Lipid rafts — ordered membrane microdomains rich in glycosphingolipids and cholesterol — are implicated in both membrane sorting and signal transduction. In the acquired immune response, they appear to play an important role in T-cell activation, serving as platforms for assembly of the signalling machinery. Kathy Triantafilou and co-workers now show that rafts also function in innate immune recognition (see). They demonstrate that several proteins involved in the cellular response to bacterial lipopolysaccharide (LPS) exist in lipid rafts: the GPI-linked LPS receptor CD14 and the heat shock proteins Hsp70 and Hsp90 are permanently present in rafts, and chemokine receptor 4 (CXCR4), growth differentiation factor 5(GDF5) and Toll-like receptor 4 (TLR4) enter rafts after stimulation of cells by LPS. The authors also demonstrate that agents that disrupt raft integrity(e.g. nystatin) block LPS-induced secretion of tumour necrosis factor α(TNF-α). They therefore conclude that that concentration of signalling molecules involved in transducing LPS-recognition signals in lipid rafts is required for an effective innate immune response to pathogenic bacteria bearing this molecule.
