Not having done BrdU in cultured cells, I may be way off.  I would
suspect your antibody might need to be titered out further and/or you
may want to try detecting the antibody using an anti-mouse Alexa 488
instead of a biotin-streptavidin system.  Also, that's quite a hearty
denaturing protocol you are using.  Do you have a publication that
recommends doing it that way?  I don't know if that is related to the
false positive staining, but it's certainly worth looking at.

Teri Johnson
Managing Director Histology Facility
Stowers Institute for Medical Research
1000 E. 50th St.
Kansas City, MO 64133

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