CD14-DEPENDENT AND CD14-INDEPENDENT SIGNALING PATHWAYS IN MURINE MACROPHAGES FROM NORMAL AND CD14 KNOCKOUT MICE STIMULATED WITH LIPOPOLYSACCHARIDE OR TAXOL

The antitumor agent, Taxol, shares with bacterial LPS the ability to a ctivate murine macrophages, and its LPS-mimetic effects are blocked by LPS analogue antagonists, Since CD14 is central to the recognition of LPS by macrophages, we sought to examine a role for CD14 in the respo nse to Taxol vs LPS. A comparison of responses of macrophages from wil d-type mice with those from mice lacking CD14 due to a targeted disrup tion of the CD14 gene (CD14-deficient knockout (CD14KO)) revealed that like LPS, Taxol induces both CD14-dependent and -independent pathways of gene activation, although the CD14 dependency of Taxol stimulation is much less striking than that observed with LPS. The macrophage int eraction with low concentrations of LPS (less than or equal to 10 ng/m l) is largely CD14 dependent, as evidenced by the lack of induction of TNF-alpha, IL-1 beta, and interferon-inducible protein-10 (IP-10) gen es by CD14KO macrophages cultured in the absence of soluble CD14 (i.e. , in autologous CD14KO -/- mouse serum). However, at high concentratio ns of LPS or Taxol, a CD14-independent pathway of activation is observ ed: this pathway leads to minimal IP-10 gene induction, even though in duction of TNF-alpha and IL-1 beta occurs. Measurements of TNF secreti on followed a similar pattern to that observed at the level of steady state mRNA. These data suggest the existence of two pathways of activa tion by both LPS and Taxol: one that is CD14 dependent and leads to in duction of TNF-alpha, IL-1 beta, and IP-10 genenduction, and a CD14-in dependent pathway that results in the induction of TNF-alpha and IL-1 beta, with minimal induction of IP-10.