Department of Pathology, Asan Medical Center, University of Ulsan College of Medicine, 88 Olympic-ro, 43-gil, Songpa-gu, Seoul 05505, Korea
© 2016 The Korean Society of Pathologists/The Korean Society for Cytopathology
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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					| Step | Protocol | 
|---|---|
| Fixation | 10% Neutral buffered formalin for 24 hr in room temperature | 
| Frozen section: cold acetone for 1 min | |
| Embedding and sectioning | Paraffin embedding | 
| Mostly 4 μm | |
| Frozen sections: between 4 μm and 6 μm in thickness | |
| Deparaffinization and hydration | 60°C hot plate | 
| Antigen (or epitope) retrieval | Heat induced epitope retrieval is most widely used | 
| Blocking | Normal sera of same species of secondary antibody or premixed | 
| Vary from 30 min to overnight, from 4°C to room temperature | |
| Add primary antibody | Antibody dilution by protein blocking solution or premixed Ab diluents | 
| Appropriate antibody selection and titration | |
| Incubate | 30–60 min, room temperature | 
| Wash (TBS-T) | 3 × 5 min | 
| Add secondary antibody | - | 
| Incubate | 30–60 min, room temperature | 
| Wash | 3 × 5 min, TBS-T | 
| Add substrate | 250 μL of 1% DAB, and 250 μL of 0.3% hydrogen peroxide to 5 mL of PBS, 1–3 minutes, room temperature | 
| Wash | 3 × 5 min, DW | 
| Counterstain | Hematoxylin, 1 min | 
| Antibody | Advantages | Disadvantages | 
|---|---|---|
| Monoclonal | Great epitope specificity and lower background | Less sensitivity or reactivity to masked epitope in a formalin fixed paraffin embedded sample | 
| Better reproducibility | ||
| Polyclonal | Higher sensitivity (recognizing multiple epitopes) | Lesser reproducibility due to batch to batch variability | 
| Higher background due to natural antibodies | ||
| Limited production | 
| Counterstain | Color | Location | Use | 
|---|---|---|---|
| Hematoxylin (4 types: Harris’s, Mayer’s, Carazzi’s, and Gill’s) | Blue | Nucleus | The most popular one | 
| Eosin | Red | Cationic group of protein | Eosin is bound by the majority of structures in any tissue | 
| Methylene blue | Blue | Nucleus | Good to differentiate between DNA and RNA in tissues | 
| Methylene green | Blue/green | Nucleus | |
| Toluidine blue | Deep blue | Nucleus | It will also stain polysaccharides a pink/red color (metachromasia) | 
| Problem | Sdution | 
|---|---|
| Weak or absent staining | |
| Antigen levels are too low | Prolong incubation time of primary antibody | 
| Use a higher sensitivity staining system | |
| Incomplete fixation | Prevent under (> 30 min) or overfixation (> 48 hr) | 
| Use of inappropriate fixative | Check manufacturer’s specifications regarding recommended fixative | 
| Insufficient dehydration | Operating regular reagent changes (i.e., alcohol) | 
| Paraffin too hot | Monitor temperature of paraffin (< 60°C) | 
| Embedding and dewaxing at high oven temperature | Oven temperature not to exceed 60°C | 
| Heating for antigen retrieval | Optimize antigen retrieval time | 
| Reagents not working, reagents in wrong order | Monitor expiration dates, storage parameters, and pH | 
| Antibody too dilute, improper antibody dilution | Determine correct concentration | 
| Check incubation time and temperature | |
| Partial drying out of tissue during processing | Immerse tissue immediately in fixative | 
| Use a huminity or moist chamber during incubation steps | |
| Avoid evaporation with humidity chamber | |
| Chromogen not working, incorrect preparation of chromogen | Add chromogen to labeling sdution | 
| Monitor for change in color | |
| Background or artifactual staining | |
| Excessive incubation | Reduce incubation time | 
| Necrotic or otherwise damaged tissue | Avoid sampling of necrotic areas | 
| Make sure tissue is properly fixed | |
| Antigen diffusion before fixation leading to specific background | Avoid delays in fixation | 
| Thick preparation | Cut sections at 4 to 6 mm | 
| Inappropriately concentrated antibody | Check titration and concentration | 
| Decrease temperature of reaction | |
| Presence of chromogen or undissolved counterstain deposits | Filter the chromogen or counterstain | 
| Insure that chromogen is completely dissolved | |
| Incomplete inadequate rinsing of slides | Follow protocol for proper slide rinsing | 
| Mildly rinse slide with wash buffer bottle and place in wash bath in 5 min | |
| Endogenous pigments | Check the negative control for the presence of these pigments | 
| Use a chromogen of contrasting color | 
						 TBS-T, Tris-buffered saline and Tween 20; DAB, diaminobenzidine; PBS, phosphate buffered saline; DW, dextrose 5% in distilled water.
						 Toluidine blue stains melanin in green so that brown color of diaminobenzidine can be differentiated.