The labeled streptavidin-biotin (LSAB) method of IHC staining is a significant improvement of the ABC method. It is highly utilized in immunohistochemistry. In the LSAB method, avidin used in the ABC method is replaced with streptavidin, a protein purified from the bacterium Streptomyces avidinii. Streptavidin is similar to avidin in structure and is highly capable of binding to biotin. However, streptavidin does not bind to tissue lectins as avidin does, which is often the cause of nonspecific staining. Use of streptavidin results in increased sensitivity. This allows for a higher dilution of primary antibody.
The staining method follows these steps, which are similar to those of the ABC method:
- Primary antibody is applied which binds to the antigen.
- The biotin-labeled secondary antibody is added and binds to the primary antibody.
- A complex of enzyme-labeled streptavidin (streptavidin molecule binds directly to enzyme molecules) is applied. This complex binds to the secondary antibody.
- The final step employs the chromogenic substrate of choice to develop the peroxidase for visualization of the antigen site.
