Editing Immune system (section)

{{Short description|Biological system protecting an organism against disease}}
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{{Use dmy dates|date=November 2020}}
[[File:Neutrophil with anthrax copy.jpg|thumb|upright=1.15|alt=See caption|A [[scanning electron microscope]] image of a single [[neutrophil]] (yellow/right), engulfing [[Bacillus anthracis|anthrax bacteria]] (orange/left) – scale bar is 5 μm (false color)]]

The '''immune system''' is a network of [[biological systems]] that protects an [[organism]] from [[diseases]]. It detects and responds to a wide variety of [[pathogen]]s, from [[virus]]es to [[bacteria]], as well as [[Tumor immunology|cancer cells]], [[Parasitic worm|parasitic worms]], and also objects such as wood [[splinter]]s, distinguishing them from the organism's own healthy [[biological tissue|tissue]]. Many species have two major subsystems of the immune system. The [[innate immune system]] provides a preconfigured response to broad groups of situations and stimuli. The [[adaptive immune system]] provides a tailored response to each stimulus by learning to recognize molecules it has previously encountered. Both use [[humoral immunity|molecules]] and [[cell-mediated immunity|cells]] to perform their functions.

Nearly all organisms have some kind of immune system. [[Bacteria]] have a rudimentary immune system in the form of [[enzyme]]s that protect against [[bacteriophage|viral]] infections. Other basic immune mechanisms evolved in ancient [[eukaryote|plants and animals]] and remain in their modern descendants. These mechanisms include [[phagocytosis]], [[antimicrobial peptides]] called [[defensin]]s, and the [[complement system]]. [[Jawed vertebrate]]s, including humans, have even more sophisticated defense mechanisms, including the ability to adapt to recognize pathogens more efficiently. Adaptive (or acquired) immunity creates an [[immunological memory]] leading to an enhanced response to subsequent encounters with that same pathogen. This process of acquired immunity is the basis of [[vaccination]].

Dysfunction of the immune system can cause [[autoimmune disease]]s, [[Inflammation|inflammatory diseases]] and [[Carcinogenesis|cancer]]. [[Immunodeficiency]] occurs when the immune system is less active than normal, resulting in recurring and life-threatening infections. In humans, immunodeficiency can be the result of a [[genetic disease]] such as [[severe combined immunodeficiency]], acquired conditions such as [[HIV]]/[[AIDS]], or the use of [[immunosuppressive drugs|immunosuppressive medication]]. [[Autoimmunity]] results from a hyperactive immune system attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include [[Hashimoto's thyroiditis]], [[rheumatoid arthritis]], [[diabetes mellitus type 1]], and [[systemic lupus erythematosus]]. [[Immunology]] covers the study of all aspects of the immune system.