The Avidin-Biotin cComplex (ABC) method of IHC staining incorporates a large glycoprotein called avidin that has a very high affinity for a low molecular weight vitamin called biotin. Avidin can be labeled with peroxidase or fluorescein. Biotin can be conjugated to antibodies. Because avidin has extreme affinity for biotin, the binding of avidin to biotin is essentially irreversible. The ABC methodology consists of using an unlabeled primary antibody, a biotinylated secondary antibody, and a complex of avidin-biotin peroxidase. The peroxidase is then developed by the DAB or other substrates to produce a colored label.
This method of IHC staining can be time-consuming especially if you are preparing all of your reagents "fresh". However, commercially developed kits with blocking reagents, secondary antibodies and the peroxidase complex reagents already prepared and "ready-to-use" are readily available from many IHC vendors.
