PSMB8 (LMP7) but not PSMB9 (LMP2) gene polymorphisms are associated to pigeon breeder's hypersensitivity pneumonitis

Abstract

Hypersensitivity Pneumonitis (HP) is a lung inflammatory disorder caused by inhalation of organic particles by a susceptible host. However, only a small proportion of individuals exposed to HP-associated antigens develop the disease, suggesting that additional host/environmental factors may play a role. We have previously found that genetic susceptibility associated to the major histocompatibility complex (MHC) plays an important role in this disease. The low molecular weight proteosome (LMP, currently named PSMB) genes code for subunits of the proteosome, a multimeric enzymatic complex that degrades proteins into peptides in order to be presented in the MHC class I pathway. We hypothesized that polymorphisms in PSMB8 or PSMB9 genes could be involved in the susceptibility to HP. Thus, in this study we analyzed the polymorphic site at amino acid position 60 (Arg/His) of the fourth exon in the PSMB9 gene and the amino acid position 49 (Gln/Lys) in the second exon of PSMB8 gene in 50 Mexican patients with HP and 50 healthy ethnically matched controls. PSMB typing was performed using polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP). Our results demonstrated that HP patients had a significant increase of the PSMB8 KQ genotype frequency (OR = 7.25, CI = 2.61-21.3; p = 0.000034). No differences were found in the distribution of PSMB9 alleles/genotypes. However, PSMB9-RH/PSMB8 KQ haplotype was significantly increased in HP patients (OR = 6.77, CI = 1.34-65.31, p < 0.02). These findings suggest that PSMB8 KQ genotype could increase the risk to develop hypersensitivity pneumonitis.