LIPOPOLYSACCHARIDE AND ITS ANALOG ANTAGONISTS DISPLAY DIFFERENTIAL SERUM FACTOR DEPENDENCIES FOR INDUCTION OF CYTOKINE GENES IN MURINE MACROPHAGES

Monocytes/macrophages play a central role in mediating the effects of lipopolysaccharide (LPS) derived from gram-negative bacteria by the pr oduction of proinflammatory mediators. Recently, it was shown that the expression of cytokine genes for tumor necrosis factor alpha (TNF-alp ha), interleukin-1 beta (IL-1 beta), and interferon-inducible protein- 10 (IP-10) by murine macrophages in response to low concentrations of LPS is entirely CD14 dependent. In this report, we show that murine ma crophages respond to low concentrations of LPS (less than or equal to 2 ng/ml) in the complete absence of serum, leading to the induction of TNF-alpha and IL-1 beta genes. In contrast to the TNF-or and IL-1 bet a genes, the IP-10 gene is poorly induced in the absence of serum. The addition of recombinant human soluble CD14 (rsCD14) had very little e ffect on the levels of serum-free, LPS-induced TNF-alpha, IL-1 beta, a nd IP-10 genes. In contrast, the addition of recombinant human LPS-bin ding protein (rLBP) had opposing effects on the LPS-induced TNF-alpha or IL-1 beta and IP-10 genes, rLBP inhibited LPS-induced TNF-alpha and IL-1 beta genes, while it reconstituted IP-10 gene expression to leve ls induced in the presence of serum. These results provide further evi dence that the induction of TNF-alpha or IL-1 beta genes occurs via a pathway that is distinct from one that leads to the induction of the I P-10 gene and that the pathways diverge at the level of the initial in teraction between LPS and cellular CD14. Additionally, the results pre sented here indicate that LPS structural analog antagonists Rhodobacte r sphaeroides diphosphoryl lipid A and SDZ 880.431 are able to inhibit LPS-induced TNF-alpha and IL-1 beta in the absence of serum, while a synthetic analog of Rhodobacter capsulatus lipid A (B 975) requires bo th rsCD14 and rLBP to function as an inhibitor.