Affinity Purified anti-HA epitope tag polyclonal antibody detects HA tagged recombinant proteins by IHC on formalin fixed paraffin embedded tissue. Arrowheads point to expression of HA tagged proteins in endothelial cells of mouse aorta. Sections of 4 µm were prepared from representative paraffin blocks. Sections were then deparaffinized and rehydrated with xylene and alcohol. Citrate buffer antigen retrieval was performed for 30 min in a boiling jar. Anti-HA was diluted in blocking buffer at 1:2,000 and reacted at 4° C overnight followed by signal detection using horseradish peroxidase with DAB as the chromogenic substrate. Tissue was counterstained with Mayer's hematoxylin.