GENE CLONING OF AN ACTINOBACILLUS-ACTINOMYCETEMCOMITANS Y4 ANTIGEN WHICH REACTS WITH PERIPHERAL-BLOOD SERA IN PATIENTS WITH ADVANCED DESTRUCTIVE PERIODONTITIS

Actinobacillus actinomycetemcomitans has been implicated in the aetiology of juvenile periodontitis and advanced destructive periodontitis. Levels of IgG antibody against A. actinomycetemcomitans in peripheral blood sera of patients with advanced destructive periodontitis are high, as are those against Bacteroides gingivalis. To clone the genes of antigens reactive with sera of such patients, a library of the A. actinomycetemcomitans strain Y4 DNA in lambda-L47 was constructed and then screened, using an immunochemical detection method, with serum from a patient with the advanced disease. Six clones from among nearly 1000 reacted with the serum and also with that of another patient. They were designated 3, 4, 5, 6, 7, 8 and 9. Restriction enzyme and Southern blot analyses indicated that clones 8 and 9 were identical and that all the clones were overlapping because they shared in common the 4 and 5 kbp Hin cII DNA fragments of A. actinomycetemcomitans. The cloned DNA fragment hybridized to the DNA of two other strains of A. actinomycetemcomitans but not to those of six periodontopathic bacteria examined. These findings suggest that A DNA sequence encoding an A. actinomycetemcomitans strain Y4 antigen strongly reactive with sera of patients with advanced destructive periodontitis was cloned. This sequence is present specifically in A. actinomycetemcomitans but not in other bacteria isolated from patients with periodontal diseases. Thus, the cloned DNA could serve as a probe for the diagnosis of periodontitis.