ROLE OF CD14 MOLECULES IN INTERNALIZATION OF ACTINOBACILLUS-ACTINOMYCETEMCOMITANS BY MACROPHAGES AND SUBSEQUENT INDUCTION OF APOPTOSIS

We report the evidence for apoptosis in 5774.1 cells by the periodonto pathic bacterium Actinobacillus actino-mycetemcomitans, suggesting tha t the ability of A. actinomycetemcomitans to promote apoptosis might b e important in the initiation and development of periodontitis. In thi s study, we examined the role of macrophage CD14, anchored by a glycer ophosphatidylinositol tail, in the induction of apoptosis by A. actino mycetemcomitans infection by using the parent 5774.1 cells and CD14-de fective mutant (LR-9) cells. A small number of A. actino-mycetemcomita ns Y4 cells inside the LR-9 cells compared with the number in 5774.1 c ells was detected by confocal scanning microscopy, We found that LR-9 cells showed a weak cytotoxic effect after being infected with A. acti nomycetemcomitans Y4. Apoptotic cell death of LR-9 cells infected with A. actinomycetemcomitans Y4, compared with that of the parent 5774.1 cells was almost undetectable, as shown by the proportion of fragmente d DNA in agarose gel electrophoresis and by the terminal deoxynucleoti dyl transferase-mediated dUTP end-labeling method, Flow cytometric cel l cycle analysis of 5774.1 cells infected with A, actinomycetemcomitan s Y4 revealed the increased percentage of apoptotic cells,vith hypodip loid DNA, However, LR-9 cells infected with A. actinomycetemcomitans Y 4 showed no increase in population of apoptotic nuclei compared with t he noninfected cells. These findings suggest that the CD14 molecules m ay contribute to the phagocytosis of A. actinomycetemcomitans by 5774. 1 cells and regulate, at least in part, apoptotic cell death of macrop hages infected with A. actinomycetemcomitans.