Hello Nancy,

I can't comment on the special stains but I've seen success and failure 
performing IHC on stored slides.  On the clinical side, the positive 
controls were typically derived from good source tissue (ie. lots of 
target rich, immunoreactive sites) and formalin-fixed paraffin embedded. 
  Further, the staining protocols were well-developed.  Not unexpectedly 
the stored (room temp) positive controls retained their immunoreactivity 
for extended periods; quality control was maintained by periodic testing 
of the control slides, independent of any patient cases, and 
continuously reconfirmed by reviewing previous cases and their controls.

Conversely, on the research side, storing positive controls was less 
dependable.  With protocols in a state of flux and desirable antigenic 
sites usually lacking, stored slides seemed to "lose" their 
immunoreactivity.  It is important to note that the experimental samples 
and positive controls were fixed in the same manner to obtain the most 
valid results.  It doesn't make much sense to detect a protein in a 
control sample fixed one way and expect the identical result in 
experimental tissue that has been fixed in another - very bad science...

What is the preferred method, and can immunoreactivity be lost? "It 
depends."  Not the answer you wanted but might be the most appropriate.
Many of the more common protocols do just fine with FFPE at RT storage, 
and I don't think the lower temperature of the refrigerator contributes 
much to antigenicty preservation since the tissue proteins are already 
fixed - ie. slowing microbial/fungal activity is less relevant in a 
fixed specimen section.  The real benefit of refrigeration probably 
comes from having the tissue in a clean, controlled, temperature-static 
(homeostatic) environment.  Also, unless rehydrated while in storage, 
there is minimal chance that the cross-linked proteins will 
spontaneously disassociate and reassociate.  In my experience 
immunoreactivity can be lost but is not usually a problem in a 
non-research setting.  Search the Histonet 
[http://www.histosearch.com/histonet.html - "control slides storage"] 
archives for previous comments about this.

Hope this helps,
Todd

HistoNet Server wrote:
> ----------------------------------------------------------------------
> 
> Date: 20 Jun 2003 17:00:15 -0500
> From: "Mitchell, Nancy" 
> Subject: storage of  control slides
> 
> Many facilities cut their control slides to be used for special and IHC
> staining in advance.  Some facilities keep these slides stored at room
> temperature in boxes and  others store them in the refridgerator . What is
> the preferred method for storing control slides and if used for IHC studies,
> will the slides, if cut in advance,  suffer loss of immunoreactivety or
> intensity in the staining? 
> 
> ----------------------------------------------------------------------
> 
> Here are the messages received yesterday!
> 

-- 
Todd Sherman
President
HistoSoft Corporation
"Biology in a new form..."
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