A possible new HLA-DR allele.

In routine screening of anti-HLA DR reagents, serum 901 was obtained from a woman of negroid origin ten days after delivery of a second child. The spouse was also of black origin. This serum contained polyspecific HLA A and B antibodies. After platelet absorption it reacted with the B cells of 10 out of 119 European Caucasoid panel donors (8.4%) typed for DR1 to DRW10 and for MT1, MT2. Each of these ten donors had only one recognized DR antigen, the other was "blank." Serum 901 gave negative reactions with the homozygous typing cells (HTC) DW1 to DW8. In 18 normal informative Caucasoid families, serum 901 recognized one HLA haplotype in one (or both) parents and segregated with this haplotype in one or more than one child. In one family in which both parents reacted with serum 901, two children were homozygous for this marker and reacted as HTCs. One of these HTCs typed as DW9 and was found to be identical to a DW9.HTC (8W207).