Mucosal induction of systemic T cell tolerance by Fusobacterium nucleatum

The present study was undertaken to determine if mucosal presentation of the periodontopathic bacterium Fusobacterium nucleatum could induce systemic tolerance. Two separate protocols of mucosal priming were carried out. In the first, mice were gastrically intubated on 2 consecutive days; this was repeated 5 days later. In the second protocol, mice were similarly primed but received another priming dose after a further 7 days. Positive control mice were similarly primed with sheep red blood cells (SRBC) while negative control animals were sham-primed with saline. Following mucosal priming, mice were systemically sensitized with the respective antigen and then subsequently challenged in the left hind footpad. The right footpad was challenged with saline and served as a negative control. Serum antibody levels were measured using enzyme-linked immunoabsorbent assay (ELISA) and haemagglutination assays. Mucosal priming with F. nucleatum was found to suppress the local delayed type hypersensitivity reaction as determined by footpad measurements. Sham-priming did not suppress the local response. On the other hand, the levels of serum antibodies were not influenced by mucosal priming. These results suggest that under the experimental conditions used, mucosal presentation of F. nucleatum can induce a degree of split tolerance in which T cell responses are suppressed while B cell responses remain intact. The implication of this finding to human periodontal disease is yet to be determined.