RE: storing controls -Reply -Reply

From:Tony Henwood <>

Since Formalin fixation is a clockwork reaction ( It gets in, binds to
proteins then cross links with other bound formalin molecules - simply
speaking), it has been proposed that the crosslinking reaction can
actually continue while the tissue is in the wax block. Some suggest that
the high temperature of wax infiltration actually aids the reaction of
formalin with nucleic acids, which require higher temperatures for the
reaction with formalin to occur.

>>> David Taylor Manager <DTMan@KINGMOWER.COM.AU>
10/April/2001 02:54pm >>>
Dear Tony, I am curious to hear by what mechanism fixation continues in
formalin fixed, paraffin embedded blocks of tissue. I thought a well
processed piece of tissue embedded in paraffin wax was stable.
 I understand that cut sections stored for an extended period don't stain
well as fresh cut sections when using certain Ab's due to (I think)
oxidation and I have heard some Ab's simply won't work unless a
section is
cut fresh from the paraffin block. David.

This might be due to antigens not reacting at all with the formalin,
remember not every molecule in a cell will react with formalin. Possibly
denaturing of epitopes in sections, though I have not found this to occur
in my hands, probably don't use the same antibodies.

David Taylor
Laboratory Manager
Drs King & Mower
Adelaide, Australia

-----Original Message-----
From: Tony Henwood []
Sent: Monday, 9 April 2001 16:56
Subject: RE: storing controls -Reply

One thought is that since formalin fixation continues in the wax block (ie
cross-linking), it might be possible that these archived blocks may need
prolonged antigen retrieval, longer than sections cut from recently
processed blocks.

Any thoughts???

Tony Henwood JP, BappSc, GradDipSysAnalys, CT(ASC)
Laboratory Manager
The Children's Hospital at  Westmead,
Locked Bag 4001, Westmead, 2145, AUSTRALIA.
Tel: (02) 9845 3306
Fax: (02) 9845 3318

>>> "George, Cheryl" <> 6/April/2001 11:14pm
Hi Ray,
    Currently we don't keep the patient blocks in the refridgerator but I
have been giving it some serious thought lately; for a subgroup of cases
(not enough space given our volume!).  Although I have never done a
study for the loss of antigenicity by antibody, I have noticed a significant
loss in breast stained for ER and PR when trying to find new controls
old patient cases. I will pull old known positive slides that are 4+ at
initial staining and when the ER and PR are tested again, they tend to
decrease to 2+ and in some cases even more.  These are the only two
that I
have noticed a problem with and so I am looking into the feasibility of
storing those blocks in the fridge.

    Has anyone else noticed this type of decrease with those antibodies?


> ----------
> From:[]
> Sent: 	Thursday, April 05, 2001 3:22 PM
> To: 	George, Cheryl
> Cc:; 'Michelle Peiffer'
> Subject: 	RE: storing controls
> Cheryl,
> Do you keep test (or patient blocks) in refrigerator?  Just curious about
> your thoughts regarding having a control  block/section nicely positive
> for
> "X" from the refrigerator stained next to a test section/block for "X"
> that
> has been stored at room temp and is negative.  Would it truly be so?
> Thanks,
> Ray
> Seattle, WA
>                     "George,
>                     Cheryl"               To:
>, 'Michelle      
>                     <CGerorge@Elli        Peiffer' <>
>           >            cc:
>                                           Subject:     RE: storing
> controls                    
>                     04/05/01 09:36
>                     AM
> Michelle,
> We store all of our control blocks and slides in the refridgerator.
> Cheryl
> > ----------
> > From:         Michelle Peiffer[]
> > Sent:         Thursday, April 05, 2001 10:28 AM
> > To: 
> > Subject:           storing controls
> >
> > Thanks to all who responded about my IHC decreased staining post.
> >
> > Several people have mentioned storage of the controls.  Some are
> purchased
> > slides, so obviously they are precut and they are stored in the
> > refrigerator.  But most are freshly cut from blocks which are stored
> > room temperature.  I was under the impression most people store
> at
> > room temperature, is this correct?  How long can controls last?  We
> > started doing histology so our oldest blocks are only 6 months old.
> >
> >
> > Michelle
> >
> >
> > Michelle Peiffer
> > *************************************************************
> > Electron Microscope Facility for the Life Sciences
> > Penn State University Biotechnology Institute
> > 001 South Frear Lab
> > University Park PA 16802
> >
> > phone: 814-865-0212
> > email:
> > **************************************************************

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