Re: [Histonet] Proof that fixation in formaldehyde solution can be reversible?

From:Rene J Buesa

  A piece of tissue sitting in PBS for 1 month after being fixed for 24-48 hours only is likely to have suffered tissue decomposition at the center of it, specially if it was a thick piece. Formalin is an extremely fast fixative but with a very slow rate of penetration, this would have determined external fixation but not complete fixation.
  Fixation is not really reversible in a strict way and that is why you need a strong Heat Inducet Epitope Retrieval (HIER) before IHC to "undo" or "unfix" the crosslinkage produced by formalin.
  The damage to the tissue could have been caused by improper storage = PBS at room temperature during 1 month. If processed that tissue is very likely to present altered microscopic appearance.
  Just my opinion!
  René J. 

GT Hebert  wrote:

I am in a heated debate with an investigator regarding his samples. They were shipped to me after (24-48hrs fixation - 10% NBF or 4% PF unsure exactly which one) and then switch to PBS for shipment. They sat at room temperature for over 1 month before being processed routinely and embedded in paraffin wax. 

Can someone tell me if indeed the fixation is reversible, or once they have been fixed for over 24hrs they remain fixed?? Can anyone refer me to books or papers that talk about this?? 

Also, what affect on antigenicity will such storage in PBS have on these samples?

Thank you all so much for your help.

G. H.
Cambridge, MA

Key words:
NBF, Alcohol, 10%, paraformaldehyde, 4%, fixation, fix, ethanol, 70%, reverse, reversible.

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