Fatty acid binding protein-4 (FABP4) is a member of a large superfamily of lipid binding proteins that are expressed in a tissue specific manner. FABP4 is one of ten cytoplasmic FABPs that are 14-15 kDa in size and range from 126-140 amino acids (aa) in length. Although all are highly conserved in their tertiary structure, there is only modest aa identity between any two members. Lipase, Hormone Sensitive (LIPE) has been identified as an interactor of FABP4, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant mouse FABP4 and recombinant human LIPE. Briefly, FABP4 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 ul were then transferred to LIPE-coated microtiter wells and incubated for 1h at 37℃. Wells were aspirated and incubated for 1h with anti-FABP4 mAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody, 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 FABP4 and LIPE was shown in Figure 1, and this effect was in a dose dependent manner. The EC50?for this effect is 0.23 ug/mL.