Romanowsky-Giemsa as a counterstain for immunohistochemistry: optimizing a traditional reagent.

We describe a detailed protocol for using Romanowsky-Giemsa (RG) counterstaining on formalin fixed, paraffin embedded tissue sections that are stained immunohistochemically (IHC) after antigen retrieval using hot acidic citrate buffer. RG staining is easy to perform and provides consistent results that are similar to hematoxylin and eosin (HE) staining. The counterstaining was applied after a variety of antibodies that used the DAB chromogen and the intensity of IHC stained structures was preserved. Moreover, RG counterstaining provided finer cell detail than HE, methyl green or nuclear fast red. A detailed troubleshooting guide is provided for the RG staining protocol.