It acts as a “repair switch” for tissue restoration, while functioning as a doubleedged sword in fibrosis and the tumor microenvironment. It is indispensable for immune homeostasis, organ remodeling and epithelialmesenchymal transition (EMT). Transforming Growth Factor-β (TGF-β) is frequently reported in top-tier journals covering fibrosis, oncology, autoimmunity, cardiovascular disorders and nephrology research.
Many researchers encounter pitfalls in TGF-β ELISA assays: low measured values, large batch-to-batch variations, confusion between total TGF-β and active TGF-β, and interference from platelet-released factors. Below we break down these key points.
What is TGF-β?
TGF-β belongs to the TGF-β superfamily. In humans, there are three major isoforms: TGF-β1, TGF-β2 and TGF-β3. Despite high sequence homology, they differ markedly in tissue distribution and biological functions and cannot be treated interchangeably:

-TGF-β1: The most extensively studied and widely expressed isoform. It is highly expressed in hematopoietic cells, connective tissues and epithelial cells. It exhibits potent pro-fibrotic and immunosuppressive effects and regulates Treg cells. It is the preferred isoform for fibrosis and tumor research.
-TGF-β2: Predominantly found in neural and reproductive tissues. It is widely investigated in developmental regulation and ocular fibrosis studies.
-TGF-β3: Involved in development and wound remodeling. Some studies suggest it exerts anti-fibrotic effects opposite to TGF-β1 and participates in scar inhibition.
⚠️ Critical note: The vast majority of TGF-β in vivo exists as latent complexes with no biological activity. Activation by proteases or acidic microenvironments is required for TGF-β to bind to TβRII/TβRI receptors. This triggers the canonical Smad2/3-Smad4 signaling cascade as well as non-Smad pathways, modulating cell proliferation, apoptosis, matrix synthesis, immune suppression and EMT.