The descent of the antibody-based immune system by gradual evolution

Jan Klein, Nikolas Nikolaidis

Research output: Contribution to journalArticlepeer-review

41 Scopus citations


The antibody-based immune system (AIS) is one of many means by which organisms protect themselves against pathogens and parasites. The AIS is present in jawed vertebrates (gnathostomes) but absent in all other taxa, including jawless vertebrates (agnathans). We argue that the AIS has been assembled from elements that have primarily evolved to serve other functions and incorporated existing molecular cascades, resulting in the appearance of new organs and new types of cells. Some molecules serving other functions have been appropriated by the AIS, whereas others have been modified to serve new functions, either after the duplication of their encoding genes or through the acquisition of an additional function without gene duplication. A few molecules may have been created de nova. The deployment and integration of the ready-made elements gives the impression of a sudden origin of the AIS. In reality, however, the AIS is an example of an organ system that has evolved gradually through a series of small steps over an extended period.

Original languageEnglish (US)
Pages (from-to)169-174
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number1
StatePublished - Jan 4 2005

All Science Journal Classification (ASJC) codes

  • General


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