BACH1 and pulmonary alveolar proteinosis: There was no significant difference in the down-regulation of HMOX1 and IFN-activated STAT1 and Bach1, as well as the up-regulation of TGFB. 42Bach1 is a transcriptional repressor that may be essential for limiting the M2 phenotype, and its deficiency worsens some forms of pulmonary alveolar proteinosis (PAP).