THP-1 is a human monocytic cell line originally isolated from a 1-year old male subject with acute monocytic leukemia (Tsuchiya et al., 1980). The cells are easy to culture and are safe, as no viruses have been reported to be present in the cells (Chanput et al., 2014). THP-1 monocytes are round, floating cells with a doubling time of 35-50 h (Chanput et al., 2014). They have been used as a model for studying immune response, monocyte and macrophage function, lipid metabolism and functions of drugs (Chanput et al., 2014). THP-1 cells can be differentiated into macrophages for use in experiments. As macrophages, the cells become adherent to the cell culture vessel. Agents used for differentiation of THP-1 cells include phorbol 12-myristate 13-acetate (PMA), vitamin D, and macrophage colony-stimulation factor M-CSF (Chanput et al., 2014). This cell line is sensitive to culture conditions; e.g. the cells react differently to differentiation substances depending on the cell density (Liu et al., 2023). The protocol presented herein is routinely used for culturing and differentiating THP-1 cells with PMA.