When, oh, when should we block endogenous peroxidase. IMO like many aspects
of IHC  it most definitely varies.
I normally blocked before HIER, however, could not get CD4 to stain well.
Changed the blocking step to after the primary - problem solved. Many
autostainers also block after primary. So in the end for MOST routine
antibodies I guess it doesn't matter much if at all. However there will
always be the oddy which breaks the rule.

Happy staining

John

John Auld FIBMS MSc
Dept of Histopathology and Clinical Cytology
Arrowe Park Hospital
Arrowe Park Road
Upton
Wirral