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#31-OR
EXTENDED HLA-DPB1 POLYMORPHISM.
Judith Reinders, MSc, Rogier van Gent, MSc, Erik H. Rozemuller, PhD and Marcel G.J. Tilanus, PhD. Utrecht Netherlands, UMC-U, Dept. of Pathology.

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The HLA region on the short arm of chromosome 6 is the most polymorphic region in the genome. Based upon exon 2 polymorphism, 107 DPB1 alleles have been identified. HLA-DP is not in linkage disequilibrium with other HLA genes and often mismatches in transplantations. It become evident that DPB1 matching is important in stem cell transplantation and second kidney transplantation. Exon 2 polymorphism is located in hypervariable regions 1-5 and alleles evolved through microgene conversion, recombination and mutations. It would be interesting to know how this exon 2 polymorphism extends to other parts of the molecule. Full length RNA analysis of the DPB1 gene provides the possibility to determine diversity of and evolutionary relationship between DPB1 alleles. A RT-PCR was set up to amplify exon 1 into the 3’UT region. Sequencing was performed using 4 sequence primers with Big Dye Terminator chemistry on an ABI 377 DNA sequencer. Full length sequences obtained were compared to available sequences. Fifteen B-cell lines, covering the 11 most frequent DPB1 alleles, were tested. In addition to exon 2 polymorphism, 22 polymorphic positions were observed: 8 in exon 3; 1 in exon 4; none in exon 5 and 13 positions in exon 6. These polymorphic positions give rise two main lineages. A non-synonymous substitution of methionine to leucine at codon 178 was observed in a cell line previously typed as DPB1*0402, giving rise to a new allele, DPB1*0402RG. A single nucleotide deletion was found directly after the TAA stop codon in the DPB1*1301 allele, which does not affect the protein. In conclusion, full length sequence polymorphism provides interesting features on DPB allele evolution which may affect the definition of allele groups. In view of the data obtained, this study will be extended to less frequent alleles.