Immunocytochemistry (ICC) and immuofluorescence (IF)
General procedure
1. 2. 3. 4. 5. 6.
Coat coverslips with polyethylineimine or poly-L-lysine for 1 hr at room temperature. Rinse coverslips well with sterile H2O (three times 5 min each).
Allow coverslips to dry completely and sterilize them under UV light for at least 4 hr. Grow cells on glass coverslips or prepare cytospin or smear preparation. Rinse briefly in phosphate-buffered saline (PBS).
For wash buffer we recommend 1x PBS 0.1% Tween 20.
Fixation
The cells may be fixed using one of two methods:
1. Incubating the cells in 100% methanol (chilled at -20°C) at room temperature for 5 min. 2. Using 4% paraformaldehyde in PBS pH 7.4 for 10 min at room temperature
The cells should be washed three times with ice cold PBS.
Antigen retrieval (optional step)
Certain antibodies work best when cells are heated in antigen retrieval buffer. Please check the product datasheets for recommendations for each primary antibody being used.
1. Preheat the antigen retrieval buffer (100 mM Tris, 5% (w/v) urea, pH 9.5) to 95°C. This can be done by
heating the buffer in a coverglass staining jar which is placed in a water bath at 95°C.
2. Using a small pair of broad-tipped forceps, place the coverslips carefully in the antigen retrieval buffer in
the cover glass staining jar, making note of which side of the coverslips the cells are on. 3. Heat the coverslips at 95°C for 10 min.
4. Remove the coverslips from the antigen retrieval buffer and immerse them, with the side containing the cells
facing up, in PBS, in the 6-well tissue culture plates. 5. Wash cells in PBS three times for 5 min.
Permeabilization
If the target protein is localized intracellularly, it is very important to permeabilize the cells.
Acetone fixed samples do not require permeabilization.
1. Incubate the samples for 10 min with PBS containing either 0.1 - 0.25% Triton X-100 (or 100 μM Digitonin or
0.5% Saponin). Triton X-100 is the most popular detergent for improving the penetration of the antibody. However, it is not appropriate for membrane-associated antigens since it destroys membranes.
The optimal percentage of Triton X-100 should be determined for each protein of interest. 2. Wash cells in PBS three times for 5 min.
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Blocking and Immunostaining
1. Incubate cells with 1% BSA in PBST, 22.52 mg/ml glycine in PBST (PBS+ 0.1% Tween 20) - for 30 min to
block unspecific binding of the antibodies (alternative blocking solutions are 1% gelatin or 10% serum from the species from which the secondary antibody was raised in. Please see antibody datasheet for recommended blocking).
2. Incubate cells in the diluted antibody in 1% BSA in PBST in a humidified chamber for 1 hr at room
temperature or overnight at 4°C.
3. Decant the solution and wash the cells three times in PBS, 5 min each wash.
4. Incubate cells with the secondary antibody in 1% BSA for 1 hr at room temperature in the dark. 5. Decant the secondary antibody solution and wash three times with PBS for 5 min each in the dark.
Multicolor Immunostaining (optional step)
In order to examine the co-distribution of two (or more) different antigens in the same sample, a double
immunofluorescence procedure can be carried out. This can be performed either simultaneously (in a mixture) or sequentially (one antigen after another).
Please ensure you have antibodies for different species and their corresponding secondary antibodies. For example, rabbit antibody against antigen A, mouse antibody against antigen B. Alternatively, you can use directly conjugated primary antibodies conjugated to different fluorophores.
Simultaneous incubation
1. Incubate cells with 1% BSA in PBST for 30 min to block unspecific binding of the antibodies (alternative
blocking solutions are 1% gelatin or 10% serum from the species that the secondary antibody was raised in). 2. Incubate cells in the mixture of two primary antibodies (e.g. rabbit against human target-1 and mouse
against human target-2, if the targets are human proteins) in 1% BSA in PBST in a humidified chamber for 1 hr at room temperature or overnight at 4°C.
3. Decant the mixture solution and wash the cells three times in PBS, 5 min each wash.
4. Incubate cells with the mixture of two secondary antibodies which are raised in different species (with two
different fluorochromes, i.e. Texas Red-conjugated against rabbit and FITC-conjugated against mouse) in 1% BSA for 1 hr at room temperature in the dark.
5. Decant the mixture of the secondary antibody solution and wash three times with PBS for 5 min each in the
dark.
Sequential incubation
1. First blocking step: incubate cells with the first blocking solution (10% serum from the species that the
secondary antibody was raised in) for 30 min to block unspecific binding of the antibodies (alternative blocking solutions are 1% gelatin or 1% BSA) at room temperature.
2. Incubate cells with the first primary antibody in 1% BSA or 1% serum in PBST in a humidified chamber for 1
hr at room temperature or overnight at 4°C depending on the concentration of the antibody and the accessibility of the antigen.
3. Decant the first primary antibody solution and wash the cells three times in PBS, 5 min each wash.
4. Incubate cells with first secondary antibody (labelled with Fluorochrome-1) in 1% BSA in PBST for 1 hr at
room temperature in the dark.
5. Decant the first secondary antibody solution and wash three times with PBS for 5 min each in the dark. 6. Second blocking step: incubate cells with the second serum (10% serum from the species that the
secondary antibody was raised in) for 30 min at room temperature to block unspecific binding of the antibodies (alternative blocking solutions are 1% gelatin or 1% BSA) in the dark.
7. Incubate cells with the second primary antibody in 1% BSA or 1% serum in PBST in a humidified chamber in
the dark for 1 hr at room temperature or overnight at 4°C depending on the concentration of the antibody and the accessibility of the antigen.
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8. Decant the second primary antibody solution and wash the cells three times in PBS, 5 min each wash in the
dark.
9. Incubate cells with second secondary antibody (labelled with Fluorochrome-2) in 1% BSA for 1 hr at room
temperature in the dark.
10. Decant the second secondary antibody solution and wash three times with PBS for 5 min each in the dark.
If you have to detect more than two antigens, continue following steps 1-5 for the rest of the antibodies.
Counter staining
1. Incubate cells on 0.1-1 μg/ml Hoechst or DAPI (DNA stain) for 1 min. 2. Rinse with PBS.
Mounting
1. Mount coverslip with a drop of mounting medium.
2. Seal coverslip with nail polish to prevent drying and movement under microscope. 3. Store in dark at -20°C or +4°C.
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