A leukotoxin from Actinobacillus actinomycetemcomitans was isolated by a procedure that includes polymyxin B extraction, ion-exchange chromatography, and gel filtration chromatography. The procedure resulted in the recovery of 48% of the toxin with a 99-fold increase in specific activity. The isolated toxin has a molecular mass of 180,000 daltons by gel filtration and 115,000 daltons by sodium dodecyl sulfatepolyacrylamide gel electrophoresis. It retains all the major biological characteristics previously documented for crude leukotoxin preparations, including susceptibility to heat and proteolytic enzymes and neutralization by sera from patients with juvenile periodontitis. The isolated leukotoxin destroys human but not rat or guinea pig polyriorphonuclear leukocytes and has no apparent effect on human erythrocytes. The availability of the A. actinomycetemcomitans leukotoxin should facilitate studies on its chemistry and mode of action as well as its role in the pathogenesis of human periodontal disease. Juvenile periodontitis is an inflammatory disease characterized by severe alveolar bone loss in young individuals. Clinical, microbiological, and immunological data implicate Actinobacillus actinomycetemcomitans as a possible etiological agent in juvenile periodontitis. For example, patients harbor relatively high proportions of A. actinomycetemcomitans in diseased sites (13, 19, 20, 22) and have high titers of antibodies against these organisms (10, 12, 15, 24). Furthermore, A. actinomycetemcomitans elaborates several

The plaque-derived gram-negative microorganism Y4 identified as a member of the genus Actinobacillus, was tested for a soluble cytotoxic factor(s). Sonication or incubation of viable Y4 microorganisms in distilled water or normal human serum resulted in liberation of a soluble material which was cytotoxic in vitro for human polymorphonuclear leukocytes (PMNs). The Y4 soluble sonic extract was also cytotoxic to human peripheral blood monocytes. However, human lymphocytes, platelets, and fibroblasts, as well as rabbit, rat, and mouse leukocytes and chicken embryo fibroblasts, were not killed by exposure to the Y4 sonic extract. No hemolytic activity was detected in the Y4 sonic extract. Consequently, the factor(s) in the Y4 sonic extract was referred to as Y4 leukotoxin. The Y4 leukotoxin was inactive at 40C, heat sensitive (560C, 30 min), and inactivated by proteases. The cytotoxic effect of Y4 leukotoxin on PMNs was dose, time, and temperature dependent. The leukotoxin did not bind to viable PMNs at 40C but

In the present study we identified a gram-negative anaerobic rod referred to as Y4 which was cytotoxic for human polymorphonuclear leukocytes. Y4 was isolated from dental plaque of a patient with juvenile periodontitis and presented most of the taxonomic characteristics of Actinobacillus species. Under experimental conditions, viable Y4 were cytotoxic for human peripheral blood polymorphonuclear leukocytes in serum-free cultures. Cytotoxicity was dependent on bacterial concentrations and was enhanced in the presence of a fresh or heat-inactivated (56 degrees C, 30 min) autologous serum. Leukotoxicity was independent of phagocytosis. Y4 leukotoxic effect was abolished when bacteria were heat treated (56 degrees C, 30 min) or when incubations were carried out at 4 degrees C instead of at 37 degrees C. The leukotoxicity was monitored by electron microscopy and biochemically by measuring lactate dehydrogenase indicator of cell viability. No cytotoxic effects of Y4 on human mononuclear cells, chicken fibroblasts, or mouse macrophages were detected under the conditions studied. Polymorphonuclear leukocytes may play an important role in the host defense against bacteria in periodontal disease. The cytotoxic effect of Y4 for polymorphonuclear leukocytes presented in this study is the first report of a direct offensive microbial vector in a plaque-derived microorganism and may prove to be relevant in the pathogenesis of juvenile periodontitis.

We have examined soluble sonic extracts of Actinobacillus actinomycetemcomitans for their ability to alter human and murine fibroblast proliferation. We found that extracts of all A. actinomycetemcomitans strains examined (both leukotoxic and nonleukotoxic) caused a dose-dependent inhibition of both murine and human fibroblast proliferation as assessed by DNA synthesis ([3H]thymidine incorporation). Addition of sonic extract simultaneously with [3H]thymidine had no effect on incorporation, indicating that suppression was not due to the presence of excessive amounts of cold thymidine. Inhibition of DNA synthesis was also

The deposition of bacterial plaques on tooth surfaces appears to be responsible for the initiation and progression of periodontal disease. In this study, human peripheral blood polymorphonuclear leukocytes (PMNs) actively released lysosomal constituents upon in vitro exposure to either viable or irradiated, supragingival or subgingival dental plaque. Plaques were obtained from the PMN donors (autologous plaque) or from pooled samples (homologous plaque) secured from patients with periodontal lesions. Fresh sera from PMN donors amplified the release reactions to supragingival and subgingival plaques. Heated (56 degrees C, 30 min) sera also enhanced release reactions, but not as consistently as fresh serum. It was postulated that modulation of PMN release by serum is mediated by complement components and/or antibodies to plaque bacteria. Electron microscopic observations indicated that degranulation and discharge of PMN lysosomal enzymes may be associated with phagocytosis of gram-positive and gram-negative plaque bacteria and with reverse endocytosis of lysosomes from cells contacting relatively large masses of aggregated plaque bacteria. These data suggest that PMN lysosome release in response to plaque may serve as a potential mechanism of tissue injury in the pathogenesis of gingival and periodontal inflammation.