Karen
liver & kidney have a high amount of endogenous biotin in them.  Several
immuno companies have an avidin-biotin blocking kit to use as a
pretreatment.  You place avidin on the slides for 15 minutes, rinse in PBS,
then place biotin on for 15 minutes, rinse, then continue with your usual
immuno procedure.  I usually perform this treatment after blocking with
Methanol/Peroxide and before applying the primary. Good luck.

Joe Nocito, B.S., HT(ASCP)QIHC
Histology Supervisor
Christus Santa Rosa Hospitals
San Antonio, Texas 

> -----Original Message-----
> From:	kkdulany@unmc.edu [SMTP:kkdulany@unmc.edu]
> Sent:	Monday, July 10, 2000 11:04 AM
> To:	histonet@pathology.swmed.edu
> Subject:	IH on Liver Tissue
> 
> How can you successfully perform immunohistochemistry on slides of liver
> tissue using horse-radish peroxidase and DAB?  How do you quench the
> endogenous peroxidase in the tissue so everything doesn't turn brown?
> I've
> tried 3, 10 and 15 % H2O2 in both methanol and di water for 20 min. up to
> 1
> hour with no success.  The tissues are formalin fixed and embeded in
> paraffin.  We then used a pH 6.0 citrate buffer/microwave antigen
> retrieval
> system for our primary Ab detection.  Even with all that the endogenous
> enzyme caused the false positive with the DAB.  Anyone have any
> suggestions?
> Thank you for all replies.
> Karen in Omaha
>