Inflammation: damaged white blood cells and mast cells release histamine at the site of infection. Histamine causes local arterioles to vasodilate, increasing the blood supply to the area. It also causes holes to open between endothelial cells in capillary walls. This causes local oedema (the swelling associated with inflammation). It allows monocytes and neutrophils into the infected area, which engulf and destroy foreign bodies and pathogens. Eventually phagocytes arrive and complete the job. Dead monocytes and pathogen form pus.
Lysozyme: an enzyme that breaks down bacterial cell walls, causing them to lyse and die. Lysozyme is made in lysosomes inside phagoctyes and is responsible for digesting engulfed bacteria. Lysozyme is also made by the skin, epithelial cells, and is present in tears
Interferon: a protein made by virus-infected cells. It blocks RNA synthesis and therefore stops virus replication
Phagocytosis: the process in which a pathogen is engulfed and destroyed. Macrophages engulf pathogens using pseudopodia (“fake feet”). The bacterium is taken into the macrophage by endocytosis and enters the macrophage inside a vacuole. Lysosomes containing lysozyme fuse with the vacuole and digest the bacterium inside.