Transforming growth factor beta (TGF-beta) is a cytokine that has critical functions in immune response by regulating Treg and Th17 cells. TGF-beta is first synthesized as pro-TGF-beta and then it is cleaved by furin proprotein convertase in the Golgi apparatus to produce the dimeric propeptides called latency-associated peptide (LAP) that non-covalently associates with the dimeric mature TGF-beta to prevent its activity. This complex can further associate with latent-TGF-beta-binding protein (LTBP) to produce a large latent form for deposition onto the extracellular matrix. The latent-TGF-beta can be expressed on the membrane of activated Treg cells, immature dendritic cells, megakaryocytes, and platelets.