Hypermutation is the central aspect to making the Acquired immune system possible. Large creatures such as vertebrates typically have a long generation time, while (micro-)parasites (such as viruses, bacteria, fungi or worms) that they play host to often have a short generation time. The immune system is the system of specialised cells and organs that protect an organism from outside biological influences. ... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... A parasite is an organism that lives in or on the living tissue of a host organism at the expense of it. ... The HIV virus A virus is a microscopic parasite that infects cells in biological organisms. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria(singular, bacterium) are a major group of living organisms. ... Divisions Chytridiomycota Zygomycota Ascomycota Basidiomycota The Fungi (singular: fungus) are a large group of organisms ranked as a kingdom within the Domain Eukaryota. ... Worm can refer to: The worm, a collection of animal phyla. ...

This means that the parasites will evolve much faster than their hosts, potentially overwhelming them if there's no rapid defence. To be able to deal with these attackers, some form of adaptation mechanism is needed.

Organisms with an acquired immune system will pick up invasions using the less efficient innate immune system , and small amounts of dead invader material will be presented to B cells in the lymph nodes. In biology and ecology, an organism (in Greek organon = instrument) is a complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... The immune system is the system of specialised cells and organs that protect an organism from outside biological influences. ... Lymph nodes are components of the lymphatic system. ...

A B cell that recognizes the antigen is stimulated to divide. During this proliferation, the B cell receptor locus undergoes mutation at an extremely high rate compared to the normal rate of mutation across the genome. The exact mechanisms for inducing this hypermutation are not clearly understood. It is possible that it involves certain DNA repair enzymes. Dividing B cells compete for growth factors. Those with B cell receptors that bind to the antigen strongest get the majority of proliferation stimulating cytokines. Thus, superior B cell receptors generated by this hypermutation survive and proliferate, while the negative or neutral mutants die via apoptosis. This develops a set of B cells, specific for the antigen, with B cell receptors (and thus antibodies) with very high affinities for the antigen (affinity maturation). Cytokines are small protein molecules that are the core of communication between immune system cells, and even between these cells and cells belonging to other tissue types. ... Apoptosis In biology, apoptosis (from the Greek words apo = from and ptosis = falling, pronounced ap-a-tow-sis[1]) is one of the main types of programmed cell death (PCD). ... Schematic of antibody binding to an antigen An antibody is a protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ... The process by which B-cells produce antibodies with increased affinity for antigen. ...

This process takes 3 weeks, and speeds up that which would otherwise require centuries of evolution. The survivors of this selection process will continue to divide and go on to produce antibodies which will now be capable of detecting and destroying the invader with exceptional efficiency.

Also a small number will be distributed to lymph nodes throughout the body as memory-cells. If the same invader ever invades again, the memory cells will rapidly divide, and confer the same defensive capability to the body again. The organism is now immune. A request has been made on Wikipedia for this article to be deleted in accordance with the deletion policy. ...

Some worm species avoid the acquired immune response by modifying their external skin or secretions every couple of weeks.

The hypermutation process also has cells auto-select against the organism's own cells: their 'signature'. Failure to auto-select against the own signature causes an auto-immune response, which is often dangerous to the organism itself. Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. ...

See also

• Immune system
• Evolution