Placental growth factor (PlGF) is a member of the PDGF/VEGF family of growth factors. Four alternatively-spliced isoforms have been identified: PlGF-1, PlGF-2, PlGF-3, and PlGF-4. All isoforms are expressed in placental tissues, with PlGF-2 being expressed specifically during early placental development. PlGF-1 and PlGF-3 are considered diffusible isoforms, while PlGF-2 and PlGF-4 each contain a unique heparin binding domain that may increase associations with cell membranes. In addition to placental tissues, PlGF is expressed in the microvasculature, bone marrow, umbilical vein endothelia, uterine keratinocytes, and NK cells. PlGF binds to both VEGF-R1 and neuropilin, but not VEGF-R2 and induces monocyte activation, migration, inflammatory cytokine production. PlGF plays a key role in maternal vascular function during pregnancy, with circulating levels reaching a peak mid-gestation. It can be used as a marker for pregnancy-associated hypertensive disorders such as pre-eclampsia. High levels of PlGF expression have also been linked to tumorigenesis; specifically PlGF-1 has been identified in both colon and mammary carcinomas.The BioLegend ELISA MAX? Deluxe Set is a sandwich Enzyme-Linked Immunosorbent Assay (ELISA). The human PlGF capture antibody is first coated on a 96-well plate. Standards and samples are added to the wells and PlGFbinds to the immobilized capture antibody. Next, biotinylated anti-human PlGF detection antibody is added, producing an antibody-antigen-antibody “sandwich”. Avidin horseradish peroxidase is subsequently added, followed by TMB Substrate Solution, producing a blue color in proportion to the concentration of PlGF present in the sample. Finally, the Stop Solution changes the reaction color from blue to yellow, and the microwell absorbance is read at 450 nm with a microplate reader.