Activin A, a homodimer of activin βA subunits, is a member of the transforming growth factor (TGF)-β super-family. Activin A is produced by the placenta during human pregnancy, has been recognized as a multifunctional cytokine expressed in a wide range of tissues and cells with roles in regulation of wound repair, cell differentiation, apoptosis, embryogenesis, and inflammation. The 14 kDa mature human beta A chain shares 100% amino acid sequence identity with bovine, feline, mouse, porcine, and rat beta A. Activin A has been proposed in several pathological processes such as carcinogenesis and fibrosis, and this cytokine may also be involved in the pathogenesis of various inflammatory disorders such as inflammatory bowel disease and rheumatoid arthritis.