Growth Differentiation Factor 15 (GDF-15), also called Macrophage Inhibitory Cytokine 1 (MIC-1), is a divergent member of the Transforming Growth Factor beta (TGF-beta ) superfamily. Human GDF-15 shares 66% and 68% amino acid sequence identity with the rat and mouse proteins, respectively. GDF-15 is highly expressed in placenta and brain, and it is expressed at lower levels in kidney, pancreas, prostate, and colon. Similar to other TGF-beta family proteins, GDF-15 is synthesized as a large precursor protein that is cleaved at a dibasic cleavage site (RxxR) to release the mature protein. Biologically active GDF-15 is a disulfide-linked homodimer of the mature protein. GDF 15 has been shown to have various functions, including inhibition of Tumor Necrosis Factor alpha (TNF-alpha ) production from lipopolysaccharide-stimulated macrophages and the induction of cartilage formation. A functional ELISA assay was conducted to detect the interaction of recombinant human GDF-15 and recombinant human Transforming Growth Factor Beta Receptor II (TGFbR2). Briefly, biotin-linked GDF-15 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 ul were then transferred to TGFbR2-coated microtiter wells and incubated for 1h at 37 ℃. Wells were washed with PBST 3 times and incubation with Streptavidin-HRP for 30min, then wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37 ℃. Finally, add 50 μl stop solution to the wells and read at 450 nm immediately. The binding activity of GDF-15 and TGFbR2 was shown in Figure 1, the EC50 for this effect is 7.002 ug/mL.