One issue for paraffin manufacturers is the lower the melt point of wax the
softer the wax and the more additive we have to add.  Most labs prefer a
firmer paraffin without the stickiness of high additive thus we look at the
55-60C melt point paraffins as the base.  The urban legend may have as much
to do with what we like to cut as it does with reality of IHC.  The lower
melt points require much colder cutting conditions for excellent ribbons or
a great deal of compression from a warming block.  Pam Marcum

> -----Original Message-----
> From: J. A. Kiernan [mailto:jkiernan@uwo.ca]
> Sent: Friday, October 18, 2002 1:19 AM
> To: histonet@pathology.swmed.edu
> Subject: Re: Paraffin temp for immuno's
>
>
> Ross Stapf (or was it Patsy Ruegg) wrote:
> > On searching ... why heat in paraffin ... might be more
> > detrimental than heat in antigen retrieval solution.
> > ... can't find if anyone came to a conclusion that this was true ...
> > I'm sure someone has studied this in order to come up with this 56
>
> The cited temperature 56C must mean that this is another urban
> laboratory
> legend!  Anyone studying effects of wax temperature would
> investigate
> steps such as 50-55-60. An investigation with a precision of one
> degree would need 20 lots of trials to cover the range, and what
> agency would fund such a study?
>
> Several anecdotal Histonet replies have reported exactly the
> opposite - that temperatures well above the mid-50s does more
> good than harm when it comes to detecting antigens
> immunohistochemically.
> These informal reports, based on firt-hand experience, carry much
> more
> weight than "someone said that..." or a photocopy of some piece
> of
> paper found in a cardboard box.
>
> There is also a Common Wisdom of Immunohistochemistry that says
> coagulation of proteins by heat or coagulant fixatives liberates
> the epitopes of insolubilized protein molecules.
>
> If the routine fixative everywhere was a simple alcohol-acetic
> mixture, would there be any of these problems with masked
> antigens?
>
> --
> -------------------------
> John A. Kiernan
> Department of Anatomy and Cell Biology
> The University of Western Ontario
> London,   Canada   N6A 5C1
>    kiernan@uwo.ca
>    http://publish.uwo.ca/~jkiernan/
>
>