Ozone-oxidized black carbon particles change macrophage fate: Crosstalk between necroptosis and macrophage extracellular traps

The impacts of environmental PM 2.5 on public health have become a major concern all over the world. Many studies have shown that PM 2.5 still poses a threat to public health even at very low levels. Physical or chemical reactions occur between primary particles and other components in the environment, which changes the properties of primary particles. Such newly formed particles with changed properties are called secondary particles. Ozone-oxidized black carbon (oBC) is a key part of PM 2.5 and a representative secondary particle. Macrophages extracellular traps (METs) is a means for macrophages to capture and destroy invading pathogens, thereby exercising innate immunity. Necroptosis is a kind of programmed cell death, which is accompanied by the destruction of membrane integrity, thus inducing inflammatory reaction. However, there is no research on the crosstalk mechanism between necroptosis and MET after oBC exposure. In our study, AO/EB staining, SYTOX Green staining, fluorescent probe, qPCR, Western blot, and immunofluorescence were applied. This experiment found that under normal physiological conditions, when macrophages receive external stimuli (such as pathogens; in our experiment: phorbol 12-myristate 13-acetate (PMA)), they will form METs, capture and kill pathogens, thus exerting innate immune function. However, exposure to oBC can cause necroptosis in macrophages, accompanied by increased levels of reactive oxygen species (ROS) and cytosolic calcium ions, as well as the expression disorder of inflammatory factors and chemokines, and prevent the formation of METs, lose the function of capturing and killing pathogens, and weaken the innate immune function. Notably, inhibition of necroptosis restored the formation of METs, indicating that necroptosis inhibited the formation of METs. This study was the first to explore the crosstalk mechanism between necroptosis and METs after oBC exposure.