HMOX1 and systemic sclerosis: Although expression levels of HO-1 in unstimulated SSc fibroblasts are not significantly different from healthy fibroblasts, exposure to 10 μM TGF-β for 24 h significantly inhibited the expression of HO-1 in healthy but not SSc fibroblasts (Figure 1A), indicating that the expression of HO-1 is already influenced by the elevated endogenous production of TGF-β in SSc fibroblasts.