HLA-DRB1 and hypersensitivity pneumonitis: The genetic factors determining individual predisposition to HP are still unclear, but in pigeon breeders disease (PBD) patients Camarena et al. [26] showed a significant increase of the alleles HLA-DRB1*1305 and HLA-DQB1*0501, while a decrease of HLA-DRB1*0802 was noticed in patients versus both control groups.