Further analysis found that seven differential inflammation-related factors were significantly correlated to 14 differential OTUs (mainly belonging to Firmicutes), and depression severity was significantly correlated to five differential inflammation-related factors (APN, APOA1, AAT, NEUT% and BASO) and 14 differential OTUs (mainly belonging to Firmicutes). The gene discussed is SERPINA1; the disease is major depressive disorder.