Role of activated natural killer cells in oral diseases

Many of the protective immune responses of old people are impaired and this leads to an increased risk of oral bacterial infections. Little is known about the interaction between the systemic immune response on one hand and oral infections and oral diseases on the other. Here, we conducted an epidemiological study of the independent elderly to determine the relationships between activated natural killer (NK) cells and oral bacterial infections: oral diseases such as dental caries and periodontal disease. One hundred independent elderly people aged 77 years old (53 males, 47 females) were examined. Blood samples were drawn, and activated NK cells were evaluated using CD16, CD56, and CD69 monoclonal antibodies with flow cytometry. Bacterial counts for oral streptococci, lactobacillus, and opportunistic pathogens were performed using culture techniques. Oral disease examinations were performed by dentists. A larger percentage of CD69(+)NK cells (CD16(+)CD56(+)) showed significant correlations to the isolation numbers of total streptococci (r=0.409, P<0.01), the species numbers of opportunistic pathogens (r=-0.318, P<0.01), the numbers of decayed teeth (r=-0.223, P<0.05), and the amount of bridge work (r=0.219, P<0.05). A higher proportion of CD69(+)NK cells is associated with the incidence of dental caries and the number of opportunistic pathogens and total streptococci in the oral cavity of the elderly. This suggests that the proportionate number of CD69(+)NK cells may be a useful indicator for oral infection in elderly subjects.