TGF beta 1

Transforming growth factor beta 1 or TGF-β1 is a polypeptide member of the transforming growth factor beta superfamily of cytokines. It is a secreted protein that performs many cellular functions, including the control of cell growth, cell proliferation, cell differentiation and apoptosis.

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.^[1] 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.^[2]

TGF-β1 plays and important role in controlling the immune system, and shows diiferent activities on different types of cell, or cells at different developmental stages. Most immune cells (or leukocytes) secrete TGF-β1.^[3]

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TGF-β1 and T cells

Some T cells (e.g. regulatory T cells) release TGF-β1 to inhibit the actions of other T cells. Interleukin 1- and interleukin 2-dependent proliferation of activated T cells,^[4][5] and the activation of quiescent helper T cells and cytotoxic T cells is prevented by the activity of TGF-β1.^[6][7] 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.^[8]

TGF-β1 and B cells

TGF-β1 has similar effects on B cells that also vary according to the differentiation state of the cell. It inhibits proliferation and apoptosis of B cells,^[9] and plays a role in controlling the expression of antibody, transferrin and MHC class II proteins on immature and mature B cells.^[3][9]

TGF-β1 and myeloid cells

The effects of TGF-β1 on macrophages and monocytes is predominantly suppressive; this cytokine can inhibit the proliferation of these cells and prevent their production of reactive oxygen (e.g. superoxide (O₂⁻)) and nitrogen (e.g. nitric oxide (NO)) intermediates. However, as with other cell types, TGF-β1 can also have the opposite effect on cells of myeloid origin. For example, TGF-β1 acts as a chemoattractant, directing an immune response to some pathogens; macrophages and monocytes respond to low levels of TGF-β1 in a chemotactic manner. Furthermore, the expression of monocytic cytokines (including interleukin-1(IL-1)-alpha, IL-1-beta, and TNF-α), ^[7] and phagocytic killing by macrophages can be increased by the action of TGF-β1.^[3]

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