Increasing evidence has shown periodontal pathogen Porphyromonas gingivalis 
(P.gingivalis) infection contributes to atherosclerosis (AS) progression. 
P.gingivalis fimbriae act as an important virulence factor in AS. Regulatory T 
cells (Tregs) may play a crucial role in autoimmune response during this 
process. However, whether P.gingivalis infection is associated with Tregs 
dysregulation during AS is still unknown and the prevalence of different 
P.gingivalis FimA genotypes during this process is unclear. Here we analyzed the 
distribution of Tregs and in P.gingivalis-infected atherosclerotic patients to 
reveal the relationship between P.gingivalis infection and Tregs 
reduction/dysfunction and to elucidate their role in periodontitis-AS 
interaction. FimA genotype was also examined to determine the prevalence of 
fimbriae. Our results showed that P.gingivalis infection reduced Tregs in 
atherosclerotic patients compared with non-atherosclerotic patients and health 
controls. Concentration of TGF-β1, which plays an important role in the 
development of Tregs, also decreased in P.gingivalis infected patients. 
Furthermore, type II FimA seems to show higher prevalence than the other five 
detected types. The population of Tregs further decreased in patients with type 
II FimA compared with the other types. P.gingivlias FimA genotype II was the 
dominant type associated with decreased Treg population. These results indicate 
that P.gingivalis infection may be associated with Tregs dysregulation in AS; 
type II FimA may be a predominant genotype in this process.