Assessment of active TGFβ with a bioassay

Background Transforming Growth Factor beta (TGFb) is a highly pleiotropic cytokine that is involved in numerous signalling pathways, including immune homeostasis. It is secreted by all immune cell lineages and is classically viewed as an anti-inflammatory cytokine. TGFb is associated with regulatory T cell (Treg) induction, and Tregfunction. However, in combination with pro-inflammatory cytokines (IL-6, IL-b and IL-23) TGFb will induce proinflammatory Th17 cells. In several autoimmune diseases, including Juvenile Idiopathic Arthritis (JIA), a disrupted Th17-Treg balance, lower Treg numbers or less functional Tregs have been described. Unfortunately TGFb production is hard to measure. Popular methods like flow cytometry or ELISA are not reliable, not sensitive or require activation of all latent TGFb present, which might not be representative.