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Abstract
Recognition of bacterial lipopolysaccharide (LPS) by the innate immune system elicits
strong pro-inflammatory responses that can eventually cause a fatal sepsis syndrome
in humans. LPS-mediated activation of mammalian cells is believed to involve the interaction
of LPS with lipopolysaccharide-binding protein (LBP) in the serum and, subsequently
with CD14. Although there is no doubt that CD14 binds LPS, CD14 is not capable of
initiating a transmembrane activation signal because it is a glycosylphosphatidylinositol
(GPI)-anchored protein. Accumulating evidence has suggested that LPS must interact
with a transmembrane receptor(s) that is responsible for signal transduction. Integrins
CD11c and/or CD18, Toll-like receptors (TLRs), as well as CD55, have been suggested
to serve this function. Recently, we have revealed that a signalling complex of receptors
is formed following LPS stimulation, which comprises heat-shock proteins (Hsps) 70
and 90, chemokine receptor 4 (CXCR4) and growth differentiation factor 5 (GDF5). Taking
into account the discovery of the TLRs and the LPS-activation cluster, we propose
a new model of LPS recognition.