The immune system ist the body's defence mechanism against disease (bacterial, viral, parastic, etc.). It consists of a variety of biological structures including organs (e.g. the lymph nodes), cells (e.g. white blood cells) and smaller structures (e.g. anitbodies). There are several different types of immunity - the innate immune system is unspecific and present from birth, the adaptive immune system is specific, i.e. it targets one specific pathogen and evolves as the body is exposed to different diseases.