HBA2 and periodontitis: Evidence exists for the involvement of hemoproteins in the development of periodontitis and some hemoglobin sub-units have been proposed as potential biomarkers for periodontitis.47 Furthermore, hemoproteins have been described as DAMP molecules48,49 and an up-regulation of iron-containing compounds has been found in periodontitis samples.13–15,50 In this study, HBB and HBA2 showed significantly higher relative abundance in PG than NP (>3-fold change, P < 0.05).