Fas
A member of the TNF receptor gene family. Engagement of Fas (CD95) on the surface of the cell by the Fas ligand present on cytotoxic cells, can trigger apoptosis in the Fas-bearing target cell.

fibrin
A white insoluble fibrous protein formed by the action of thrombin on fibrinogen when blood clots; it forms a network that traps red cells and platelets

fibroblast
Connective tissue cell which produces collagen and plays an important part in wound healing.

fibrosis
The growth of scar tissue possibly due to infection, inflammation, injury, or even healing.