Making tissue arrays by re-embedding affects staining "down the road" 
because of basic chemistry.

Each time a specimen is exposed to air there will be some loss of some 
antigens and nucleic acids due to oxidation from atmospheric ozone, acids, 
etc circulating in the lab. Not all antigens are affected, not every 
antibody has a problem with it, but it does happen and is well recognized in 
tissue array labs.

Many labs have documented this phenomenon. Most notable is David Rimm's lab 
at Yale that has made an art out of preserving antigens on tissue arrays by 
storing them in a special cabinet filled with nitrogen gas. They see 
dramatic losses in staining intensity in sections left in air for just a few 
days.

The problem with reheating tissue array cores is that this oxidation effect 
is grossly accelerated by the higher temperatures and air is allowed to 
penetrate farther into the core once the paraffin has softened from the 
heat. Some labs have stopped anealing cores into tissue array blocks at 37 
degrees because they see a loss in staining. I have had presonal experience 
with loss of in-situ signal in blocks annealed at 32 degrees versus ones 
kept at room temp. I remember at least one study that shows slides stored at 
higher tempuatures (25 degrees, I think) lose some anitgens in fairly short 
order.

If you haven't seen a problem it's probably because of the antibodies you're 
using. Many polyclonals will do fine, many monoclonals won't. The more the 
heat+time+exposure to the atmosphere the more the effect. As with everything 
else in histotechnology it just depends on your specific circumstances.

The basic message is that less physical manipulation of a specimen is ALWAYS 
better than more. There's no reason to heat a specimen to make an array when 
you can do it perfectly well at room temp. Re-embedded tissue arrays may 
work great for a lot of things, but experience shows that they do have 
problems in some applications.

HistoJock


>Date: Mon, 10 May 2004 04:49:52 +0000
>From: "Thom Jensen" 
>Subject: Re: [Histonet] Tissue Array
>To: Histonet@lists.utsouthwestern.edu
>Message-ID: 
>Content-Type: text/plain
>
>
>   How  does  melting paraffin  embedded tissues effect the staining down
>   the  road?   That  doesn't make since.  I have made dozens of multiple
>   punch  arrays  by  melting the punches and embedding them as you would
>   normally  embed  tissues and it has never effected the staining, "DOWN
>   THE ROAD....."
>
>   Thom

   >>From: "Histo Jock" 
   >>To: Histonet@lists.utsouthwestern.edu
   >>Subject: Re: [Histonet] Tissue Array
   >>Date: Fri, 07 May 2004 20:03:31 -0400
   >>
   >>
   >>You might want to be careful using Zymed's arrays. I don't think
   >>they are made with the standard coring method. Rather, I think that
   >>they use some sort of melting / re-embedding process that can effect
   >>staining down the road.
   >>
   >>HistoJock

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