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.
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.