[Histonet] Re: Modified Mowry (Long discussion)

[John Kiernan]

gJeannie Heck wrote:
> 
> I would deeply appreciate a procedure for a modified
> Mowry Colloidal Iron using 3% as a mordant before the
> colloidal iron stain. I am currently using the Muller
> Mowry and I am getting inconsistent results. All help
> is appreciated. Please post to this list or e-mail me
> directly at heckj <@t> hhosp.com. Thanks in advance.
> Jeannie Heck HT (ASCP)
___________________________________________________

3% what? Nothing in any colloidal iron method involves
mordanting, because no dye is involved (except as a
counterstain, which might include a mordant as in
the case of aluminium-nuclear fast red or brazalum).

Mowry's technique is a modification of Hale's original, 
which wasn't much good. Pearse's Histochemistry reviews 
the various colloidal iron methods. It is the best
reference, and has been translated into several 
languages.

Is there any reason for using colloidal iron
instead of an equivalent alcian blue method? 

Alcian blue techniques are more reproducible 
and have greater histochemical validity. Certified 
dye is available (tested in the Biological Stain 
Commission's lab, which is a non-profit outfit that
serves both vendors and users of stains). The solid
dye powder can deteriorate on the shelf, very
unpredictably (I've had this happen 3 times). The
deteriorated dye is insoluble; I have suspicions 
about why. Solutions of alcian blue at pH1 or 
pH3 keep working for a long time (a few years) even 
with repeated use. Alcian blue has its faults, but
it's a better histochemical reagent than colloidal
iron. 

There are several clever PAS variants developed by
Scott et al in Britain and by Reid, Culling et al in
Canada, from the late 1960s to the early 1990s. These 
methods have numerous steps but they stain 
macromolecular carbohydrates with well defined 
chemical specificity. These splendid methods are 
respectfully explained in textbooks but I suspect
that they are seldom used in labs.

There are also dozens of labeled lectins, which have 
high specificity and have been commercially available 
for 20+ years. There may be a lectin that binds 
specifically to the macromolecular carbohydrate that 
you are trying to stain with colloidal iron. Lectin
histochemistry is EASY++ but you must do all the
needed controls or your spectacularly specific 
pictures might be worthless artifacts. Lectins are
the plant kingdoms's equivalent of antibodies. They
recognize sugars and oligosaccharide sequences 
rather than the amino acid sequences (epitopes)
that adhere to antibody molecules.
--
-------------------------
John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London,   Canada   N6A 5C1
   kiernan <@t> uwo.ca
   http://publish.uwo.ca/~jkiernan/