 It can then either form a receptor complex with activin A receptor, type IB (ACVR1B) or with activin A receptor, type IC (ACVR1C).When the receptor-ligand binding occurs via local action, this is classified as paracrine signalling.The TGF beta ligand binds to a type II receptor dimer, which recruits a type I receptor dimer forming a hetero-tetrameric complex with the ligand.