Historical recombinant sites in extended HLA haplotypes

Each ancestral or extended HLA haplotype contains a unique combination of a lleles among which some may be entirely specific for that haplotype (haplos pecific alleles). In the course of evolution many recombination events occu rred which disrupted the original haplotypic combination. We analysed the s ites of historical recombinations in four extended HLA haplotypes (B8-DR3; B18-DR3; B50-DR7 and B57-DR7) in 60 random Italian individuals selected thr ough the presence of haplospecific alleles. In general the distribution of recombinations in each interval was similar for the four extended haplotype s and no haplospecific recombination "hot spot" could be detected. However some differences between the four haplotypes can be pointed out: a) only 48 % fragmented B8-DR3 were found in contrast to 83% B18-DR3, 89% B50-DR7 and 88% B57-DR7; b) in the B8-DR3 haplotype recombinations fall preferentially in the B/TNF interval. In fact among 22 historical recombination events, 50 % were mapped in this region; c) conversely, no recombination event was det ected in the B/TNF interval among the 19 disrupted B18-DR3 haplotypes thus evidencing the presence of a putative recombination "cold spot".