Dear Debra,
  I think you are confusing two separate blocking steps.
There is a block for endogenous BIOTIN which uses milk and eggs, however,
this is not a specifically a protein block. (Although the milk probably
functions fairly well as a protein block).

    Nonetheless, PROTEIN blocks generally involve blocking in serum.  For
example, if you have a primary mouse anti-human antibody, and a secondary
anti-mouse IgG (made in a horse), you would want to do a protein block in a
1-5% solution of normal HORSE serum.  This is to (hopefully) block any
non-specific reactivity on the part of your horse anti-mouse secondary.
Incubate in the serum solution for 5-30 minutes at room temperature, tap it
off but DO NOT RINSE.  Apply primary antibody and continue as usual.  Of
course if your secondary antibody was made in another species, use serum of
that species as your protein block.
    Other methods of protein blocking involve the addition of a protein such
as Bovine Serum Albumin (BSA) to the antibody diluent.

    For concise, yet relatively comprehensive discussion of
immunohistochemical methods, including causes of background (such as
non-specific protein interactions), I refer you to DAKO's "Handbook (of)
Immunochemical Staining Methods" (copyright 1989).  Contact your DAKO rep
for how to obtain it (we got ours with our Autostainer).

Best of luck,

Phyllis Davie
PhenoPath Laboratories, Seattle, WA


on 5/7/01 10:55 AM, Debra Lloyd at dlloyd@neuro.mcg.edu wrote:

> The Immuno lab is currently using a protein block manufactored by DAKO.
> Does anyone have the recipe for a protein block using egg whites and
> milk?  We've heard of this method (that could save some money) but don't
> have the specifics.  Any help would be appreciated.
> Thanks,
>