Moran, I find that in IHC procedures mast cell granules take up the
secondary label. If you are doing this to try to see if your IHC is
labeling mast cells, I agree with Rene's assessment - I doubt you will
get histochemical staining over the chromogen, but it might be worth a
try.

Do your IHC procedure first with DAB, then you will stain with Tol.
Blue, air dry, and mount with permanent mounting medium. The Tol blue
will also stain your nuclei, just as if you were doing a regular nuclear
counterstain.

If this stain will obscure nuclear IHC signal, consider doing the
Tolduidine blue stain first, coverslip, photograph, decoverslip and
hydrate back to water, and then perform your IHC procedure, coverslip,
and photograph.  No need to remove the Tolduidine blue before doing your
IHC procedures, as it should wash out in exposure to alcohols and water
prior to and during the IHC procedures.

Hope this helps!

Teri Johnson, HT(ASCP)QIHC
Managing Director Histology Facility
Stowers Institute for Medical Research
1000 E. 50th St.
Kansas City, MO 64110

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