Mapping SB in relation to HLA and GLO1 using cells from first-cousin marriage offspring.

A newly defined leukocyte antigen system, the secondary B-cell (SB) system, was shown to be linked to HLA. The SB marker has been investigated in lymphocyte donors presumed to be genetically homozygous for HLA-A through HLA-D/DR by virtue of descent from a first-cousin marriage and of phenotypic homozygosity for these HLA markers. Of 19 donors, 3 were found to be heterozygous for SB. Studies of the families of these three donors could not distinguish with certainty whether the heterozygosity resulted from SB/DR recombination or from "pseudohomozygosity" for HLA-A through -D/DR by inheritance of two genetically unrelated but similar haplotypes. However, our data favored the occurrence of SB/DR recombination with a meiotic distance perhaps as large as 3.3 cMorgan. Recombinations were identified which mapped SB between HLA-B and GLO1. These studies demonstrate the usefulness of cells from first-cousin marriage offspring in mapping a polymorphic genetic system.