Introduction: The present study examined whether induction of an adaptive immune response to orally colonizing non-pathogenic Pasteurella pneumotropica by immunization with the phylogenetically closely related bacterium, Actinobacillus actinomycetemcomitans, can result in periodontal bone loss in mice.
Methods: BALB/c mice harboring P. pneumotropica (P. pneumotropica+ mice) in the oral cavity or control P. pneumotropica-free mice were immunized with fixed A. actinomycetemcomitans. The animals were sacrificed on day 30, and the following measurements were carried out: (i) serum immunoglobulin G and gingival T-cell responses to A. actinomycetemcomitans and P. pneumotropica; (ii) periodontal bone loss; and (iii) identification of receptor activator of nuclear factor-κB ligand (RANKL) -positive T cells in gingival tissue.
Results: Immunization with A. actinomycetemcomitans induced a significantly elevated serum immunoglobulin G response to the 29-kDa A. actinomycetemcomitans outer membrane protein (Omp29), which showed strong cross-reactivity with P. pneumotropica OmpA compared to results in the control non-immunized mice. The A. actinomycetemcomitans-immunized P. pneumotropica+ mice developed remarkable periodontal bone loss in a RANKL-dependent manner, as determined by the abrogation of bone loss by treatment with osteoprotegerin-Fc. The T cells isolated from the gingival tissue of A. actinomycetemcomitans-immunized P. pneumotropica+ mice showed an in vitro proliferative response to both A. actinomycetemcomitans and P. pneumotropica antigen presentation, as well as production of soluble(s)RANKL in the culture supernatant. Double-color confocal microscopy demonstrated that the frequency of RANKL+ T cells in the gingival tissue of A. actinomycetemcomitans-immunized P. pneumotropica+ mice was remarkably elevated compared to control mice.
Conclusion: The induction of an adaptive immune response to orally colonizing non-pathogenic P. pneumotropica results in RANKL-dependent periodontal bone loss in mice.