Higher levels of HLA-related genes, such as HLA-DP alpha 1 (DPA1), HLA-B, and HLA-C (Supplementary Figure S1A), more infiltrating immune cells, such as B cells, CD8+ T cells, and neutrophils (Supplementary Figure S1B), and higher activation of immune pathways, such as type II interferon (IFN) response, inflammation promoting, and chemokine receptors (CCR) (Supplementary Figure S1C), were detected in periodontitis compared to healthy controls. Here, HLA-DPA1 is linked to periodontitis.