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In message <199505190428.XAA16061@electra.cc.umanitoba.ca> Confocal Microscopy
List writes:
> Hi everyone,
> We are immunostaining for
> macrophages and dendritic cells.
> and have encountered what appears to be endogenous biotin as avidin
> conjugates alone seemed to stain tissue.  Has anyone encountered this
> problem before and are they aware of
> any techniques that block endogenous biotin in tissue prior to staining?
> Look forward to your replies.
>
> Natalia Bilyk
> Dept Anatomy and Human Biology
> University of Western Australia
>  email nbilyk@uniwa.uwa.edu.au

What kind of avadin conjugates are you using?  If it is ABC (peroxidase based
detection), you're probably just picking up endogenous peroxidase and the
mystery biotin may not be the problem.  However, you can try lavamisole (sorry
if the spelling is wrong) to block endogenous biotin activity; although we have
never seen much of a difference with or without it.
Our own experience with staining immune cells, spleen, etc., has led
us to use an alkaline phosphatase detection system.  We have never been able to
completely whip the endogenous peroxidase activity present in some immune cells,
and we have tried everything from H2O2, azide, acid, methanol, (alone, in
combination, etc.) with only marginal success.  The AP system also gives us
sensitivity the is as good or better than the PAP, ABC, etc. system even with AP
labeled secondary antibodies.