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From the Merck Research Laboratories, Rahway, New Jersey 07065
We have recently shown that monomeric bacterial LPS is rapidly delivered from the plasma
membrane to an intracellular site and that agents that block vesicular transport block responses of neutrophils to lipopolysaccharide (LPS) (Detmers, P.A., N. Thiéblemont, T. Vasselon, R. Pironkova, D.S. Miller, and S.D. Wright. 1996. J. Immunol. 157:5589-5596). To examine further the connection between intracellular transport of LPS and signaling, we observed internalization of fluorescently labeled LPS in cells from LPS-hyporesponsive (Lpsd) mice. Binding of
fluorescent LPS from LPS-soluble CD14 (sCD14) complexes by peritoneal macrophages from
Lpsd and control (Lpsn) mice was quantitatively similar, and confocal images obtained from
these cells exhibited an identical appearance immediately after labeling. Incubation of labeled
Lpsn macrophages at 37°C caused movement of the fluorescence from the cell perimeter in one
or two spots in the perinuclear region. However, in Lpsd cells the fluorescence remained dispersed, suggesting a defect in vesicular transport. LPS resembles ceramide, and Lpsd mice fail to
respond to ceramide. As with LPS, we found that binding of fluorescent ceramide by Lpsd and
Lpsn macrophages was quantitatively similar, and the label moved rapidly to one to two spots in
the perinuclear region in Lpsn mice. However, in Lpsd macrophages the fluorescence remained
dispersed. These results show that cells deficient in responses to LPS exhibit defective vesicular
transport of LPS and ceramide and point to a role for vesicular transport in responses to these
mediators.
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