Human transforming growth factor-b1 (TGF-b1) is a signalling molecule with strong regulatory functions on our immune system. For this reason, TGF-b1 is a promising candidate for treating several inflammatory disorders. However, TGF-b1 is a complex protein and requires specific proteolytic cleavage for its activity and is therefore difficult to produce in heterologous expression system. In this manuscript we co-express TGF-b1 with furin (a serine protease) in plants, which enables the post-translational proteolytic processing of TGF-b1. The proteolytic processing of TGF-b1 also enhances the accumulation of biologically active TGF-b1 in plant leaves.