Additionally, a positive relationship has been observed between levels of salivary IgA directed against GroEL and periodontal disease severity [8], and a P. gingivalis GroEL protein vaccine reduces bacterially induced multiple periodontopathogenic alveolar bone loss [9], indicating that P. gingivalis GroEL is a potential immunodominant antigen in patients with periodontitis and may contribute to pathogenic processes. This evidence concerns the gene HSPD1 and periodontitis.