Lara;

They  probably are macrophages - which are not expressing endogenous biotin.
Endogenous biotin on NBF paraffin sections is usually not a problem unless you
do HIER.  I would suggest you add about 2% serum (of the tissue species) to the
blocking serum.  Or you could use a specific IgG secondary reagent to tag only
the primary antibody to help rid of this problem.  Hope that helps.

Barb Wright
Genentech, Inc
bwright@gene.com

"L. Muffley" wrote:

> I've been having a terrible time with endogenous biotin in spleen.
> Yesterday i tried Phyllis Davis' biotin blocking recipie (posted 5/01).
> The Grocery store concoction of eggs and milk is so wonderfully simple.
> It did fail however to knock out all non-specific label in my NBF fixed
> paraffin embedded mouse spleen.
> The non-specific label i'm getting localizes in cells that look a bit like
> macrophages. I'm used to looking at skin-not spleen. Does anyone have any
> suggestions?
> Thanks!
> Lara
> Dermatology Dept
> University of Washington Seattle, WA
> muffley@u.washington.edu
>
> On Fri, 7 Sep 2001 DDittus787@aol.com wrote:
>
> > Almost all tissue has biotin, however :liver , and spleen, seem to be the
> > worst.
> >                                                 Dana
> >