Periodontal disease is thought to be initiated by a bacterial infection and subsequently developed by immunopathological mechanisms thorough host-parasite interactions. The macrophage and lymphocyte are the major functional cell types in the lesion of the disease and participate in tissue destruction and alteration of the periodontal connective tissue as well as in host defense mechanisms. However, the detailed implications of macrophages in development of the disease is still unclear. The aim of this study was to gain more understanding of the functional role of macrophages in periodontal disease. In this study, we examined the inducing effects of sonicated extracts from some gram-negative and gram-positive bacteria associated with the pathogenesis of periodontal disease, including Bacteroides gingivalis, Fusobacterium nucleatum, Haemophilus actinomycetemcomitans, and Actinomyces viscosus, on activation of macrophage functions and IL-1 production by the macrophages from the mouse peritoneum. At a dose as low as 1 microgram/ml (dry weight) sonicated extracts from B. gingivalis induced an increase in acid phosphatase activity and in glucose consumption of mouse peritoneal macrophages in vitro. A significant increase in the acid phosphatase and in glucose consumption was observed in the cultures at 24 h and 48 h, respectively, after the addition of the sonicate. Sonicated extracts from A. viscosus, a gram-positive bacterium, as well as B. gingivalis, F. nucleatum, and H. actinomycetemcomitans, gram-negative ones, were able to induce the increase in acid phosphatase activity and in glucose consumption of the macrophages. These periodontopathic bacteria were found to strongly induce IL-1 production by the macrophages as early as 24 h after addition of the sonicates. A significant increase in the IL-1 production was observed at a dose of 1 microgram/ml of the sonicates. The inducing ability was equivalent to 1 microgram/ml Escherichia coli lipopolysaccharide. The highest production of IL-1 was observed in the macrophages treated with H. actinomycetemcomitans among these sonicates. Sonicated extracts from both gram-negative and gram-positive bacteria were able to induce the IL-1 production by macrophages from C3H/HeJ mice, which are LPS low-responders. These results suggest that periodontopathic bacteria have potent ability to induce macrophage activation and IL-1 production and that the activated macrophages may play an important role in development of periodontal disease.(ABSTRACT TRUNCATED AT 400 WORDS)