A fibroblast mitogen present in scleroderma but not control sera: inhibition by proteinase inhibitors.

Fibroblast mitogenic activity (MA) has been identified in scleroderma (SD) sera. Control and scleroderma skin fibroblasts in early passage were observed for replication (cell counts) after 72 h of serum exposure. SD sera at 15% concentration induced a significant increase in control fibroblast numbers when compared with control sera; this effect was not seen with SD cells while at higher serum concentrations (30%); SD cells were slightly responsive to the MA. MA was completely abrogated by the proteinase inhibitors STI and TLCK which did not affect mitogens in healthy sera. Circulating mitogenic proteinases selective for fibroblasts could play a role in the fibrosis of SD by modulating fibroblast replication.