LD homozygous cells in the Warao population: a possible new allele at the LD1 locus within the main histocompatibility region in man.

A Venezuelan isolate indigenous population, the Warao, with a very large proportion of HL-A identical unrelated subjects non-reacting in MLC, has been considered a good potential source of LD homozygous cells. Cultures with lymphocytes from the members of several selected Warao families were performed with this aim and results obtained from three families are reported. In two of the families the parents share haplotype 2,5 and two of the siblings are SD double homozygous 2,5; in the third family, the common haplotype was 2,W15 and two of the siblings are also double homozygous 2,W15. Mixed lymphocyte cultures within the families have revealed that the SD homozygous children do not stimulate the cells from either parent thus being LD homozygous as well. Negative bilateral stimulation between 2,5 LD homozygous cells indicates that the LD1 allele carried by these individual's lymphocytes is the same; the negative MLC response of the 2,W15 LD homozygous cells to the 2,5 cells used as stimulators suggest either that their LD determinant is identical or the LD W15 allele is included in the LD5. As the Warao show a very large proportion of MLC identical individuals and a very high incidence of HL-A5 and W15, it is postulated that the LD allele(s) here described will be found in high frequency in this population.