LOCALIZATION OF THE RECOMBINATION POINTS IN A FAMILY WITH 2 DR DP RECOMBINATIONS/

In a family with a maternal DR/GLO recombination, cellular DP typing s howed it to be located between DR and DP. RFLB studies done during the 9th international histocompatibility workshop gave anomalous segregat ion patterns of DPA and DPB bands that could be interpreted as being d ue to a second, paternal DR/DP recombination. This assumption was conf irmed later by PCR-SSO typing. A more precise mapping has been done by new markers showing the maternal recombination to be within the TAP2 locus and the paternal recombination to be between DQB1 and DQB3. This supports earlier suggestions of a hot spot of recombination in the TA P region. The recombinations involve parental haplotypes that presentl y show DR/DP linkage disequilibrium in the French population and it is proposed that DR/DP recombinations occur randomly while B/DR recombin ations preferentially occur on haplotypes without strong linkage diseq uilibrium. Existing DR/DP linkage disequilibria in a given population will thus be broken down with time. The mixed lymphocyte culture respo nse towards an isolated DP difference was tested in this and another D R/DP recombinant family. It showed that an alloresponse towards DP may be highly variable and this suggests that it might be important to de fine the rules for the strength of this reaction and the possible impl ications for allotransplantation.