Open AccessThe lipopolysaccharide‐recognition mechanism in cells expressing TLR4 and CD14 but lacking MD‐2
Author(s) -
Ohnishi Takahiro,
Muroi Masashi,
Tanamoto Kenichi
Publication year - 2007
Publication title -
fems immunology & medical microbiology
Language(s) - English
Resource type - Journals
eISSN - 1574-695X
pISSN - 0928-8244
DOI - 10.1111/j.1574-695x.2007.00281.x
Subject(s) - tlr4 , cd14 , lipopolysaccharide , biology , hek 293 cells , microbiology and biotechnology , signal transduction , transmembrane protein , cell culture , biochemistry , receptor , immunology , flow cytometry , genetics
We analysed the lipopolysaccharide (LPS)‐recognition mechanism in cells expressing TLR4 and CD14 but lacking MD‐2. When TLR4 and CD14 were transiently expressed in HEK293 cells, cell‐surface expression of TLR4 was observed, although the expression level was lower than that in cells coexpressing MD‐2. We found that membrane CD14–TLR4 complexes were formed in these cells in response to LPS stimulation even in the absence of MD‐2 expression, although NF‐κB‐dependent reporter activity was not induced. A strong activation of NF‐κB was observed when these cells were stimulated with LPS followed by soluble MD‐2 in this order, even when excess LPS was removed after formation of the CD14–TLR4 complex by washing cells prior to sMD‐2 addition. From these results, we propose an additional LPS‐recognition mechanism. In cells expressing TLR4 and CD14 but lacking MD‐2, LPS is first transferred to membrane CD14 with the aid of LPS binding protein, which leads to the formation of the TLR4–CD14 complex. Then, the binding of soluble MD‐2 to this complex triggers the transmembrane signal transduction. Cells expressing TLR4 and CD14 but lacking MD‐2, such as airway epithelial cells, may be activated in response to LPS by this mechanism.