The autoimmune dermatologic disease pemphigus vulgaris (PV) is associated with the HLA serotypes DR4and DRw6. Susceptibility to PV could be conferred either by sequences shared between the DR4 and DRw6 haplotypes or by different sequences in these haplotypes. We have examined the distribution of DR and DQ fl-chain and DQ a-chain alleles in PV patients and in control subjects by hybridization with oligonucleotide probes and sequence analysis of in vitro ampli- (8). In population studies, PV is strongly associated with the serotypes HLA-DR4 and HLADRw6 (9, 10), with <5% of the patients possessing neither marker. Disease associations with two different HLA haplotypes could mean either that these two haplotypes share a common allele or epitope or that different alleles in the two haplotypes can confer disease susceptibility.As noted above, molecular analysis of serologically defined class II haplotypes (e.g., DR4 and DRw6) has revealed significant variation at the DR and DQ loci. Sequence analysis of class II genes from various haplotypes demonstrated that a DR/I epitope at amino acid positions 67-71 (termed here "IDE", based on one-letter symbols for Ile-67, Asp-70, and Glu-71) was shared between a subset of DR4 haplotypes ("DwlO") (11) and a subset of DRw6 haplotypes (DRw13) (ref. 12 and unpublished data). This observation suggests that these shared polymorphic residues of the DR,8I chain, which determines the DR specificity, may contribute to PV autoimmunity and account for both the DR4-and the DRw6-associated susceptibility. However, Szafer et al. (10) reported that specific restriction-fragment length polymorphisms (RFLPs) detected with a DQP cDNA probe subdivided the DR4 and DRw6 haplotypes and showed significantly higher associations with PV than did the serologic markers. Analysis of allelic coding-sequence variation in patients and in controls is needed to identify the putative class II alleles or epitopes that contribute to PV.Sequence analysis of DR,3I, DRfIII, and DQB alleles from three U.S. DR4+ PV patients (DR4/4, -4/5, and -4/5) revealed that all the patients had the Dw1O DRf3I allele (13) found in only 10o of U.S. DR4+ controls (14). Further, three of the four DQP alleles from the DR4 haplotypes were the DQB3.2 allele present in 60-80% of control DR4 haplotypes. These sequence data, although obtained from only three patients, suggest that, for the DR4 susceptibility to PV, the Dw1O DR,6I allele may contribute to autoimmunity but that the DQ, allele does not. These data were obtained by using the polymerase chain-reaction (PCR) method for the in vitro amplification of specific genomic sequences (15)(16)(17).We report here the use of sequence-specific oligonucleotide (SSO) probes to determine the distribution of DR4 DRBI and DQB alleles in a panel of PV patients and controls. The frequency of the IDE sequence in patient and control DRw6 haplotypes was also determined, to test the "shared epitope" model of PV susceptibility. In addition, we describe the Abbreviations: PV, pemphigus vulgaris; ...