Figure 2. Up-regulation of matrilysin expression in epithelial cells cultured in the presence of oral bacteria. Bacteria (a stock solution, OD₆₀₀ = 0.5) were added at a 1:50 dilution to semiconfluent porcine periodontal ligament epithelial cell cultures. After 24-hour culture in the absence of serum, total RNA (20 µg/sample) isolated from the cells was analyzed by Northern hybridization, with specific cDNA probes for human matrilysin and glyceraldehyde-3-phosphate dehydrogenase (GAPD; a loading control). The expression levels of matrilysin were quantified by densitometric scanning (bar graph).