TGF-beta 1 (Transforming Growth Factor beta 1) is a pleiotrophic cytokine that regulates immune function, proliferation, and epithelial-mesenchymal transition. TGF-beta 1 associates with LAP to form a latent complex. It can be is activated from latency by plasmin, matrix metalloproteases, thrombospondin 1, and a subset of integrins. TGF-beta 1 signals through complexes of TGF-beta RII with TGF-beta RI/ALK-5 or ALK-1. TGF-beta signaling is modulated by the accessory receptors TGF-beta RIII/Betaglycan and Endoglin/CD105.