Leukotoxic activity in different strains of the bacterium Actinobacillus actinomycetemcomitans isolated from juvenile periodontitis in man

Type culture strains and dental isolates (from juvenile periodontitis) of Act. actinomycetemcomitans (Aa) were tested for their ability to kill human polymorphonuclear leukocytes (PMN) in vitro. The majority of Aa, as well as sonic extracts prepared from these organisms, rapidly destroyed PMNs, shown by the extracellular release of lactate dehydrogenase from PMNs and by degenerative ultrastructural alterations. The leukotoxic properties of Aa could be modulated by serum: normal human sera enhanced killing but juvenile periodontitis or various rabbit anti- Aa sera neutralized toxic activity. Whereas toxic and non-toxic strains of Aa shared common antigens, immunologic analyses revealed a unique antigen in sonic extracts of leukotoxic organisms. Thus Aa-derived leukotoxin may be an aetiologic vector in juvenile periodontitis.