MMP1 and systemic sclerosis: Some SSc lesional fibroblasts regain production of MMP-1 after several subpassages, and when these fibroblasts lines are then cultured for 3 weeks with IL-13 or PDGF-BB, then cultured in plain medium before TNFα stimulation, the production of MMP-1 in response to TNF-α stimulation is markedly reduced compared to normal donor fibroblasts similarly treated with IL-13 or PDGF-BB (348).