Serum components enhance bacterial lipopolysaccharide‐induced tissue factor expression and tumor necrosis factor‐ α secretion by bovine alveolar macrophages in vitro

We have compared the effect of bacterial lipopolysaccharide (LPS) in combination with normal adult bovine serum (NBS), fetal bovine serum (FBS), or a bovine serum fraction on tissue factor expression and tumor necrosis factor α (TNF‐ α ) secretion by bovine alveolar macrophages. At a concentration of 1 ng/ml, bacterial LPS alone failed to induce measurable tissue factor expression by the macrophages, but the presence of FBS, NBS, or a fraction of normal pooled bovine serum isolated by ion‐exchange chromatography (fraction 2) markedly potentiated the effect of LPS. A protein concentration of 64 μ g/ml NBS, 192 μ g/ml FBS, and only 640 ng/ml fraction 2 was required to induce maximal tissue factor expression on the macrophages in combination with 1 ng/ml LPS. Comparison of quantities of added serum protein required to induce maximal potentiating effects indicated that fraction 2 was 100 times more potent than1 whole NBS and 300 times more potent than whole FBS. We similarly found that TNF‐ α secretion by macrophages exposed to LPS was responsive to serum and was highly responsive to fraction 2. LPS alone (1 ng/ml) induced a relatively low level of TNF‐ α secretion by the macrophages, and the presence of FBS, NBS, or fraction 2 potentiated the effect of LPS. A concentration of 64.0 μ g/ml NBS, 320.0 μ g/ml FBS, and 3.2 μ g/ml fraction 2 serum protein induced near‐maximal TNF‐ α secretion by the macrophages. Comparison of the concentration of serum protein required to induce these potentiating effects indicated that fraction 2 was approximately 20 times more potent than whole NBS and 100 times more potent than whole FBS. The stimulatory effect of LPS plus fraction 2 serum proteins was dependent on the CD14 receptor, as monoclonal antibodies directed against CD14 (My4, 60bd; 10 μ g/ml) inhibited tissue factor expression and TNF‐ α secretion by the macrophages. J. Leukoc. Biol. 55: 483–488; 1994.