This sandwich ELISA is designed with polyclonal antibodies coated onto the plate for capturing ANNEXIN A1 (ANXA1) in the tested sample. Following a washing step, captured ANXA1 is tagged with a peroxidase-labelled polyclonal antibody, which binds onto the free epitopes in a dose-dependent manner. After washing away the excess of immunoconjugate, the substrate, 3,3',5,5' Tetramethylbenzidine (TMB) with hydrogen peroxide (H2O2) is introduced and a blue color develops, which turns yellow when the reaction is stopped with sulfuric acid. This color is measured at 450nm, and the measured value is directly proportional to the amount of ANXA1 present in the tested sample. Results are expressed in ng/ml, by reference to a calibrated internal reference preparation of human recombinant ANXA1.

ANXA1, or Lipocortin I, is a 37 kDa protein from the annexin family with strong anti-inflammatory and pro-resolving activities (Perretti and D'Aquisto, Nat Rev Immunol 2009). ANXA1 is highly expressed in neutrophils, monocytes and macrophages and modestly in mast cells, endothelial cells, epithelial cells and fibroblasts.The 5-ELISA Annexin A1 Antigen kit is a two-site enzyme immunoassay for measuring Annexin A1 antigen in plasma or in any biological fluid where it must be tested.