Lipopolysaccharide (LPS) recognition in macrophages. Participation of LPS-binding protein and CD14 in LPS-induced adaptation in rabbit peritoneal exudate macrophages.

Exposure of rabbit peritoneal exudate macrophages (PEM) or whole blood to picomolar concentrations ofLPS induces adapta- tion or hyporesponsiveness to LPS.Because of the importance of plasma LPS-binding protein (LBP) and the macrophage cell membrane protein CD14 in recognition of LPS, we examined the effect of LBP on LPS-induced adaptation in PEM.PEM exposed to LPS in the presence of LBP for 8 h were markedly less responsive to subsequent stimulation by LPS than mono- cytes/macrophages (M+) adapted in the absence of LBP.LPS-induced expression of TNF was sharply reduced in LBP- LPS-adapted PEM, but in contrast these cells remained fully responsive to Staphylococcus aureus peptidoglycan.We consid- ered that specific hyporesponsiveness in LPS-adapted My or in blood monocytes could be due to decreased expression of CD14 or diminished binding of LBP-LPS complexes to CD14.However, flow cytometry analysis revealed only minimal reduc- tion of CD14 expression or CD14-dependent binding of a fluo- rescent LPS derivative when normo-and hyporesponsive cells were compared.These results show that complexes of LPS and LBP are more effective than LPS alone in inducing adaptation to LPS, and LPS-induced hyporesponsiveness probably results from changes in cellular elements distinct from CD14 that are involved in either LPS recognition or LPS-specific signal trans- duction.(J.Clin.Invest.1993.92:2053-2059.)Key words: LPSadaptation -LBP * CD14 * macrophage hyporesponsive Mb'.Methods Animals.Outbred NZW rabbits (male, 1.8-2.2kg) were obtained from Western Oregon Rabbit Co. (Philomath, OR) and maintained on a standard pelleted diet for 7-14 d before use.All protocols used in these studies were approved by the Animal Research Committee of The Scripps Research Institute.Lipopolysaccharide-induced Adaption in Macrophages 2053