Effect of aging on BCG immunostimulation of Porphyromonas gingivalis infection in mice.

The need for population care increases with the age of the population. Pneumonia is the fourth leading cause of death in Japan, yet the risk of pneumonia could be reduced by eliminating opportunistic infection sources such as oral bacteria (e.g. Porphyromonas gingivalis). Previously, we reported removal of P. gingivalis by macrophages during the early stages of cellular immunity, although neither neutrophils nor antibodies participated in the antimicrobial activity. BCG is a live vaccine against tuberculosis, and is thought to maintain cellular immunity as the antigen remains in vivo for longer periods. In this experiment, we attempted to clarify the relationship between aging and the elimination of P. gingivalis by examining the protective capacity of BCG against P. gingivalis infection in mice of various ages. In young mice, the reduction in numbers of P. gingivalis was accompanied by increased IFN-γ and IL-12 levels, and nitric oxide was continuously produced. The augmentation of bactericidal activity, namely the effects of the vaccine, was clear in young mice, but weaker in older mice. Activation of cellular immunity was not observed in older mice, even when boosters were administered.