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They perform distinct, critical functions: especially, MHC class I in case of antivirus and antitumor defenses, and MHC class II, in case of effective antibody responses. This important class diversification has long been enigmatic, as vestiges of the evolutionary molecular changes have not been found. The revealed ancient MHC category represents a plausible intermediate group between the two classes, and the data suggest that class II preceded class I in molecular evolution. Fundamental understanding of the molecular evolution of MHC molecules should contribute to understanding the basis of our complex biological defense system.<\/jats:p>","DOI":"10.1073\/pnas.2108104118","type":"journal-article","created":{"date-parts":[[2021,12,13]],"date-time":"2021-12-13T16:25:35Z","timestamp":1639412735000},"update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":23,"title":["Discovery of an ancient MHC category with both class I and class II features"],"prefix":"10.1073","volume":"118","author":[{"given":"Kazuhiko","family":"Okamura","sequence":"first","affiliation":[{"name":"Faculty of Clinical Engineering, School of Health Sciences, Fujita Health University, Toyoake 470-1192, Japan;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7097-3826","authenticated-orcid":false,"given":"Johannes M.","family":"Dijkstra","sequence":"additional","affiliation":[{"name":"Institute for Comprehensive Medical Science, Fujita Health University, Toyoake 470-1192, Japan;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0544-9811","authenticated-orcid":false,"given":"Kentaro","family":"Tsukamoto","sequence":"additional","affiliation":[{"name":"Laboratory for Proteins and Genes, Center for Joint Research Facilities Support, Fujita Health University, Toyoake 470-1192, Japan;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0202-8061","authenticated-orcid":false,"given":"Unni","family":"Grimholt","sequence":"additional","affiliation":[{"name":"Fish Health Research Group, Norwegian Veterinary Institute 1433 Aas, Norway;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Geert F.","family":"Wiegertjes","sequence":"additional","affiliation":[{"name":"Aquaculture and Fisheries Group, Department of Animal Sciences, Wageningen University and Research, 6700 AH Wageningen, The Netherlands;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5342-1237","authenticated-orcid":false,"given":"Akiko","family":"Kondow","sequence":"additional","affiliation":[{"name":"Advanced Comprehensive Research Organization, Teikyo University, Tokyo 173-0003, Japan;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4507-9598","authenticated-orcid":false,"given":"Hisateru","family":"Yamaguchi","sequence":"additional","affiliation":[{"name":"Department of Medical Technology, School of Nursing and Medical Care, Yokkaichi Nursing and Medical Care University, Yokkaichi 512-8045, Japan;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Keiichiro","family":"Hashimoto","sequence":"additional","affiliation":[{"name":"Emeritus Professor of Department of Biomedical Polymer Science, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake 470-1192, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"341","published-online":{"date-parts":[[2021,12,13]]},"reference":[{"key":"e_1_3_4_1_2","doi-asserted-by":"publisher","DOI":"10.1146\/annurev.genet.39.073003.112240"},{"key":"e_1_3_4_2_2","doi-asserted-by":"publisher","DOI":"10.1146\/annurev-genom-091212-153455"},{"key":"e_1_3_4_3_2","doi-asserted-by":"publisher","DOI":"10.3389\/fimmu.2017.00292"},{"key":"e_1_3_4_4_2","doi-asserted-by":"publisher","DOI":"10.1016\/0092-8674(84)90068-0"},{"key":"e_1_3_4_5_2","doi-asserted-by":"publisher","DOI":"10.1016\/0092-8674(85)90133-3"},{"key":"e_1_3_4_6_2","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.83.23.9154"},{"key":"e_1_3_4_7_2","first-page":"131","article-title":"Vertebrates and the evolution of the major histocompatibility complex (MHC) class I and class II molecules","volume":"81","author":"Kaufman J.","year":"1988","unstructured":"J. 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