A cell that shows antigen on its surface to other cells of the immune system. This is an important part of an immune response.
A cell that breaks down antigens and displays their fragments on surface receptors next to major histocompatibility complex molecules. This presentation is necessary for some T lymphocytes that are unable to recognize soluble antigens. Macrophages are the primary antigen-presenting cells, but B cells and dendritic cells also can act as APCs.
A phagocyte, which is a type of immune system cell, engulfs antigens and presents them to other immune cells, thereby activating them to target and eliminate any cells that exhibit the same antigen.