Contribution of TAP genes to genetic predisposition for diffuse panbronchiolitis

Diffuse panbronchiolitis is a chronic obstructive pulmonary disease found in Asian populations. Although diffuse panbronchiolitis is considered to be a multifactorial disease of unknown etiology, the disease susceptibility appears to be determined by a genetic predisposition unique to Asians. An earlier study showed that human leukocyte antigen (HLA)-B54 predominantly found in East Asians was strongly associated with the disease. A possible interpretation of this association is that the class I molecule or class I antigen presenting system is directly involved in its pathogenesis. Recent observations in which impaired expression of class I molecules causes a syndrome resembling diffuse panbronchiolitis further prompted us to test this possibility. Genes of the molecules implicated in the class I pathway, TAP1, TAP2 and LMP2, which are located in the HLA region of the sixth chromosome were analyzed in 76 patients with diffuse panbronchiolitis and 120 normal controls. The combination of Ala-665 and Gln-687 in exon 11 of the TAP2 gene was associated with the disease (P=0.0028, Pc<0.05). Although this positive association might be partly explained by linkage disequilibrium with HLA-B*5401, this TAP2 variation was associated with the disease even in the B*5401-negative subgroup. On the other hand, the His-60 substitution within the LMP2 gene exhibited a negative association with the disease. This negative association, however, could be explained by a strong linkage disequilibrium with HLA-B44 which showed a negative association with the disease in the previous study. These results support the notion that diffuse panbronchiolitis is influenced by genetic factors in the HLA region. Besides the class I gene itself, genes relevant to the class I antigen presenting system might contribute to its genetic predisposition.