TNF and systemic sclerosis: To evaluate the effect of sildenafil on CXCL10 protein release or mRNA expression in SSc Hdfbs, we treated SSc primary and immortalized cell lines with IFNγ (1000 U/mL) + TNFα (10 ng/mL) with/without sildenafil at scalar doses (1 × 10−7, 2.5 × 10−7, 5 × 10−7, 1 × 10−6, 2.5 × 10−6, 5 × 10−6, 1 × 10−5, 2.5 × 10−5 M) or at fixed concentration (1 × 10−6 M) or for 24 h (Figure 4A); drug concentrations have been selected on the basis of the near therapy dose according to the pharmacokinetics (Cmax and area under the time–concentration curve, AUC).