The MaxDiscovery™ Human/Mouse TGF-ß1 ELISA Test Kit is designed for quantitative determination of the concentration of human and mouse TGF-ß1 in serum, plasma, and cell culture supernatant. Human Transforming Growth Factor-beta (TGF-ß) is a pleiotropic cytokine which exists in five isoforms, known as TGF-ß1-5, with homologies of 70-80% and no homology to TGF-a. TGF-ß1 is the most abundant form in lymphoid organs and is found almost ubiquitously while other isoforms are expressed in a more restricted distribution. The biologically active forms of all isoforms are disulfide-linked homodimers. The heat- and acid-stable monomeric subunits have a length of 112 amino acids. The isoforms of TGF-ß arise by proteolytic cleavage of longer precursors; the isoforms are derived from the carboxyl terminal ends of these precursors. Isoforms isolated from different species are evolutionarily closely conserved and have sequence identities on the order of 98%. Mature human, porcine, simian, chicken and bovine TGF-ß1s are identical and differ from mouse TGF-ß1 in a single amino acid. TGF-ß1 is produced in very high levels by platelets, macrophages, lymphocytes, endothelial cells, chondrocytes, and leukemic cells. TGF-ß1 secretion can be induced by steroids, retinoids, EGF, NGF, vitamin D3, and IL-1. Activities of TGF-ß1 include inhibition of cell growth for normal and transformed epithelial cells, endothelial cells, fibroblasts, neurons, and lymphoid cells and other hematopoietic cell types. TGF-ß1 inhibits the proliferation of T cells and NK cells and down-regulates the activities of activated macrophages. TGF-ß1 blocks the anti-tumor activity of IL-2 – bearing lymphokine-activated killer (LAK) cells and plays a critical role in the development of regulatory T cells. Moreover, TGF-ß1 has been shown to act as a co-stimulatory factor for expression of Foxp3, leading to the differentiation of CD4+CD25+ Treg cells from peripheral CD4+CD25- progeny.