Abstract:Polymorphic MHC class II molecules determine immune responsiveness towards pathogens and also contribute to susceptibility or resistance to a number of different autoimmune diseases, including systemic lupus erythematosus (SLE). The HLA‐DR and ‐DQ alleles of 52 patients with SLE were analyzed by serology and, for 42 patients, HLA‐DRB1, ‐B3 and DQB1 allelic polymorphism was determined by oligotyping on PCR‐amplified DNA. While we confirm the increase of DR3 (44.2% versus 16% in controls; p<0.001) reported by others, we observed a complete absence of DRwl5(2)/DR3 and DRwl5(2)/DR7 heterozygotes among Caucasian patients. Moreover HLA‐DQB1 oligotyping revealed the absence of DQB 1*0602/0201 heterozygotes in our panel of Caucasoid SLE patients. Since both DR3 and DR7 haplotypes share the same DQB 1*0201‐encoded DQβ chain, and since DRwl5 is known to be in linkage disequilibrium with DQA1*0102, it can be predicted that DQA1*0102/DQB1*0201 combinations are absent in Caucasian patients. We therefore propose that a DQA 1*0201/DQB 1*0201‐encoded HLA‐DQ transdimer formed in these heterozygotes might function as a supressor‐inducer molecule that confers re