The influence of a 6 mT static magnetic field on apoptotic cell phagocytosis depends on monocyte/macrophage differentiation

In a previous work we showed that a 6 mT static magnetic field (SMF) interferes with monocyte/macrophage 12-otetradecanoylphorbol-13-acetate (TPA)-induced differentiation of promonocytes (U937 cells) and monocytes (THP-1 cells). In this study we investigated whether in the same cells and under the same conditions, phagocytosis of apoptotic cells is influenced by 6 mT SMF exposure. Fluid phase endocytosis and phagocytosis of latex particles were also analyzed for comparison. The results indicate that SMF exposure has effects on phagocytosis but not on fluid phase endocytosis, and that these effects are greater at the late stages of macrophage differentiation (THP-1 > U937 cells). The phagocytosis index and rate of phagocytosis decreased under SMF exposure while the number of latex particles bound to the plasma membrane of TPA-differentiated U937 and THP-1 cells increased. Conversely, the rate of phagocytosis of apoptotic cells increased under SMF exposure, while the number of apoptotic cells bound to the plasma membrane of isolated human Kupffer cells, Raw 264.7 macrophages and TPA-differentiated THP-1 and U937 cells decreased. In non-differentiated U937 and THP-1 cells, the SMF exposure enhanced the number of cell-surface bound apoptotic cells and latex beads.