TGF-β is capable of producing a variety of effects and virtually all cell types respond to this factor in some way. The inappropriate presence of active TGF-β1 has been implicated in a variety of pathological conditions Because of the necessity for regulating its activity tightly, TGF-β is secreted by cells in the form of an inactive complex. This complex consists of TGF-β1 associated non-covalently with a protein designated the latency associated peptide (LAP).

TGF-β1 and LAP represent components of a pro-peptide that is cleaved in a post-golgi compartment prior to secretion. LAP and TGF-β1 each consist of a disulfide-linked homodimer and the association of these two components renders TGF-β1 inactive and inaccessible to anti-TGF-β antibodies.