Interaction of Fusobacterium nucleatum 191 with human peripheral blood lymphocytes

Fusobacterium nucleatum is frequently isolated in high numbers from the subgingival plaque of patients with periodontal diseases. Adherence of these bacteria to several host tissues is lectin-like in that it is inhibited by galactose, lactose, and N-acetyl-galactosamine. Since F. nucleatum has the capacity to activate human peripheral blood lymphocytes, the purpose of this study was to determine whether F. nucleatum adheres to lymphocytes and, if so, to determine whether lectin-like interactions facilitate lymphocyte activation. Adherence of F. nucleatum strain 191 to lymphocytes was confirmed by agglutination assays, scanning electron microscopy, and by using fluorescein- or [3H]-labeled bacteria. Saturation of adherence was reached at about 35 bacteria per lymphocyte. F. nucleatum adhered to greater than 90% of the lymphocytes, and adhered in higher numbers to B cell-enriched subpopulations than to T cell-enriched subpopulations. Adherence was inhibited by N-acetyl-galactosamine, lactose greater than galactose, alpha- and beta-methyl galactoside, but not by 100 mM glucose, mannose, N-acetyl-glucosamine, or other sugars tested. Lymphocytes underwent mitogenesis when preincubated with bacteria and washed to remove weakly adherent and non-adherent bacteria. Mitogenesis induced by low concentrations of F. nucleatum was reduced, but not completely eliminated, by N-acetyl-galactosamine. However, N-acetyl-galactosamine had no effect on mitogenesis induced by preincubation with high concentrations of bacteria. These results suggest that adherence of F. nucleatum facilitates activation of lymphocytes, particularly at low concentrations of bacteria.