNA-IC), an RNA-oligonucleotide (ORN8L), or inactivated herpes simplex virus (HSV) targeting TLR7, TLR8, and TLR9, respectively. IFN-α, -β, -λ1 and -λ2 levels were measured by immunoassays. IFN-α producing cells were analyzed by flow cytometry.

Results SSc-PBMCs produced type I and III IFNs in response to all three stimuli, with HSV inducing the strongest response. Compared to controls, SSc-PBMCs produced less IFN-α (p<0.02), while IFN-β levels were higher in HSV-stimulated SSc-monocytes (342 vs. 59.9 pg/ml, p=0.041). Expression of IFN-λ1/2 was lower than type I IFNs. The IFN responses to TLR7/8 stimulation increased in PBMCs in the presence of IFN-α (priming). Strong HSV-induced IFN-α production was associated with diffuse cutaneous SSc, anti-RNA-polymerase III autoantibodies, and interstitial lung disease (ILD).

Conclusions Leukocytes from SSc patients generally have a reduced IFN-producing capacity, except for virus-induced IFN-β production by monocytes. However, type I IFN priming enhanced the IFN response to TLR-7/8 stimulation, suggesting that viral infections may amplify IFN synthesis in response to endogenous TLR activators, that might aggravate the SSc disease process including development of ILD.

The authors have declared no competing interest.

The work was supported by grants from the Swedish Rheumatism Association, the Uppsala University Hospital Development Foundation; Department of Medical Sciences, Uppsala University, Sweden., the King Gustaf V 80-year Foundation.

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Ethics committee of Swedish National Etikprovningsmyndigheten gave ethical approval for this work.

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The work was supported by grants from the Swedish Rheumatism Association, the Uppsala University Hospital Development Foundation; Department of Medical Sciences, Uppsala University, Sweden., the King Gustaf V 80-year Foundation.

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