Formalin fixation produces excessive
cross linking of proteins (formation of methylene
cross bridges) which "mask" antigens.
This "masking" prevents the
mouse anti-BrdU IgG from attaching to the
incorporated BrdU. Staining is very weak to
non-existent in this example
Formalin fixed / Heat Induced Epitope
The HIER technique was able
to recover some, but not all of the BrdU epitopes.
Staining is moderate in this example.
Methacarn is a precipitant fixative
and does not "mask" the antigen.
Note the intense BrdU stain. Methacarn is
an excellent fixative for most cell cycle
related proteins and cytoskeletal proteins.
However, it is not recommended for demonstration
of hormone receptors (ER/PR) and for PCR/in