Plasma proteins detected in osteoarthritic synovial fluid stimulate macrophage TNF production via TLR4. Levels of TNF produced by wild-type (wt) or TLR4-deficient (Tlr4lps-del) mouse bone-marrow-derived macrophages stimulated for 24 hours with 50 μg/ml of Gc-globulin, α1-microglobulin (α1m), or α2-macroglobulin (α2m), after which TNF levels in the supernatants were determined with ELISA. Lipopolysaccharide (LPS; 1 ng/ml) was used as a positive control for TLR4-dependent TNF production, and peptidoglycan (PGN; 5 μg/ml) as a positive control for TLR4-independent TNF production. Data are shown as the mean ± SEM of triplicates from one of three representative experiments. *P < 0.05; **P < 0.01.