Culture the THP-1 cells on a poly-L-lysine coverslip at 10,000 cells per milliliter, or at a concentration recommended by your protocol.
Fix the cells with a 10 percent formaldehyde solution for one hour, or a time period recommended by your protocol. Optionally, fix the cells after permeabilization
Wash the cells with phosphate-buffered saline three times by dipping the coverslips into a PBS solution. .
Permeabilize the THP-1 cells with 0.5 percent Triton X-100 solution for 25 minutes, or 0.05 percent saponin solution for 20 minutes at room temperature. Make the 0.5 percent Triton X-100 solution by adding 500 microliters of 10 percent Triton X-100 to 9500 microliters of PBS. Make the 0.05 percent saponin solution by adding 500 microliters of 1 percent saponin solution into 9500 microliters of PBS.
Wash three times with PBS. The THP-1 cells are now permeabilized and ready for blocking and incubation with your antibody.