HLA-C and periodontitis: Cell–cell communication analysis further demonstrated that plasma cells in the HLA-C-positive group exhibited more frequent and stronger interactions with other immune cells, suggesting that HLA-C may participate in the immune response of periodontitis by regulating interactions between plasma cells and other immune cells.In terms of drug prediction, analysis based on the DSigDB database identified metronidazole as the most promising HLA-C-associated therapeutic agent.