Cellular response to subgingival injection of bacterial products in the rat

Various bacterial products were injected in the oral mucosa of 74 conventional weanling rats of the Holtzman strain. The site of injection was lingual to the mesial cusp of the first molar of the maxilla or mandible. The bacterial products were whole dead cells, cell walls or cytoplasm obtained from Actinomyces naeslundii. Saline was injected into control animals. The animals were killed at intervals 0 to 48 hours subsequently, and the tissues examined by standard histological methods. In all cases there was an initial polymorphonuclear response at the site of injection which had usually disappeared by 24 hours. In addition, osteoblasts on the adjacent alveolar bone were destroyed and in no case had they reappeared at 48 hours. Osteocytes were also missing after whole dead cell or cytoplasm injections, but not after cell wall injections. The most striking difference between the various reactions was an early appearance of lymphocytes after cell wall injections, which overshadowed the polymorphonuclear response, and which persisted up to 24 hours post injection. The disappearance of osteoblasts and osteocytes after injection of bacterial products from an organism associated with periodontal disease in man may explain in part the bone loss in this condition.