One of these, bare lymphocyte syndrome I (BLS I), exhibits a number of similarities with DPB in those affected, including chronic sinusitis, bronchiolar inflammation and nodules, and the presence of H. influenzae. Also like DPB, BLS I responds favorably to erythromycin therapy by showing a resolution of symptoms. The similarities between these two diseases, the corresponding success with the same mode of treatment, and the fact that the gene responsible for BLS I is located within the DPB-causing area of HLA narrows the establishment of a gene responsible for DPB.[9] Environmental factors such as inhaling toxic fumes and cigarette smoking are not believed to play a role in DPB, and unknown environmental and other non-genetic causes—such as unidentified bacteria or viruses—have not been ruled out.[4][6][7]