Induction of TNF production by plasma proteins is not due to endotoxin contamination. RAW264.7 macrophages were stimulated for 24 hours with 50 μg/ml of Gc-globulin, α1-microglobulin (α1m), or α2-macroglobulin (α2m) that had been incubated with proteinase K (20 μg/ml) at 55°C for 4 hours in the presence of β-mercaptoethanol and then heated to 100°C for 10 minutes. TNF levels in the supernatants were determined with ELISA. Lipopolysaccharide (LPS; 1 ng/ml) was used as a positive control. Data are shown as the mean ± SEM of duplicates from one of two representative experiments. *P < 0.05; **P < 0.01.