These findings improve our understanding of the potential roles of the immune response in periodontitis, and our study suggests the role of the nine immune-related genes (PRKCQ, CR1, LYN, CFI, CXCL12, CD19, CXCL1, CD27 and CXCR4) as potential targets for the diagnosis of periodontitis. The gene discussed is CD27; the disease is periodontitis.