Griffin:Antigen Retrieval Technique
Antigen Retrieval is a proven and effective method for optimizing tissue antigen detection of formalin-fixed, paraffin-embedded tissue sections. Pretreatment with an antigen retrieval reagent (Antigen unmasking) that reverses protein cross-links formed by formalin fixation allows greater exposure for the antibody to associate with antigenic sites. There are heat-based (Microwave Oven, Pressure Cooker or Steamer/Roce Cooker) are the most commonly used heating devices. Certain antigenic determinants are masked by formalin fixation and paraffin embedding and may be exposed. Below are the most popular and effective methods from researchers performing these experiments.
Heat Treatment
10-20 minute heat treatment is a common range that is widely effective. The cooling process taking ~20 minutes. The main mechanism of heat-induced antigen retrieval is disruption of the cross-links and pH is also an essential factor for proper refolding of epitopes. For this reason a low pH and high pH buffer is a good contrast in optimizing the staining protocol.
- 10 mM sodium citrate buffer, pH 6.0.
- 50 mM glycine-HCl buffer, pH 3.5, with 0.01% (w/v) EDTA.
Heat at 95º C for 5 minutes. Top off with fresh buffer and heat at 95º C for 5 minutes (optimal incubation time may vary for each tissue type). Allow slides to cool in the buffer for approximately 20 minutes. Wash in deionized H2O three times for 2 minutes each. Aspirate excess liquid from slides.
- 0.05% citraconic anhydride solution, pH 7.4
Formaldehyde reacts predominantly with the lysyl residues and forms intramolecular cross-links. Citraconic anhydride reacts with the free amino groups of proteins and replaces the positively charged NH3 groups of lysyl residues with negatively charged carboxyl groups. Citraconic anhydride solution efficiently releases formaldehyde cross-links. Heat deparaffinized formalin fixed tissue sections in 0.05% citraconic anhydride solution, pH 7.4, at 98C for 45 min., followed by 3 wash steps.
- Yamashita S and Okada Y. Mechanisms of heat-induced antigen retrieval: analyses in vitro employing SDS-PAGE and immunohistochemistry. J Histochem Cytochem. 2005 Jan;53(1):13-21. DOI:10.1177/002215540505300103 |
- Namimatsu S, Ghazizadeh M, and Sugisaki Y. Reversing the effects of formalin fixation with citraconic anhydride and heat: a universal antigen retrieval method. J Histochem Cytochem. 2005 Jan;53(1):3-11. DOI:10.1177/002215540505300102 |
Enzymatic Treatment
- Trypsin: Incubate sections for 10–20 minutes in 0.1% Trypsin PBS at room temperature. Wash slides several times in deionized H2O. Aspirate excess liquid from slides.
- Pepsin: Incubate sections for 10–20 minutes in 0.1% pepsin in 0.01 N HCl at room temperature. Wash slides several times in deionized H2O. Aspirate excess liquid from slides.
Detergent Treatment
- Saponin: Incubate sections for 30 minutes in 0.05% saponin in deionized H2O at room temperature. Wash at least three times in PBS. Aspirate excess liquid from slides.
