Editing Immune system (section)

===Alternative adaptive immune system ===
[[adaptive immune system#Evolution|Evolution of the adaptive immune system]] occurred in an ancestor of the [[jawed vertebrates]]. Many of the classical molecules of the adaptive immune system (for example, [[immunoglobulin]]s and [[T-cell receptor]]s) exist only in jawed vertebrates. A distinct [[lymphocyte]]-derived molecule has been discovered in primitive [[agnatha|jawless vertebrates]], such as the [[lamprey]] and [[hagfish]]. These animals possess a large array of molecules called [[Variable lymphocyte receptor]]s (VLRs) that, like the antigen receptors of jawed vertebrates, are produced from only a small number (one or two) of [[gene]]s. These molecules are believed to bind pathogenic [[antigen]]s in a similar way to [[antibody|antibodies]], and with the same degree of specificity.<ref>{{cite journal | vauthors = Alder MN, Rogozin IB, Iyer LM, Glazko GV, Cooper MD, Pancer Z | title = Diversity and function of adaptive immune receptors in a jawless vertebrate | journal = Science | volume = 310 | issue = 5756 | pages = 1970–73 | date = Dec 2005 | pmid = 16373579 | doi = 10.1126/science.1119420 | bibcode = 2005Sci...310.1970A | doi-access = free }}</ref>