Periodontal pathogen Lipopolysaccharide Induced Secretion of SLPI by Monocytes

Secretory leukocyte protease inhibitor (SLPI) is a non-glycosylated protein, found in mucosal fluids and saliva and shown to be produced by macrophages when induced with lipopolysaccharide (LPS). It is a potent inhibitor of proteases, elastase and cathepsin G and has been shown to suppress the secretion of inflammatory cytokines by the mononuclear cells. Objective: The study was designed to examine if the LPS of periodontal pathogens differ in their ability to stimulate production of SLPI by monocytes. Methods: LPS was isolated from P. gingivalis (Pg), Prevotella denticola (Pd), and Fusobacterium nucleatum (Fn), by hot-phenol method. Pro-monocytic THP-1 cells were cultured and differentiated by incubating the cells with PMA for 48 h and then used in the study. Monocytic cells (5X10⁵) were incubated with 1 to10ng/ml of Pg, Pd, and Fn LPS for 24 h in triplicate. Culture supernatants were collected and then assayed for the quantity of SLPI secreted by an ELISA kit (R and D systems). Results: Results show that the quantity of SLPI secreted dependent upon the type of bacterial LPS. Cells incubated with LPS of Pg secreted 134and 688 pg/ml of SLPI, when stimulated with 1 and 10 ng/ml of LPS, respectively. Pd LPS (1 and 10 ng/ml) stimulated the cells to secrete secreted slightly lesser 98 and 620 pg/ml SLPI, respectively. THP-1 cells stimulated with Fn LPs (1 and 10 ng/ml) secreted 46 and 386 pg/ml of SLPI. Conclusion: The results of the study suggest that periodontal pathogens differ in their ability to stimulate monocytes to secrete SLPI. Increased stimulation to secrete SLPI by LPS of Pg and Pd may suggest that pathogenic organisms may use this protein as an aid to avoid stimulation of pro-inflammatory cytokines, and escape detection by mononuclear cells.