TGF-β is a multifunctional set of peptides that controls
proliferation,
differentiation, and other functions in many cell types. TGF-β acts synergistically with
transforming growth factor-alpha (TGF-α) in inducing
transformation. It also acts as a negative
autocrine growth factor. Dysregulation of TGF-β activation and signaling may result in
apoptosis. Many cells synthesize TGF-β and almost all of them have specific receptors for this peptide. TGF-β1,
TGF-β2, and
TGF-β3 all function through the same receptor signaling systems. TGF-β1 was first identified in human
platelets as a protein with a molecular mass of 25
kilodaltons with a potential role in
wound healing. It was later characterized as a large
protein precursor (containing 390
amino acids) that was
proteolytically processed to produce a mature peptide of 112 amino acids. TGF-β1 plays an important role in controlling the
immune system, and shows different activities on different types of cell, or cells at different developmental stages. Most immune cells (or
leukocytes) secrete TGF-β1.
T cells Some
T cells (e.g.
regulatory T cells) release TGF-β1 to inhibit the actions of other T cells. Specifically, TGF-β1 prevents the
interleukin(IL)-1- &
interleukin-2-dependent
proliferation in activated T cells, as well as the activation of quiescent
helper T cells and
cytotoxic T cells. Similarly, TGF-β1 can inhibit the secretion and activity of many other
cytokines including
interferon-γ,
tumor necrosis factor-alpha (TNF-α), and various
interleukins. It can also decrease the expression levels of cytokine receptors, such as the
IL-2 receptor to down-regulate the activity of immune cells. However, TGF-β1 can also
increase the expression of certain cytokines in T cells and promote their proliferation, particularly if the cells are immature. and controls the expression of
antibody,
transferrin and
MHC class II proteins on immature and mature B cells. == Interactions ==