It recognizes an oncofetal glycoprotein with a single chain of 70kDa, which is identified as alpha fetoprotein (AFP). This MAb is highly specific to AFP and shows no cross-reaction with other oncofetal antigens or serum albumin. The yolk sac and the liver produce AFP during fetal life. AFP expression in adults is often associated with hepatoma or teratoma. However, hereditary persistence of alpha-fetoprotein may also be found in individuals with no obvious pathology. The protein is thought to be the fetal counterpart of serum albumin, and the AFP and albumin genes are present in tandem in the same transcriptional orientation on chromosome 4. AFP is found in monomeric as well as dimeric and trimeric forms, and binds copper, nickel, fatty acids and bilirubin. The level of AFP in amniotic fluid is used to measure renal loss of protein to screen for spinal bifida and anencephaly.