The promyelocytic HL-60 cell line was examined for susceptibility to leukotoxin from Actinobacillus actinomycetemcomitans. Strains of A. actinomycetemcomitans which caused lysis of human peripheral blood polymorphonuclear leukocytes also lysed HL-60 cells as determined by release of intracellular lactate dehydrogenase. The killing of HL-60 cells by A. actinomycetemcomitans was dose dependent and temperature dependent, reached maximal levels after 45 min of incubation, and was inhibited by rabbit antisera to A. actinomycetemcomitans. Of 100 oral isolates of A. actinomycetemcomitans from 55 subjects, 16% from 11 healthy subjects, 43% from 13 adult periodontitis patients, 75% from 4 insulindependent diabetics, 66% from 2 generalized juvenile periodontitis patients, and 55% from 25 localized juvenile periodontitis patients produced leukotoxin. The same subject could harbor both leukotoxin-producing and-nonproducing isolates. The significantly higher proportion of leukotoxin-producing isolates in the disease groups compared with the healthy group is consistent with the hypothesis that leukotoxin from A. actinomycetemcomitans is an important virulence factor in the pathogenesis of certain forms of periodontal disease.

Localized juvenile periodontitis (ljp) is a progressively destructive infection of the supporting tissues of the teeth, primarily affecting adolescents. In this disease, patients' polymorphonuclear leukocytes (PMN) exhibit decreased Chemotaxis (CTX) and decreased binding of the chemotactic peptide N‐formyl‐l‐methionyl‐l‐leucyl‐l‐phenyl‐alanine (FMLP) to specific receptors on the PMN surface. Since the FMLP receptor is involved in the activation of the PMN, and its subsequent response to chemotactic stimuli, a decrease in the chemotactic peptide receptor, as seen in LJP patients, is suspected to be a predisposing factor for this disease. To define differences in the FMLP receptor between CTX defective LJP patients and CTX normal donors, a battery of monoclonal antibodies reactive against the FMLP receptor was prepared. The FMLP receptor was affinity‐purified, and was found to be comprised of two components, one of 68 kDa, and the other of 94 kDa. Only the 68 kDa component specifically bound a radioiodinated FMLP analogue in a photoaffinity experiment. Seven monoclonal antibodies were selected on the basis of their reactivity with the 68 kDa receptor component, and of these, 5 showed reduced binding against PMN from CTX defective LJP donors when compared to their reactivity against PMN from CTX normal subjects. Two of the 7 anti‐68 kDa antibodies reacted with PMN from both sets of subjects at a comparable extent. Furthermore, the presence of 20 nmol of FMLP inhibited the binding of 5 of the anti‐receptor antibodies to whole PMN, including one that showed no difference in binding between CTX normal and defective PMN, and 4 of the 5 that did show such difference. These results show that a difference in the binding of antibodies to the FMLP receptor complex exists between neutrophils from chemotactically depressed LJP patients as compared to normal controls. These differences in binding may be due to qualitative differences in the receptor or may represent reduced expression of receptor components on the surface of LJP neutrophils. These results add further support to the concept that alterations in the surface of PMN from LJP patients are associated with reduced Chemotaxis. J Periodontol 1990;61:609‐617.

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