RE: Avidin/Biotin blocking

From:Chris van der Loos

Dear Fernando,
After the antigen retrieval step!
In non-antigen retrieval treated FFPE tissue sections there is no 
detectable endogenous biotin, probably due to fixation/embedding. Realize 
that antigen retrieval methods may reveal endogenous biotin again, 
especially when using Tris/EDTA pH9.0.

Apart from the streptavidin-biotin pitfalls mentioned by Gayle Callis, I 
would like to add another pitfall that should be regarded as "endogenous 
(strept)avidin-like".  Van den Oord et al. described the specific binding 
of biotinylated secondary reagents to hepatitis B surface antigen infected 
cells in Bouin- or formalin-fixed human liver (J Histochem Cytochem 37: 
551-554, 1989). This "endogenous (strept)avidin" is probably not blocked 
effectively by regular endogenous biotin blocking methods.

Chris van der Loos
Dept. of Cardiovascular Pathology
Academical Medical Center
Amsterdam - The Netherlands

Fernando Capela e Silva wrote:
 >Date: 14 Apr 2003 12:36:47 -0600
 >From: Fernando Capela e Silva 
 >Subject: Avidin/Biotin blocking
 >In general immunohistochemistry protocol where should I use avidin/biotin
 >1. Peroxidase quenching solution
 >2. Pre-treatment/Antigen Retrieval
 >3. Serum blocking solution (10% non-imune serum)
 >4. Primary antibody
 >5. Secondary Antibody
 >6. Streptavidin/Peroxidase
 >7. Substrate/Chromogen
 >8. Counterstaining
 >9. Mounting
 >Best Regards
 >Fernando Capela e Silva
 >Laborat#243#rio de Biologia da Conserva#231##227#o
 >Departamento de Biologia
 >Universidade de ...vora
 >Apartado 94
 >7002-554 ...vora

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