Hallikainen J, Pyysalo M, Keränen S, et al. - Researchers aimed at determining the role of two key periodontal pathogens Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans in the formation and rupture of intracranial aneurysms (IA). Enzyme immune assay was used to measure immunoglobulin A and G (IgA,IgG) antibodies against P. gingivalis and A. actinomycetemcomitans in the serum of 227 IA patients, of whom 64 underwent also clinical oral examination. The control group comprised 1,096 participants of a cross sectional health survey, Health 2000, on whom serological studies and oral examination were performed. IA patients more frequently had widespread gingivitis and severe periodontitis relative to controls (2x and 1.5x respectively). Unruptured and ruptured IA patients had 1.5x and 3-3.4x higher IgA antibodies against P. gingivalis and A. actinomycetemcomitans, respectively, compared with controls. Overall findings suggest that the risk of IA formation and IA rupture may increase in correlation with exposure to the periodontal pathogen P. gingivalis and A. actinomycetemcomitans and dysfunctional acquired immune response against them.