Activin A is also implicated in the stimulation of fibrosis in a range of experimental models [26] and this action can be inhibited by its binding protein, follistatin; for instance, in a model (carbon tetrachloride (CCl4) -induced) of hepatic fibrosis [27] or bleomycin induced pulmonary fibrosis [28]. Here, FST is linked to pulmonary fibrosis.