Nonspecific staining avidin

Among the sandwich techniques, the ABC is the most universal, with the PAP being the least prone to nonspecific staining. More sensitivity can be had with labeled avidin methods or the newer more-inventive amplified amplifications. A universally applied method with an alternate technique available, like the PAP for occasional problem specimens, will most often suffice. 

The presence of this artifact poses a distinct risk of its being interpreted as positive staining, as the artifact can be intense and may be precisely located in the cells of interest with a clean background. It is known that liver and kidney can retain high amounts of retrievable biotin-avidin activity in neoplasms. The need for adequate controls or biotinblocking procedures is obvious when histochemical or immunohistochemical procedures are used. Negative controls facilitate identification of such nonspecific staining. 

Block nonspecific staining due to cross reaction with endogenous avidin or biotin by incubation with avidin solution followed by biotin solution, both for 20 min (use Vectorstain kit, as directed, Vector Labs, Burlingame, CA). 

Endogenous biotin may be a cause for nonspecific background staining (see Sect. 5.4). To eliminate this unwanted staining, apply an avidin/biotin block (for instance Avidin/Biotin blocking kit from VECTASTAIN, Cat. No. SP-2001). Usually, paraffin tissue sections are free from endogenous biotin, and this step may be omitted. 

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