[Histonet] IHC pos. & neg. control question

[Amos Brooks]

Hi,
     This is simply a question of definitions. They are actually both right.
If you have the patient tissue as a negative control you are not using the
primary antibody on it but are replacing it (ideally) with an Ig with the
same isotype AND dilution (universal negative is stupid). So if your primary
is an IgG1 from a mouse and you use it at 1:100, your negative control would
be a non-immune mouse serum IgG1 diluted to 1:100. Running this on unrelated
material will not show you anything in this case. what it will show you is
that the detection system you are using is specific to the antibody you put
on the tissue and not to A) something else in the tissue or B) something on
the Ig that is not the epitope itself.
     Although, If you run the same primary antibody on tissue that you
expect will not react with the primary antibody, this would prove that the
antibody reaction is specific to the antigenin question. This does raise the
question of what to do about ubiquitous antigens (like ubiquitin) that are
actually everywhere. Every cell has a cell cycle so they will all at one
point or another show proliferation or degeneration for example. Does this
mean you don't run a negative control? No you need to look at it in the
perspective of expected results.
     There are various ways of using negative (and positive) controls. It
would actually be cost prohibitive to run ALL the possible positive and
negative controls for every test that we as histologists do. We need to
discuss with our pathologists what they want to have done to give them the
confidence in our testing to support their diagnosis. But remember that just
because another lab and another pathologist does it differently doesn't mean
it is wrong. It's just different.

Happy Friday Folks,
Amos


Message: 5
Date: Thu, 19 May 2011 13:25:49 -0400
From: "Jean-Martin Lapointe" <jm.lapointe <@t> accellab.com>
Subject: [Histonet] IHC pos. & neg. control question
To: <histonet <@t> lists.utsouthwestern.edu>
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Hi Curt,
I agree with your pathologist. The section that you use as a negative
control (without primary) in an IHC run should ideally be tissue that is a
known positive, and of the same nature as the test sample. Therefore the
best sample is often a section of your positive control tissue.
The purpose of this negative control is to make sure that any positive
staining observed in the test sample is not due to a spurious
cross-reaction, unrelated to the primary. I don't think the issue per se is
that you are using tissue from the same patient; rather, it is that you are
using a sample for which the staining characteristics are not known. For
instance, if are using a lymph node section as a negative, for a stain that
targets an epithelial marker (eg Her2) in the test breast sample, then your
negative tissue is not appropriate, because since lymph node contains no
epithelial tissue, it will not stain no matter what. Therefore if your test
sample shows a positive reaction in the epithelial tissue, but for some
reason that reaction is a spurious false-positive, then the lymph node
negative will not reveal that.
I realize that this is all very theoretical and hypothetical, but I
understand the pathologist wanting to be confident in the knowledge that all
potential technical issues are eliminated before making his diagnosis.

Jean-Martin