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Immunohistochemistry (Paraffin)

Immunohistochemical analysis of paraffin-embedded human breast carcinoma using p21 Waf1/Cip1 (12D1) Rabbit mAb #2947 in the presence of control peptide (left) or p21 Waf1/Cip1 Blocking Peptide (right).

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Immunohistochemistry (Paraffin)

A. Solutions and Reagents

NOTE: Prepare solutions with reverse osmosis deionized (RODI) or equivalent grade water.

  1. Xylene.
  2. Ethanol, anhydrous denatured, histological grade (100% and 95%).
  3. Deionized water (dH2O).
  4. Hematoxylin (optional).
  5. Wash Buffer:
    1. 1X Tris Buffered Saline with Tween® 20 (TBST): To prepare 1L 1X TBST add 100 ml 10X Tris Buffered Saline with Tween® 20 (#9997) to 900 ml dH20, mix.
  6. SignalStain® Antibody Diluent (#8112).
  7. 1X Citrate Unmasking Solution: To prepare 250 mL of 1X citrate unmasking solution, dilute 25 ml of SignalStain® Citrate Unmasking Solution (10X) (#14746) with 225 mL of dH2O.
  8. 3% Hydrogen Peroxide: To prepare 100 ml, add 10 ml 30% H2O2 to 90 ml dH2O.
  9. Blocking Solution: TBST/5% Normal Goat Serum or 1X Animal-Free Blocking Solution.
    1. TBST/5% Normal Goat Serum: to 5 ml 1X TBST, add 250 µl Normal Goat Serum (#5425).
    2. 1X Animal-Free Blocking Solution: to 4 mL of dH2O add 1 ml of Animal-Free Blocking Solution (5X) (#15019).
  10. Detection System: SignalStain® Boost IHC Detection Reagents (HRP, Rabbit #8114).
  11. Substrate: SignalStain® DAB Substrate Kit (#8059).
  12. Hematoxylin: Hematoxylin (#14166).
  13. Mounting Medium: SignalStain® Mounting Medium (#14177).

B. Deparaffinization/Rehydration

NOTE: Do not allow slides to dry at any time during this procedure.

  1. Deparaffinize/hydrate sections:
    1. Incubate sections in three washes of xylene for 5 min each.
    2. Incubate sections in two washes of 100% ethanol for 10 min each.
    3. Incubate sections in two washes of 95% ethanol for 10 min each.
  2. Wash sections two times in dH2O for 5 min each.

C. Antigen Unmasking

For Citrate: Heat slides in a microwave submersed in 1X citrate unmasking solution until boiling is initiated; follow with 10 min at a sub-boiling temperature (95°-98°C). Cool slides on bench top for 30 min.

D. Staining

  1. Wash sections in dH2O three times for 5 min each.
  2. Incubate sections in 3% hydrogen peroxide for 10 min.
  3. Wash sections in dH2O two times for 5 min each.
  4. Wash sections in wash buffer for 5 min.
  5. Block each section with 100–400 µl of preferred blocking solution for 1 hr at room temperature.
  6. Remove blocking solution and add 100–400 µl primary antibody diluted in SignalStain® Antibody Diluent (#8112) to each section. Incubate overnight at 4°C.
  7. Equilibrate SignalStain® Boost Detection Reagent (HRP, Rabbit #8114) to room temperature.
  8. Remove antibody solution and wash sections with wash buffer three times for 5 min each.
  9. Cover section with 1–3 drops SignalStain® Boost Detection Reagent (HRP, Rabbit #8114) as needed. Incubate in a humidified chamber for 30 min at room temperature.
  10. Wash sections three times with wash buffer for 5 min each.
  11. Add 1 drop (30 µl) SignalStain® DAB Chromogen Concentrate to 1 ml SignalStain® DAB Diluent and mix well before use.
  12. Apply 100–400 µl SignalStain® DAB to each section and monitor closely. 1–10 min generally provides an acceptable staining intensity.
  13. Immerse slides in dH2O.
  14. If desired, counterstain sections with hematoxylin (#14166).
  15. Wash sections in dH2O two times for 5 min each.
  16. Dehydrate sections:
    1. Incubate sections in 95% ethanol two times for 10 sec each.
    2. Repeat in 100% ethanol, incubating sections two times for 10 sec each.
    3. Repeat in xylene, incubating sections two times for 10 sec each.
  17. Mount sections with coverslips and mounting medium (#14177).

posted February 2010

revised March 2016

Protocol Id: 283

Product Description

This peptide is used to block p21 Waf1/Cip1 (12D1) Rabbit mAb #2947 reactivity in immunohistochemistry protocols.


Quality Control

The quality of the peptide was evaluated by reversed-phase HPLC and by mass spectrometry. The peptide blocks p21 Waf1/Cip1 (12D1) Rabbit mAb #2947 signal in immunohistochemistry.

Product Usage Information

Use as a blocking reagent to evaluate the specificity of antibody reactivity in immunohistochemistry protocols. For immunohistochemistry, add twice the volume of peptide as volume of antibody used in 100 μl total volume. Incubate for a minimum of 30 minutes prior to adding the entire volume to the slide. Recommended antibody dilutions can be found on the product data sheet.


Storage: Supplied in 20 mM potassium phosphate (pH 7.0), 50 mM NaCl, 0.1 mM EDTA, 1 mg/ml BSA, 5% glycerol and 1% DMSO. Store at –20°C.

The tumor suppressor protein p21 Waf1/Cip1 acts as an inhibitor of cell cycle progression. It functions in stoichiometric relationships forming heterotrimeric complexes with cyclins and cyclin-dependent kinases. In association with CDK2 complexes, it serves to inhibit kinase activity and block progression through G1/S (1). However, p21 may also enhance assembly and activity in complexes of CDK4 or CDK6 and cyclin D (2). The carboxy-terminal region of p21 is sufficient to bind and inhibit PCNA, a subunit of DNA polymerase, and may coordinate DNA replication with cell cycle progression (3). Upon UV damage or during cell cycle stages when cdc2/cyclin B or CDK2/cyclin A are active, p53 is phosphorylated and upregulates p21 transcription via a p53-responsive element (4). Protein levels of p21 are downregulated through ubiquitination and proteasomal degradation (5).


1.  Pestell, R.G. et al. (1999) Endocrine Rev. 20, 501-534.

2.  Cheng, J. et al. (1999) EMBO J. 18, 1571-1583.

3.  Flores-Rozas, H. et al. (1994) Proc. Natl. Acad. Sci. USA 91, 8655-8659.

4.  Wang, Y. and Prives, C. (1995) Nature 376, 88-91.

5.  Sheaff, R.J. et al. (2000) Cell 5, 403-410.


Entrez-Gene Id 1026
Swiss-Prot Acc. P38936


For Research Use Only. Not For Use In Diagnostic Procedures.
Cell Signaling Technology is a trademark of Cell Signaling Technology, Inc.

1055
p21 Waf1/Cip1 Blocking Peptide