Label-Free and Real-Time Electrical Impedance Monitoring of Macrophage Polarization of THP-1 Monocytes on Indium Tin Oxide Electrode

Macrophages are immune cells that play important roles in the human body’s initial immune responses against pathogens and tumor cells. We investigated the use of electrical impedance monitoring to assess the differentiation of THP-1 monocyte into macrophages, which is necessary for immunotherapy research conducted. The change in resistance at 1 kHz and capacitance at 100 kHz measured were proportionally increased according to not only the increase in the density of resting macrophages differentiated by Phorbol-12-myristate-13-acetate treatment but also the initial number of THP-1 cells seeded on the electrode. Additionally, real-time impedance data from THP-1 cells after 48 h of cultivation demonstrated greater recognition of the resting macrophage phenotypes (adhesion cells) covered microelectrode surface with a significant increase of impedance signal in comparison with monocytes phenotypes (suspended cells). Furthermore, during the polarization phase of macrophages, the alternatively activated macrophage phenotype was larger and flatter than that of classically activated macrophage and resting macrophage phenotypes, indicating a correlation with a higher resistance and lower capacitance impedances at 1 kHz and 100 kHz of alternatively activated macrophages (4750 Ω and – 3.5 nF) than that of classically activated macrophages (2000 Ω and – 1.5 nF) and resting macrophages (3500 Ω and – 2.0 nF), respectively. The study’s findings demonstrated that the impedance measurement system is high sensitivity and confidence in monitoring macrophages differentiation and polarization. The electrical impedance, which has significance for each macrophage phenotype, is compatible with macrophages characteristic features observed using flow cytometry and a microscope.