Cell-mediated cytotoxicity against rat fibroblasts induced by Actinomyces viscosus

Cell-mediated cytotoxicity against syngeneic fetal rat fibroblasts that require in vitro exposure of effector cells to Actinomyces viscosus Ny1 fractions was investigated by measuring the uptake of radioactivity by fibroblasts during a 2-h pulse with [14C]aminoisobutyric acid after 1 to 3 days of coculture with splenic effector cells. By using splenocytes from inbred RIC-Sprague-Dawley rats as effector cells and syngeneic embryonic rat fibroblasts as target cells, strong cell-mediated cytotoxicity dependent on the in vitro exposure to an A. viscosus Ny1 fraction was observed, but only within a small range of effector-to-target cell ratios (3:1 to 10:1). Concanavalin A and lipopolysaccharide from Escherichia coli induced a comparable cytotoxicity, indicating that the effect might be connected with the mitogenic activity of the A. viscosus NY1 fraction. Splenocytes from rats immunized with A. viscosus Ny1 and from control rats induced similar levels of cytotoxicity in 72-h cytotoxicity assays. In shorter assays (24 h), however, splenocytes from immune animals induced low cytotoxicity, which was, however, significantly higher than that induced by splenocytes from control animals. We conclude that both antigen- and mitogen-dependent cell mediated effector mechanisms are operative in this system and that the two normally overlapping effects can be experimentally separated. This new system describes a fibroblast impairment in the presence of splenocytes and bacterial components and may provide a useful model for studying pathogenic mechanisms operative in periodontal disease.