Effects of a Fusobacterium nucleatum extract on immunoregulation in mice

The purpose of this study was to examine the effect of an extract of Fusobacterium nucleatum on humoral and cell-mediated immunity and phagocyte functions in mice. The extract was obtained from the heat-inactivated supernatant of sonicated F. nucleatum. Mouse splenocytes were cultured with sheep red blood cells (SRBC), and antibody formation was assayed by counting the plaque-forming cells (PFC). After C3H mouse skin was grafted onto the BALB/c mouse, cytotoxicity of BALB/c mouse splenocytes to L-cells was enumerated, T- and B-cell blastogenesis was determined by the uptake of 3H-thymidine. In vivo phagocyte functions were measured using carbon clearance test, bactericidal, and acid phosphatase activity assays. The number of SRBC-specific and non-specific PFC in splenocytes stimulated with the extract increased 2.5-8.7-fold over that of unstimulated splenocytes. Cytotoxicity of splenocytes from the extract-injected mice decreased in a dose-dependent fashion at 12 days after grafting. T-cell mitogenicity of the extract was observed. The carbon clearance rate was reduced, and bactericidal and acid phosphatase activities were elevated by the extract injection of the mice. In conclusion, F. nucleatum extract has an adjuvant effect on humoral immunity, and a suppressive effect on cell-mediated immunity and activated phagocyte functions.