IFN increases TLR3-induced interleukin (IL)-6 production in cultured dermal fibroblasts. (A) Healthy control fibroblasts (n = 10) and (B) SSc dermal fibroblasts (n = 10) were preincubated with media alone or with 50 ng/mL IFNα for 24 hours, washed and then stimulated with Pam3CysK4 (TLR2 agonist); polyinosinic:polycytidylic acid, or poly(I:C) (TLR3 agonist); lipopolysaccharide (TLR4 agonist) and Gardiquimod (TLR7/8 agonist; [1-(4-amino-2-ethylaminomethylimidazo[4,5-c]quinolin-1-yl)-2-methylpropan-2-ol]) for 48 hours (10 μg/mL). Culture supernatants were assessed for IL-6 and CC chemokine ligand 2 (CCL2). Preincubation with IFNα increased poly(I:C)-stimulated IL-6 but not CCL2 production from healthy control and SSc dermal fibroblasts. *P < 0.05, **P < 0.01 (Wilcoxon signed-rank test).