Effect of Actinobacillus actinomycetemcomitans, Wolinella recta and Bacteroides gingivalis on the viability of retinoic acid‐induced and dimethyl sulfoxide‐induced HL‐60 cells

We studied the interactions between viable and heat‐killed, opsonized and unopsonized periodontopathic bacteria with both uninduced and induced HL‐60 promyelocytic leukemia cells. The cells were induced to differentiate into granulocyte‐like cells by incubation with retinoic acid (RA) or dimethyl sulfoxide (DMSO). When unopsonized, Wolinella recta ATCC 33228 significantly suppressed the net Proliferation of uninduced HL‐60 cells, Actinobacillus actinomycetemcomitans strain Y4 was markedly lethal to the cells, and Bacteroides gingivalis ATCC 33277 had no effect. Unopsonized and opsonized A. actinomycetemcomitans and W. recta had equally potent lethal effects on induced HL‐60 cells. Unopsonized B. gingivalis Was not lethal to the induced cells in the dose used (100 bacteria/HL‐60 cell), but opsonized B. gingivalis was lethal, especially in the first 24 h. The killing effects of A. actinomycetemcomitans and W. recta were largely eliminated if they were heated (56°C, 30 min) before being added to the induced HL‐60 cells. RA‐induced HL‐60 cells were more sensitive to the lethal effects of A. actinomycetemcomitans and W. recta than were DMSO‐induced cells. The results suggest that the HL‐60 cell line may be a useful model for studying granulocyte‐bacteria interactions.