**Abstract**

Macrophages are phagocytes and one of the white blood cells discovered by Ilya I. Mechnikov in 1892. They engulf and digest foreign substances like pathogens and conduct antigen presentation, mature from haematopoietic stem cells in bone marrow, moving into blood vessels and become monocytes, and differentiate into macrophages in the tissue. Macrophages have intracellular granules called lysosome accumulating digestive enzymes. Their life span is several months and proliferates by cell division. There are three roles: First one is phagocytosis. Macrophages incorporate pathogens and work in natural immunity. In inflammation, macrophages aggregate after neutrophils recruitment and engulf pathogens into cellular phagosomes, fused with lysosomes and degrade. Second role is antigen presentation. Macrophages present fragment of digested foreign substances on cell surface MHC class II molecules and release cytokines. Dendritic cells and B cells are also APCs expressing MHC class II. CD4+ T cells recognize antigens presented on macrophages by using TCR. Only well-matched helper T cells *via* MHC class II-TCR interaction are activated. The third is activation of immunity. Cytokines produced by T cells activate macrophages and differentiate them into inflammatory M1 and wound-healing M2 macrophages.

**Keywords:** macrophages, phagocytosis, antigen presentation, activation of immunity, tissue regeneration
