Linkage disequilibrium between HLA class II (DR, DQ, DP) and antigen processing (LMP, TAP, DM) genes of the major histocompatibility complex.

TAP, LMP and DM genes map within the major histocompatibility complex (MHC) class II region between the DQB1 and DPB1 loci, and are involved in the processing of peptides bound to HLA class I or class II molecules. In order to determine the various linkage disequilibria existing between these genes and HLA class II genes, we have analyzed TAP1, TAP2, LMP2, DMA, DMB, DRB1, DQA1, DQB1 and DPB1 polymorphisms in 162 unrelated healthy Caucasian individuals. Many positive or negative associations were observed between alleles at these loci, such as between DR/DQ and TAP2, DM or LMP, between DP and DMB, and between TAP2 and DM, TAP2 and LMP. Conversely, no linkage disequilibrium was detected between some closely related genes (DR/DQ and TAP1, TAP1 and TAP2, LMP2 and DM), in agreement with the existence of recombination hot spots in this region. Other weak linkage disequilibria are likely to exist in this region. These data allow to define some conserved MHC class II haplotypes including HLA class II and TAP, LMP and DM alleles. Furthermore, the knowledge of such linkage disequilibria is of outstanding importance in order to avoid misinterpretation of the data when studying MHC class II associations with autoimmune diseases.