DP polymorphism in HLA-A1,-B8,-DR3 extended haplotypes associated with membranoproliferative glomerulonephritis and systemic lupus erythematosus.

We and others have shown an association between autoimmune disorders and the major histocompatibility complex extended haplotype HLA-A1,-B8,-SCO1,-DR3. The primary gene or genes within this haplotype conferring such susceptibility, however, have not been defined. In this study, we tested the hypothesis that linkage disequilibrium in this haplotype extends through the DP locus, and that DP type may be linked to membranoproliferative glomerulonephritis (MPGN) and systemic lupus erythematosus (SLE). DP and DQ typing was performed by restriction fragment length polymorphism analysis for 43 chromosomes (19 healthy controls, 9 SLE, 15 MPGN) bearing the -A1,-B8,-SCO1,-DR3 extended haplotype. Although all were DQw2, a variety of DP types were identified (DPw1, 0.26; DPw2, 0.09; DPw3, 0.14; DPw4, 0.44). Although DPw1 was represented on extended haplotypes with greater frequency than on 113 non-A1,-B8,-SCO1,-DR3 haplotypes (0.26 vs. 0.03; P < 0.001), there were no significant differences between healthy individuals with this haplotype and those with autoimmune disease. We conclude that the strong linkage disequilibrium of this haplotype breaks down between the DQ and DP loci. Loci important to disease susceptibility, therefore, are more likely to occur telomeric to DP.