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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en">HLA-DR and -DQ gene polymorphism in West Africans is twice as extensive as in north European Caucasians: evolutionary implications.</title><author><name sortKey="Olerup, O" sort="Olerup, O" uniqKey="Olerup O" first="O" last="Olerup">O. Olerup</name></author><author><name sortKey="Troye Blomberg, M" sort="Troye Blomberg, M" uniqKey="Troye Blomberg M" first="M" last="Troye-Blomberg">M. Troye-Blomberg</name></author><author><name sortKey="Schreuder, G M" sort="Schreuder, G M" uniqKey="Schreuder G" first="G M" last="Schreuder">G M Schreuder</name></author><author><name sortKey="Riley, E M" sort="Riley, E M" uniqKey="Riley E" first="E M" last="Riley">E M Riley</name></author></titleStmt><publicationStmt><idno type="wicri:source">PMC</idno><idno type="pmid">1681538</idno><idno type="pmc">52532</idno><idno type="url">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC52532</idno><idno type="RBID">PMC:52532</idno><date when="1991">1991</date><idno type="wicri:Area/Pmc/Corpus">000106</idno><idno type="wicri:explorRef" wicri:stream="Pmc" wicri:step="Corpus" wicri:corpus="PMC">000106</idno></publicationStmt><sourceDesc><biblStruct><analytic><title xml:lang="en" level="a" type="main">HLA-DR and -DQ gene polymorphism in West Africans is twice as extensive as in north European Caucasians: evolutionary implications.</title><author><name sortKey="Olerup, O" sort="Olerup, O" uniqKey="Olerup O" first="O" last="Olerup">O. Olerup</name></author><author><name sortKey="Troye Blomberg, M" sort="Troye Blomberg, M" uniqKey="Troye Blomberg M" first="M" last="Troye-Blomberg">M. Troye-Blomberg</name></author><author><name sortKey="Schreuder, G M" sort="Schreuder, G M" uniqKey="Schreuder G" first="G M" last="Schreuder">G M Schreuder</name></author><author><name sortKey="Riley, E M" sort="Riley, E M" uniqKey="Riley E" first="E M" last="Riley">E M Riley</name></author></analytic><series><title level="j">Proceedings of the National Academy of Sciences of the United States of America</title><idno type="ISSN">0027-8424</idno><idno type="eISSN">1091-6490</idno><imprint><date when="1991">1991</date></imprint></series></biblStruct></sourceDesc></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en"><p>The HLA genes are the most polymorphic coding loci known in humans. DRB-DQA-DQB gene polymorphism was investigated by Taq I restriction fragment length polymorphism analysis in more than 700 West Africans and found to be almost twice as extensive in West Africans as in North European Caucasians. This finding indicates that Africans comprise the oldest and genetically most diverse human population and supports the hypothesis of the occurrence of a population bottleneck in the emergence of the White race. As in Caucasians, less than one-third of possible cis-encoded DQA-DQB combinations were encountered, indicating constraints on the pairing of DQ alpha and beta polypeptides. Heterozygote advantage (i.e., positive selection) was found for DRB, DQA, and DQB alleles as well as for DQA-DQB combinations. However, in West Africans as well as in North Europeans the observed frequencies of DRB-DQA-DQB homozygotes were close to neutrality expectations. Although the hypothesis that HLA polymorphism is maintained by parasite-driven overdominant selection is attractive, there is little evidence to support that view. We propose instead that one of the forces maintaining a low frequency of HLA homozygotes might be a decreased likelihood of potentially autoreactive T-cell clones escaping thymic selection in HLA heterozygotes. This would be consistent with the central role of HLA molecules as self/non-self discriminators.</p><sec sec-type="scanned-figures"><title>Images</title><fig id="F1"><graphic xlink:href="pnas01069-0209-a" xlink:role="8480"></graphic></fig></sec></div></front></TEI><pmc article-type="research-article"><pmc-comment>The publisher of this article does not allow downloading of the full text in XML form.</pmc-comment>
<front><journal-meta><journal-id journal-id-type="nlm-ta">Proc Natl Acad Sci U S A</journal-id><journal-title>Proceedings of the National Academy of Sciences of the United States of America</journal-title><issn pub-type="ppub">0027-8424</issn><issn pub-type="epub">1091-6490</issn></journal-meta><article-meta><article-id pub-id-type="pmid">1681538</article-id><article-id pub-id-type="pmc">52532</article-id><article-categories><subj-group subj-group-type="heading"><subject>Research Article</subject></subj-group></article-categories><title-group><article-title>HLA-DR and -DQ gene polymorphism in West Africans is twice as extensive as in north European Caucasians: evolutionary implications.</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Olerup</surname><given-names>O</given-names></name></contrib><contrib contrib-type="author"><name><surname>Troye-Blomberg</surname><given-names>M</given-names></name></contrib><contrib contrib-type="author"><name><surname>Schreuder</surname><given-names>G M</given-names></name></contrib><contrib contrib-type="author"><name><surname>Riley</surname><given-names>E M</given-names></name></contrib></contrib-group><aff>Center for BioTechnology, Karolinska Institute, NOVUM, Huddinge, Sweden.</aff><pub-date pub-type="ppub"><day>1</day><month>10</month><year>1991</year></pub-date><volume>88</volume><issue>19</issue><fpage>8480</fpage><lpage>8484</lpage><abstract><p>The HLA genes are the most polymorphic coding loci known in humans. DRB-DQA-DQB gene polymorphism was investigated by Taq I restriction fragment length polymorphism analysis in more than 700 West Africans and found to be almost twice as extensive in West Africans as in North European Caucasians. This finding indicates that Africans comprise the oldest and genetically most diverse human population and supports the hypothesis of the occurrence of a population bottleneck in the emergence of the White race. As in Caucasians, less than one-third of possible cis-encoded DQA-DQB combinations were encountered, indicating constraints on the pairing of DQ alpha and beta polypeptides. Heterozygote advantage (i.e., positive selection) was found for DRB, DQA, and DQB alleles as well as for DQA-DQB combinations. However, in West Africans as well as in North Europeans the observed frequencies of DRB-DQA-DQB homozygotes were close to neutrality expectations. Although the hypothesis that HLA polymorphism is maintained by parasite-driven overdominant selection is attractive, there is little evidence to support that view. We propose instead that one of the forces maintaining a low frequency of HLA homozygotes might be a decreased likelihood of potentially autoreactive T-cell clones escaping thymic selection in HLA heterozygotes. This would be consistent with the central role of HLA molecules as self/non-self discriminators.</p><sec sec-type="scanned-figures"><title>Images</title><fig id="F1"><graphic xlink:href="pnas01069-0209-a" xlink:role="8480"></graphic></fig></sec></abstract></article-meta></front></pmc></record>Pour manipuler ce document sous Unix (Dilib)
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