What is Immune system?
[[File:Ilya Mechnikov nobel.jpg|thumb|right|210px|[[Ilya Mechnikov]], one of the founders of [[immunology]]]] [[Image:Neutrophil with anthrax copy.jpg|thumb|right|210px|A [[scanning electron microscope]] photo of a single [[neutrophil]] (in yellow), engulfing some [[Anthrax (disease)|anthrax]] bacteria (in orange).]] The '''immune system''' is the set of [[tissues]] which work together to resist [[infection]]s. The immune mechanisms help an organism identify a [[pathogen]], and b its threat.<ref name=Janeway>Janeway C.A ''et al'' 2001. Basic concepts in immunology, Chapter 1 in ''Immunobiology'', 5th ed, New York: Garland Science. {{ISBN|978-0-8153-4101-7}}</ref> The immune system can detect and identify many different kinds of '''disease''' agents. Examples are [[virus]]es, [[bacteria]] and [[parasite]]s. The immune system can detect a difference between the body's own healthy cells or tissues, and 'foreign' cells. Detecting an unhealthy intruder is complicated, because intruders can [[Evolution|evolve]] and adapt so that the immune system will no longer detect them. Once a foreign cell or protein is detected, the immune system creates [[antibody|antibodies]] to fight the intruders, and sends special cells ('[[phagocyte]]s') to eat them up. == Innate immune system == Even simple [[microorganism|unicellular]] organisms such as [[bacteria]] possess [[enzyme]] systems that protect against [[virus|viral]] infections. Basic immune mechanisms appeared in ancient life forms and remain in their modern descendants, such as [[plant]]s and [[insect]]s. These mechanisms include antimicrobial [[peptides]] (called [[defensin]]s), [[phagocytosis]], and the [[complement system]]. These make up the '''[[innate immune system]]''', which defends the host from infections in a non-specific way.<ref name=Beck>{{cite journal |last= Beck |first= Gregory |author2= Gail S. Habicht| title=Immunity and the invertebrates| journal =Scientific American | pages=60–66 | year =1996 |volume= 275 |issue= 5 |doi= 10.1038/scientificamerican1196-