Phagocytosis of a pathogen during contamination, rapid immune response. Phagocytes are cells of the immune system of the leucocyte category. In particular, monocytes/macrophages, neutrophils, dendritic cells are distinguished. They intervene during a rapid immune reaction. It responds to the invasion of the body by pathogens (bacteria or virus). These immune cells migrate to the site of infection, absorb (phagocyte) pathogens and destroy them. Then they reject the fragments of these agents. This is the first reaction of the immune system during a bacterial or viral invasion. This scientific illustration shows this principle of phagocytosis in four stages: adhesion, internalization, digestion, rejection.