In the body, after the antibody forms a cell complex, the cell complex looks for foreign bodies. Other antibodies can recognize foreign molecules and activate a special plasma defense mechanism called the complement system. This system, when activated, causes the rupture and death of foreign microbes. A phagocyte is a cell that ingests or devours other cells. In the body, phagocytes ingest and break down bacteria, foreign particles, dead tissue, and degenerated cells.
Phagocytes act as a sort of cleaning service for the body.
Histamine causes blood vessels to dilate by binding to H1 receptors in the walls of the blood vessels. Histamine can cause smooth muscle contraction in the stomach, intestines , respiratory system and other sites when it binds to receptors on the smooth muscle there.