Hyaluronan

http://www.nature.com/nm/journal/v11/n11/images/nm1105-1161-F1.jpg

One of the chief components of the extracellular matrix, hyaluronan contributes significantly to cell proliferation and migration, and may also be involved in the progression of some malignant tumors. It is secreted by fibroblasts (synovial in RA)

http://en.wikipedia.org/wiki/Hyaluronan