[Histonet] Long term storage for IHC ?

[Rene J Buesa]

Hi Mikael:
Long term storage of formalin fixed tissue is usually never a good option. If you keep them in NBF the antigenic sites could be so compromised that their unmasking could prove to be unsuccessful.
In 70% EthOL they will macerate and, as you point out, could end as if they were alcohol fixed. There are really 2 options:
1- process the tissues and  save the uncut blocks, or
2- select the most interesting pieces and fix them for 48 hours to assure full fixation and after washing in PBS freeze them and keep them frozen at -80ºC. When the moment arises that you will need them, thaw and process them. I think that  you should go with cryoperservation. I am attaching an article I wrote about formalin fixation.
René J.
 
Dear Histonetters,

what do you think is the best way to store formalin-fixed tissues for 
immunohistochemistry, long-term (several years)?

We are currently fixing overnight, then rinsing in buffer and storing in 
70% or 100% ethanol, +4C or -20C. However, I don't really KNOW what 
happens here and how the tissues will work after the years. I guess 
basically the formalin fixation will be at least somewhat reversed and 
after some time the tissues will be more like ethanol fixed. But are 
there better options? Long term storage in formalin will make IHC 
difficult. And this is about large numbers of tissue samples, only some 
of which will be actually used later, so we wouldn't like to process all 
of them to paraffin either.

With best regards,
Mikael Niku
University of Helsinki, Finland

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