The action of IL-17A in systemic sclerosis is complex: studies have demonstrated that IL-17A (in conjunction with TNF) can be anti-fibrotic through the upregulation of matrix metalloproteinases 1 (MMP-1) and the inhibition of collagen synthesis in human dermal fibroblasts [46,77], although this may not be as effective in fibroblasts isolated from disease sites. Here, MMP1 is linked to systemic sclerosis.