2
in 100% methanol fixation (methanol is best for structure, acetone permeabilizes
well and is less damaging). Try 10 min in solvent at -20°C as a starting point.
Triton/NP-40/Digitonin or Saponin
Permeabilization helps the antibodies get into the fixed cells. Cell surface proteins
don't require much/any permeabilization. If the target protein is expressed
intracellularly, it is very important to permeabilize the cells.
Triton X-100 is the most popular detergent for improving the penetration of the
antibody. However, it is not appropriate for the use of membrane-associated
antigens since it destroys membranes.
Prepare primary-antibody in 3% BSA/PBS, dilute antibodies according to the
recommended manufacturer specification data sheet or reference publications.
Selection of the secondary antibody is depended on the donor species of the primary
antibody and the desired fluorochrome.
Procedure
Note: Incubate samples in the dark and cover whenever possible.
It is advisable to run the appropriate negative controls. Negative controls establish background
fluorescence and non-specific staining of the primary and secondary antibodies.
Rinse cells with PBS x2
Fixation: fix the cells either in cold methanol, acetone (1-10 min) at -20
o
C or in 2-4%
paraformaldehyde (PFA) (10-20 min) in PBS (freshly prepared) at RT.
Wash the samples with PBS 10min x3 on shaker
Permeabilization: incubate the samples for 10-15 min with 0.05-0.25% Triton X-100 in
PBS (or 100 μM digitonin or 0.5% saponin).
Wash the samples with PBS 10min x3 on shaker
Blocking: incubate the cells for 30-60min with 1-3% BSA in PBS 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).
Remove the blocking buffer by holding each coverslip on its edge with forceps and
draining it onto a sheet of Kimwipes.
Primary Ab: Incubate cells the primary antibody dilution in 3%BSA/PBS (keep cells
dark in a humidified chamber) 1-4 hr at room temperature/37
o
C or overnight at 4
o
C.
A simple chamber can be made from a small box with water-soaked filter papers.
If it is desirable to examine the co-distribution of two different antigens in the
same cell, a double immunofluorescence procedure may be used. Cells may be
incubated simultaneously with two primary antibodies, provided they are
monospecific and can be distinguished with secondary antibodies conjugated to
different fluorochromes (or with primary antibodies directly conjugated to
different fluorochromes).
Wash the samples with PBS 10min x3 on shaker